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Advanced nondestructive monitoring and evaluation of damage in concrete materials

University of Florida Institutional Repository

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ADVANCED NONDESTRUCTIVE MONI TORING AND EVALUATION OF DAMAGE IN CONCRETE MATERIALS By CHRISTOPHER C. FERRARO A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ENGINEERING UNIVERSITY OF FLORIDA 2003

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Copyright 2003 by Christopher C. Ferraro

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This thesis is dedicated to my loving famil y, my parents, Ronald and Victoria Ferraro, my sister Alicia Ferraro, my brother Ronald Ferraro Jr. and to my loving girlfriend Aliza Bar-David as they have offered their support and love throughout this endeavor. It is with the love and support of my family and friends that I am able to reach my goals.

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iv ACKNOWLEDGMENTS The author would like to thank all of th e members of his supervisory committee for their help and ideas throughout this effo rt. Dr. Andrew Boyd, the committee chair, provided valuable time and knowledge of th e subject, as well as financial support, making this research successful. Acknowledgement is owed to Dr. H.R. Hamilton and Dr. David Bloomquist for their contribution of time and knowledge, which provided to be invalu able assistance and guidance during this effort. The author would also like to express gratitude to all of those within the Department of Civil and Coastal Engineer ing Department including George Lopp, Chuck Broward and Scott Cumming. For her enormous efforts the author would like to extend his grat itude to Ms. Eileen Czarnecki. Her time and assistance were crucia l to the completion of this research in a timely manner. The author would also acknowledge PhD ca ndidates Christos Drakos and Forrest Masters. Their mentoring and assistance on a professional and personal level were greatly appreciated. The author would also like to thank his best friend, Aliza Bar-David, for the unyielding support and patience she offered me during the research a nd writing of this thesis.

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v TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES...........................................................................................................viii LIST OF FIGURES...........................................................................................................ix ABSTRACT....................................................................................................................... xv CHAPTER 1 INTRODUCTION........................................................................................................1 2 LITERATURE REVIEW.............................................................................................4 Introduction to Nondestructive Testing........................................................................4 Literature Review.........................................................................................................4 Visual Inspection...................................................................................................4 Liquid Penetrant Methods...................................................................................10 Acoustic Sounding...............................................................................................13 Surface Hardness Methods..................................................................................18 Penetration Resistance Methods..........................................................................20 Pullout Test..........................................................................................................21 Break-Off Test.....................................................................................................23 Ultrasonic Testing...............................................................................................25 Impact Echo.........................................................................................................53 Acoustic Emission...............................................................................................81 Impulse Response................................................................................................95 Magnetic Methods.............................................................................................102 Ground Penetrating Radar.................................................................................107 Resonant Frequency..........................................................................................111 Infrared Thermography.....................................................................................115 Radioactive Testing...........................................................................................123 3 SURVEY OF RELEVANT BRIDGE STRUCTURES IN FLORIDA....................129 Definition of Sufficiency Rating..............................................................................130 Methodology.............................................................................................................131 Results.......................................................................................................................1 34 Conclusions...............................................................................................................135

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vi 4 BRIDGE INSPECTIONS.........................................................................................137 Document Review....................................................................................................137 NDT Methods Used for Inspection...........................................................................138 Bahia Honda Bridge.................................................................................................138 Site Information.................................................................................................138 Procedures.........................................................................................................138 Results...............................................................................................................139 Conclusions.......................................................................................................141 Niles Channel Bridge................................................................................................147 Site Information.................................................................................................147 Procedures.........................................................................................................147 Results...............................................................................................................148 Conclusions.......................................................................................................150 Sebastian River Bridge.............................................................................................153 Site Information.................................................................................................153 Procedures.........................................................................................................153 Results...............................................................................................................153 Conclusions.......................................................................................................155 Wabasso Bridge........................................................................................................158 Site Information.................................................................................................158 Procedures.........................................................................................................158 Results...............................................................................................................159 Conclusions.......................................................................................................160 Sebastian Inlet Bridge...............................................................................................163 Site Information.................................................................................................163 Procedures.........................................................................................................164 Results...............................................................................................................165 Conclusions.......................................................................................................166 5 NONDESTRUCTIVE LABORATO RY SPECIMEN TESTING............................169 Prior Research...........................................................................................................169 Methodology.............................................................................................................170 Procedure..................................................................................................................170 Results and Discussion.............................................................................................173 Conclusions...............................................................................................................179 6 LABORATORY SIMULATION OF DAM AGE OBSERVED IN THE FIELD....181 Prior Research...........................................................................................................181 Methodology.............................................................................................................182 Procedure..................................................................................................................182 Results and Discussion.............................................................................................186 Conclusions...............................................................................................................192

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vii APPENDIX A SUMMARY OF PONTIS RESULTS......................................................................193 B SUMMARY OF DEFICIENT BRIDGES................................................................211 C NDT DATA AND RESULTS FROM BRIDGE TESTING....................................212 D LABORATORY DATA OF CYLINDER SPECIMENS.........................................225 E LABORATORY DATA AND GRAPHI CAL RESULTS OF LARGE SCALE SPECIMENS............................................................................................................231 F SUMMARY OF STASTICAL RE SULTS OF ULTRASONIC PULSE VELOCITY DATA..................................................................................................282 LIST OF REFERENCES.................................................................................................286 BIOGRAPHICAL SKETCH...........................................................................................293

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viii LIST OF TABLES Table page 2.1 Standard sizes of pin and probe used for penetration tests......................................21 2.2 Acoustic velocities of common ma terials used in construction...............................37 2.3 Relationship between pulse velo city and concrete quality.......................................52 2.4 Emissivities of common engineering materials.....................................................118 5.1 Mixture proportions for NDT and strength tests....................................................170 5.2 Compressive strength vs. resonant frequency of concrete samples.......................178 6.1 Mixture proportions for NDT and strength tests....................................................183

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ix LIST OF FIGURES Figure page 2.1 Flexible borescope......................................................................................................7 2.2 Flexible borescope and monitor.................................................................................7 2.3 Rigid borescope..........................................................................................................7 2.4 Robot used for visual surv ey at the WTC disaster site..............................................9 2.5 Robot used for visual surv ey at the WTC disaster site............................................10 2.6 Cracks in concrete pavement with moisture present................................................11 2.7 Contact angles for various liquids............................................................................12 2.8 Coin tap test results (a) Force-time hist ories of solid and disbonded areas of a carbon fiber reinforced skinned honeycomb structure, (b) Spectra of time histories....................................................................................................................14 2.9 Illustration of t ypical pullout test.............................................................................22 2.10 Typical cross section of the brea koff test, all dimensions in mm............................24 2.11 Sinusoidal oscillation of a loaded spring..................................................................27 2.12 Model of an elastic body..........................................................................................28 2.13 Graphical illustrati on of Snell’s law.........................................................................30 2.14 A portable ultrasonic test ing device used at the University of Florida....................32 2.15 Schematic of a pulse velocity apparatus..................................................................34 2.16 Idealized scans of a material defect : a) A-scan, b) Bscan, c) C-scan,....................35 2.17 Typical ultrasonic test procedure.............................................................................36 2.18 Methods of pulse velocity measurements : a) direct method, b) indirect method, c) surface method.....................................................................................................39

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x 2.20 Schematic of pulse-echo and pitch and catch techniques.........................................42 2.21 Pulse echo schematic (a)Typical test setup, and (b) resulting display.....................43 2.22 Reflections of stress waves fr om internal discontinuities........................................44 2.23 Signal scatter due to uneven reflecting surface morphology...................................44 2.24 Setup of ultrasonic tomographc ray paths................................................................48 2.25 Measurement of crack depth....................................................................................50 2.26 Schematic of a typical piezoelectric tr ansducer used for impact echo testing.........55 2.27 View of a typical imp act-echo equipment system....................................................57 2.28 Illustration of typical wave propagati on through a cross section of a solid.............58 2.29 Illustration of wave propagation mode l through a cross s ection of a solid..............59 2.30 The typical force-time function for the el astic impact of a sphere on a solid..........60 2.31 Example of frequency analysis usin g FFT (a) represents the frequency distribution, (b) represents the corresponding amplitude spectrum.........................62 2.32 Plots of P, S and R-waves at va rious times after an impact (a) 125 s, (b)150 s, (c)200 s and (d) 250 s..........................................................................64 2.33 The ray path of typical P-wave propagation through a solid media.........................64 2.34 Impact echo ray paths (a) A phase change at both boundaries(b) A phase change at upper boundary only................................................................................67 2.35 Schematic representations of (a) P-wave ray reflections a nd (b) the resulting idealized waveform..................................................................................................68 2.36 Actual waveform on an impact-echo test plate........................................................70 2.37 Schematic representation of the test set up for wave speed measurements.............71 2.38 Example waveform obtained in wave speed measurements....................................72 2.39 Illustration of the smallest detectab le crack and its dependency on depth...............73 2.40 A crack at depth ‘d’ gives the same response as a void at that depth......................74 2.41 Surface-opening cracks: (a) perpendicu lar, (b) inclined, and (c) curved.................76

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xi 2.42 Measuring the depth of a surface-openi ng crack: (a) schematic of experimental test setup, and (b) sample waveforms......................................................................76 2.43 The impact-echo response of a concrete slab on soil subgrade: (a) cross-section, (b) waveform, and (c) spectrum...............................................................................78 2.44 The impact-echo response obtained from a concrete slab at a location where a void exists in the soil subgrade (a) cross-sectio n; (b) waveform; and (c) spectrum...................................................................................................................78 2.45 Burst acoustic emission signal with properties........................................................82 2.46 Acoustic emission process.......................................................................................82 2.47 Basic setup of acoustic emission equipment............................................................85 2.48 Various acoustic emission sensors...........................................................................85 2.49 Transient recorder with multiple output acoustic emission signals.........................88 2.50 Acoustic emission calibration block........................................................................89 2.51 Placement of sensors on a concrete cube.................................................................92 2.52 The instrumented sledgehammer and geophone used in the IR method..................97 2.53 Schematic of the impulse response technique..........................................................97 2.54 Theoretical impulse response mobility spectrum.....................................................98 2.55 Typical mobility plot for sound concrete.................................................................99 2.56 Mobility plots for sound and debonded concrete...................................................100 2.57 Mobility plots for sound and delaminated concrete...............................................101 2.58 Schematic of a typical magnetic fi eld induced by an electric current....................103 2.59 Covermeter used by the Civil Engineeri ng Department at the University of Florida....................................................................................................................106 2.60 Typical configuration of c overmeter testing apparatus..........................................107 2.61 Typical display of a GPR Scan. Th e white portion denotes an anomaly...............110 2.62 Typical forced resonant frequency setup...............................................................113 2.63 Dynamic modulus of elasticity vs. cylinder compressive strength........................114

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xii 2.64 The electromagnetic spectrum...............................................................................116 2.65 Typical thermograph revealing defects..................................................................118 2.66 Schematic of a scanning radiometer IR camera.....................................................121 2.67 Schematic description of therm ographic void detection process.............................122 2.68 Radiography schematic..........................................................................................124 2.69 Schematics of direct radiometry: (a) w ith an internal signal detector and external source, (b) with an exte rnal signal detector and source...........................126 2.70 Schematic of backscatter radiometry.....................................................................126 2.71 Image of prestressing cable anchorage in concrete (a) X-radi oscopic image of a prestressing cable anchorage embedded in aconcrete, (b) schematic and brief explanation of the radiographic image...................................................................127 3.1 Summary of sufficien cy rating factors...................................................................130 3.2 The result of a typical bri dge query by sufficiency rating....................................132 3.3 Examples of Pontis codes vs. sufficiency ratings..................................................133 4.1 Plan view of Bahia Honda br idge pilecap and column 54.....................................144 4.2 Photo location plan Bahia Honda bridge pile cap and column 54.........................144 4.3 View of bridge superstructure from water-level....................................................145 4.4 View of footing......................................................................................................145 4.5 View of crack in column........................................................................................146 4.6 View of crack in column. Efflorescence of the gunite toppi ng on the strut can be seen in the background......................................................................................146 4.7 Plan view of crack orientation on column 54.........................................................147 4.8 Plan view of Niles Channel Bridge column line 20...............................................151 4.9 General view of Niles Channel Br idge underside, column line 20 in foreground..............................................................................................................151 4.10 Impact-echo testing on bridge column...................................................................152 4.11 View of typical strut and column repair.................................................................152

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xiii 4.12 Plan view of Sebastian Ri ver Bridge column line 11.............................................156 4.13 General view of Sebastian River Bridge................................................................156 4.14 Column line 11 with column 11-5 in foreground...................................................157 4.15 Column 11-4...........................................................................................................157 4.16 Cracked and delaminated repair in column 11-4...................................................158 4.17 Plan view of Wabasso Bridge column...................................................................162 4.18 General view of Wabasso Bridge...........................................................................162 4.19 Column / pilecap 5.................................................................................................163 4.20 Close-up of exposed seashe ll aggregate on pile cap 5...........................................163 4.21 Plan view of column / pile cap of Sebastian Inlet Bridge......................................167 4.22 General view of Sebastian Inlet Br idge underside. Column line 7 in foreground adjacent to stairs..................................................................................167 4.23 Column line 6.........................................................................................................168 4.24 Plan view of crack orientation on column 12.........................................................168 5.1 Ultrasonic pulse veloci ty experimental setup.........................................................171 5.2 Resonant frequency experimental setup.................................................................172 5.3 Impact echo experimental setup.............................................................................172 5.5 Frequency spectrum of outlying data point............................................................176 5.6 Frequency spectrum of typical impact echo data point..........................................176 5.7 Compressive strength vs. resonant frequency for Mixtures A and B.....................178 6.1 Setup of laboratory experiment..............................................................................183 6.2 Ultrasonic pulse veloci ty testing on specimen.......................................................185 6.3 Impact-echo testing on specimen...........................................................................186 6.4 Wave velocity vs. age for a sample from Mixture A exposed to limewater..........187 6.5 Wave velocity vs. age for a sample from Mixture A exposed to sulfate solution...................................................................................................................187

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xiv 6.6 Close up view of a sample exposed to sulfate solution. The arrow denotes the area of precipitated salt crystals.............................................................................189 6.7 Wave velocity vs. age for a sample from Mixture B exposed to limewater..........190 6.8 Wave velocity vs. age for a sample from Mixture B exposed to sulfate solution...................................................................................................................190

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xv Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Engineering ADVANCED NONDESTRUCTIVE MONI TORING AND EVALUATION OF DAMAGE IN CONCRETE MATERIALS By Christopher Charles Ferraro December 2003 Chair: Andrew J. Boyd Major Department: Civil and Coastal Engineering The objective of this work is to perform research that will enable the FDOT to nondestructively assess and monitor the quality of in-situ concrete bridge structures. As part of the research, a literature revi ew of relevant nondestructive methods was performed. Also survey of rele vant bridge structures within the FDOT’s bridge database system was conducted in an attempt to categor ize prevalent bridge de ficiencies occurring throughout the state. Field research concentrated on the a pplication of the most appropriate nondestructive testing (NDT) methods and thei r application to materials assessment and interpretation of typical NDT data. The at tempt of qualifying the onset of damage was attempted using the applicable NDT method. General material properties of good quality bridge materials were tested nondestructively. Laboratory research focused on the establ ishment of the nondestructive material properties and their relationship to strength properties, which were obtained via the use of

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xvi destructive tests after NDT was performed. Other laboratory research monitored the changes of NDT data within concrete sa mples under constant exposure to severe environments. This experiment was designed to differentiate the effects certain solutions have on field-size samples of concrete when exposed over periods of time. The primary objective of this experiment was to observe th e effect of exposure of concrete to sulfate solutions with respect to surface wave velocity and through wave velocity. Field studies suggest that the wave veloci ty of concrete samples decreases with increasing damage. However, the lack of c ontrolled experiments, involving continuous laboratory monitoring, with respect to stress wave velocity and damage prevents the quantification of th e two parameters.

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1 CHAPTER 1 INTRODUCTION Performance testing of Portland cement conc rete materials dates back to the early 1830’s, when systematic tests were performe d on concrete samples in Germany. Since then, standards for Portland concrete have been created and published by various organizations throughout the world. The concept of nondestructive testing (NDT) is to obtain material properties of inplace specimens without the destruction of the specimen nor the structure from which it is taken. However, one problem that has been prevalent within the concrete industry for years is that the true properties of an in-p lace specimen have never been tested without leaving a certain degree of damage on the st ructure. For most cast-in-place concrete structures, construction specifications require that test cylinders be cast for 28-day strength determination. Usually, representati ve test specimens are cast from the same concrete mix as the larger structural elemen ts. Unfortunately, test specimens are not an exact representation of in-situ concrete, and may be affected by variations in specimen type, size, and curing procedures (Neville 1996). Virtually all concrete stru ctures exposed to nature experience deterioration over time. Inspection personnel have diffi culty determining the quality of in-situ concrete that has experienced decay without direct materi al sampling. The disadvantage to material sampling is that an inspector must remove a portion of the structure, usually by means of coring, and make repairs to the sample area. Removing cores from a concrete structure is

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2 an intrusive process that can weaken the structure and usually leads to long-term durability concerns. The majority of bridges in the state of Florida are constructed of concrete. The Florida Department of Transportation (FDOT ) has been experiencing increased costs for bridge rehabilitation and recons truction due to deterioration of concrete bridge elements as a result of exposure. The objective of this work is to perform research that will enable the FDOT to nondestructively assess and monitor the quality of in-situ concrete bridge structures. As part of the research, a literature review of any relevant nondestructive methods was performed. Also, relevant bridge structures within the FDOT’s bridge database system were reviewed in an attempt to categori ze prevalent bridge deficiencies occurring throughout the state. Field research concentrated on the app lication of the most appropriate NDT methods and their application to the materials assessment and the interpretation of typical NDT data. The attempt of qualifying the onset of damage was attempted using applicable NDT methods. General material properties of good quality bridge materials were established nondestructively. Laboratory research focused on the establ ishment of the nondestructive material properties and their relation to strength properties, which were obtained via the use of destructive tests after NDT was performed. Other laboratory research monitored the changes in NDT data within concrete sa mples under constant exposure to severe environments.

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3 Concrete specimens of dimensions were creat ed to simulate the effect of curing and damage on field-sized specimens. Two differe nt mixtures of specimens were cast and placed in solutions to observe changes in th e material properties. One set of specimens was partially submersed in sulfate solution to simulate the effect of a harsh environment and its effects on concrete specimens with ag e. The other set of specimens was partially submersed in limewater solution to simu late the effect of a control group. The testing regimen consisted of weekly NDT testing of the concrete samples, at ages of one day, one week, two weeks, three we eks, four weeks, six weeks, eight weeks, 10 weeks 12 weeks and 13 weeks. The samples were removed from their respective solutions at the age of 90 days. Nondestruc tive testing was carried out to asses the material property changes over time.

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4 CHAPTER 2 LITERATURE REVIEW Introduction to Nondestructive Testing The purpose of establishing standard pro cedures for nondestruc tive testing (NDT) of concrete structures is to qualify and quantif y the material properties of in-situ concrete without intrusively examining the material pr operties. There are many techniques that are currently being research for the NDT of materials today. This chapter focuses on the NDT methods relevant for the inspection and monitoring of concrete materials. Literature Review Visual Inspection Visual inspection refers to evaluation by means of eyesight, either directly or assisted in some way. The visual inspection of a structure is the “fir st line of defense” and typically involves the search for large-scal e deficiencies and deformities. Perhaps the most important aspect related to the preparation for visual inspection is the review of available literature related to the structure or structural element. This should include original drawings, notes and reports from previous inspec tions, and interviews with personnel familiar with the structure or st ructural element to be inspected. Although interviews are usually not in themselves c onsidered a type of visual inspection, the interview process can often precipitate a visit to the structure or st ructural element that can then focus on visible defects noted by s ite personnel, who usually have the most familiarity with the structure.

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5 Direct visual inspection The basic principle of direct visual insp ection is a meticulous attention to detail. The most common tools used by inspectors include calipers, gauges, templates, micrometers, rulers, levels, chalk, illumina tion devices, cameras, not e taking devices, and other miscellaneous equipment. Direct visual inspection can be app lied to most methods of preventative maintenance and rehabilitation work. Many insp ectors are usually so involved with the search for small-scale deficiencies within a structure that large-scale deficiencies are sometimes overlooked. It is important for the in spector to periodically take a step back and look for larger scale deficiencies. This “can’t see the forest for the trees” syndrome occurs more often in the consulting industry than most people reali ze, especially when lesser-experienced inspecti on personnel are involved. Remote visual inspection Often, field conditions are not conducive to the direct insp ection of a structure or its component elements. Sight limitations could be a result of inaccessibility due to obstructions, hazardous conditions or deficiencies of a scale not visible to the naked eye. When such unfavorable field conditions arise, aids may be required to permit effective visual inspection. Usually, remote visual insp ection involves the effective use of optical instruments. These instruments include mi rrors, borescopes, charged coupled devices (CCD), and remote miniature cameras. Borescopes A borescope is an optical instrument com posed of a tube designed for the remote inspection of objects. A person at one end of the tube can view an image obtained at the other end. The image is transmitted through the tube via fiber optic bundles, running

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6 though the tube, camera, video projection system or lenses. A boresc ope that utilizes fiber bundles for its image projection is common ly referred to as a fiber optic borescope or fiberscope. Another method of image transfer is through the use of a small camera at one end of the tube and a monitor at the othe r end. Lenses can also be used to convey the image to the observer through an eyepiece. Due to the variety of needs created by industry, there are several types of borescopes. The basic categories are rigid or flexible, as dict ated by the configuration of the tube. Figures 2.1 through 2.3 illustrate flexible and rigid borescopes. The borescopes most commonly used today are: fiber opt ic borescopes, camera borescopes, lens borescopes and microborescopes. The fiber opt ic and camera variety are usually of the flexible type, while the lens borescope is typically rigid. Microborescopes can be either rigid or flexible. Borescopes are commonly used for the in spection of objects that have areas of inaccessibility. They are preval ent in the mechanical engineering field more than any other area and are instrumental in the inspec tion and condition assessment of engines and engine parts. However, borescopes are valuab le to civil/structural inspectors and are commonly employed in the inspection of inacces sible structural elements, such as the interior of masonry block or multi-wythe brick walls. Borescopes were instrumental in the Statue of Liberty restor ation project, which began in 1984 and was completed in 1990. Olympus Corporation donated flexible fibe rscopes, rigid borescopes, halogen light sources and photo recording accessories to th e project. The equipment was used by the National Parks Service engineers to ex amine the Lady’s iron skeleton. In depth observations revealed a hazardous array of warp s, sags, leaks, and failed joints (Hellier

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7 2001). Without the use of borescopes, the inspect ors’ efforts would have resulted in an incomplete assessment of the structure. Figures 2.1-2.3 are photogr aphs of the most commonly used borescopes. Figure 2.1: Flexible bor escope (Hellier 2001) Figure 2.2: Flexible borescope and monitor (Hellier 2001) Figure 2.3: Rigid bores cope (Hellier 2001) Charged coupled device Willard Boyle and George Smith of Bell Laboratories invented the Charged Coupled Device (CCD) in 1970. Since then, CCDs have been used in many of the

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8 computer-based optical equipment in use today. CCDs can be found in photocopiers, facsimile machines, cameras, scanners a nd other optical com puter based products. A CCD is composed of thousands of light sensitive cells, usually referred to as pixels that produce an electrica l charge proportional to the am ount of light they receive. These pixels can be arranged in either a linear or two-dime nsional array, which in turn can be used to produce a digital image. Th e typical facsimile machine and computer scanner used today have a linear arrangement of CCDs, which progressively traverses the original object in order to progressively bui ld a digital copy. Digital cameras use a two dimensional CCD, also called an area CCD, to instantly create a digital image. CCDs are of value to the inspection industr y as they allow insp ectors to capture images of specimens as the traditional cam era has done for decades. The advantage of using CCD based technology over film-based ca meras is primarily the speed in which the images are developed. Digital photos ar e usually viewable through the camera instantaneously, which allows personnel on si te to observe the image without delay. The person taking the digital photo can then make an on-site decision concerning the quality of the image and whether it needs to be recaptured. Robotic cameras Miniature cameras are sometimes considered a variation of fiber optic cameras. In the recent past, both miniature cameras and fi ber optic cameras both required a wire or some physical connection to the monitor or viewing device. However, as technology progresses, limitations diminish. Miniature robotic cameras were instrumental in the initial stages of the inspection of the Wo rld Trade Center (WTC ) disaster site in September 2001. The robots deployed at the WT C site were completely free of cables and were able to gain access to areas wh ere human access was impossible or hazardous.

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9 The equipment used in this case employed artificial inte lligence, robotics, and CCD technology. Dr. Robin Murphy, an A ssociate Professor at the Univ ersity of South Florida, is also the Director of Research for the Center for Robot-Assisted Search and Rescue (CRASAR) in Tampa, Florida. Her research primarily encompasses artificial intelligence in robotics and robot tasking (Murphy 2000). The robots employed at the WTC disaster site depicted in 2.4 and 2.5, were used to explore and inspect the inner areas of the wreckage. Remote exploration of the site allowed inspectors to locate victims and visual ly inspect the structural integrity of the wreckage. The robots were used in several areas of the site, in cluding the collapsed Towers One and Two. This was the first known robot-assisted search and rescue response, and represented the culmination of six years of research and training. The robots were successfully used to find at leas t five victims, helped rescue teams select voids for further searching, and assisted in the building clearing effo rts. Videos of the robots, their interfaces, and views from their sensors were used to illustrate key findings on mobility, sensing, control, and human-robot interaction. Figure 2.4 : Robot used for visual survey at the WTC disaster site (Casper 2002)

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10 Figure 2.5 : Robot used for visual survey at the WTC disaster site (Casper 2002) Although disaster inspection is a highly sp ecialized and limited field of research, the technology developed and implemented for th is work will become more prevalent in the visual inspection industry. Applications of Visual Inspection Visual inspection is a fast, convenient and relatively inexpensive technique used to evaluate the overall condition of structures. This technique allows inspectors to make real-time evaluations and recommendations of a given structure, which is particularly valuable in emergency or safety inspections. Some limitation of the visual inspection t echnique is sight obstructions, which can be due to lighting, access or obstruction. Anothe r disadvantage of visual inspection is the “human factor” that is often encountered. Th e susceptibility to human misinterpretation and the requirement for establishing a baseline for defects in gene ral, especially under poor conditions, can lead to inconsistent identi fication of anomalies, which can give rise to contradicting evaluations (Qasrawi 2000). Liquid Penetrant Methods The liquid penetrant examination method can be used to nondes tructively evaluate certain nonporous materials. The American Society for Testing and Materials (ASTM) has developed material specific test standa rds for the penetrant examination of solids

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11 (ASTM E165 – 95). Liquid penetrant methods are nondestructive te sting methods for detecting discontinuities open to the surface, such as cracks, seams, laps, cold shuts, laminations, through leaks, or lack of fusion. These methods are appli cable to in-process, final, and maintenance examinations. They can be effectively used in the examination of nonporous, metallic materials, both ferrous and nonferrous, and of nonmetallic materials such as glazed or fully densified cerami cs, certain nonporous plastics, and glass. Hardened Portland cement concrete is a perm eable material due to the properties of the cement matrix. As concrete is batched and mixed, capillary pores are formed in the hydrated cement matrix; penetrant methods of i nvestigation, as described in the relevant ASTM standard, do not apply to concrete b ecause they were developed for testing of nonporous materials. At present, there is no st andardized test method available for liquid penetrant examination of porous materials. However, it is possible to use water as an aid to detect surface flaws in concrete. Inspectors can apply water to a concrete surf ace and observe the rate of drying. As the water evaporates from the surface, areas containing cracks will hold moisture. As illustrated in Figure 2.6, these moist areas wi ll result in local di scoloration of the concrete, which facilitates the visual detection of cracks. Figure 2.6: Cracks in concrete pavement with moisture present (ACI 201.1 R92)

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12 The principle upon which the liquid penetrati on method is based is that of capillary suction, a physical phenomenon in which the surf ace tension of liquids causes them to be drawn into small openings such as cracks, seam s, laps, cold shuts, laminations and other similar material deficiencies. The most important property affecting the ability of a penetrant to enter an opening is “wetability”. Wetability refe rs to a liquid's behavior when in contact with a surface (Hellier 2001). The angle created between the free surface of a liquid and a solid surface is referred to as the contact angle. It is an important characteristic related to the penetrability of the liquid. Liquids that have small contact angl es have better penetrability than those liquids exhibiting large contact angles. Figure 2.7 depicts contact angles for various liquids. Figure 2.7: Contact angles for various liquids (Hellier, 2001) Viscosity is another signifi cant property of liquid penetr ants. Viscosity is defined as the resistance to flow in a fluid, or semi fluid. Liquids with lower viscosities are more desirable for use in liquid penetrant examinati on since they have superior flow properties. The visibility of the liquid penetrant is a valuable quality in the penetrant examination procedure. Usually, the visibili ty or contrast of a liquid penetrant is measured by the dye concentration, which ma kes the liquid penetrant more visible. Contrast ratio is used to measure the visibili ty of a penetrant. The contrast ratio scale ranges from 50:1 to 1:1, where a contrast ratio of 1:1 would re present a color in reference

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13 to itself, for example, red dye on a red solid surface. Contrast ratios of 40:1 can be achieved through the use of fluorescent dye pe netrants under ultraviolet illumination. As a result, ASTM has recognized fluorescent pe netrant examination, and standard test methods have been developed. ASTM D4799-03 is the standard test that describes the conditions and procedures for fluorescent pe netrant testing for bituminous materials. Although liquid penetrant methods have been beneficial in the location of surface defects in solids, they have several limitations. Existing liquid penetrant examination techniques are applicable to the inspection of nonporous solids and are thus not applicable to the survey and inspection of concrete structur es and buildings. The majority of these are composed of concrete and mas onry; both of which are porous materials. Acoustic Sounding Acoustic sounding is used for surveying c oncrete structures to ascertain the presence of delaminations. Delaminations can be a result of poor concrete quality, debonding of overlays or applied composites, corrosion of reinforcement, or global softening. The test procedures used fo r delineating delaminations through sounding include: coin tap, chain drag, hammer drag, and an electro-mechan ical sounding device. The purpose of each test is to sonically dete ct deficiencies in the concrete. ASTM has created a standard, ASTM D 4580 – 86 which covers the evaluation of delaminations. The standard describes procedures for both automated and manual surveys of concrete. A major advantage to sonic te sting is that it produces immediate results on near surface anomalies. The effectiveness of sonic te sting relies heavily on the user's expertise in signal interpretation and consistency.

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14 Coin tap test The coin tap test is one of the oldest a nd most widely researched methods of sonic testing. The test procedure requires the insp ector to tap on the conc rete sample with a small hammer, coin, or some other rigid object while listening to the sound resulting from the impact. Areas of nondelaminated concre te will create a clear ringing sound upon impact while regions of delaminated, disbonded, or softened concrete will create a dull or hollow sound. This change in sonic characteri stics is a direct result of a change in effective stiffness of the material. As a result the force-time function of an impact and its resulting frequencies of an impact differ be tween areas of good and poor quality concrete (Cawley & Adams, 1988). ASTM D 4580-86 describes the procedure for manually surveying concrete structures for delami nations using the coin tap procedure. Figure 2.8: Coin tap test result s (a) Force-time histories of so lid and disbonded areas of a carbon fiber reinforced skinned honeycom b structure, (b) Spectra of time histories (Cawley & Adams, 1988)

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15 Figure 2.8 illustrates the shorter force-time history and larger resulting frequency produced by impacts on solid material as opposed to disbonded/delaminated material. Understanding the force-time function aids an in spector’s abilities to sonically evaluate a material, as it takes less time for two elastic so lids to separate subse quent to a collision. A similar analogy could be made by comparing the effect of walking on a sidewalk to walking in the mud. The sinking phenomenon that one experiences in the mud is similar to the extended time length of impact produced by a delaminated material. The “sinking” of the hammer or coin into the delaminated ma terial results in a plas tic deformation of the material, resulting in a more dull or hollow sound. The electronics industry has pr ovided inspectors with equi pment that is capable of detecting and recording the sonic wave si gnals that are produced by an impact. As a result, there are currently several commercia lly available products available for such signal acquisition. The most common devices for sonic data acquisition are the instrumented hammer and the smart hammer. The instrumented hammer was developed for the airline industry to be used in the detection of anomalies in airplane material s. It measures and records the force-time history and amplitude frequency of an impact via the use of an accelerometer embedded in the head of the hammer. The smart hammer was developed for the sh ipbuilding industry. This instrument measures and records the sonic response of an impact through a microphone. The microphone uses the sonic data, instead of the force data, to create an acoustic signal. Both impact-force data generators and impact-sound data generators have been proven to generate useful signals for nondestru ctive sonic testing. The information gained

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16 from both sources has demonstrated their ca pability of producing consistent and valid experimental results. At the present time, re search is being conduc ted into both impactforce and impact-sound devices to develop im proved testing methods. Both devices have created the opportunity for improved standa rdization of acoustic sounding tests. The objective nature of testing with mechanical devices th at are capable of producing consistent and repeatable results can help to improve testing standa rds for structural and material inspectors. Although the instrumented hammer and smart hammer are considered to be automated delamination in spection equipment, the testing data and procedures produced by these devices are still in the initial stages and an ASTM standard test method for these devices has not yet been created. Chain drag survey The chain drag survey provides a low-cost method to inspect delaminated areas in concrete surfaces. The survey allows inspectors to traverse a large area with reasonable accuracy in a short period of tim e. Since the test is quick a nd inexpensive it may be used for an initial evaluation to determine the need for further investiga tion. Like the coin tap and hammer sounding methods, the chain drag te st is subjective, and therefore requires an experienced inspector to perform the surve y. Due to the nature of the test, localized areas of delaminations are more difficult to detect. Concrete decks or slabs that have comparatively large percentages of deficien cies may require the use one of the more localized tests, like the coin tap or hamme r sounding methods, to provide a more accurate picture of the tested structure. The chain drag survey consists of draggi ng a chain over the concrete surface. This approach suffers from limitations similar to the electro-mechanical sounding device. The chain drag survey cannot be performed on vert ical members of a structure and thus is

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17 limited to the topside of concre te slabs and decks. Similar to the coin tap test, areas of nondelaminated concrete will create a clea r ringing sound upon contact, and areas of delaminated, disbonded or softened concre te will create a dull or hollow sound. The typical chain used for inspection is composed of four or five segments of 1 inch link chain of ” diameter steel approximately 18 inches long a ttached to an aluminum or copper tube two to three feet in length. The test is perfor med by dragging the chain across the entire surface of the conc rete slab and marking the areas that produce a dull sound. The deficient areas can be recorded and fu rther investigated using other techniques. Electro-mechanical sounding device The Electro-Mechanical sounding device is a small, wheeled device equipped with tapping wheels and sonic receivers. Two rigi d steel tapping wheels provide the impacts for the delamination survey. The sonic receivers are composed of oil filled tires coupled with piezoelectric transducers. The data acq uisition equipment is composed of a data recorder that stores the si gnals from the sonic receiver s (ASTM D4580-86). The electromechanical sounding device has become some what antiquated as the development of other, more reliable and more efficient, delamination survey techniques have been developed. ASTM D 4580-86 (pro cedure A) defines the standard practice for performing a delamination survey using this device. It is primarily limited by the nature of the equipment employed, as it cannot perform tests on vertical concrete su rfaces, and is thus restricted to the top surface of concrete decks and slabs. Applications of acoustic sounding Acoustic sounding has proven to be a reliable supplement to visual and other forms of evaluation due to its capability to conduct near-surface investigatio ns at a relatively rapid rate. These techniques are also valuable in that they are usually relatively low in

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18 cost and can be conducted in conjunction with most visual inspections. However, the method is limited in several respects. It remains largely subjective to human interpretation and can be a confusing techni que when background noise is prevalent. The method lacks the ability to detect small defects and subsurface defects, as it is strictly a near-surface investigation method. Surface Hardness Methods Essentially, the surface hardness methods for nondestructive testing of concrete consist of impact type tests based on the re bound principle. Some of these methods have been effectively used to test concrete since the 1930’s. Due to the complexity of concrete as a material and the disparity between th e concrete surface and the inner structure, surface methods are inherently limited in th eir results. However, surface methods have been proven to give an effective evaluation of the uniformity of a concrete member and in comparing concrete specimens in a relative sense. The most widely used surface hardness methods are the testing pistol by Williams, the pendulum hammer by Einbeck, the sp ring hammer by Frank and the rebound hammer by Schmidt. The Schmidt rebound hammer has become the industry favorite in the use of surface hardness measurements today. The Schmidt hammer is basically a hand-held spring plunger that is suitable for lab or field-testing. Th e capabilities of the Schmidt hammer have been extensively tested, and there are over 50,000 Schmidt hammers in use world-wide (Malho tra & Carino 1991). The basic rebound principle cons ists of a spring-driven mass that is driven against the surface of a concrete specimen with a known energy. The rebound distance of the mass is measured and the "hardness" of the concrete surface is estimated from this value. A harder surface results in a longer rebound distance due to the increase in energy

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19 reflected back to the impinging mass. Howe ver, despite its appa rent simplicity, the rebound hammer test involves complex problems of impact and the associated stress wave propagation (Neville 1995). The energy absorbed by a conc rete sample is related to both its strength and its stiffne ss. Therefore, it is the combination of concrete strength and stiffness that influe nces the rebound number. There is no unique relation between su rface hardness and in-situ strength of concrete. This relationship is dependent upon an y factor affecting th e concrete surface, such as surface finish, degree of saturation, and surface preparation. The concrete mix design, including the type of aggregate, wa ter/cementitious materials ratio and cement type can also affect hammer results. Th e method cannot accurately determine the subsurface condition of concrete. It tests only a localized area of concrete to a depth of perhaps 20 or 30mm (BSI, 1986). The condition of the concrete will further affect the rebound number. Areas of honeycombing, scal ing, rough surfaces and high porosity will decrease the rebound number. Areas of car bonation will increase the rebound number. Therefore, the user must insure careful select ion of a representative area of concrete and must understand the limitations inherent in the test. The Schmidt rebound hammer is, in principle, a surface hardness tester with little apparent theoretical relati onship between the strength of concrete and the rebound number of the hammer. However, within limits, empirical correlations have been established between strengt h properties and the rebound number (Malhotra & Carino 1991). The accuracy of the rebound hammer has been estimated between 15-20% under laboratory testing conditions and 25% in field-testing conditions. Such accuracy, however, requires a proper calibration of th e hammer with the concrete in question.

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20 The American Society for Testing and Materials (ASTM) has created a standard test for the Rebound Number of Hardened Concrete (ASTM C 805-97). This test specification should be referenced and strict ly followed for proper testing procedures. Penetration Resistance Methods The basic principle behind penetration resi stance methods is the application of force to a “penetrating object,” and then dete rmining the resistance of a specific concrete to such penetration by measur ing the depth of penetration. Penetration resistance methods have been effectively used to test concrete since the 1960’s. The limitations of penetration methods are similar to the limita tions of surface hardness methods. The depth of penetration is usually only a small percentage of the full de pth of the concrete member. Penetration methods have been proven to give an effective near surface evaluation of insitu compressive strength, uniformity of conc rete and soundness at different locations. The two most commonly used penetration re sistance methods are the Pin Penetration Method and the Windsor Probe. The Pin Penetration method uses a springdriven mechanism to drive a 30 mm long, 3.6 mm diameter steel pin into the conc rete surface. The pin is subsequently removed and the depth of the resulting hole is measured. The Windsor Probe test uses the same principle, although larger diameter steel probe is used. Table 2-1 contains a schedule of probe sizes for each test. The Windsor Probe test requires a larger driving force and employs a gunpowder charge to de velop the necessary impetus. ASTM has approved a standard test for the Penetration Resistance of Hardened Concrete (ASTM C 803-97), which covers both tests. This test sp ecification should be referenced for proper testing procedures.

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21 Table 2.1: Standard sizes of pin and probe used for penetration tests. Pin Penetration Method Windsor Probe Test Size of Penetration: 30 mm length 3.6 mm diameter 80mm length 6.3/7.9mm diameter Usable Range of Concrete Strength: 450 – 4000 psi 3-28 MPa 450 – 6000psi 3 – 40 MPa The ASTM standard requires three firmly em bedded test probes in a given test area to constitute as one test for both pe netration test methods (ASTM C803-97)The penetration methods are still near-surf ace tests but do offer reliable empirical relationships between concrete strength and penetration resistance. Consistent empirical correlations have been successfully esta blished between stre ngth and penetration resistance. The penetration methods ha ve been estimated to be within 5% accuracy under both laboratory and field-te sting conditions when the test procedure is performed properly and a valid correl ation has been developed. The primary limitation of penetration methods is that they do not offer a full-depth appraisal of the concrete that they are testing. They are c onsidered to be surface-testing methods only and they do not yield absolute values for the strength of concrete in a structure. They are effective at estimating in situ concrete strength only when the proper correlations are performed subsequent to te sting. Penetration me thods are not purely nondestructive in nature since they induce some damage to the tested specimen. It is more accurate to consider penetr ation tests as semi-destructive. Pullout Test The basic purpose of the pullout test is to estimate the in situ strength of a concrete structure. Pullout tests consist of measuri ng the force required to extract a mechanical insert embedded in a concrete structure. The measured pullout force can then be used to

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22 estimate the compressive, tensile and shear stre ngth of the concrete. The pullout test was originally developed in the former Soviet Union in the 1930’s and later independently developed in the United States in the early 1940’s. Further research has led to several modifications since then. The test that is most commonly used in industry today is the pullout test as modified by Kaindl in the 1970’s. The pullout test, illustrated in Figure 2.9, uses a metal insert that is inserted into fresh concrete or mechanically installed into hardened concrete. The tensile or “pullout” force required to extract the embedded insert, an d the core of concrete between the insert and the surface, can give accurate estimates of the concrete's compressive, tensile and shear strengths. The pullout test has beco me a proven method for the evaluation of the in situ compressive strength of c oncrete and has several industr y applications. The pullout test is used to determine whether the streng th of the concrete has reached a sufficient level such that post-tensioning may commence; cold weather curing of concrete may be terminated or forms and shores may be removed. Figure 2.9: Illustration of typical pu llout test (Malhotra & Carino 1991)

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23 Consistent empirical correla tions can be established be tween strength properties and pullout test methods. Pull out test results have been estimated to be within 8% accuracy for laboratory and field-testing condi tions when the test procedure has been performed properly and a proper co rrelation has been developed. The pullout test method does not provide a full-depth appraisal of the concrete structure that is being teste d. It is not truly nond estructive in nature since it induces significant damage to the tested member. It is more accurate to consider the pullout test as semi-destructive. The damage incurre d during pullout testi ng is usually more significant than most other “NDT” methods and patching of the tested structure is usually required. Figure 2.9 shows a schematic of the pullout test. ASTM has created a standard test for th e Pullout Strength of Hardened Concrete (ASTM C 900-99). This test specification s hould be referenced for proper testing procedures. Break-Off Test The primary purpose of the break-off test is to estimate the strength of a concrete structure. This test involves the breaking off of an intern al cylindrical piece of the in situ concrete at a failure plane parallel to the surface of the concrete component. The measured break-off force can then be used to estimate the compressive and tensile strength of the concrete. The break-off test was originally developed in Norway in 1976. It was later introduced into the United States in the early 1980’s. The test procedure used today is essentially the same as when the test was originally introduced. The break-off test can use a cylindrical sleeve that is inserted into fresh concrete to create the embedded cylinder. Alternatively, the embedded concrete cylinder can be

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24 drilled into hardened concre te using a core drill bit. The embedded cylinder size is usually 55mm in diameter and 70mm in hei ght. Figure 2.10 illustrates a typical cross section of the breakoff test. Figure 2.10: Typical cross section of the breakof f test, all dimensions in mm (Malhotra & Carino 1991) The actual test method involves the applic ation of a horizontal force to the upper edge of the embedded concrete cylinder, wh ich is slowly increased until failure. The force required to break the embedded cylinder is then used to estimate the concrete compressive and tensile streng th. The break-off test is a pr oven method of evaluation of the in situ compressive strength of concrete a nd has several industry uses. Like the pullout test (described later) it is used to determine whether the stre ngth of the concrete has reached a specified value so that pos t-tensioning of a bridge structure may commence, cold weather curing of concrete ma y be terminated, or forms and shores can be removed. Consistent empirical correlations have b een established between strength properties and break-off test methods. The break-off test results have been estimated to be within

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25 7% accuracy for laboratory and field-testing conditions when the test procedure has been performed properly and sufficient data is available to formulate a proper correlation. The primary limitation of the break-off test is that it is not tr uly nondestructive in nature. It induces sign ificant damage to the tested memb er. Thus, it is more accurate to consider the break-off test as semi-destruc tive. The volume of removed material is 667 cm3 or 41 in3. Thus, the damage incurred during br eak-off testing is typically more extensive than other “NDT” methods, and patc hing of the tested structure is usually required. ASTM has approved a standard test fo r the Break-Off Number of Hardened Concrete (ASTM C 1150-96). Th is test specification shoul d be referenced for proper testing procedures. Ultrasonic Testing Ultrasonic testing is a NDT method that is used to obtain the properties of materials by measuring the time of travel of stre ss waves through a solid medium. The time of travel of a stress wave can then be used to obtain the speed of sound or acoustic velocity of a given material. The acoustic velocity of the material can enable inspectors to make judgments as to the integrity of a structure. The term ultrasonic is defined as a sound having a frequency above the human ear's audibility limit of about 20,000 hertz. Ultrasonics are very popular in the medical industry and have been used there for ove r thirty years, allowing doctors to nonintrusively investigat e internal organs and monitor blood flow in the human body. The materials industry has also been able to uti lize ultrasonics for non-intrusive investigation

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26 of assorted materials such as metals, compos ites, rock, concrete, li quids and various other nonmetals. The first studies of ultrasonics are recorded as far back as the Sixth Century B.C. when Greek philosopher, Pythagorus performe d experiments on vibrating strings. Galileo Galilei is credited with performing the first of the modern studies of acoustics. He was the first scientist to correlate pitch with frequency of sound. The earliest known study of the speed of sound in a liquid medium t ook place in 1822 when Daniel Colladen, a Swiss physicist/engineer, and Francois Sturm, a Swiss mathematician, used flash ignition and a bell to successfully estimate the speed of sound in Lake Geneva, Switzerland. In 1915, Paul Langevin pioneered the study of highfrequency acoustic waves for submarine detection during the outbreak of World War I (Guenther 1999). The age of ultrasonic testing of material s was establised in 1928 by Sergei Y. Sokolov, a scientist at the Leni n Electrotechnical Institute in Leningrad, Russia. Sokolov proposed and demonstrated that he could tr anslate ultrasonic waves or sound pressures into visual images. In the 1920’s he advan ced the idea of creating a microscope using high frequency sound waves. He then applied hi s ideas to detect abnormalities in metals and other solid materials. As technologies ha ve developed over the twentieth century, the knowledge gained through the use of the high frequency microscope has been applied to other ultrasonic systems (e.g. radar) (Guenther 1999). In the United States, the development of the ultrasonic test is attributed to Dr. Floyd Firestone, who, in 1942, introduced what is now called the pulse echo technique (described later) as a method of nondestructiv e testing. Dr. Firestone successfully used the pulse echo technique for ultrasonic flaw detection. Ultrasonics have since been used

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27 to evaluate the quality of concrete for appr oximately 60 years. The method can be used for non-intrusively detecting in ternal defects, damage, and deterioration in concrete. These flaws include deterioration due to sulf ate and other chemical attacks, cracking, and changes due to freeze-thaw cycling. Theory Ultrasonic testing of materials utilizes the vibrations of the particles that comprise a given medium. Sound waves and ultrasonic wa ves are simply the vibrations of the particles that make up a solid, liquid, or gas. As an energy form, the waves are an example of mechanical energy. The motion of vibration is described as a periodic motion of the particles of an elastic body or medium, in alternately oppos ite directions from the position of equilibrium when that equilibrium was dist urbed. However, vibration can also be described as an oscillation, which is the act of swinging back and fourth between points. An elastic oscillation is one in which the driving force behind the oscillation (e.g. a spring) is proportional to the displacement of the object. Figure 2.11 illustrates the basic sinusoidal oscillation of a free body on a loaded spring and the resul ting sine curve that can be achieved when the motion is plotted with respect to time. Figure 2.11: Sinusoidal oscillation of a loaded spring (Krautkramer 1979)

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28 The sinusoidal waveform that is cr eated by sound waves is a convenient characteristic of the wave motion that allo ws scientists to quantify sound in terms of amplitude and frequency. The frequency of these waves differentiates sonic from ultrasonic waves. The unit of frequency is th e hertz or Hz, and is de fined as one cycle of vibration per second. Sounds below approximately 16 Hz are below the lower limit of human audibility, whereas sounds of 20,000 Hz are above the upper limit of human audibility. The basis of ultrasonic testing is part icle vibration within a medium upon the application of mechanical energy. Figure 2.11 shows the free body motion of a single mass and its interaction with a single spring. Considering th e mass from the diagram in Figure 2.11 to be a particle, and the spring to be the connection of particles, the simple principle of free body motion to fit a particle interaction model can be expanded as seen in Figure 2.12. Figure 2.12: Model of an elas tic body (Krautkramer 1979) The model depicted in Figure 2.12 is the basic model used in wave science. Mechanical waves propagate through materials by means of particle motion. Wave propagation is largely dependent upon the type of excitation or energy input, the mass of the individual particles, and the spring stiffness of their internal connections. A wave initiated by an external event such as nor mal or shear force, travels by vibratory

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29 movement transmitted from particle to particle If the springs that connect the particles were infinitely stiff, all particles of the materi al would start to oscill ate at the same instant and the wave would be transmitted at an infi nite speed. Hence, the material’s elasticity and density play an important role in wave propagation (Kaiser & Karbhari 2002). Internal friction and other forces resist particle motion upon excitation, and wave propagation occurs at a finite rate. This rate is referred to as its wave velocity and is dependent upon material composition. Although sound waves can propagate through all three forms of matter (solids, liquids and gases), the type of waveform able to move though a material is dependent on the material phase. For materials in the ga seous or liquid phase, dilatational waves are typically the only form that travels well. Dilatational waves are also referred to as compression or longitudinal waves and are th e primary stress waves produced by material excitation. The particle motion in a longitudi nal wave is parallel to the direction of propagation. The result is a co mpressive or tensile stress wave. Distortional waves are the s econdary stress waves that are produced upon forced contact. These waves are also called shear or transverse waves. In shear waves, the particle motion of the wave front is normal to the direction of pr opagation, resulting in shear stress. Rayleigh waves, also called surface wave s, differ from longitudinal and shear waves because they do not propagate through a solid. Rayleigh waves propagate along the surface in an elliptical motion. Lamb waves are similar to Rayleigh waves because they also do not travel through a material and are also considered surface waves. Lamb waves, however, occur only in

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30 solids that are a few wavelengths in thic kness and have a uniform thickness. Common objects subject to the development of lamb wa ves are plates, pipes, tubes, and wires. The behavior of waves at material interfaces The term interface is defined as a surface forming a common boundary of two bodies, spaces, densities or phases. One of the most common interfaces people are familiar with is the oil-water interface. In materials science, an interface is usually defined as a fringe between tw o materials, which have differe nt properties such as density or phase. Another possible difference in materi al properties is acoustic impedance, which is defined as a material's density multiplied by its wave speed. When stress waves collide with material interfaces, portions of the wave s are reflected and refracted. The principle of refraction is best described by Snell’s law, which relates the angl e of refraction and the wave velocity to the refrac tion angle of two materials. 2 1sin sin V R V i (1) where : io = angle of incidence Ro = angle of refraction V2 = wave velocity in Medium 2 Figure 2.13: Graphical illustrati on of Snell’s law (Hellier 2001)

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31 Figure 2.13 shows a typical example of the refraction angle of an ultrasonic wave as it enters a different material. The concrete -air and the concrete-s teel interfaces are the two most common interfaces encountered in non destructive testing of civil engineering structures. Most of the illustrations used to describe the characteristics of ultrasonics consider the sound or ultrasound as a two-dimensional ray, which is somewhat simplified for the study of ultrasonics and nondestructive testi ng. A more accurate representation of the sound energy is a three dimensional beam. The study of a sound beam is more complicated than a sound ray. As the comple xity of the physical characteristics in a material increases, different mechanical mech anisms become factors in their analysis. Scientists define attenuation as the gradual loss of sound wave energy through a medium. Attenuation can be more accurately described as the comb ined effect of a number of parameters: Interference from diffraction effects Interference adsorption (friction and heat) Interference scatter Interference beam spread (Hellier 2001) The combination of these effects can create disturbances and erratic signals within a material. One of the early challenges of scientists using ultrasonic equipment was deciphering and filtering the interference signals created by material properties. Instrumentation Commercial ultrasonic equipment has been under development since World War II. The first equipment available to the materi als engineering industry was produced in the 1950’s. Since then, a variety of ultrasonic detec tion devices have become available. Most of the ultrasonic devices used for material inspection and flaw det ection are portable and

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32 battery powered. A portable ultrasonic testi ng device is illustrated in 2.14. Portability enables material inspection in the field and a high degree of user flexibility. Figure 2.14: A portable ultrasoni c testing device used at th e University of Florida The typical testing apparatus used for ultr asonic testing consists of the following: Transducer Time Measuring Circuit Receiver/Amplifier Display Reference Bar Coupling Agent Transducer A transducer is used for transforming elec trical pulses into bursts of mechanical energy. A typical pulse velocity apparatus consists of a transmitting transducer and a receiving transducer. The transmitting trans ducer generates an u ltrasonic pulse through the test specimen, and the receiving transduc er receives the pulse. The generation and reception of ultrasonic waves is accomplished using piezoelectric crystals. Piezoelectric elements are reciprocal, whic h means an applied voltage ge nerates a deformation, or an

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33 impinging stress generates a voltage. This physic al property makes piezoelectric elements ideal as transducer s (Papadakis 1999). Time measuring circuit The time measuring circuit or clock is an essential component of the ultrasonic pulse velocity equipment. It controls the frequency output of th e pulse by signaling the pulser to provide a high-volta ge pulse to the transducer. The time measuring circuit measures the time of travel of a pulse or st ress wave through the test specimen. Since the primary function of the time measuring circ uit is to regulate pulse generation, it is commonly referred to as a pulse r. It provides an output to the display when the receiving transducer receives a pulse. The time measuri ng circuit is capable of producing an overall time-measurement resolution of 1 microsecond ( s). ASTM C597-97 requires a constant signal with a varying voltage of 15% at a temperature range of 0 C 40 C. Receiver/amplifier The receiver is the term applied to all of the circuit functions that amplify the weak echoes and determine their amplitude. It has f our basic components, the preamplifier, the logarithmic amplifier, the rectifier and the low pass amplifier. The function of the preamplifier is to en sure that any signal from the receiving transducer arrives at the tim e measuring circuit. Since el ectrical outputs from the transducer are relatively small, signal am plification is necessary to overcome the resistance in the transducer cable, which can be relatively long The function of the logarithmic amplifier is to process weak echo signals. Once the weak signals are amplified, the rectifier and the low pass filter process the signals. After processing by the

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34 receiver/amplifier, a useable signal can be sent to the display. A sc hematic of a typical ultrasonic pulse velocity me ter is shown in Figure 2.15. Figure 2.15: Schematic of a pulse velocity apparatus (ASTM C597-97 2001) Display The signal received by the ultrasonic test e quipment is typically displayed digitally with modern equipment. The results consist of a direct reading of display time on an x-y coordinate system. The x-axis becomes the time trigger and the y-axis represents the mechanical energy received. The display units can also illustrate defect or anomaly locations and sizes, depending on the type of data requested by the user. The information obtained in the ultrasonic te st is referred to as a scan. Currently there are three types of scans th at are applicable to ultrasoni c testing: A-scans, B-scans, and C scans. The A-scan is the simplest scan form. It is a spot scan of the material and results in the most basic form of displayed informati on. The resulting scan is a waveform where regions of high frequency sound waves are recorded and displayed as peaks on the screen. B-scans are a bit more sophisticated. They incorporate a linear scan instead of a point or spot scan. B-scans are essentially th e summation of a series of A-scans that are produced by “sweeping” the transducer over the material specimen. C-scans are even

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35 more complicated than B-scans because they incorporate a two dimensional grid system. C-scans are comprehensive scans that are most applicable to nonde structive testing of materials. Figure 2.16 illustrates the differen ces between these three types of scans. Figure 2.16:Idealized scans of a ma terial defect: a) A-scan, b) B-scan, c) C-scan, (Kaiser & Karbhari 2002) Reference bar The reference bar is a piece of material that is used to calibrate the ultrasonic apparatus. Ultrasonic instruments, which use a microprocessor to record delay time, do not require a reference bar. These instru ments can be calibrated by compressing both transducer together to obtain a zero read ing. Otherwise, ASTM C597-97 requires that a bar of metal or some other material for wh ich the transit time of compressional waves is known. The reference bar is used as a functi onal check of ultrasonic equipment prior to testing. Coupling agent A coupling agent is usually required to ensu re the efficient transfer of mechanical energy between the transducer and the test ed material. The purpose of placing the coupling material between the transducer and test specimen is to eliminate air between the respective surfaces. Typically, coupling agents consist of viscous liquids such as grease, petroleum jelly, or water-soluble jelly. Ponded surface water is also considered an

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36 acceptable couple. Water is considered as an acceptable couple for underwater ultrasonic testing. Acoustic velocity calculation The acoustic velocity wave speed of a given concrete specimen can easily be obtained with the travel time of a stress wave and the length of the specimen. The pulse is sent from the sending transducer to the receiving transducer through the concrete specimen as see in Figure 2.17. The relations hip of a specimen’s acoustic velocity is simply calculated from a time and a length measurement. It should be noted that cracks, flaws, voids and other anomalies within a mate rial specimen could in crease time of travel therefore decreasing the materials acoustic ve locity. However, assuming the specimen in Figure 2.17 is free of anomalies, its acoustic velocity can be calculated simply by. The length of the specimen is 200 mm. Figure 2.17: Typical ultr asonic test procedure V = L/T; V= 0.2m/47.5 s = 4210 m/s (2) The experiment shown in Figure 2.17 provide s the user with a quantitative result. The pulse velocity acoustic velo city, V, of stress waves throu gh a concrete mass is related to its physical properties (ASTM C597-97). is a function of Young’s Modulus of

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37 Elasticity E, the mass density and Poisson’s Ratio The relevant equation for wave speed is: ) 2 1 )( 1 ( ) 1 ( E V (3) The acoustic velocity of a solid varies given its composition. Therefore, different materials have different acous tic velocities. The acoustic ve locities of common materials are shown in Table 2.2 (Krautkramer 1991). Table 2.2 Acoustic velocities of co mmon materials used in construction Flaw detection The immersion testing method involves t ypical ultrasonic equipment, though the test specimen is completely submerged in water. The water acts as a coupling agent, which aids in the transfer of a clear signal from the transducer to the material being tested. Immersion testing is usually performed in a laborat ory on relatively small test specimens, but can be applied to structures in the field. It is possible to perform immersion testing on structures using a technique called ponding. This technique involves the creation of a layer of water or pond between the specimen and the transducer Material Acoustic Velocity (m/s) Aluminum 6320 Cast Iron 3500-5800 Concrete 2000-5500 Glass 4260-5660 Iron 5900 Steel 5900 Water 1483 Ice (water) 3980

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38 and thus is only applicable to the upper su rface of structures or submerged sections of underwater structures. Contact methods are the most commonl y used methods in the ultrasonic nondestructive testing of materials. Contact me thods require the use of a coupling agent, as described in the Coupling Agent section. The development of contact methods allow more versatility in the ultrasonic testing of specimens, since they enable inspectors to test structures and components regard less of orientation. The ultr asonic pulse velocity testing method, as described in ASTM C597-97, is a contact method. As illustrated in Figure 2.18, there are three possible transducer arrangements in ultrasonic pulse velocity testi ng. These variations include th rough or direct transmission, semidirect transmission, and su rface or indirect transmission. The through transmission arrangement is cons idered to be the preferred approach. It is the most energy efficient arrangement becau se the pulse receiver is directly opposite the pulse transmitter. Since the distance between the two transducers is minimized, the amount of pulse energy lost through ma terial friction is also minimized. The semidirect arrangement is less ener gy efficient than the through transmission arrangement due to the geometry of the tr ansducer arrangement. The angles involved cause signal interference and th erefore are more likely to produce errors. The semidirect arrangement is still useful fo r inspections where through transm ission testing is not due to unfavorable structure configuration. The met hod is also useful for testing of composite columns that contain heavy reinforcing steel w ithin their core. The semidirect transducer arrangement facilitates ultrasonic testing of the concrete in the column while avoiding interference from the embedded steel.

