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Effect of Environment on the Stiffness of Carbon Fiber Reinforced Polymer Repaired Concrete

Permanent Link: http://ufdc.ufl.edu/UFE0022708/00001

Material Information

Title: Effect of Environment on the Stiffness of Carbon Fiber Reinforced Polymer Repaired Concrete
Physical Description: 1 online resource (103 p.)
Language: english
Creator: Van Etten, Nathaniel
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: environment, epoxy, moisture, stiffness
Civil and Coastal Engineering -- Dissertations, Academic -- UF
Genre: Civil Engineering thesis, M.E.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: The use of carbon fiber reinforced polymer (CFRP) composites for repair and strengthening of concrete has been become increasingly popular in recent years. In the past, research has been conducted to evaluate the mechanical properties of CFRP and its effectiveness as reinforcement. More recently, research has focused on the durability of CFRP on concrete. Unfortunately, the majority of durability research conducted on CFRP has focused on strength while the effects of moisture on stiffness have remained relatively ignored. The goal of the research reported in this thesis was to investigate how the stiffness properties of CFRP reinforced concrete beams are altered due to moisture immersion. Slotted beam specimens reinforced with CFRP composite strips were placed in exposure tanks created to provide full immersion in water at elevated temperatures of 30?C, 40?C, 50?C and 60?C. The effects of tidal exposure on stiffness on CFRP reinforced beams were also investigated by placing beam specimens on bridge fenders found in Crescent Beach, FL. After immersion durations of 6, 12, and 18 months a group of CFRP specimens were tested in flexure, and the stiffness values for each beam system were recorded. Analysis of the load deflection data showed that beam specimens reinforced with CFRP exhibit three different stiffness characteristics: uncracked, stiffness behavior at the cracking point, and post-cracking stiffness. When exposed to moisture it was discovered that water immersion produced lower uncracked stiffness values than the control specimens. However, there appeared to be little correlation between stiffness performance and immersion temperature. Specimens exposed to tidal conditions show decreased flexural stiffness compared to the control specimens. Behavior at the cracking point was found to be highly dependant on the debonded length of the concrete and the composite strip. Specimens that experienced small debonded lengths exhibited bilinear behavior between the recorded uncracked and post-cracking stiffness values. Composite systems immersed at elevated temperatures are more likely to exhibit bilinear behavior than the control specimens. Meanwhile, tidal exposure was found to reduce the likelihood of bilinear behavior for beam specimens reinforced with CFRP. It was speculated that both of these phenomena were related to changes in the debonding length created by moisture exposure. Moisture exposure was found to have little effect on the post-cracking stiffness values. In some instances it was recorded that moisture exposure could produce post-cracking stiffness values higher than the control specimens. It was speculated that the high post-cracking stiffness values noticed for the immersed composite beam specimens was caused by unchanged or improved debonding behavior.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Nathaniel Van Etten.
Thesis: Thesis (M.E.)--University of Florida, 2008.
Local: Adviser: Hamilton, Homer R.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2009-02-28

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022708:00001

Permanent Link: http://ufdc.ufl.edu/UFE0022708/00001

Material Information

Title: Effect of Environment on the Stiffness of Carbon Fiber Reinforced Polymer Repaired Concrete
Physical Description: 1 online resource (103 p.)
Language: english
Creator: Van Etten, Nathaniel
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: environment, epoxy, moisture, stiffness
Civil and Coastal Engineering -- Dissertations, Academic -- UF
Genre: Civil Engineering thesis, M.E.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: The use of carbon fiber reinforced polymer (CFRP) composites for repair and strengthening of concrete has been become increasingly popular in recent years. In the past, research has been conducted to evaluate the mechanical properties of CFRP and its effectiveness as reinforcement. More recently, research has focused on the durability of CFRP on concrete. Unfortunately, the majority of durability research conducted on CFRP has focused on strength while the effects of moisture on stiffness have remained relatively ignored. The goal of the research reported in this thesis was to investigate how the stiffness properties of CFRP reinforced concrete beams are altered due to moisture immersion. Slotted beam specimens reinforced with CFRP composite strips were placed in exposure tanks created to provide full immersion in water at elevated temperatures of 30?C, 40?C, 50?C and 60?C. The effects of tidal exposure on stiffness on CFRP reinforced beams were also investigated by placing beam specimens on bridge fenders found in Crescent Beach, FL. After immersion durations of 6, 12, and 18 months a group of CFRP specimens were tested in flexure, and the stiffness values for each beam system were recorded. Analysis of the load deflection data showed that beam specimens reinforced with CFRP exhibit three different stiffness characteristics: uncracked, stiffness behavior at the cracking point, and post-cracking stiffness. When exposed to moisture it was discovered that water immersion produced lower uncracked stiffness values than the control specimens. However, there appeared to be little correlation between stiffness performance and immersion temperature. Specimens exposed to tidal conditions show decreased flexural stiffness compared to the control specimens. Behavior at the cracking point was found to be highly dependant on the debonded length of the concrete and the composite strip. Specimens that experienced small debonded lengths exhibited bilinear behavior between the recorded uncracked and post-cracking stiffness values. Composite systems immersed at elevated temperatures are more likely to exhibit bilinear behavior than the control specimens. Meanwhile, tidal exposure was found to reduce the likelihood of bilinear behavior for beam specimens reinforced with CFRP. It was speculated that both of these phenomena were related to changes in the debonding length created by moisture exposure. Moisture exposure was found to have little effect on the post-cracking stiffness values. In some instances it was recorded that moisture exposure could produce post-cracking stiffness values higher than the control specimens. It was speculated that the high post-cracking stiffness values noticed for the immersed composite beam specimens was caused by unchanged or improved debonding behavior.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Nathaniel Van Etten.
Thesis: Thesis (M.E.)--University of Florida, 2008.
Local: Adviser: Hamilton, Homer R.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2009-02-28