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39 The surface method is the least efficient of the three ultrasonic pulse velocity configurations. This is due to the nature of the waves that travel through the surfaces of materials. The amplitudes of waves received via the receiving tran sducer are typically less than 5% of waves received by the direct transmission method. Such a small amount of wave energy obtained by the receiving tran sducer can result in errors in the measurement and analysis of a wave signal. Although the arrangement is the least efficient of the three methods, it is useful in situations where only one surface of a structure or specimen is accessible, such as a floor slab. Surface wave speed and surface crack depth are acquirable through the surface method as well. These methods are explained in the impact echo section of this chapter. Impact-echo and ultrasonics utilize the same principle for crack depth measurement. Figure 2.18: Methods of pulse velocity meas urements: a) direct method, b) indirect method, c) surface method, (Malhotra & Carino 1991)

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40 Noncontact methods of ultrasonic testing ar e under continuous research. This field of study has many desirable attributes and similar fields of study include acoustic levitation and transportation. At the present time, there are severa l noncontact acoustical techniques being developed for the nondestructive testing of materials and struct ures. New acoustical techniques are now available as a result of the development of the piezoelectric transducer. Three techniques exist: electromagnetic transducers (EMATs), laser beam optical generators, and air or gascoupled transducers (Bergander 2003). Most contact ultrasonic tes ting requires the use of a piezoelectric transducer to send and receive the stress wave signa ls. The signals are introduced into and received from the test specimen through physical contact of the transducers coupled to the test surface. EMATS are composed of an RF coil and a permanent magnet. The RF coil is excited by an electric pulse which sends an electrom agnetic wave along the surface. The EMATS technique requires the test surface to be magnetically conductive. (Green 2002). Laser ultrasound facilitate s the non-contact ultrasoni c testing of materials regardless of the materials' electrical conductivity. It provides the opportunity to make truly non-contact ultrasonic measurements in both electrically conduc ting and electrically nonconducting materials, in materials at elevat ed temperatures, in corrosive and other hostile environments, and in locations generally difficult to reach, all at relatively large distances from the test surface (Green 2002) Laser ultrasound techniques are able to produce compression, shear, Rayleigh and Lamb waveforms, increasing the test's versatility and serviceability. Laser generate d and air coupled ultrasonics have been successful in the characterization of materi als which are non-elect rically conducting but

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41 are not yet serviceable for flaw detection and material investigation. However, the contemporary non-contact ultrasonic methods ha ve been proven to be scientifically applicable in the aeronautics and metallurgical disciplines. A schematic representation of contact transducers vs. non-contact transducers is illustrated in Figure 2.19 Figure 2.19: Illustration of contact and noncontact techniques (Green 2002) Pulse-echo testing The pulse-echo test is based upon stress wave propagation. It uses the same principles and concepts as the impact-echo method (described later). The basic principle behind both methods is referred to as the “pitch and catch” technique. In pulse-echo testing, a stress wave or pulse is created by a transmitting transducer, just as it is with ultrasonic pulse velocity method. Some type s of pulse-echo equipm ent utilize the same transducer to receive while ot hers require separate sendi ng and receiving transducers. This latter type of arrangement is often termed as "pitch and catch." However, the receiver and transmitter need not necessarily be separate transducers placed at different points on the test specimen but can be combin ed to a single trans ducer. This type of

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42 testing is referred to as “t rue pulse echo.” Figure 2.20 provi des a schematic of the pulse echo principle. Figure 2.20: Schematic of pulse-echo and p itch and catch techniques (Malhotra & Carino 1991) The echo wave coming from the flaw is described by its transit time from the transmitter to the flaw and back to the receiv er. Later, the reflected wave from the back side of the specimen, for example the back echo or bottom echo, arrives after a correspondingly longer delay. Both echoes are indicated acc ording to the intensity, or rather amplitude, which is referred to as ec ho height because of th eir usual presentation as peaks above the horizontal zero line. (Krautkramer 1990). Figures 2.21 a and b provides a schematic of the typical set up and results from pulse echo scans. The primary difference between the pulse-echo method and the impact-echo method is that the former technique utilizes a transmitting transducer while the latter employs a mechanical impactor Both methods use a receiving transducer, which is used to detect the reflected waveform. The diffe rence between the transmitting transducer and

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43 the mechanical impactor is the waveform created. The mechanical impact creates a spherical wave front, whereas the transmitti ng transducer creates a pulse wave beam, resulting in a much smaller material examination area. Figure 2.21: Pulse echo schematic (a)Typica l test setup, and (b) resulting display (Boving 1989) The biggest limitation to the pulse-echo met hod can be attributed to the geometry of the specimen. The reflections of internal anomalies are dependent upon their orientation. In cases where discontinu ities, and opposite surfaces, are oriented unfavorably or parallel to the ultrasonic ray path, it may be unable to receive reflected

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44 pulse wave signals. The orientation of anoma lies and defects is equally important to size in the pulse echo method. The most favorable orientation for an anomaly is perpendicular to the ultrasonic ray path. Figure 2.22 provides an illustration of th e signal response due to the orientation of an anomaly. Reflections due to uneven surface morphology can cause signal scatter as shown in Figure 2.23, resulti ng in the test missing the backwall echoes. This phenomenon can make it di fficult to determine anomaly location. Figure 2.22: Reflections of st ress waves from internal discontinuities (Kaiser & Karbhari 2002) Figure 2.23: Signal scatter due to unev en reflecting surface morphology (Kaiser & Karbhari 2002)

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45 Applications of ultrasonics Ultrasound has been used to determine the integrity of variou s materials including metal and alloys, welds, forgings and cas tings. Ultrasound has also been applied to concrete in an attempt to nondestructively determine in situ concrete features such as: Compressive strength Defect location Surface crack measurement Corrosion damage Strength determination The material properties of concrete are va riable, and strength determination is a difficult and complicated process. The basic i ngredients of concrete are hydrated cement paste, aggregates, water and air. The hydr ated cement paste is a highly complex multiphase material. The mineral aggregates are porous composite materials differing greatly from the cement paste matrix. The in terface between paste a nd aggregate particles has its own special properties. Concrete can aptly be considered a composite of composites, heterogeneous at both the micr oscopic and macroscopic levels (Popovics 2001). Concrete, unique in its placement, is on e of the only materials used in construction that is usually batched and tran sported to a construction site for placement in the form of a viscous liquid. The concrete liquid is then fo rmed and left to form a hardened paste. It is this hardened concrete for which material properties can be estimated in construction practice. Minimum concrete strengths can be accura tely predicted and estimated. However, the most commonly accepted method of meas uring the compressive strength of in situ concrete is through core testi ng. Many studies have shown that there is no particular correlation between the strength of concrete defined by ASTM standards and the strength

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46 of concrete actually in a st ructure (Mindess et al. 2003). Since some of the material properties of concrete, like strength, change with time and exposure, determining the strength of in situ concrete nondestructively is a valuable ability. Concrete is the only engineering material in which strength determination is attempted by ultrasonic measurements. The demand to test ultrasonica lly has been created by industry needs. Using NDT methods to achieve a reliable conclusion regarding the condition of a structure allows engineers to mo re efficiently plan repairs. At the present time, there is no theoretical relationship between ultrasonic pulse velocity, or wave velocity and the compre ssive strength of concrete. However, in infinitely elastic solids, the P-Wave Cp is a function of Young’s Modulus of Elasticity E, the mass density and Poisson’s Ratio The relevant equation for wave speed is: ) 2 1 )( 1 ( ) 1 ( E Cp(4) Using this formula, it is possible to use the wave speed from ultrasonic testing to obtain other physical properties of concrete, such as comp ressive strength. However, most prior studies have been laboratory cont rolled and were perfor med on concretes with consistent mix parameters. These studies tend to neglect the effects of age and weathering on hardened concrete, which is a limiting factor when considering ultrasonic testing for strength determination in older structures (Lemming 1996, Popovics et al.1999, 2000, Popovics 2001, Gudra & Stawiski 2000, La ne 1998, Krautkramer 1990, Malhotra 1984, 1994, Malhotra & Carino1991). The ultrasonic determination of concrete strength has been intensively researched. Although some studies have shown positive results (Lemming 1998, Popovics et al.1999, 2000, Popovics 2001, Gudra & Stawiski 2000, Lane 1998, Krautkramer 1990, Malhotra

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47 1984, 1994, Malhotra & Carino1991), there is no completely acceptable method for the determination of concrete strength using ultrasonics. This is due to the complexities of the material, the generated waveform, and the structure. Thus, continued research toward the development of a concrete strength versus ultrasonic pulse velo city relationship is justified (Popovics 2001). Defect detection The most successful applica tion of ultrasonics has b een in the detection and location of the presence of discontinuities in concrete specimens and structures. Ultrasonic testing has been proven to be capab le of detecting various anomalies including rebar, prestressed tendons, conduit delaminatio ns, voids, and cracks. The reliability of ultrasonic tests has been confirmed when applied to the testing of concrete and masonry structures. Ultrasonics are useful in th e evaluation of construction a nd in the rehabilitation of structures. The sonic test is a reliable tech nique used to evaluate the effectiveness of grout injection. Investigations repeated before and after repair, allow for control of the distribution of the grout in the masonry. Nevertheless, in the tested case, it was impossible to distinguish between the effects of each grout, the materials being injected having similar modalities (Binda 2001). Recent research has been conducted using array systems and ultrasonic tomography to evaluate concrete specimens and struct ures. Tomography is de fined as a method of producing a three-dimensional image of the in ternal structure of a solid object by the observation and recording of th e differences in the effects on the passage of waves of energy impinging on those structures. Ultr asonic tomography can be performed by measuring the times-of-flight of a series of stress pulses along different paths of a

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48 specimen. The basic concept is that the stre ss pulse on each projection travels through the specimen and interacts with its internal construction. Figure 2.24 illustrates the basic concept behind ultrasonic tomography. Variatio ns of the internal conditions result in different times of flight being measured (Martin et al. 2001). Figure 2.24: Setup of ultrasonic tomogr aphc ray paths (Martin et al. 2001) Field research has revealed that ultrasoni c tomography constitutes a reliable method for investigating concrete st ructures. However, it is time cons uming, and thus the practicality of using this method for global insp ection of structures is limited. Ultrasonic imaging and tomography methods have incorporated the use of array systems for transducer arrangements to be utili zed for the inspection a nd defect detection. The practical application of the system shows that it is possible to measure the concrete cover of large construction elements, even be hind dense reinforcing bars. The data is evaluated by means of time-of-f light corrected superposition. The array system together with a three-dimensional reconstruction calcu lation can be used for the examination of transversal prestressing ducts. The system has already been used successfully on site (Krause et al. 2001). The most recent research in ultrasonics and its uses in nondestructive testing has been the automated interpretation of data. The interpretation of NDT data is a difficult

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49 task, and those who do so must be trained a nd skilled in the NDT discipline. However, when large engineering structures are insp ected, the amount of data produced can be enormous and a bottle neck can arise at th e manual interpretation stage. Boredom and operator fatigue can lead to unreliable, inconsistent results where significant defects are not reported. Therefore, there is great potenti al for the use of computer systems to aid such interpretation (Cornwell & Mc Nab 1999). At present, the automated data analysis systems are unreliable for industry use. Howeve r, the value of automated flaw analysis has been successfully demonstrated on exampl es of real defects and made correct flaw diagnoses (Cornwell & McNab 1999). It appear s as though the biggest limiting factor of the automated interpretation of NDT data is a general lack of knowledge involving defect and flaw detection. The information obtaine d via the use of ultrasonics and other NDT methods requires the interpretation of an expe rienced technician or engineer. Scientists have yet to find the simple answers with resp ect to ultrasonic data that allow computers and computer programs to be utilized for interpretation. Surface crack measurement Surface crack measurement has been studied by several researchers and the results are considered to be reliable when the te sting procedure is prope rly performed. In a concrete specimen with a known wave speed, a crack that is presen t will cause the path length of the ultrasonic pulse to become larger. Using simple geometric calculations, it is possible to obtain the depth of a surface initiated crack within a specimen, as long as that crack represents significant void space (i.e. is wide enough to eliminate contact of the sides). The limitation of this method is smalle r cracks that lack large void space. In such cases, the pulse may be able to cross the crack due to the small discontinuity in the

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50 concrete, thus shortening the path length. Figure 2.25 illustrates the concept of crack depth measurement. Figure 2.25: Measurement of crack depth (Malhotra 1991) Detection of corrosion damage Corrosion of reinforcing steel is one of the most prevalent problems plaguing concrete structures. The most commonly used methods of corrosion detection are electrochemical methods, such as the DC polarization method, the AC impedance method, and the open circuit potential met hod. Such electrochemi cal methods can only obtain overall information theoretically. Howe ver, pitting corrosion often occurs in reinforcing steel in reinforced-concrete me mbers. The local environment surrounding the metal surface is not uniform, and inappropria te loading may induce cracks in concrete that allow, or even draw, chloride ions from the environment. These ions can penetrate the concrete along the cracks faster than at other, uncracked areas. Electrochemical measurements for the detection of corrosion damage in reinforced concrete members may underestimate the local pitting corrosion rate because the electrochemical parameters represent global information ob tained by taking an average of the total amount of local corrosion on the whole metal surface area (Yeih & Huang 1998).

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51 Laboratory research has been performe d that has correlated ultrasonic wave amplitude attenuation to corrosion damage in re inforced concrete specimens. Some of the limitations of this approach include the test control conditions. Most of the research involving corrosion degradation in reinforced concrete specimens has involved the corrosion of steel in intact concrete specimens However, structures observed in the field typically exhibit co rrosion damage as a result of material deficiencies in the concrete that encases it, usually a result of both the conc rete and the steel. This problem requires further analysis of the combined effect of both materials for field applications. Laboratory studies have yet to incorporate both materials. The ultrasonic investigation of a deteriorated reinforced concrete specimen essentially requires the comprehension of ultrasonic wave forms that account for dissimilar material effects from the steel and complex multiphase heterogeneous material that is concrete. Ultrasonic testing analysis of the resulting damage of such complex c onditions is difficult to perform. Further research and testing is needed before ultras onic testing can be reas onably applied in field use for the detection of corro sion effects in reinforcing steel. Engineers need to understand the shortcomings of nondestructive te sting tests so that they can make proper determinations and accurate evaluations of structures (Boyd et al. 2002). Structural health monitoring Structural health monitoring is at the forefr ont of structural and materials research. Structural health monitoring systems enable inspectors and engineers to gather material data of structures and structur al elements used for analysis. Ultrasonics can be applied to structural monitoring programs to obtain such data, which would be especially valuable since the wave properties could be used to obtain material properties. There is scarce

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52 literature available on the monitoring of in-p lace concrete struct ures and structural elements. Current research in structural monitori ng relates to the pe rformance of fiber reinforced polymer composites and other stru ctural strengthening methods. Fiber optics have given rise to remote structural health monitoring, remote sensing, and nondestructive load testing. Ultrasound has b een applied to concrete strength, crack detection, thickness measurements, and wave speeds of concrete structures. The concept behind using ultrasonics for st ructural health monitoring is observing changes in the structure’s wave speed over time As previously discussed, the wave speed is a function of Young’s Modulus of Elasticity E, the mass density and Poisson’s Ratio The overall quality of the concrete is associ ated with the ultrasonic wave speed (Ryall 2001). Table 2.3 Relationship between pulse velocity and concrete quality This testing approach may be used to a ssess the uniformity and relative quality of the concrete, to indicate the presence of voids and cracks, and to evaluate the effectiveness of crack repairs. It may also be used to indicate changes in the properties of concrete, and in the survey of structures, to estimate the severity of deterioration or cracking. When used to monitor changes in th e condition over time, tests are repeated at the same positions (ASTM C597-97). Decreases in ultrasonic waves speeds over time can Longitudinal Pulse Velocity (m/s) Quality of Concrete > 4500 excellent 3500-4500 good 3000-3500 doubtful 2000-3000 poor < 2000 verypoor

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53 reveal the onset of damage before visible deficiencies become evident. This allows inspectors and engineers to implement repair recommendations before minor deficiencies become safety hazards. Impact Echo The term “ultrasonic” refers to sound wa ves having a frequency above the human ear's audibility limit, which is about 20, 000 Hz. Ultrasonic testing has been used to successfully evaluate the quality of concrete for approximately 60 years. This method can be used for non-intrusively det ecting internal def ects in concrete. Some of these flaws include deterioration due to sulfates or other mineral at tack, and cracking and changes due to freeze-thaw cycling. One type of u ltrasonic testing is the impact-echo method. Development of method Nicholas Carino of the National Bureau of Standards (NBS) developed the impactecho method in the 1970’s and 1980’s for assess ment of buildings and bridges that failed during construction (Sansalone & Streett, 1997). Mary Sansal one focused her research on the refinement and application of the impact -echo method for her Ph. D thesis at Cornell University. Their research comprises the majority of impact-echo research and development performed in the United States applicable to concrete and concrete structures. Early research focused on laboratory studi es involved the locat ion of defects and voids in concrete. There have been four ke y research breakthroughs since research began to successfully develop impact echo as an NDT method (Sansalone & Streett, 1997). The concerns utilization of the num erical simulation of stress wa ves in solids using finite element computer models. This method wa s implemented to help facilitate the interpretation of early experimental results The models created were two-dimensional

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54 finite element models based on Green’s functions, which simulate stress wave propagation in plates. Green’s functions are widely used in determining responses in solids to an applied unit force. These functi ons can be used to obtain the propagation of elastic waves in solids. This mathematical formulation was essential in the interpretation of results obtained th rough experimentation. The second key research breakth rough relates to the use of steel ball bearings to produce impact generated stress waves. Th e impacting of objects on the surface of a given solid produces stress wave s that facilitate signal acquisition. This elastic impact results in a force-time function that is de fined and mathematically applicable. The impact-echo method does not use a pulse-genera ting transducer to generate stress waves, rather, the impacting of an object, typically a small steel ball, provides the stress wave. The development of the impact method overcame the need for a pulse generating transducer. Typical steel balls range from 4 to15 mm in diameter but can be larger or smaller depending on the desired waveform need ed for the test. Typical impact speeds are 2 to 10 meters per second but can also vary depending upon the desired waveform. The contact time typically ranges from 15 to 80 s. Proper selection of steel ball diameter and impact speed is essential in flaw dete ction to create the co rrect wave frequency, which is typically less than 80 kHz. This range can vary depending on the properties and dimensions of the test sample. The third key research advancement was th e development of a transducer that can acquire impact generated stress waves. The development of the correct receiving transducer was an integral phase in the advancement of the impact-echo method. The receiving transducer was developed by T.M. Proctor (Hamstad and Fortunko, 1995). The

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55 intended use for the receiving transducer was the acoustic emission testing of metals. However, it was discovered that the transducer was compatible with impact-echo testing of concrete. The receiving tr ansducer is composed of a small conical piezoelectric element bonded to a larger brass block. Fo r protection of the transducer tip, a lead element is fitted between the transducer tip and the material to be tested. Some tests use coupling materials such as gels to provide an effective test surface. In areas where a smooth concrete surface is not available, th e concrete is usuall y grinded to a smooth surface to ensure proper transducer-to-surface coupling. Figure 2.26 is a schematic of a typical piezoelectric transducer. Figure 2.26: Schematic of a typical piezoelectri c transducer used for impact echo testing (Carino 2001) The final key research advance pertains to the use of frequency domain analysis for signal interpretation. Waveform analysis is the determining component in the use of NDT. In many cases the operator has difficulty in interpreting the wave signals received in the time-domain by the piezoelectric transducer. Using a Fourier transform on the time-domain signals, it is possible to gra ph the wave’s frequency-domain signal. The result is a frequency vs. amplitude plot also called an amplitude spectrum.

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56 Recent research advances Much of the research and development of the impact-echo method has been carried out at Cornell University. This research pr imarily involves the rele vant application of impact-echo to the evaluation and inspec tion of concrete and masonry materials (Sansalone & Streett, 1997). Through this research, the methods for determining wave speeds in concrete, grout, and masonry were im proved for industry use. The research also helped develop applicable methods for loca ting and determining flaws in concrete and masonry. Some of the flaw types that have been accurately detect ed using the impactecho method include cracks, voids, bonding voi ds, honeycombing, and concrete damage. The method can also be used to obtain the thic kness of a material such as concrete or asphalt pavement. The advances in the impact-echo method made at Cornell University used a combination of research techniques. These techniques include nume rical models, finiteelement analysis, eigenvalue analysis, resonant frequency analysis a nd laboratory testing. The first portable impact-echo system was developed by Mary Sansalone and Donald Pratt and was patented by Cornell University. The patented system has five basic components including spring-mounted impactors (ball bearings), a receiving transducer, a high-speed digital-to-analog data-acquisition system, a rugged and powerful laptop-size computer, and software for transferring anal yzing and storing test data (Sansalone & Streett, 1997). Figure 2.27 is an illustrati on of a typical impact-e cho equipment system. The portable impact-echo system has been successfully developed as a commercial product and is available for retail purchase. Most portable impact-echo systems that are available for consumer use are purchased with four components, with the laptop computer being omitted.

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57 Figure 2.27: View of a typical impact-echo equipment system Stress wave theory The effective use of the impact-echo syst em requires that the user have a basic understanding of the properties and fundamentals of stress wa ves. In solid mechanics, when any two objects collide local disturbanc es take place within a given material. The disturbances can cause deformations that may be plastic or elastic in nature. A plastic deformation is defined as a deformation in which the material is permanently deformed. Elastic deformations are the type in which th e material is temporarily deformed but then returns to its original shape. When an elastic collision occurs between objects, a disturbance is generated that travels through the solid in the form of stress waves. There are three primary modes of stress wave propa gation through elastic media: dilatational, distortional, and Rayleigh wa ves (Sansalone & Carino, 1989). Dilatational waves ar e the primary stress waves produced upon impact. They are also referred to as primary waves, P-waves, or compression waves. The particle motion of the wavefront of P-waves is parallel to the direction of impact pr opagation. The result is a compressive or tensile stress wave (San salone & Streett 1997). The P-wave velocity is the fastest of the three stress waves pr oduced from the impact. Typical P-wave speeds

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58 for concrete ranges from approximately 3000 m/s to 5500 m/s. For normal strength concrete, P-wave speed usually ranges from 3500 m/s-4500 m/s. Distortional waves are the s econdary stress waves that are produced upon forced contact. These waves are also called shear wa ves or S-waves. In Swaves, the particle motion of the wave front is normal to the di rection of propagation producing shear stress. (Sansalone & Streett 1997). S-wave speed in normal concrete is usually about 62 percent of the P-wave speed. Rayleigh waves are also calle d R-waves or surface waves. Rayleigh waves, unlike P-waves and S-waves, do not propagate th rough the solid. Rayleigh waves propagate along the surface of a given conc rete specimen in an ellipt ical motion. P-waves and Swaves propagate through a concrete specime n in spherical wavefronts. Rayleigh wave speed is usually 56 percent of P-wave speed. Figures 2.28 and 2.29 illustrate the typical relationship between stress wave types. Figure 2.28: Illustration of typical wave pr opagation through a cro ss section of a solid (Carino 2001)

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59 Figure 2.29: Illustration of wave propagati on model through a cross section of a solid (Carino 2001) The wave speeds in elastic solids are rela ted to Young’s Modulus of Elasticity E, Poisson’s ratio and the density (Sansalone & Streett, 1997) In the equations below Cp, Cs and Cr, describe the P-wave, S-wave a nd R-wave speeds respectively. ) 2 1 )( 1 ( ) 1 ( E Cp (5) G CS ; ) 1 ( 2 2 1 SC (6) S RC C 1 12 1 87 0 (7) Where G is the Shear Modulus of Elasticity. The typical range of valu es for Poisson’s ratio “ ” is typically 0.17-0.22. Inserting this value for into the above equations, along with the typical density and modulus of elasticity values, will give typical wave speeds found in concrete. The modulus of elasticity of a concrete specimen, the comp ressive strength, and the appropriate wave speed of the concrete can be obtained. Equation 5 can be used as an example obtain a typical wave

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60 P-wave speed for a concrete sample as follows: Using: E=30x109 Pa, = 2400 kg/m3, and = 0.18 ) 2 1 )( 1 ( ) 1 ( E Cp )) 18 (. 2 1 )( 18 1 ( 2400 ) 18 1 ( 10 309 x Cp = 3700m/s As discussed above, 3700 m/s is an acceptable P-wave speed for concrete. Force-time function of impact Stress waves can be produced by several di fferent instruments. The ultrasonic pulse velocity method uses a stress wave transm itting piezoelectric transducer. The impactecho method applies the collision of a stee l sphere generating stress waves. The parameters that characterize the duration of the impact or contact time are sphere size, and the kinetic energy of the sphere at the point of impact. The variation of impact force with time is called the force-time function, accurately represented by a half sine curve (Sansalone & Streett 1997). The contact time duration between a small steel sphere and a concrete surface is relatively short, ranging from 30 s to 100+ s. Figure 2.30 illustrates the typical force-time relationship. Figure 2.30: The typical force-ti me function for the elastic im pact of a sphere on a solid (Sansalone & Streett 1997)

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61 One result of the impact of a steel sphere on a concrete specimen is the transfer of kinetic energy from the sphere to the conc rete. The energy transf er takes place in the form of particle displacements resulting in stress waves on the impacted solid. The maximum force is proportional to the kinetic energy of the moving sphere at impact, and the particle displacements ar e proportional to this force (S ansalone & Streett 1997). The time of contact, however, has a faint reliance on the kinetic energy of the sphere, being a linear function of sphere diameter. The stress waves generated by the imp act contain a wide distribution of frequencies. The frequency distribution is influenced by the force-time function of the collision. The objective of frequency analys is is to determine the dominant frequency components in the digital waveform. The optimum technique used to create the amplitude spectrum is the fast Fourier transform (FFT ) technique. The FFT technique assumes that any waveform, no matter how complex, can be represented by a series of sine waves added together. The FFT displays the amplit udes of the various frequency components in the waveform. The amplitude spectrum obtained by the FFT contains half as many points as the time domain waveform. The maximum frequency in the spectrum is one-half the sampling rate. This shows the initial portion of the computed amplitude spectrum. Each of the peaks corresponds to one of the component sine curves (Carino 2001). Figure 2.31a illustrates a typical group of sine wa ves which is transformed into a typical frequency spectrum in Figure 2.31b.

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62 Figure 2.31: Example of frequency analysis using FFT: (a) represents the frequency distribution, (b) represents the co rresponding amplitude spectrum (Carino 2001) The linear relationship between time of contact and sphere diameter can be described as: tc= 0.0043D (8) (Sansalone & Streett 1997) where D is the sphere diameter in meters and tc is the contact time in seconds. For an impact using a sphere of a given diameter a maximum frequency of useful energy is created. This relationship, like the sphere diam eter and contact time relationship, can also be described as a linear function. D 291 fmax (9) (Sansalone & Streett 1997)

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63 where fmax is the maximum frequency of useful energy in hertz and D is the sphere diameter in meters. The interesting concept behind Equation 9 is that maximum usable frequencies are smaller when larger diameter spheres produ ce impacts. However, larger spheres produce larger forces and larger maximum stress wa ve amplitudes. The contact time decreases with decreasing sphere diameter but the range of useful frequencies increases with a smaller diameter sphere. However, using sma ller spheres increases the likelihood that the higher frequency stress will be scattered by the natural inhomogenities inherent in concrete. In practice, it has been found that the smallest sphere useful in impact-echo testing has a diameter of approximate ly 3mm (Sansalone & Streett 1997). Behavior of stress waves at material interfaces The term interface is defined as a surface forming a common boundary of two bodies, spaces, or phases. One of the most common interfaces people are familiar with is the oil-water interface. In material science, an interface is usually defined as a fringe between two materials which have different pr operties, such as density and phase. Other differences in material prope rties are acoustic properties (such as acoustic impedance). Acoustic impedance is defined as the material density multiplied by the materials stress wave velocity. When stress waves collide with material interfaces, portions of the waves are reflected and refracted. In obtaining the depth of a flawless concrete specimen, users assume stress waves are being reflected at the concrete/air interface as seen in Figure 2.32. In the development of the impact echo me thod, the use of finite element models (FEMs) was prominent in the study of pa rticle motion and stress wave propagation through a concrete medium. The use of FEMs permitted the developers of the impact-

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64 echo technique to study waveforms at project ed instantaneous phases in the wave’s displacement. The model studies provided necessary information concerning the reflection of stress waves in a concrete medi a. Figure 2.33, illustrates the ray paths of typical P-wave propagation in a solid. Figure 2.32: Plots of P, S and R-waves at various times after an impact: (a) 125 s, (b)150 s, (c)200 s and (d) 250 s (Sansalone & Streett 1997) Figure 2.33: The ray path of typical Pwave propagation through a solid media (Sansalone & Streett 1997)

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65 Stress wave behavior between interfaces of solids is more complicated than the stress wave behavior between a solid-gas interface. Upon collis ion with a solid-gas interface, most of the P-wave energy is reflec ted back into the solid media. However, in a stress wave collision with a solid-solid inte rface, the P-wave energy is partially reflected and partially refracted. The amount of energy th at is allowed to pass through or refract the second solid medium depends upon its acous tic impedance. It is possible to get a coefficient of refraction if the acoustic impe dance of the materials involved is known and the amplitude of the particle motion is obtained for the initial P-wave. 1 2 1 2 i reflectedZ Z Z Z A A R (10) 1 2 2 i refractedZ Z 2Z A A R (11) (Sansalone & Streett 1997) Where R is the coefficient of refraction, Areflected & Arefracted are the reflected and refracted P-wave amplitudes; Ai is the amplitude of the initial P-wave; Z1 is the acoustic impedance of the initial medium; and Z2 is the acoustic impedance of the medium beyond the interface. There are three basic relationships between Z1 and Z2. The first relationship exists when Z1 is notably greater than Z2. Due to this relationship, the Z1/Z2 relationship is comparable to the solid-gas interface in which the P-wave is completely reflected and virtually no refraction takes place. This situ ation is common in the application because most defects in concrete are related to void space in the concrete matrix. A second relationship between solid-solid interfaces is when the Z2 is much greater than Z1. Consider Z1 to approach zero and cons ider Equation 11 above, then Arefracted

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66 approaches 2Ai. When this condition exists, the amplitude of the wave is equal to that of the incident wave, while the amplitude of the re fracted wave is twice that of the incident wave. There is no phase change in the reflecte d or refracted wave. In impact-echo testing, the no phase change case occurs, for example, when the first region is concrete and the second region is steel or rock as the acoustic impedances of those materials are several times grater than that of conc rete (Sansalone & Streett 1997). The third relationship between soli d-solid interfaces exists when Z2 is approximately equal to Z1. When a value of 1 is used for both Z1 and Z2, Areflected becomes zero and Areflected becomes one. In this situation, most of the stress wave energy is transmitted through the interface to the second solid. This situation is possible when a concrete specimen is bonded to another concre te structure or a c oncrete structure has been properly patched. Inserting Z1 and Z2, into Equation 10 and Z1 is greater than Z2, a negative value is obtained coefficient of fricti on “R”. The negative R value denotes a phase change in the stress wave at the point of reflection. Since impact induced P-waves are compression waves, a phase change indicates the wave s will become tension waves upon reflection. This phenomenon is important to consider because when P-waves are reflected and Z1 is less than Z2, as in a case when steel is the soli d behind the interface, the reflected waves do not undergo phase change. Figure 2.34 below illustrates the phase changes that take place in stress waves upon reflection. As seen in figure 2.34a illustrates the return of a tension wave in each reflection. In 2.34b, the return of a compression wave is alternated with the return of a tension wave for each stress wave reflection. The arrival of a tension wave caus es an inward displacement

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67 of the surface, while the arrival of a co mpression wave causes an outward displacement on the material surface. The reason stress wave s do not change phase when reflected on a solid medium with a higher acoustic impeda nce is because the stress wave “bounces” off the second material and returns to the impact source. The “bouncing” takes place because materials with higher acoustic impedances have higher densities and the small surface displacements that usually ta ke place at solid/gas interf aces, do not take place at boundaries more dense than the original medium. Figure 2.34: Impact echo ray paths (a) A pha se change at both boundaries. (b) A phase change at upper boundary only (Sansalone & Streett 1997) Waveform analysis idealized case As stated in the introduction to stress waves section, su ch waves are the particle motion caused by the energy of an impact. When wavefronts reach the surface, the particle motion causes small displacements, which are detected by the receiving transducer. The transducer converts the surf ace displacement into a proportional voltage signal. The voltage signal becomes the primar y output to the testing software. The output produced requires proper understanding of wavefo rm analysis. For each test, the operator must properly interpret the waveform in or der to ascertain the quality of the data obtained.

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68 A common scenario in impact -echo testing is the testi ng of a solid plate with solid/gas interfaces at both concrete surfaces. As seen in Figure 2.35, the principle features of the idealized waveform detected by the transducer are those produced by the P-wave, which travels into the structure a nd undergoes multiple refractions between the two surfaces, and the R-wave, which travel s outward across the surface (Sansalone & Streett 1997). Figure 2.35: Schematic representations of (a) P-wave ray reflections and (b) the resulting idealized waveform (San salone & Streett 1997) The typical elapsed time for the above wa veform recorded is less than four milliseconds. As previously noted, R-waves pr opagate through a solid as surface waves and reflections of R-waves will not be recorded unless the distance between the receiving transducer and the horizontal solid-gas in terface is less than the specimen depth. However, since the impact between the stee l ball and the concrete specimen does not occur at a point directly below the transducer the R-wave causes a negative displacement at the receiving transducer. As shown in the Figure 2.35, th e amplitude of the R-wave is larger than any other feature in the wave sp ectrum. Figure 2.35 also illustrates that the time elapsed for the R-wave to return back to zero in the displacement spectrum is the time of contact “tc” of the impacting sphere. In this event, the point of the impacting

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69 sphere is relatively far from the receiving tran sducer, the arrival of the P-wave reflection may occur before the arrival of the R-wave. To avoid this phenome non, the operator must ensure that the impact point of the sphere is relatively close to the transducer. Since the P-wave and S-wave speeds are greater th an the R-wave speed, there is a small displacement just prior to the arrival of the R-wave. This small displacement is due to the arrival of the P and S wavefronts. The reflections of the P-wave with the solid-gas interface shown in Figure 2.35, illustrate the expected phase change. The arrival of the tension wave at the impacting surface causes a small inward displacement causing the wave reflections shown at times t1, t2 and t3. The elapsed time t1, between the impact and arri val of the 2P wave at the surface is the distance the wave has traveled, being twice the solid thickness. The P-wave arrivals at the upper surface cause displacem ents that are periodic in nature. This periodicity is the dominant feature of the wa veform after the passage of the R-wave. The period of the waveform in Figure 2.35 is t1 and its frequency is 1/t1, the reciprocal of the period. This yields a simple re lationship shown in Figure 2.33, which is at the heart of the impact-echo method (Sansa lone & Streett 1997). T 2 C fp (12) (Sansalone & Streett 1997) Waveform analysis actual case The technique presented in the previous pa ragraph is an accurate description of waveform analysis, but it illustrates wave form circumstances under idealized conditions. One difference between the idealized case and th e actual case is that the reactions of the transducer to the material displacements is caused by stress waves. As the stress waves

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70 reflect due to the solid-gas interface, the recei ving transducer experiences its own particle motions. This additional movement is referre d to as “overshoot”. Overshoot causes the waveform displayed by the digital analysis so ftware to have only the negative portion of each wave. This wave analysis software phenomenon is illustrated in Figure 2.36. Figure 2.36: Actual waveform on an impactecho test plate (Sansa lone & Street 1997) Figure 2.36 shows the actual waveform as it would be received and displayed by impact-echo software in fieldtesting. Another phenomenon that this figure illustrates is the decay of the spectral amplitude with the increasing number of wave reflections. This decay is a result of energy lo sses due to friction as the wave propagates within the solid matrix. Through rigorous testing in the developmen t of impact echo, it was observed that the frequencies obtained in labo ratory testing of concrete specimens were not equal to the frequencies calculated in Equa tion 12. The use of finite element models and laboratory testing revealed a deviation of approximately 5% between the observed laboratory data and the expected results obtained by Equation 12. After considering the geometry of the specimen, the developers found that it was n ecessary to include a shape factor in the frequency equation. In the case of a solid pl ate, the characteristic dimension is the thickness T, and the shape factor is 0.96 (Sansalone & Streett 1997).

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71 T 2 C fp T 2 C 96 0p (13) (Sansalone & Streett 1997) Field measurement of material stress wave speed In field-testing, it is crucial to establish the wave speed of the solid before specimen dimensions and qualities are to be test ed. The most common method for directly measuring the wave speed of a solid is thr ough the use of two receiving transducers. The transducers are commonly placed in a space r device, at a known fixed length from each other. Once the transducers are properly spa ced and fixed to the concrete specimen, a single P-wave can be used to measure th e wave speed of the concrete. Figure 2.37 illustrates the typical test set up behind the measurement of wave speed. Figure 2.38 is an example of a typical output obtained in acquisition of the wave speed. Figure 2.37: Schematic representation of th e test set up for wave speed measurements (ASTMC 1383-R98a 2001)

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72 Figure 2.38: Example waveform obtained in wave speed measurements (ASTM 2001) When the test is performed, the output would simply record the time at which the P-wave is received by each transducer The wave speed would then be: 1 2t t L Cp (14) (ASTM C1383 2001) However, it is important to create the im pact far enough from the initial transducer to allow for P-wave separation from the S a nd R-waves. This is the basis for having the minimum distance between the impact of the sp here and the first transducer set to L. For the example of output illustrate d in Figure 2.38, the results are t2 = 156 s, t1 = 80 s and L=300 mm. Using Equation 14, the wave ve locity of the sample is obtained by the following: s 80 s 156 mm 300 CP = 3950 m/s Once the wave speed has been established for the concrete specimen, then testing for the specimen’s thickness, concrete qua lity, flaw and anomaly detection may be performed.

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73 The effect of flaws on impact-echo response Impact-echo was developed to nondestructiv ely investigate concrete. One of the advantages of impact-echo testing is the versatile equipment and the relatively brief duration of the testing procedure. This allo ws inspectors to efficiently and accurately investigate structures and concrete specime ns for condition assessment. The impact echo responses of materials can be classified acco rding to the type, depth, and size of flaw. For the purposes of impact-echo testing, a crack is defined as an interface or separation where the minimum opening is 0.08 mm or larger. Stress waves are able to propagate across voids that are smaller th an 0.08 mm, hence there is not enough wave reflection to detect these smaller deficiencies Since water has a coefficient of reflection of approximately 0.7, the majority of the stre ss wave energy at a so lid-water interface is reflected and water filled voids can also be detected using th e impact-echo method. As the depth of a void from the surface increases, the smallest size that can be detected also increases. Base d on analytical and la boratory studies, it has been suggested that if the lateral dimensions of a planar cr ack or void exceed 1/3 of its depth, the flaw depth can be measured. If the lateral dimensions exceed 1.5 times the flaw depth, the flaw behaves as an infinite boundary and the respons e is that of a plate with thickness equal to the flaw depth (Carino 2001). Figure 2.39 illust rates the relationship between crack depth and detectability. Figure 2.39: Illustration of the smallest de tectable crack and it s dependency on depth.

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74 If the flaw is located entirely within the white area, the crack depth cannot be measured (Carino 2001) When larger cracks or voids are present, the impact-echo response will be essentially the same as if th ere was a solid/gas boundary at that interface. The test will produce results that represent the termination of the material at the depth of the flaw. A crack or void within a concrete structure forms a concrete/air interface. Laboratory experiments have shown that cracks with a mi nimum width (crack opening) of about 0.08mm (0.003 inches) cause almost total reflection of a P-wave. The responses from cracks and voids are similar, since stress waves are reflected from the first concrete/air interf ace encountered. Thus a crack at a depth d will give the same response as a void whose upper surface (nearest to the imp act surface) is at the same depth (Figure 2.40). d l d l(a)(b) Figure 2.40: A crack at depth “d” gives th e same response as a void at that depth (Sansalone & Streett 1997) In cases where the lateral dimensions of the crack are about equal or less than the depth of the crack, propagating stress waves are both reflected and refracted from the surface. Hence, they are diffracted around the edges of the crack (S ansalone & Streett 1997). For similar cases where more compli cated waveforms exist, the frequency spectrums are affected accordingly.

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75 Applications When properly used, the impact-echo method has achieved unparalleled success in locating flaws and defects in highway paveme nts, bridges, buildings, tunnels, dams, piers, sea walls and many othe r types of structures. It can also be used to measure the thickness of concrete slabs (pavements, floors, walls, etc.) with an accuracy of 3 percent or better. Impact-echo is not a "black-box" system that can perform blind tests on concrete and masonry structures and always tell what is inside. The method is used most successfully to identify and quantify suspected problems within a structure, in quality control applications (such as measuring th e thickness of highway pavements) and in preventive maintenance programs (such as rou tine evaluation of bridge decks to detect delaminations). In each of these situations impact-echo testing has a focused objective, such as locating cracks, voids or delaminati ons, determining the thickness of concrete slabs or checking a post-tens ioned structure for voids in the grouted tendon ducts. Determining the depth of surface-opening cracks A surface-opening crack is any crack that is visible at the surface. Such cracks can be perpendicular, inclined to the surf ace, or curved, as shown in Figure 2.41. The two waveforms, labeled 1 and 2, in Figure 2.42(b), are the signals from transducers 1 and 2 in Figure 2.42(a). The ar rival of the direct P-wave, a compression wave, at transducer 1 causes an upward surf ace displacement and a pos itive voltage (time t1), while the diffracted wave that first reac hes transducer 2 is a tension wave, which causes a downward displacement and a sudden voltage drop (time t2). The elapsed time between t1 and t2, the wave speed, and the known distances H1, H2 and H3, are used to calculate the depth D.

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76 (a) (b)(c) Figure 2.41: Surface-opening cracks: (a) perpe ndicular, (b) inclined, and (c) curved (Sansalone & Street 1997) A B C D 1 2 TimeVoltaget1t2 t01 2 (b) (a) H1H2H3 Figure 2.42: Measuring the depth of a surface-opening crack: (a) schematic of experimental test setup, and (b) samp le waveforms (Sansalone & Street 1997) Voids under plates Detecting voids under concrete plates is one of the simplest applications of the impact-echo method. It relies on the clear and easily recognizable difference between waveforms and spectra obtained from plates in contact with soil, on the one hand, and plates in contact with air (a voi d under the slab) on the other. Figure 2.42 shows a typical set of results obtained from an impact-echo test on a concrete plate in contact with soil. The waveform shows periodic displacements caused

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77 by P-wave reflections within the concrete plate, but because energy is lost to the soil each time a P-wave is incident on the concrete/soil interface, the amplitude of the displacements (indicated by the signal voltage) decay s rapidly. The corresponding spectrum shows a single peak corresponding to th e frequency of P-wave reflections from the concrete/soil interface. Note however, that the peak is somewhat rounded and is broader than those obtained from plates in contact with air. In Figure 2.43 only a few wave reflections were recorded before th e signal decayed to an undetectable level. For comparison, Figure 2.44 shows a typica l result obtained from an impact-echo test on the same plate at a location where a void exists in the soil just below the plate. In this case P-wave reflections occur from a conc rete/air interf ace at the bottom of the plate. Because virtually all of the wave energy is reflected at a concrete/air interface, surface displacements caused by the arrival of reflect ed P-waves decay more slowly compared to those reflected from a concrete/soil interface. The response is essentially the same as that obtained from a simple concrete plate in cont act with air. The spect rum exhibits a very sharp, high amplitude peak corresponding to the P-wave thickness fr equency. If the concrete slab is relatively thin (about 150mm or less) a lower frequency, lower amplitude peak, labeled fflex in Figure 2.44(c), may also be present, as a result of flexural vibrations of the unsupported portion of the plate above the void. Flexural vibrations occur because the unsupported section above the void is restrained at its ed ges where it contacts the soil. The response is similar to that produced by an impact above a shallow delamination. However, because the thickness of the slab is relatively large, the amplitude of the flexural vibrations is smaller relati ve to the P-wave thickness response.

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78 Frequency, kHz Time, sAmplitude Voltage Soil T (a) (b) (c) Concrete 0 10 20 30 40 50 0 2048 fT Figure 2.43: The impact-echo response of a concrete slab on soil subgrade: (a) crosssection, (b) waveform, and (c) spec trum (Sansalone & Streett, 1997) 01020304050 Frequency, kHz Time, s 01024Amplitude Voltage(b) (c) Soil T (a) Concrete fflexfT Figure 2.44: The impact-echo response obtained from a concrete slab at a location where a void exists in the soil s ubgrade: (a) cross-section; (b) waveform; and (c) spectrum (Sansalone & Streett, 1997) Steel reinforcing bars Impact-echo is primary used to locate flaw s in, or thickness of, concrete structures. Impact-echo may also be used to determin e the location of stee l reinforcing, though

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79 magnetic or eddy current meters are better suited to this purp ose. The acoustical impedance of steel is 5 times that of the conc rete. If the sizes of reinforcement bars are known the impact-echo response can be esti mated. If information is not known the reinforcing size can be estimated from a c over meter. Impact echo can be applied to evaluate the corrosion of reinfo rcing bars. The response is similar to solid plates, with single large amplitude peak P-wave thic kness frequency. Waves travel around the corroding bar, instead of propagating through it since the corrosion forms an acoustically soft layer around the bar. Short duration impact s result in peaks at higher frequencies, corresponding to reflections from the corrodi ng surfaces. This method has been able to identify corrosion on reinforcement bars and ha s proven to be cost-effi cient in identifying wall repair locations. Voids in the tendon ducts of post-tensioned structures The impact-echo method can be used to detect voids in grouted tendon ducts in many, but not all, situations. The method’s applicability depends on the geometry of a structure and the locations and arrangemen t of tendon ducts. Small voids in tendon ducts cannot be detected if the ratio of the size of the void to its depth beneath the surface is less than about 0.25. In addition, complicat ed arrangements of multiple ducts, such as often occur in the flanges of concrete I-beams, can preclude detection of voids in some or all of the ducts. In other cas es, portions of structures can be successfully tested and information can be gained that permits an engineer to draw conclusions about the condition of the grouting along th e length of the duct. The simp lest case is that of posttensioned ducts in a plate structure, such as a bridge deck or the web of a large girder, in which there is only one duct directly beneat h the surface at any poi nt. In all cases, the impactecho method is restrict ed to situations where the walls of the ducts are metal

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80 rather than plastic. Effective use of th e impact-echo method for detecting voids in grouted tendon ducts requires knowledge of the location of the ducts within the structure. This information is typically obtained from plans and/or the use of magnetic or eddycurrent cover meters to locate the centerlines of the metal ducts. Once the duct locations are known, impact-echo tests can be performed to search for voids. Metal ducts Tendon ducts in post-tensioned structures ar e typically made of steel with a wall thickness of about 1mm (0.04 inches). The sp ace not occupied by tendons inside the duct is (or should be) filled with grout, which has acoustic impedance similar to that of concrete. Because the wall thickness of a duct is small relative to the wavelengths of the stress waves used in impact-echo testing, and because a steel duct is a thin layer of higher acoustic impedance between two materials of lower acoustic impedance (concrete and grout), it is transparent to pr opagating stress waves. Therefore, the walls of thin metal ducts are not detected by impact-echo tests. (In contrast, plastic ducts have a lower acoustic impedance than concrete or grout, and they are not transparent, complicating attempts to detect voids within plastic ducts.) Benefits to using impact-echo Applications of the IE method include qua lity control programs (such as measuring pavement thickness or assessing pile integrity), routine maintenance evaluations to detect cracks, voids, or delaminati ons in concrete slabs, delin eating areas of damage and corrosion in walls, canals, and other concrete structures. Impact echo can be used to assess quality of bonding and condition of t unnel liners, the inte rface of a concrete overlay on a concrete slab, concrete with asphalt overlay, mineshaft and tunnel liner thickness.

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81 Concrete pavements and structures can be tested in less time, and at lower cost, meaning more pavements and structures can be tested. No damage is done to the concrete and highway workers spend less time in tempor ary work zones, reducing the chance of injury and minimizing downtime for the tr aveling public. Impact -echo, according to ASTM, may substitute for core drilling to determine thickness of slabs, pavements, walks, or other plate structures. Acoustic Emission Acoustic emission (AE) is defined as a tran sient elastic wave generated by the rapid release of energy within a material. Thes e deformations can come from plastic deformation such as grain boundary slip, phase transformations, and crack growth. (Davis 1997). Unlike most nondestructive testing techniques, acoustic emission is completely passive in nature. In fact, acoustic emission cannot truly be considered nondestructive, since acoustic signals are only emitted if a permanent, nonreversible deformation occurs inside a material. As such, only nonreversibl e processes that are often linked to a gradually processing material degradation can be detected (Kai ser & Karbhari 2002). Acoustic emission is used to monitor crack ing, slip between concrete and steel reinforcement, failure of strands in pr estressing tendons, and fr acture or debonding of fibers in fiber reinforced concrete. Theory There are two types of acoustic emissi on signals: continuous signals and burst signals. A continuous emission is a sustained signal level, produced by rapidly occurring emission events such as plastic deformation. A burst emission is a discrete signal related to an individual emission event occurring in a material, such as a crack in concrete. An acoustic emission burst signa l is shown in Figure 2.45.

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82 Figure 2.45: Burst acoustic emission si gnal with properties (Malhotra 1991) The term “Acoustic emission signal” is of ten used interchangeably with acoustic emission. An AE signal is defined as the electrical signal received by the sensor in response to an acoustic wave propogating throu gh the material. The emission is received by the sensor and transformed into a si gnal, then analyzed by acoustic emission instrumentation, resulting in information abou t the material that generated the emission. An acoustic emission system se tup is shown in Figure 2.46. Figure 2.46: Acoustic emission process (Hellier 2001) Method development Acoustic emission testing is used to obt ain noise sounds produced by material deformation and fracture. Early term inology for acoustic emission testing was

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83 “microseismic activity.” AE signals occur wh en micro or small fr actures are detected within the material. The first documented observations of Acoustic Emission activities occurred in 1936 by two men, Forster and Sche il, who detected clicks occurring during the formation of martensite in high-nickel steel. In 1941, research by Obert, who used subaudible noise for prediction of rock burst s, noted that noise rate increased as a structure’s load increased. In 1950, Kaiser submitted a PhD thesis entitled “Results and Conclusions of Sound in Metallic Materi als Under Tensile Stress” (Scott 1991). Kaiser’s research is considered to be the beginning of acous tic emission as it is known today. In 1954 Schofield became aware of Kaiser’s early work, and initiated the first research program in the United States related to materials engineering applications of acoustic emission (Scott 1991). During the early developmental testing for AE, several correlations were formed. Acoustic emission readings in materials of high toughness differed in amount and size from low toughness material. This was attributed to the differences in failure modes (Scott, 1991). Early acoustic emission testing signals were small and required a relatively calm environment for proper testi ng. With the use of an additional sensor, background noise could be isolated which enabled testing to be carried out in a relatively noisy environment. The preliminary results of acoustic emission testing required massive data calculations due to the extensive nu merical output the acoustic emission signals produced. This phenomenon distracted scientists, diverting too much of their attention to signal analysis instead of evaluation of the signal itself. Acoustic emission testing proved to be a highly sensitive indicator of crack formation and propagation.

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84 Early use of acoustic emissi on testing proved to be valuable, but the first acoustic emission signals acquired contained large amoun ts of noise signals. This made it difficult as scientists were unable to develop AE as a quantita tive technique. The material sensitivity and initial research results gave birth to a successful future for acoustic emission as a reliable nondestructive test. Kaiser effect One of the most common uses of acoustic em ission is in load testing of a structure or specimen. The generation of the acous tic emission signals usually requires the application of a stress to the test object. However, acoustic emissions were found not to occur in concrete that had been unloaded until the previously applied maximum stress was exceeded during reloading (Malhotra 1991). This phenomenon takes place for stress levels below 75 – 85% of ultimate strength and is found to be only temporary. Therefore, it cannot be used to determine the stress hi story of a structural specimen. Additional theory can be found in several references (Ohtsu et al. 2002; Hearn 1997; Tam & Weng 1995; Yuyama et al. 1992; Malhotra 1991; Scott 1991; Lew et al. 1988). Equipment and instrumentation An acoustic emission system has the same basic configuration as seen in ultrasonic testing systems. The typical testing apparatus used for acoustic emission (shown in Figure 2.47 consists of the following: Transducer Reveiver/Amplifier Signal Processors Transient Digitizers Display Calibration Block Coupling Agent

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85 Figure 2.47: Basic setup of acoustic emission equipment (Miller 1985) Transducer The acoustic emission transducer is more comm only referred to as a sensor. It is the most important part of the instrumentation. Sensors must be properly mounted to assure the proper configuration to attain the desire d signal. Sensors are calibrated using test methods stated by societies. An array of di fferent sensors is shown in Figure 2.48. Figure 2.48: Various acoustic em ission sensors (Miller 1985) An important factor in acoustic monito ring is the location of sensors. For monitoring cases in which the location of a cr ack or deficiency is known, a single sensor

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86 is sufficient for monitoring. However, for the detection of defi ciencies in a two dimensional plane or three dimensional solid, the geometric configur ation of the sensors is vital to the location of the deficiencies. ASTM Standard Guide for Mounting Piezoelectric Acoustic Emission Sensors spec ifies guidelines for mounting piezoelectric acoustic emission sensors. The performance of sensors relies heav ily upon the methods and procedures used in mounting. Detecti on of acoustic emission signals requires both appropriate sensor–mounting fixtures and consistent sensor–mounting procedures (ASTM E-650-97). Receiver/amplifier “Receiver” is the term applie d to all of the circuit func tions that amplify the weak signals and prevent loss in sensor activity. The receiver has four basic components: the preamplifier, the logarithmic amplifier, the rectifier and the low pass amplifier. The function of the preamplifier is to ensure that any signal from the transducers arrives at the time measuring circuit. Since electrical outputs from the transducer are relatively small, signal amplification is n ecessary to overcome the resistance from the transducer cable, which can be relatively long. The function of the logarithmic amplifier is to process weak echo signals. Once the ec ho signals are amplified, the low pass filter processes the signals. After the signal has been processed by the receiver/amplifier, a useable signal can be transmitted to the display. Microprocessor-based systems have become more widely used in recent years. Such units perform single channel analysis, along with source location, for up to eight AE channels.

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87 Signal processors Signal processors are designed to allow data collection only on certain portions of a load cycle. Envelope processors attempt to filter out the high frequencies, leaving only the signal envelope to be counted. Logarithmic converters allow the output of the signal analyzer electronics to be plotted in loga rithmic form. A unit allows combination of several preamplifier outputs so that several sensors can be monitored by one channel of electronics (Reese 1993). Transient digitizers Transient digitizers (also calle d transient r ecorders) are used to study individual AE burst signals. A signal is digiti zed in real time and then stored into memory. A transient digitizer is used in sequence with an oscill oscope or spectrum analyzer to display AE signals at visible speeds. Digital rates vary on transient digitizers. The fastest sampling rate becomes the limiting rate, with some instruments sampling up to 1 pulse/ns. Sampling rates can be modified for testing purposes. One advantage of transient digitizers is an additional m ode of triggering, the pretri ggering mode, where the input signal is continuously being di gitized and the data fed in to the memory (Reese 1993). This configuration allows a di gitized picture of th e signal to be displayed as received. More advanced digitizers a llow recording of multiple signals simultaneously. The recording of more than one acoustic emi ssion signal is shown in Figure 2.49. Display The signal received by acoustic emission te st equipment is typically displayed digitally. The display uses an interval timer and a direct reading of display time on an x-y coordinate system. The x-axis displays the time trigger and the y-axis represents the mechanical energy received. The display uni ts can also illustrate defect and anomaly

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88 locations and sizes depending on the type of scan request by the user. Older acoustic emission systems used monitors to display received acoustic emission signals, however, most current acoustic emission systems use co mputer software and monitors to display results. Figure 2.49: Transient recorder with multiple output acoustic emission signals (Sypeck 1996) Calibration block ASTM states that annual ca libration and verification of pressure transducers, AE sensors, preamplifiers (if applicable), signal processors, (particularly the signal processor time reference), and AE electronic simula tors (waveform generators) should be performed. Equipment should conform to ma nufacturer’s specifi cations. Instruments should be calibrated to National Institute for Standards and Technology (NIST) (ASTM E 1932-97). An AE electronic simulator, used in making evaluations, must have each channel respond with a peak amplitude reading within 2dBV of the electronic

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89 waveform output. (ASTM E 1932-97) Fi gure 2.50 is a photograph of a typical calibration block. Figure 2.50. Acoustic emi ssion calibration block A system performance check should be done immediately before and after an acoustic emission examination. The preferred technique is the pencil lead break test. A description of the test procedure is described in ASTM E 750-98. Acoustic emission signals are introduced in to the structure and examined on an oscilloscope or with an AE system used in th e test. If any doubt occurs in the sensor’s response, it should be remounted. Three sources of the acoustic signal are the Hsu–pencil source, the gas–jet, and the elec trical pulse to another sensor mounted on the structure. A description of the sources can be found in ASTM E-976. Two types of verification are periodic verification and post verification. ASTM defines periodic verification as the verification of the sensors peri odically during the test. Post verification is defined as verifying the condition of the sensors to be in working condition at the end of the test. Coupling agent A coupling agent is usually required to ensu re the efficient transfer of mechanical energy between the tested material and th e transducer. The purpose of placing the coupling material between the transducer and test specimen is to eliminate air between

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90 the contact surfaces. Typical coupling agents are viscous liquids such as grease, petroleum jelly, and water-soluble jelly. In acoustic emission testing it is common to bond the sensors to the test specimen. This setup is used for tong term testing or monitoring of structures and specimens. When applying bonds, it is possible to damage the se nsor or the surface of the structure during sensor removal. Evaluation of acoustic emission activity Acoustic emission activity may be determin ed as the cumulative acoustic emission or as an event count. Analysis techniques should be uniform and repeatable. Techniques of evaluation include event c ounting, rise time, signal dura tion, frequency analysis and energy analysis. Field and laboratory evalua tions include damage analysis and proof loading. The measurement of the acoustic em ission count rate is one of the easiest and most applicable methods of analyzing ac oustic emission data (Reese 1993). Acoustic emission count indicates the occurrence of acoustic emissi on and gives a rough estimate of the rate and amount of emission. The amplified signal is fed into an electronic counter. The counter output is often transformed by a digitalto-analog converter so that it can be plotted on a X-Y recorder (Reese 1993). An event count will result in the number of burst emissions signals that are produced during an event. An acoustic emission event is defined as a detected acoustic emission burst. This means that an acoustic emission event describes the acoustic emission signal and not the ac oustic emission. For the event count to be correct, the decay constants of the AE signals must be the same. A mixture of decay constants will often confuse the event-c ounting circuitry (Reese 1993).

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91 For most experiments, the count or the energy per event will give about the same results (Reese, 1993). Acoustic emission bursts are larger when a loaded specimen is approaching failure. It is only when there is a change in either the damping factor or the frequency that the energy per event is th e better parameter (Reese, 1993). The energy released per event will result in the amount of AE signals received. Signal rise time The signal rise time can be defined as th e interval between the time when the AE signal is first detectable above the noise le vel and the time when the peak amplitude occurs (Reese 1993). Rise depends on the di stance between the acoustic emission source and the sensor. It can help to determine the type of damage mechanism. Signal duration Signal duration is defined as the length of time that the burst emission signal is detectable It is dependent upon the preamplifier noise level and detection of the signal. A trigger circuit is used to stop and start a se parate counter that c ounts clock pulses. The signal duration is independent of the freque ncy content of the burst signal. The signal duration method is useful when repeating the sa me test. A change in either the average signal duration or the distributi on of durations can indicate ei ther a change in the signal path to the sensor or a change in the generating mech anism (Reese, 1993 Sensor location Determination of the number of sensors required for the test, their placement strategy and location on the part to be monitored is need ed. Placement of sensors on a concrete specimen during a fiber pullout test is shown in Figure 2.51.

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92 Figure 2.51: Placement of sensors on a concrete cube A single sensor used near the expected source of AE is sufficient when background noise can be controlled or does not exist. When background noise is limited, the use of a single AE data sensor near the expected s ource plus guard sensor s near any background source will suffice. ASTM defines a guard se nsor as one whose primary function is the elimination of extraneous noise based on a rrival sequences. The guard sensors will effectively block noises that emanate from a regi on closer to the guard sensors than to the AE data sensor. Another technique involve s the placement of two or more sensors to perform spatial discrimination of background noise and allow AE events to occur. ASTM defines spatial discrimination as the process of using one or more guard and data sensors to eliminate extraneous noise. In situations where irrelevant noise cannot be controlled during testing and could be emanating from any and all directions, a multiple sensor location strategy should be considered. Using a linear or planar location strategy will allow for an accurate source lo cation of the acoustic emission. Applications of spatial filtering and/or spatial discrimination will only allow data emanating from the region of interest to be processe d as relevant AE data. Applications of acoustic emission Acoustic emission has been used to determine the integrity of various materials, including metal and alloys, welds, forgings and castings. Acoustic emission has been

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93 applied to concrete in an effort to nondestru ctively evaluate in situ concrete for load testing and structural monitoring. Load testing The most successful application of acousti c emission is detecting the presence of discontinuities or cracks, a nd their location, in concrete specimens and structures. Perhaps the most researched application of ac oustic emission testing has been used in the load testing of concrete st ructures and specimens. Since acoustic emission is a passive nondestructive testing technique, acoustic si gnals are only emitted if a permanent, nonreversible deformation occurs inside a material. Therefore, acoustic emission is extremely useful for detecting the forma tion of cracks and microcracks occurring in concrete structures. Consideration of the load intensity in rela tion to the integrity of the test object results in the success of an acoustic emissi on examination. Applied load is defined by ASTM as the controlled or known force or stress that is applie d to an object under test for the purpose of analyzing the object’s reacti on by means of acoustic emission monitoring of that stress. If the load is not of sufficient intensity, th e tested object will not undergo sufficient stress and will not pr oduce acoustic emissions. If the applied load is part of the monitoring process, a suitable time for acous tic emission examination is when process noise is low and the applied load at a maximu m. Appropriate stress levels are used to excite the “latent defects” without damaging the object (ASTM E-1932-97). A reinforced concrete slab under fatigue loading from the initia l loading to final failure in the laboratory was compared to th e acoustic emission monitoring of reinforced concrete slabs under traffic loading by co mparing visual observations of cracking processes and acoustic emission source locati on (Yuyama et al. 1992). The experiment

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94 concluded that, by comparing crack density history and acoustic emission activity history, cracking processes under fatigue loading can be predicted and evaluated by monitoring the acoustic emission signals. The research paper also revealed that the damaged area due to cracking can be roughly identified by th e acoustic emission source location. One valuable conclusion from laboratory te sting is that the area of reinforced concrete near the initial emanation of acousti c emission signals will result in the cracking area during the final load. The fatigue process in reinforced concrete structures can be evaluated by periodical ly monitoring these structures unde r service loads (Yuyama et al. 1992). A fundamental study was made of acoustic em issions generated in the joint of rigid frames of reinforced concrete under cyclic loading. The test conc luded that different acoustic emission sources, such as tensile cracks or shear cracks, could be clearly discriminated by comparing the results of the visual observation and the crack width measurement (Yuyama et al. 1992). Studies have been performed on fiber reinfo rced concrete specimens to observe the response of fiber reinforced concrete to loading. Based on the experiment, several conclusions can be drawn. The examination of acoustic emission act ivities and source location maps reveal that the microscopi c fracture response recorded by acoustic emission monitoring is consistent with the m acroscopic deformation of the material. Steel fibers are more efficient than PVA fibers in blunting microcrack nucleation (Li & Li 2000).

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95 Structural monitoring Most highway bridge inspection is pe rformed via visual inspection. When deficiencies are observed, th e action taken usually involves increased inspection of the defective area. Given that the rate of deterioration is us ually unknown, the frequency of inspection is increased without a reasonable forecast of the behavior of the defect. Acoustic emission testing utilizes the indu ced stress waves that are released when microstructural damage occurs. This passive NDT technique is commonly referred to as structural health monitoring. At present, portable AE sensors are ava ilable for the continuous monitoring of known flaws. Research to date has provided a reasonable scientific base upon which to build an application of acoustic emission as part of a bridge management program (Sison et al. 1996). This techniqu e could be best utilized by implementing a continuous monitoring system with an array of se nsors on newly constructed bridges. The technology is available for instrumentation conf igured with portable data acquisition and transfer systems, making it possible for e ngineers to continuously monitor bridge condition. Engineers could use the informati on gained via AE systems to decrease the frequency of inspection on sound structur es and monitor profound AE events to determine the need for essential inspections. Other successful uses of AE have been appl ied to leak detection in tanks, pipelines, and conduits. It has also been used to m onitor the integrity of dams and other mass concrete construction. Impulse Response The impulse response (IR) test has several applications relating to civil engineering and to the condition assessment of structures. Researchers originally developed it in the

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96 1960's for evaluating the integrity of concrete drilled shafts. Engin eers are less familiar with its widespread capabilities in relation to testing of reinforced concrete structural components such as floors, pavement slabs, bridge decks and other structures. The impulse response technique is similar to the impact-echo test method previously discussed in this chapter. T hough the two methods are quite sim ilar in theory, they differ in several respects, such as having different uses. In essence, the IR method is a fast, coar se method of evaluating structures while the alternative methods are for more detailed invest igations. The IR method is likened to a vague diagnosis made by a family doctor and subsequently referred to a medical specialist for further diagnosis. Testing equipment The impulse response method uses a low-stra in impact to propagate stress waves through an element. Most testing appara tuses are comprised of a one-kilogram sledgehammer with a load cell in the head. The hammer has a fifty-millimeter diameter double-sided head. One end is rubber-tipped for low stress level impacts, typically around 700 psi, while the other is aluminumtipped for impacts that can reach stress levels of more than 7000 psi. A structure's response to the impact is measured by a geophone. Both the geophone and the instrumented hammer are linked to a portable computer for data acquisition. Figure 2.52 is a photograph of a hammer and geophone. Figure 2.53 is a schematic of the typical equipment setup. Principles of the impulse response method Most acoustic testing tec hniques are based on stress-wa ve propagation theory and monitor the behavior of such waves as th ey travel through a material. The impulse

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97 response method differs from this approach; it in stead measures the response of the tested material to the impact itself. Figure 2.52: The instrumented sledgeha mmer and geophone used in the IR method (Davis 2003) Figure 2.53: Schematic of the impul se response technique (Davis 2003) Since the stress that is applied to a struct ure in the IR test is quite large, the structure responds to the impact in a bendi ng mode over a relatively low frequency range (0 – 1000 Hz). This differs from structur es being evaluated with the impact-echo method, which would respond to the generate d stress waves in a reflective mode over a higher frequency range.

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98 When testing a structure using the impul se response method, a geophone is placed upon the surface that is then struck with the instrumented sledgehammer. The geophone is usually attached to the surf ace of the concrete so that it can act in the same plane as the hammer blow. The time records for the hammer force and the veloc ity response from the transducer are received by the computer as vo ltage-time signals and then processed using the Fast Fourier Transform (FFT) algorithm. At that point, velocity and force spectra are generated, and the velocity spectrum is divi ded by the force spectrum, yielding a transfer function more commonly known as the mobility of the structure. A plot of mobility versus frequency can be generated. This pl ot represents velocity per unit force versus frequency and provides information regarding th e condition of the stru cture being tested. Additional material properties that can be obtained include dynamic stiffness, mobility and damping, and the peak/mean mobility ratio. The transfer function When an IR test is performed, the data ga thered can be used to generate force and velocity spectra. The velocity spectrum is divided by the force spectrum to produce a transfer function more commonly referred to as the mobility of the structure. A theoretical impulse response spectrum is shown below in Figure 2.54. Figure 2.54: Theoretical impulse response mobility spectrum

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99 The first portion of the transfer function is the dynamic stiffness portion (usually in the range of 0 – 100 Hz), which has a linear slope. This linear slope quantifies the flexibility of the area around the test point for a normalized force input. The dynamic stiffness of the material is the inverse of this flexibility. The mobility of the structure being tested is the quotient of the velocity spectrum divided by the force spectrum, typically expres sed in units of seconds per kilogram. The average mobility value over the frequency range of 100 1000 Hz is related to the thickness and the density of the specimen. Above a fr equency level of approximately 100 Hz the measured mobility value osci llates around an average mobility value, N, which is a function of the specimen’s thickne ss and its elastic prope rties. A reduction in thickness of the specimen correlates to an in crease in average mobility. Figure 2.55 is a schematic of a typical mobility plot. When a material is impacted, an elastic wave is generated. The decay of the spectral amplitude is due to the energy losses attributed to friction as the wave propagates through the solid matrix. When cracking, honeycombing or consolidation voids are present in the concrete, there will be an a ssociated reduction in the damping and stability of the mobility plots over the fre quency range that is evaluated. Figure 2.55: Typical mobility pl ot for sound concrete (Davis 2003)

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100 Peak/mean mobility ratio When there is an area below a slab on grad e that has been undermined, or there are debonding or delaminations present within a co ncrete sample, the response behavior of the uppermost layer controls the results of the IR test. There will be a noticeable increase in average mobility between the frequency range of 100 to 1000 Hz, and the dynamic stiffness will be considerably reduced. The ra tio of this peak to the mean mobility is an indicator of loss of support below a slab on grade or the presence and degree of debonding within the sample. This concept is illustrated in Figure 2.56. Notice that the mobility of the concrete in the upper curve is considerably more than the mobility of the sound concrete shown in the lower curve. The impulse response test is capable of de tecting delaminations up to nine inches below the surface of a structure. Traditional me thods, such as acoustic sounding, are able to detect concrete deficiencies up to approxima tely two to three inches below the surface. The impulse response method is able to test for delaminations through asphalt overlays when ambient temperatures are low enough to preserve relatively high asphalt stiffness. Figure 2.57 depicts typical mobility plot s for sound and delaminated concrete. Figure 2.56: Mobility plots for sound and debonded concrete (Davis et al. 2001)

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101 Figure 2.57: Mobility plots for sound and delaminated concrete (Davis et al. 2001) Further development for concrete applications The inspection industry has focused on the practicality of this testing method, which has resulted in the development of more efficient testing procedures. Improvements have focused mainly on more rapid data acquisition and the storage of data from testing of large concrete surfaces, with computer extraction of the IR stiffness and mobility parameters for each test result. The time required for the impulse response method to perform the “family doctor” version of testing is approximate ly five percent of the time it would take for the impact-echo method to assess the same area. In the early 1990's, the Federal Highwa ys Administration (FHWA) published a report regarding the evaluation of bored concrete piles; the IR method was a less reliable test method than the cross-hole sonic l ogging method. Although the IR method has not been used in North America for evaluation of pile integrity, it is still applicable for material testing in other capacitates.

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102 Magnetic Methods Materials containing iron, nickel, cobalt, gadolinium and dysprosium have a high degree of magnetic alignment to each other and to themselves when they are magnetized. Therefore, they are called ferromagnetic ma terials. Other materials such as oxygen are faintly attracted or repelled by a magnetic fi eld. These materials are referred to as paramagnetic materials. Diamagnetic material s have the magnetic equivalent of induced electric dipole moments, which are present in all substances. However, this is such a weak effect that its presence is masked in substances made of atoms that have a permanent fixed magnetic dipole moment. The idea of using magnetic techniques fo r nondestructive testing and evaluation of ferromagnetic materials originated in 1905. In 1922, E.W Hoke was granted the first United States patent on a particular ferroma gnetic inspection method. In recent history, this inspection technique has been used in the petroleum, aerospace and automotive industries, as well as in othe r industries that re quire quality control of ferromagnetic materials. Magnetic fields A magnetic field is a volume of space containing energy that magnetizes a ferromagnetic material. The magnetic field is created by the in troduction of electric current and perturbates outward in a radial pattern. Figure 2.58 is a schematic of a typical magnetic field induced by an electrical current. The density of the magnetic lines, referred to as the flux density, increases when the field strength and the magnetic permeability increase.

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103 Figure 2.58: Schematic of a typical magnetic field induced by an electric current Types of magnetizing energy Two sources of magnetizing energy used in magnetic testing are permanent magnets and electric currents. Permanent ma gnets usually consist of bar or horseshoe configurations. They are inexpensive methods of magnetization but are limited by a lack of control of field strength and the difficu lty of removing strong permanent magnets from the tested specimens. The horseshoe type of magnet forms a uniform longitudinal field between the poles. It provides low levels of magnetization. Electric currents characterize the second category of magnetizing energy. Longit udinal or circular fi elds can be formed by the correct implementation of electric cu rrents. Direct current (DC), alternating current (AC), and rectified alternating current are used to magnetize test materials. DC and rectified AC penetrate deeper into a material than AC, primarily due to a phenomenon called the “skin effect”. The skin effect is more defined in ferromagnetic materials than in nonmagnetic types of material s. Thus, DC or rectified AC is used when test requirements include the detection of deep flaws.

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104 Magnetization classifications The most common magnetizati on techniques are classified as direct or indirect. Direct magnetization involves the passage of an electric current through a material. Indirect magnetization is caused by an adj acent magnetic field, which is excited by current flow through a po rtion of the material. Magnetic flux leakage Magnetic flux leakage (MFL), formerly re ferred to as magnetic field perturbation testing (MFP), consists of subjecting a magnetically permeable material to a magnetic field. The field strength requi rements depend on the permeability of the material and the sensitivity of the test probes. The principles of magneto-statics de monstrate that wh en a homogeneous magnetically permeable material is immersed in a static, uniform, external magnetic field, the magnetic field within the material approaches the same magnitude as the magnetic field in which it is immersed. These perturbed fields are called leakage fields due to the “leakage” of magnetic flux out of the material and into the air. Leakage is caused by the reduction in cross-sectional area of the ma gnetic material due to the anomaly. Inspections using magnetic flux leakage techniques The preferred characteristic of the MFL t echnique is that mechanical contact with the test specimen is not necessary. In many cases, both the exciting coil and the sensing coil may be operated without directly cont acting the material. This advantage has particular importance in the structural concrete industry. Another benefi t of MFL is that it requires no specific surface preparation othe r than cleaning. This method is easily automated for high-speed, detailed testing. It is also useful for identifying surface cracks, near-surface inclusions, and nonmagnetic co ating thickness on a perm eable base, as well

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105 as in monitoring physical and mechanical properties that cause changes in magnetic permeability. Sensitivity is limited by ambient noise and magnetic fields. The test specimen must be magnetically saturated, thereby limiting demagnetization concerns. The extreme sensitivity of the method has been utilized to de tect surface cracks and subsurface inclusions on the order of 0.3 mm. The magnetic flux leakage method has been applied to the determination of nonmagnetic coating thickness, the depth of cas e hardening, and the carbon content of a material. Another major application has been in testing steel beari ng raceways and gear teeth. In its most refined form, MFL is one of the most sensitive methods for the detection of surface and nea r-surface cracks and flaws in ferromagnetic materials. Electric current injection The Electric Current Injection (ECI) t echnique, also called the eddy current method, is an extension of the magnetic field perturbation method. It is used in materials that are electrically conductive but not magnetically permeable. ECI is classified as a non-particulate magnetic field method. The parameter sensed is the magnetic field perturbation near the surface of the test object. This testing method is carried out by inducing an electric current between two points of an elect ric current. Defects and flaws are obtained by recording the magnetic field signals in a manner similar to the MFP method. Applications to concrete Currently, magnetic testing methods have no relevant use in the nondestructive testing of concrete itself. Concrete is nonmagnetic in natu re, so the use of magnetic flux leakage for the detection of fl aws and anomalies in concrete devoid of reinforcing steel is insignificant. However, the use of magnetic methods for the inspection of ferromagnetic

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106 materials embedded within concrete structur es has proven to be extremely valuable. Magnetic methods have been applied to detect defects in prestre ssing tendons and steel rebar within concrete structures. They have proven effective in the detection and location of embedded steel. Covermeter The concrete covermeter, also referred to as the pacometer, was developed in 1951 in England. Since its original developmen t, the covermeter has gone through several generations of revisions. Pres ently available, systems are reasonably priced for use in inspection. A photograph of a typical covermeter shown in Figure 2.59. Figure 2.59: Covermeter used by the Civil E ngineering Department at the University of Florida The principle operation of the covermeter is based on ferromagnetic principles. The covermeter detects a bar by briefly magnetiz ing it, then registering the magnetic field as it tapers off. The typical c onfiguration of the covermeter testing technique is depicted in Figure 2.60. The covermeter utilizes the e ddy current method of ma gnetic testing. This method induces "eddy-currents" to flow around the circumference of the bar, producing a

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107 magnetic field. The head of the device pick s up the magnetic signal. Pulse techniques separate the received signal from the tran smitted one. Therefore, no signal is produced in the absence of a metalli c material. The strength of the induced magnetic field primarily depends on the depth of the ferromagnetic el ement beneath the probe and the size of the element being detected. The concrete industry primarily uses covermeters to detect the presence, size, and depth of rebars. Figure 2.60. Typical configuration of covermeter testing apparatu Applications of magnetic flux leakage Magnetic flux leakage has been effectively a pplied to the detection of deficiencies in steel members within concrete structures. The use of an array system has successfully identified ruptures of steel in prestresse d tendons and rebar crack s in bridge decks (Krause et al. 2002). Due to the extreme sensitivity of magnetic flux leakage sensors, the system is well suited for condition monitoring of the steel components in bridge decks. Slight changes in the metallic structure of embedded steel and te ndons can be detected in order to monitor the onset of damage in the metallic components of bridge structures. Ground Penetrating Radar The ground penetrating radar (GPR) method us es reflected waves to construct an image of the subsurface, in much the same way as seismic-reflection profiling. The source consists of a transmitter loop, which emits a short pulse of high-frequency (10

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108 1000 MHz) electromagnetic energy into the grou nd. The reflection response is measured using a receiver loop, which is generally kept at a fixed distance from the transmitter. GPR is used in a variety of applications including soil stratigra phy, groundwater flow studies, mapping bedrock fractures, determining depth to the water table, and measuring the thickness of glaciers (Malhorta & Carino 1991). Theory Both the GPR and ultrasonic pulse velocity techniques involve pulsing waves into a solid material. GPR differs from ultrasonics since it uses radar waves rather than stress waves. Radar waves and stress waves behave in a similar manner when introduced into a solid. GPR is governed by the reflection of the wavefronts in the host material in the same manner as the stress waves produced dur ing impact-echo and ultrasonic testing. The basic theory behind GPR is analogous to the th eory discussed in th e impact echo section of this paper and will not be restated here. In principle, the propagation of radar waves, or signals, is affect ed by the dielectric properties of the media, so that the attenuation and reflected components vary accordingly (Colla & Brunside 1998). Concrete is a low loss dielectric material, with the exception of any metal which may be pr esent within the concrete. When an electromagnetic signal passes through a di electric medium, the amplitude will be attenuated (Casas et al. 1996). The main parameter which controls the subsurface response is the dielectric constant, K*, which is a dimensionless and complex number. The velocity at which radar signals propagate is given by: 2 / 1 K c (15) (Casas et al. 1996)

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109 where the speed of light c = 3108 m/s, and K is the real part of K*. Reflections occur when a radar pulse strikes a boundary where ther e is an abrupt change in the dielectric constant. The reflection coefficient, whic h represents the ratio of reflected-wave amplitude to the incident wave, is given by: 2 / 1 2 2 / 1 1 2 / 1 1 2 / 1 2K K K K R (16) (Casas et al. 1996) Equations 15 and 16 are the principle e quations upon which the theory of GPR is based. The wave velocity and reflection coe fficient of dissimilar materials within the same medium can be distinguished subsequent to signal processing. Instrumentation The use of ground penetrating radar is fa irly popular within the geological and geophysical fields throughout the world. Although GPR is becoming increasingly popular for the nondestructive testing of concrete structures, it is a highly specialized system. The primary components in a radar system are a waveform generator, an antenna, a signal processing unit and a display unit. Generator Waveform generators are used to transmit a signal to the antenna. The signal can be a continuous or a pulsed excitation signal, which is then transmitted into the test material. Generators are capable of emitting varying or continuous frequencies of signals depending on the type of testing being performed. Antenna Antennas for GPR radiate and receive el ectromagnetic waves. The GPR antenna performs basically the same f unctions as the “head” of the covermeter device. However, instead of using magnetic fields, it sends and receives an electromagnetic beam. The

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110 beam is usually driven at 1 GHz for use in concrete and is much more focused than the excitation fields utilized in the covermeter device. The dipole ante nna is most commonly used today. It is a contact based antenna that provides a diverging beam. Alternatively, the horn antenna employs a more focused b eam and has found use in vehicle-mounted surveying of highway and bridge decks, wher e the antenna is usually located 30cm above the surface of inspection (Kaiser & Karbhari 2002). Display Most of the GPR systems in service today employ a visual display that instantaneously produces an image of the scan An oscilloscope produces the image after the antenna receives it. Internal discontinui ties are produced by the reflected signal and are visualized through the use of grayscale or color. Figure 2.61 shows a typical GPR scan. Figure 2.61: Typical display of a GPR S can. The white portion denotes an anomaly Applications GPR has been studied and applied to the nondestructive testing of materials for the past several decades. Several successful applications of GPR in the concrete industry include (Casas et al. 1996): the identification of reinforcing bars in concrete the identification of large cracks and voids in concrete

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111 concrete quality and appraisal duct location in post-tensioned bridges void identification in post-tensioned ducts A logical classification fo r GPR would be to include it as a qualitative NDT technique that can effectively be used to aid in structural condition assessment and evaluation. Its performance in the rapid de tection of anomalies embedded in concrete structures is an extremely valuable tool for inspectors, especially when identifying problems with post-tensioned ducts. The pr oper grouting of post-tensioned bridge structures has been a prevalent problem th roughout the state of Florida for the past several decades. GPR offers an immediate inspection method that would enable owners of bridges to inspect the qua lity of post-tensioned struct ures before closing future contracts. Resonant Frequency Powers originally developed the resonant frequency method in 1938. He discovered that the resonant frequency of a material can be matched with a harmonic tone produced by materials when tapped with a hammer (M alhorta & Carino 1991). Since then, the method has evolved and incorporated the use of electrical equipment for measurement. Theory An important property of any elastic material is its natu ral frequency of vibration. A material’s natural frequenc y of vibration can be relate d to its density and dynamic modulus of elasticity. Durability studies of concrete mate rials have been performed indirectly using resonant frequency as an indicator of strength and static modulus of elasticity. These relationships for resonant frequency were originally derived for homogenous and elastic materials. However, the method also applies to concrete

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112 specimens if the specimens are large in relation to their constituent materials. (Malhorta & Carino 1991). The study of physics has determined re sonant frequencies for many shapes, including slender rods, cyli nders, cubes, prisms and va rious other regular threedimensional objects. Young’s dynamic modulus of elasticity of a specimen can be calculated from the fundamental frequency of vibration of a specimen according to Equation 17 (Malhorta & Carino 1991). 2 4 2 4 24 k m d N L E (17) Where E = Young’s dynamic modulus of elasticity d = density of the material L = length of the specimen N = fundamental flexural frequency k = the radius of gyration about the bending axis m = a constant (4.73) Testing ASTM has created a standard test that covers measurement of the fundamental transverse, longitudinal and torsional resonant frequencies of concrete specimens for the purpose of calculating dynamic Young’s Modulus of elasticity. (C-215-97, 2001) This test method calculates the resonant frequencies using two types of procedures, the forced resonance method or the impact resonance method. The forced resonance method is more co mmonly used than the impact resonance method due to the ease of testing and inte rpretation of results. The forced vibration

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113 method uses a vibration generator to induce vibration in the test specimen while the vibration pickup transducer is coupled to the specimen. The driving frequency is varied until the pickup signal reaches a peak voltage. The specimen’s maximum response to the induced vibration occurs at the resonant fr equency. Figure 2.62 illustrates the typical setup of a resonant frequency device. The vibr ation generator is coupled to the right side of the specimen while the pickup is coupled to the left. Figure 2.62: Typical forced resonant frequency setup The impact resonance method is similar to the impact-echo and impulse response methods. The impact resonance method employs a small impactor to induce a stress wave into the specimen. However, the forced re sonant frequency met hod uses a lightweight accelerometer to measure the output signal. Th e signal is then processed to isolate the fundamental frequenc y of vibration. The standard test method is limited to the testing of laboratory specimens (i.e. cylinders or prisms), and at present there is no standardized met hod applying the use of resonant frequency to larger specimens or to specimens of irregular shape. Limitations The resonant frequency method has been su ccessfully applied to the nondestructive testing of laboratory specimens. The test is somewhat limited by a number of inherent

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114 problems in the method. Resonant frequenc y testing is usually performed on test specimens to non-destructively calculate cy linder compressive strength. However, the test actually calculate s the dynamic modulus of elasticity. Extensiv e laboratory testing has revealed that cylinder co mpressive strength and dynamic modulus of elasticity are not an exact correlation. Thus, when concrete strength is extrapolated from resonant frequency testing, two sources of error exist. The first source of error is experimental error, which can be fairly significant when performing the resonant frequency test. “Limited data are available on the reproducibili ty of the dynamic modulus of elasticity based on resonance tests” (Mal horta & Carino 1991, p155). Th e second source of error is the assumption that has to be made when converting dynamic modulus to compressive strength. Since the correlation between the two properties is not absolu te, sources of error will be present in any modulus to strength conversion. Figure 2.63 graphically displays the experimental results obt ained relating cylinder compre ssive strength with dynamic modulus of elasticity. The experiment al data can be predicted within 10% assuming the results from a given resonant frequency test have zero e rror. In reality, converting dynamic elasticity to compressive strength w ould yield an uncertainty greater than 10%. Figure 2.63: Dynamic modulus of elasticity vs. cylinder co mpressive strength(Malhorta & Carino 1991)

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115 Applications Resonant frequency can be a useful tool for detecting material changes regardless of whether an actual dynamic modulus or compressive strength can be calculated. Resonant frequency can be used to measure qualitative changes in a material property if used as a monitoring technique. The existence of structural damage in an engineering system leads to a modification of the moda l parameters, one of which is resonant frequency. It is possible to monitor a given complex structural element with shape parameters that prohibit an accurate calculation of geometri c parameters such as radius of gyration or density. Complex structures are often too large or have immeasurable properties, such as the exact location of internal steel members, to extract relatively simple material properties that are easily calculated in the labo ratory setting. However, when used as a quantitative technique resonant frequency can detect materi al changes between tests. A review of methods of damage detection us ing natural frequencies has shown that the approach is potentially practical for the routin e integrity assessment of concrete structures (Salawu 1997). Using the natural frequency chan ges of a structure may not be useful for identifying the location and assessment of specific cracks and anomalies within a structure. The technique can detect changes in a structure or structural element, if an acceptable baseline is establishe d at the time of construction. Infrared Thermography Infrared thermography (IRT) is a non-destr uctive evaluation (NDE) technique that characterizes the properties of a material by monitoring its response to thermal loading. The term “thermal loading“ is commonly used to describe the transfer of energy from a heat source to a solid object. This techni que is currently being used on an array of

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116 structures and materials rangi ng from carbon fiber reinforced polymers (CFRP) to human teeth. Due to this widespread applicability the field of IRT has grown considerably in recent years. Recently, IR has been used fo r the nondestructive examination of concrete structures and stru ctural repairs. Theory The term “infrared” refers to a specif ic portion of the electromagnetic spectrum containing waves with frequencies just less than those of red visible light, infrared means less than red. Figure 2.64 illustrates the electromagnetic spectrum, depicting where infrared waves are classified. Figure 2.64: The electromagnetic spectrum (Halliday et al. 1997) Sir Isaac Newton (1642-1727) was the firs t person to perform an experiment revealing the presence of IR waves. The rela tionship between visibl e light and heat had long been recognized, since sunlight had an obvious effect on the temperature of an object. The important observation in Newton’s experiment was that objects could still be heated if they were placed outside of the visible spectrum observed when a beam of light passes through a prism. Newton knew some thing was responsible for generating the heat, but it could not be observed wi th the naked eye (Maldague 2001).

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117 The first person to formally quantify a th ermal image was Max Planck. Planck’s theory of radiation can be summarized as follows: All objects emit quantities of electromagnetic radiation Higher temperature objects emit gr eater quantities of radiation. The electromagnetic radiation emitted from a body consists of a “broadband” signal in that it contains radiation w ith a spectrum of wavelengths. Since IR waves are essentially the same as visible light waves, it is important to understand how they interact with the surf ace being measured. For IR thermography images to contain the desired temperature data it is important to distinguish between the radiation emitted from an object (which is related to its temperature) and radiation that is reflected off of the object from other sources. Emissivity ( ) is the quantity used to describe a particular surface’s ability to ab sorb and emit radiation. For the case of a “blackbody”, the emissivity is assumed to be 1. This means that all of the incident radiation falling on the surface is absorbed and results in an increase in temperature of the object. This increase in temperature then resu lts in increased radiation by the object. For the case of a mirrored surface (a perfect reflector), the emissivity is assumed to be zero. This implies that none of the radiatio n being emitted by the surface was actually generated by the object. Emissivites for common engine ering materials are provided in Table 2.4. Note that materials with a low emissivity are not particularly well suited for inspection by IR thermography. However, it is possible to increase the emissivity of shiny objects by treating the surface w ith flat paint. Another interesting phenomenon is the emi ssivity of glass. The relatively high value of 0.94 indicates that gla ss is essentially opaque to IR waves. As a result, an IR camera pointed at a glass window will provid e temperature information for the glass

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118 surface as opposed to the temperature of any visible objects on the other side. This phenomenon is of significant importance when considering which materials are suitable for use in IR camera lenses and associated optics. Table 2.4: Emissivities of common engineering materials Material Emissivity Steel Buffed .16 Oxidized .80 Concrete .92 Graphite .98 Wood .95 Window Glass .94 IR thermography and material assessment The fundamental concept behind using IR thermography as a non-destructive evaluation technique is that sound and unsound materials have different thermal conductivity properties. If a constant heat flux is applied to the surface of a uniform homogeneous material, the increase in temper ature on the surface of the object should be uniform. If, however, the material is non-homogeneous, the temperature along the surface will vary (see Figure 2.65). Figure 2.65: Typical therm ograph revealing defects Passive thermography The passive approach to IR thermogra phy is simple and involves collecting temperature data from a scene without applyi ng an external heat source. This method provides qualitative information about a situation and can be us ed to quickly determine if a problem exists. In the construction industr y, passive IR thermography has been used

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119 for many years to evaluate thermal insulation in buildings and moisture infiltration in roofs. Passive thermography is also used to detect delaminations in reinforced concrete bridge decks (ASTM D4788-88). The following sections contain detailed descriptions of each test standard and special cons iderations for each case are noted. ASTM D4788-88: delaminati ons in RC bridge decks In this test, a vehicle mounted IR imaging scanner is driven slowly over the bridge deck under consideration. If the evaluati on is performed during daylight hours, the delaminated areas will appear as “hot spots”. During the evening time as the bridge is cooling down, the delaminated areas will a ppear “cooler” relative to the sound bridge deck. The IR scanner can also be incorpor ated with an electronic distance-measuring device so the resulting thermographs can be overlaid onto scaled CAD drawings. If any areas of concern appear in the thermographs a more detailed inspection of the suspect area can be performed (usually by coring or ultrasonic evaluation). For delaminations to be detected, there must be a minimum temperature difference of 0.5 C between the delaminated area and sound ar eas. The test standard indicates that roughly three hours of direct sunshine is sufficient to develop this temperature differential. It is also specified that th e bridge deck should be dry for at least 24 hours prior to testing. Windy conditions should also be avoided and care must be taken when interpreting results in areas where shade ma y have influenced the surface temperature distribution. Passive thermography is a non-destruc tive testing techni que that provides qualitative information about a situation. Once potential problem areas have been

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120 identified, further testing (usu ally destructive in nature) can be conducted in the suspect areas. The primary advantage of this techni que is that large areas can be surveyed relatively quickly and without disrupt ion to the users of a structure. Active thermography In active thermography, heat is applied (by the inspector) to the surface of the object under investigation while an IR camera monitors the temperature variations on the surface. The advantage of active thermogr aphy over passive is that a quantitative analysis of the data collected can reveal impor tant defect characteristics (size and depth). This type of IR thermography is not usually employed in civi l engineering structures for overall NDE since the required energy inputs would be large. However, thermal input from the sun or a building’s heating/cooling sy stem and subsequent IR measurements is a form of active thermography. Since IR thermography is only capable of monitoring the surface temperature of an object, the technique is usually limited to situ ations where defects are located near the surface. As defect depth increases and def ect size decreases, assessment becomes more difficult. Active IR involves more elaborate te st setups than are encountered in passive thermography. The required minimum resolvab le temperature difference (MRTD) of IR camera equipment is smaller and heating of the specimen surface must be carefully controlled. As a result, most applications of active IR th ermography are performed in a laboratory or well controlled manufacturing environment. Equipment Scanning radiometers are devices capabl e of generating 320 x 240 pixel digital images containing the exact temperature data for each pixel. The precise temperature data is obtained by comparing the IR image si gnal to the signal generated by an internal

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121 reference object. Depending on the data acq uisition system employed, thermal images containing 76,800 unique temperat ure values can be obtained at a rate of 50 to 60 frames per second (see Figure 2.66). Applications Current applications of IRT include the eval uation of concrete and composite structures for delaminations, coating thickness, and the integrity of coatingsubstrate bonds. With the increased use of advanced composites in civil engineering structures, IRT becomes a potential means of evaluating the quality of installation and long-te rm durability of the composite strengthening system. Figure 2.66: Schematic of a scanning radiometer IR camera (Maldague, 2001) In an experiment performed at the Univ ersity of Florida (Hamilton & Levar 2003), reinforced concrete beams were bonded with CFRP composites and tested to failure. During the test procedure, the beams were periodically IR inspected for initial bond quality and bond failure under load testing. The use of acoustic sounding to detect unbonded or disbonded CFRP laminates can leav e as much as 25% of voids undetected. The use of IR thermography for the inspection of concrete structures strengthened with

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122 CFRP laminates is the most efficient method of qualitative inspection for structures with this type of repair. IRT was proven to be effective as a qualitative NDT technique for the inspection and repair of the concrete r oof shell at the Seattle Kingdome prior to its demolition. “In 1992, ceiling tiles attached to the roof unders ide fell approximately 300ft onto the seating area prior to the venue opening for a baseball game. The safety problem initiated a major rehabilitation program for the concrete shell roof of the almost 25 year old structure” (Weil & Rowe 1998, p389). IRT was used as the primary NDT method to locate subsurface anomalies in the roof structure. Delaminated or voided areas of concrete will prevent solar energy from passing through the ro of structure causing a “hot spot” to form when the roof is thermally loaded. Unbonded ar eas in concrete repaired with CFRP are detected in the same manner. Figure 2.67. pr ovides an illustration of the effect that delaminations and voids in concrete have on the conduction of heat the through the roof structure. Figure 2.67 Schematic description of ther mographic void detection process (Weil & Rowe 1998)

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123 The inspectors were able to thermographi cally survey the entire roof structure, which was 360,000 ft2 in area, in three days of testi ng using a single camera. Inspectors performed a more detailed inspection at each anomaly with sounding techniques and impact-echo for quantitative material analys is. Repairs to the roof shell were made according to test results and inspector recommendations. Radioactive Testing Radioactive testing dates back to the discovery of X-rays by Ivan Pului and Wilhelm Roentgen in the late 1880’s and 90’s. While Pului published material relating to X-ray experiments in the "Notes" of the [Aus trian] Imperial Academy of Sciences in 1883 several years before Roentgen’s first publ ication on X-ray technology, Roentgen is credited as the discoverer of X-ray technology and won the 1901 Nobel Prize based on his achievements (Kulynak 2000). The contributions by Marie and Pierre Curie are the most profound advances regarding radioactivity, a term they coined. Th e Curies discovered gamma rays in the late 1800’s while working with several different elements including bismuth, barium and uranium. They discovered polonium and ra dium, and the experiments the Curies conducted with radium and its radioactive e ffects were presented in Marie’s doctoral thesis in 1903. As a result, Marie won the Nobel Prize in 1903 (Hellier 2001). Radiography A radiograph is a picture produced on a se nsitive surface by a form of radiation other than visible light, typi cally an X-ray or a gamma ray. Radiography is the NDT technique that employs the use of radiographs for material inspection. X-rays are a form of electromagnetic radiation with a relatively short wa velength, about 1/10,000 the wavelength of visible light. Gamma rays are 1/1,000,000 that of visible light. It is this

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124 extremely short wavelength that enables X-rays or gamma rays to penetrate through most materials (Reese 2003). Structural radiography is very similar to the X-ray technique people experience during a doctor’s visit. Th e method involves a wa ve source, usually Xrays or radioisotopes, and a detector, which is most co mmonly photographic film. Figure 2.68 depicts a typical radiography setup. Figure 2.68: Radiography schematic (Lew et al. 1998) A limitation of radiography as an NDT techni que is that both sides of the material to be tested must be accessibl e for inspection. Therefore, structural elements like slabs and foundation walls are not typically accessibl e for testing with radiography. ASTM has developed a testing standard covering the practices to be employed in the radiographic examination of materials and components The standard outlines a guide for the

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125 production of neutron radiographs that possess consistent qu ality characteristics, as well as a guide for the applicability of radiography (ASTM E 748-02). Radiometry Often the terms radiometry and radiography are used interchangeably despite the fact that the tests are different. While radiogr aphy produces a visible image, radiometry is more quantitative in nature and is used to ascertain material properties. While both NDT techniques implement the use of radiation en ergy to analyze material properties, some radiometry techniques require only one side of a material to perform testing. The backscatter mode and certain aspects of the direct transmission mode (for both radiometry techniques) can send and receive ra diation signals from a single side of the material. The direct transmission mode of radiomet ry uses the same principles as the radiography test, though the radioi sotope source can be oriented in several configurations to enable personnel to perform surface testing of a material. The direct transmission mode of radiometry uses the same theory as ra diography, the main difference being that the equipment is configured differently. The dire ct transmission mode of radiometry usually has one or two probes that penetrate into the test material. A radi oisotope source emits pulses, which are received by the detector. The ra te of arrival of the pulses is related to the density of the material. This technique is commonly used in geotechnical engineering for the rapid calculation of soil composition, water content and density. Figure 2.69a illustrates a direct radiometry configuration wi th an internal signal detector and external source. Figure 2.69b is a schematic of a dir ect radiometry device with both an external signal detector and source (Malhorta & Carino 1991).

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126 Figure 2.69a Figure 2.69b Figure 2.69: Schematics of direct radiometry: (a) with an internal signal detector and external source, (b) with an external signal detector and source (Lew et al. 1998) In the backscatter measurement of radi ometry, the source and the detector are adjacent to each other, but are separated by a lead radiation shield. The backscatter method is basically the same test as direct transmission and measures the same material properties. The only difference between the two tests is equipment configuration. Figure 2.70 illustrates a backscatter radiometry configuration. Figure 2.70: Schematic of backscatter radiometry (Lew et al. 1998)

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127 Applications Radioactive methods have various applic ations in the nondest ructive testing and monitoring of structures. Ra diography may be the most pow erful qualitative means of NDT since it offers inspectors a view of the in ternal structural elements unrivaled by any other nondestructive inspection technique. One example of th e enhanced capabilities of radiography compared to any other NDT method is illustrated in Figures 2.71a and 2.71b. Figure 2.71a Figure 2.71b Figure 2.71:Image of prestressing cable anchorag e in concrete (a) X -radioscopic image of a prestressing cable anchorage embedded in a concrete, (b) schematic and brief explanation of the radiogra phic image (Malhorta & Carino 1991) Radiography can be applied to virtually any structural element in which two opposite sides are accessible. The method permits inspectors to assess every component on a visual basis, comparable to a medical do ctor’s ability to examine internal organs non-intrusively. Radiometry has been successfully used to quantitatively determine properties of concrete such as density, porosity, water c ontent and thickness. Th e techniques used for determining material properties and integrity using radiation waves is comparable to the techniques used in determining material pr operties via stress waves. However, stress waves are of a lower energy and less versat ile for material inspection than radiation waves.

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128 Limitations Although radiation testing is among th e most powerful methods used in nondestructive testing today, it has several lim itations that prevent it from becoming the most widely used NDT technique. Radiation te sting techniques are the most expensive of NDT methods available for the testing of conc rete materials. The technique is so much more expensive than the other techniques in service today, that many inspectors don’t consider it to be practical fr om a cost-benefit standpoint. Radiation testing presents many safety concer ns that are not easily addressed in the field. It is usually feasible to protect operating personnel while conducting testing. However, it is not always practical to us e radiographic testing due to public safety concerns. An example of this problem was demonstrated by the FDOT in February of 2002. Before the removal of an abandoned bridge adjacent to the Ft. Lauderdale airport, the FDOT contracted several consultants to demonstrate the capabilit ies of different NDT systems on the bridge deck. Among the tech niques demonstrated on the bridge were impact-echo testing, GPR, magnetic flux leakage and radiography. The radiographic method was the only method that required the br idge structure and the roadway beneath it to be completely free of personnel for testi ng, and that both roadways were completely closed to traffic. In most ur ban areas it is not feasible for such roadway closures since bridge structures are usually built in high traffic volume areas. The same types of problems arise when performing radiogra phic testing of build ings and building components.

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129 CHAPTER 3 SURVEY OF RELEVANT BRIDGE STRUCTURES IN FLORIDA The National Bridge Inventory (NBI) c overs 600,000 bridges on the nation’s interstate highways, U.S. highw ays, state and county roads, and other routes of national significance. The NBI is maintained by the Federal Highway Administration using data provided by the state and local transportation department s (Bhide 2001). The FDOT’s “Pontis” Bridge Management System (BMS) is the client run server application used to inventory the bridge stru ctures for the state. The majority of bridges in the state of Florida are constructed of concrete. These bridges are classified in the 25-50 year age ra nge. Deterioration rate studies suggest that structures in this category deteriorate slowly during the fi rst few decades of their design life (typically 50 years), followed by a rapid d ecline. (NBI 2003) If these predictions are correct, Florida, as well as the U.S. will incur extensive rehabilitation and reconstruction costs over the next two decades. The Department of Civil Engineering at University of Florida conducted a survey of bridge structures within the Pontis system in an attempt to categorize prevalent bridge deficien cies occurring th roughout the state. Currently, the FDOT’s Pontis system ha s inventoried a total of 12,573 bridge structures sign structures. Of the 12,573 are bridge structures, 9,585 were constructed with concrete. The survey conducted by the University of Florida, inventoried and categorized relevant concrete bridge structures. In additi on, personnel from the FDOT’s State Maintenance Office, Materials Office a nd District Offices we re interviewed to ascertain any prevalent probl ems within concrete bri dges throughout the state.

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130 Definition of Sufficiency Rating A bridge sufficiency rating is a numerical value assigned to a bridge structure subsequent to inspection, based on its condi tion. The major factors used to determine sufficiency rating are structural adequacy, se rviceability and essentia lity for public use. Therefore, the structural condition of a bridge and its sufficiency rating are not completely dependent upon each other. Figure 3.1: is a summary the factors used for calculating sufficiency rating. Figure 3.1: Summary of sufficiency rating factors (FHWA 1995) Figure 3.1 illustrates the percentages of each factor used in the calculation of bridge sufficiency rating. Structural adequacy and sa fety comprise 55 percent of the total bridge rating. Since there are several components that affect a bridges sufficiency rating, it is not completely accurate to use the sufficiency rating as part of the methodology for a

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131 materials or structural survey Interviews with FDOT personnel confirmed that presently the sufficiency rating is the best way to que ry bridge structures based for structural deficiencies. Methodology Originally, the purpose of the bridge surv ey was to identify prevalent bridge deficiencies that were typical among concrete structures throughout the state. However, the Pontis system is limited in its queryi ng abilities and does not allow for specific problems, deficiencies, or inspector recomm endations. Presently, the Pontis system can execute queries based on bridge ID numb er, structure name, name of the feature intersected, county, age, length and sufficiency rating. Another limitati on of Pontis is that it lacks the ability to form more than one que ry at a time. Therefor e, without printing, reading, and manually categorizing each of th e 12,573 bridge reports, it was not possible to determine prevalent material or structural problems. Pontis lacks the ability to make queries of specific bridge structure deficiencies. Therefore, the bridge queries were based solely on sufficiency rating. However, the structural condition of a bri dge and its sufficiency rating are not completely dependent upon each other. The Pontis system was used to query th e bridges by sufficiency rating. A typical query is illustrated in Figure 3.2. Since the Pontis system cannot query by more than one item, all of the relevant bridges queried had to be categorized by hand. As an attempt to create a baseline of structure performance, the bridges were categorized by condition, age and feature intersected. All bridges that were 40 years of age and older with a sufficiency rating of 85 or above set the baseline for durable structur es. All bridges 20 years or

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132 younger with a sufficiency rating of 75 or belo w were considered to be less durable and should be monitored for material and structural problems. Figure 3.2: The result of a typical bridge query by sufficiency rating The FDOT uses visual inspection the pr imary method of gathering data that is imputed into the Pontis system. As discussed in Chapter 2 visual inspection is often subjective and is dependent upon ‘human f actor’ that is often encountered during structural inspection. The susceptibility to human misinterpretation and the requirement for establishing a baseline for defects in ge neral, especially under poor conditions, can lead to inconsistent identification of anomalies, resulting contradicting evaluations (Quaswari 2000). Another limitation of using the Pontis system is that a bridge sufficiency rating is calculated by quantifying the results from vi sual inspections. Cont radicting evaluations can alter a bridge sufficiency rating dras tically. Interviews with FDOT personnel corroborated with the indicati on that discrepancies in eval uation ratings, as a result of

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133 inconsistencies in visual inspection results a ffect the value bridge sufficiency rating when inputted into the Pontis system. According to the FHWA’s recording and coding guide for bridges, the deck, superstructure, and substructure are given a general condition code ba sed on a scale of a 0-9, 0-code represents a bri dge closed and a 9-code is s uperior to present desirable criteria. Rigorous attempts to classify data using the genera l condition codes were unsuccessful because the bridge sufficiency ra ting is dependent of the general condition code. Figure 3.3 shows examples of bridges th at are approximately the same age, and the same structural code classifications bu t have different sufficiency ratings. Figure 3.3: Examples of Pontis codes vs. sufficiency ratings. The inability of the Pontis system to so rt and classify bridges with regard to structural or material integrity is the most limiting feature of the system. Due to the lack of such a feature, a statically significant da ta analysis based on structural sufficiency cannot be performed.

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134 Results Pontis Data Analysis Currently the Pontis system has 12,573 bri dge structures invent oried. However, the report published by the FHWA in 2002 has a total of 11,526 bridge structures inventoried. There are several reasons for th e discrepancy between the current count and the 2002 published count The first reason is that as new bridges are constructed on an annual basis, the number of bridges in the Pontis system w ill rise accordingly. Another reason for the inconsistency among the figures is that the NB I publishes the number of bridges that are completely constructed. While the Pontis syst em has an inventory of all bridges that are completely constructed, as well as bridges currently under construc tion. A third reason for the difference in numbers is due to errors in the inputs of the bridge data. The FDOT has downsized a large percentage of its sta ff. Private consultants are now performing the majority of the bridge inspection and data en tering into to the Pontis system. Recently, there are instances in which bridges are mist akenly entered or duplicated within Pontis. For the purposes of this survey, we will use the numbers published from the 2002, NBI for overall quantities. However, the cate gorized figures were obtained through an analysis of data performed by the University of Florida. Of the 11,526 bridge structures in the stat e, 9,585 were constructed with concrete. The concrete bridges were analyzed and 686 of them fit into the two durability categories previously stated. Of the 686 bridges, 202 br idges fit into the deficient new structure (DNS) category (i.e. 20 years or younger with a sufficiency rating of 75.0 or less). However, 41 of the DNS 202 bridges are made of concrete. The majority of the deficient bridges are steel or wood st ructures, accounting for 161 of the 202 bridges. Of the 41

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135 DNS bridges made of concrete, 21 are functi onally obsolete. Accordingly, 19 of the 21 DNS bridges, were functionally obsolete and had sufficiency ratings above 60.0. These 19 functionally obsolete bridges were consider ed to have a low deficiency rating based on the “S3” sufficiency rating input paramete r from the equation in Figure 3.2. For the uses of this survey, they are considered to be structurally sufficient. Therefore, 22 of the 9,585 concrete bridges throughout the state can be classified as newly constructed and structurally deficient. Over 90% of the concrete bridge structur es within the state employ slab design and multi beam/girder design. Consequently, the 17 of the 22 newly constructed deficient bridges are slab and beam/girder design. Upon review of the individua l bridge reports, it was found that the most prevalent deficiency in these structures is deterioration of the bridge deck. According to the FHWA’s reco rding and coding guide for bridges, the bridge deck average general c ode is 6.73 out of 10, for the 22 newly constructed deficient bridges (Where 7 is considered to be good condition and 6 is satisfactory condition.) Again, we see some inconsistency when tr ying to deduce a struct ural condition based on sufficiency rating. Conclusions Subsequent to using the Pontis system for ove r a year, it is apparent that there is a need for more quality contro l regarding interpretation of structural deficiencies and disposition of the data with in system. Private consultants rather than FDOT personnel performed most of the bridge inspections. As a result, consistency in the interpretations of bridge conditions is being compromised. It appears as though a more exact definition of conditions is needed to regain the nece ssary quality control of inspection reports.

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136 The system appears to lack a protocol to maintain the consis tency among units of physical properties (i.e. some reports use the English syst em of measurement, where others use SI units). Since the system lacks user consistency between such simple parameters, it is difficult to rely on the quality control of sufficiency ratings to draw any statistical conclusions based on the data within the system. Consequently, a statistical analysis was not performed on the bridge data within the Pontis system. Deductive arguments made from the data available would be insufficient to infer reliable conclusions. Limitations of Pontis system include: The inability to process data sorts of more than one data field within the system for a single data query The inability to perform data sorts based on material type The expansion of the Pontis system to include multiple data sorts would allow for more complicated data analyses to be unde rtaken. The addition of a sorting material based query would enable users to perform sta tistically significant data analysis on bridge structures based on material type. As a result of our survey, it has been dete rmined that 22 newly constructed concrete bridge structures were cla ssified as deficient. Since 17 of the 22 deficient bridge structures are typical designs, they provide a good baseline fo r testing. Upon plan review, these bridges should be considered for condition monitoring. The use of several qualitative and quantitative NDT methods should be employed to further assess the material integrity of each bridge.

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137 CHAPTER 4 BRIDGE INSPECTIONS Document Review As part of the bridge survey, the Universi ty of Florida conduct ed interviews with Mr. Charles Ishee and Mr. Ivan Lasa of the FDOT State Materials Office for the purpose of identifying prevalent bridge structure defi ciencies that could be considered typical among concrete bridge struct ures throughout the state. Th e personnel interviews, in conjunction with the results from the bridge su rvey discussed in Chapter 2, were used to establish a sample of bridges to be surveyed and nondestructively tested. The purpose of performing the bridge re search conducted in Chapter 3 was to identify relevant structures through the Pontis BMS. The data gathered was originally to be used to identify bridges that contai ned typical deficiencies that warranted nondestructive testing and field inspection. Unfortunately, the Pontis system does not have the capacity to act as a stand alone sy stem for these purposes. Therefore, it was essential to incorporate FDOT personnel interviews to establis h a sample of bridges that were suitable for NDT tes ting and field inspection. As a result of the survey and FDOT personnel interviews, the following bridges were visited: Bahia Honda Bridge Niles Channel Bridge Sebastian River Bridge Sebastian Inlet Bridge (R obert W. Graves Bridge) Wabasso Bridge

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138 Each bridge was examined to locate typical deficiencies and to a ssess the overall quality of concrete used for construction. NDT Methods Used for Inspection The literature review performed in Chapter 1 served as an evaluation of NDT technology currently available today. The NDT techniques most suitable for use in concrete materials inspection are: visual inspection, acoustic sounding, rebound hammer, impact-echo and ultrasonic pulse velocity. The penetration resistance methods and the breakoff test were considered suitable for material inspection but due to their partially destructive nature they were not permitted by the FDOT for use. Inspections were thus limited to non-intrusive testing techniques. Bahia Honda Bridge Site Information The Bahia Honda Bridge was constructed in 1972 and spans the big Spanish Channel waterway between Bahia Honda Ke y and Big Pine Key in Monroe County, Florida. The new bridge was built to repl ace the Old Bahia Honda Bridge, which was originally built in 1912 as part of the Flag ler’s Overseas Railroad. After the 1935 Labor Day Hurricane destroyed the railroad, a paved roadway was built on top of the steel trestles of the old bridge. The new bridge was built to replace the old bridge with a newer and wider double span crossing to increase traffic capacity. Procedures The evaluation began with a site visit by Mr. Christopher Ferraro and Dr. Andrew Boyd of the University of Florida, accomp anied by Mr. Olen Hunter and Mr. Andrew Eiland of the FDOT, on May 20, 2003. During the visit the personnel observed the Bahia Honda bridge substructure and superstructu re accessible from a boat provided by the

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139 FDOT. The general condition of the bri dge was observed and documented with photographs. No plans were available for review. During the course of the fieldwork, th e personnel performed materials testing on pile cap 55 and the accessibl e portion of its corresponding column. As part of the materials survey, the pile cap and the co lumn were sounded, impact-echo tested, ultrasonically, and rebound hammer tested. (see Figures 4.1 and 4.2 for locations). Results Site observations The bridge superstructure is composed of prestressed concrete girders resting on top of a concrete cap beams. The substructu re is composed of concrete cylindrical columns with struts resting on top of pile caps. The submerged piles were not visible during the inspection. Refer to Figures 4. 3 and 4.4 for photographs of the bridge structural elements. The entire bridge structure was visually su rveyed to get an overall appraisal of the structural integrity. The bri dge girders showed little or no deterioration, though some locations of discoloration, efflorescence, and superficial cracking were noted. The concrete columns exhibited a range of deteri oration levels. Few columns exhibited little or no deterioration. The majority of th e columns displayed moderate to severe deterioration. Severe deficiencies such as large cracks, spalls, delaminations and section loss have been repaired. In sp ite of the extensive repair-wor k performed on the columns, some of the repairs have experienced deteri oration and new deficiencies have developed since the columns were last maintained. Th e struts have gunite cover. The gunite is cracked and delaminated with random spalls throughout. The pile caps have experienced

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140 the same types of deterioration as the columns. However, the majority of pile caps are in satisfactory condition whereas the majority of the columns are experiencing deficiencies. Upon completion of the visual survey, it wa s decided that pile cap and column 55 exhibited typical deficiencies and had not yet been repaired, and thus were suitable for materials inspection. The crack observed on the column on pile cap 55 appears to be a typical deficiency observed throughout the br idge. However, most of the other columns observed had already undergone repairs in th e same location, at the connection of the column, strut and pilecap. NDT Analysis The column and pile cap were sounded, rebound hammer tested, impact-echo tested and ultrasonically tested in order to determine material quality. The tests were performed in accordance with relevant ASTM sta ndards (ASTM C 805-97, ASTM C 597-97, ASTM C 1983-98a). The column was tested using the soundi ng method, the ultrasonic pulse velocity meter and the impact-echo device. An ultrasoni c pulse velocity meter was used to obtain a tomography of the column using through wavespeed of the ma terial. The average through wavespeed was calculated to be 4530 m/s. Impact-echo was used to gather surface acoustic velocities. The average of th e impact echo wavespeed was determined to be 3893 m/s. The column has two cracks on opposite sides of each other. Figures 4.5 and 4.6 consist of photographs of the cracks. Acoustic sounding adjacent to the crack revealed that the crack propagates inwa rd. Ultrasonic tomography confirmed the orientation and crack depth. Figure 4.7 is a schematic of the calculated crack depth and orientation as a result of the acoustic and ultrasonic tomogr aphy testing. The impact echo device was also used to confirm obtai ned surface acoustic velo cities using ASTM

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141 C-1383a procedure B, which is described in th e impact echo material thickness section of chapter 2. The through acoustic velocities we re confirmed within acceptable tolerances. The pile cap was tested using a rebound ha mmer, ultrasonic pulse velocity meter, and impact echo device. The average rebound number was determined to be 43.3, producing a corresponding streng th value of approximately 5700 psi (Malhotra & Carino 1991). The average through wavespeed obtaine d using the pulse ve locity meter was calculated to be 3676 m/s. The average imp act-echo surface wavespeed was determined to be 3543 m/s. The impact echo device was also used to confirm surface wavespeeds obtained using ASTM C-1383a, as it was for the column, and again the average acoustic velocities were confirmed within acceptable tolerances. Conclusions Previously published research has suggested that the qual ity of a concrete specimen is related to its wavespeed, with changes being proportional to changes in concrete strength. (Benedetti 1998, Neville 1996, Mindess et al. 2003, Lemming et al.1996, Popovics et al.1999, 2000, Popovics 2001, Gutra 2000, Lane 1998, Krautkramer 1990, Malhotra 1984, 1994, Malhotra & Carino 1991) Table 2.3 classifies concrete with wavespeeds in the range of 3500-4500 m/s as good quality. Though the quality of the concrete is most likely good in terms of compressive streng th, the permeability of the concrete cannot be determined through th e use of any NDT method to date. The deficiencies exhibited throughout the bridge structure appear to be a result of the rebar corrosion. Concrete exposed to seawater can be subjected to chemical attack including the chloride-induced corrosion of steel reinforcement (Nev ille 1996). Therefore, it is possible to have a structure undergo structur al deterioration even with concrete of adequate strength.

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142 The disparity between the through wavesp eed and the surface wavespeed suggests that the column has sustained surface damage due to exposure. The through wavespeeds obtained with the impact echo were approxima tely 16% lower than those obtained by the ultrasonic pulse velocity met hod. There are several factors that contribute to this difference: An ultrasonic pulse is more likely to tr avel through the material with the fastest acoustic velocity. Large amounts of steel re bar within the colu mn can distort the true acoustic velocity. The flow of traffic on the bridge can distort the through column signal. Circular columns can have di fferent modes of frequency. Therefore, the response of circular columns can be complex. The frequency resolution is 32% of the total frequency, therefore producing a relatively large uncertainty in through wavespeed. Although there was discrepancy between th e ultrasonic wavespeed and the impact echo wavespeed, the differences were within acceptable tolerances. The disparities are most likely due to a combination of the reasons listed above. It is lik ely that the through acoustic velocities obtained with the ultrasoni c pulse velocity meter are slightly high due to interactions with the rebar. As discussed in Chapter 2, the wave speed of a solid is dependent upon the material type. Therefore, it is possible for a combined effect to occur when measuring the time of travel of ultras onic signals through composite materials. The pulse velocity method is depende nt upon the time of travel of a pulse through the material from one transducer to the other. It is pr obable that any embedded steel will serve as a transport mechanism for the pulse within th e concrete column. Since steel has a higher acoustic velocity, the resulting acoustic veloc ity for the column will be slightly higher than a concrete specimen without embedded steel.