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022708:00001


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EFFECT OF ENVIRONMENT ON THE STIFFNESS OF CARBON FIBER-REINFORCED POLYMER (CFRP) REPAIRED CONCRETE By NATHANIEL ALLEN VAN ETTEN 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 2008 1

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2008 Nathaniel Allen Van Etten 2

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To my family, my friends, and myself 3

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ACKNOWLEDGMENTS The completion of this thesis and the accompa nying research would not have been possible without the efforts of an amazing group of individua ls. First, I thank Dr. Trey Hamilton for his continual support. He offered a wealth of knowledge and a willingness to help under all circumstances and time frames. Despite all of the difficulties endured th roughout this process, I am glad to have learned from such a talented and hard working individual. I also recognize Sungwon Choi for all of his assistance during the te sting phase of this research. He provided a tireless work ethic that greatly simplified a complex process. Others deserving recognition in clude my parents and family for their continual support and willingness to listen to my research-related speeches. I thank Kara Kleinfelt for her unwavering support, companionship and the wonderful meals that fueled the final phases of this research. Finally, I thank Dr. Elliot Douglas, and Dr. Ron Cook for serving on my supervisory committee. Their insight and willingness to help was greatly appreciated. 4

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TABLE OF CONTENTS page ACKNOWLEDGMENTS ............................................................................................................... 4 LIST OF TABLES ...........................................................................................................................7 LIST OF FIGURES .........................................................................................................................8 LIST OF FIGURES .........................................................................................................................8 ABSTRACT ...................................................................................................................... .............10 CHAPTER 1 INTRODUCTION ................................................................................................................ ..12 2 BACKGROUND ....................................................................................................................14 Previous Research in CFRP Stre ngth and Stiffness Durability ..............................................14 Moisture ...................................................................................................................... ............14 Moisture/Salt ...........................................................................................................................15 Conclusions of Previous CFRP Environmental Durability Research.....................................16 3 TEST SET-UP ................................................................................................................. .......18 Concrete Mix Design ..............................................................................................................18 Epoxy Systems ........................................................................................................................19 Commercial Epoxy Systems ............................................................................................19 Composite A .............................................................................................................19 Composite B .............................................................................................................20 Composite C .............................................................................................................21 Formulated Epoxy System ..............................................................................................21 Exposure System ....................................................................................................................22 Fresh Water Exposure Conditions ...................................................................................22 Tidal Zone Exposure .......................................................................................................23 Testing Procedure ............................................................................................................. ......24 4 SUMMARY OF STRENGTH RESULTS .............................................................................41 CFRP System A: Water Immersion ........................................................................................41 CFRP System B: Water Immersion ........................................................................................41 CFRP System C: Water Immersion ........................................................................................42 CFRP System D: Water Immersion ........................................................................................42 CFRP System E: Water Immersion ........................................................................................42 5 EFFECT OF ENVIRONMENT ON STIFFNESS .................................................................50 5