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143 Although the impact-echo through wavepseeds were calculated with relatively poor resolution, the impact echo testing method is used to confirm acoustic velocities through the use of frequency analysis and specimen geometry. Therefore any materials with higher acoustic velocity embedded within conc rete typically do not affect the through wavespeed of an impact echo signal with a combined material effect. The impact echo method requires the analysis of a frequency spec trum to verify the acoustic velocity of a material. The impact echo section of chap ter 2 discusses the analysis of frequency spectrums of impact echo testing. With the data available, it is possible to conclude that the concrete material of the column is in good condition with some signs of distress. The crack in the column is most likely a torsional crack, which is due to loadi ng or shifting of the structure. In marine environments, it is common for bridge column s to shift over time. However, the purpose of this survey was to examine the concrete ma terial of the structure and not the structure itself. The pile cap was found to be in relatively good condition. The surface wavespeed of the pile cap was slightly lower than the though wavespeed of the cap. The slight discrepancy between surface and through wavesp eed is most likely a result of exposure. However, due to the small difference in wave speeds, it can be concluded that exposure conditions have not distressed the concrete to a great extent. This is most likely due to the loading conditions on the pile cap, as they are not as likely to facilitate damage within. The strength estimates produced by rebound hamm er tests are, at most, reliable to within 25 percent (Malhotra & Carino 1991). The rebound hammer results verify the

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144 concrete is in generally good condition. In conc lusion, the concrete material of the pile cap is in good overall material condition. Figure 4.1: Plan view of Bahia H onda bridge pilecap and column 54 Figure 4.2: Photo location plan Bahia Honda bridge pile cap and column 54

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145 Figure 4.3: View of bridge s uperstructure from water-level Figure 4.4: View of footing

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146 Figure 4.5: View of crack in column Figure 4.6: View of crack in column. Efflor escence of the gunite t opping on the strut can be seen in the background

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147 Figure 4.7: Plan view of cr ack orientation on column 54 Niles Channel Bridge Site Information The Niles Channel Bridge was constructed in 1983. It spans th e big Niles Channel Waterway between Summerland Key and Ramrod Key in Monroe County, Florida. Like the Bahia Honda Bridge, the Niles Channel Br idge replaced an older bridge which was originally built as part of the Flagler Overseas Railroad. Procedures The evaluation began with a site visit by Mr. Christopher Ferraro and Dr. Andrew Boyd of the University of Florida, accomp anied by Mr. Olen Hunter and Mr. Andrew

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148 Eiland of the FDOT, on May 21, 2003. During th e visit, the personnel observed the Niles Channel bridge substructure and superstruc ture accessible from a boat provided by the FDOT. The general condition of the bri dge was observed and documented with photographs. No plans were available for review. During the course of the fieldwork, th e personnel performed materials testing on Column Line 20. As part of the material s survey, the accessible portion of the column and strut were tested by means of sounding, impact-echo and ultrasonic pulse velocity. Locations of testing on Column Line 20 are depicted in Figure 4.8. Results Site observations The bridge superstructure is composed of a prestressed concrete segmental box resting on girder concrete columns. The substr ucture is composed of concrete cylindrical columns with struts resting on top of cylindrical drill shafts. The submerged drill shafts were not visible during the inspection. Figur es 4.9 and 4.10 contai n photographs of the bridge structural elements. The entire bridge structure was visually su rveyed to obtain an overall appraisal of its structural integrity. The segmental box gird er showed little or no deterioration, though there were some locations of discoloration, efflorescence, and superficial cracking. Some of the concrete columns were observed to ha ve experienced delamina tions and spalls and have been repaired. However, the majori ty of the columns displayed minor or no deterioration. Some of the struts exhibited little or no deterioration. However, the majority of the struts displayed moderate to se vere deterioration. Severe deficiencies such as large cracks, spalls, delaminations and sect ion loss have been repaired. In spite of the extensive repair-work performed on the stru ts, some of the repairs have experienced

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149 deterioration and new deficiencies have developed since the columns were last maintained. Figure 4.11 is a photograph of a typical column st rut repair, and new deficiency. The drill shafts s howed little or no deterioration. There were some locations of discoloration, efflorescen ce, and superficial cracking. Upon completion of the visual survey, it was decided that Column Line 20 exhibited typical deficiencies, yet had not been repaired. Thus, this column line was deemed suitable for materials inspection. Th e crack delamination of the concrete on the lower portion of Strut 20 appeared to be a prevalent deficiency observed throughout the bridge. NDT Analysis The column and pile cap were tested by means of acoustic sounding, impact-echo, and ultrasonic pulse velocity in order to determine material quality. The tests were performed in accordance with relevant ASTM standards (ASTM C 597-97, ASTM C 1983-98a). The columns were tested using the imp act echo device. The average impact echo surface wavespeed for both columns was determined to be 3981 m/s. The impact echo device was used to confirm surface wavespeed s as it was for the Bahia Honda Bridge. The average impact echo through wavesp eed was calculated to be 4083 m/s. The strut was tested using the ultrasonic pulse velocity meter and the impact echo device. The ultrasonic pulse ve locity meter was used to obtain a tomography of the strut using the through wavespeed of the materi al. The average through wavespeed obtained using the pulse velocity meter was calcu lated to be 4358 m/s. Acoustic sounding and ultrasonic tomography confirme d that the lower portion of the strut is cracked and delaminated. The average impact-echo surface wavespeed was determined to be 3930

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150 m/s. The impact echo device was used to c onfirm obtained surface ac oustic velocities as it was for the Bahia Honda Bridge. The average impact echo through wavespeed was calculated to be 4083 m/s. Conclusions The data obtained from the nondestructive te sting of the strut wa s similar to that obtained from the column of the Bahi a Honda Bridge. The ultrasonic through wavespeeds taken from the strut were greate r than the impact echo surface and through wavespeeds. The discrepancy between the ultras onic pulse velocity data and the impact echo data can be attributed to the effect s of the embedded steel on pulse velocity measurements. The slight disparity be tween the surface and through impact echo wavespeeds is consistent with the results from the Bahia Honda pile cap and most likely a result of exposure. However, due to the s light difference in wavespeeds, it can be concluded that exposure conditions have not distressed the conc rete to a great extent. The lower portion of the strut was delaminated, most likely due to the corrosion of the embedded rebar. Figure 4.11 is a photograph of a typical deficiency of the strut. The deficiency is most likely a resu lt of rebar exposure to chloride s, as the struts are partially submerged under severe weather conditions. The columns on Line 20 were found to be in satisfactory condition with little or no signs of distress. The wavespeeds acquired from impact echo testing of column 20 indicate that the concrete is in good condition in that column. The overall condition of the structure was not determined fo r the purposes of this survey.

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151 Figure 4.8: Plan view of Nile s Channel Bridge column line 20 Figure 4.9: General view of Niles Cha nnel Bridge underside, column line 20 in foreground

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152 Figure 4.10: Impact-echo te sting on bridge column Figure 4.11: View of typical strut and column repair. Note spalls in strut underside

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153 Sebastian River Bridge Site Information The Sebastian River Bridge was constructe d in 1957, and spans the St. Sebastian River Waterway between Indian River County and Brevard County, Florida. The bridge was built to service an increased traffic fl ow on U.S. Highway 1, which is the only throughway from the State of Maine to the Florida Keys. Procedures The evaluation began with a site visit by Mr. Christopher Ferraro of the University of Florida, accompanied by Mr. Ronald Ferra ro, on June 12, 2003. During the visit the personnel observed the Sebastian River bridge substructure and s uperstructure accessible from a boat provided by the University of Fl orida. The general condition of the bridge was observed and documented with photographs No plans were available for review. During the course of the fieldwork, th e personnel performed materials testing on Column Line 11. As part of the material s survey, the accessible portion of the column and strut were tested by means of s ounding, rebound hammer, impact-echo, and ultrasonic pulse velocity meter. Locations of testing on Column Line 11 are depicted in Figure 4.12. Results Site observations The bridge superstructure is composed of prestressed concrete girders resting on concrete cap beams. The substructure is co mposed of prestressed concrete piles with concrete pile jackets. The submerged drill sh afts were not visible during the inspection. Figures 4.13 through 4.16 are photographs of the bridge structural elements.

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154 The entire bridge structure was visually surveyed in order to obtain an overall appraisal of the structural inte grity. The bridge girders show ed little or no deterioration, though there are some locations of discolorati on, efflorescence, and superficial cracking. The concrete columns were observed to have experienced a range of deterioration levels. Approximately 20 percent of the pile jackets were observed to have been replaced with non-structural fiberglass jacket s filled with grout or epoxy. Severe cracks, spalls and delaminations were observed on the repaired pile jackets. Distress on the prestressed concrete columns was not observed. However, the prestressed column interiors were not visible. Upon completion of the visual survey, it was decided that Column Line 11 exhibited a typical representati on of the bridge superstructure. Of the five columns on this column line, three are intact. The other tw o columns have been previously repaired. Column 11-5 is an example of a column that has not been repaired, and Column 11-4 is an example of a typical repaired column. Figures 4.14 through 4.16 contain photographs of the columns. According to inspection reports the column repairs were performed approximately 12 years ago. NDT Analysis Columns 11-4 and 11-5 were tested by means of sounding, rebound hammer, impact-echo, and ultrasonic pulse velocity me ter in order to determine material quality. The tests were performed in accordance with relevant ASTM standards (ASTM C 80597, ASTM C 597-97, ASTM C 1983-98a). The pile jacket of Column 11-4 is compos ed of a mortar mix and was observed to be in poor condition. It appeared as though se vere segregation of the constituents of the mortar took place prior to, or during placemen t. Severe cracking and delamination were

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155 evident throughout. Figure 4-16 co ntains a photograph of a vert ical crack, approximately 8 feet in length and approximately 0.07in wide that was observed on the north side of the column. The column was acoustically sounded with a ball peen hammer to determine the presence of delaminations. As a result of the survey it was determined that approximately 50 percent of the pile jacket has delaminated from the pile. The extremely poor condition of the mortar resulted in large variances in the wavespeeds obtained with the impact echo device. Some impact echo tests did not produ ce data because the concrete permanently deformed upon impact. Therefore, data obtai ned from the impact echo was relatively unusable for analysis. The obtained surface wavespeeds ranged from 2400 m/s to 4000 m/s. Ultrasonic testing also produced data w ith a considerable range. Ten of the twenty UPV readings taken were above 3200m/s. A considerable range of through wavespeeds was produced by the UPV test. Column 11-5 was observed to be in satis factory condition. Ac oustic sounding did not reveal any delaminations in the pile j acket. The average through wavespeed obtained using the pulse velocity meter was calculate d to be 4354 m/s. The average impact-echo surface wavespeed was determined to be 4485 m/s. The data obtained using the impact echo through measurement did not verify the wa vespeeds due to signal scatter, which was most likely produced by the presence of se veral material interf aces within the pile. Conclusions The NDT data received from Column 11-4 reve aled that the pile jacket is in poor condition. The severity of the deterioration combined with the relatively young age of the repairs indicates faulty repair work in the replacement of the pile jacket. Column 11-5 was found to be in satisfact ory condition with little or no sign of distress. The acoustic sounding, rebound ha mmer, impact echo and ultrasonic pulse

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156 velocity data acquired from the column confir med that the concrete is in good condition. The impact-echo though wavespeeds could not be accurately obtained due to the interaction between the stress waves and several material in terfaces within the pile. Figure 4.12: Plan view of Sebastian River Bridge column line 11 Figure 4.13: General view of Sebastian River Bridge

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157 Figure 4.14: Column line 11 with column 11-5 in foreground Figure 4.15: Column 11-4

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158 Figure 4.16: Cracked and delaminated repair in column 11-4 Wabasso Bridge Site Information The Wabasso Bridge, constructed in 1970, spans the Indian River waterway in Indian River, Florida. This bridge serves as the easternmost se gment of the Wabasso causeway. The bridge was built to service traffic flow on County Road 510, between Indian River Lagoon Scenic Highway (A1A) and U.S. Highway 1 in Indian River County, Florida. Procedures The evaluation began with a site visit by Mr. Christopher Ferraro of the University of Florida accompanied by Mr. Ronald Ferraro on June 13, 2003. During the visit, they observed the bridge substruc ture and superstructure fr om a boat provided by the

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159 University of Florida. The general conditi on of the bridge was observed and documented with photographs. No bridge plan s were available for review. During the course of the fieldwork, th e personnel performed materials testing on Pier 5 and Pile Cap 5. As part of the ma terials survey, the acc essible portion of the column and strut were tested by mean s of acoustic sounding, rebound hammer, and impact-echo. Figure 4.17 depicts test ing locations on the Wabasso Bridge. Results Site observations The Wabasso Bridge superstructure is com posed of prestressed concrete girders. The substructure is composed of concrete hammerhead piers with a concrete pile cap. The submerged piles were not visible duri ng the inspection. Figures 4.18 and 4.19 contain photographs of the br idge’s structural elements. The bridge superstructure and substructure were visually surveyed to get an overall appraisal of the structural inte grity. The bridge girders showed little or no deterioration. There were some areas of discoloration, efflorescence, and superficial cracking. The concrete piers showed little or no evidence of deterioration. The accessible portions of concrete pile caps revealed that crushed seashe ll was used as a constituent in the concrete mix, as shown in Figure 4.20. The pile cap s were observed to be in good condition with little or no signs of distress. NDT Analysis Pier 5 and Pile Cap 5 were tested by m eans of acoustic sounding, rebound hammer, and impact-echo in order to determine material quality. The tests were performed in accordance with relevant ASTM standa rds (ASTM C 805-97, ASTM C 1983-98a).

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160 The average surface wavespeed for Pier 5, obtained by the impact echo device, was 3157 m/s. Through wavespeeds were confirmed within acceptable to lerances, using the impact echo device. The average rebound nu mber was determined to be 58.5. The corresponding strength value, extrapolated from the best -fit equations (Malhotra & Carino 1991), was approximately 11,000 psi. The average surface wavespeed for pile cap 5, obtained by the impact echo device, was measured to be 2515 m/s. The th rough wavespeeds were confirmed within acceptable tolerances, using the impact ec ho device. The average rebound number was determined to be 46.25. The corresponding streng th value, extrapolated from the best-fit equations (Malhotra & Carino 1991), was approximately 8,100 psi. No material defects on any of the accessible structural components were revealed as a result of acoustic sounding. Conclusions The NDT data collected from the bridge elements appear to contain some conflicting values. The data obtained from th e rebound hammer indicate that the concrete elements are in good condition, whereas the data obtained from the impact echo device suggest that the concrete elements show signs of distress. The aggr egate used in the mix design, which was observed to contain crus hed seashell, most probably caused this disparity between surface har dness measurements versus wavespeed measurements. Crushed seashell or calcium carbonate is less dense and more porous than conventional coarse aggregates used for conc rete production. As disc ussed in Chapter 2, density and porosity are two pr operties of a solid that can reduce its acoustic impedance or wavespeed. The use of crushed seashell in the structural com ponents resulted in low

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161 wavespeeds. However, the low wavespeeds ca lculated for the conc rete components does not correlate to distress of the actual structure. The large values obtained using the rebound hammer appear to suggest that the material is in good condition. Rebound values corresponding to strengths of 11,000 and 8,000 psi are extremely high. One possibl e reason for the high rebound hammer values could be due to the carbonation of the c oncrete surface. Surface carbonation can result in rebound numbers 50% higher than those obtai ned on an uncarbonated surface (Malhotra & Carino 1991). Carbonation of concrete is pr omoted in environments where the relative humidity is maintained between 50 and 75 pe rcent (ACI 201.2R92). Consequently, it is unlikely that carbonation is taking place on the surface of the bridge because the average relative humidity exceeds 85 pe rcent approximately 11 months of each year (NOAA 2003). The most probable cause of the high rebound number values is the material constituents in the concrete mix design. Resear ch has revealed that the type of aggregate and cement can significantly affect rebound hammer readings (Malhotra & Carino1991). Due to the angularity of seashe lls, it is common to require additional cement in a concrete mix to increase workability (Neville 1996). At pr esent, there is no research available that correlates compressive strength with concrete containing crus hed seashells as aggregate. Unfortunately, the mix design is not available for review and the uncertainties within the exact mix design prohibit specifi c material based conclusions.

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162 Figure 4.17: Plan view of Wabasso Bridge column Figure 4.18: General view of Wabasso Bridge

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163 Figure 4.19: Column / pilecap 5 Figure 4.20: Close-up of exposed seashell aggregate on pile cap 5 Sebastian Inlet Bridge Site Information In 1886, the first inlet (Gib son’s cut) was dug by hand approximately 3 miles south of the present day inlet. In 1924, the Sebast ian Inlet was opened at its current location. Between 1924 and 1941 the Inlet opened and cl osed several times due to the shifting

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164 sands caused by storms. For safety reasons, it was left closed during World War II, then permanently blasted open in 1947. The Sebastian Inlet Bridge, also known as the Robert W. Graves Bridge was completed in 1967. The 1,548 foot long bridge sp ans the inlet and is part of the Indian River Lagoon Scenic Highway (A1A). The wate rway serves as part of the borderline between Indian River County and Brevard County, Florida. Procedures The evaluation began with an interview of Mr. Ivan Lasa on June 10, 2003 by Mr. Christopher Ferraro. Mr. Lasa reported that the bridge had recen tly undergone repair work, including the rehabilita tion of deficiencies in the bridge superstructure and substructure. Portions of the bridge, including the columns, were painted as part of the repair work. Mr. Christopher Ferraro of the University of Florida, accompanied by Mr. Ronald Ferraro, performed site visits on June 14 a nd 15 of 2003. During the site visit, they accessed by foot and observed the bridge substr ucture and superstructure. The general condition of the bridge was observed and doc umented with photographs. No plans were available for review. During the course of the fieldwork, th e personnel performed materials testing on Pile Cap 12 and Pile Cap 16, as well as the a ccessible portion of Column 12. As part of the survey, portions of elements were tested by means of acoustic sounding, ultrasonic pulse velocity, impact-echo, and rebound ha mmer. Figure 4.21 depicts locations of testing on the Sebastian Inlet Bridge.

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165 Results Site observations The bridge superstructure is composed of prestressed concrete girders resting on concrete cap beams. The substructure is com posed of concrete cylindrical columns with struts resting on pile caps. The submerged p iles were not visible during the inspection. Figures 4.22 and 4.23 contain photographs of the bridge’s structural elements. The entire bridge structure was visually su rveyed to get an overall appraisal of the structural integrity. The bri dge girders showed little or no deterioration, although there were some areas of discoloration, efflores cence, and superficial cracking. The concrete columns showed little or no evid ence of deterioration. The pile caps were observed to be in good condition with little or no sign of distress. NDT Analysis Pile Cap 12 and Pile Cap 16 were tested by means of sounding, rebound hammer, and impact-echo in order to determine material quality. The tests were performed in accordance with relevant ASTM standard s (ASTM C 805-97, ASTM C 597-97, ASTM C 1983-98a). The column was tested using the sounding method and the ultrasonic pulse velocity meter. The ultrasonic pulse velocity mete r was used to obtain a tomography of the column using through wavespeeds of the ma terial. The average through wavespeed was calculated to be 3675 m/s. The column has two cracks on opposite sides of each other. The cracks were not visible due to recent repa irs performed on the surface of the column. Ultrasonic tomography confirmed the orientat ion and depth of the crack. Figure 4.24 is a schematic of the calculated crack depth and orientation as a result of the acoustic and ultrasonic tomography testing.

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166 The pile caps were tested using the sounding method, the rebound hammer, and the impact-echo device. The average surface wavespeed obtained by the impact echo device was measured to be 3622 m/s. The through wa vespeeds were confirmed using the impact echo device within acceptabl e tolerances. The average re bound number was determined to be 47.22, corresponding to a strength valu e of approximately 8,500 psi, extrapolated from the best-fit equations (Malhotra & Carino1991). No material defects on any of the accessible structural components were revealed as a result of acoustic sounding. Conclusions With the data available, it is possible to conclude that the concrete material on the column is in good condition, with some signs of distress. The cracks in the column are most likely torsional cracks, which are due to loading or shifting of the structure. The crack found on the Bahia Honda bridge structure was of the same orientation as the strut. It is possible that results of the NDT testi ng revealed a design flaw in the column-strut connection for bridges of this type. However, further testing is needed to confirm this hypothesis. The purpose of this survey was to examine the concrete material on the structure and not the structure itself. The NDT data recorded from the bridge el ements appear to have some conflicting values. The data received from the rebound hamm er indicate that the concrete elements are in good condition, whereas the data obtaine d from the impact echo device suggest the concrete elements show signs of distress. The aggregate used in the mix design is the most probable cause of the disparity be tween surface hardness measurements and wavespeed measurements. The same circumstan ces were encountered in the analysis of the NDT data at the Wabasso Bridge. It is possible that the same mix design was used on

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167 the pile caps at the Sebastian Inlet Bri dge and the Wabasso Bridge given their construction was within the same time period and the bridges are located in relatively close proximity of each other. Figure 4.21: Plan view of column / pile cap of Sebastian Inlet Bridge Figure 4.22: General view of Sebastian In let Bridge underside. Column line 7 in foreground adjacent to stairs

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168 Figure 4.23: Column line 6 Figure 4.24: Plan view of cr ack orientation on column 12

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169 CHAPTER 5 NONDESTRUCTIVE LABORATO RY SPECIMEN TESTING Concrete is among the most complex material s used in constructi on today. It is a mixture of Portland cement, mineral aggregates water, air, and often includes chemical and mineral admixtures. Unlike other materials used in construction, concrete is usually designed specifically for a partic ular project using locally ava ilable materials (Mindess et al. 2003). Therefore, it is common for the phys ical properties of concrete within a particular structure or even a structural el ement to differ. The internal structure of concrete is more complex than any other construction material (Popovics 2001)because: Hardened cement paste is a multiphase material. Mineral aggregate is a porous composite material which has varying material properties depending on type. The interface between the cement paste and the aggregates has unique properties. Thus, concrete can be aptly consider ed as a composite of composites, heterogeneous at both the microscopic a nd macroscopic levels (Popovics 2001, p 125). Therefore it is difficult to pr ecisely determine the physical properties of any one specific concrete specimen without know ledge of its components. Prior Research Research has been conducted using stress wave propagation methods such as the ultrasonic pulse velocity me thod and the impact echo method to correlate stress wave velocity with concrete strength. The resear ch has shown that many factors can influence the strength and the wave velocity of concre te, such as porosity, age, and composition. However, the factors that influence wave velo city do not influence strength in the same way or to the same extent. In an attempt to develop empirical equations, experiments

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170 have been conducted to establish a strength/ wave velocity relationship of concrete (Pessiki & Carino 1988, Popovics 2001, Qaswar i 2000). Literature s uggests that Young’s modulus of elasticity can be obtained through the use of resonant frequency. Methodology The purpose of performing nondestructive la boratory testing on c oncrete cylinders was to establish correlations between stress wave velocity, longitudinal resonant frequency and compressive strength change ove r time. The other objective of the research was to evaluate the variation in NDT data related to mixture design. Procedure Two separate groups of concrete cylinde rs were created for this study. The proportions given in Table 5.1 were used in an attempt to reproduce actual mix designs used in residential concrete footings and foundations. Larger specimens were cast from the same batches as the cylinders to ensure consistency of the concrete used for each design. Table 5.1: Mixture proportions for NDT and strength tests.

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171 Casting of the concrete specimens t ook place at the Florida Department of Transportation State Materials Office. After cas ting, the cylinders were transported to the University of Florida for curing and testing. The samples were cured in limewater bath until preparation and testing. The testing regimen consisted of testing three cylinders per day, at ages of one, two, three, seven, 14, 21, 28, 42, and 56 days. The cylinders were kept in limewater until the predetermined ag e of testing. All nonde structive testing and destructive testing was performed within a 6 hour period after rem oval of the specimens from the bath to ensure complete saturation of the specimen. The preparation of cylinders included grindi ng of the ends to create a planar surface in accordance with ASTM C-39-01. Nondestructive testing was carried out using a NDT James Instruments ultrasonic pulse velocity meter, and a Germann Instru ments Docter-1000 impact echo device. Each of the tests was performed in accordance w ith the relative ASTM standard (ASTM C59797, ASTM C1383-98a). The ultrasonic pulse velocity meter was used to obtain through wave velocities for the concrete cylinders. As described in Chapte r 2, travel times and cylinder lengths were recorded for each cylinder. Figure 5.1 cont ains a photograph of the ultrasonic pulse velocity experimental setup. Figure 5.1: Ultrasonic pulse ve locity experimental setup.

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172 Longitudinal resonant frequency testing was also determined for each of the cylinders. The test method, described in Chapter 2, was performed and the results recorded. Figure 5.2 contains a photograph of the torsional resonant frequency experimental setup. Figure 5.2: Resonant fre quency experimental setup The impact echo device was used to obt ain through wavespeeds for the cylinders. As described in Chapter 2, the frequency sp ectrums and cylinder lengths were recorded for each cylinder. Figure 5.3 contains a phot ograph of the impact echo experimental setup. Figure 5.3: Impact ec ho experimental setup

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173 Upon completion of the nondestructive tes ting on the cylinders, their ultimate compressive strength was determined in accordance with ASTM C39-01. Results and Discussion Relationships were developed between wa ve velocity and compressive strength. The wavespeeds were obtained with the ultrasonic pulse velocity meter, then confirmed with the use of the impact echo device. The impact echo method provides a resulting wave spectrum of the tested material identif ying possible defects in the specimen. This can facilitate a reduction in the specimen’s ultimate strength. Defect detection within specimens can aid users in ra tionalizing the existence of outlying data points based on material consistency. Figure 5.4 shows the relationship between the compressive strength and wave velocity for Mixtures A and B. Compressive Strength vs. Wavespeed, Mix A and Mix B0.65 w/c Equation y = 0.0606e0.0014xR2 = 0.9408 0.45 w/c Equation y = 0.0487e0.0016xR2 = 0.87740 10 20 30 40 50 60 70 250030003500400045005000 Wave Velocity (m/s)Compressive Strength (MPa) Mix A (w/c = 0.45) Mix B (w/c =0.65) Best Fit Mix A Best Fit Mix B Figure 5.4: Compressive strength vs. wave velocity for Mixtures A and B

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174 The results indicate that differences in mixture design create differences in the strength versus wave velocity relationship. The data shows that the Mixture B, with a higher water to cement ratio, produced sample s with lower compressive strengths than Mixture A (as expected). The concrete in Mi xture B produced lower wave velocities than Mixture A as well. Pessiki & Carino 1988, sugge sts that the water to cement ratio does not affect the compressive strength and wave velocity relationship. However, the data obtained in this experiment and an experi ment performed by Yan et al. 2003 suggest otherwise. However, the proportion of coarse to fine aggregate varied betw een the mixtures. It is possible that the difference in wave velo cities between Mixtur e A and Mixture B can be attributed to the change in proportion of coarse aggregat e to fine aggregate between the mixes. Presently, no research is ava ilable regarding the relationship between the compressive strength and wave velocity of mi xtures, and the effect of coarse to fine aggregate proportion on wave velo city. Therefore, further testing is needed to determine what effect this proportion has on wave velocity. As indicated by the results, the wave velocity verses compressive strength relationship increases in a relative trend. Th e results were compared with the equations developed by Pessiki & Cari no 1988, Qaswari 2000 and Yan et al. 2002. The estimated compressive strength based on the experime ntal equations, using the wave velocities obtained in the lab wave velocity equati ons differed from the actual compressive strengths by an average of approximately 35 pe rcent. However, the general trend of the data appears to correlate to th e Equation 1 presented by Pessiki. b P cn C a f 1 '(1)

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175 Where: f’c is compressive strength (MPa); Cp is wave velocity; a, b and n are constants. The equation used by Qaswari to relate co mpressive strength to wavespeed is a linear equation. Figure 5.5 rela tes the strength and wave velocity for the experimental data from Mixture A to equations used by Pessiki & Carino and Qaswari. The experimental wave velocity data for Mixture A was used to calculate the predicted trends in Figure 5.5. Compressive Strength vs. Wavespeed, Mix A (w/c = 0.45) Best Fit Equation (experimental data): y = 0.0487e0.0016xR2 = 0.8774y = 0.0569e0.0016xR2 = 1 y = 5E-21x6.074R2 = 1 y = 0.0367x 129.08 R2 = 10.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 35003750400042504500 Wavespeed (m/s)Compressive Strength (MPa) Obtained Data Best Fit (Obtained Data) Predicted Yan Predicted Pessiki Predicted Qaswari Figure 5.5: Results from comp ressive strength vs. wave ve locity results for Mixture A The use of a power equation properly correlates the earl y strength verses wavespeed of concrete when the wavespeeds are relatively low. The equation presented by Qaswari is a linear equation that intercepts the compressi ve strength/axis at 3515 m/s. The equation obtained by Yan et al., Pessiki & Carino and the expe rimental data are

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176 power functions as they interc ept the strength/axis at 0 m/ s. Consequently, using this equation to predict strengths of early age is inappropriate. The concrete mixture designs used in the experiment performed by Pessiki contained different proportions of cement, aggregates, and water than Mixtures A and B used in this experiment. As stated earlier in this chapter, differences within the material properties of the concrete constituents will usually result in variability within the compressive strengths and wavespeeds of concrete. The experimental results plot ted in Figure 5.4 are within acceptable tolerances with the exception of one data point The outlying data point had a compressive strength of 42.84 MPa and a corresponding wavespeed of 4020 m/s. The use of the impact echo device provided an alternate method for obtai ning wave speeds. The graph shown in Figure 5.5 is the resulting fre quency spectrum of the outlying data point. Figure 5.6 is the frequency spectrum of a typical data point. Figure 5.5: Frequency spectru m of outlying data point. Figure 5.6: Frequency spectrum of typical impact echo data point.

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177 The impact echo section of Chapter 2 describes the results of frequency spectrums. The frequency spectrum shown in Figure 5.6 is a spectrum typical for concrete with numerous voids and cracks. A slower calculated wave velocity using the ultrasonic pulse velocity for a concrete samp le would be expected for a heavily voided concrete specimen As discussed in the ultras onic pulse velocity portion of Chapter 2, the travel path for a given wave in a voided c oncrete specimen is longe r than in a specimen without voids. Therefore, improper preparation of the concrete sample is most likely the reason for the outlying data point. Resonant frequency analysis has been performed with concrete specimens to develop relationships between compressive st rength and longitudinal resonant frequency Literature has suggested that Young’s modulus of elasticity can be obtained through the use of resonant frequency (Malhotra & Cari no1991). The resonant fr equency section of Chapter 2 discussed some of the limitations of the resonant frequency test. Lack of reproducibility of the test results is one such limitation. Figure 5.7 shows the relationship between the compressive strength and res onant frequency for Mixtures A and B. Figure 5.7 shows the compressive strength ve rses resonant frequency for concrete specimens. This is similar to the data obtaine d from the compressive strength verses wave velocity relationship. The results show that differences in mixture design create differences in the strength versus resonant frequency relationship. The data shows that Mixture B, with a higher water to cement ratio, produced samples with lower compressive strengths than Mixture A (as expected). The concrete in Mixture B produced lower resonant frequencies than Mixture A as well.

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178 Compressive Strength vs. Resonant Frequency, Mix A and Mix B 0 10 20 30 40 50 60 0500100015002000250030003500 Resonant Frequency (Hz)Compressive Strength (MPa) Mix A (w/c = 0.45) Mix B (w/c = 0.65) Best Fit Mix A Best Fit Mix B Figure 5.7: Compressive strength vs. re sonant frequency for Mixtures A and B The results did not produce reliable data for the purposes of predicting compressive strength. Most of the cylinde rs tested produced resonant frequencies in the 2000 to 2600 Hz range, but the corresponding compressive strengths ranged from 12 to 58 MPa. Table 5.2: Compressive strength vs. re sonant frequency of concrete samples. Compressive Strength (MPa) Resonant Frequency (Hz) 24.85 2700 24.97 2590 28.10 2197 29.04 2020 27.26 1980 29.25 2700 Table 5.2 shows the distributi on of the data. Note that the resonant frequency vs. compressive strength does not follow a partic ular pattern for the data provided. Thus,

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179 using resonant frequency for predicting the stre ngth of concrete cylinders was not proven to be a viable NDT technique. A significant relationship was not produced from the data due to the extreme variation of the data points. However, th e resonant frequency test was useful for establishing a general trend in the data, and was useful in determining early strength gain in the cylinders. The data grouping at lower ages and compressive strengths experienced less variability than those of highe r ages and compressive strengths. Conclusions The results of these studies have demonstrated that th e ultrasonic pulse velocity technique is a practical met hod for monitoring the strength of concrete samples. The results of the resonant frequency studies de monstrated that the technique shows some validity for monitoring the strength of early age concrete samples. The objective of the study was to relate th e ultrasonic pulse velocity and resonant frequency to the strength of concrete samp les. Presently, there is no acceptable method for the nondestructive determina tion of concrete strength (Popovics 2001). However, the use of the nondestructive testing methods can successfully monitor the changes within concrete samples in relation to strength increase. Although the resonant frequency experiment produced less conclusive results than the ultrasonic pulse velocity tests for predic ting the strength of c oncrete cylinders, the technique did produce a general trend for resonant frequency and compressive strength and did show some promise as to the early age testing of concrete for compressive strength. The experiment did have value, as it is a secondary test for the nondestructive testing of concrete samples. Perhaps the value of the resonant freque ncy technique, is that is can easily be implemented into a laboratory which specializes in NDT. The laboratory

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180 test equipment is relatively inexpensive and qui ck to implement. From a labor standpoint, the use of the technique is advantageous. The use of ultrasonic pulse velocity has pot ential to determine in place strength of concrete materials. However, to achieve an accurate strength verses wave velocity relationship, experiments have to be perfor med on specific concrete mixture designs in order to create a valid correlation. Presentl y there is not enough research available correlating ultrasonic wave veloc ity and concrete mix design. Most of the research that has been applied to the nondest ructive testing of concrete has focused on the abilities and improvement of the method itself. As the applications of NDT methods become more complex, research needs to focus on the interactions of NDT techniques with the concrete material. Further investigation should be conducte d using varying ingredients with varying concrete mixture designs. Additi onal research may result in a family of curves similar to those produced by this experiment.

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181 CHAPTER 6 LABORATORY SIMULATION OF DAMAGE OBSERVED IN THE FIELD This experiment was designed to differentiate between the effects that certain solutions have on field-size samples of conc rete when exposed over periods of time. Solid salts do not attack concrete but, when present in solution, can react with the hydrated cement paste. Part icularly common are the sulf ates of sodium, potassium, magnesium and calcium, which can occur in soil, groundwater or seawater (Neville 1996). The reaction between the salt solution and hydrated cement paste can lead to several material problems with the concrete such as: Expansion and cracking Strength and mass loss Leaching of hydrated cement paste components The primary objective of this experiment was to observe the effect of concrete exposure to a sulfate solution on ultrasonic wave velocity. Anothe r objective of the experiment was to correlate the effects of su ch exposure to the physical properties of the concrete and the corresponding NDT data. Prior Research Research has been conducted using stress wave propagation methods such as the ultrasonic pulse velocity met hod and the impact echo method to correlate the stress wave velocity and strength of concrete. Currently th ere is no research avai lable on the effect of laboratory damage within concrete specimens relative to changes in stress wave velocity. However, concrete samples in field studies s uggest that the wave velocity of concrete samples decreases with increasing damage. Despite this, the quantification of the two

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182 parameters has been prevented by the lack of controlled experiments involving continuous laboratory monitoring. Methodology While it is known that sulfates tend to reduce wavespeed in concrete when specimens are exposed over time, the exact effect is unknown. Concrete specimens were cast and placed in solutions to observe changes in the material properties. One set of specimens was partially submersed in sulfate solution to simulate the effect of a harsh environment and its effect s on concrete specimens over time. A different set of specimens was concurrently partially submersed in limewater solution to simulate the effect of a control group. Partial submer sion was used in an attempt to more closely duplicate field conditions, where complete immersion is rare. By exposing the upper portion of the block to air, an evaporation cycles is created as the surrounding solution is drawn into the bottom portion of the block, mi grates upward toward the exposed surface, and then evaporates. This cycle greatly acce lerates the ingress of sulfates into the concrete due to the pressure head developed. Procedure Two separate groups of concrete specimens were created for this study. The concrete mixture proportions seen in Table 6.1 were used in an attempt to reproduce actual mixture designs used to construct c oncrete footings and foundations. The larger specimens were cast from the same batches as the cylinders in order to ensure consistency of the concrete used for each design.

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183 Table 6.1: Mixture proportions for NDT and strength tests Figure 6.1: Setup of la boratory experiment

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184 Casting of the concrete specimens t ook place at the Florida Department of Transportation State Materials O ffice. As depicted in Figure 6.1, the sample dimensions were 900mm in length by 480mm in height by 245 mm in width. These dimensions varied little between blocks. After casting, the specimens were transpor ted to the University of Florida for exposure and monitoring. Two concrete samp les from each mixture design A and B (4 samples total) were exposed to a 5 percent sulfate solution for a period of 90 days. Two additional samples from each mixture design (4 samples total) were exposed to a limewater solution for a period of 90 days. E xposure consisted of partial submersion in a bath to a depth of 150mm, approximately 1/3 of the total height of the concrete samples. Laboratory temperature was maintained at 22C. The testing regimen consisted of regular nondestructive evaluation of the concrete samples at ages of 1 day, and 1, 2, 3, 4, 6, 8, 10, 12, and 13 weeks. The samples were removed from their respective solutions at the ag e of 90 days. Nondest ructive testing was carried out using a James Instruments V-meter Model, ultrasonic pulse velocity meter, and a Germann Instruments Docter-1000 impact echo device. Each of the tests was performed in accordance with the relative ASTM standard (ASTM C597-97, ASTM C1383-98a). Figures 6.2 and 6.3 contain phot ographs of ultrasonic and impact echo testing on the specimens. The weekly ultrasonic tests consisted of 15 measurements per specimen. Through width measurements were taken at height s of 75 mm (which corresponded to the mid height of the saturated zone), 240 mm (which was just above the immersion line ) and 405 mm ( well above the immersion line). Four measurements were made at each height.

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185 The other 3 measurements consisted of thr ough length measurements at the same height intervals stated above. The four through wave velocity measurements at each height were averaged to provide a weekly av erage wave velocity for that height. Figure 6.2: Ultrasonic pulse velocity testing on specimen The weekly impact echo tests consiste d of 6 surface wave measurements per specimen. Two measurements were taken at e ach of three height intervals in order to compare surface wave velocity measurements with through wave velocity measurements. The two surface wave velocities obtained at each height were averaged to provide a weekly value for each height.

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186 Figure 6.3: Impact-ec ho testing on specimen Upon completion of the exposure period (90 da ys), the blocks were removed from their respective solutions and cored. The re sulting cores were then trimmed to obtain standard 101mm x 202 mm (4”x 8”) cores. Thes e cores were then nondestructively tested with the ultrasonic pulse velocity meter in accordance with ASTM standard C597-97. Upon the completion of the nondestructive tes ting on the cylinders they were submerged in a limewater bath for a period of 7 days in or der to establish full saturation. Half of the cylinders were tested for compressive stre ngth (in accordance with ASTM C39-01) while the other half were tested in splitting te nsion (in accordance with ASTM C496-96). Results and Discussion Relationships were developed between through wave velocity and surface wave velocity over time. Figures 6.4 and 6.5 are gr aphical representations of the data obtained for two of the blocks for Mixture A with a water/cement ratio of 0.45

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187 Wave Velocity vs. Age Block 8 (w/c = 0.45, Lime Water) 3300 3500 3700 3900 4100 4300 4500 02468101214Age (weeks)Wave Velocity (m/s) upvtop ietop upvmid iemid upvlower ielower 28 days Figure 6.4: Wave velocity vs. age for a sa mple from Mixture A exposed to limewater. Wave Velocity vs. age Block 6 (w/c = 0.45, SO4)3300 3500 3700 3900 4100 4300 4500 02468101214Age (weeks)Wave Velocity (m/s) upvtop ietop upvmid iemid upvlower ielower 28 days Figure 6.5: Wave velocity vs. age for a sa mple from Mixture A exposed to sulfate solution.

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188 Figures 6.4 and 6.5 are graphi cal representations of the average wave velocities per specimen height level for each exposure condition for Mixture A. In the legend, lines names beginning with ‘ie’ refer to surface wa ve velocity readings obtained with the impact echo technique. Those beginning w ith ‘upv’ represent through wave readings measured with the ultrasonic pulse velocity meter. The figure indicates that the lower wave velocities occur at higher heights on th e block. This is to be expected due to segregation during casting. As large samp les of concrete ar e poured, the larger aggregates and denser materials within the matrix tend to migrate toward the bottom, whereas the water and less dense materials tend to migrate toward the top. As stated in Chapter 2, denser materials tend to have higher wave velocities. Figures 6.4 and 6.5 illustrate a trend app earing in the wave velocity related to height level for the concrete sample. It a ppears as though the portion of the concrete sample that was constantly immersed in either solution tends to have a more rapid gain in wave velocity for both surface and through wave velocities (ielower, upvlower). This can be attributed to the curing of the lower portion of the sample, as it was constantly immersed in the solution. “In order to obt ain good quality concrete, the placing of an appropriate mix must be followed by curing in a suitable environment during the early stages of hardening: (Neville 1996 p. 318). It is likely that the development of higher surface wave velocities in the lower portion of the specimen is due to superior curing. Permeability variations within the concrete is the most probable explanation for the curing effect not being as prominent for th e through wave velocities. The improvement due to curing is a near surface effect that has a continuously decrea sing influence relative to distance forms the surface.

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189 However, it is possible that that some of the curing effects did permeate upward through the sample. Concrete samples that ar e kept continuously in air tend to lose strength over time (Nevi lle 1996). At week 12, we see that the through wave velocities at the top levels tend to drop off, whereas the mid-level wave velocities tend to maintain a constant wave velocity. The cause is most likely due to some saturation of the middle portion of the sample, whereas the water did not migrate into the upper portion of the block, instead evaporating out of the vertical surfaces. Therefore, it is likely that little or no curing took place at the upper portions of the specimens. Evidence of the evaporation cycle was seen in the samples exposed to the sulfate solution. Salt crystals formed in a regi on approximately 75 mm above immersion line. These crystals were a result of the evaporati on of sulfate solution from the surface of the blocks. A similar effect was observed on th e blocks exposed to lime water, as the evaporation cycle resulted in the formati on of a lime precipitate on the surface of the block. The region containing the lime precip itate was roughly in the same place as the region observed on the samples exposed to sulfate solution. Figure 6.6: Close up view of a sample exposed to sulfate solution. The arrow denotes the area of precipitated salt crystals.

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190 Relationships were developed between through wave velocity and surface wave velocity over time. Figures 6.7 and 6.8 are gr aphical representations of the data obtained for two of the blocks for Mixture B w ith a water/cement ratio of 0.65. Wavespeed vs. Age Block 21 (w/c = 0.65, Lime Water)3000 3200 3400 3600 3800 4000 4200 4400 02468101214Age (weeks)Wave Velocity (m/s) Upvtop Ietop upvmid iemid upvbott iebott 28 days Figure 6.7: Wave velocity vs. age for a sa mple from Mixture B exposed to limewater Wave Velocity vs. Age Block 24, (w/c = 0.65, SO4)3000 3200 3400 3600 3800 4000 4200 4400 02468101214Age (weeks)Wave Velocity (m/s) Upvtop Ietop upvmid iemid upvlower ielower 28 days Figure 6.8: Wave velocity vs. age for a sa mple from Mixture B exposed to sulfate solution

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191 Figures 6.7 and 6.8 are graphi cal representations of the average wave velocities per specimen height level for each exposure condi tion for Mixture B. Similar to the results obtained for Mixture A, the lower wave velo cities occurred at higher heights on the block. Again, this is due to segregation or migration of the constituents toward the bottom of the concrete specimens during casting. Figures 6.7 and 6.8 illustrate that the tr end developed for wave velocity versus height level for Mixture B wa s similar to that for Mixture A. It appears as though the portion of the concrete sample that was constantly immersed in either solution tends to have a more rapid gain in wave velocity for both surface and through wave velocities (ielower, upvlower). Similar to the effects seen for Mixtur e A, the week 12 through wave velocities on the top levels for Mixture B tend to decrease compared to previous values, andthe mid-level wave velocities tend to remain maintain constant. Again, the cause is most likely due to some saturation of the middle portion of the sample, and no transport of water to the upper portion of the sample. Results obtained for the samples expos ed to limewater exhibited several differences. Mixture A and Mixt ure B differ in the decay rate of the wavespeeds in the later weeks. Block 21 (from Mi xture B) experienced a profou nd decline in the top-level wavespeeds after week 10. Similar to block 8 (f rom Mixture A), this is most likely due to the lack of curing in the t op portion of the specimen. The larger decay of top-level wavespeeds in Block 21 is most likely due to the higher water/cement ratio. The hydration of the concrete was curtailed because water loss was not prevented in the upper portion of the sample. As discussed in Chap ter 5, concretes with lower water/cement ratios are less permeable; Therefore, the samples in Mixture A (0.45 w/c) did not

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192 experience as much water loss as the sample s in Mixture B (0.65 w/c), even though the upper levels in each specimen were continuously exposed to air. Figure 6.8 illustrates that the surface wave velocities for block 24 decayed after week 6. The portion of the block that was s ubmersed in the sulfate solution exhibited a decay of nearly 15 percent. By comparison, the same portion of the block that was exposed to lime water exhibite d a negligible decay of wave velocity. However, the upper level of block 24 experienced the same decay in wave velocity as the upper level of block 21. Therefore, it can be concluded that the d ecay in wave velocity in the lower level of the blocks exposed to sulfat e solution is due to the onset of damage caused by sulfate attack. Conclusions The results of these studies have demons trated that the th ere are significant differences between the surface wave velociti es and through wave velocities of largescale concrete samples under different exposur e conditions. The study also revealed that it is possible to detect the ons et of damage due to sulfate attack on concrete specimens. The study confirmed that the water / cemen t ratio does have a dramatic effect on the flow properties within concrete samples which, in turn, has an effect on the durability of the concrete. Most of the research that has been applied to the nondest ructive testing of concrete has focused on the ability and improvement of the method itself. As the applications of NDT methods become more complex it will be necessary for research needs to focus on the interactions of NDT techniques with th e concrete material. Further investigation should be conducted using varyi ng ingredients with varying c oncrete mixture designs as well as varied exposure times to cu ring solutions and salt solutions.

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APPENDIX A SUMMARY OF PONTIS RESULTS

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194 UF ID Number Type Year Rating Length (m) Inventory List 1 Prestr/String 1961 87.2 171 2 Slab 1935 98.4 20 3 Slab 1955 86.9 23 4 Slab 1950 88.0 14 5 Slab 1950 88.0 18 6 Slab 1955 94.8 32 7 Slab 1960 95.9 18 8 Slab 1962 91.7 23 9 Slab 1962 91.7 23 10 Prestr/Slab 1962 90.8 41 Posted/Closed 11 Prestr/Slab 1962 90.8 31 12 Prestr/Slab 2001 66.5 28 Func Obs 13 Prestr/String 1961 88.4 85 14 Slab 1948 92.5 12 15 Slab 1948 91.5 16 16 Prestr/Slab 1958 85.2 52 Posted/Closed 17 Prestr/Slab 1955 89.5 29 Posted/Closed 18 Prestr/String 1961 97.4 37 19 Slab 1944 99.5 59 20 Slab 1961 85.3 22 Posted/Closed 21 Prestr/String 1960 91.8 30 22 Slab 1948 86.0 32 23 Prestr/Slab 1982 69.6 46 24 Prestr/Slab 1950 92.2 11 25 Prestr/Slab 1920 97.2 22 26 Prestr/Slab 1985 73.6 16 27 Prestr/Slab 1960 87.0 12 28 Prestr/Slab 1960 85.4 12 29 Prestr/Slab 1997 72.2 18 30 Prestr/String 1992 74.5 102 31 Slab 1960 87.3 14 Posted/Closed 32 Prestr/ChBeam 1950 92.3 9 Posted/Closed 33 Prestr/ChBeam 1960 94.3 6 34 Prestr/ChBeam 1960 96.8 6 Posted/Closed 35 Prestr/ChBeam 1960 96.8 6 36 Prestr/ChBeam 1960 87.9 24 Posted/Closed 37 Prestr/ChBeam 1960 96.8 18 38 Prestr/ChBeam 1960 96.8 18 Posted/Closed 39 Prestr/ChBeam 1960 91.4 15 40 Prestr/ChBeam 1960 96.9 12

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195 UF ID Number Type Year Rating Length (m) Inventory List 41 Prestr/ChBeam 1955 97.0 13 42 Prestr/Teebeam 1950 85.0 21 Posted/Closed 43 Prestr/ChBeam 1960 88.0 13 Posted/Closed 44 Slab 1958 90.4 37 45 Prestr/String 1955 85.8 10 46 Prestr/String 1958 90.0 16 47 Prestr/ChBeam 1957 88.5 7 48 Prestr/Slab 1982 72.5 66 Func Obs 49 Tee Beam 1937 89.7 10 50 Prestr/ChBeam 1960 86.5 9 51 Slab 1947 89.1 14 52 Slab 1947 89.2 9 53 Slab 1947 89.3 9 54 Slab 1947 89.4 32 55 Slab 1947 86.1 19 56 String-Gir 1963 85.5 82 Func Obs 57 Prestr/String-Gir 1963 90.9 80 58 Prestr/String-Gir 1963 91.1 37 Func Obs 59 Prestr/String-Gir 2002 36.5 112 60 Slab 1961 88 31 61 prestr slab 1962 88.5 46 62 prestr slab 1962 89.5 73 63 Prestr/String-Gir 1961 97 44 64 Slab 1983 49 8 Func Obs 65 Prestr/String-Gir 1962 90.9 91 66 Prestr/String-Gir 1962 91.1 54 67 Prestr/String-Gir 1962 87.6 90 68 Prestr/String-Gir 1962 86.3 54 func Obs 69 Prestr/String-Gir 1962 89.2 52 70 Prestr/String-Gir 1962 91.5 102 71 Prestr/String-Gir 1963 86 110 72 Slab 1987 37.1 18 Posted/Closed 73 Slab 1987 54.1 14 Posted/Closed 74 Slab 1986 50.2 37 Posted/Closed 75 Slab 1987 55.9 9 Posted/Closed 76 Steel Strring-Gir 1940 86.1 18 77 Steel Strring-Gir 1940 86.1 31 78 Steel Strring-Gir 1940 86.1 31 79 Steel Strring-Gir 1940 86.3 31 80 prestr slab 1963 88.4 82 Func Obs

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196 UF ID Number Type Year Rating Length (m) Inventory List 81 prestr slab 1963 87.4 55 Func Obs 82 Tee Beam 1946 88.4 55 Func Obs 83 Tee Beam 1946 87.4 23 Func Obs 84 Slab 1948 85.1 23 Func Obs 85 Prestr/String-Gir 1961 88.1 69 86 Tee Beam 1963 88 30 87 Prestr/String-Gir 1959 86 110 88 Wood String-Gir 1988 56.2 16 89 Wood String-Gir 1989 45.7 21 Func Obs 90 Wood String-Gir 1995 53.9 13 Posted/Closed 91 Wood String-Gir 1996 49 13 Posted/Closed 92 Wood String-Gir 1996 58.8 23 Posted/Closed 93 Steel Cont-Gir 1940 88 37 Posted/Closed 94 Wood String-Gir 1996 55.6 24 95 Tee Beam 2000 75 46 96 Steel Strring-Gir 1952 85.2 96 97 Slab 1984 52.5 27 98 Slab 1987 45.8 23 Posted/Closed 99 Wood String-Gir 1989 49.6 9 Posted/Closed 100 Steel Spread Box 1994 20.8 16 Posted/Closed 101 Wood String-Gir 1997 72.7 18 102 Wood String-Gir 1997 72.7 22 103 Slab 1942 87.1 55 104 Slab 1942 87.1 55 Func Obs 105 Slab 1942 88.2 55 Func Obs 106 Slab 1942 87 46 107 Prestr/String-Gir 1986 68 121 Func Obs 108 Prestr/String-Gir 1986 68 121 Func Obs 109 Steel Strring-Gir 1994 49.5 16 110 Tee Beam 1922 91.3 10 111 prestr slab 1960 90.6 11 112 Prestr/String-Gir 1961 88 43 113 Prestr/String-Gir 1959 87.2 80 114 Prestr/String-Gir 1961 89.2 138 115 Tee Beam 1952 90.2 60 116 Prestr/String-Gir 1961 86.8 42 117 Prestr/String-Gir 1960 90.8 138 118 Prestr/String-Gir 1962 90.6 67 Func Obs 119 Mult Box Beam 1961 88 166 120 Prestr/String-Gir 1961 86.7 44

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197 UF ID Number Type Year Rating Length (m) Inventory List 121 Prestr/String-Gir 1959 85 55 Func Obs 122 Prestr/String-Gir 1957 87.7 42 Func Obs 123 Prestr/String-Gir 1959 90.9 38 Func Obs 124 Prestr/String-Gir 1958 85 46 125 Prestr/String-Gir 1959 85 65 126 Prestr/String-Gir 1959 89.5 37 127 Prestr/String-Gir 1959 90.6 11 Func Obs 128 Prestr/String-Gir 1959 90.6 49 129 Prestr/String-Gir 1960 88.9 40 130 Prestr/String-Gir 1959 87.8 27 131 Prestr/String-Gir 1959 89.2 20 132 Prestr/String-Gir 1959 90.5 37 133 Steel Strring-Gir 1967 85.7 1 134 Tee Beam 1925 86.6 13 135 prestr slab 1924 90.6 19 136 prestr slab 1926 86.7 59 137 prestr slab 1957 90.8 18 138 prestr slab 1960 89.6 51 139 prestr slab 1955 90.8 37 140 Wood Truss 1986 72.1 46 141 Wood Truss 1996 0 45 142 Arch Deck 1940 91.5 9 143 Steel Strring-Gir 1990 38.4 12 Func Obs 144 Steel Strring-Gir 1991 37.4 12 Posted/Closed 145 Slab 1991 75 18 146 Wood/String-Gir 1993 25.9 9 147 Prestr/String-Gir 2002 40 432 148 Wood Slab 1991 71.5 9 Func Obs 149 Wood Truss 1986 57.2 31 150 Slab 1957 92.5 37 151 Prestr/String-Gir 1960 98.8 69 152 Prestr/String-Gir 1963 91.8 53 Func Obs 153 Prestr/String-Gir 1963 96.9 37 154 Prestr/String-Gir 1963 92 83 155 Prestr/String-Gir 1963 92.9 53 Func Obs 156 Prestr/String-Gir 1963 94.9 37 157 Prestr/String-Gir 1963 95.9 83 158 Prestr/String-Gir 1960 98.8 80 159 Prestr/String-Gir 1963 98 69 160 Prestr/String-Gir 1960 97.4 93

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198 UF ID Number Type Year Rating Length (m) Inventory List 161 Prestr/String-Gir 1960 96 54 162 Prestr/String-Gir 1960 96.6 71 163 Prestr/String-Gir 1962 92.9 68 164 Prestr/String-Gir 1962 92.9 68 165 Prestr/String-Gir 1961 97.0 44 166 Prestr/String-Gir 1960 97.4 93 167 Prestr/String-Gir 1960 96 54 168 Prestr/String-Gir 1960 96.6 71 169 Prestr/String-Gir 1962 96.5 42 170 Prestr/String-Gir 1962 94.5 42 171 Slab 1941 98 19 172 Slab 1941 98 28 173 Slab 1942 95.9 46 174 Steel Strring-Gir 1958 93.7 159 175 Prestr/String-Gir 1962 97 63 176 Prestr/String-Gir 1962 92.6 94 177 Prestr/String-Gir 1962 98 92 178 Prestr/String-Gir 1963 96 58 179 Prestr/String-Gir 1962 96 68 180 Prestr/String-Gir 1962 98 92 181 Prestr/String-Gir 1962 97.2 63 182 Prestr/String-Gir 1962 93.1 54 183 Prestr/String-Gir 1962 96.2 54 184 Prestr/String-Gir 1962 96.6 102 185 Prestr/String-Gir 1962 92.1 48 186 Prestr/String-Gir 1962 96.6 38 187 Prestr/String-Gir 1962 96.6 38 188 Prestr/String-Gir 1962 95.8 48 189 Prestr/String-Gir 1963 96 58 190 Prestr/String-Gir 1963 97.1 110 191 Prestr Slab 1963 98.9 23 192 Prestr Slab 1963 98.9 27 193 Prestr Slab 1963 98.9 23 194 Prestr Slab 1962 98.9 27 195 Prestr Slab 1962 98.9 41 196 Prestr Slab 1963 98.9 46 197 Prestr Slab 1963 98.9 31 198 Prestr Slab 1963 98.9 31 Func Obs 199 Prestr Slab 1962 98.9 31 200 Prestr Slab 1962 98.9 23

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199 UF ID Number Type Year Rating Length (m) Inventory List 201 Prestr Slab 1963 98.9 23 202 Prestr/String-Gir 1962 97.3 52 203 Prestr/String-Gir 1962 95.3 117 204 Prestr/String-Gir 1962 97.3 79 205 Prestr/String-Gir 1961 97.4 46 206 Prestr/String-Gir 1962 97.2 116 207 Prestr/String-Gir 1962 97.3 79 208 Prestr/String-Gir 1961 97.4 46 209 Prestr/String-Gir 1962 97.2 52 210 Prestr/String-Gir 1962 97.3 85 211 Prestr/String-Gir 1962 97.3 76 212 Prestr/String-Gir 1962 92.3 85 213 Prestr/String-Gir 1962 97.4 104 214 Prestr/String-Gir 1961 99.8 50 215 Steel Strring-Gir 1931 97.8 8 216 Tee Beam 1924 93.2 55 217 Tee Beam 1939 95.5 60 218 Tee Beam 1939 99.5 40 219 Steel Strring-Gir 1947 97 108 220 Prestr/String-Gir 1961 100 42 221 Prestr/String-Gir 1961 96 45 222 Prestr/String-Gir 1961 99 43 223 Prestr/String-Gir 1959 94.7 26 224 Steel Strring-Gir 1958 95.9 34 225 Steel Strring-Gir 1958 94.3 51 226 Prestr/String-Gir 1961 94.8 60 227 Prestr Slab 1961 92.4 27 228 Steel Strring-Gir 1957 92.4 42 229 Prestr/String-Gir 1959 95 37 230 Prestr/String-Gir 1959 95 96 231 Prestr/String-Gir 1959 95 46 232 Prestr/String-Gir 1959 94 41 Func Obs 233 Prestr/String-Gir 1957 97 37 234 Prestr/String-Gir 1959 97 60 235 Prestr/String-Gir 1960 98 43 236 Prestr/String-Gir 1960 94.9 43 237 Cont Slab 1960 96.6 46 238 Prestr/String-Gir 1960 93.3 58 239 Steel Strring-Gir 1961 93.9 116 240 Prestr/String-Gir 1960 95 42

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200 UF ID Number Type Year Rating Length (m) Inventory List 241 Cont Slab 1960 97 46 242 Prestr/String-Gir 1960 94.7 41 Func Obs 243 Cont Slab 1960 97 46 244 Steel Strring-Gir 1957 91.9 42 245 Prestr/String-Gir 1959 93 27 246 Prestr/String-Gir 1959 93 27 247 Prestr/String-Gir 1959 94.7 37 248 Prestr/String-Gir 1959 97 60 249 Prestr/String-Gir 1960 98 43 250 Prestr/String-Gir 1960 95 40 251 Prestr/String-Gir 1960 96.8 55 252 Prestr/String-Gir 1960 91.8 56 253 Prestr/String-Gir 1960 93.8 43 254 Prestr Slab 1960 96.6 46 255 Prestr/String-Gir 1960 93.3 58 256 Prestr/String-Gir 1961 92.9 116 257 Prestr/String-Gir 1960 95 42 258 Prestr/String-Gir 1960 94.7 41 259 Prestr/String-Gir 1958 97.1 60 260 Prestr Slab 1957 97.1 34 261 Prestr Slab 1956 96.3 66 262 Cont Slab 1960 98.8 40 263 Tee Beam 1940 96.2 8 264 Prestr Tee Beam 1950 96.4 14 265 Prest Chann Beam1959 94.4 27 266 Prest Chann Beam1952 95.4 18 267 Prest Chann Beam1955 97.7 18 268 Prestr Slab 1956 94.5 18 269 Prest Chann Beam1955 96.4 18 270 Prest Chann Beam1961 97.9 28 271 Prest Chann Beam1955 95 38 272 Prest Chann Beam1958 93.6 27 273 Prestr Slab 1960 99.8 13 274 Slab 1956 99.7 37 275 Slab 1956 99.7 31 276 Slab 1956 99.8 37 277 Prestr Slab 1931 97.9 40 278 Slab 1922 96 13 279 Prestr/String-Gir 1965 96 64 280 Prestr/String-Gir 1958 97.3 736

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201 UF ID Number Type Year Rating Length (m)Inventory List 281 Wood 1984 58.6 7 Func Obs 282 Steel Truss 1997 44 12 Str Def 283 Steel Truss 1997 47 12 Str Def 284 Steel Truss 2001 19.7 18 285 Steel String-Gird1994 51.8 20 Str Def 286 Steel Spread Box1999 38.1 14 287 Wood/String 1984 56.5 13 Func Obs 288 Wood/String 1984 48.7 13 Func Obs 289 Wood/String 1984 47.7 8 Func Obs 290 Wood/String 1989 51.1 8 Func Obs 291 Wood/String 1986 52.8 8 Func Obs 292 Wood/String 1994 25.9 8 Func Obs 293 Wood/String 1983 43.8 8 Func Obs 294 Wood/String 1994 35.7 7 Func Obs 295 Wood/String 1994 52.9 8 Str Def 296 Wood/String 1994 50.8 8 Str Def 297 Wood/String 2003 40.9 9 Str Def 298 Wood/String 2003 37.9 8 Func Obs 299 Wood/String 1989 50.8 8 Func Obs 300 Wood/String 1991 48.6 8 Func Obs 301 Wood/String 1991 54.2 15 Func Obs 302 Wood/String 1991 56.3 12 Func Obs 303 Wood/String 1991 55.2 8 Func Obs 304 Wood/String 1991 55.2 14 Func Obs 305 Wood/String 1991 54.2 7 Func Obs 306 Wood/String 1995 45.3 7 Func Obs 307 Wood/String 1996 42.9 9 Func Obs 308 Steel String 1996 74.9 53 309 Wood/String 1987 43.9 17 Func Obs 310 Wood/String 1984 38.9 27 Str Def 311 Wood/String 1984 55.5 7 Posted/Closed 312 Wood/String 1987 44.4 7 Posted/Closed 313 Wood/String 1986 39 7 Str Def 314 Wood/String 1994 57.5 7 Str Def 315 Wood/String1986 57.9 22 Str Def 316 Wood/String 1986 55 9 Str Def 317 Wood/String 1985 57.3 36 Str Def 318 Wood/String 1989 38 17 Str Def 319 Wood/String 1990 54.6 21 Str Def 320 Wood/String 1990 50.1 10 Str Def