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Flexural Behavior ...................................................................................................................51 Analysis of Uncracked Stiffness .............................................................................................54 Control Specimens ...........................................................................................................54 Heated Water Exposure ...................................................................................................55 Coastal Exposure .............................................................................................................56 Analysis of Cracking Point Behavior .....................................................................................58 Control Specimens ...........................................................................................................58 Heated Water Exposure ...................................................................................................62 Coastal Exposure .............................................................................................................63 Analysis of Post-Cracking Stiffness .......................................................................................64 Control Specimens ...........................................................................................................64 Heated Water Exposure ...................................................................................................66 Coastal Exposure .............................................................................................................68 6 CONCLUSIONS ................................................................................................................. ...98 APPENDIX UNCRACKED FL EXURAL BEHAVIOR ..............................................................99 LIST OF REFERENCES .............................................................................................................101 BIOGRAPHICAL SKETCH .......................................................................................................103 6

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LIST OF TABLES Table page 3-1 Twenty eight day compressive strength and modulus of rupture ......................................26 3-2 Material properti es for composite A ..................................................................................27 3-3 Material properti es for Composite B .................................................................................28 3-4 Material properti es for Composite C .................................................................................29 3-5 Summary of environmental conditions used to weather the specimens ............................30 5-1 Measured vs calculated URc va lues for all composite systems .........................................70 5-2 Percent control strengths at various immersion temperatures for composite D ................71 5-3 Percent control strengths at various immersion temperatures for composite E .................72 7

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LIST OF FIGURES Figure page 3-1 Final beam specimen configuration. ..................................................................................31 3-2 Procedure to apply composite system A ............................................................................32 3-3 Construction techni que for composite C ............................................................................33 3-4 Completed construction of composites D and E ................................................................34 3-5 University of Florid a exposure tank set-up ........................................................................35 3-6 Fender beams to be used to hang concrete beams .............................................................36 3-7 Typical real time beam installation ....................................................................................37 3-8 Typical specimen layout after coastal exposure ................................................................38 3-9 Typical specimen after sc raping and flexural testing ........................................................39 3-10 Specimen loaded in testing apparatus ................................................................................40 4-1 Strength ratio for UF and UW CFRP system A for different temp erature submersion .....44 4-2 Strength ratio for CFRP system B fo r different immersion temperatures .........................45 4-3 Control flexural streng th ratio for composite C .................................................................46 4-4 Failure modes for composite C at various temperatures ....................................................47 4-5 Strength ratio for CFRP system D for different immersion temperatures .........................48 4-6 Strength ratio for CFRP System E for different immersion temperatures .........................49 5-1 Typical load deflection cu rve with bilinear uncracked and post-cracking behavior .........73 5-2 Typical load deflection cu rve with linear uncracked s tiffness and approximated postcracking stiffness ...............................................................................................................74 5-3 Typical flexural crack propagation ....................................................................................75 5-4 Typical debonding damage observed for we t lay-up systems just before failure ..............76 5-5 Typical plots for the three s tiffness behaviors at cracking ................................................77 5-6 URC values at all exposure lengths .....................................................................................78 8

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5-7 Relative effect of heated water exposure on uncracked stiffnesses of CFRP systems. .....79 5-8 Effect of prolonged coasta l exposure for composites A, B, and C on stiffness ratio ........80 5-9 Stiffness reduction behavior at cracking for control specimens ........................................81 5-10 Illustration showing typical corn er cracking for beam specimens .....................................82 5-11 Typical corner cracking beha vior for control specimens ...................................................83 5-12 Illustration of debonding in beam specimens ....................................................................84 5-13 Illustration showing mode II crack ex tension for half of a beam specimen ......................85 5-14 Stress distribution along composite strip for a half beam specimen ..................................86 5-15 Stiffness reduction frequencies for composite D for all exposed specimens .....................87 5-16 Stiffness reduction frequencies for composite E for all exposed specimens .....................88 5-17 Typical interfacial fail ure mode for composite C ..............................................................89 5-18 Stiffness reduction freque ncy caused by tidal exposure ....................................................90 5-19 Cracked stiffness ratios at all te sting dates for control specimens .....................................91 5-20 Ultimate flexural capacities for all of the control specimens ............................................92 5-21 Cracked stiffness ratio for the CFRP systems ....................................................................93 5-22 Cracked stiffness ratio for the CFRP systems ....................................................................94 5-23 Cracked stiffness ratio performance with exposure time ...................................................95 5-24 Typical load deflecti on plot for composite B ....................................................................96 5-25 Failure modes for composite C in various exposure systems ............................................97 9