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202 UF ID Number Type Year Rating Length (m)Inventory List 321 Wood/String 1990 54.2 18 Str Def 322 Wood/String 1991 55.8 13 Str Def 323 Wood/String 1991 37.5 13 Str Def 324 Wood/String 1994 35.6 8 Posted/Closed 325 Steel String 1985 52.1 60 Posted/Closed 326 Steel String 1985 57.2 124 Posted/Closed 327 String-Gird 1985 58.8 55 Str Def 328 Wood/String 1985 31.2 13.0 Str Def 329 Wood/String 1990 53.6 7 330 Steel Spread Box1997 56.5 20 Fract/Crit 331 Wood/String 1999 40 7 Posted/Closed 332 Wood/String 2001 52.4 18 Posted/Closed 333 Wood/String 2002 55.3 10 Posted/Closed 334 Wood/String 2002 54.7 8 Posted/Closed 335 Wood/String 1986 53.1 24 Posted/Closed 336 Wood/String 1986 55.9 22 Posted/Closed 337 Wood/String 1987 39.9 12 Posted/Closed 338 Wood/String 1987 53.4 32 Posted/Closed 339 Wood/String 1985 47.3 17 Posted/Closed 340 Wood/String 1988 30.9 13 Posted/Closed 341 Wood/String 1984 55 9 Func Obs 342 Wood/String 1984 40 10 Str Def 343 Wood/String 1990 42.2 26 Str Def 344 Wood/String 2002 30.7 9 Func Obs 345 Slab 1962 91.8 7 346 Slab 1962 91.8 30 347 Slab 1951 85 36 348 Steel String-Gird1951 96.6 84 349 Steel String-Gird1949 89.4 69 350 Steel String-Gird1949 90.6 92 351 Slab 1957 86.6 23 352 Slab 1957 87.3 439 353 Steel Cont-Gird 1934 85.9 26 354 Steel Cont-Gird 1949 85.6 61 355 Slab 1939 96.8 20 356 Prestr/String-Gird1958 99.8 44 357 Prestr/String-Gird1958 98.8 66 358 Prestr/String-Gird1961 85 86 359 Prestr/String-Gird1961 96 57 360 Prestr/String-Gird1961 90 86

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203 UF ID Number Type Year Rating Length (m) Inventory List 361 Prestr/String-Gird1961 86.6 57 362 Prestr/String-Gird1962 91.5 80 Func Obs 363 Tee Beam 1955 87.8 53 364 Prestr/String-Gird1960 85.2 268 365 Slab 1961 90.9 27 366 Wood/String 1989 70.9 46 Posted/Closed 367 Steel Truss 1997 74 6 Fract/Crit 368 Steel Truss 1997 74 6 Fract/Crit 369 Steel Truss 1997 74 27 Fract/Crit 370 Steel Truss 1997 74 9 Fract/Crit 371 Steel Truss 2001 71 64 Fract/Crit 372 Steel Truss 2001 71 43 Fract/Crit 373 Steel Truss 2001 71 12 Fract/Crit 374 Steel Truss 2001 71 6 Fract/Crit 375 Steel Truss 2001 71 6 Fract/Crit 376 Steel Truss 2001 71 6 Fract/Crit 377 Steel Truss 2001 71 6 Fract/Crit 378 Steel Truss 2001 71 6 Fract/Crit 379 Steel Truss 2001 71 9 Fract/Crit 380 Steel Truss 2001 71 6 Fract/Crit 381 Steel Truss 2001 71 15 Fract/Crit 382 Steel Truss 2001 71 12 Fract/Crit 383 Steel Truss 2001 71 6 Fract/Crit 384 Steel Truss 2001 71 9 Fract/Crit 385 Steel Truss 2001 71 9 Fract/Crit 386 Steel Truss 2001 71 9 Fract/Crit 387 Steel Truss 2001 71 9 Fract/Crit 388 Steel Truss 2001 71 9 Func Obs 389 Steel Truss 1999 62 9 Fract/Crit 390 Steel String-Gird 1960 97 9 391 Steel Truss 1996 74.9 46 Fract/Crit 392 Slab 1961 89.7 14 393 Steel Truss 1950 86.5 34 394 Wood/String 1988 66.6 12 Posted/Closed 395 Wood/String 1989 69.7 9 Posted/Closed 396 Wood/String 1989 64.5 19 Posted/Closed 397 Steel Spread Box 1993 61.8 21 Fract/Crit 398 Steel Gird/Flow 1993 73.4 21 Fract/Crit 399 Tee Beam 1950 88.6 50 400 Tee Beam 1955 99.8 141

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204 UF ID Number Type Year Rating Length (m) Inventory List 401 Tee Beam 1955 99.8 50 402 Slab 1992 60.1 14 403 Wood/String 1994 65.2 17 404 Wood/String 1994 65.2 8 405 Wood/String 2000 71.6 16 406 Wood/String 2002 68.7 12 407 Wood/String 2002 74.3 8 408 Steel Gird 1959 93.8 499 409 Wood/String 1991 63.4 17 Posted/Closed 410 Wood/String 1947 85.6 15 411 Channel Beam 1962 86.1 10 Func Obs 412 Channel Beam 1954 100 7 413 Prestr/String-Gird1951 86.1 93 Func Obs 414 Steel Truss 2000 74.9 64 Fract/Crit 415 Steel Truss 2000 74.9 19 Fract/Crit 416 Slab 1961 92.4 127 Fract/Crit 417 Tee Beam 1954 95.9 120 418 Slab 1947 91 9 419 Slab 1958 93.9 30 Func Obs 420 Slab 1929 92 9 421 Steel Spread Box 1996 72.7 21 Fract/Crit 422 Steel Spread Box 1996 72.7 14 Fract/Crit 423 Steel Spread Box 1996 70.7 14 Fract/Crit 424 Steel Spread Box 1996 70.7 21 Fract/Crit 425 Steel Spread Box 1996 70.7 21 Fract/Crit 426 Steel Spread Box 1996 70.7 21 Fract/Crit 427 Steel Spread Box 2001 71 18 Fract/Crit 428 Prestr/String-Gird1962 97.6 466 429 Prestr/String-Gird1958 85.7 443 430 Seg Box Gird 1993 72.3 5871 Posted/Closed 431 Steel Truss 2002 60.6 18 Func Obs 432 Steel Truss 2002 67.7 9 Func Obs 433 Wood/String 1935 88.8 23 434 Wood/String 1984 72.1 24 Str Def 435 Wood/String 1983 62.8 14 Func Obs 436 Wood/String 1989 74.2 18 437 Tee Beam 1951 89.1 121 438 Tee Beam 1949 92.2 101 439 Tee Beam 1953 97.2 423 440 Tee Beam 1953 87.5 332

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205 UF ID Number Type Year Rating Length (m)Inventory List 441 Tee Beam 1951 88.5 91 442 Prestr/String-Gird1962 99 66 443 Wood 1988 74.8 17 Posted/Closed 444 Wood/String 1991 67.2 7 445 Steel String 1960 96 19 446 Prestr Slab 1960 96 9 447 Steel String-Gird1960 88.2 18 448 Wood/String 1987 68.6 7 Posted/Closed 449 Wood/String 1987 68.3 17 450 Wood/String 1988 60 23 Func Obs 451 Wood/String 1988 68.4 13 452 Wood/String 1989 65.2 26 Posted/Closed 453 Wood/String 1989 66.5 13 Posted/Closed 454 Wood/String 1990 73 20 Posted/Closed 455 Wood/String 1992 64.7 22 Posted/Closed 456 Wood/String 1993 71.6 13 Posted/Closed 457 Wood/String 1992 68.8 13 Posted/Closed 458 Steel String-Gird1960 95 9 459 Steel Spread Box1994 65.6 13 Fract/Crit 460 Slab 1963 90.7 31 Posted/Closed 461 Wood/String 1985 60.7 6 Func Obs 462 Wood/String 1985 71.2 8 Posted/Closed 463 Wood/String 1988 59.2 15 Posted/Closed 464 Wood/String 1990 60.2 11 Posted/Closed 465 Wood/String 1992 71.2 15 Str Def 466 Wood/String 1994 71.4 22 Str Def 467 Wood/String 1994 72.2 14 Str Def 468 Wood/String 1995 66.7 12 Str Def 469 Wood/String 1996 63.8 13 Str Def 470 Wood/String 1999 59.7 10 Str Def 471 Wood/String 2002 59.1 20 Str Def 472 Wood/String 1960 85.1 6 Str Def 473 Tee Beam 1953 89.5 141 Str Def 474 Tee Beam 1952 91.6 131 475 Slab 1994 70.2 8 476 Steel String-Gird1930 91.6 31 477 Slab 1963 93.5 24 478 Prestr/String-Gird1963 91.6 44 479 Prestr/Slab 1954 99.8 36 480 Prestr/Slab 1954 99.6 36

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206 UF ID Number Type Year Rating Length (m) Inventory List 481 Prestr/Slab 1961 97.2 49 482 Tee Beam 1956 85 50 483 Slab 1949 87 24 484 Tee Beam 1957 87.7 23 485 Prestr/String-Gird1962 91.5 45 486 Prestr/Slab 1962 98.1 46 487 Prestr/Slab 1963 88.7 46 488 Prestr/String-Gird1962 91.5 45 489 Slab 1957 92.7 8 490 Prestr/Slab 1954 99.8 36 491 Slab 1963 91.3 21 492 Slab 1957 85.1 7 493 Slab 1993 71.3 11 494 Prestr/String-Gird1995 0 495 Slab 1963 85.4 23 496 Slab 1962 94.2 18 497 Steel String-Gird 1956 98.5 60 498 Steel String-Gird 1956 98.5 60 499 Prestr/Seg Box Gird 2001 74 909 Func Obs 500 Slab 1958 99.3 18 501 Prestr/String-Gird1995 0 173 502 Prestr/Slab 1963 96.5 47 503 Prestr/Slab 1959 94.5 32 504 Prestr/Slab 1954 91.7 27 505 Slab 1957 92.7 37 506 Wood/String 1985 23.6 13 Str Def 507 Slab 1959 86 14 508 Prestr/Slab 1961 91.9 14 509 Prestr/Slab 1989 71.4 32 510 Wood/String 1989 39.8 19 Str Def 511 Prestr/Slab 1962 93.5 18 512 Prestr/Slab 1988 73.2 37.0 513 Prestr/Slab 1988 74.4 37 514 Slab 1990 73.1 34 515 Slab 1990 71.1 34 516 Slab 1962 89.7 18 Posted/Closed 517 Slab 1962 85.6 31 Posted/Closed 518 Slab 1962 88.6 31 Posted/Closed 519 Slab 1963 95.9 8 520 Slab 1963 95.9 8

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207 UF ID Number Type Year Rating Length (m) Inventory List 521 Tee Beam 1948 91 81 522 Slab 1961 87.4 49 523 Prestr/Slab 1963 94.2 54 524 Prestr/Slab 1962 89.3 68 Str Def 525 Steel String-Gird 1957 87.6 153 526 Arch Deck 1925 97 14 527 Slab 1961 93 14 528 Slab 1961 91.3 14 529 Slab 1961 92.4 14 530 Slab 1961 94.6 14 531 Prestr/Slab 1958 94.4 61 532 Slab 1952 87.5 46 533 Slab 1960 92.9 37 534 Prestr/Slab-Gird 1961 97.4 62 535 Prestr/Slab-Gird 1998 18.4 8 Posted/Closed 536 Prestr/Slab 1959 89.4 101 537 Prestr/Slab 1993 0 76 538 Prestr/ChBeam 1963 93.8 13 539 Prestr/String-Gird1959 91.6 53 540 Tee Beam 1927 90.7 46 541 Prestr/Slab 1962 90.6 27 542 Steel String-Gird 2002 0 56 543 Steel String-Gird 2002 0 14 544 Prestr/Slab 1963 96 44 545 Prestr/Slab 1960 88.3 9 Posted/Closed 546 Prestr 1991 0 68 547 Slab 1983 44.2 55 Func Obs 548 Slab 1939 91.3 9 549 Prestr/Slab 1937 93.6 27 550 Prestr/Slab 1937 93.6 27 551 Prestr/Slab 1960 92.8 48 552 Prestr/String-Gird1959 89.2 94 553 Prestr/String-Gird1959 90.7 94 554 Prestr/String-Gird1958 95.6 66 555 Prestr/String-Gird1961 85.5 456 Func Obs 556 Prestr/String-Gird1963 92.2 85 Func Obs 557 Prestr/String-Gird1963 88.1 48 558 Prestr/String-Gird1963 88.1 48 Func Obs 559 Prestr/String-Gird1963 85.9 74 Func Obs 560 Prestr/String-Gird1960 89.6 27

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208 UF ID Number Type Year Rating Length (m) Inventory List 561 Prestr/String-Gird1960 91.7 48 562 Prestr/String-Gird1960 91.4 49 563 Prestr/String-Gird1960 86.1 65 564 Prestr/String-Gird1960 93.1 57 565 Prestr/String-Gird1959 90.7 73 566 Prestr/String-Gird1959 92.3 59 567 Prestr/String-Gird1963 97.6 91 568 Steel String-Gird 1961 97.1 82 569 Prestr/String-Gird1960 92.9 46 570 Prestr/String-Gird1960 90.3 47 571 Prestr/String-Gird1960 91.3 123 572 Prestr/String-Gird1960 92.2 58 573 Prestr/String-Gird1959 91.8 51 574 Prestr/String-Gird1959 93.3 60 575 Prestr/String-Gird1963 92.1 85 576 Prestr/String-Gird1963 92.2 44 577 Prestr/ChBeam 1961 88.4 24.0 578 Prestr/ChBeam 1961 86 16 579 Prestr/ChBeam 1961 86 16 580 Prestr/Slab 1988 70.2 15 Func Obs 581 Tee Beam 1942 88.7 9 582 Prestr/String-Gird1963 91.3 69 583 Prestr/String-Gird1991 74.1 81 Func Obs 584 Prestr/Slab 1984 71.7 13 Func Obs 585 Slab 1989 68.5 12 586 Prestr/Slab 2003 60.8 17 587 Prestr/Slab 1990 58.3 27 Func Obs 588 Steel Truss 1998 0 234 589 Tee Beam 1935 95.9 19 590 Prestr/String-Gird1963 95 45 Func Obs 591 Prestr/String-Gird1963 85.9 87 592 Prestr/String-Gird1963 91.2 74 593 Prestr/String-Gird1963 95.1 45 594 Prestr/Slab 1988 66 41 595 Tee Beam 1931 93.3 12 596 Slab 1957 90.2 37 597 Slab 1957 88 25 598 Slab 1957 85 49 599 Prestr/String-Gird1959 93.9 46 600 Prestr/String-Gird1959 93.2 100

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209 UF ID Number Type Year Rating Length (m) Inventory List 601 Prestr/String-Gird 1998 20.3 9 Func Obs 602 Prestr/String-Gird 1959 89.4 46 603 Prestr/ChBeam 1962 89.5 16 604 Wood/String 1983 54.1 17 Posted/Closed 605 Prestr/String-Gird 1960 95.4 54 606 Prestr/String-Gird 1960 93.9 101 607 Prestr/ChBeam 1963 89.9 15 608 Slab 1956 86.8 41 609 Prestr/String-Gird 1995 64.6 50 610 PreStr Slab 1962 33 89.7 Fun Obs 611 PreStr-Str Gir 1960 58 90.2 Fun Obs 612 Slab 1956 46 86.0 613 PreStr Slab 1960 28 87.7 614 Slab 1951 31 89.5 615 Str Gir 1954 37 87.5 616 Tee Beam 1948 40 98.0 617 Tee Beam 1948 40 85.0 618 Slab 1959 27 95.3 619 PreStr-Str Gir 1961 30 99.0 620 Slab 1960 36 88.1 621 Slab 1960 38 90.0 622 Slab 1960 37 87.7 623 Slab 1959 27 95.1 624 PreStr-Str Gir 1960 40 88.0 625 PreStr-Str Gir 1961 54 95.4 626 PreStr-Str Gir 1959 347 85.0 627 PreStr-Str Gir 1961 57 88.6 Fun Obs 628 PreStr-Str Gir 1961 42 88.0 Fun Obs 629 PreStr-Str Gir 1961 343 88.0 630 PreStr Slab 1961 56 96.1 631 Slab 1959 44 95.5 632 Slab 1959 40 95.1 633 Slab 1961 48 87.6 634 PreStr Slab 1958 21 85.7 635 Type Year Rating 636 PreStr Slab 1956 24 85.5 637 PreStr-Str Gir 1959 49 86.9 638 Arch Deck 1956 17 95.2 639 Slab 1951 77 92.6 640 PreStr-Str Gir 1996 748 61.9 Fun Obs

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210 UF ID Number Type Year Rating Length (m) Inventory List 641 PreStr-Str Gir 1995 748 60.7 Fun Obs 642 Slab 1960 8 86.2 643 Slab 1960 21 97.0 644 PreStr-Str Gir 1959 121 93.3 645 Slab 1960 90 87.1 646 Tee Beam 1960 40 97.0 647 PreStr Slab 1962 79 98.5 648 PreStr Slab 1960 91 93.0 649 PreStr Slab 1960 25 92.4 650 Slab 1950 22 88.9 651 Seg-Box Gir 1991 2521 62 652 Slab 1988 613 74.0 653 Slab 2000 61 33.7 Fun Obs 654 Tee Beam 1956 139 96.4 655 PreStr-Box Gir 1982 4923 73.0 656 PreStr-Box Gir 1983 72.0 657 Tee Beem 1922 94.9 31 658 Prestr/Channel 1961 90.4 41 659 Prestr/Channel 1963 86.5 24 660 Stringer Girder 1962 99.4 190 661 Prestr/Channel 1960 85.4 26 662 Prestr/Channel 1982 52.8 45 Deficient List 663 Tee Beem 1982 93.1 20 664 Prestr/Girder 1982 95.8 83 Deficient List 665 Prestr/Girder 1982 95.8 83 Deficient List 666 Prestr/String 1981 93.2 474 Deficient List 667 Cont.Girder 1997 97.3 4226 Deficient List 668 Prestr/String 1988 66.1 100 669 Prestr/Channel 1960 90.2 9 670 Prestr/Slab 1982 76.8 11 Deficient List 671 Culvert 1957 98.6 8 672 Conc Slab 1941 85.7 14 673 Tee Beem 1926 85.7 13 674 Stayed Girder 1986 63.9 6668 Deficient List 675 Cont.Girder 1991 89 4846 Deficient List 676 Prestr/Slab 1958 91.6 10 Closed/Posted 677 Conc Slab 1928 89.5 66 678 Prestr/Girder 1956 99 79 679 Prestr/Girder 1957 99.8 78 680 Prestr/Girder 1922 93.8 64 681 Prestr/Girder 1962 92 41 682 Prestr/Girder 1961 91.9 58 Func/Obs 683 Prestr/Girder 1959 89.5 58 684 Steel Girder 1952 89.3 65 685 Prestr/Girder 1962 89 41 686 Steel Girder 1957 87.7 165 Fracture Crit. 687 Prestr/Girder 1962 86.1 44 Func/Obs

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211 APPENDIX B SUMMARY OF DEFICIENT BRIDGES UF ID Number Year Rating Deck SuperS SubS Channel Type 609 1995 64.6 7 8 8 8 prestressed str-girder 26 1985 73.6 7 7 7 7 prestressed slab 30 1992 74.5 7 7 7 7 prestressed str-girder 29 1997 89.2 7 7 7 7 prestressed slab 73 1987 54 6 6 6 6 slab 74 1986 50.2 6 6 6 6 slab 75 1987 62.1 6 6 6 6 slab 97 1984 52.7 6 6 6 7 slab 98 1987 45.8 5 5 6 7 slab 145 1991 75 6 6 6 6 slab 475 1994 70.2 8 8 8 8 slab 512 1988 73.2 7 7 7 7 prestressed slab 513 1988 74.4 7 7 7 7 prestressed slab 514 1990 73.1 7 7 7 7 slab 515 1990 71.1 7 7 7 7 slab 652 1988 79 7 7 7 7 slab 655 1982 73 7 6 7 8 prestressed str-girder 656 1983 72 7 6 6 9 prestressed str-girder 651 1991 62 8 8 8 8 continuous box girder 668 1988 66.1 7 7 7 7 prestressed str-girder 1982 51.8 7 6 7 7 Channel Beam 674 1986 63.9 6 6 5 7 Continuous stayed girder

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APPENDIX C NDT DATA AND RESULTS FROM BRIDGE TESTING

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213 Data Sheet for Bahia Honda Bridge Date: 5/20/2003 Location: Column Tomography Row A (Top Row) Point # UPV Time ( s) Distance (ft) UPV Wavespeed (m/s) 1-5 247.4 43.66 4482.47 1-6 268.5 47.51 4494.43 1-7 268.4 47.51 4496.10 1-8 247.0 43.66 4489.73 2-6 247.2 43.66 4486.10 2-7 267.8 47.51 4506.18 2-8 268.5 47.51 4494.43 2-9 245.9 43.66 4509.82 3-7 246.8 43.66 4493.37 3-8 267.6 47.51 4509.54 3-9 267.1 47.51 4517.99 3-10 246.4 43.66 4500.67 4-8 247.2 43.66 4486.10 4-9 265.0 47.51 4553.79 4-10 266.3 47.51 4531.56 4-11 246.0 43.66 4507.98 5-9 242.1 43.66 4580.60 5-10 266.1 47.51 4534.96 5-11 267.9 47.51 4504.49 6-10 244.8 43.66 4530.08 6-11 268.4 47.51 4496.10 7-11 248.3 43.66 4466.23 Data Sheet for Bahia Honda Bridge Date: 5/20/2003 Location: Column Tomography Row B Point # UPV Time ( s) Distance (in) UPV Wavespeed (m/s) 1-5 249.6 43.66 4442.96 1-6 269.1 47.51 4484.41 1-7 316.4 47.51 3814.01 1-8 245.7 43.66 4513.49 2-6 247.1 43.66 4487.92 2-7 316 47.51 3818.84 2-8 267.4 47.51 4512.92 2-9 245.8 43.66 4511.65 3-7 299 43.66 3708.91 3-8 265.3 47.51 4548.64 3-9 265.4 47.51 4546.93 3-10 245.4 43.66 4519.01 4-8 242.2 43.66 4578.71 4-9 261.5 47.51 4614.74 4-10 265.7 47.51 4541.79 4-11 246.5 43.66 4498.84 5-9 240.5 43.66 4611.08 5-10 266.6 47.51 4526.46 5-11 267.2 47.51 4516.29 6-10 240.5 43.66 4611.08 6-11 266.2 47.51 4533.26 7-11 290 43.66 3824.01

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214 Data Sheet for Bahia Honda Bridge Date: 5/20/2003 Column Tomography Row C Point # UPV Time ( s) Distance (ft) UPV Wavespeed (m/s) 1-5 246.5 43.66 4498.84 1-6 265.5/359.1 47.51 #VALUE! 1-7 267.5 47.51 4511.23 1-8 266 43.66 4169.04 2-6 242.1/302.2 43.66 #VALUE! 2-7 264.3 47.51 4565.85 2-8 266.2 47.51 4533.26 2-9 250.9 43.66 4419.94 3-7 239.8 43.66 4624.54 3-8 267.1 47.51 4517.99 3-9 271.1 47.51 4451.32 3-10 249.9 43.66 4437.63 4-8 242.3 43.66 4576.82 4-9 266 47.51 4536.67 4-10 268.9 47.51 4487.74 4-11 357.5 43.66 3102.00 5-9 239.1 43.66 4638.08 5-10 265 47.51 4553.79 5-11 345.9 47.51 3488.74 6-10 240.1/511.7 43.66 #VALUE! 6-11 357.7/546.7 47.51 #VALUE! 7-11 360.3 43.66 3077.89 Data Sheet for Bahia Honda Bridge Date: 5/20/2003 Column Tomography Row D Point # UPV Time ( s) Distance (ft) UPV Wavespeed (m/s) 1-5 244.5 43.66 4535.64 1-6 265.2 47.51 4550.35 1-7 323.3 47.51 3732.61 1-8 43.66 2-6 243.9 43.66 4546.80 2-7 351.9 47.51 3429.25 2-8 47.51 2-9 43.66 3-7 377.3 43.66 2939.21 3-8 47.51 3-9 47.51 3-10 43.66 4-8 43.66 4-9 47.51 4-10 47.51 4-11 325.3 43.66 3409.05 5-9 43.66 5-10 47.51 5-11 47.51 6-10 43.66 6-11 47.51 7-11 43.66

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215 Data Sheet for Bahia Honda Bridge Date: 5/20/2003 Column Tomography Row E Point # UPV Time ( s) Distance (ft) UPV Wavespeed (m/s) 1-5 240.5 43.664611.08 1-6 258.0 47.514677.34 1-7 264.0 47.514571.04 1-8 43.66 2-6 240.2 43.664616.84 2-7 261.6 47.514612.97 2-8 47.51 2-9 43.66 3-7 235.8 43.664702.99 3-8 47.51 3-9 47.51 3-10 43.66 4-8 43.66 4-9 47.51 4-10 47.51 4-11 43.66 5-9 43.66 5-10 47.51 5-11 47.51 6-10 43.66 6-11 47.51 7-11 43.66 Data Sheet for Bahia Honda Bridge Date: 5/20/2003 Column Tomography Row F (Bottom Row) Point # UPV Time ( s) Distance (ft) IE Wavespeed (m/s) 1-5 235.9 43.664700.99 1-6 258.6 47.514666.49 1-7 261.0 47.514623.58 1-8 43.66 2-6 235.7 43.664704.98 2-7 260.3 47.514636.01 2-8 47.51 2-9 43.66 3-7 233.9 43.664741.19 3-8 47.51 3-9 47.51 3-10 43.66 4-8 43.66 4-9 47.51 4-10 47.51 4-11 280.3 43.663956.35 5-9 43.66 5-10 47.51 5-11 263.0 47.514588.42 6-10 43.66 6-11 262.6 47.514595.41 7-11 242.4 43.664574.93

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216 Data Sheet for Bridge Testing Date: 5/20/2003 Bahia Honda Bridge Impact Echo Column Data Point #IE Wavespeed (m/s ) IE Wavespeed (m/s) Row B Row E 1 3711 3789 2 3583 4000 3 3673 3893 4 3812 4261 5 3602 3831 6 3916 4001 7 4187 3801 8 4188 4100 9 3851 10 4092 11 3750 3800 Data Sheet for Bridge Testing Date: 5/20/2003 Bahia Honda Bridge Impact Echo Pile Cap Data Point #Distance (ft) IE Wavespeed (m/s) 1 1.5 3514 2 1.5 3788 3 4.0 3279 4 4.0 3770 5 6.5 3445 6 6.5 3463 Data Sheet for Bridge Testing Date: 5/20/2003 Bahia Honda Bridge Ultrasonic Pile Cap Data Point # UPV Time ( s) Distance (in) IE Wavespeed (m/s) 1 647.3 963767.03 2 664.2 963671.18 3 661.7 963685.05 4 668.5 963647.57 5 624 963907.69 6 662.4 963681.16 7 723.1 963372.15 8 662.7 963679.49

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217 Data Sheet for Bridge Testing Date: 5/20/2003 Bahia Honda Bridge Ultrasonic Tomographic Crack Data from Column Row B Point # UPV Time ( s) Distance (in) Length Traveled (in) 1-7 316.4 47.51 54.06 2-7 316 47.51 53.99 3-7 299 43.66 51.09 7-11 290 43.66 49.55 Row C Point # UPV Time ( s) Distance (in) Length Traveled (in) 1-6 265.5/359.1 47.51 61.36 2-6 242.1/302.2 43.66 51.64 6-10 240.1/511.7 43.66 87.43 6-11 357.7/546.7 47.51 93.41 7-11 360.3 43.66 61.56 Row D Point # UPV Time ( s) Distance (in) Length Traveled (in) 2-7 351.9 47.5160.13 3-7 377.3 43.6664.47 4-11 325.3 43.6655.58

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218 Data Sheet for Niles Channel Bridge Date 5/20/2003 Column Tomography Using Ultrasonic Pulse Velocity Point # UPV Time ( s) Distance (in) UPV Wavespeed (m/s) IE Wavespeed (m/s) S1 148.4 26 4450.13 4001 S2 150.5 26 4388.04 3840 S3 151.4 26 4361.96 3911 S4 159.6 26 4137.84 3892 S5 151 26 4373.51 4175 S6 151.1 26 4370.62 4001 S7 151.6 26 4356.20 3944 S8 151.8 26 4350.46 4056 S9 154.7 26 4268.91 3608 S10 149.2 26 4426.27 4001 S11 150.1 26 4399.73 3827 S12 150.4 26 4390.96 3998 S13 151.2 26 4367.72 3894 S14 304.4 26 2169.51 4298 S15 149.8 26 4408.54 3839 S16 153.2 26 4310.70 3842 S17 150.7 26 4382.22 3617 S18 332.2 26 1987.96 3998 S19 331.8 26 1990.36 3944 S20 325 26 2032.00 N/A Data Sheet for Niles Channel Bridge Date 5/20/2003 Surface wave velocities using impact echo Point # IE Wavespeed (m/s) N Col 1 3841.00 N Col 2 4058.00 N Col 3 3601.00 N Col 4 4113.00 N Col 5 3759.00 N Col 6 3998.00 S Col 1 4000.00 S Col 2 4090.00 S Col 3 4014.00 S Col 4 4068.00 S Col 5 4056.00 S Col 6 4000.00

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219 Data Sheet for Bridge Testi ng, Sebastian River Bridge Date: 6/12/2003 NDT Data from Column 11-4 North to South Point # UPV Time (ms) UPV Wavespeed (m/s) IE Wavespeed (m/s) Hammer # S1 592 986.8 4000.0 S2 180.6 3234.8 52 S3 174.9 3340.2 difficulty/thru wave 44 S4 136.8 4270.5 S5 802 728.4 N/A S6 345.2 1692.4 48 S7 226 2585.0 48 S8 136.7 4273.6 S9 254 2300.0 2436.0 S10 548/1600 #REF! 42 S11 175.5 3328.8 52 S12 132.2 4419.1 S13 596 980.2 S14 608 960.9 2535.0 38 S15 408 1431.9 49 S16 132.6 4405.7 S17 144.8 4034.5 S18 138.3 4224.2 S19 438 1333.8 34 S20 132.8 4399.1 42 Data Sheet for Bridge Testi ng, Sebastian River Bridge Date: 6/12/2003 NDT Data from Column 11-4 East to West Point # UPV Time (ms) UPV Wavespeed (m/s) Hammer # W1 351 1664.4 W2 420 1391.0 52 W3 248 2355.6 52 W4 139.2 4196.8 W5 356 1641.0 W6 309 1890.6 49 W7 265 2204.5 51 W8 306 1909.2 W9 219 2667.6 W10 449 1301.1 53 W11 345 1693.3 50 W12 335 1743.9 W13 934 625.5 W14 273 2139.9 40 W15 753 775.8 44 W16 446 1309.9 W17 407 1435.4 W18 251 2327.5 W19 146.9 3976.9 46 W20 248 2355.6 44

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220 Data Sheet for Bridge Testi ng, Sebastian River Bridge Date: 6/12/2003 NDT Data from Column 11-5 North to South Point # UPV Time (ms) UPV Wavespeed (m/s) IE Wavespeed (m/s) Hammer # S1 176.4 4463.7 S2 182 4326.4 3979 52 S3 183.6 4288.7 55 S4 178.8 4403.8 S5 173.6 4535.7 4366 S6 183 4302.7 54 S7 184.3 4272.4 54 S8 174.4 4514.9 S9 174.4 4514.9 S10 184.1 4277.0 5296 54 S11 183.2 4298.0 50 S12 174.6 4509.7 S13 166.1 4740.5 S14 180.2 4369.6 3600 54 S15 179.1 4396.4 56 S16 174.1 4522.7 S17 173.3 4543.6 S18 177.6 4433.6 54 S19 173.6 4535.7 45 S20 172.6 4562.0 4298 Data Sheet for Bridge Testi ng, Sebastian River Bridge Date: 6/12/2003 NDT Data from Column 11-5 East to West Point # UPV Time (ms) UPV Wavespeed (m/s) Hammer # W1 174.1 4376.8 W2 183.2 4159.4 56 W3 184.3 4134.6 54 W4 177.1 4302.7 W5 176.8 4310.0 W6 186.3 4090.2 51 W7 182.8 4168.5 54 W8 176.8 4310.0 W9 175.1 4351.8 W10 186.8 4079.2 51 W11 186.2 4092.4 32 W12 175.7 4336.9 W13 173.3 4397.0 W14 182.4 4177.6 54 W15 180.2 4228.6 53 W16 172.1 4427.7 W17 169.9 4485.0 W18 174.5 4366.8 52 W19 176.2 4324.6 54 W20

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221 Data Sheet for Bridge Testing, Wabasso Bridge Date: 6/13/2003 NDT Data Pile Cap 5 Grid #1 Point # IE Wavespeed (m/s) Hammer # 1-1 2647 45 1-2 2536 46 1-3 2405 45 1-4 2419 35 2-1 2342 40 2-2 2250 40 2-3 2233 46 2-4 2307 48 3-1 2500 52 3-2 2028 48 3-3 2229 48 3-4 2199 48 4-1 2267 42 4-2 2312 39 4-3 2368 47 4-4 2950 48 Data Sheet for Bridge Testing, Wabasso Bridge Date: 6/13/2003 NDT Data Pile Cap 5 Grid #2 Point # IE Wavespeed (m/s) Hammer # 1-1 2338 46 1-2 2369 49 1-3 2275 46 1-4 2466 46 2-1 2951 49 2-2 2535 41 2-3 2774 50 2-4 2250 48 3-1 3052 49 3-2 2400 52 3-3 2360 49 3-4 2770 50 4-1 2500 50 4-2 2743 47 4-3 2902 52 4-4 2686 48

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222 Data Sheet for Bridge Testing, Wabasso Bridge Date: 6/13/2003 NDT Data Column 5 Grid #3 Point # IE Wavespeed (m/s) Hammer # 1-1 2465 54 1-2 2916 62 1-3 2441 62 1-4 2457 60 2-1 3214 54 2-2 3117 58 2-3 3477 60 2-4 3326 62 3-1 3159 64 3-2 3600 58 3-3 2608 64 3-4 3829 58 4-1 3157 58 4-2 3601 58 4-3 3611 53 4-4 3529 55

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223 Data Sheet for Bridge Testing Data Sheet for Bridge Testing Date: 6/14/2003 Date: 6/14/2003 Sebastian Inlet Bridge Sebastian Inlet Bridge NDT Data Pilecap #12 Grid 1 NDT Data Pilecap #12 Grid 2 Point # IE Wavespeed (m/s) Hammer # Point #IE Wavespeed (m/s) Hammer # 1-1 2697 48 1-1 3231 44 1-2 3829 44 1-2 3461 46 1-3 3274 38 1-3 3758 48 1-4 3808 50 1-4 3907 47 2-1 2687 44 2-1 3300 44 2-2 3831 42 2-2 4032 44 2-3 3808 43 2-3 3971 46 2-4 3751 50 2-4 3763 46 3-1 3529 46 3-1 3333 47 3-2 4000 48 3-2 3821 52 3-3 3333 46 3-3 3653 46 3-4 4000 46 3-4 2781 47 4-1 3810 46 4-1 3521 48 4-2 3894 50 4-2 3675 48 4-3 3829 56 4-3 3803 47 4-4 3764 49 4-4 3731 45 Data Sheet for Bridge Testing Data Sheet for Bridge Testing Date: 6/14/2003 Date: 6/14/2003 Sebastian Inlet Bridge Sebastian Inlet Bridge NDT Data Pilecap #16 Grid 3 NDT Data Pilecap #12 Grid 1 Point # IE Wavespeed (m/s) Hammer # Point #IE Wavespeed (m/s) Hammer # 1-1 3421 44 1-1 50 1-2 3573 44 1-2 48 1-3 3729 52 1-3 50 1-4 3991 42 1-4 52 2-1 3399 40 2-1 54 2-2 3253 52 2-2 55 2-3 3751 50 2-3 52 2-4 3908 52 2-4 50 3-1 4023 44 3-1 53 3-2 3821 45 3-2 50 3-3 3753 47 3-3 48 3-4 4120 46 3-4 46 4-1 3406 43 4-1 50 4-2 3329 43 4-2 54 4-3 3501 52 4-3 54 4-4 3299 52 4-4 52

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224 Data Sheet for Bridge Testing Date: 6/14/2003 Sebastian Inlet Bridge Column Tomography Data Point # UPV Time (ms) UPV Time (ms) UPV Time (ms) UPV Time (ms) UPV Time (ms) UPV Time (ms) Row A Row B Row C Row D Row E Row F 1-5 246.7 231.2 515.8 424.6 552.0 401.0 1-6 251.8 241.5 449.3 481.6 646.9 740.0 1-7 228.8 217.9 341.6 343.7 820.2 402.5 2-6 248.4 237.7 239.8 234.8 454.0 616.0 2-7 251.7 241.6 293.5 242.6 399.6 427.9 2-8 231.5 212.8 3-7 243.9 237.6 3-8 255.6 241.7 3-9 233.6 249.8 4-8 249.1 239.2 4-9 252.6 238.9 4-1 211.9 192.8 436.3 251.9 382.0 294.9 5-9 249.5 236.4 5-2 215.6 201.0 3-6 213.8 204.7 294.5 199.5 320.0 457.3 Data Sheet for Bridge Testing Date: 6/14/2003 Sebastian Inlet Bridge Column Tomography Calculations Point # UPV Time (ms) Wavespeed (m/s) UPV Time (m s) Wavespeed (m/s) UPV Time (ms) Wavespeed (m/s) Row A Row B Row C 1-5 246.7 3649.898662 231.2 3894.593426 515.8 1745.696006 1-6 251.8 3575.972994 241.5 3728.488613 449.3 2004.073002 1-7 228.8 3460.305944 217.9 3633.400642 341.6 2317.675644 2-6 248.4 3624.919485 237.7 3788.094236 239.8 3754.920767 2-7 251.7 3577.393723 241.6 3726.945364 293.5 3067.9046 2-8 231.5 3419.948164 212.8 3720.479323 3-7 243.9 3691.799918 237.6 3789.688552 3-8 255.6 3522.809077 241.7 3725.403393 3-9 233.6 3389.203767 249.8 3169.407526 4-8 249.1 3614.733039 239.2 3764.339465 4-9 252.6 3564.647664 238.9 3769.066555 4-1 211.9 3736.281265 192.8 4106.421162 436.3 1814.618382 5-9 249.5 3608.937876 236.4 3808.92555 5-2 215.6 3672.16141 201.0 3938.895522 3-6 213.8 3703.077643 204.7 3867.699072 294.5 2688.34635

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225 APPENDIX D LABORATORY DATA OF CYLINDER SPECIMENS Raw Data for Cylinder Samples w/c ratio = 0.45 Load (N) Compressive Strength (Mpa) UPV Time ( s) Impact Echo Wave Speed (m/s) Resonant Frequency (Hz) Age 112095.2 13.83 56.7 3580.2 1530 1 day 113420.8 13.99 55.4 3646.2 1695 113563.1 14.01 54.1 3678.4 1692 177003.6 21.83 50.9 3988.2 2060 3 days 191576 23.63 49.5 4020.2 2561 197309.8 24.34 50.8 3976.4 2433 259776.2 32.04 47.2 4279.7 2640 7days 247988.4 30.59 46.6 4291.8 2430 256929.3 31.69 47.0 4297.9 2790 341054.1 42.07 45.3 4437.1 2700 14days 333678.9 41.16 46.3 4384.4 2687 347357.2 42.84 50.0 4020.0 2295 390424.9 48.16 46.5 4311.8 2590 21days 356467.2 43.97 46.8 4359.0 2270 399623.8 49.29 46.5 4344.1 2350 413720.2 51.03 45.5 4461.5 2460 28 days 405508.8 50.02 46.1 4425.2 2360 365817.3 45.12 46.2 4415.6 2400 444822.2 54.86 45.3 4470.2 2670 45days 444822.2 54.86 45.2 4458.0 2750 443554.5 54.71 45.3 4448.1 2680 416020 51.31 45.6 4429.8 2620 60 days 435698.9 53.74 45.6 4429.8 2550 469002.7 58 46.0 4391.3 2520

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226 Calculations for Predicted Strength Data Using obtained Laboratory Data Mixture A (w/c = 0.45) Predicted Strength (MPa) by Author Wave Velocity Observed (km/s) Yan Qaswari Pessiki Actual Compressive Strength (Mpa) 3.580 15.84 2.39 18.03 13.83 3.646 17.57 4.81 19.91 13.99 3.678 18.48 5.99 20.90 14.01 3.988 30.08 17.37 33.28 21.83 4.020 31.63 18.54 34.92 23.63 3.976 29.53 16.94 32.70 24.34 4.280 47.56 28.07 51.53 32.04 4.292 48.48 28.52 52.48 30.59 4.298 48.94 28.74 52.96 31.69 4.437 60.92 33.85 65.24 42.07 4.384 56.08 31.92 60.29 41.16 4.020 31.62 18.54 34.91 42.84 4.312 50.03 29.25 54.08 48.16 4.359 53.88 30.98 58.04 43.97 4.344 52.63 30.44 56.76 49.29 4.462 63.30 34.75 67.67 51.03 4.425 59.79 33.41 64.09 50.02 4.416 58.89 33.06 63.17 45.12 4.470 64.17 35.07 68.56 54.86 4.458 62.95 34.62 67.31 54.86 4.448 61.98 34.26 66.33 54.71 4.430 60.23 33.59 64.53 51.31 4.430 60.23 33.59 64.53 53.74 4.391 56.69 32.17 60.92 57.85

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227 Compressive Strength vs. Wave Velocity, Mix A (w/c = 0.45) Best Fit Equation = y = 0.0487e0.0016xR2 = 0.8774 y = 0.0569e0.0016xR2 = 1 y = 5E-21x6.074R2 = 1 y = 0.0367x 129.08 R2 = 1 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 35003750400042504500 Wavespeed (m/s)Compressive Strength (MPa) Obtained Data Best Fit (Obtained Data) Predicted Yan Predicted Pessiki Predicted Qaswari Compressive Strength vs. Resonant Frequency Mix A, (w/c = 0.45)Best Fit Equation = y = 7E-07x2.2769R2 = 0.62590.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 10001500200025003000Wavespeed (m/s)Compressive Strength (MPa) Series1 Best Fit

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228 Raw Data for Cylinder Samples w/c ratio = 0.65 Load (N) Compressive Strength (Mpa) UPV Time (ms) Impact Echo Wave Speed (m/s) Resonant Frequency (Hz) Age 38655 4.77 67.8 2949.9 1100 1 day 34874.1 4.30 70.2 2849.0 1020 29981 3.70 73.8 2737.1 970 64321.3 7.93 56.8 3521.1 1450 2 day 61163.1 7.54 55.9 3542.0 1810 62897.9 7.76 57.0 3561.4 1880 94871.7 11.70 54.0 3666.7 2350 3day 100668 12.42 53.5 3700.9 2450 97620.7 12.04 54.5 3633.0 1950 145372 17.93 48.7 4127.3 2235 7day 140537 17.33 50.2 4043.8 2213 140804 17.37 49.6 4052.4 1800 177809 21.93 51.0 3980.4 2250 14day 182978 22.57 49.4 4109.3 2550 180767 22.30 49.7 4084.5 2860 201553 24.86 49.0 4102.0 2700 21 Day 202510 24.98 48.2 4149.4 2590 202274 24.95 48.7 4086.2 2460 227807 28.10 48.2 4149.4 2197 28 day 235422 29.04 48.7 4106.8 2020 220997 27.26 48.2 4128.6 1980 241125 29.74 48.1 4220.4 2570 42 day 248024 30.59 47.2 4194.9 2470 237184 29.25 47.0 4255.3 2700 262690 32.40 47.4 4219.4 2650 56 day 252085 31.09 48.5 4164.9 2650 262209 32.34 47.5 4221.1 2670

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229 Calculations for Predicted Strength Data Using obtained Labotatory Data Mixture B A (w/c = 0.65) Predicted Strength (MPa) by Author Wave Velocity Observed (km/s) Yan Qaswari Pessiki Actual Compressive Strength (Mpa) 2.95 5.88 -20.76 6.98 4.77 2.85 5.02 -24.46 5.99 4.30 2.74 4.21 -28.57 5.06 3.70 3.52 14.43 0.22 16.50 7.93 3.54 14.92 0.99 17.02 7.54 3.56 15.38 1.70 17.53 7.76 3.67 18.15 5.56 20.53 11.70 3.70 19.15 6.82 21.62 12.42 3.63 17.21 4.33 19.52 12.04 4.13 37.43 22.48 41.01 17.93 4.04 32.83 19.41 36.18 17.33 4.05 33.28 19.73 36.65 17.37 3.98 29.71 17.08 32.89 21.93 4.11 36.39 21.82 39.92 22.57 4.08 35.00 20.91 38.46 22.30 4.10 35.98 21.55 39.48 24.86 4.15 38.75 23.29 42.39 24.98 4.09 35.09 20.97 38.56 24.95 4.15 38.75 23.29 42.39 28.10 4.11 36.24 21.72 39.76 29.04 4.13 37.51 22.53 41.09 27.26 4.22 43.33 25.90 47.15 29.74 4.19 41.63 24.96 45.38 30.59 4.26 45.78 27.18 49.69 29.25 4.22 43.26 25.86 47.08 32.40 4.16 39.71 23.86 43.39 31.09 4.22 43.38 25.92 47.20 32.34

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230 Compressive Strength vs. Wave Velocity Mix B (WC = 0.65) Best Fit Equation = y = 0.0606e0.0014xR2 = 0.9408y = 0.0569e0.0016xR2 = 1 y = 3E-18x5.2754R2 = 1 y = 0.0367x 129.08 R2 = 10.00 10.00 20.00 30.00 40.00 50.00 25003000350040004500 Wave Velocity (m/s)Compressive Strength (MPa) Obtained Data Best Fit Experimental Data Predicted Yan Predicted Pessiki Predicted Qaswari Compressive Strength vs. Resonant Frequency Mix B(w/c = 0.65)Best Fit Equation = y = 1.691e0.001xR2 = 0.71340.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 0500100015002000250030003500Resonant Frequency (Hz)Compressive Strength (MPa) Series1 Best Fit

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231 APPENDIX E LABORATORY DATA AND GRAPHICA L RESULTS OF LARGE SCALE SPECIMENS Summary Sheet for Block Samples Summary of Block Identi fication and Conditioning Block Number (w/c ratio) Solution type 5 0.45 Sulfate Solution 6 0.45 Sulfate Solution 7 0.45 Lime water 8 0.45 Lime water 21 0.65 Lime water 22 0.65 Lime water 23 0.65 Sulfate Solution 24 0.65 Sulfate Solution

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232 Date2/9/2003 Temp72F Block #5 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 64.6 3761.6 1 3519 2 64.5 3767.4 2 3831 3 64.6 3761.6 3 3802 4 64.8 3750.0 4 3808 5 61.5 3951.2 5 3831 6 61.6 3944.8 6 3945 7 61.3 3964.1 8 61.4 3957.7 9 58.7 4139.7 10 58.9 4125.6 11 57.5 4226.1 12 57.3 4240.8 13 231.0 3896.1 14 226.4 3984.1 15 220.4 4101.6 Date2/13/2003 Temp72F Block #5 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 64.4 3773.3 1 3672 2 64.1 3791.0 2 3751 3 64.3 3779.2 3 3887 4 62.3 3900.5 4 3918 5 59.7 4070.4 5 4285 6 59.6 4077.2 6 4187 7 59.8 4063.5 8 60.0 4050.0 9 58.4 4161.0 10 58.3 4168.1 11 59.3 4097.8 12 60.0 4050.0 13 223.2 4032.3 14 218.0 4137.6 15 213.1 4242.1

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233 Date2/21/2003 Temp72F Block #5 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 59.4 4090.9 1 3673 2 60.0 4050.0 2 3751 3 60.2 4036.5 3 4021 4 59.9 4056.8 4 4000 5 58.0 4189.7 5 4171 6 58.1 4182.4 6 4287 7 58.2 4175.3 8 58.4 4161.0 9 55.8 4354.8 10 56.1 4331.6 11 56.6 4293.3 12 56.1 4331.6 13 224.7 4005.3 14 217.3 4150.9 15 212.8 4248.1 Date2/27/2003 Temp72F Block #5 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 58.9 4125.6 1 3913 2 58.7 4139.7 2 3831 3 59.0 4118.6 3 4056 4 59.2 4104.7 4 3914 5 57.3 4240.8 5 4312 6 57.5 4226.1 6 4199 7 57.5 4226.1 8 58.3 4168.1 9 56.2 4323.8 10 56.8 4278.2 11 57.1 4255.7 12 56.3 4316.2 13 215.4 4178.3 14 211.4 4266.8 15 208.0 4346.2

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234 Date3/7/2003 Temp72F Block #5 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 58.3 4168.1 1 3977 2 57.8 4204.2 2 4000 3 58.4 4161.0 3 3999 4 58.6 4146.8 4 4101 5 56.8 4278.2 5 4287 6 56.8 4278.2 6 4390 7 56.6 4293.3 8 57.4 4233.4 9 55.0 4418.2 10 55.4 4386.3 11 55.6 4370.5 12 55.2 4402.2 13 212.5 4235.3 14 210.0 4295.2 15 206.6 4375.6 Date3/27/2003 Temp72F Block #5 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 58.1 4182.4 1 3913 2 57.8 4204.2 2 3826 3 58.3 4168.1 3 4187 4 58.4 4161.0 4 4301 5 57.0 4263.2 5 4392 6 56.9 4270.7 6 4388 7 56.4 4308.5 8 57.1 4255.7 9 54.8 4434.3 10 56.0 4339.3 11 56.9 4270.7 12 55.5 4378.4 13 211.0 4265.4 14 208.2 4332.4 15 203.9 4433.5

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235 Date4/17/2003 Temp72F Block #5 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 58.1 4182.4 1 3983 2 57.9 4196.9 2 3741 3 58.2 4175.3 3 4255 4 58.4 4161.0 4 4233 5 57.1 4255.7 5 4307 6 56.7 4285.7 6 4393 7 56.4 4308.5 8 56.7 4285.7 9 55.0 4418.2 10 55.2 4402.2 11 55.9 4347.0 12 54.6 4450.5 13 210.7 4271.5 14 207.6 4344.9 15 200.4 4511.0 Date5/1/2003 Temp72F Block #5 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 58.3 4168.1 1 3788 2 57.9 4196.9 2 3936 3 58.2 4175.3 3 4101 4 58.3 4168.1 4 4387 5 56.7 4285.7 5 4176 6 56.7 4285.7 6 4287 7 56.6 4293.3 8 56.8 4278.2 9 54.7 4442.4 10 55.3 4394.2 11 55.2 4402.2 12 54.8 4434.3 13 210.4 4277.6 14 207.5 4347.0 15 202.7 4459.8

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236 Tomography Data Sheet for Test blocks. Date 5/8/2003 Block # 5 Point # Time ( s) Point # Time ( s) Point # Time ( s) A1 61.0 B1 58.4 C1 57.0 A2 60.0 B2 58.1 C2 57.1 A3 58.1 B3 57.6 C3 56.8 A4 59.6 B4 57.5 C4 56.8 A5 60.6 B5 57.6 C5 56.7 A6 59.9 B6 57.8 C6 56.7 A7 58.6 B7 57.5 C7 56.8 A8 59.5 B8 58.1 C8 57.0 A9 60.1 B9 58.3 C9 56.5 D1 55.6 E1 55.2 D2 57.0 E2 53.5 D3 55.6 E3 54.5 D4 56.3 E4 55.1 D5 55.4 E5 55.3 D6 55.6 E6 54.9 D7 56.1 E7 54.9 D8 56.6 E8 53.7 D9 55.1 E9 54.6 X1 111.4 Y1 113.1 Z1 111.0 X2 112.6 Y2 111.9 Z2 111.6 X3 111.2 Y3 110.8 Z3 111.3 X4 113.0 Y4 111.5 Z4 111.4 X5 112.9 Y5 112.3 Z5 112.6 X6 112.6 Y6 111.9 Z6 113.5 X7 113.5 Y7 110.6 Z7 110.9 X8 112.2 Y8 112.1 Z8 112.8 X9 110.9 Y9 110.1 Z9 108.4 XA 214.6 YA 214.6 ZA 215.5 XB 210.4 YB 211.1 ZB 211.5 XC 210.6 YC 208.7 ZC 208.9 XD 206.9 YD 207.7 ZD 205.6 XE 196.2 YE 202.3 ZE 201.6

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237 Wave Velocity vs. Age (Block 5)3500 3600 3700 3800 3900 4000 4100 4200 4300 4400 4500 02468101214Age (weeks)Wavespeed (m/s) Upvtop Ietop upvmid iemid upvbott iebott 28 days

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238 Date2/9/2003 Temp72F Block #6 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 63.5 3811.0 1 3345 2 63.3 3823.1 2 3454 3 63.4 3817.0 3 3477 4 63.1 3835.2 4 3526 5 63.1 3835.2 5 3840 6 63.6 3805.0 6 4092 7 62.7 3859.6 8 63.6 3805.0 9 63.6 3805.0 10 63.6 3805.0 11 63.6 3805.0 12 63.6 3805.0 13 231.4 3889.4 14 227.0 3967.0 15 222.3 4053.1 Date2/13/2003 Temp72F Block #6 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 61.9 3909.5 1 3396 2 65.0 3723.1 2 3461 3 64.3 3763.6 3 3462 4 62.0 3903.2 4 3672 5 61.5 3935.0 5 3828 6 61.8 3915.9 6 4100 7 61.8 3915.9 8 60.8 3980.3 9 59.5 4067.2 10 60.4 4006.6 11 59.8 4046.8 12 58.6 4129.7 13 222.9 4037.7 14 218.7 4117.5 15 215.6 4179.0

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239 Date2/21/2003 Temp72F Block #6 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 63.3 3823.1 1 3648 2 60.9 3973.7 2 3555 3 61.2 3954.2 3 3914 4 61.0 3967.2 4 3821 5 60.5 4000.0 5 4090 6 60.8 3980.3 6 3913 7 60.7 3986.8 8 59.9 4040.1 9 58.7 4122.7 10 62.3 3884.4 11 64.0 3781.3 12 59.7 4053.6 13 217.6 4136.0 14 214.0 4207.9 15 210.8 4274.2 Date2/27/2003 Temp72F Block #6 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 59.3 4080.9 1 3597 2 59.9 4040.1 2 3704 3 59.4 4074.1 3 4021 4 59.9 4040.1 4 3945 5 58.6 4129.7 5 4187 6 59.3 4080.9 6 4091 7 59.6 4060.4 8 59.6 4060.4 9 57.0 4245.6 10 58.2 4158.1 11 58.4 4143.8 12 57.6 4201.4 13 215.3 4180.2 14 212.0 4247.6 15 209.6 4298.7

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240 Date3/7/2003 Temp72F Block #6 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 58.6 4129.7 1 3673 2 58.7 4122.7 2 3751 3 59.2 4087.8 3 3829 4 58.6 4129.7 4 4092 5 58.7 4122.7 5 4186 6 58.8 4115.6 6 4188 7 58.7 4122.7 8 57.8 4186.9 9 56.6 4275.6 10 57.3 4223.4 11 57.0 4245.6 12 56.0 4321.4 13 213.3 4219.4 14 211.4 4259.7 15 207.0 4352.7 Date3/27/2003 Temp72F Block #6 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 59 4101.7 1 3841 2 58.8 4115.6 2 3912 3 59.2 4087.8 3 4009 4 58.7 4122.7 4 4000 5 58.9 4108.7 5 4114 6 58.6 4129.7 6 4235 7 58.7 4122.7 8 57.9 4179.6 9 57.6 4201.4 10 58.3 4150.9 11 58.3 4150.9 12 56.5 4283.2 13 210.5 4275.5 14 209.0 4308.6 15 206.3 4367.4

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241 Date4/17/2003 Temp72F Block #6 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 58.4 4143.8 1 3989 2 58.7 4122.7 2 4001 3 58.9 4108.7 3 4211 4 58.6 4129.7 4 4090 5 58.9 4108.7 5 4186 6 58.7 4122.7 6 4175 7 58.5 4136.8 8 57.8 4186.9 9 56.4 4290.8 10 57.1 4238.2 11 56.7 4268.1 12 55.9 4329.2 13 210.8 4269.4 14 207.8 4333.5 15 204.9 4397.3 Date5/1/2003 Temp72F Block #6 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 58.8 4115.6 1 2 58.6 4129.7 2 3 59.3 4080.9 3 4 58.7 4122.7 4 5 58.9 4108.7 5 6 58.6 4129.7 6 7 58.3 4150.9 8 57.6 4201.4 9 56.7 4268.1 10 58.3 4150.9 11 56.9 4253.1 12 56.0 4321.4 13 210.1 4283.7 14 207.3 4343.9 15 204.6 4403.7

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242 Tomography Data Sheet for Test blocks. Date5/9/2003 Block #6 Point # Time ( s) Point # Time ( s) Point # Time ( s) A1 59.6 B1 58.4 C1 57.9 A2 59.3 B2 58.1 C2 58.6 A3 58.3 B3 58.4 C3 58.6 A4 59.1 B4 59.4 C4 58.5 A5 58.9 B5 58.9 C5 58.5 A6 58.5 B6 59.0 C6 58.5 A7 59.0 B7 58.6 C7 58.0 A8 58.9 B8 58.2 C8 57.9 A9 59.8 B9 58.0 C9 57.6 D1 55.8 E1 55.5 D2 57.6 E2 55.6 D3 57.8 E3 57.2 D4 57.9 E4 56.7 D5 57.8 E5 56.5 D6 58.4 E6 56.4 D7 57.3 E7 56.1 D8 57.2 E8 55.1 D9 55.9 E9 54.4 X1 108.2 Y1 109.8 Z1 110.1 X2 111.7 Y2 111.6 Z2 111.3 X3 111.9 Y3 110.9 Z3 110.9 X4 113.5 Y4 112.8 Z4 113.7 X5 114.5 Y5 113.5 Z5 114.9 X6 112.8 Y6 113.0 Z6 115.2 X7 112.5 Y7 112.4 Z7 111.2 X8 111.2 Y8 113.3 Z8 111.8 X9 112.2 Y9 111.3 Z9 112.4 XA 214.7 YA 214.5 ZA 214.5 XB 211.5 YB 209.3 ZB 212.0 XC 208.9 YC 207.9 ZC 209.4 XD 205.2 YD 205.0 ZD 205.8 XE 198.0 YE 202.5 ZE 201.2

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243 Wave Velocity vs. age Block 6 (w/c = 0.45, SO4)3300 3500 3700 3900 4100 4300 4500 02468101214Age (weeks)Wave Velocity (m/s) upvtop ietop upvmid iemid upvbott iebott 28 days

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244 Date2/9/2003 Temp72F Block #7 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 61.5 3935.0 1 3692 2 61.5 3935.0 2 3645 3 60.8 3980.3 3 3674 4 61.4 3941.4 4 3840 5 62.0 3919.4 5 3850 6 61.5 3951.2 6 3674 7 61.6 3944.8 8 61.7 3938.4 9 61.5 3967.5 10 61.4 3973.9 11 61.4 3973.9 12 61.5 3967.5 13 224.0 4031.3 14 221.8 4080.3 15 216.4 4191.3 Date2/13/2003 Temp72F Block #7 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 60.3 4013.3 1 3673 2 61.0 3967.2 2 3653 3 60.2 4019.9 3 3680 4 63.0 3841.3 4 3966 5 61.0 3983.6 5 3900 6 60.4 4023.2 6 4185 7 61.1 3977.1 8 60.4 4023.2 9 59.3 4114.7 10 60.0 4066.7 11 60.6 4026.4 12 59.3 4114.7 13 215.7 4186.4 14 214.5 4219.1 15 211.3 4292.5

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245 Date2/21/2003 Temp72F Block #7 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 58.0 4172.4 1 3691 2 57.7 4194.1 2 3684 3 57.0 4245.6 3 3893 4 58.0 4172.4 4 3924 5 58.4 4161.0 5 4100 6 57.5 4226.1 6 4285 7 57.6 4218.8 8 57.5 4226.1 9 56.7 4303.4 10 57.4 4250.9 11 57.5 4243.5 12 57.6 4236.1 13 210.8 4283.7 14 209.5 4319.8 15 206.0 4402.9 Date2/28/2003 Temp72F Block #7 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 57.8 4186.9 1 3600 2 57.8 4186.9 2 3902 3 57.6 4201.4 3 4090 4 57.6 4201.4 4 3810 5 58.0 4189.7 5 4393 6 57.8 4204.2 6 4007 7 57.8 4204.2 8 57.4 4233.4 9 57.0 4280.7 10 57.3 4258.3 11 57.7 4228.8 12 56.8 4295.8 13 209.3 4314.4 14 208.4 4342.6 15 204.9 4426.5

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246 Date3/6/2003 Temp72F Block #7 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 57.3 4223.4 1 3831 2 57.1 4238.2 2 3749 3 57.1 4238.2 3 4091 4 57.2 4230.8 4 4090 5 57.4 4233.4 5 4390 6 57.3 4240.8 6 4187 7 57.5 4226.1 8 57.4 4233.4 9 56.5 4318.6 10 57.3 4258.3 11 57.3 4258.3 12 57.3 4258.3 13 207.8 4345.5 14 207.1 4369.9 15 202.4 4481.2 Date3/20/2003 Temp72F Block #7 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 57.1 4238.2 1 3770 2 56.7 4268.1 2 3902 3 56.5 4283.2 3 4101 4 56.7 4268.1 4 4186 5 57.5 4226.1 5 4357 6 57 4263.2 6 4287 7 57.3 4240.8 8 57.2 4248.3 9 57.4 4250.9 10 57.1 4273.2 11 57.4 4250.9 12 57.9 4214.2 13 206.4 4375.0 14 205.6 4401.8 15 200.9 4514.7

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247 Date3/27/2003 Temp72F Block #7 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 57.3 4223.4 1 2 57.1 4238.2 2 3 57.1 4238.2 3 4 57.0 4245.6 4 5 57.6 4218.8 5 6 57.2 4248.3 6 7 57.5 4226.1 8 57.5 4226.1 9 56.3 4333.9 10 57.3 4258.3 11 57.4 4250.9 12 57.7 4228.8 13 206.0 4383.5 14 205.1 4412.5 15 202.1 4487.9 Date4/10/2003 Temp72F Block #7 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 57.2 4230.8 1 3900 2 57.4 4216.0 2 3800 3 57.2 4230.8 3 4104 4 57.2 4230.8 4 4116 5 57.6 4218.8 5 4272 6 57.4 4233.4 6 4429 7 57.6 4218.8 8 57.5 4226.1 9 56.7 4303.4 10 57.7 4228.8 11 59.0 4135.6 12 58.3 4185.2 13 206.2 4379.2 14 204.6 4423.3 15 202.5 4479.0

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248 Date4/24/2003 Temp72F Block #7 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 57.2 4230.8 1 3861 2 57.2 4230.8 2 3954 3 57.2 4230.8 3 4114 4 57.2 4230.8 4 4092 5 57.8 4204.2 5 4300 6 57.4 4233.4 6 4388 7 57.7 4211.4 8 57.5 4226.1 9 57.5 4243.5 10 58.5 4170.9 11 58.0 4206.9 12 58.3 4185.2 13 208.2 4337.2 14 204.7 4421.1 15 202.4 4481.2

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249 Tomography Data Sheet for Test blocks. Date5/7/2003 Block #7 Point # Time ( s) Point # Time ( s) Point # Time ( s) A1 57.7 B1 56.0 C1 55.5 A2 57.1 B2 56.5 C2 56.9 A3 56.7 B3 56.4 C3 56.5 A4 56.4 B4 56.6 C4 56.5 A5 57.2 B5 56.8 C5 56.8 A6 56.4 B6 56.2 C6 56.8 A7 56.9 B7 56.6 C7 57.0 A8 56.9 B8 56.3 C8 56.8 A9 56.8 B9 56.3 C9 55.9 D1 54.5 E1 53.7 D2 56.2 E2 54.8 D3 56.5 E3 55.7 D4 57.1 E4 55.8 D5 56.4 E5 55.8 D6 56.6 E6 56.2 D7 56.5 E7 56.1 D8 56.5 E8 54.3 D9 54.4 E9 52.6 X1 113.0 Y1 110.7 Z1 113.7 X2 114.7 Y2 114.7 Z2 115.3 X3 114.1 Y3 113.2 Z3 114.7 X4 114.8 Y4 113.0 Z4 113.8 X5 115.7 Y5 113.4 Z5 115.2 X6 114.9 Y6 113.1 Z6 114.2 X7 114.2 Y7 113.3 Z7 114.7 X8 112.9 Y8 112.6 Z8 113.1 X9 113.2 Y9 112.6 Z9 113.3 XA 208.5 YA 206.8 ZA 208.3 XB 206.1 YB 203.6 ZB 205.4 XC 205.8 YC 202.8 ZC 204.2 XD 201.4 YD 203.4 ZD 202.4 XE 195.4 YE 198.1 ZE 197.4

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250 Wave Velocity vs. age (Block 7)3500 3600 3700 3800 3900 4000 4100 4200 4300 4400 4500 02468101214Age (weeks)Wave Velocity (m/s) Upvtop Ietop upvmid iemid upvbott iebott 28 days

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251 Date2/9/2003 Temp72F Block #8 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 63.5 3779.5 1 3684 2 60.7 3953.9 2 3349 3 64.0 3750.0 3 3610 4 63.4 3785.5 4 3630 5 63.6 3773.6 5 3655 6 60.6 3960.4 6 3674 7 61.0 3934.4 8 63.8 3761.8 9 59.9 4006.7 10 61.0 3934.4 11 57.6 4166.7 12 60.1 3993.3 13 227.0 3964.8 14 218.2 4136.1 15 212.3 4262.8 Date2/13/2003 Temp72F Block #8 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 62.8 3821.7 1 2 60.9 3940.9 2 3 58.8 4081.6 3 4 59.8 4013.4 4 5 58.8 4081.6 5 6 58.2 4123.7 6 7 58.8 4081.6 8 59.4 4040.4 9 57.3 4188.5 10 57.6 4166.7 11 56.6 4240.3 12 57.2 4195.8 13 216 4166.7 14 215.1 4195.7 15 210.8 4293.2

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252 Date2/21/2003 Temp72F Block #8 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 57.5 4173.9 1 3645 2 57.6 4166.7 2 3682 3 57.4 4181.2 3 3849 4 57.6 4166.7 4 3789 5 56.8 4225.4 5 3913 6 56 4285.7 6 4093 7 56.4 4255.3 8 56.9 4217.9 9 54.1 4436.2 10 53.9 4452.7 11 54.3 4419.9 12 54.3 4419.9 13 210.7 4271.5 14 210.4 4289.4 15 206.4 4384.7 Date2/28/2003 Temp72F Block #8 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 56.9 4217.9 1 3830 2 56.6 4240.3 2 3828 3 56.5 4247.8 3 3882 4 57.0 4210.5 4 3918 5 56.3 4262.9 5 4092 6 55.9 4293.4 6 4186 7 56.3 4262.9 8 56.7 4232.8 9 54.6 4395.6 10 54.3 4419.9 11 54.9 4371.6 12 54.9 4371.6 13 209.1 4304.2 14 208.6 4326.5 15 204.5 4425.4

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253 Date3/6/2003 Temp72F Block #8 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 57.0 4210.5 1 3674 2 56.4 4255.3 2 3914 3 56.4 4255.3 3 3914 4 56.9 4217.9 4 3977 5 56.3 4262.9 5 4401 6 56.0 4285.7 6 4284 7 56.3 4262.9 8 56.7 4232.8 9 53.7 4469.3 10 53.7 4469.3 11 54.9 4371.6 12 54.6 4395.6 13 208.8 4310.3 14 207.7 4345.2 15 204.6 4423.3 Date3/20/2003 Temp72F Block #8 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 56.7 4232.8 1 3808 2 56.4 4255.3 2 3749 3 56.2 4270.5 3 3914 4 56.3 4262.9 4 3829 5 55.9 4293.4 5 4390 6 55.6 4316.5 6 4300 7 55.8 4301.1 8 56.5 4247.8 9 54.5 4403.7 10 54.7 4387.6 11 54.3 4419.9 12 54.3 4419.9 13 205.8 4373.2 14 205.4 4393.9 15 202.5 4469.1

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254 Date3/27/2003 Temp72F Block #8 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 56.6 4240.3 1 2 56.4 4255.3 2 3 56.4 4255.3 3 4 56.5 4247.8 4 5 56.2 4270.5 5 6 56.1 4278.1 6 7 56.4 4255.3 8 56.7 4232.8 9 54.8 4379.6 10 55.2 4347.8 11 55.3 4340.0 12 54.6 4395.6 13 206.6 4356.2 14 205.0 4402.4 15 201.9 4482.4 Date4/10/2003 Temp72F Block #8 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 56.8 4225.4 1 3933 2 56.6 4240.3 2 4114 3 56.3 4262.9 3 4012 4 56.3 4262.9 4 4080 5 56.2 4270.5 5 4285 6 55.6 4316.5 6 4365 7 56.0 4285.7 8 56.5 4247.8 9 54.9 4371.6 10 54.6 4395.6 11 55.7 4308.8 12 54.6 4395.6 13 206.8 4352.0 14 204.9 4404.6 15 201.5 4491.3

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255 Date4/24/2003 Temp72F Block #8 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 56.9 4217.9 1 4033 2 56.7 4232.8 2 3967 3 56.7 4232.8 3 4100 4 56.6 4240.3 4 4100 5 56.9 4217.9 5 4285 6 55.7 4308.8 6 4315 7 56.4 4255.3 8 56.8 4225.4 9 55.0 4363.6 10 55.0 4363.6 11 55.6 4316.5 12 55.5 4324.3 13 206.6 4356.2 14 204.0 4424.0 15 200.4 4516.0

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256 Tomography Data Sheet for Test blocks. Date 5/8/2003 Block # 8 Point # Time ( s) Point # Time ( s) Point # Time ( s) A1 58.2 B1 56.9 C1 55.8 A2 57.2 B2 56.7 C2 56.8 A3 57.3 B3 56.2 C3 56.0 A4 57.7 B4 56.1 C4 55.8 A5 57.4 B5 56.2 C5 56.4 A6 57.4 B6 56.2 C6 56.2 A7 57.4 B7 56.5 C7 56.5 A8 57.3 B8 56.7 C8 56.6 A9 58.3 B9 55.8 C9 55.1 D1 55.0 E1 53.2 D2 55.2 E2 53.6 D3 55.1 E3 54.5 D4 55.2 E4 53.9 D5 55.5 E5 54.2 D6 55.1 E6 54.3 D7 56.1 E7 54.6 D8 55.2 E8 53.6 D9 54.1 E9 53.0 X1 113.3 Y1 113.7 Z1 113.6 X2 112.7 Y2 112.7 Z2 113.6 X3 112.8 Y3 112.9 Z3 114.2 X4 113.4 Y4 113.8 Z4 113.4 X5 113.9 Y5 113.3 Z5 114.1 X6 113.7 Y6 112.7 Z6 113.7 X7 112.6 Y7 112.6 Z7 113.6 X8 112.7 Y8 111.7 Z8 112.7 X9 110.8 Y9 113.5 Z9 110.0 XA 213.1 YA 211.3 ZA 210.8 XB 210.3 YB 207.5 ZB 208.1 XC 206.7 YC 206.9 ZC 208.3 XD 200.9 YD 204.9 ZD 204.5 XE 199.7 YE 202.7 ZE 199.8

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257 Wave Velocit y vs. a g e Block 8 ( w/c = 0.45, Lime Water ) 3300 3500 3700 3900 4100 4300 4500 02468101214Age (weeks)Wave Velocity (m/s) upvtop ietop upvmid iemid upvbott iebott 28 days

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258 Date2/16/2003 Temp72F Block #21 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 1 3273 2 2 3213 3 3 3389 4 4 3333 5 5 3462 6 6 3528 7 8 9 10 11 12 13 14 15 Date2/21/2003 Temp72F Block #21 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 67.8 3628.3 1 3404 2 69.3 3549.8 2 3600 3 69.2 3554.9 3 3600 4 68.4 3596.5 4 3530 5 65.6 3750.0 5 3601 6 66.6 3693.7 6 3850 7 67.0 3671.6 8 67.0 3671.6 9 62.4 3942.3 10 63.5 3874.0 11 64.3 3825.8 12 61.2 4019.6 13 240.4 3743.8 14 233.6 3874.1 15 226.9 4010.6

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259 Date2/27/2003 Temp72F Block #21 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 66.8 3682.6 1 3500 2 70.4 3494.3 2 3506 3 67.0 3671.6 3 3660 4 66.8 3682.6 4 3533 5 64.6 3808.0 5 3799 6 65.1 3778.8 6 3799 7 64.4 3819.9 8 65.2 3773.0 9 61.3 4013.1 10 63.5 3874.0 11 64.2 3831.8 12 61.1 4026.2 13 234.7 3834.7 14 229.0 3952.0 15 221.6 4106.5 Date3/6/2003 Temp72F Block #21 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 65.0 3784.6 1 3396 2 66.0 3727.3 2 3529 3 65.7 3744.3 3 3529 4 65.3 3767.2 4 3670 5 67.0 3671.6 5 4001 6 63.8 3855.8 6 4092 7 63.6 3867.9 8 63.3 3886.3 9 60.0 4100.0 10 60.6 4059.4 11 62.4 3942.3 12 59.4 4141.4 13 232.6 3869.3 14 225.6 4011.5 15 218.2 4170.5

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260 Date3/13/2003 Temp72F Block #21 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 63.7 3861.9 1 3529 2 64.2 3831.8 2 3600 3 64.8 3796.3 3 3752 4 63.5 3874.0 4 3433 5 62.0 3967.7 5 3913 6 62.5 3936.0 6 3913 7 62.7 3923.4 8 62.2 3955.0 9 58.6 4198.0 10 59.8 4113.7 11 59.8 4113.7 12 58.1 4234.1 13 228.0 3947.4 14 223.1 4056.5 15 216.7 4199.4 Date3/27/2003 Temp72F Block #21 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 65.1 3778.8 1 3611 2 65.9 3732.9 2 3461 3 65.7 3744.3 3 3752 4 64.5 3814.0 4 3598 5 63.2 3892.4 5 4005 6 64.4 3819.9 6 3996 7 64.1 3837.8 8 63.2 3892.4 9 59.5 4134.5 10 60.0 4100.0 11 61.0 4032.8 12 59.6 4127.5 13 228.8 3933.6 14 222.7 4063.8 15 216.6 4201.3

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261 Date4/17/2003 Temp72F Block #21 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 65.0 3784.6 1 3600 2 66.9 3677.1 2 3529 3 65.9 3732.9 3 3789 4 64.9 3790.4 4 3749 5 62.9 3911.0 5 4002 6 63.6 3867.9 6 3996 7 63.3 3886.3 8 63.2 3892.4 9 59.5 4134.5 10 60.1 4093.2 11 61.0 4032.8 12 58.8 4183.7 13 228.5 3938.7 14 221.6 4083.9 15 216.2 4209.1 Date5/1/2003 Temp72F Block #21 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 64.5 3814.0 1 2 65.3 3767.2 2 3 65.3 3767.2 3 4 65.0 3784.6 4 5 61.9 3974.2 5 6 62.2 3955.0 6 7 62.5 3936.0 8 63.3 3886.3 9 59.1 4162.4 10 60.4 4072.8 11 61.9 3974.2 12 59.2 4155.4 13 228.7 3935.3 14 222.1 4074.7 15 216.5 4203.2

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262 Date5/1/2003 Temp72F Block #21 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 64.5 3814.0 1 2 65.3 3767.2 2 3 65.3 3767.2 3 4 65.0 3784.6 4 5 61.9 3974.2 5 6 62.2 3955.0 6 7 62.5 3936.0 8 63.3 3886.3 9 59.1 4162.4 10 60.4 4072.8 11 61.9 3974.2 12 59.2 4155.4 13 228.7 3935.3 14 222.1 4074.7 15 216.5 4203.2

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263 Tomography Data Sheet for Test blocks. Date 5/13/2003 Block # 21 Point # Time ( s) Point # Time ( s) Point # Time ( s) A1 64.8 B1 62.5 C1 60.2 A2 64.6 B2 63.6 C2 62.5 A3 65.5 B3 64.2 C3 62.9 A4 66.5 B4 64.2 C4 63.3 A5 65.8 B5 65.0 C5 63.5 A6 65.9 B6 64.9 C6 63.4 A7 65.5 B7 64.8 C7 63.6 A8 65.4 B8 64.5 C8 62.8 A9 66.4 B9 63.5 C9 62.5 D1 60.3 E1 56.7 D2 60.7 E2 58.6 D3 61.2 E3 60.6 D4 61.6 E4 59.8 D5 62.4 E5 61.0 D6 62.6 E6 60.1 D7 62.1 E7 58.6 D8 60.9 E8 58.6 D9 59.5 E9 58.4 X1 117.2 Y1 118.2 Z1 116.4 X2 119.6 Y2 118.8 Z2 118.6 X3 120.4 Y3 119.1 Z3 120.2 X4 120.9 Y4 121.0 Z4 120.7 X5 122.7 Y5 120.8 Z5 121.6 X6 120.6 Y6 121.9 Z6 122.1 X7 119.0 Y7 117.9 Z7 119.4 X8 118.9 Y8 118.3 Z8 118.3 X9 116.5 Y9 118.7 Z9 116.6 XA 237.5 YA 231.1 ZA 235.4 XB 229.1 YB 225.5 ZB 227.8 XC 223.5 YC 221.3 ZC 222.0 XD 217.6 YD 218.2 ZD 214.3 XE 209.2 YE 213.0 ZE 209.5

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264 Date2/16/2003 Temp72F Block #22 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 1 3396 2 2 3348 3 3 3529 4 4 3272 5 5 3461 6 6 3528 7 8 9 10 11 12 13 14 15 Date2/20/2003 Temp72F Block #22 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 70 3485.7 1 3389 2 67.3 3625.6 2 3397 3 68.3 3572.5 3 3788 4 69.7 3500.7 4 3839 5 65.1 3748.1 5 3852 6 66.3 3680.2 6 3831 7 63.8 3824.5 8 63.6 3836.5 9 63 3873.0 10 62.8 3885.4 11 62.3 3916.5 12 60.5 4033.1 13 240.8 3737.5 14 233.7 3861.8 15 228.7 3957.1

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265 Date2/27/2003 Temp72F Block #22 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 64.6 3777.1 1 3662 2 64.8 3765.4 2 3893 3 65 3753.8 3 3798 4 65 3753.8 4 4104 5 62.1 3929.1 5 3894 6 62.1 3929.1 6 4285 7 61.6 3961.0 8 61.6 3961.0 9 61.2 3986.9 10 61.6 3961.0 11 60.4 4039.7 12 58.8 4149.7 13 232.3 3874.3 14 226.7 3981.0 15 220.5 4104.3 Date3/6/2003 Temp72F Block #22 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 64.3 3794.7 1 3600 2 64.7 3771.3 2 3600 3 64.3 3794.7 3 4092 4 67 3641.8 4 3674 5 64.6 3777.1 5 4114 6 64.6 3777.1 6 3902 7 60.7 4019.8 8 60.2 4053.2 9 61.1 3993.5 10 60.9 4006.6 11 58.8 4149.7 12 58.4 4178.1 13 230.8 3899.5 14 225.3 4005.8 15 218.7 4138.1

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266 Date3/12/2003 Temp72F Block #22 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 1 3396 2 2 3672 3 3 3913 4 4 3935 5 5 4090 6 6 3998 7 8 9 10 11 12 13 14 15 Date3/27/2003 Temp72F Block #22 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 63.9 3818.5 1 3600 2 63.7 3830.5 2 3463 3 63.7 3830.5 3 3751 4 63.7 3830.5 4 3749 5 60.6 4026.4 5 4091 6 60.4 4039.7 6 3913 7 60.6 4026.4 8 60.6 4026.4 9 58.9 4142.6 10 59.1 4128.6 11 57.6 4236.1 12 57.0 4280.7 13 227.4 3957.8 14 220.6 4091.1 15 215.4 4201.5

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267 Date4/17/2003 Temp72F Block #22 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 63.4 3848.6 1 3600 2 64.1 3806.6 2 3601 3 63.3 3854.7 3 3841 4 63.6 3836.5 4 3828 5 60.9 4006.6 5 3913 6 60.4 4039.7 6 4068 7 60.3 4046.4 8 60.1 4059.9 9 58.5 4170.9 10 59.2 4121.6 11 57.3 4258.3 12 56.9 4288.2 13 227.3 3959.5 14 219.5 4111.6 15 214.3 4223.1 Date5/1/2003 Temp72F Block #22 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 64.0 3812.5 1 2 64.4 3788.8 2 3 63.2 3860.8 3 4 64.0 3812.5 4 5 60.4 4039.7 5 6 59.6 4094.0 6 7 59.7 4087.1 8 59.2 4121.6 9 61.8 3948.2 10 59.9 4073.5 11 57.9 4214.2 12 58.1 4199.7 13 225.6 3989.4 14 219.3 4115.4 15 215.2 4205.4

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268 Tomography Data Sheet for Test blocks. Date5/13/2003 Temp72F Block #22 Point # Time ( s) Point # Time ( s) Point # Time ( s) A1 64.1 B1 61.2 C1 59.4 A2 64.4 B2 61.7 C2 60.7 A3 64.9 B3 62.0 C3 60.5 A4 65.1 B4 61.6 C4 60.4 A5 65.3 B5 61.5 C5 60.2 A6 65.7 B6 61.4 C6 60.4 A7 65.2 B7 62.3 C7 60.6 A8 64.4 B8 61.7 C8 60.4 A9 65.4 B9 62.1 C9 60.0 D1 58.5 E1 55.9 D2 59.5 E2 56.9 D3 59.8 E3 56.9 D4 59.7 E4 58.2 D5 59.3 E5 58.6 D6 59.1 E6 57.4 D7 59.0 E7 57.6 D8 58.4 E8 56.8 D9 58.6 E9 55.4 X1 112.1 Y1 115.0 Z1 112.4 X2 115.9 Y2 115.7 Z2 115.0 X3 117.3 Y3 117.0 Z3 117.0 X4 118.3 Y4 118.7 Z4 118.1 X5 117.6 Y5 117.8 Z5 117.5 X6 116.8 Y6 118.0 Z6 117.9 X7 117.1 Y7 115.9 Z7 116.4 X8 116.7 Y8 115.7 Z8 116.5 X9 116.5 Y9 117.3 Z9 116.8 XA 235.2 YA 232.0 ZA 236.5 XB 225.8 YB 223.8 ZB 226.7 XC 219.1 YC 219.1 ZC 220.5 XD 214.4 YD 217.2 ZD 214.7 XE 208.4 YE 211.3 ZE 208.0

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269 Wavespeed vs. age (Block 22)3000 3200 3400 3600 3800 4000 4200 4400 02468101214Age (weeks)Wavespeed (m/s) Upvtop Ietop upvmid iemid upvbott iebott 28 days

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270 Date2/10/2003 Temp72F Block #23 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 1 3287 2 2 3272 3 3 3470 4 4 3430 5 5 3674 6 6 3600 7 8 9 10 11 12 13 14 15 Date1/20/2003 Temp72F Block #23 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 68.7 3493.4 1 3272 2 70 3428.6 2 3328 3 68.6 3498.5 3 3653 4 67.5 3555.6 4 3768 5 65.3 3706.0 5 4090 6 65.7 3683.4 6 3789 7 65.6 3689.0 8 65.1 3717.4 9 61.5 3967.5 10 64.4 3788.8 11 64.5 3782.9 12 63.7 3830.5 13 245.6 3664.5 14 235.8 3829.5 15 224.8 4030.2

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271 Date2/28/2003 Temp72F Block #23 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 66.5 3609.0 1 3462 2 66.7 3598.2 2 3601 3 67.7 3545.1 3 4000 4 65.1 3686.6 4 3830 5 64.3 3763.6 5 4002 6 63.2 3829.1 6 4090 7 63.6 3805.0 8 62.2 3890.7 9 60.0 4066.7 10 62.0 3935.5 11 62.6 3897.8 12 61.7 3954.6 13 234.8 3833.0 14 226.7 3983.2 15 218.5 4146.5 Date3/6/2003 Temp72F Block #23 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 65.4 3669.7 1 3397 2 65.6 3658.5 2 3670 3 64.7 3709.4 3 3752 4 63.4 3785.5 4 3751 5 62.4 3878.2 5 4009 6 62.4 3878.2 6 4001 7 63.3 3823.1 8 62.0 3903.2 9 58.3 4185.2 10 61.5 3967.5 11 61.2 3986.9 12 60.8 4013.2 13 232.1 3877.6 14 224.6 4020.5 15 216.3 4188.6

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272 Date3/20/2003 Temp72F Block #23 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 63.7 3767.7 1 3513 2 63.6 3773.6 2 3751 3 63.3 3791.5 3 3831 4 62.6 3833.9 4 3749 5 60.8 3980.3 5 4176 6 60.6 3993.4 6 4185 7 60.5 4000.0 8 59.6 4060.4 9 57.4 4250.9 10 59.7 4087.1 11 59.9 4073.5 12 59.5 4100.8 13 228.2 3943.9 14 219.6 4112.0 15 212.0 4273.6 Date3/27/2003 Temp72F Block #23 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 64.8 3703.7 1 2 64.8 3703.7 2 3 64.8 3703.7 3 4 63.9 3755.9 4 5 62.2 3890.7 5 6 61.6 3928.6 6 7 61.9 3909.5 8 60.8 3980.3 9 58.7 4156.7 10 60.9 4006.6 11 61.6 3961.0 12 61.0 4000.0 13 228.6 3937.0 14 220.5 4095.2 15 211.9 4275.6

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273 Date4/10/2003 Temp72F Block #23 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 65.6 3658.5 1 3598 2 65.6 3658.5 2 3599 3 65.6 3658.5 3 3693 4 64.2 3738.3 4 3674 5 62.1 3896.9 5 4298 6 61.9 3909.5 6 4287 7 63.1 3835.2 8 62.1 3896.9 9 60.0 4066.7 10 62.4 3910.3 11 61.9 3941.8 12 61.0 4000.0 13 227.0 3964.8 14 220.2 4100.8 15 214.3 4227.7 Date4/24/2003 Temp72F Block #23 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 65.8 3647.4 1 3618 2 65.8 3647.4 2 3581 3 65.1 3686.6 3 3693 4 64.1 3744.1 4 3680 5 61.7 3922.2 5 4050 6 62.5 3872.0 6 4150 7 63.7 3799.1 8 61.3 3947.8 9 60.0 4066.7 10 61.0 4000.0 11 62.3 3916.5 12 62.4 3910.3 13 227.3 3959.5 14 220.6 4093.4 15 213.5 4243.6

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274 Tomography Data Sheet for Test blocks. Date 5/13/2003 Block # 23 Point # Time ( s) Point # Time ( s) Point # Time ( s) A1 67.0 B1 61.7 C1 60.4 A2 66.9 B2 63.2 C2 61.9 A3 67.0 B3 64.3 C3 62.5 A4 67.6 B4 64.5 C4 62.0 A5 66.5 B5 63.3 C5 62.3 A6 65.9 B6 63.9 C6 62.1 A7 65.4 B7 63.3 C7 62.4 A8 65.4 B8 63.2 C8 60.8 A9 66.7 B9 64.3 C9 60.8 D1 58.1 E1 56.4 D2 59.6 E2 57.8 D3 60.7 E3 59.0 D4 61.3 E4 60.9 D5 61.3 E5 60.9 D6 61.1 E6 61.1 D7 61.2 E7 61.2 D8 60.6 E8 59.5 D9 58.7 E9 57.2 X1 115.7 Y1 116.2 Z1 117.0 X2 117.4 Y2 116.6 Z2 118.8 X3 118.4 Y3 116.8 Z3 118.1 X4 119.5 Y4 119.2 Z4 119.3 X5 119.3 Y5 118.5 Z5 118.6 X6 118.5 Y6 117.7 Z6 118.5 X7 117.6 Y7 116.4 Z7 118.5 X8 118.4 Y8 116.2 Z8 117.3 X9 115.9 Y9 116.5 Z9 116.0 XA 237.9 YA 233.5 ZA 239.5 XB 28.4 YB 225.6 ZB 226.8 XC 222.6 YC 220.2 ZC 220.4 XD 214.7 YD 216.4 ZD 214.9 XE 208.5 YE 211.0 ZE 207.4

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275 Waves Velocity vs. Age (Block 23)3000 3200 3400 3600 3800 4000 4200 4400 02468101214Age (weeks)Wave Velocity (m/s) Upvtop Ietop upvmid iemid upvbott iebott 28 days

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276 Date2/10/2003 Temp72F Block #24 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 1 3348 2 2 3332 3 3 3531 4 4 3547 5 5 3692 6 6 3674 7 8 9 10 11 12 13 14 15 Date2/21/2003 Temp72F Block #24 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 67 3641.8 1 3599 2 67.8 3598.8 2 3530 3 70.9 3441.5 3 3944 4 68.2 3577.7 4 3555 5 66.5 3669.2 5 4000 6 66.3 3680.2 6 3617 7 67.4 3620.2 8 65.1 3748.1 9 60.2 4053.2 10 61.5 3967.5 11 62.2 3922.8 12 61 4000.0 13 244.3 3684.0 14 232.2 3882.4 15 225.4 4006.2

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277 Date2/28/2003 Temp72F Block #24 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 65.8 3708.2 1 3601 2 65.4 3730.9 2 3600 3 65.7 3713.9 3 3731 4 65.3 3736.6 4 3675 5 62.5 3904.0 5 4000 6 62.2 3922.8 6 4009 7 61.0 4000.0 8 61.6 3961.0 9 59.1 4128.6 10 59.6 4094.0 11 59.6 4094.0 12 58.0 4206.9 13 235.6 3820.0 14 227.6 3960.9 15 219.7 4110.2 Date3/6/2003 Temp72F Block #24 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 64.0 3812.5 1 3599 2 64.3 3794.7 2 3529 3 64.7 3771.3 3 3752 4 65.0 3753.8 4 3672 5 61.1 3993.5 5 4080 6 61.1 3993.5 6 4090 7 62.0 3935.5 8 62.3 3916.5 9 57.9 4214.2 10 58.8 4149.7 11 58.7 4156.7 12 57.7 4228.8 13 234.5 3838.0 14 224.5 4015.6 15 219.4 4115.8

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278 Date3/20/2003 Temp72F Block #24 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 62.2 3922.8 1 3601 2 62.5 3904.0 2 3601 3 63.3 3854.7 3 3758 4 63.7 3830.5 4 3735 5 59.0 4135.6 5 4135 6 59.1 4128.6 6 4138 7 60.6 4026.4 8 60.9 4006.6 9 57.5 4243.5 10 59.2 4121.6 11 58.5 4170.9 12 57.8 4221.5 13 229.9 3914.7 14 220.4 4090.3 15 214.7 4205.9 Date3/27/2003 Temp72F Block #24 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 63.3 3854.7 1 2 63.3 3854.7 2 3 63.8 3824.5 3 4 64.8 3765.4 4 5 60.0 4066.7 5 6 59.9 4073.5 6 7 60.9 4006.6 8 61.6 3961.0 9 60.0 4066.7 10 59.4 4107.7 11 59.2 4121.6 12 58.8 4149.7 13 230.4 3906.3 14 221.5 4070.0 15 214.0 4219.6

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279 Date4/10/2003 Temp72F Block #24 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 1 63.8 3824.5 1 3770 2 63.8 3824.5 2 3581 3 64.0 3812.5 3 3600 4 65.0 3753.8 4 3674 5 60.5 4033.1 5 3829 6 60.5 4033.1 6 3947 7 60.5 4033.1 8 61.0 4000.0 9 59.8 4080.3 10 60.3 4046.4 11 60.0 4066.7 12 59.2 4121.6 13 229.5 3921.6 14 221.6 4068.1 15 215.3 4194.1 Date4/24/2003 Temp72F Block #24 Ultrasonic Pulse Velocity Testing Impact Echo Testing Point # Time ( s) Wave Velocity (m/s) Reading # Wave Velocity (m/s) 2 63.4 3848.6 2 3461 3 64.6 3777.1 3 3602 4 65.3 3736.6 4 3545 5 59.9 4073.5 5 3742 6 60.4 4039.7 6 3913 7 60.9 4006.6 8 62.0 3935.5 9 58.9 4142.6 10 62.7 3891.5 11 60.1 4059.9 12 60.9 4006.6 13 229.8 3916.4 14 219.1 4114.6 15 215.1 4198.0

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280 Side Tomography Data Sheet for Test blocks. Date5/13/2003 Block #24 Point # Time (ms) Point # Time (ms) Point # Time (ms) A1 68.7 B1 63.9 C1 60.3 A2 66.3 B2 63.5 C2 61.4 A3 66.5 B3 63.9 C3 61.6 A4 66.3 B4 64.1 C4 61.0 A5 66.1 B5 62.7 C5 61.5 A6 66.4 B6 63.3 C6 60.7 A7 65.4 B7 63.1 C7 60.5 A8 66.6 B8 63.0 C8 60.9 A9 69.0 B9 63.7 C9 61.1 D1 58.3 E1 56.7 D2 59.2 E2 56.5 D3 59.0 E3 57.9 D4 59.7 E4 58.5 D5 59.5 E5 59.0 D6 59.4 E6 58.3 D7 58.9 E7 56.9 D8 59.7 E8 56.1 D9 59.0 E9 58.1 X1 116.1 Y1 117.9 Z1 116.3 X2 117.8 Y2 117.0 Z2 118.3 X3 118.8 Y3 117.4 Z3 119.1 X4 118.0 Y4 118.7 Z4 120.1 X5 118.2 Y5 118.0 Z5 119.4 X6 117.9 Y6 118.8 Z6 120.0 X7 118.4 Y7 117.4 Z7 118.0 X8 118.2 Y8 117.5 Z8 117.9 X9 118.1 Y9 118.7 Z9 118.1 XA 238.1 YA 234.3 ZA 238.7 XB 229.1 YB 226.2 ZB 229.3 XC 223.0 YC 220.2 ZC 222.1 XD 215.4 YD 216.0 ZD 213.6 XE 209.3 YE 212.3 ZE 207.0

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281 Wave Velocity vs. Age Block 243000 3200 3400 3600 3800 4000 4200 4400 02468101214Age (weeks)Wave Velocity (m/s) Upvtop Ietop upvmid iemid upvbott iebott 28 days

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282 APPENDIX F SUMMARY OF STASTICAL RESULTS OF ULTRASONIC PULSE VELOCITY DATA ANOVA Summary Table (Block 5) Ultrasonic Pulse Velocity Results One Way ANOVA Bartlet's Test for Equal Variances Coefficient of Variation Date P-Value Are means significantl y different? (P < 0.05) Bartlet's Statistic P-Value Are variances significantly different? (P < 0.05) Coefficient of Variation for top row of block Coefficient of Variation for middle row of block Coefficient of Variation for bottom row of block 9-Feb 0.0001 Yes 0.0474 Ye s 1.61% 0.38% 1.50% 13-Feb 0.0002 Yes 0.1160 No 2.90% 0.83% 1.77% 21-Feb 0.0001 Yes 0.2238 No 0.77% 0.38% 0.97% 27-Feb 0.0001 Yes 0.8623 No 0.68% 0.86% 0.85% 7-Mar 0.0001 Yes 0.5068 No 0.86% 0.58% 0.45% 27-Mar 0.0005 Yes 0.3502 No 1.00% 0.77% 1.55% 17-Apr 0.0001 Yes 0.5198 No 1.03% 0.77% 1.37% 1-May 0.0001 Yes 0.5807 No 1.12% 0.62% 0.91% 10-May 0.0001 Yes 0.0002 Ye s 1.85% 0.52% 1.44% ANOVA Summary Table (Block 6) Ultrasonic Pulse Velocity Results One Way ANOVA Bartlet's Test for Equal Variances Coefficient of Variation Date P-Value Are means significantly different? (P < 0.05) Bartlet's Statistic PValue Are variances significantly different? (P < 0.05) Coefficient of Variation for top row of block Coefficient of Variation for middle row of block Coefficient of Variation for bottom row of block 9-Feb 13-Feb 0.0126 Yes 0.4935 No 3.26% 2.14% 1.68% 21-Feb 0.7103 No 0.3387 No 2.80% 2.35% 4.84% 27-Feb 0.0303 Yes 0.8246 No 1.41% 1.92% 1.52% 7-Mar 0.0026 Yes 0.8970 No 1.18% 1.49% 1.24% 27-Mar 0.2654 No 0.9266 No 1.85% 1.97% 2.21% 17-Apr 0.0162 Yes 0.6985 No 1.57% 2.20% 1.43% 1-May 0.0919 No 0.9351 No 1.90% 2.25% 2.17% 10-May 0.0001 Yes 0.0503 No 1.32% 2.06% 2.47%

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283 ANOVA Summary Table (Block 7) Ultrasonic Pulse Velocity Results One Way ANOVA Bartlet's Test for Equal Variances Coefficient of Variation Date P-Value Are means significantly different? (P < 0.05) Bartlet's Statistic PValue Are variances significantly different? (P < 0.05) Coefficient of Variation for top row of block Coefficient of Variation for middle row of block Coefficient of Variation for bottom row of block 9-Feb 0.4840 No 0.2859 No 1.05% 1.63% 2.46% 13-Feb 0.2617 No 0.8967 No 3.09% 2.46% 2.47% 21-Feb 0.1622 No 0.8008 No 1.17% 1.35% 1.63% 27-Feb 0.1643 No 0.8100 No 1.29% 1.47% 1.77% 7-Mar 0.3820 No 0.4426 No 1.19% 1.44% 2.24% 20-Mar 0.9304 No 0.2673 No 1.22% 1.67% 2.82% 27-Mar 0.6364 No 0.6740 No 1.55% 1.93% 2.46% 10-Apr 0.9988 No 0.3947 No 1.53% 2.09% 3.14% 24-Apr 0.9923 No 0.2143 No 1.12% 2.14% 3.01% 10-May 0.0001 Yes 0.0100 No 1.03% 1.47% 2.50% ANOVA Summary Table (Block 8) Ultrasonic Pulse Velocity Results One Way ANOVA Bartlet's Test for Equal Variances Coefficient of Variation Date P-Value Are means significantly different? (P < 0.05) Bartlet's Statistic PValue Are variances significantly different? (P < 0.05) Coefficient of Variation for top row of block Coefficient of Variation for middle row of block Coefficient of Variation for bottom row of block 9-Feb 0.0178 Yes 0.7487 No 2.70% 3.93% 3.45% 13-Feb 0.0088 Yes 0.1292 No 3.30% 1.43% 1.19% 21-Feb 0.0001 Yes 0.4125 No 0.38% 0.78% 0.57% 27-Feb 0.0001 Yes 0.7654 No 0.87% 0.83% 0.58% 7-Mar 0.0001 Yes 0.9828 No 0.93% 0.98% 0.99% 20-Mar 0.0013 Yes 0.5167 No 1.27% 1.23% 0.69% 27-Mar 0.0145 Yes 0.8310 No 1.12% 1.55% 1.30% 10-Apr 0.0171 Yes 0.8580 No 1.15% 1.42% 1.49% 24-Apr 0.0635 Yes 0.7266 No 1.33% 1.98% 1.85% 10-May 0.0001 Yes 0.9636 No 1.10% 1.15% 1.70%

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284 ANOVA Summary Table (Block 21) Ultrasonic Pulse Velocity Results One Way ANOVA Bartlet's Test for Equal Variances Coefficient of Variation Date P-Value Are means significantly different? (P < 0.05) Bartlet's Statistic PValue Are variances significantly different? (P < 0.05) Coefficient of Variation for top row of block Coefficient of Variation for middle row of block Coefficient of Variation for bottom row of block 21-Feb 0.0002 Yes 0.9871 No 2.19% 2.29% 2.15% 27-Feb 0.0027 Yes 0.6170 No 3.29% 1.91% 2.87% 6-Mar 0.0006 Yes 0.3567 No 1.46% 3.15% 2.18% 13-Mar 0.0001 Yes 0.9910 No 1.46% 1.32% 1.32% 27-Mar 0.0001 Yes 0.6936 No 2.13% 2.47% 1.48% 17-Apr 0.0001 Yes 0.8296 No 2.58% 2.25% 1.71% 1-May 0.0002 Yes 0.8383 No 1.85% 1.75% 2.22% 10-May 0.0001 Yes 0.3301 No 2.24% 2.89% 3.02% ANOVA Summary Table (Block 22) Ultrasonic Pulse Velocity Results One Way ANOVA Bartlet's Test for Equal Variances Coefficient of Variation Date P-Value Are means significantly different? (P < 0.05) Bartlet's Statistic PValue Are variances significantly different? (P < 0.05) Coefficient of Variation for top row of block Coefficient of Variation for middle row of block Coefficient of Variation for bottom row of block 21-Feb 0.0001 Yes 0.662 No 2.86% 1.97% 1.64% 27-Feb 0.0001 Yes 0.0981 No 1.35% 0.57% 1.95% 6-Mar 0.0023 Yes 0.6142 No 2.43% 3.50% 2.11% 13-Mar 0.0001 Yes 0.311 No 1.52% 0.69% 1.52% 27-Mar 0.0001 Yes 0.5793 No 1.50% 0.94% 1.59% 17-Apr 0.0004 Yes 0.0926 No 2.10% 0.79% 2.81% 1-May 0.0001 Yes 0.1732 No 2.02% 3.23% 3.16%

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285 ANOVA Summary Table (Block 23) Ultrasonic Pulse Velocity Results One Way ANOVA Bartlet's Test for Equal Variances Coefficient of Variation Date P-Value Are means significantly different? (P < 0.05) Bartlet's Statistic PValue Are variances significantly different? (P < 0.05) Coefficient of Variation for top row of block Coefficient of Variation for middle row of block Coefficient of Variation for bottom row of block 21-Feb 0.0002 Yes 0.5129 No 2.51% 1.61% 2.89% 27-Feb 0.0006 Yes 0.8762 No 3.06% 2.22% 2.58% 6-Mar 0.0004 Yes 0.7510 No 2.45% 1.87% 2.69% 20-Mar 0.0001 Yes 0.5818 No 1.91% 1.38% 2.33% 27-Mar 0.0017 Yes 0.6626 No 2.69% 2.08% 3.24% 10-Apr 0.0072 Yes 0.8664 No 3.55% 2.57% 3.13% 24-Apr 0.0192 Yes 0.8980 No 3.32% 2.89% 3.59% 10-May 0.0001 Yes 0.0430 Ye s 2.44% 2.24% 3.79% ANOVA Summary Table (Block 24) Ultrasonic Pulse Velocity Results One Way ANOVA Bartlet's Test for Equal Variances Coefficient of Variation Date P-Value Are means significantly different? (P < 0.05) Bartlet's Statistic PValue Are variances significantly different? (P < 0.05) Coefficient of Variation for top row of block Coefficient of Variation for middle row of block Coefficient of Variation for bottom row of block 21-Feb 0.0001 Yes 0.3826 No 2.56% 2.73% 1.21% 27-Feb 0.0001 Yes 0.9023 No 1.21% 0.95% 1.14% 6-Mar 0.0001 Yes 0.8016 No 0.88% 1.07% 1.13% 20-Mar 0.0001 Yes 0.7788 No 1.04% 1.44% 1.14% 27-Mar 0.0001 Yes 0.9671 No 1.34% 1.24% 1.38% 10-Apr 0.0001 Yes 0.2259 No 1.57% 0.60% 1.43% 24-Apr 0.002 Yes 0.4473 No 1.80% 1.69% 2.94% 10-May 0.0001 Yes 0.1508 No 2.66% 1.32% 1.98%

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286 LIST OF REFERENCES American Concrete Institut e. Committee 224. (1993). Causeses, Evaluation and Repair of Cracks in Concrete Structures (No. 0-87031-006-2). Detroit, Michigan: American Concrete Institute. American Concrete Institut e. Committee 546. (1996). Concrete Repair Guide (No. 087031-022-4). Detroit, Michigan: Am erican Concrete Institute. American Concrete Institut e. Committee 224. (1998). Nondestructive Test Methods for Evaluation of Concre te in Structures Detroit, Michigan: American Concrete Institute. ASTM (2001a). Standard Test for the Compressive Stre ngth of Cylindrical Concrete Specimens, C39-01. West Conshohocken, Penns ylvania: American Society for Testing and Materials. ASTM (2001b). Standard Test for the Fundamenta l Transvrese, Longitudional and Torsional Resonant Frequencie s of Concrete Specimens, C215-97. West Conshohocken, Pennsylvania: American Society for Testing and Materials. ASTM (2001c). Standard Test Method for Liqui d Penetrant Examination, E165-95. West Conshohocken, Pennsylvania: American Society for Testing and Materials. ASTM (2001d). Standard Test for the Pulse Velocity Through Concrete, C597-97. West Conshohocken, Pennsylvania: American Society for Testing and Materials. ASTM (2002a). Dye Penetration of Solid Fiberg lass Reinforced Pultruded Stock, D511796. West Conshohocken, Pennsylvania: American Society for Testing and Materials. ASTM (2002b). Standard Guide for Acoustic Examination of Small Parts, E1932-97. West Conshohocken, Pennsylvania: American Society for Testing and Materials. ASTM (2002c). Standard Guide for Mounting Piezoelectric Acoustic Emission Sensors E650-97. West Conshohocken, Pennsylvani a: American Society for Testing and Materials. ASTM (2002d). Standard Practice for Characterizing Acoustic Emission Instrumentation, E750-98. West Conshohocken, Pe nnsylvania: American Society for Testing and Materials.

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287 ASTM (2002e). Standard Practices for Thermal Neutron Radiography of Materials, E748-02. West Conshohocken, Pennsylvani a: American Society for Testing and Materials. Benedetti, A. (1998). On the Ultrasonic Pu lse Propagation into Fire Damaged Concrete. ACI Structural Journal, 95(3), 259-271. Bergander, M. J. (2003). EMAT Thickness Meas urement for Tubes in Coal-fired Boilers. Applied Energy, 74(3-4), 439-444. Bhide, S. (2001). Material Usage and Condition of Existing Bridges in the U.S. Skokie, Illinois: Portland Cement Association. Binda, L., Lenzi, G., & Saisi, A. (1998). NDE of Masonry Structures: Use of Radar Tests for the Characterization of Stone Masonries. NDT & E International, 31(6), 411419. Binda, L., Saisi, A., & Tiraboschi, C. (2001). Application of Sonic Tests to the Diagnosis of Damaged and Repaired Structures. NDT & E International, 34(2), 123-138. Boving, K. G. (1989). NDE Handbook : Non-Destructi ve Examination Methods for Condition Monitoring. London: Butterworths. Boyd, A. J., Mindess, S., & Skalny, J. (2001). Designing Concrete for Durability. Materiales De Construccion, 51(263-64), 37-53. Carino N.J. 2001, The Impact-Echo Met hod: An Overview Buildings and Fire Research Laboratory, NIST Gaithersburg, MD. Reprinted from the Proceedings of the 2001 Structures Congress and Exposition, ASCE, May 21-23 Washington D.C. Chang P.C. Editor. Casas, J. R., Klaiber, F. W., Mari, A. R ., Universidad Politecnica de Catalunya, & Iowa State University. (1996). Recent Advances in Bridge Engineering: Evaluation, Management and Repair: Proceedings of the US-Europe Workshop on Bridge Engineering, Barcelona, 15-17 July 1996 (1st ed.). Barcelona, Spain: Artes Graficas Torres. Casper, J. (2002). Human-Robot Interactions During the Robot-Assisted Urban Search and Rescue Response at th e World Trade Center. Thesis (M.S.C.S.) University of South Florida. Cawley, P., & Adams, R. D. (1988). The M echanics of the Coin -Tap Method of NonDestructive Testing. Journal of Sound and Vibration, 122(2), 299-316. Colla, C., Burnside, C. D., Clark, M. R ., Broughton, K. J., & Forde, M. C. (1998). Comparison of Laboratory and Simulated Data for Radar Image Interpretation. NDT & E International, 31(6), 439-444.

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288 Cornwell, I., & McNab, A. (1999). Towards Au tomated Interpretation of Ultrasonic NDT Data. NDT & E International, 32(2), 101-107. Davis, A. G. (1997). A Place for Nondestruc tive Evaluation in the Maintenance of Our Concrete Infrastructure. Materials Evaluation, 55(11), 1234-1237. Davis, A. G. (1999). Review of Nondes tructive Evaluation Techniques of Civil Infrastructure. Journal of Performance of Constructed Facilities, 11(4), 47-48. Davis, A. G. (2003). The Nondestructive Im pulse Response Test in North America: 1985-2001. NDT & E International, 36(4), 185-193. Davis, A. G., Evans, J. G., & Hertlein, B. H. (1997). Nondestructive Evaluation of Concrete Radioactive Waste Tanks. Journal of Performance of Constructed Facilities, 11(4), 161-167. Davis, A. G., Olson, C. A., & Michols, K. A. (2001). Evaluation of Historic Reinforced Concrete Bridges. Paper Presented at the Procee dings of the 2001 Structural Congress and Exposition, held May 21-23, 2001, Washington, D.C. FHWA, U.S. Department of Transportation. Federal Highway Administration. (1995). Recording and Coding Guide for the Stru cture Inventory and Appraisal of the Nations Bridges (No. FHWA-PD-96-001). Washington, DC: U.S. Department of Transportation. Green, R. E. (2002). Noncontact Acous tical Techniques for Nondestructive Characterization of Mate rials and Structures. International Applied Mechanics, 38(3), 253-259. Gudra, T., & Stawiski, B. ( 2000). Non-Destructive Strength Characterization of Concrete Using Surface Waves. NDT & E International, 33(1), 1-6. Guenther, N. (1999). Internship Report (No. SS99). Soquel, Ca lifornia: Ultrasonic Devices, Inc. Halliday, D., Resnick, R., & Walker, J. (1997). Fundamentals of Physics (5th ed.). New York: Wiley. Hamilton, H. R., & Levar, J. M. (2003) Nondestructive Evaluation of Carbon FiberReinforced Polymer-Concrete Bond Using Infrared Thermography. ACI Materials Journal, 100(1), 63-72. Hearn, S. W., & Shield, C. K. (1997). Acous tic Emission Monitoring as a Nondestructive Testing Technique in Reinforced Concrete. ACI Materials Journal, 94(6), 510-519. Hellier, C. (2001). Handbook of Nondestructive Evaluation. New York: McGraw-Hill.

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289 Institute of British Standards. (1986). Recommendations for Surface Hardness Testing by Rebound Hammer (No. 1881 pt. 202:1986). United Kingdom: British Standards Institute. Kaiser, H., & Karbhari, V. M. (2002). Quality and Monitoring of Structural Rehabilitation Measures (Contract #18347): Oregon Depart ment of Transportation. Kearl, P. M. (1997). Observations of Partic le Movement in a Monitoring Well Using the Colloidal Borescope. Journal of Hydrology, 200(1-4), 323-344. Krause, H. J., Wolf, W., Glaas, W., Zimmerma nn, E., Faley, M. I., Sawade, G., et al. (2002). SQUID Array for Magnetic Inspecti on of Prestressed Concrete Bridges. Physica C, 368(1-4), 91-95. Krause, M., Mielentz, F., Milman, B., Mulle r, W., Schmitz, V., & Wiggenhauser, H. (2001). Ultrasonic Imaging of Concrete Members Using an Array System. NDT & E International, 34(6), 403-408. Krautkramer, J., & Krautkramer, H. (1990). Ultrasonic Testing of Materials (4th fully rev. ed.). New York: Springer-Verlag. Kulynyak, D. (2000). Ivan Pului, the Discoverer of X-rays. The Ukrainian Weekly, 68(28). Lane, D. S. (1998). Evaluation of Concrete Charac teristics for Rigid Pavements. Charlotsville, Virginia: Virginia Transportation Research Council. Lew, H. S., & ACI Committee 228 Nondest ructive Testing of Concrete. (1988). Nondestructive Testing. Detroit: American Concrete Institute. Li, F. M., & Li, Z. J. (2000). Acoustic Emission Monitoring of Fracture of FiberReinforced Concrete in Tension. ACI Materials Journal, 97(6), 629-636. Maldague, X. (2001). Theory and Practice of Infrared Technology for Nondestructive Testing. New York: Wiley. Malhotra, V. M. (1984). In Situ/Nondestructive Testing of Concrete. Detroit, Michigan: American Concrete Institute. Malhotra, V. M., & Carino, N. J. (1991). CRC Handbook on Nondestructive Testing of Concrete. Boca Raton: CRC Press. Malhotra, V. M., & Mehta, P. K. (1994). Concrete Technology: Past, Present, and Future: Proceedings of V. Mohan Malhotra Symposium. Detroit, Michigan: American Concrete Institute.

PAGE 306

290 Martin, J., Broughton, K. J., Giannopolous, A., Ha rdy, M. S. A., & Forde, M. C. (2001). Ultrasonic Tomography of Grouted Duct Post-Tensioned Reinforced Concrete Bridge Beams. NDT & E International, 34(2), 107-113. Miller, R. K. (1985). Bridge Testing (No. TR-103-68-12/85). Princeton Junction, New Jersey: Physical Ac oustic Corporation. Mindess, S., Young, J. F., & Darwin, D. (2003). Concrete (2nd ed.). Upper Saddle River, New Jersey: Prentice Hall. Murphy, R. (2000). Introduction to AI Robotics. Cambridge, Mass achusetts: MIT Press. NBI (2003) http://www.nationalbridgeinvent ory.com/new_page_1.htm Last accessed August 20, 2003 Neville, A. M. (1996). Properties of Concrete (4th and final ed.). New York: J. Wiley. NOAA (2003) http://www.srh.noaa.gov/tulsa/cl imate/rh.html Last accessed August 20, 2003 Ohtsu, M., Uchida, M., Okamoto, T., & Yuyama, S. (2002). Damage Assessment of Reinforced Concrete Beams Qualified by Acoustic Emission. ACI Structural Journal, 99(4), 411-417. Papadakis, E. P. (1999). Ultrasonic Instruments and Devices: Reference for Modern Instrumentation, Techniques, and Technology. San Diego, California: Academic Press. Pessiki, S. P., & Carino, N. J. (1988). Setting Time and Strength of Concrete Using the Impact-Echo Method. ACI Materials Journal, 85(5), 389-399. Popovics, J. S., Achenbach, J. D., & Song, W. J. (1999). Applicati on of New Ultrasound and Sound Generation Methods for Testing Concrete Structures. Magazine of Concrete Research, 51(1), 35-44. Popovics, S. (2001). Analysis of the Concrete Strength Versus Ultrasonic Pulse Velocity Relationship. Materials Evaluation, 59(2), 123+. Popovics, S., Bilgutay, N. M., Karaoguz, M., & Akgul, T. (2000). High-Frequency Ultrasound Technique for Testing Concrete. ACI Materials Journal, 97(1), 58-65. Qasrawi, H. Y. (2000). Concrete Strengt h by Combined Nondestructive Methods Simply and Reliably Predicted. Cement and Concrete Research, 30(5), 739-746. Reese, R. T., Kawahara, W. A., & Society for Experimental Mechanics (U.S.). (1993). Handbook on Structural Testing. Englewood Cliffs, New Jersey: Fairmont Press. Ryall, M. J. (2001). Bridge Management. Boston: Butterworth-Heinemann.

PAGE 307

291 Salawu, O. S. (1997). Detection of Structur al Damage through Changes in Frequency: A Review. Engineering Structures, 19(9), 718-723. Sansalone, M., & Streett, W. B. (1997). Impact-Echo: Non-Destructive Evaluation of Concrete and Masonry. Ithaca, New York: Bullbrier Press. Scott, I. G. (1991). Basic Acoustic Emission. New York: Gordon and Breach Science Publishers. Shaw, R. E. (2002). Ultrasonic Testing Proce dures, Technician Skills, and Qualifications. Journal of Materials in Civil Engineering, 14(1), 62-67. Sison, M., Duke, J. C., Clemena, G., & Lo zev, M. G. (1996). Acoustic Emission: A Tool for the Bridge Engineer. Materials Evaluation, 54(8), 888+. Sypeck, D. J. (1996). Damage Evolution In Titanium Matrix Composites. Unpublished Ph.D. Dissertation, University of Virginia, Charlottesville. Tam, M. T., & Weng, C. C. (1995). AcousticEmission Kaiser Effect in Fly-Ash Cement Mortar under Compression. Journal of Materials in Civil Engineering, 7(4), 212217. Washer, G. A. (1998). Developments for th e Non-Destructive Evaluation of Highway Bridges in the USA. NDT & E International, 31(4), 245-249. Weil, G. J., & Rowe, T. J. (1998). Nondestru ctive Testing and Repa ir of the Concrete Roof Shell at the Seattle Kingdome. NDT & E International, 31(6), 389-400. Wells, P. N. T. (1974). Medi cal Ultrasonic Diagnostics. Electronics and Power, 20(9), 367-370. Wu, H. D., & Siegel, M. ( 2000). Correlation of Accelerometer and Microphone Data in the "Coin Tap Test". IEEE Transactions on Instrumentation and Measurement, 49(3), 493-497. Wu, K., Chen, B., & Yao, W. (2000). St udy on the AE Characteristics of Fracture Process of Mortar, Concrete and Steel -Fiber-Reinforced Concrete Beams. Cement and Concrete Research, 30(9), 1495-1500. Yan, T Lin, Y. C.,& Lai, C. P., (2003). Pred iction of Ultrasonic Puls e Velocity (UPV) in Concrete. ACI Materials Journal, 100(1), 21-28. Yeih, W., & Huang, R. (1998). Detection of the Corrosion Damage in Reinforced Concrete Members by Ultrasonic Testing. Cement and Concrete Research, 28(7), 1071-1083. Young, J. F., Mindess, S., Gray, R. J., & Bentur, A. (1998). The Science and Technology of Civil Engineering Materials: Prentice Hall.

PAGE 308

292 Yuyama S., Okamoto, T., Tomita, R., Fugiwara H., Kajio S., Ohtsu, S., & Shigeishi M. (1992). Discrimination of Cracking Width De veloped in Reinforced Concrete Structures by Acoustic Emission. Seattle, Washington: Physical Acoustics Corporation.

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293 BIOGRAPHICAL SKETCH Christopher C. Ferraro was born March 1, 1974, in Huntington, New York, to Ronald and Victoria Ferraro. He gradua ted from Walt Whitman High School in June 1992. He received his Associate of Arts de gree in December of 1994 from Palm Beach Community College, and transferred to the Univ ersity of Florida to pursue a Bachelor of Science in Civil Engineering in the summer of 1995. While attending the Un iversity of Florida full time, Christopher worked part tim e for the Department of Civil Engineering, for two years as a teaching assi stant and research assistant for Dr. Fazil T. Najafi. He received his Bachelor of Sc ience in Civil Engineering in May of 1998, graduating with honors. Upon graduation he relocated to Long Isla nd, New York, and worked full time in Manhattan, New York, as an Engineer Intern for Law Engineering Inc. After a year with Law, he transferred to STV Incorporated where he worked on several inspection projects under the supervision of Ms. Marjorie M. Lync h, P.E. who aided him in gaining expertise and knowledge which inspired him to resume his education. Christopher continued with his education, entering graduate school to pursue a Master of Engineering in the Materials Group of the Civil and Coastal Engineering Department in August 2000. After graduati ng from the University of Florida with a Master of Engineering, Christopher plan s on working with Andrew Boyd in the Department of Civil and Coastal Engineering fo r the fall of 2003, afte r which he plans to

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294 pursue a career in the exciting and challeng ing field of civil engineering inspection, research and design.


Permanent Link: http://ufdc.ufl.edu/UFE0001325/00001

Material Information

Title: Advanced nondestructive monitoring and evaluation of damage in concrete materials
Physical Description: Mixed Material
Language: English
Creator: Ferraro, Christopher C. ( Dissertant )
Boyd, Andrew J. ( Thesis advisor )
Publisher: University of Florida. Coastal and Oceanographic Dept., University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2003
Copyright Date: 2003

Subjects

Subjects / Keywords: Civil and Coastal Engineering thesis, M.E
Dissertations, Academic -- UF -- Civil and Coastal Engineering

Notes

Abstract: The objective of this work is to perform research that will enable the FDOT to nondestructively assess and monitor the quality of in-situ concrete bridge structures. As part of the research, a literature review of relevant nondestructive methods was performed. Also survey of relevant bridge structures within the FDOT's bridge database system was conducted in an attempt to categorize prevalent bridge deficiencies occurring throughout the state. Field research concentrated on the application of the most appropriate nondestructive testing (NDT) methods and their application to materials assessment and interpretation of typical NDT data. The attempt of qualifying the onset of damage was attempted using the applicable NDT method. General material properties of good quality bridge materials were tested nondestructively. Laboratory research focused on the establishment of the nondestructive material properties and their relationship to strength properties, which were obtained via the use of destructive tests after NDT was performed. Other laboratory research monitored the changes of NDT data within concrete samples under constant exposure to severe environments. This experiment was designed to differentiate the effects certain solutions have on field-size samples of concrete when exposed over periods of time. The primary objective of this experiment was to observe the effect of exposure of concrete to sulfate solutions with respect to surface wave velocity and through wave velocity. Field studies suggest that the wave velocity of concrete samples decreases with increasing damage. However, the lack of controlled experiments, involving continuous laboratory monitoring, with respect to stress wave velocity and damage prevents the quantification of the two parameters.
Abstract: concrete, evaluation, materials, monitoring, ndt, nondestructive, testing
General Note: Title from title page of source document.
General Note: Includes vita.
Thesis: Thesis (M.E.)--University of Florida, 2003.
Bibliography: Includes bibliographical references.
General Note: Text (Electronic thesis) in PDF format.