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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 EFFECT OF ENVIRONMENT ON THE STIFFNESS OF CARBON FIBER-REINFORCED POLYMER (CFRP) REPAIRED CONCRETE By Nathaniel Allen Van Etten August 2008 Chair: H.R. Hamilton, III Major: Civil Engineering The use of carbon fiber reinforced poly mer (CFRP) composites for repair and strengthening of concrete has b een become increasingly popular in recent years. In the past, research has been conducted to evaluate the mech anical properties of CFRP and its effectiveness as reinforcement. More recently, research has focused on the durability of CFRP on concrete. Unfortunately, the majority of durability resear ch conducted on CFRP has focused on strength while the effects of moisture on stiffness have remained relatively ignored. The goal of the research reported in this thesis was to investig ate how the stiffness propert ies of CFRP reinforced concrete beams are altered due to moisture imme rsion. Slotted beam specimens reinforced with CFRP composite stri ps were placed in exposure tanks creat ed to provide full immersion in water at elevated temperatures of 30C, 40C, 50C and 60C. The effects of tidal exposure on stiffness on CFRP reinforced beams were also in vestigated by placing beam specimens on bridge fenders found in Crescent Beach, FL. After immersion durations of 6, 12, and 18 mont hs a group of CFRP specimens were tested in flexure, and the stiffness values for each beam system were recorded. Analysis of the load deflection data showed that beam specimens re inforced with CFRP exhibit three different 10

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stiffness characteristics: uncracked, stiffness be havior at the cracking point, and post-cracking stiffness. When exposed to moisture it was discove red that water immersion produced lower uncracked stiffness values than the control speci mens. However, there appeared to be little correlation between stiffness performance and i mmersion temperature. Specimens exposed to tidal conditions show decreased flexural stiffness compared to the control specimens. Behavior at the cracking point was found to be highly dependent on the debonded length of the concrete and the composite strip. Speci mens that experienced small debonded lengths exhibited bilinear behavior between the recorded uncracked and post-crac king stiffness values. Composite systems immersed at elevated temper atures are more likely to exhibit bilinear behavior than the control specimens. Mean while, tidal exposure was found to reduce the likelihood of bilinear behavior for beam specimens re inforced with CFRP. It was speculated that both of these phenomena were related to change s in the debonding length created by moisture exposure. Moisture exposure was found to have little eff ect on the post-cracking stiffness values. In some instances it was recorded that moisture exposure could produce post-cracking stiffness values higher than the control sp ecimens. It was speculated that the high post-cracking stiffness values noticed for the immersed composite beam specimens was caused by unchanged or improved debonding behavior. 11

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CHAPTER 1 INTRODUCTION Externally bonded carbon fiber reinforced polym er (CFRP) is a relatively new construction material that provides additional strengthening to reinforced concrete structures that have undergone severe degree of flexural cracking. As a result of its ability to be installed externally, CFRP has become increasingly pop ular in a number of civil engineering applications ranging from column wrapping for increased concrete containment during seismic occurrences, and providing additional flexural and shear reinforcement for walls, beams and slabs. Due to the relatively recent application of CFRP to civil infrastructure as a reinforcing material, the durability of the system has not been extensively researched. Several CFRP systems are available for surf ace-bonded treatment of concrete. The two methods of CFRP installation are pre-cured lamina tes and wet lay-up systems. In the wet lay-up system, dry sheets of unidirectional or multidirectional carbon based fabric are saturated in an engineered specified epoxy at the job site and rolled onto the surface using the saturant as the adhesive. Sometimes a primer is needed to fi ll any existing voids on the surface layer of the concrete and to aid in bonding the CFRP to the substrate surface. All parts of the aforementioned system including the epoxy used fo r saturation and priming are formed in the field. Pre-cured systems are manuf actured in a controlled factory setting and can be purchased in various sizes and quantities. These pre-cured sy stems are then cut to length in the field and bonded to the surface of the concre te with an adhesive putty to provide stress transfer. The adhesive putty components are t ypically mixed in the field. Currently, the emphasis of durab ility research conducted regard ing the effect of CFRP on concrete specimens has focused on ultimate stre ngth capacity. This investigation plans to 12

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examine the changes in flexural stiffness of CFRP reinforced beam specimens created by prolonged exposure to various moisture environments. In a study jointly conducted by th e University of Florida and the University of Wyoming the effects of moisture on the ultimate streng th of CFRP (Carbon Fiber Reinforced Polymers) reinforced concrete were investigated for the National Cooperative Highway Research Program (NCHRP). This thesis uses th e data collected from the aforem entioned study to investigate the effects of heated water and tidal exposure on the flexural stiffness of concrete beams externally reinforced with CFRP (Carbon Fiber Reinforced Polymers). The milestones reached in this investigation were the successful completion of environmental exposure on the beam specimens, and the successful investigation of flexural s tiffness changes created by various environmental exposures. The objective of the environmental conditioni ng study was to investigate any noticeable trends between varying environmen tal conditions and degrading flexur al stiffness behavior of the CFRP reinforced concrete specimens. The st udy required a large number of specimens to be exposed to varying temperatures and envir onmental conditioning. For each environmental condition, multiple composite systems were inves tigated. Each composite system was created from a unique combination of carbon fiber weaves epoxies, and fabrication techniques to be described later in this report 13