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 002987965
System ID: UFE0001325:00001

Permanent Link: http://ufdc.ufl.edu/UFE0001325/00001

Material Information

Title: Advanced nondestructive monitoring and evaluation of damage in concrete materials
Physical Description: Mixed Material
Language: English
Creator: Ferraro, Christopher C. ( Dissertant )
Boyd, Andrew J. ( Thesis advisor )
Publisher: University of Florida. Coastal and Oceanographic Dept., University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2003
Copyright Date: 2003

Subjects

Subjects / Keywords: Civil and Coastal Engineering thesis, M.E
Dissertations, Academic -- UF -- Civil and Coastal Engineering

Notes

Abstract: The objective of this work is to perform research that will enable the FDOT to nondestructively assess and monitor the quality of in-situ concrete bridge structures. As part of the research, a literature review of relevant nondestructive methods was performed. Also survey of relevant bridge structures within the FDOT's bridge database system was conducted in an attempt to categorize prevalent bridge deficiencies occurring throughout the state. Field research concentrated on the application of the most appropriate nondestructive testing (NDT) methods and their application to materials assessment and interpretation of typical NDT data. The attempt of qualifying the onset of damage was attempted using the applicable NDT method. General material properties of good quality bridge materials were tested nondestructively. Laboratory research focused on the establishment of the nondestructive material properties and their relationship to strength properties, which were obtained via the use of destructive tests after NDT was performed. Other laboratory research monitored the changes of NDT data within concrete samples under constant exposure to severe environments. This experiment was designed to differentiate the effects certain solutions have on field-size samples of concrete when exposed over periods of time. The primary objective of this experiment was to observe the effect of exposure of concrete to sulfate solutions with respect to surface wave velocity and through wave velocity. Field studies suggest that the wave velocity of concrete samples decreases with increasing damage. However, the lack of controlled experiments, involving continuous laboratory monitoring, with respect to stress wave velocity and damage prevents the quantification of the two parameters.
Abstract: concrete, evaluation, materials, monitoring, ndt, nondestructive, testing
General Note: Title from title page of source document.
General Note: Includes vita.
Thesis: Thesis (M.E.)--University of Florida, 2003.
Bibliography: Includes bibliographical references.
General Note: Text (Electronic thesis) in PDF format.

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 002987965
System ID: UFE0001325:00001


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ADVANCED NONDESTRUCTIVE MONITORING AND EVALUATION OF
DAMAGE IN CONCRETE MATERIALS




















By

CHRISTOPHER C. FERRARO


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF ENGINEERING

UNIVERSITY OF FLORIDA


2003

































Copyright 2003

by

Christopher C. Ferraro
































This thesis is dedicated to my loving family, my parents, Ronald and Victoria Ferraro,
my sister Alicia Ferraro, my brother Ronald Ferraro Jr. and to my loving girlfriend Aliza
Bar-David as they have offered their support and love throughout this endeavor. It is
with the love and support of my family and friends that I am able to reach my goals.















ACKNOWLEDGMENTS

The author would like to thank all of the members of his supervisory committee for

their help and ideas throughout this effort. Dr. Andrew Boyd, the committee chair,

provided valuable time and knowledge of the subject, as well as financial support,

making this research successful.

Acknowledgement is owed to Dr. H.R. Hamilton and Dr. David Bloomquist for

their contribution of time and knowledge, which provided to be invaluable assistance and

guidance during this effort.

The author would also like to express gratitude to all of those within the

Department of Civil and Coastal Engineering Department including George Lopp, Chuck

Broward and Scott Cumming.

For her enormous efforts the author would like to extend his gratitude to Ms. Eileen

Czarnecki. Her time and assistance were crucial to the completion of this research in a

timely manner.

The author would also acknowledge PhD candidates Christos Drakos and Forrest

Masters. Their mentoring and assistance on a professional and personal level were greatly

appreciated.

The author would also like to thank his best friend, Aliza Bar-David, for the

unyielding support and patience she offered me during the research and writing of this

thesis.
















TABLE OF CONTENTS
page

A C K N O W L E D G M E N T S ................................................................................................. iv

L IS T O F T A B L E S .................................................................... ......... .... ....... ....... v iii

LIST OF FIGURES ......... ......................... ...... ........ ............ ix

A B S T R A C T .......................................... ..................................................x v

CHAPTER

1 IN TRODU CTION ................................................. ...... .................

2 LITER A TU R E REV IEW ............................................................. ....................... 4

Introduction to N ondestructive Testing ................................... ........... ...................4
L literature R review ................. ..... .... .......................... ...... ........ .......... ...... .
V isual Inspection ................................................................ .. ......... 4
Liquid Penetrant M ethods ............................................................................10
Acoustic Sounding.............. ..... .. ............. ....... .......13
Surface H ardness M ethods ....................................................................18
Penetration R resistance M ethods................................... ..................................... 20
P u llo u t T e st................................................... ................ 2 1
B re ak -O ff T e st ............................................................................................... 2 3
U ltrasonic Testing .................................. .. ............. ............ 25
Im pact E cho ............................................................................................... 53
A acoustic Em mission .......................................... ........ ........ .. .......... 1
Im pulse R response .............................................................. .. ...... .......... 95
M agnetic M ethods ..................................... ...... .. ... ..... ............... 102
G round Penetrating R adar ........................................... ................................ 107
Resonant Frequency .................. ......................... ... ........ .............. 111
Infrared Thermography ................................. .......... .................... 115
Radioactive Testing ................. .......................... ..... .... ................. 123

3 SURVEY OF RELEVANT BRIDGE STRUCTURES IN FLORIDA....................129

D definition of Sufficiency R ating ................................................... .....................130
Methodology ............... .............................. 131
Results ......................................... ................. 134
C o n c lu sio n s......................................................................................................... 1 3 5


v











4 B R ID G E IN SPE C TIO N S ........................................... ..................... ............... 137

Document Review ................... ........................... .........137
N D T M methods U sed for Inspection........................................................................ 138
B ahia H on da B ridg e ......................................................................... ................... 13 8
Site Inform action ......... ......................................... ........ .... ... 138
P ro c ed u re s ...............................................................13 8
R e su lts ...............................................................1 3 9
C o n clu sio n s ...............................................................14 1
Niles Channel Bridge.................................................. 147
S ite In fo rm atio n ............................................................................................ 14 7
P ro cedu res ...............................................................14 7
R e su lts ...............................................................14 8
C o n clu sio n s ...............................................................15 0
Sebastian R iver B ridge .................................... .................... .... 153
S ite In fo rm atio n ............................................................................................ 1 5 3
P ro c ed u re s ...............................................................15 3
R e su lts ...............................................................1 5 3
C o n clu sio n s ...............................................................15 5
W abasso B ridge .............................................................................................. .......158
S ite In fo rm atio n ............................................................................................ 15 8
P ro c ed u re s ...............................................................15 8
R e su lts ...............................................................1 5 9
C o n clu sio n s ...............................................................16 0
S eb astian In let B ridg e .......................................................................................... 16 3
S ite In fo rm atio n ............................................................................................ 16 3
P ro cedu res ...............................................................16 4
R e su lts ...............................................................1 6 5
C o n clu sio n s ...............................................................16 6

5 NONDESTRUCTIVE LABORATORY SPECIMEN TESTING ............................169

P rio r R e se a rc h ...................................................................................................... 1 6 9
M eth odology ...............................170...............................
P procedure .. ....... ........................................................... ..................................... 170
R results and D discussion ......................................173............................
C o n c lu sio n s.......................................................................................................... 1 7 9

6 LABORATORY SIMULATION OF DAMAGE OBSERVED IN THE FIELD ....181

P rio r R e se a rc h ...................................................................................................... 1 8 1
M eth odology ...............................182...............................
P procedure .. ....... ........................................................... ..................................... 182
R results and D discussion ......................................186............................
Conclusions ......................................... 192









APPENDIX

A SUMMARY OF PONTIS RESULTS ........................................... ... ............193

B SUMMARY OF DEFICIENT BRIDGES ...............................................................211

C NDT DATA AND RESULTS FROM BRIDGE TESTING ...................................212

D LABORATORY DATA OF CYLINDER SPECIMENS........................................225

E LABORATORY DATA AND GRAPHICAL RESULTS OF LARGE SCALE
SPECIM EN S ..................................... ................................ .......... 231

F SUMMARY OF STASTICAL RESULTS OF ULTRASONIC PULSE
V E L O C IT Y D A T A ......................................................................... ...................282

L IST O F R EFER EN CE S .......................................................................... ..............286

B IO G R A PH IC A L SK E T C H ........................................ ............................................293
















LIST OF TABLES


Table pge

2.1 Standard sizes of pin and probe used for penetration tests. ............. ...............21

2.2 Acoustic velocities of common materials used in construction ............................37

2.3 Relationship between pulse velocity and concrete quality....................................52

2.4 Emissivities of common engineering materials ................................ ...............1.18

5.1 Mixture proportions for NDT and strength tests.......................... ...............170

5.2 Compressive strength vs. resonant frequency of concrete samples .....................178

6.1 Mixture proportions for NDT and strength tests.............................................183
















LIST OF FIGURES


Figure pge

2.1 Flexible borescope................................ ...... ... ...... ........7

2.2 Flexible borescope and m monitor ........................................................................ ........7

2.3 Rigid borescope ..................................................................... ...............

2.4 Robot used for visual survey at the WTC disaster site ...........................................9

2.5 Robot used for visual survey at the WTC disaster site ........................................10

2.6 Cracks in concrete pavement with moisture present..............................................11

2.7 Contact angles for various liquids................................ ......................... ........ 12

2.8 Coin tap test results (a) Force-time histories of solid and disbonded areas of a
carbon fiber reinforced skinned honeycomb structure, (b) Spectra of time
h isto rie s ............................................................................. 14

2.9 Illustration of typical pullout test ..................................... ........................ .......... 22

2.10 Typical cross section of the breakoff test, all dimensions in mm ............................24

2.11 Sinusoidal oscillation of a loaded spring....................................... ............... 27

2.12 M odel of an elastic body ................................................ .............................. 28

2.13 Graphical illustration of Snell's law ..................................... ........................ 30

2.14 A portable ultrasonic testing device used at the University of Florida.................32

2.15 Schem atic of a pulse velocity apparatus ...................................... ............... 34

2.16 Idealized scans of a material defect: a) A-scan, b) B-scan, c) C-scan, ....................35

2.17 Typical ultrasonic test procedure ........................................ ......................... 36

2.18 Methods of pulse velocity measurements: a) direct method, b) indirect method,
c) surface m ethod ......................... ........ ...... .. ..... ............... 39









2.20 Schematic of pulse-echo and pitch and catch techniques .....................................42

2.21 Pulse echo schematic (a)Typical test setup, and (b) resulting display ...................43

2.22 Reflections of stress waves from internal discontinuities .....................................44

2.23 Signal scatter due to uneven reflecting surface morphology .................................44

2.24 Setup of ultrasonic tomographc ray paths............. ...............................................48

2.25 M easurem ent of crack depth ............................................................................. 50

2.26 Schematic of a typical piezoelectric transducer used for impact echo testing .........55

2.27 View of a typical impact-echo equipment system..................................................57

2.28 Illustration of typical wave propagation through a cross section of a solid.............58

2.29 Illustration of wave propagation model through a cross section of a solid .............59

2.30 The typical force-time function for the elastic impact of a sphere on a solid..........60

2.31 Example of frequency analysis using FFT (a) represents the frequency
distribution, (b) represents the corresponding amplitude spectrum .......................62

2.32 Plots of P, S and R-waves at various times after an impact (a) 125 ts,
(b)150 |ts, (c)200 |ts and (d) 250 s............................................... .....................64

2.33 The ray path of typical P-wave propagation through a solid media.........................64

2.34 Impact echo ray paths (a) A phase change at both boundaries(b) A phase
change at upper boundary only ........................................ .......................... 67

2.35 Schematic representations of (a) P-wave ray reflections and (b) the resulting
idealized w aveform ......................... ........................ .. .. ....... ........... 68

2.36 Actual waveform on an impact-echo test plate ................................. ............... 70

2.37 Schematic representation of the test set up for wave speed measurements ............71

2.38 Example waveform obtained in wave speed measurements ..................................72

2.39 Illustration of the smallest detectable crack and its dependency on depth...............73

2.40 A crack at depth 'd' gives the same response as a void at that depth ....................74

2.41 Surface-opening cracks: (a) perpendicular, (b) inclined, and (c) curved.................76









2.42 Measuring the depth of a surface-opening crack: (a) schematic of experimental
test setup, and (b) sample waveform s ........................................... ............... 76

2.43 The impact-echo response of a concrete slab on soil subgrade: (a) cross-section,
(b) w aveform and (c) spectrum ........................................ .......................... 78

2.44 The impact-echo response obtained from a concrete slab at a location where a
void exists in the soil subgrade (a) cross-section; (b) waveform; and (c)
sp e ctru m .......................................................................... 7 8

2.45 Burst acoustic emission signal with properties ................................ ............... 82

2.46 A acoustic em mission process .............................................. ............................. 82

2.47 Basic setup of acoustic emission equipment .............................. ............... 85

2.48 V various acoustic em mission sensors ........................................ ........ ............... 85

2.49 Transient recorder with multiple output acoustic emission signals .........................88

2.50 Acoustic em mission calibration block ............................................. ............... 89

2.51 Placement of sensors on a concrete cube ...................................... ............... 92

2.52 The instrumented sledgehammer and geophone used in the IR method................97

2.53 Schematic of the impulse response technique............ .......................................97

2.54 Theoretical impulse response mobility spectrum.............. .... ...............98

2.55 Typical mobility plot for sound concrete ...................................... ............... 99

2.56 M obility plots for sound and debonded concrete..................................................100

2.57 M obility plots for sound and delaminated concrete..............................................101

2.58 Schematic of a typical magnetic field induced by an electric current....................103

2.59 Covermeter used by the Civil Engineering Department at the University of
F lo rid a .......................................................................... 1 0 6

2.60 Typical configuration of covermeter testing apparatus .............. ... ................107

2.61 Typical display of a GPR Scan. The white portion denotes an anomaly .............10

2.62 Typical forced resonant frequency setup ...........................................113

2.63 Dynamic modulus of elasticity vs. cylinder compressive strength.....................14









2.64 The electromagnetic spectrum .............. .. ........ ..................... 116

2.65 Typical thermograph revealing defects................................ ............ ............. 118

2.66 Schematic of a scanning radiometer IR camera...............................................121

2.67 Schematic description of thermographic void detection process ...........................122

2.68 R adiography scheme atic ................................................ .............................. 124

2.69 Schematics of direct radiometry: (a) with an internal signal detector and
external source, (b) with an external signal detector and source .........................126

2.70 Schem atic of backscatter radiom etry ........................................ ............... 126

2.71 Image of prestressing cable anchorage in concrete (a) X-radioscopic image of a
prestressing cable anchorage embedded in concrete, (b) schematic and brief
explanation of the radiographic image.......... .......... ............ .. ..... ............. 127

3.1 Sum m ary of sufficiency rating factors................................................ ............. 130

3.2 The result of a typical bridge query by sufficiency rating ..................................132

3.3 Examples of Pontis codes vs. sufficiency ratings. .............................................. 133

4.1 Plan view of Bahia Honda bridge pilecap and column 54 ...................................144

4.2 Photo location plan Bahia Honda bridge pile cap and column 54 .......................144

4.3 View of bridge superstructure from water-level ...................................................145

4.4 V iew of footing .................................................... ........................ ................... 145

4.5 View of crack in colum n ........................... .... ............... ...............146

4.6 View of crack in column. Efflorescence of the gunite topping on the strut can
be seen in the background .......................................................................... ..... 146

4.7 Plan view of crack orientation on column 54.............................. ............... 147

4.8 Plan view of Niles Channel Bridge column line 20.............................................. 151

4.9 General view of Niles Channel Bridge underside, column line 20 in
foreground ...................................................................... .......... 151

4.10 Impact-echo testing on bridge column ........................................................152

4.11 View of typical strut and column repair.............. ............. ................. 152









4.12 Plan view of Sebastian River Bridge column line 11.......................................... 156

4.13 General view of Sebastian River Bridge............................. ........... ..........156

4.14 Column line 11 with column 11-5 in foreground ...........................................157

4 .1 5 C o lu m n 1 1 -4 ..................................................................................................... 1 5 7

4.16 Cracked and delaminated repair in column 11-4 ....................................... ...... 158

4.17 Plan view of Wabasso Bridge column ..........................................................162

4.18 General view of W abasso Bridge............................................... ........ ....... 162

4.19 Colum n / pilecap 5 ......................... ....... ..... .... .. .. ............... 163

4.20 Close-up of exposed seashell aggregate on pile cap 5 ....................................... 163

4.21 Plan view of column / pile cap of Sebastian Inlet Bridge .............. .....................167

4.22 General view of Sebastian Inlet Bridge underside. Column line 7 in
foreground adjacent to stairs ......... .................. .... ............... 167

4.23 Column line 6 ..... ........... .. .......... ....... ........168

4.24 Plan view of crack orientation on column 12............................... ............... 168

5.1 Ultrasonic pulse velocity experimental setup ....... ... ....................................... 171

5.2 Resonant frequency experimental setup............. ........... ....................172

5.3 Impact echo experim ental setup... ... ...................................................... .. ............... 172

5.5 Frequency spectrum of outlying data point..........................................................176

5.6 Frequency spectrum of typical impact echo data point ............................... 176

5.7 Compressive strength vs. resonant frequency for Mixtures A and B.....................178

6.1 Setup of laboratory experiment............... ....... .............. ................. 183

6.2 Ultrasonic pulse velocity testing on specimen .............................................185

6.3 Impact-echo testing on specimen ......... ....... .... .... ......... .... ............... 186

6.4 Wave velocity vs. age for a sample from Mixture A exposed to limewater. .........187

6.5 Wave velocity vs. age for a sample from Mixture A exposed to sulfate
solution .............................................................................187









6.6 Close up view of a sample exposed to sulfate solution. The arrow denotes the
area of precipitated salt crystals ........... ............. ...................... .. ...... ..... .... 189

6.7 Wave velocity vs. age for a sample from Mixture B exposed to limewater ..........190

6.8 Wave velocity vs. age for a sample from Mixture B exposed to sulfate
solution .................................. .................. ............... .......... 190















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Engineering

ADVANCED NONDESTRUCTIVE MONITORING AND EVALUATION OF
DAMAGE IN CONCRETE MATERIALS

By

Christopher Charles Ferraro

December 2003

Chair: Andrew J. Boyd
Major Department: Civil and Coastal Engineering

The objective of this work is to perform research that will enable the FDOT to

nondestructively assess and monitor the quality of in-situ concrete bridge structures. As

part of the research, a literature review of relevant nondestructive methods was

performed. Also survey of relevant bridge structures within the FDOT's bridge database

system was conducted in an attempt to categorize prevalent bridge deficiencies occurring

throughout the state.

Field research concentrated on the application of the most appropriate

nondestructive testing (NDT) methods and their application to materials assessment and

interpretation of typical NDT data. The attempt of qualifying the onset of damage was

attempted using the applicable NDT method. General material properties of good quality

bridge materials were tested nondestructively.

Laboratory research focused on the establishment of the nondestructive material

properties and their relationship to strength properties, which were obtained via the use of









destructive tests after NDT was performed. Other laboratory research monitored the

changes of NDT data within concrete samples under constant exposure to severe

environments. This experiment was designed to differentiate the effects certain solutions

have on field-size samples of concrete when exposed over periods of time. The primary

objective of this experiment was to observe the effect of exposure of concrete to sulfate

solutions with respect to surface wave velocity and through wave velocity.

Field studies suggest that the wave velocity of concrete samples decreases with

increasing damage. However, the lack of controlled experiments, involving continuous

laboratory monitoring, with respect to stress wave velocity and damage prevents the

quantification of the two parameters.














CHAPTER 1
INTRODUCTION

Performance testing of Portland cement concrete materials dates back to the early

1830's, when systematic tests were performed on concrete samples in Germany. Since

then, standards for Portland concrete have been created and published by various

organizations throughout the world.

The concept of nondestructive testing (NDT) is to obtain material properties of in-

place specimens without the destruction of the specimen nor the structure from which it is

taken. However, one problem that has been prevalent within the concrete industry for

years is that the true properties of an in-place specimen have never been tested without

leaving a certain degree of damage on the structure. For most cast-in-place concrete

structures, construction specifications require that test cylinders be cast for 28-day

strength determination. Usually, representative test specimens are cast from the same

concrete mix as the larger structural elements. Unfortunately, test specimens are not an

exact representation of in-situ concrete, and may be affected by variations in specimen

type, size, and curing procedures (Neville 1996).

Virtually all concrete structures exposed to nature experience deterioration over

time. Inspection personnel have difficulty determining the quality of in-situ concrete that

has experienced decay without direct material sampling. The disadvantage to material

sampling is that an inspector must remove a portion of the structure, usually by means of

coring, and make repairs to the sample area. Removing cores from a concrete structure is









an intrusive process that can weaken the structure and usually leads to long-term

durability concerns.

The majority of bridges in the state of Florida are constructed of concrete. The

Florida Department of Transportation (FDOT) has been experiencing increased costs for

bridge rehabilitation and reconstruction due to deterioration of concrete bridge elements

as a result of exposure.

The objective of this work is to perform research that will enable the FDOT to

nondestructively assess and monitor the quality of in-situ concrete bridge structures. As

part of the research, a literature review of any relevant nondestructive methods was

performed. Also, relevant bridge structures within the FDOT's bridge database system

were reviewed in an attempt to categorize prevalent bridge deficiencies occurring

throughout the state.

Field research concentrated on the application of the most appropriate NDT

methods and their application to the materials assessment and the interpretation of typical

NDT data. The attempt of qualifying the onset of damage was attempted using applicable

NDT methods. General material properties of good quality bridge materials were

established nondestructively.

Laboratory research focused on the establishment of the nondestructive material

properties and their relation to strength properties, which were obtained via the use of

destructive tests after NDT was performed. Other laboratory research monitored the

changes in NDT data within concrete samples under constant exposure to severe

environments.









Concrete specimens of dimensions were created to simulate the effect of curing and

damage on field-sized specimens. Two different mixtures of specimens were cast and

placed in solutions to observe changes in the material properties. One set of specimens

was partially submersed in sulfate solution to simulate the effect of a harsh environment

and its effects on concrete specimens with age. The other set of specimens was partially

submersed in limewater solution to simulate the effect of a control group.

The testing regimen consisted of weekly NDT testing of the concrete samples, at

ages of one day, one week, two weeks, three weeks, four weeks, six weeks, eight weeks,

10 weeks 12 weeks and 13 weeks. The samples were removed from their respective

solutions at the age of 90 days. Nondestructive testing was carried out to asses the

material property changes over time.














CHAPTER 2
LITERATURE REVIEW

Introduction to Nondestructive Testing

The purpose of establishing standard procedures for nondestructive testing (NDT)

of concrete structures is to qualify and quantify the material properties of in-situ concrete

without intrusively examining the material properties. There are many techniques that are

currently being research for the NDT of materials today. This chapter focuses on the

NDT methods relevant for the inspection and monitoring of concrete materials.

Literature Review

Visual Inspection

Visual inspection refers to evaluation by means of eyesight, either directly or

assisted in some way. The visual inspection of a structure is the "first line of defense" and

typically involves the search for large-scale deficiencies and deformities. Perhaps the

most important aspect related to the preparation for visual inspection is the review of

available literature related to the structure or structural element. This should include

original drawings, notes and reports from previous inspections, and interviews with

personnel familiar with the structure or structural element to be inspected. Although

interviews are usually not in themselves considered a type of visual inspection, the

interview process can often precipitate a visit to the structure or structural element that

can then focus on visible defects noted by site personnel, who usually have the most

familiarity with the structure.









Direct visual inspection

The basic principle of direct visual inspection is a meticulous attention to detail.

The most common tools used by inspectors include calipers, gauges, templates,

micrometers, rulers, levels, chalk, illumination devices, cameras, note taking devices, and

other miscellaneous equipment.

Direct visual inspection can be applied to most methods of preventative

maintenance and rehabilitation work. Many inspectors are usually so involved with the

search for small-scale deficiencies within a structure that large-scale deficiencies are

sometimes overlooked. It is important for the inspector to periodically take a step back

and look for larger scale deficiencies. This "can't see the forest for the trees" syndrome

occurs more often in the consulting industry than most people realize, especially when

lesser-experienced inspection personnel are involved.

Remote visual inspection

Often, field conditions are not conducive to the direct inspection of a structure or its

component elements. Sight limitations could be a result of inaccessibility due to

obstructions, hazardous conditions or deficiencies of a scale not visible to the naked eye.

When such unfavorable field conditions arise, aids may be required to permit effective

visual inspection. Usually, remote visual inspection involves the effective use of optical

instruments. These instruments include mirrors, borescopes, charged coupled devices

(CCD), and remote miniature cameras.

Borescopes

A borescope is an optical instrument composed of a tube designed for the remote

inspection of objects. A person at one end of the tube can view an image obtained at the

other end. The image is transmitted through the tube via fiber optic bundles, running









though the tube, camera, video projection system, or lenses. A borescope that utilizes

fiber bundles for its image projection is commonly referred to as a fiber optic borescope

or fiberscope. Another method of image transfer is through the use of a small camera at

one end of the tube and a monitor at the other end. Lenses can also be used to convey the

image to the observer through an eyepiece.

Due to the variety of needs created by industry, there are several types of

borescopes. The basic categories are rigid or flexible, as dictated by the configuration of

the tube. Figures 2.1 through 2.3 illustrate flexible and rigid borescopes. The borescopes

most commonly used today are: fiber optic borescopes, camera borescopes, lens

borescopes and microborescopes. The fiber optic and camera variety are usually of the

flexible type, while the lens borescope is typically rigid. Microborescopes can be either

rigid or flexible.

Borescopes are commonly used for the inspection of objects that have areas of

inaccessibility. They are prevalent in the mechanical engineering field more than any

other area and are instrumental in the inspection and condition assessment of engines and

engine parts. However, borescopes are valuable to civil/structural inspectors and are

commonly employed in the inspection of inaccessible structural elements, such as the

interior of masonry block or multi-wythe brick walls. Borescopes were instrumental in

the Statue of Liberty restoration project, which began in 1984 and was completed in

1990. Olympus Corporation donated flexible fiberscopes, rigid borescopes, halogen light

sources and photo recording accessories to the project. The equipment was used by the

National Parks Service engineers to examine the Lady's iron skeleton. In depth

observations revealed a hazardous array of warps, sags, leaks, and failed joints (Hellier









2001). Without the use of borescopes, the inspectors' efforts would have resulted in an

incomplete assessment of the structure. Figures 2.1-2.3 are photographs of the most

commonly used borescopes.


Figure 2.1: Flexible borescope (Hellier 2001)


Figure 2.2: Flexible borescope and monitor (Hellier 2001)


Figure 2.3: Rigid borescope (Hellier 2001)

Charged coupled device

Willard Boyle and George Smith of Bell Laboratories invented the Charged

Coupled Device (CCD) in 1970. Since then, CCDs have been used in many of the









computer-based optical equipment in use today. CCDs can be found in photocopiers,

facsimile machines, cameras, scanners and other optical computer based products.

A CCD is composed of thousands of light sensitive cells, usually referred to as

pixels that produce an electrical charge proportional to the amount of light they receive.

These pixels can be arranged in either a linear or two-dimensional array, which in turn

can be used to produce a digital image. The typical facsimile machine and computer

scanner used today have a linear arrangement of CCDs, which progressively traverses the

original object in order to progressively build a digital copy. Digital cameras use a two

dimensional CCD, also called an area CCD, to instantly create a digital image.

CCDs are of value to the inspection industry as they allow inspectors to capture

images of specimens as the traditional camera has done for decades. The advantage of

using CCD based technology over film-based cameras is primarily the speed in which the

images are developed. Digital photos are usually viewable through the camera

instantaneously, which allows personnel on site to observe the image without delay. The

person taking the digital photo can then make an on-site decision concerning the quality

of the image and whether it needs to be recaptured.

Robotic cameras

Miniature cameras are sometimes considered a variation of fiber optic cameras. In

the recent past, both miniature cameras and fiber optic cameras both required a wire or

some physical connection to the monitor or viewing device. However, as technology

progresses, limitations diminish. Miniature robotic cameras were instrumental in the

initial stages of the inspection of the World Trade Center (WTC) disaster site in

September 2001. The robots deployed at the WTC site were completely free of cables

and were able to gain access to areas where human access was impossible or hazardous.









The equipment used in this case employed artificial intelligence, robotics, and CCD

technology. Dr. Robin Murphy, an Associate Professor at the University of South Florida,

is also the Director of Research for the Center for Robot-Assisted Search and Rescue

(CRASAR) in Tampa, Florida. Her research primarily encompasses artificial intelligence

in robotics and robot tasking (Murphy 2000).

The robots employed at the WTC disaster site, depicted in 2.4 and 2.5, were used to

explore and inspect the inner areas of the wreckage. Remote exploration of the site

allowed inspectors to locate victims and visually inspect the structural integrity of the

wreckage. The robots were used in several areas of the site, including the collapsed

Towers One and Two. This was the first known robot-assisted search and rescue

response, and represented the culmination of six years of research and training. The

robots were successfully used to find at least five victims, helped rescue teams select

voids for further searching, and assisted in the building clearing efforts. Videos of the

robots, their interfaces, and views from their sensors were used to illustrate key findings

on mobility, sensing, control, and human-robot interaction.


Figure 2.4 : Robot used for visual survey at the WTC disaster site (Casper 2002)




















Figure 2.5 : Robot used for visual survey at the WTC disaster site (Casper 2002)

Although disaster inspection is a highly specialized and limited field of research,

the technology developed and implemented for this work will become more prevalent in

the visual inspection industry.

Applications of Visual Inspection

Visual inspection is a fast, convenient and relatively inexpensive technique used to

evaluate the overall condition of structures. This technique allows inspectors to make

real-time evaluations and recommendations of a given structure, which is particularly

valuable in emergency or safety inspections.

Some limitation of the visual inspection technique is sight obstructions, which can

be due to lighting, access or obstruction. Another disadvantage of visual inspection is the

"human factor" that is often encountered. The susceptibility to human misinterpretation

and the requirement for establishing a baseline for defects in general, especially under

poor conditions, can lead to inconsistent identification of anomalies, which can give rise

to contradicting evaluations (Qasrawi 2000).

Liquid Penetrant Methods

The liquid penetrant examination method can be used to nondestructively evaluate

certain nonporous materials. The American Society for Testing and Materials (ASTM)

has developed material specific test standards for the penetrant examination of solids









(ASTM E165 95). Liquid penetrant methods are nondestructive testing methods for

detecting discontinuities open to the surface, such as cracks, seams, laps, cold shuts,

laminations, through leaks, or lack of fusion. These methods are applicable to in-process,

final, and maintenance examinations. They can be effectively used in the examination of

nonporous, metallic materials, both ferrous and nonferrous, and of nonmetallic materials

such as glazed or fully densified ceramics, certain nonporous plastics, and glass.

Hardened Portland cement concrete is a permeable material due to the properties of

the cement matrix. As concrete is batched and mixed, capillary pores are formed in the

hydrated cement matrix; penetrant methods of investigation, as described in the relevant

ASTM standard, do not apply to concrete because they were developed for testing of

nonporous materials. At present, there is no standardized test method available for liquid

penetrant examination of porous materials.

However, it is possible to use water as an aid to detect surface flaws in concrete.

Inspectors can apply water to a concrete surface and observe the rate of drying. As the

water evaporates from the surface, areas containing cracks will hold moisture. As

illustrated in Figure 2.6, these moist areas will result in local discoloration of the

concrete, which facilitates the visual detection of cracks.













Figure 2.6: Cracks in concrete pavement with moisture present (ACI 201.1 R92)









The principle upon which the liquid penetration method is based is that of capillary

suction, a physical phenomenon in which the surface tension of liquids causes them to be

drawn into small openings such as cracks, seams, laps, cold shuts, laminations and other

similar material deficiencies.

The most important property affecting the ability of a penetrant to enter an opening

is "wetability". Wetability refers to a liquid's behavior when in contact with a surface

(Hellier 2001). The angle created between the free surface of a liquid and a solid surface

is referred to as the contact angle. It is an important characteristic related to the

penetrability of the liquid. Liquids that have small contact angles have better penetrability

than those liquids exhibiting large contact angles. Figure 2.7 depicts contact angles for

various liquids.






Good Welability Poor Wetability

Figure 2.7: Contact angles for various liquids (Hellier, 2001)

Viscosity is another significant property of liquid penetrants. Viscosity is defined

as the resistance to flow in a fluid, or semifluid. Liquids with lower viscosities are more

desirable for use in liquid penetrant examination since they have superior flow properties.

The visibility of the liquid penetrant is a valuable quality in the penetrant

examination procedure. Usually, the visibility or contrast of a liquid penetrant is

measured by the dye concentration, which makes the liquid penetrant more visible.

Contrast ratio is used to measure the visibility of a penetrant. The contrast ratio scale

ranges from 50:1 to 1:1, where a contrast ratio of 1:1 would represent a color in reference









to itself, for example, red dye on a red solid surface. Contrast ratios of 40:1 can be

achieved through the use of fluorescent dye penetrants under ultraviolet illumination. As

a result, ASTM has recognized fluorescent penetrant examination, and standard test

methods have been developed. ASTM D4799-03 is the standard test that describes the

conditions and procedures for fluorescent penetrant testing for bituminous materials.

Although liquid penetrant methods have been beneficial in the location of surface

defects in solids, they have several limitations. Existing liquid penetrant examination

techniques are applicable to the inspection of nonporous solids and are thus not

applicable to the survey and inspection of concrete structures and buildings. The majority

of these are composed of concrete and masonry; both of which are porous materials.

Acoustic Sounding

Acoustic sounding is used for surveying concrete structures to ascertain the

presence of delaminations. Delaminations can be a result of poor concrete quality,

debonding of overlays or applied composites, corrosion of reinforcement, or global

softening. The test procedures used for delineating delaminations through sounding

include: coin tap, chain drag, hammer drag, and an electro-mechanical sounding device.

The purpose of each test is to sonically detect deficiencies in the concrete. ASTM has

created a standard, ASTMD 4580 -86, which covers the evaluation of delaminations.

The standard describes procedures for both automated and manual surveys of concrete.

A major advantage to sonic testing is that it produces immediate results on near

surface anomalies. The effectiveness of sonic testing relies heavily on the user's expertise

in signal interpretation and consistency.











Coin tap test

The coin tap test is one of the oldest and most widely researched methods of sonic


testing. The test procedure requires the inspector to tap on the concrete sample with a


small hammer, coin, or some other rigid object while listening to the sound resulting from


the impact. Areas of nondelaminated concrete will create a clear ringing sound upon


impact while regions of delaminated, disbanded, or softened concrete will create a dull or


hollow sound. This change in sonic characteristics is a direct result of a change in


effective stiffness of the material. As a result, the force-time function of an impact and its


resulting frequencies of an impact differ between areas of good and poor quality concrete


(Cawley & Adams, 1988). ASTMD 4580-86 describes the procedure for manually


surveying concrete structures for delaminations using the coin tap procedure.


5C

40- Top over good area


30
T / / p over defect

S20-


10 -


0 400 800 1200 1600
Time (ts)
50

I' 40 -Good oreo

S30
2 ?Defect
a 20-



0 400 800 1200 1600 2000
Frequency (Hz)
Figure 2.8: Coin tap test results (a) Force-time histories of solid and disbanded areas of a
carbon fiber reinforced skinned honeycomb structure, (b) Spectra of time
histories (Cawley & Adams, 1988)









Figure 2.8 illustrates the shorter force-time history and larger resulting frequency

produced by impacts on solid material as opposed to disbonded/delaminated material.

Understanding the force-time function aids an inspector's abilities to sonically evaluate a

material, as it takes less time for two elastic solids to separate subsequent to a collision. A

similar analogy could be made by comparing the effect of walking on a sidewalk to

walking in the mud. The sinking phenomenon that one experiences in the mud is similar

to the extended time length of impact produced by a delaminated material. The "sinking"

of the hammer or coin into the delaminated material results in a plastic deformation of the

material, resulting in a more dull or hollow sound.

The electronics industry has provided inspectors with equipment that is capable of

detecting and recording the sonic wave signals that are produced by an impact. As a

result, there are currently several commercially available products available for such

signal acquisition. The most common devices for sonic data acquisition are the

instrumented hammer and the smart hammer.

The instrumented hammer was developed for the airline industry to be used in the

detection of anomalies in airplane materials. It measures and records the force-time

history and amplitude frequency of an impact via the use of an accelerometer embedded

in the head of the hammer.

The smart hammer was developed for the shipbuilding industry. This instrument

measures and records the sonic response of an impact through a microphone. The

microphone uses the sonic data, instead of the force data, to create an acoustic signal.

Both impact-force data generators and impact-sound data generators have been

proven to generate useful signals for nondestructive sonic testing. The information gained









from both sources has demonstrated their capability of producing consistent and valid

experimental results. At the present time, research is being conducted into both impact-

force and impact-sound devices to develop improved testing methods. Both devices have

created the opportunity for improved standardization of acoustic sounding tests. The

objective nature of testing with mechanical devices that are capable of producing

consistent and repeatable results can help to improve testing standards for structural and

material inspectors. Although the instrumented hammer and smart hammer are

considered to be automated delamination inspection equipment, the testing data and

procedures produced by these devices are still in the initial stages and an ASTM standard

test method for these devices has not yet been created.

Chain drag survey

The chain drag survey provides a low-cost method to inspect delaminated areas in

concrete surfaces. The survey allows inspectors to traverse a large area with reasonable

accuracy in a short period of time. Since the test is quick and inexpensive it may be used

for an initial evaluation to determine the need for further investigation. Like the coin tap

and hammer sounding methods, the chain drag test is subjective, and therefore requires

an experienced inspector to perform the survey. Due to the nature of the test, localized

areas of delaminations are more difficult to detect. Concrete decks or slabs that have

comparatively large percentages of deficiencies may require the use one of the more

localized tests, like the coin tap or hammer sounding methods, to provide a more accurate

picture of the tested structure.

The chain drag survey consists of dragging a chain over the concrete surface. This

approach suffers from limitations similar to the electro-mechanical sounding device. The

chain drag survey cannot be performed on vertical members of a structure and thus is









limited to the topside of concrete slabs and decks. Similar to the coin tap test, areas of

nondelaminated concrete will create a clear ringing sound upon contact, and areas of

delaminated, disbonded or softened concrete will create a dull or hollow sound. The

typical chain used for inspection is composed of four or five segments of 1 inch link

chain of 1/4 diameter steel approximately 18 inches long attached to an aluminum or

copper tube two to three feet in length. The test is performed by dragging the chain across

the entire surface of the concrete slab and marking the areas that produce a dull sound.

The deficient areas can be recorded and further investigated using other techniques.

Electro-mechanical sounding device

The Electro-Mechanical sounding device is a small, wheeled device equipped with

tapping wheels and sonic receivers. Two rigid steel tapping wheels provide the impacts

for the delamination survey. The sonic receivers are composed of oil filled tires coupled

with piezoelectric transducers. The data acquisition equipment is composed of a data

recorder that stores the signals from the sonic receivers (ASTM D4580-86). The electro-

mechanical sounding device has become somewhat antiquated as the development of

other, more reliable and more efficient, delamination survey techniques have been

developed. ASTM D 4580-86 (procedure A) defines the standard practice for performing

a delamination survey using this device. It is primarily limited by the nature of the

equipment employed, as it cannot perform tests on vertical concrete surfaces, and is thus

restricted to the top surface of concrete decks and slabs.

Applications of acoustic sounding

Acoustic sounding has proven to be a reliable supplement to visual and other forms

of evaluation due to its capability to conduct near-surface investigations at a relatively

rapid rate. These techniques are also valuable in that they are usually relatively low in









cost and can be conducted in conjunction with most visual inspections. However, the

method is limited in several respects. It remains largely subjective to human

interpretation and can be a confusing technique when background noise is prevalent. The

method lacks the ability to detect small defects and subsurface defects, as it is strictly a

near-surface investigation method.

Surface Hardness Methods

Essentially, the surface hardness methods for nondestructive testing of concrete

consist of impact type tests based on the rebound principle. Some of these methods have

been effectively used to test concrete since the 1930's. Due to the complexity of concrete

as a material and the disparity between the concrete surface and the inner structure,

surface methods are inherently limited in their results. However, surface methods have

been proven to give an effective evaluation of the uniformity of a concrete member and

in comparing concrete specimens in a relative sense.

The most widely used surface hardness methods are the testing pistol by Williams,

the pendulum hammer by Einbeck, the spring hammer by Frank and the rebound hammer

by Schmidt. The Schmidt rebound hammer has become the industry favorite in the use

of surface hardness measurements today. The Schmidt hammer is basically a hand-held

spring plunger that is suitable for lab or field-testing. The capabilities of the Schmidt

hammer have been extensively tested, and there are over 50,000 Schmidt hammers in use

world-wide (Malhotra & Carino 1991).

The basic rebound principle consists of a spring-driven mass that is driven against

the surface of a concrete specimen with a known energy. The rebound distance of the

mass is measured and the "hardness" of the concrete surface is estimated from this value.

A harder surface results in a longer rebound distance due to the increase in energy









reflected back to the impinging mass. However, despite its apparent simplicity, the

rebound hammer test involves complex problems of impact and the associated stress

wave propagation (Neville 1995). The energy absorbed by a concrete sample is related to

both its strength and its stiffness. Therefore, it is the combination of concrete strength

and stiffness that influences the rebound number.

There is no unique relation between surface hardness and in-situ strength of

concrete. This relationship is dependent upon any factor affecting the concrete surface,

such as surface finish, degree of saturation, and surface preparation. The concrete mix

design, including the type of aggregate, water/cementitious materials ratio and cement

type can also affect hammer results. The method cannot accurately determine the

subsurface condition of concrete. It tests only a localized area of concrete to a depth of

perhaps 20 or 30mm (B SI, 1986). The condition of the concrete will further affect the

rebound number. Areas of honeycombing, scaling, rough surfaces and high porosity will

decrease the rebound number. Areas of carbonation will increase the rebound number.

Therefore, the user must insure careful selection of a representative area of concrete and

must understand the limitations inherent in the test.

The Schmidt rebound hammer is, in principle, a surface hardness tester with little

apparent theoretical relationship between the strength of concrete and the rebound

number of the hammer. However, within limits, empirical correlations have been

established between strength properties and the rebound number (Malhotra & Carino

1991). The accuracy of the rebound hammer has been estimated between 15-20% under

laboratory testing conditions and 25% in field-testing conditions. Such accuracy,

however, requires a proper calibration of the hammer with the concrete in question.









The American Society for Testing and Materials (ASTM) has created a standard

test for the Rebound Number of Hardened Concrete (ASTM C 805-97). This test

specification should be referenced and strictly followed for proper testing procedures.

Penetration Resistance Methods

The basic principle behind penetration resistance methods is the application of

force to a "penetrating object," and then determining the resistance of a specific concrete

to such penetration by measuring the depth of penetration. Penetration resistance methods

have been effectively used to test concrete since the 1960's. The limitations of

penetration methods are similar to the limitations of surface hardness methods. The depth

of penetration is usually only a small percentage of the full depth of the concrete member.

Penetration methods have been proven to give an effective near surface evaluation of in-

situ compressive strength, uniformity of concrete and soundness at different locations.

The two most commonly used penetration resistance methods are the Pin Penetration

Method and the Windsor Probe.

The Pin Penetration method uses a spring-driven mechanism to drive a 30 mm

long, 3.6 mm diameter steel pin into the concrete surface. The pin is subsequently

removed and the depth of the resulting hole is measured. The Windsor Probe test uses the

same principle, although larger diameter steel probe is used. Table 2-1 contains a

schedule of probe sizes for each test. The Windsor Probe test requires a larger driving

force and employs a gunpowder charge to develop the necessary impetus. ASTM has

approved a standard test for the Penetration Resistance of Hardened Concrete (ASTM C

803-97), which covers both tests. This test specification should be referenced for proper

testing procedures.









Table 2.1: Standard sizes of pin and probe used for penetration tests.
Pin Penetration Method Windsor Probe Test
Size of Penetration: 30 mm length 80mm length
3.6 mm diameter 6.3/7.9mm diameter
Usable Range of 450 4000 psi 450 6000psi
Concrete Strength: 3-28 MPa 3 40 MPa


The ASTM standard requires three firmly embedded test probes in a given test area

to constitute as one test for both penetration test methods (ASTM C803-97)The

penetration methods are still near-surface tests but do offer reliable empirical

relationships between concrete strength and penetration resistance. Consistent empirical

correlations have been successfully established between strength and penetration

resistance. The penetration methods have been estimated to be within +5% accuracy

under both laboratory and field-testing conditions when the test procedure is performed

properly and a valid correlation has been developed.

The primary limitation of penetration methods is that they do not offer a full-depth

appraisal of the concrete that they are testing. They are considered to be surface-testing

methods only and they do not yield absolute values for the strength of concrete in a

structure. They are effective at estimating in situ concrete strength only when the proper

correlations are performed subsequent to testing. Penetration methods are not purely

nondestructive in nature since they induce some damage to the tested specimen. It is

more accurate to consider penetration tests as semi-destructive.

Pullout Test

The basic purpose of the pullout test is to estimate the in situ strength of a concrete

structure. Pullout tests consist of measuring the force required to extract a mechanical

insert embedded in a concrete structure. The measured pullout force can then be used to









estimate the compressive, tensile and shear strength of the concrete. The pullout test was

originally developed in the former Soviet Union in the 1930's and later independently

developed in the United States in the early 1940's. Further research has led to several

modifications since then. The test that is most commonly used in industry today is the

pullout test as modified by Kaindl in the 1970's.

The pullout test, illustrated in Figure 2.9, uses a metal insert that is inserted into

fresh concrete or mechanically installed into hardened concrete. The tensile or "pullout"

force required to extract the embedded insert, and the core of concrete between the insert

and the surface, can give accurate estimates of the concrete's compressive, tensile and

shear strengths. The pullout test has become a proven method for the evaluation of the in

situ compressive strength of concrete and has several industry applications. The pullout

test is used to determine whether the strength of the concrete has reached a sufficient

level such that post-tensioning may commence; cold weather curing of concrete may be

terminated or forms and shores may be removed.








25 m




Expandable
Ring


25 mm

Figure 2.9: Illustration of typical pullout test (Malhotra & Carino 1991)









Consistent empirical correlations can be established between strength properties

and pullout test methods. Pullout test results have been estimated to be within +8%

accuracy for laboratory and field-testing conditions when the test procedure has been

performed properly and a proper correlation has been developed.

The pullout test method does not provide a full-depth appraisal of the concrete

structure that is being tested. It is not truly nondestructive in nature since it induces

significant damage to the tested member. It is more accurate to consider the pullout test

as semi-destructive. The damage incurred during pullout testing is usually more

significant than most other "NDT" methods and patching of the tested structure is usually

required. Figure 2.9 shows a schematic of the pullout test.

ASTM has created a standard test for the Pullout Strength of Hardened Concrete

(ASTM C 900-99). This test specification should be referenced for proper testing

procedures.

Break-Off Test

The primary purpose of the break-off test is to estimate the strength of a concrete

structure. This test involves the breaking off of an internal cylindrical piece of the in situ

concrete at a failure plane parallel to the surface of the concrete component. The

measured break-off force can then be used to estimate the compressive and tensile

strength of the concrete. The break-off test was originally developed in Norway in 1976.

It was later introduced into the United States in the early 1980's. The test procedure used

today is essentially the same as when the test was originally introduced.

The break-off test can use a cylindrical sleeve that is inserted into fresh concrete to

create the embedded cylinder. Alternatively, the embedded concrete cylinder can be










drilled into hardened concrete using a core drill bit. The embedded cylinder size is

usually 55mm in diameter and 70mm in height. Figure 2.10 illustrates a typical cross

section of the breakoff test.


mee-an


F ~b~j31


(-NW^


Nytar


Bf


70



55CROSS SECTION

CROSS SECTION


Figure 2.10: Typical cross section of the breakofftest, all dimensions in mm (Malhotra &
Carino 1991)

The actual test method involves the application of a horizontal force to the upper

edge of the embedded concrete cylinder, which is slowly increased until failure. The

force required to break the embedded cylinder is then used to estimate the concrete

compressive and tensile strength. The break-off test is a proven method of evaluation of

the in situ compressive strength of concrete and has several industry uses. Like the

pullout test (described later) it is used to determine whether the strength of the concrete

has reached a specified value so that post-tensioning of a bridge structure may

commence, cold weather curing of concrete may be terminated, or forms and shores can

be removed.

Consistent empirical correlations have been established between strength properties

and break-off test methods. The break-off test results have been estimated to be within









+7% accuracy for laboratory and field-testing conditions when the test procedure has

been performed properly and sufficient data is available to formulate a proper correlation.

The primary limitation of the break-off test is that it is not truly nondestructive in

nature. It induces significant damage to the tested member. Thus, it is more accurate to

consider the break-off test as semi-destructive. The volume of removed material is 667

cm3 or 41 in3. Thus, the damage incurred during break-off testing is typically more

extensive than other "NDT" methods, and patching of the tested structure is usually

required.

ASTM has approved a standard test for the Break-Off Number of Hardened

Concrete (ASTM C 1150-96). This test specification should be referenced for proper

testing procedures.

Ultrasonic Testing

Ultrasonic testing is a NDT method that is used to obtain the properties of materials

by measuring the time of travel of stress waves through a solid medium. The time of

travel of a stress wave can then be used to obtain the speed of sound or acoustic velocity

of a given material. The acoustic velocity of the material can enable inspectors to make

judgments as to the integrity of a structure.

The term ultrasonic is defined as a sound having a frequency above the human ear's

audibility limit of about 20,000 hertz. Ultrasonics are very popular in the medical

industry and have been used there for over thirty years, allowing doctors to non-

intrusively investigate internal organs and monitor blood flow in the human body. The

materials industry has also been able to utilize ultrasonics for non-intrusive investigation









of assorted materials such as metals, composites, rock, concrete, liquids and various other

nonmetals.

The first studies of ultrasonics are recorded as far back as the Sixth Century B.C.

when Greek philosopher, Pythagorus performed experiments on vibrating strings. Galileo

Galilei is credited with performing the first of the modern studies of acoustics. He was

the first scientist to correlate pitch with frequency of sound. The earliest known study of

the speed of sound in a liquid medium took place in 1822 when Daniel Colladen, a Swiss

physicist/engineer, and Francois Sturm, a Swiss mathematician, used flash ignition and a

bell to successfully estimate the speed of sound in Lake Geneva, Switzerland. In 1915,

Paul Langevin pioneered the study of high-frequency acoustic waves for submarine

detection during the outbreak of World War I (Guenther 1999).

The age of ultrasonic testing of materials was established in 1928 by Sergei Y.

Sokolov, a scientist at the Lenin Electrotechnical Institute in Leningrad, Russia. Sokolov

proposed and demonstrated that he could translate ultrasonic waves or sound pressures

into visual images. In the 1920's he advanced the idea of creating a microscope using

high frequency sound waves. He then applied his ideas to detect abnormalities in metals

and other solid materials. As technologies have developed over the twentieth century, the

knowledge gained through the use of the high frequency microscope has been applied to

other ultrasonic systems (e.g. radar) (Guenther 1999).

In the United States, the development of the ultrasonic test is attributed to Dr.

Floyd Firestone, who, in 1942, introduced what is now called the pulse echo technique

(described later) as a method of nondestructive testing. Dr. Firestone successfully used

the pulse echo technique for ultrasonic flaw detection. Ultrasonics have since been used









to evaluate the quality of concrete for approximately 60 years. The method can be used

for non-intrusively detecting internal defects, damage, and deterioration in concrete.

These flaws include deterioration due to sulfate and other chemical attacks, cracking, and

changes due to freeze-thaw cycling.

Theory

Ultrasonic testing of materials utilizes the vibrations of the particles that comprise a

given medium. Sound waves and ultrasonic waves are simply the vibrations of the

particles that make up a solid, liquid, or gas. As an energy form, the waves are an

example of mechanical energy.

The motion of vibration is described as a periodic motion of the particles of an

elastic body or medium, in alternately opposite directions from the position of

equilibrium when that equilibrium was disturbed. However, vibration can also be

described as an oscillation, which is the act of swinging back and fourth between points.

An elastic oscillation is one in which the driving force behind the oscillation (e.g. a

spring) is proportional to the displacement of the object. Figure 2.11 illustrates the basic

sinusoidal oscillation of a free body on a loaded spring and the resulting sine curve that

can be achieved when the motion is plotted with respect to time.


Amplifude






Time --


Figure 2.11: Sinusoidal oscillation of a loaded spring (Krautkramer 1979)









The sinusoidal waveform that is created by sound waves is a convenient

characteristic of the wave motion that allows scientists to quantify sound in terms of

amplitude and frequency. The frequency of these waves differentiates sonic from

ultrasonic waves. The unit of frequency is the hertz or Hz, and is defined as one cycle of

vibration per second. Sounds below approximately 16 Hz are below the lower limit of

human audibility, whereas sounds of 20,000 Hz are above the upper limit of human

audibility.

The basis of ultrasonic testing is particle vibration within a medium upon the

application of mechanical energy. Figure 2.11 shows the free body motion of a single

mass and its interaction with a single spring. Considering the mass from the diagram in

Figure 2.11 to be a particle, and the spring to be the connection of particles, the simple

principle of free body motion to fit a particle interaction model can be expanded as seen

in Figure 2.12.










Figure 2.12: Model of an elastic body (Krautkramer 1979)

The model depicted in Figure 2.12 is the basic model used in wave science.

Mechanical waves propagate through materials by means of particle motion. Wave

propagation is largely dependent upon the type of excitation or energy input, the mass of

the individual particles, and the spring stiffness of their internal connections. A wave

initiated by an external event such as normal or shear force, travels by vibratory









movement transmitted from particle to particle. If the springs that connect the particles

were infinitely stiff, all particles of the material would start to oscillate at the same instant

and the wave would be transmitted at an infinite speed. Hence, the material's elasticity

and density play an important role in wave propagation (Kaiser & Karbhari 2002).

Internal friction and other forces resist particle motion upon excitation, and wave

propagation occurs at a finite rate. This rate is referred to as its wave velocity and is

dependent upon material composition.

Although sound waves can propagate through all three forms of matter (solids,

liquids and gases), the type of waveform able to move though a material is dependent on

the material phase. For materials in the gaseous or liquid phase, dilatational waves are

typically the only form that travels well. Dilatational waves are also referred to as

compression or longitudinal waves and are the primary stress waves produced by material

excitation. The particle motion in a longitudinal wave is parallel to the direction of

propagation. The result is a compressive or tensile stress wave.

Distortional waves are the secondary stress waves that are produced upon forced

contact. These waves are also called shear or transverse waves. In shear waves, the

particle motion of the wave front is normal to the direction of propagation, resulting in

shear stress.

Rayleigh waves, also called surface waves, differ from longitudinal and shear

waves because they do not propagate through a solid. Rayleigh waves propagate along

the surface in an elliptical motion.

Lamb waves are similar to Rayleigh waves because they also do not travel through

a material and are also considered surface waves. Lamb waves, however, occur only in









solids that are a few wavelengths in thickness and have a uniform thickness. Common

objects subject to the development of lamb waves are plates, pipes, tubes, and wires.

The behavior of waves at material interfaces

The term interface is defined as a surface forming a common boundary of two

bodies, spaces, densities or phases. One of the most common interfaces people are

familiar with is the oil-water interface. In materials science, an interface is usually

defined as a fringe between two materials, which have different properties such as density

or phase. Another possible difference in material properties is acoustic impedance, which

is defined as a material's density multiplied by its wave speed. When stress waves collide

with material interfaces, portions of the waves are reflected and refracted. The principle

of refraction is best described by Snell's law, which relates the angle of refraction and the

wave velocity to the refraction angle of two materials.

sin io sin R
(1)
V ~ V2


where: iP = angle of incidence

R = angle of refraction

V2 = wave velocity in Medium 2


Figure 2.13: Graphical illustration of Snell's law (Hellier 2001)









Figure 2.13 shows a typical example of the refraction angle of an ultrasonic wave

as it enters a different material. The concrete-air and the concrete-steel interfaces are the

two most common interfaces encountered in nondestructive testing of civil engineering

structures.

Most of the illustrations used to describe the characteristics of ultrasonics consider

the sound or ultrasound as a two-dimensional ray, which is somewhat simplified for the

study of ultrasonics and nondestructive testing. A more accurate representation of the

sound energy is a three dimensional beam. The study of a sound beam is more

complicated than a sound ray. As the complexity of the physical characteristics in a

material increases, different mechanical mechanisms become factors in their analysis.

Scientists define attenuation as the gradual loss of sound wave energy through a

medium. Attenuation can be more accurately described as the combined effect of a

number of parameters:

* Interference from diffraction effects
* Interference adsorption (friction and heat)
* Interference scatter
* Interference beam spread (Hellier 2001)

The combination of these effects can create disturbances and erratic signals within

a material. One of the early challenges of scientists using ultrasonic equipment was

deciphering and filtering the interference signals created by material properties.

Instrumentation

Commercial ultrasonic equipment has been under development since World War II.

The first equipment available to the materials engineering industry was produced in the

1950's. Since then, a variety of ultrasonic detection devices have become available. Most

of the ultrasonic devices used for material inspection and flaw detection are portable and









battery powered. A portable ultrasonic testing device is illustrated in 2.14. Portability

enables material inspection in the field and a high degree of user flexibility.






I,










Figure 2.14: A portable ultrasonic testing device used at the University of Florida

The typical testing apparatus used for ultrasonic testing consists of the following:

* Transducer
* Time Measuring Circuit
* Receiver/Amplifier
* Display
* Reference Bar
* Coupling Agent


Transducer

A transducer is used for transforming electrical pulses into bursts of mechanical

energy. A typical pulse velocity apparatus consists of a transmitting transducer and a

receiving transducer. The transmitting transducer generates an ultrasonic pulse through

the test specimen, and the receiving transducer receives the pulse. The generation and

reception of ultrasonic waves is accomplished using piezoelectric crystals. Piezoelectric

elements are reciprocal, which means an applied voltage generates a deformation, or an









impinging stress generates a voltage. This physical property makes piezoelectric elements

ideal as transducers (Papadakis 1999).

Time measuring circuit

The time measuring circuit or clock is an essential component of the ultrasonic

pulse velocity equipment. It controls the frequency output of the pulse by signaling the

pulser to provide a high-voltage pulse to the transducer. The time measuring circuit

measures the time of travel of a pulse or stress wave through the test specimen. Since the

primary function of the time measuring circuit is to regulate pulse generation, it is

commonly referred to as a pulser. It provides an output to the display when the receiving

transducer receives a pulse. The time measuring circuit is capable of producing an overall

time-measurement resolution of 1 microsecond ([is). ASTM C597-97 requires a constant

signal with a varying voltage of +15% at a temperature range of 0OC 400C.

Receiver/amplifier

The receiver is the term applied to all of the circuit functions that amplify the weak

echoes and determine their amplitude. It has four basic components, the preamplifier, the

logarithmic amplifier, the rectifier and the low pass amplifier.

The function of the preamplifier is to ensure that any signal from the receiving

transducer arrives at the time measuring circuit. Since electrical outputs from the

transducer are relatively small, signal amplification is necessary to overcome the

resistance in the transducer cable, which can be relatively long. The function of the

logarithmic amplifier is to process weak echo signals. Once the weak signals are

amplified, the rectifier and the low pass filter process the signals. After processing by the









receiver/amplifier, a useable signal can be sent to the display. A schematic of a typical

ultrasonic pulse velocity meter is shown in Figure 2.15.

Transmitting Receivinmg
Transducer Transducer












Figure 2.15: Schematic of a pulse velocity apparatus (ASTM C597-97 2001)
Display

The signal received by the ultrasonic test equipment is typically displayed digitally

with modern equipment. The results consist of a direct reading of display time on an x-y

coordinate system. The x-axis becomes the time trigger and the y-axis represents the

mechanical energy received. The display units can also illustrate defect or anomaly

locations and sizes, depending on the type of data requested by the user.

The information obtained in the ultrasonic test is referred to as a scan. Currently

there are three types of scans that are applicable to ultrasonic testing: A-scans, B-scans,

and C scans.

The A-scan is the simplest scan form. It is a spot scan of the material and results in

the most basic form of displayed information. The resulting scan is a waveform where

regions of high frequency sound waves are recorded and displayed as peaks on the

screen. B-scans are a bit more sophisticated. They incorporate a linear scan instead of a

point or spot scan. B-scans are essentially the summation of a series of A-scans that are

produced by "sweeping" the transducer over the material specimen. C-scans are even









more complicated than B-scans because they incorporate a two dimensional grid system.

C-scans are comprehensive scans that are most applicable to nondestructive testing of

materials. Figure 2.16 illustrates the differences between these three types of scans.








__ e_ _

Figure 2.16:Idealized scans of a material defect: a) A-scan, b) B-scan, c) C-scan, (Kaiser
& Karbhari 2002)

Reference bar

The reference bar is a piece of material that is used to calibrate the ultrasonic

apparatus. Ultrasonic instruments, which use a microprocessor to record delay time, do

not require a reference bar. These instruments can be calibrated by compressing both

transducer together to obtain a zero reading. Otherwise, ASTM C597-97 requires that a

bar of metal or some other material for which the transit time of compressional waves is

known. The reference bar is used as a functional check of ultrasonic equipment prior to

testing.

Coupling agent

A coupling agent is usually required to ensure the efficient transfer of mechanical

energy between the transducer and the tested material. The purpose of placing the

coupling material between the transducer and test specimen is to eliminate air between

the respective surfaces. Typically, coupling agents consist of viscous liquids such as

grease, petroleum jelly, or water-soluble jelly. Ponded surface water is also considered an









acceptable couple. Water is considered as an acceptable couple for underwater ultrasonic

testing.

Acoustic velocity calculation

The acoustic velocity wave speed of a given concrete specimen can easily be

obtained with the travel time of a stress wave and the length of the specimen. The pulse is

sent from the sending transducer to the receiving transducer through the concrete

specimen as see in Figure 2.17. The relationship of a specimen's acoustic velocity is

simply calculated from a time and a length measurement. It should be noted that cracks,

flaws, voids and other anomalies within a material specimen could increase time of travel

therefore decreasing the materials acoustic velocity. However, assuming the specimen in

Figure 2.17 is free of anomalies, its acoustic velocity can be calculated simply by. The

length of the specimen is 200 mm.











Figure 2.17: Typical ultrasonic test procedure

V = L/T; V= 0.2m/47.5[ts 4210 m/s (2)

The experiment shown in Figure 2.17 provides the user with a quantitative result.

The pulse velocity acoustic velocity, V, of stress waves through a concrete mass is related

to its physical properties (ASTM C597-97). is a function of Young's Modulus of









Elasticity E, the mass density p, and Poisson's Ratio v. The relevant equation for wave

.E(1- v)
speed is: V E = v) (3)
p(l + v)(1 2v)

The acoustic velocity of a solid varies given its composition. Therefore, different

materials have different acoustic velocities. The acoustic velocities of common materials

are shown in Table 2.2 (Krautkramer 1991).

Table 2 2 Acoustic velocities of common materials used in construction


Material Acoustic Velocity
(m/s)
Aluminum 6320
Cast Iron 3500-5800
Concrete 2000-5500
Glass 4260-5660
Iron 5900
Steel 5900
Water 1483
Ice (water) 3980


Flaw detection

The immersion testing method involves typical ultrasonic equipment, though the

test specimen is completely submerged in water. The water acts as a coupling agent,

which aids in the transfer of a clear signal from the transducer to the material being

tested. Immersion testing is usually performed in a laboratory on relatively small test

specimens, but can be applied to structures in the field. It is possible to perform

immersion testing on structures using a technique called ponding. This technique

involves the creation of a layer of water or pond between the specimen and the transducer









and thus is only applicable to the upper surface of structures or submerged sections of

underwater structures.

Contact methods are the most commonly used methods in the ultrasonic

nondestructive testing of materials. Contact methods require the use of a coupling agent,

as described in the Coupling Agent section. The development of contact methods allow

more versatility in the ultrasonic testing of specimens, since they enable inspectors to test

structures and components regardless of orientation. The ultrasonic pulse velocity testing

method, as described in ASTM C597-97, is a contact method.

As illustrated in Figure 2.18, there are three possible transducer arrangements in

ultrasonic pulse velocity testing. These variations include through or direct transmission,

semidirect transmission, and surface or indirect transmission.

The through transmission arrangement is considered to be the preferred approach. It

is the most energy efficient arrangement because the pulse receiver is directly opposite

the pulse transmitter. Since the distance between the two transducers is minimized, the

amount of pulse energy lost through material friction is also minimized.

The semidirect arrangement is less energy efficient than the through transmission

arrangement due to the geometry of the transducer arrangement. The angles involved

cause signal interference and therefore are more likely to produce errors. The semidirect

arrangement is still useful for inspections where through transmission testing is not due to

unfavorable structure configuration. The method is also useful for testing of composite

columns that contain heavy reinforcing steel within their core. The semidirect transducer

arrangement facilitates ultrasonic testing of the concrete in the column while avoiding

interference from the embedded steel.









The surface method is the least efficient of the three ultrasonic pulse velocity

configurations. This is due to the nature of the waves that travel through the surfaces of

materials. The amplitudes of waves received via the receiving transducer are typically

less than 5% of waves received by the direct transmission method. Such a small amount

of wave energy obtained by the receiving transducer can result in errors in the

measurement and analysis of a wave signal. Although the arrangement is the least

efficient of the three methods, it is useful in situations where only one surface of a

structure or specimen is accessible, such as a floor slab. Surface wave speed and surface

crack depth are acquirable through the surface method as well. These methods are

explained in the impact echo section of this chapter. Impact-echo and ultrasonics utilize

the same principle for crack depth measurement.


6( .
R

I .

6-f

A e




-





Figure 2.18: Methods of pulse velocity measurements: a) direct method, b) indirect
method, c) surface method, (Malhotra & Carino 1991)









Noncontact methods of ultrasonic testing are under continuous research. This field

of study has many desirable attributes and similar fields of study include acoustic

levitation and transportation.

At the present time, there are several noncontact acoustical techniques being

developed for the nondestructive testing of materials and structures. New acoustical

techniques are now available as a result of the development of the piezoelectric

transducer. Three techniques exist: electromagnetic transducers (EMATs), laser beam

optical generators, and air or gas-coupled transducers (Bergander 2003).

Most contact ultrasonic testing requires the use of a piezoelectric transducer to send

and receive the stress wave signals. The signals are introduced into and received from the

test specimen through physical contact of the transducers coupled to the test surface.

EMATS are composed of an RF coil and a permanent magnet. The RF coil is excited by

an electric pulse which sends an electromagnetic wave along the surface. The EMATS

technique requires the test surface to be magnetically conductive. (Green 2002).

Laser ultrasound facilitates the non-contact ultrasonic testing of materials

regardless of the materials' electrical conductivity. It provides the opportunity to make

truly non-contact ultrasonic measurements in both electrically conducting and electrically

nonconducting materials, in materials at elevated temperatures, in corrosive and other

hostile environments, and in locations generally difficult to reach, all at relatively large

distances from the test surface (Green 2002). Laser ultrasound techniques are able to

produce compression, shear, Rayleigh and Lamb waveforms, increasing the test's

versatility and serviceability. Laser generated and air coupled ultrasonics have been

successful in the characterization of materials which are non-electrically conducting but










are not yet serviceable for flaw detection and material investigation. However, the

contemporary non-contact ultrasonic methods have been proven to be scientifically

applicable in the aeronautics and metallurgical disciplines. A schematic representation of

contact transducers vs. non-contact transducers is illustrated in Figure 2.19



Contact Noncontact

Piezoelectric transducer EMAT



Immersion lank Gas coupled transduer




Waler squirr Laer






Figure 2.19: Illustration of contact and noncontact techniques (Green 2002)

Pulse-echo testing

The pulse-echo test is based upon stress wave propagation. It uses the same

principles and concepts as the impact-echo method (described later). The basic principle

behind both methods is referred to as the "pitch and catch" technique. In pulse-echo

testing, a stress wave or pulse is created by a transmitting transducer, just as it is with

ultrasonic pulse velocity method. Some types of pulse-echo equipment utilize the same

transducer to receive while others require separate sending and receiving transducers.

This latter type of arrangement is often termed as "pitch and catch." However, the

receiver and transmitter need not necessarily be separate transducers placed at different

points on the test specimen but can be combined to a single transducer. This type of









testing is referred to as "true pulse echo." Figure 2.20 provides a schematic of the pulse

echo principle.

TRUE PULSE-ECHO PITCH -CATCH


S3V


Time Time
SPulser/Oscllloscope
I C

Transmitter/ Transmitter Receiver
Receiver




Figure 2.20: Schematic of pulse-echo and pitch and catch techniques (Malhotra & Carino
1991)

The echo wave coming from the flaw is described by its transit time from the

transmitter to the flaw and back to the receiver. Later, the reflected wave from the back

side of the specimen, for example the back echo or bottom echo, arrives after a

correspondingly longer delay. Both echoes are indicated according to the intensity, or

rather amplitude, which is referred to as echo height because of their usual presentation

as peaks above the horizontal zero line. (Krautkramer 1990). Figures 2.21 a and b

provides a schematic of the typical setup and results from pulse echo scans.

The primary difference between the pulse-echo method and the impact-echo

method is that the former technique utilizes a transmitting transducer while the latter

employs a mechanical impactor. Both methods use a receiving transducer, which is used

to detect the reflected waveform. The difference between the transmitting transducer and











the mechanical impactor is the waveform created. The mechanical impact creates a


spherical wave front, whereas the transmitting transducer creates a pulse wave beam,


resulting in a much smaller material examination area.


Coupling compound
transfers mechanical
ncrillationc frnm


crystal to o


Damping mas:


object




Test object


Signal ampli-
tude = sound
energy received


1. Emits mechanical
oscillations in
Normal probe: phase with the ap-
plied alternating
voltage
s- Piezoelectric 2. Receives mechanical
oscillations which
-crystal are converted to al-
ternating voltage

S Sound impulse prop-
agates as a narrow beam
with constant velocity

--'- Defect reflects a small
portion of the sound
pulse. Th
.-- The interface ref-
*i.. lects the remainder
of the sound impulse
like a mirror


CV .. Time axis =
v* sound path length
Start Defect Bottom
pulse echo echo
Figure 2.21: Pulse echo schematic (a)Typical test setup, and (b) resulting display
(Boving 1989)

The biggest limitation to the pulse-echo method can be attributed to the geometry


of the specimen. The reflections of internal anomalies are dependent upon their


orientation. In cases where discontinuities, and opposite surfaces, are oriented


unfavorably or parallel to the ultrasonic ray path, it may be unable to receive reflected


Damping mass
-- __ __







44


pulse wave signals. The orientation of anomalies and defects is equally important to size

in the pulse echo method. The most favorable orientation for an anomaly is perpendicular

to the ultrasonic ray path. Figure 2.22 provides an illustration of the signal response due

to the orientation of an anomaly. Reflections due to uneven surface morphology can

cause signal scatter, as shown in Figure 2.23, resulting in the test missing the backwall

echoes. This phenomenon can make it difficult to determine anomaly location.





FrPro Suac



f I nf Backwatl












Figure 2.22: Reflections of stress waves from internal discontinuities (Kaiser & Karbhari
2002)




Front Surlace






BDck Sun
Ats
Figure 2.23: Signal scatter due to uneven reflecting surface morphology (Kaiser &
Karbhari 2002)









Applications of ultrasonics

Ultrasound has been used to determine the integrity of various materials including

metal and alloys, welds, forgings and castings. Ultrasound has also been applied to

concrete in an attempt to nondestructively determine in situ concrete features such as:

* Compressive strength
* Defect location
* Surface crack measurement
* Corrosion damage

Strength determination

The material properties of concrete are variable, and strength determination is a

difficult and complicated process. The basic ingredients of concrete are hydrated cement

paste, aggregates, water and air. The hydrated cement paste is a highly complex

multiphase material. The mineral aggregates are porous composite materials differing

greatly from the cement paste matrix. The interface between paste and aggregate particles

has its own special properties. Concrete can aptly be considered a composite of

composites, heterogeneous at both the microscopic and macroscopic levels (Popovics

2001). Concrete, unique in its placement, is one of the only materials used in construction

that is usually batched and transported to a construction site for placement in the form of

a viscous liquid. The concrete liquid is then formed and left to form a hardened paste. It

is this hardened concrete for which material properties can be estimated in construction

practice.

Minimum concrete strengths can be accurately predicted and estimated. However,

the most commonly accepted method of measuring the compressive strength of in situ

concrete is through core testing. Many studies have shown that there is no particular

correlation between the strength of concrete defined by ASTM standards and the strength









of concrete actually in a structure (Mindess et al. 2003). Since some of the material

properties of concrete, like strength, change with time and exposure, determining the

strength of in situ concrete nondestructively is a valuable ability. Concrete is the only

engineering material in which strength determination is attempted by ultrasonic

measurements. The demand to test ultrasonically has been created by industry needs.

Using NDT methods to achieve a reliable conclusion regarding the condition of a

structure allows engineers to more efficiently plan repairs.

At the present time, there is no theoretical relationship between ultrasonic pulse

velocity, or wave velocity and the compressive strength of concrete. However, in

infinitely elastic solids, the P-Wave Cp is a function of Young's Modulus of Elasticity E,

the mass density p, and Poisson's Ratio v. The relevant equation for wave speed is:

E(1- v)
C = (4)
p p(l + v)( 2v))

Using this formula, it is possible to use the wave speed from ultrasonic testing to

obtain other physical properties of concrete, such as compressive strength. However,

most prior studies have been laboratory controlled and were performed on concretes with

consistent mix parameters. These studies tend to neglect the effects of age and weathering

on hardened concrete, which is a limiting factor when considering ultrasonic testing for

strength determination in older structures (Lemming 1996, Popovics et al.1999, 2000,

Popovics 2001, Gudra & Stawiski 2000, Lane 1998, Krautkramer 1990, Malhotra 1984,

1994, Malhotra & Carinol991).

The ultrasonic determination of concrete strength has been intensively researched.

Although some studies have shown positive results (Lemming 1998, Popovics et al.1999,

2000, Popovics 2001, Gudra & Stawiski 2000, Lane 1998, Krautkramer 1990, Malhotra









1984, 1994, Malhotra & Carinol991), there is no completely acceptable method for the

determination of concrete strength using ultrasonics. This is due to the complexities of

the material, the generated waveform, and the structure. Thus, continued research toward

the development of a concrete strength versus ultrasonic pulse velocity relationship is

justified (Popovics 2001).

Defect detection

The most successful application of ultrasonics has been in the detection and

location of the presence of discontinuities in concrete specimens and structures.

Ultrasonic testing has been proven to be capable of detecting various anomalies including

rebar, prestressed tendons, conduit delaminations, voids, and cracks. The reliability of

ultrasonic tests has been confirmed when applied to the testing of concrete and masonry

structures.

Ultrasonics are useful in the evaluation of construction and in the rehabilitation of

structures. The sonic test is a reliable technique used to evaluate the effectiveness of

grout injection. Investigations, repeated before and after repair, allow for control of the

distribution of the grout in the masonry. Nevertheless, in the tested case, it was

impossible to distinguish between the effects of each grout, the materials being injected

having similar modalities (Binda 2001).

Recent research has been conducted using array systems and ultrasonic tomography

to evaluate concrete specimens and structures. Tomography is defined as a method of

producing a three-dimensional image of the internal structure of a solid object by the

observation and recording of the differences in the effects on the passage of waves of

energy impinging on those structures. Ultrasonic tomography can be performed by

measuring the times-of-flight of a series of stress pulses along different paths of a










specimen. The basic concept is that the stress pulse on each projection travels through the

specimen and interacts with its internal construction. Figure 2.24 illustrates the basic

concept behind ultrasonic tomography. Variations of the internal conditions result in

different times of flight being measured (Martin et al. 2001).

Receivers


Source

Receivers
Anomaly




Source
Figure 2.24: Setup of ultrasonic tomographc ray paths (Martin et al. 2001)

Field research has revealed that ultrasonic tomography constitutes a reliable method for

investigating concrete structures. However, it is time consuming, and thus the practicality

of using this method for global inspection of structures is limited.

Ultrasonic imaging and tomography methods have incorporated the use of array

systems for transducer arrangements to be utilized for the inspection and defect detection.

The practical application of the system shows that it is possible to measure the concrete

cover of large construction elements, even behind dense reinforcing bars. The data is

evaluated by means of time-of-flight corrected superposition. The array system together

with a three-dimensional reconstruction calculation can be used for the examination of

transversal prestressing ducts. The system has already been used successfully on site

(Krause et al. 2001).

The most recent research in ultrasonics and its uses in nondestructive testing has

been the automated interpretation of data. The interpretation of NDT data is a difficult









task, and those who do so must be trained and skilled in the NDT discipline. However,

when large engineering structures are inspected, the amount of data produced can be

enormous and a bottle neck can arise at the manual interpretation stage. Boredom and

operator fatigue can lead to unreliable, inconsistent results where significant defects are

not reported. Therefore, there is great potential for the use of computer systems to aid

such interpretation (Cornwell & Mc Nab 1999). At present, the automated data analysis

systems are unreliable for industry use. However, the value of automated flaw analysis

has been successfully demonstrated on examples of real defects and made correct flaw

diagnoses (Cornwell & McNab 1999). It appears as though the biggest limiting factor of

the automated interpretation of NDT data is a general lack of knowledge involving defect

and flaw detection. The information obtained via the use of ultrasonics and other NDT

methods requires the interpretation of an experienced technician or engineer. Scientists

have yet to find the simple answers with respect to ultrasonic data that allow computers

and computer programs to be utilized for interpretation.

Surface crack measurement

Surface crack measurement has been studied by several researchers and the results

are considered to be reliable when the testing procedure is properly performed. In a

concrete specimen with a known wave speed, a crack that is present will cause the path

length of the ultrasonic pulse to become larger. Using simple geometric calculations, it is

possible to obtain the depth of a surface initiated crack within a specimen, as long as that

crack represents significant void space (i.e. is wide enough to eliminate contact of the

sides). The limitation of this method is smaller cracks that lack large void space. In such

cases, the pulse may be able to cross the crack due to the small discontinuity in the









concrete, thus shortening the path length. Figure 2.25 illustrates the concept of crack

depth measurement.





Transduser Transduser I







Figure 2.25: Measurement of crack depth (Malhotra 1991)

Detection of corrosion damage

Corrosion of reinforcing steel is one of the most prevalent problems plaguing

concrete structures. The most commonly used methods of corrosion detection are

electrochemical methods, such as the DC polarization method, the AC impedance

method, and the open circuit potential method. Such electrochemical methods can only

obtain overall information theoretically. However, pitting corrosion often occurs in

reinforcing steel in reinforced-concrete members. The local environment surrounding the

metal surface is not uniform, and inappropriate loading may induce cracks in concrete

that allow, or even draw, chloride ions from the environment. These ions can penetrate

the concrete along the cracks faster than at other, uncracked areas. Electrochemical

measurements for the detection of corrosion damage in reinforced concrete members may

underestimate the local pitting corrosion rate because the electrochemical parameters

represent global information obtained by taking an average of the total amount of local

corrosion on the whole metal surface area (Yeih & Huang 1998).









Laboratory research has been performed that has correlated ultrasonic wave

amplitude attenuation to corrosion damage in reinforced concrete specimens. Some of the

limitations of this approach include the test control conditions. Most of the research

involving corrosion degradation in reinforced concrete specimens has involved the

corrosion of steel in intact concrete specimens. However, structures observed in the field

typically exhibit corrosion damage as a result of material deficiencies in the concrete that

encases it, usually a result of both the concrete and the steel. This problem requires

further analysis of the combined effect of both materials for field applications.

Laboratory studies have yet to incorporate both materials. The ultrasonic investigation of

a deteriorated reinforced concrete specimen essentially requires the comprehension of

ultrasonic wave forms that account for dissimilar material effects from the steel and

complex multiphase heterogeneous material that is concrete. Ultrasonic testing analysis

of the resulting damage of such complex conditions is difficult to perform. Further

research and testing is needed before ultrasonic testing can be reasonably applied in field

use for the detection of corrosion effects in reinforcing steel. Engineers need to

understand the shortcomings of nondestructive testing tests so that they can make proper

determinations and accurate evaluations of structures (Boyd et al. 2002).

Structural health monitoring

Structural health monitoring is at the forefront of structural and materials research.

Structural health monitoring systems enable inspectors and engineers to gather material

data of structures and structural elements used for analysis. Ultrasonics can be applied to

structural monitoring programs to obtain such data, which would be especially valuable

since the wave properties could be used to obtain material properties. There is scarce









literature available on the monitoring of in-place concrete structures and structural

elements.

Current research in structural monitoring relates to the performance of fiber

reinforced polymer composites and other structural strengthening methods. Fiber optics

have given rise to remote structural health monitoring, remote sensing, and

nondestructive load testing. Ultrasound has been applied to concrete strength, crack

detection, thickness measurements, and wave speeds of concrete structures.

The concept behind using ultrasonics for structural health monitoring is observing

changes in the structure's wave speed over time. As previously discussed, the wave speed

is a function of Young's Modulus of Elasticity E, the mass density p and Poisson's Ratio

v. The overall quality of the concrete is associated with the ultrasonic wave speed (Ryall

2001).

Table 2.3 Relationship between pulse velocity and concrete quality

Longitudinal Pulse Quality of Concrete
Velocity (m/s)

> 4500 excellent
3500-4500 good
3000-3500 doubtful
2000-3000 poor
< 2000 verypoor

This testing approach may be used to assess the uniformity and relative quality of

the concrete, to indicate the presence of voids and cracks, and to evaluate the

effectiveness of crack repairs. It may also be used to indicate changes in the properties of

concrete, and in the survey of structures, to estimate the severity of deterioration or

cracking. When used to monitor changes in the condition over time, tests are repeated at

the same positions (ASTM C597-97). Decreases in ultrasonic waves speeds over time can









reveal the onset of damage before visible deficiencies become evident. This allows

inspectors and engineers to implement repair recommendations before minor deficiencies

become safety hazards.

Impact Echo

The term "ultrasonic" refers to sound waves having a frequency above the human

ear's audibility limit, which is about 20,000 Hz. Ultrasonic testing has been used to

successfully evaluate the quality of concrete for approximately 60 years. This method can

be used for non-intrusively detecting internal defects in concrete. Some of these flaws

include deterioration due to sulfates or other mineral attack, and cracking and changes

due to freeze-thaw cycling. One type of ultrasonic testing is the impact-echo method.

Development of method

Nicholas Carino of the National Bureau of Standards (NBS) developed the impact-

echo method in the 1970's and 1980's for assessment of buildings and bridges that failed

during construction (Sansalone & Streett, 1997). Mary Sansalone focused her research on

the refinement and application of the impact-echo method for her Ph. D thesis at Comell

University. Their research comprises the majority of impact-echo research and

development performed in the United States applicable to concrete and concrete

structures.

Early research focused on laboratory studies involved the location of defects and

voids in concrete. There have been four key research breakthroughs since research began

to successfully develop impact echo as an NDT method (Sansalone & Streett, 1997). The

concerns utilization of the numerical simulation of stress waves in solids using finite

element computer models. This method was implemented to help facilitate the

interpretation of early experimental results. The models created were two-dimensional









finite element models based on Green's functions, which simulate stress wave

propagation in plates. Green's functions are widely used in determining responses in

solids to an applied unit force. These functions can be used to obtain the propagation of

elastic waves in solids. This mathematical formulation was essential in the interpretation

of results obtained through experimentation.

The second key research breakthrough relates to the use of steel ball bearings to

produce impact generated stress waves. The impacting of objects on the surface of a

given solid produces stress waves that facilitate signal acquisition. This elastic impact

results in a force-time function that is defined and mathematically applicable. The

impact-echo method does not use a pulse-generating transducer to generate stress waves,

rather, the impacting of an object, typically a small steel ball, provides the stress wave.

The development of the impact method overcame the need for a pulse generating

transducer. Typical steel balls range from 4 tol5 mm in diameter but can be larger or

smaller depending on the desired waveform needed for the test. Typical impact speeds

are 2 to 10 meters per second but can also vary depending upon the desired waveform.

The contact time typically ranges from 15 to 80 jts. Proper selection of steel ball diameter

and impact speed is essential in flaw detection to create the correct wave frequency,

which is typically less than 80 kHz. This range can vary depending on the properties and

dimensions of the test sample.

The third key research advancement was the development of a transducer that can

acquire impact generated stress waves. The development of the correct receiving

transducer was an integral phase in the advancement of the impact-echo method. The

receiving transducer was developed by T.M. Proctor (Hamstad and Fortunko, 1995). The









intended use for the receiving transducer was the acoustic emission testing of metals.

However, it was discovered that the transducer was compatible with impact-echo testing

of concrete. The receiving transducer is composed of a small conical piezoelectric

element bonded to a larger brass block. For protection of the transducer tip, a lead

element is fitted between the transducer tip and the material to be tested. Some tests use

coupling materials such as gels to provide an effective test surface. In areas where a

smooth concrete surface is not available, the concrete is usually grinded to a smooth

surface to ensure proper transducer-to-surface coupling. Figure 2.26 is a schematic of a

typical piezoelectric transducer.

fOutput Lead
Spring Strip



Plastics II
Case


Unity Gain /
Amplifier Brass Conical
Cylinder Piezoelectric
Element

Figure 2.26: Schematic of a typical piezoelectric transducer used for impact echo testing
(Carino 2001)

The final key research advance pertains to the use of frequency domain analysis for

signal interpretation. Waveform analysis is the determining component in the use of

NDT. In many cases the operator has difficulty in interpreting the wave signals received

in the time-domain by the piezoelectric transducer. Using a Fourier transform on the

time-domain signals, it is possible to graph the wave's frequency-domain signal. The

result is a frequency vs. amplitude plot, also called an amplitude spectrum.









Recent research advances

Much of the research and development of the impact-echo method has been carried

out at Cornell University. This research primarily involves the relevant application of

impact-echo to the evaluation and inspection of concrete and masonry materials

(Sansalone & Streett, 1997). Through this research, the methods for determining wave

speeds in concrete, grout, and masonry were improved for industry use. The research also

helped develop applicable methods for locating and determining flaws in concrete and

masonry. Some of the flaw types that have been accurately detected using the impact-

echo method include cracks, voids, bonding voids, honeycombing, and concrete damage.

The method can also be used to obtain the thickness of a material such as concrete or

asphalt pavement.

The advances in the impact-echo method made at Cornell University used a

combination of research techniques. These techniques include numerical models, finite-

element analysis, eigenvalue analysis, resonant frequency analysis and laboratory testing.

The first portable impact-echo system was developed by Mary Sansalone and Donald

Pratt and was patented by Cornell University. The patented system has five basic

components including spring-mounted impactors (ball bearings), a receiving transducer, a

high-speed digital-to-analog data-acquisition system, a rugged and powerful laptop-size

computer, and software for transferring analyzing and storing test data (Sansalone &

Street, 1997). Figure 2.27 is an illustration of a typical impact-echo equipment system.

The portable impact-echo system has been successfully developed as a commercial

product and is available for retail purchase. Most portable impact-echo systems that are

available for consumer use are purchased with four components, with the laptop

computer being omitted.






















Figure 2.27: View of a typical impact-echo equipment system

Stress wave theory

The effective use of the impact-echo system requires that the user have a basic

understanding of the properties and fundamentals of stress waves. In solid mechanics,

when any two objects collide local disturbances take place within a given material. The

disturbances can cause deformations that may be plastic or elastic in nature. A plastic

deformation is defined as a deformation in which the material is permanently deformed.

Elastic deformations are the type in which the material is temporarily deformed but then

returns to its original shape. When an elastic collision occurs between objects, a

disturbance is generated that travels through the solid in the form of stress waves. There

are three primary modes of stress wave propagation through elastic media: dilatational,

distortional, and Rayleigh waves (Sansalone & Carino, 1989).

Dilatational waves are the primary stress waves produced upon impact. They are

also referred to as primary waves, P-waves, or compression waves. The particle motion

of the wavefront of P-waves is parallel to the direction of impact propagation. The result

is a compressive or tensile stress wave (Sansalone & Streett 1997). The P-wave velocity

is the fastest of the three stress waves produced from the impact. Typical P-wave speeds









for concrete ranges from approximately 3000 m/s to 5500 m/s. For normal strength

concrete, P-wave speed usually ranges from 3500 m/s-4500 m/s.

Distortional waves are the secondary stress waves that are produced upon forced

contact. These waves are also called shear waves or S-waves. In S-waves, the particle

motion of the wave front is normal to the direction of propagation producing shear stress.

(Sansalone & Streett 1997). S-wave speed in normal concrete is usually about 62 percent

of the P-wave speed.

Rayleigh waves are also called R-waves or surface waves. Rayleigh waves, unlike

P-waves and S-waves, do not propagate through the solid. Rayleigh waves propagate

along the surface of a given concrete specimen in an elliptical motion. P-waves and S-

waves propagate through a concrete specimen in spherical wavefronts. Rayleigh wave

speed is usually 56 percent of P-wave speed. Figures 2.28 and 2.29 illustrate the typical

relationship between stress wave types.



Impact
R-wave

0.95





S-wave

v=0.2wav
numberss irncate relate wve-speed


Figure 2.28: Illustration of typical wave propagation through a cross section of a solid
(Carino 2001)






















Figure 2.29: Illustration of wave propagation model through a cross section of a solid
(Carino 2001)

The wave speeds in elastic solids are related to Young's Modulus of Elasticity E,

Poisson's ratio v, and the density p (Sansalone & Streett, 1997). In the equations below

Cp, Cs and Cr, describe the P-wave, S-wave and R-wave speeds respectively.

E(1- v)
C (5)
S p( + v)( -2v) (5)

G 1-2v
Cs =C s = (6)
P 2p(1 + v)

C 0.87 +1.12c (7)
CR =S (7)
I+v

Where G is the Shear Modulus of Elasticity.

The typical range of values for Poisson's ratio "v" is typically 0.17-0.22. Inserting

this value for v into the above equations, along with the typical density and modulus of

elasticity values, will give typical wave speeds found in concrete. The modulus of

elasticity of a concrete specimen, the compressive strength, and the appropriate wave

speed of the concrete can be obtained. Equation 5 can be used as an example obtain a

typical wave









P-wave speed for a concrete sample as follows:

Using: E=30x109 Pa, p = 2400 kg/m3, and v = 0.18


E(1- v) 30x109(1-.18)
C = C \ = 3700m/s
p(1+ v)(1- 2v) p 2400(1+.18)(1- 2(.18))

As discussed above, 3700 m/s is an acceptable P-wave speed for concrete.

Force-time function of impact

Stress waves can be produced by several different instruments. The ultrasonic pulse

velocity method uses a stress wave transmitting piezoelectric transducer. The impact-

echo method applies the collision of a steel sphere generating stress waves. The

parameters that characterize the duration of the impact or contact time are sphere size,

and the kinetic energy of the sphere at the point of impact. The variation of impact force

with time is called the force-time function, accurately represented by a half sine curve

(Sansalone & Streett 1997). The contact time duration between a small steel sphere and a

concrete surface is relatively short, ranging from 30 |ts to 100+ hts. Figure 2.30 illustrates

the typical force-time relationship.





C










0 tc Time
Figure 2.30: The typical force-time function for the elastic impact of a sphere on a solid
(Sansalone & Streett 1997)









One result of the impact of a steel sphere on a concrete specimen is the transfer of

kinetic energy from the sphere to the concrete. The energy transfer takes place in the

form of particle displacements resulting in stress waves on the impacted solid. The

maximum force is proportional to the kinetic energy of the moving sphere at impact, and

the particle displacements are proportional to this force (Sansalone & Streett 1997). The

time of contact, however, has a faint reliance on the kinetic energy of the sphere, being a

linear function of sphere diameter.

The stress waves generated by the impact contain a wide distribution of

frequencies. The frequency distribution is influenced by the force-time function of the

collision. The objective of frequency analysis is to determine the dominant frequency

components in the digital waveform. The optimum technique used to create the amplitude

spectrum is the fast Fourier transform (FFT) technique. The FFT technique assumes that

any waveform, no matter how complex, can be represented by a series of sine waves

added together. The FFT displays the amplitudes of the various frequency components in

the waveform. The amplitude spectrum obtained by the FFT contains half as many points

as the time domain waveform. The maximum frequency in the spectrum is one-half the

sampling rate. This shows the initial portion of the computed amplitude spectrum. Each

of the peaks corresponds to one of the component sine curves (Carino 2001). Figure

2.31 a illustrates a typical group of sine waves which is transformed into a typical

frequency spectrum in Figure 2.3 lb.




















oo
Times
4.2 T ---- ---- ----
4.2






02 ...... ...

o so 400 6o0
FrequLeny, Hz
Figure 2.31: Example of frequency analysis using FFT: (a) represents the frequency
distribution, (b) represents the corresponding amplitude spectrum (Carino
2001)

The linear relationship between time of contact and sphere diameter can be

described as:

t,= 0.0043D (8)

(Sansalone & Streett 1997)

where D is the sphere diameter in meters and to is the contact time in seconds. For an

impact using a sphere of a given diameter, a maximum frequency of useful energy is

created. This relationship, like the sphere diameter and contact time relationship, can also

be described as a linear function.

291
fmax = (9)

(Sansalone& Streett 1997)
(Sansalone & Streett 1997)









where fmax is the maximum frequency of useful energy in hertz and D is the sphere

diameter in meters.

The interesting concept behind Equation 9 is that maximum usable frequencies are

smaller when larger diameter spheres produce impacts. However, larger spheres produce

larger forces and larger maximum stress wave amplitudes. The contact time decreases

with decreasing sphere diameter but the range of useful frequencies increases with a

smaller diameter sphere. However, using smaller spheres increases the likelihood that the

higher frequency stress will be scattered by the natural inhomogenities inherent in

concrete. In practice, it has been found that the smallest sphere useful in impact-echo

testing has a diameter of approximately 3mm (Sansalone & Streett 1997).

Behavior of stress waves at material interfaces

The term interface is defined as a surface forming a common boundary of two

bodies, spaces, or phases. One of the most common interfaces people are familiar with is

the oil-water interface. In material science, an interface is usually defined as a fringe

between two materials which have different properties, such as density and phase. Other

differences in material properties are acoustic properties (such as acoustic impedance).

Acoustic impedance is defined as the material density multiplied by the materials stress

wave velocity. When stress waves collide with material interfaces, portions of the waves

are reflected and refracted. In obtaining the depth of a flawless concrete specimen, users

assume stress waves are being reflected at the concrete/air interface as seen in Figure

2.32.

In the development of the impact echo method, the use of finite element models

(FEMs) was prominent in the study of particle motion and stress wave propagation

through a concrete medium. The use of FEMs permitted the developers of the impact-







64


echo technique to study waveforms at projected instantaneous phases in the wave's

displacement. The model studies provided necessary information concerning the

reflection of stress waves in a concrete media. Figure 2.33, illustrates the ray paths of

typical P-wave propagation in a solid.


Figure 2.32: Plots of P, S and R-waves at various times after an impact: (a) 125 |ts,
(b)150 Lts, (c)200 Lts and (d) 250ps (Sansalone & Streett 1997)


(C)




(d)


Figure 2.33: The ray path of typical P-wave propagation through a solid media
(Sansalone & Streett 1997)









Stress wave behavior between interfaces of solids is more complicated than the

stress wave behavior between a solid-gas interface. Upon collision with a solid-gas

interface, most of the P-wave energy is reflected back into the solid media. However, in a

stress wave collision with a solid-solid interface, the P-wave energy is partially reflected

and partially refracted. The amount of energy that is allowed to pass through or refract

the second solid medium depends upon its acoustic impedance. It is possible to get a

coefficient of refraction if the acoustic impedance of the materials involved is known and

the amplitude of the particle motion is obtained for the initial P-wave.

A Z Z7
SAreflected 2 Z (10)
A, Z, + Zi

A 2Z
R refracted (11)
A, Z, + Z,

(Sansalone & Streett 1997)

Where R is the coefficient of refraction, Areflected & Arefracted are the reflected and

refracted P-wave amplitudes; Ai is the amplitude of the initial P-wave; Z1 is the acoustic

impedance of the initial medium; and Z2 is the acoustic impedance of the medium beyond

the interface.

There are three basic relationships between Z1 and Z2. The first relationship exists

when Zi is notably greater than Z2. Due to this relationship, the Z1/Z2 relationship is

comparable to the solid-gas interface in which the P-wave is completely reflected and

virtually no refraction takes place. This situation is common in the application because

most defects in concrete are related to void space in the concrete matrix.

A second relationship between solid-solid interfaces is when the Z2 is much greater

than Z1. Consider Z1 to approach zero and consider Equation 11 above, then Arefracted









approaches 2Ai. When this condition exists, the amplitude of the wave is equal to that of

the incident wave, while the amplitude of the refracted wave is twice that of the incident

wave. There is no phase change in the reflected or refracted wave. In impact-echo testing,

the no phase change case occurs, for example, when the first region is concrete and the

second region is steel or rock, as the acoustic impedances of those materials are several

times grater than that of concrete (Sansalone & Streett 1997).

The third relationship between solid-solid interfaces exists when Z2 is

approximately equal to Z1. When a value of 1 is used for both Zi and Z2, Areflected

becomes zero and Areflected becomes one. In this situation, most of the stress wave energy

is transmitted through the interface to the second solid. This situation is possible when a

concrete specimen is bonded to another concrete structure or a concrete structure has

been properly patched.

Inserting Zi and Z2, into Equation 10 and Zi is greater than Z2, a negative value is

obtained coefficient of friction "R". The negative R value denotes a phase change in the

stress wave at the point of reflection. Since impact induced P-waves are compression

waves, a phase change indicates the waves will become tension waves upon reflection.

This phenomenon is important to consider because when P-waves are reflected and Zi is

less than Z2, as in a case when steel is the solid behind the interface, the reflected waves

do not undergo phase change. Figure 2.34 below illustrates the phase changes that take

place in stress waves upon reflection.

As seen in figure 2.34a illustrates the return of a tension wave in each reflection. In

2.34b, the return of a compression wave is alternated with the return of a tension wave for

each stress wave reflection. The arrival of a tension wave causes an inward displacement









of the surface, while the arrival of a compression wave causes an outward displacement

on the material surface. The reason stress waves do not change phase when reflected on a

solid medium with a higher acoustic impedance is because the stress wave "bounces" off

the second material and returns to the impact source. The "bouncing" takes place because

materials with higher acoustic impedances have higher densities and the small surface

displacements that usually take place at solid/gas interfaces, do not take place at

boundaries more dense than the original medium.


Impact

_ 2P 4P


(a) I pact (b)

6P __ 2P 4P 6P 8P

I ,



Compression Wave
----.---- Tension Wave


Figure 2.34: Impact echo ray paths (a) A phase change at both boundaries. (b) A phase
change at upper boundary only (Sansalone & Streett 1997)

Waveform analysis idealized case

As stated in the introduction to stress waves section, such waves are the particle

motion caused by the energy of an impact. When wavefronts reach the surface, the

particle motion causes small displacements, which are detected by the receiving

transducer. The transducer converts the surface displacement into a proportional voltage

signal. The voltage signal becomes the primary output to the testing software. The output

produced requires proper understanding of waveform analysis. For each test, the operator

must properly interpret the waveform in order to ascertain the quality of the data

obtained.









A common scenario in impact-echo testing is the testing of a solid plate with

solid/gas interfaces at both concrete surfaces. As seen in Figure 2.35, the principle

features of the idealized waveform detected by the transducer are those produced by the

P-wave, which travels into the structure and undergoes multiple refractions between the

two surfaces, and the R-wave, which travels outward across the surface (Sansalone &

Street 1997).

(a) t r bJ
Impact Q r
SP j 41 | 61'
______ 21 411 1P 8 I



p 3P 5P 7P
Compre.rsion Wave T
Time
----------> Tension Wavt
Figure 2.35: Schematic representations of (a) P-wave ray reflections and (b) the resulting
idealized waveform (Sansalone & Streett 1997)

The typical elapsed time for the above waveform recorded is less than four

milliseconds. As previously noted, R-waves propagate through a solid as surface waves

and reflections of R-waves will not be recorded unless the distance between the receiving

transducer and the horizontal solid-gas interface is less than the specimen depth.

However, since the impact between the steel ball and the concrete specimen does not

occur at a point directly below the transducer, the R-wave causes a negative displacement

at the receiving transducer. As shown in the Figure 2.35, the amplitude of the R-wave is

larger than any other feature in the wave spectrum. Figure 2.35 also illustrates that the

time elapsed for the R-wave to return back to zero in the displacement spectrum is the

time of contact "t," of the impacting sphere. In this event, the point of the impacting









sphere is relatively far from the receiving transducer, the arrival of the P-wave reflection

may occur before the arrival of the R-wave. To avoid this phenomenon, the operator must

ensure that the impact point of the sphere is relatively close to the transducer. Since the

P-wave and S-wave speeds are greater than the R-wave speed, there is a small

displacement just prior to the arrival of the R-wave. This small displacement is due to the

arrival of the P and S wavefronts.

The reflections of the P-wave with the solid-gas interface shown in Figure 2.35,

illustrate the expected phase change. The arrival of the tension wave at the impacting

surface causes a small inward displacement causing the wave reflections shown at times

ti, t2 and t3. The elapsed time ti, between the impact and arrival of the 2P wave at the

surface is the distance the wave has traveled, being twice the solid thickness. The P-wave

arrivals at the upper surface cause displacements that are periodic in nature. This

periodicity is the dominant feature of the waveform after the passage of the R-wave. The

period of the waveform in Figure 2.35 is ti and its frequency is l/ti, the reciprocal of the

period. This yields a simple relationship shown in Figure 2.33, which is at the heart of the

impact-echo method (Sansalone & Streett 1997).


f =CP (12)
2T

(Sansalone & Streett 1997)

Waveform analysis actual case

The technique presented in the previous paragraph is an accurate description of

waveform analysis, but it illustrates waveform circumstances under idealized conditions.

One difference between the idealized case and the actual case is that the reactions of the

transducer to the material displacements is caused by stress waves. As the stress waves









reflect due to the solid-gas interface, the receiving transducer experiences its own particle

motions. This additional movement is referred to as "overshoot". Overshoot causes the

waveform displayed by the digital analysis software to have only the negative portion of

each wave. This wave analysis software phenomenon is illustrated in Figure 2.36.

S21'
I jr dIi181
---





Figure 2.36: Actual waveform on an impact-echo test plate (Sansalone & Street 1997)

Figure 2.36 shows the actual waveform as it would be received and displayed by

impact-echo software in field-testing. Another phenomenon that this figure illustrates is

the decay of the spectral amplitude with the increasing number of wave reflections. This

decay is a result of energy losses due to friction as the wave propagates within the solid

matrix.

Through rigorous testing in the development of impact echo, it was observed that

the frequencies obtained in laboratory testing of concrete specimens were not equal to the

frequencies calculated in Equation 12. The use of finite element models and laboratory

testing revealed a deviation of approximately 5% between the observed laboratory data

and the expected results obtained by Equation 12. After considering the geometry of the

specimen, the developers found that it was necessary to include a shape factor in the

frequency equation. In the case of a solid plate, the characteristic dimension is the

thickness T, and the shape factor 3 is 0.96 (Sansalone & Streett 1997).









Bf C 0.96C (13)
f= =-" (13)
2T 2T

(Sansalone & Streett 1997)

Field measurement of material stress wave speed

In field-testing, it is crucial to establish the wave speed of the solid before specimen

dimensions and qualities are to be tested. The most common method for directly

measuring the wave speed of a solid is through the use of two receiving transducers. The

transducers are commonly placed in a spacer device, at a known fixed length from each

other. Once the transducers are properly spaced and fixed to the concrete specimen, a

single P-wave can be used to measure the wave speed of the concrete. Figure 2.37

illustrates the typical test set up behind the measurement of wave speed. Figure 2.38 is an

example of a typical output obtained in acquisition of the wave speed.


Figure 2.37: Schematic representation of the test set up for wave speed measurements
(ASTMC 1383-R98a 2001)







72


0.15
::--- iTransducer 1
0.1 -- ..- -- -- ......... --- Transducer 2

0 .05 ---- -- ... .. ... ..... ..... ..


0-.
-o^ os o --,- "..-..... ............. ...... ................. .. ...... ..



t = 2 s, L = 300mm

60 80 100 120 140 160 180 200
Time, ps
Figure 2.38: Example waveform obtained in wave speed measurements (ASTM 2001)

When the test is performed, the output would simply record the time at which the

P-wave is received by each transducer. The wave speed would then be:

L
Cp = (14)
t2 -t

(ASTM C1383 2001)

However, it is important to create the impact far enough from the initial transducer

to allow for P-wave separation from the S and R-waves. This is the basis for having the

minimum distance between the impact of the sphere and the first transducer set to 1/2L.

For the example of output illustrated in Figure 2.38, the results are t2 = 156 jts, ti = 80 jts

and L=300 mm. Using Equation 14, the wave velocity of the sample is obtained by the

following:

300 mm
Cp = = 3950 m/s
156 ys 80 us

Once the wave speed has been established for the concrete specimen, then testing

for the specimen's thickness, concrete quality, flaw and anomaly detection may be

performed.









The effect of flaws on impact-echo response

Impact-echo was developed to nondestructively investigate concrete. One of the

advantages of impact-echo testing is the versatile equipment and the relatively brief

duration of the testing procedure. This allows inspectors to efficiently and accurately

investigate structures and concrete specimens for condition assessment. The impact echo

responses of materials can be classified according to the type, depth, and size of flaw.

For the purposes of impact-echo testing, a crack is defined as an interface or

separation where the minimum opening is 0.08 mm or larger. Stress waves are able to

propagate across voids that are smaller than 0.08 mm, hence there is not enough wave

reflection to detect these smaller deficiencies. Since water has a coefficient of reflection

of approximately 0.7, the majority of the stress wave energy at a solid-water interface is

reflected and water filled voids can also be detected using the impact-echo method.

As the depth of a void from the surface increases, the smallest size that can be

detected also increases. Based on analytical and laboratory studies, it has been suggested

that if the lateral dimensions of a planar crack or void exceed 1/3 of its depth, the flaw

depth can be measured. If the lateral dimensions exceed 1.5 times the flaw depth, the flaw

behaves as an infinite boundary and the response is that of a plate with thickness equal to

the flaw depth (Carino 2001). Figure 2.39 illustrates the relationship between crack depth

and detectability.


Depth can be Depth cannot -Infinite" flaw
measured be measured dT > 1.5
d/<0.3
Figure 2.39: Illustration of the smallest detectable crack and its dependency on depth.









If the flaw is located entirely within the white area, the crack depth cannot be

measured (Carino 2001) When larger cracks or voids are present, the impact-echo

response will be essentially the same as if there was a solid/gas boundary at that interface.

The test will produce results that represent the termination of the material at the depth of

the flaw. A crack or void within a concrete structure forms a concrete/air interface.

Laboratory experiments have shown that cracks with a minimum width (crack opening)

of about 0.08mm (0.003 inches) cause almost total reflection of a P-wave. The responses

from cracks and voids are similar, since stress waves are reflected from the first

concrete/air interface encountered. Thus a crack at a depth d will give the same response

as a void whose upper surface (nearest to the impact surface) is at the same depth (Figure

2.40).

(a) (b)


dd






Figure 2.40: A crack at depth "d" gives the same response as a void at that depth
(Sansalone & Streett 1997)

In cases where the lateral dimensions of the crack are about equal or less than the

depth of the crack, propagating stress waves are both reflected and refracted from the

surface. Hence, they are diffracted around the edges of the crack (Sansalone & Streett

1997). For similar cases where more complicated waveforms exist, the frequency

spectrums are affected accordingly.









Applications

When properly used, the impact-echo method has achieved unparalleled success in

locating flaws and defects in highway pavements, bridges, buildings, tunnels, dams,

piers, sea walls and many other types of structures. It can also be used to measure the

thickness of concrete slabs (pavements, floors, walls, etc.) with an accuracy of 3 percent

or better. Impact-echo is not a "black-box" system that can perform blind tests on

concrete and masonry structures and always tell what is inside. The method is used most

successfully to identify and quantify suspected problems within a structure, in quality

control applications (such as measuring the thickness of highway pavements) and in

preventive maintenance programs (such as routine evaluation of bridge decks to detect

delaminations). In each of these situations, impact-echo testing has a focused objective,

such as locating cracks, voids or delaminations, determining the thickness of concrete

slabs or checking a post-tensioned structure for voids in the grouted tendon ducts.

Determining the depth of surface-opening cracks

A surface-opening crack is any crack that is visible at the surface. Such cracks can

be perpendicular, inclined to the surface, or curved, as shown in Figure 2.41.

The two waveforms, labeled 1 and 2, in Figure 2.42(b), are the signals from

transducers 1 and 2 in Figure 2.42(a). The arrival of the direct P-wave, a compression

wave, at transducer 1 causes an upward surface displacement and a positive voltage (time

tl), while the diffracted wave that first reaches transducer 2 is a tension wave, which

causes a downward displacement and a sudden voltage drop (time t2). The elapsed time

between ti and t2, the wave speed, and the known distances H1, H2 and H3, are used to

calculate the depth D.






76












(a) (b) (c)


Figure 2.41: Surface-opening cracks: (a) perpendicular, (b) inclined, and (c) curved
(Sansalone & Street 1997)





3 Hi 2 (a) to ti (b)

1 \

\ I1 *-
D 2t


B
Time


Figure 2.42: Measuring the depth of a surface-opening crack: (a) schematic of
experimental test setup, and (b) sample waveforms (Sansalone & Street 1997)

Voids under plates

Detecting voids under concrete plates is one of the simplest applications of the

impact-echo method. It relies on the clear and easily recognizable difference between

waveforms and spectra obtained from plates in contact with soil, on the one hand, and

plates in contact with air (a void under the slab) on the other.

Figure 2.42 shows a typical set of results obtained from an impact-echo test on a

concrete plate in contact with soil. The waveform shows periodic displacements caused









by P-wave reflections within the concrete plate, but because energy is lost to the soil each

time a P-wave is incident on the concrete/soil interface, the amplitude of the

displacements (indicated by the signal voltage) decays rapidly. The corresponding

spectrum shows a single peak corresponding to the frequency of P-wave reflections from

the concrete/soil interface. Note however, that the peak is somewhat rounded and is

broader than those obtained from plates in contact with air. In Figure 2.43 only a few

wave reflections were recorded before the signal decayed to an undetectable level.

For comparison, Figure 2.44 shows a typical result obtained from an impact-echo

test on the same plate at a location where a void exists in the soil just below the plate. In

this case P-wave reflections occur from a concrete/air interface at the bottom of the plate.

Because virtually all of the wave energy is reflected at a concrete/air interface, surface

displacements caused by the arrival of reflected P-waves decay more slowly compared to

those reflected from a concrete/soil interface. The response is essentially the same as that

obtained from a simple concrete plate in contact with air. The spectrum exhibits a very

sharp, high amplitude peak corresponding to the P-wave thickness frequency. If the

concrete slab is relatively thin (about 150mm or less) a lower frequency, lower amplitude

peak, labeled fflex in Figure 2.44(c), may also be present, as a result of flexural vibrations

of the unsupported portion of the plate above the void. Flexural vibrations occur because

the unsupported section above the void is restrained at its edges where it contacts the soil.

The response is similar to that produced by an impact above a shallow delamination.

However, because the thickness of the slab is relatively large, the amplitude of the

flexural vibrations is smaller relative to the P-wave thickness response.















Concrete T

Soil





(b) (c)
fT







0 2048 0 10 20 30 40 50
Time, ps Frequency, kH z

Figure 2.43: The impact-echo response of a concrete slab on soil subgrade: (a) cross-
section, (b) waveform, and (c) spectrum (Sansalone & Streett, 1997)


Figure 2.44: The impact-echo response obtained from a concrete slab at a location where
a void exists in the soil subgrade: (a) cross-section; (b) waveform; and (c)
spectrum (Sansalone & Streett, 1997)


Steel reinforcing bars


Impact-echo is primary used to locate flaws in, or thickness of, concrete structures.


Impact-echo may also be used to determine the location of steel reinforcing, though


(a)


Concrete T

Soil




(b) (c)

ff T






0 1024 0 10 20 30 40 50


Frequency, kHz


Time, ips









magnetic or eddy current meters are better suited to this purpose. The acoustical

impedance of steel is 5 times that of the concrete. If the sizes of reinforcement bars are

known the impact-echo response can be estimated. If information is not known the

reinforcing size can be estimated from a cover meter. Impact echo can be applied to

evaluate the corrosion of reinforcing bars. The response is similar to solid plates, with

single large amplitude peak P-wave thickness frequency. Waves travel around the

corroding bar, instead of propagating through it, since the corrosion forms an acoustically

soft layer around the bar. Short duration impacts result in peaks at higher frequencies,

corresponding to reflections from the corroding surfaces. This method has been able to

identify corrosion on reinforcement bars and has proven to be cost-efficient in identifying

wall repair locations.

Voids in the tendon ducts of post-tensioned structures

The impact-echo method can be used to detect voids in grouted tendon ducts in

many, but not all, situations. The method's applicability depends on the geometry of a

structure and the locations and arrangement of tendon ducts. Small voids in tendon ducts

cannot be detected if the ratio of the size of the void to its depth beneath the surface is

less than about 0.25. In addition, complicated arrangements of multiple ducts, such as

often occur in the flanges of concrete I-beams, can preclude detection of voids in some or

all of the ducts. In other cases, portions of structures can be successfully tested and

information can be gained that permits an engineer to draw conclusions about the

condition of the grouting along the length of the duct. The simplest case is that of post-

tensioned ducts in a plate structure, such as a bridge deck or the web of a large girder, in

which there is only one duct directly beneath the surface at any point. In all cases, the

impact- echo method is restricted to situations where the walls of the ducts are metal









rather than plastic. Effective use of the impact-echo method for detecting voids in

grouted tendon ducts requires knowledge of the location of the ducts within the structure.

This information is typically obtained from plans and/or the use of magnetic or eddy-

current cover meters to locate the centerlines of the metal ducts. Once the duct locations

are known, impact-echo tests can be performed to search for voids.

Metal ducts

Tendon ducts in post-tensioned structures are typically made of steel with a wall

thickness of about 1mm (0.04 inches). The space not occupied by tendons inside the duct

is (or should be) filled with grout, which has acoustic impedance similar to that of

concrete. Because the wall thickness of a duct is small relative to the wavelengths of the

stress waves used in impact-echo testing, and because a steel duct is a thin layer of higher

acoustic impedance between two materials of lower acoustic impedance (concrete and

grout), it is transparent to propagating stress waves. Therefore, the walls of thin metal

ducts are not detected by impact-echo tests. (In contrast, plastic ducts have a lower

acoustic impedance than concrete or grout, and they are not transparent, complicating

attempts to detect voids within plastic ducts.)

Benefits to using impact-echo

Applications of the IE method include quality control programs (such as measuring

pavement thickness or assessing pile integrity), routine maintenance evaluations to detect

cracks, voids, or delaminations in concrete slabs, delineating areas of damage and

corrosion in walls, canals, and other concrete structures. Impact echo can be used to

assess quality of bonding and condition of tunnel liners, the interface of a concrete

overlay on a concrete slab, concrete with asphalt overlay, mineshaft and tunnel liner

thickness.









Concrete pavements and structures can be tested in less time, and at lower cost,

meaning more pavements and structures can be tested. No damage is done to the concrete

and highway workers spend less time in temporary work zones, reducing the chance of

injury and minimizing downtime for the traveling public. Impact-echo, according to

ASTM, may substitute for core drilling to determine thickness of slabs, pavements,

walks, or other plate structures.

Acoustic Emission

Acoustic emission (AE) is defined as a transient elastic wave generated by the rapid

release of energy within a material. These deformations can come from plastic

deformation such as grain boundary slip, phase transformations, and crack growth. (Davis

1997). Unlike most nondestructive testing techniques, acoustic emission is completely

passive in nature. In fact, acoustic emission cannot truly be considered nondestructive,

since acoustic signals are only emitted if a permanent, nonreversible deformation occurs

inside a material. As such, only nonreversible processes that are often linked to a

gradually processing material degradation can be detected (Kaiser & Karbhari 2002).

Acoustic emission is used to monitor cracking, slip between concrete and steel

reinforcement, failure of strands in prestressing tendons, and fracture or debonding of

fibers in fiber reinforced concrete.

Theory

There are two types of acoustic emission signals: continuous signals and burst

signals. A continuous emission is a sustained signal level, produced by rapidly occurring

emission events such as plastic deformation. A burst emission is a discrete signal related

to an individual emission event occurring in a material, such as a crack in concrete. An

acoustic emission burst signal is shown in Figure 2.45.












Pak OmplfludF



Bi~ ji~ilL^,L


Figure 2.45: Burst acoustic emission signal with properties (Malhotra 1991)

The term "Acoustic emission signal" is often used interchangeably with acoustic

emission. An AE signal is defined as the electrical signal received by the sensor in

response to an acoustic wave propogating through the material. The emission is received

by the sensor and transformed into a signal, then analyzed by acoustic emission

instrumentation, resulting in information about the material that generated the emission.

An acoustic emission system setup is shown in Figure 2.46.

A^ SIGNAL
SENSOR SIGNAL
ELECTRONICS

STIMULUS STIMULUS
(FORCE) (FORCE)




SOURCE WAVE PROPAGATION

Figure 2.46: Acoustic emission process (Hellier 2001)

Method development

Acoustic emission testing is used to obtain noise sounds produced by material

deformation and fracture. Early terminology for acoustic emission testing was









"microseismic activity." AE signals occur when micro or small fractures are detected

within the material. The first documented observations of Acoustic Emission activities

occurred in 1936 by two men, Forster and Scheil, who detected clicks occurring during

the formation of martensite in high-nickel steel. In 1941, research by Obert, who used

subaudible noise for prediction of rock bursts, noted that noise rate increased as a

structure's load increased. In 1950, Kaiser submitted a PhD thesis entitled "Results and

Conclusions of Sound in Metallic Materials Under Tensile Stress" (Scott 1991).

Kaiser's research is considered to be the beginning of acoustic emission as it is

known today. In 1954 Schofield became aware ofKaiser's early work, and initiated the

first research program in the United States related to materials engineering applications of

acoustic emission (Scott 1991).

During the early developmental testing for AE, several correlations were formed.

Acoustic emission readings in materials of high toughness differed in amount and size

from low toughness material. This was attributed to the differences in failure modes

(Scott, 1991). Early acoustic emission testing signals were small and required a

relatively calm environment for proper testing. With the use of an additional sensor,

background noise could be isolated, which enabled testing to be carried out in a relatively

noisy environment. The preliminary results of acoustic emission testing required massive

data calculations due to the extensive numerical output the acoustic emission signals

produced. This phenomenon distracted scientists, diverting too much of their attention to

signal analysis instead of evaluation of the signal itself. Acoustic emission testing proved

to be a highly sensitive indicator of crack formation and propagation.









Early use of acoustic emission testing proved to be valuable, but the first acoustic

emission signals acquired contained large amounts of noise signals. This made it difficult

as scientists were unable to develop AE as a quantitative technique. The material

sensitivity and initial research results gave birth to a successful future for acoustic

emission as a reliable nondestructive test.

Kaiser effect

One of the most common uses of acoustic emission is in load testing of a structure

or specimen. The generation of the acoustic emission signals usually requires the

application of a stress to the test object. However, acoustic emissions were found not to

occur in concrete that had been unloaded until the previously applied maximum stress

was exceeded during reloading (Malhotra 1991). This phenomenon takes place for stress

levels below 75 85% of ultimate strength and is found to be only temporary. Therefore,

it cannot be used to determine the stress history of a structural specimen. Additional

theory can be found in several references (Ohtsu et al. 2002; Hearn 1997; Tam & Weng

1995; Yuyama et al. 1992; Malhotra 1991; Scott 1991; Lew et al. 1988).

Equipment and instrumentation

An acoustic emission system has the same basic configuration as seen in ultrasonic

testing systems. The typical testing apparatus used for acoustic emission (shown in

Figure 2.47 consists of the following:

* Transducer
* Reveiver/Amplifier
* Signal Processors
* Transient Digitizers
* Display
* Calibration Block
* Coupling Agent