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CHAPTER 2 BACKGROUND Previous Research in CFRP Strength and Stiffness Durability The bulk of CFRP durability research has been focused on the ultimate strength capacities of CFRP composite system. Cu rrently, little research has be en conducted on the changes in stiffness created by exposing external CFRP reinfo rced concrete beams to moisture. Changes in the mechanical properties of CFRP bonded concrete beams tested in flexure have not been widely studied. Relevant research performed on CFRP materials exposed to fresh water and saltwater exposures are given below. Moisture Exposure to fresh water can have degrading e ffects on CFRP. The addition of moisture on CFRP systems can lower the glass transition temperature (Tg) and also cause relaxation in the polymer matrix. The overall effects of moistu re exposure on CFRP systems are a reduction of the mechanical properties of the CFRP system. Karbhari and Engineer (1996) used two different epoxies with varying glass transition temperatures to impregnate carbon fiber sheets for wet lay-up external reinforcement installation on small beams (305-mm (L) x 51-mm (W) x 25.4-mm (D)). The beam specimens were placed in ambient air (20C) and submerged in water (2 0C) for a period of 60 days. At the conclusion of the exposure period, the beam specimens were te sting in 4 point bendin g. Flexural stiffness reductions of 2.5% and 21% were calculated from specimens fabricated from low Tg epoxies and high Tg epoxies, respectively. The calculated decr ease in mechanical properties was determined to be caused from plasticization of th e resin, which makes it more compliant. Hulatt et al. (2002) exposed satu rant CFRP coupons to wet-dr y cycles of complete water submersion for 5 hours and 2 days of drying in 50% relative humidit y. The aforementioned 14

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cycle was run until the coupons were submerged in water for a total of 2000 hours. The coupons were then tested in tension according to ASTM D3039M. When compared to unexposed coupon specimens the exposed specimens were found to ha ve a 3.8% reduction in failure stress. This reduction has been attributed to water infiltra tion weakening the fiber/matrix bond and therefore causing stress relaxation within the specimen. Bank et al. (2004) immersed saturant CFRP coupons at 65C for 330 days. After the exposure period, the specimens underwent dielectr ic measurements to determine moisture absorption and shear testing. It was found that the failure mode of the coupons changed from fiber tear to adhesive failure. Moisture was found to be bound to the adhesive rather than located as free water in the voids of the coupon. Ferrier and Hemelin (2002) constructed wet lay-up CFRP samples and submerged them in water at 20C and 45C for a period of 2500 hours. The specimens were tested using Barcol hardness, Differential Scanning Calorimetry (DSC ) and water absorption an alysis. It was found that increased water exposure decrea sed the glass transition temperature (Tg), surface hardness and mechanical properties of the CFRP. It was also discovered that increasing the water temperatures increased water absorption of the sa mples, which decreased mechanical properties. Moisture/Salt Research conducted by exposing CFRP to salt water has shown to produce similar results to CFRP exposed to fresh water. Moisture wi ll penetrate the composite and cause the matrix material to swell and relax. The addition of salt in fresh water has been found to accelerate the degradation of the polymer matrix further. Ti dal saltwater exposure has been found to produce varying failure modes due to decreased bond st rength, without producing any losses in tensile strength. 15

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Karbhari and Engineer (1996) used two different epoxies with varying glass transition temperatures to impregnate carbon fiber sheets for wet lay-up external reinforcement installation on small beams (305 mm (L) x 51 mm (W) x 25.4 mm (D)). The beam specimens were placed in ambient air (20C) and ASTM D1141 synthetic seawater (20C) for a period of 60 days. At the conclusion of the exposure period, the beam specimens were tested in 4 point bending. Flexural stiffness reductions of 7.5% and 22.5% were calculated fr om specimens fabricated from low Tg epoxies and high Tg epoxies, respectively. The decrease in flexural stiffness was found to be related to the decreases in Tg by both epoxy systems due to s eawater exposure causing matrix plasticization. El-Hawary et al. (2000) exposed epoxy bonded concrete to tida l saltwater for periods of 6, 12 and 18 months. Split tension a nd slant shear tests were perfor med on exposed specimens. It was found that the failure mode changed from c ohesive to adhesive with increased exposure times. No changes were observed in tensile strength, and a 25% decrease in bond strength was observed after an 18 month exposure time. Specimens appeared to be protected from deterioration due to the build-up of barnacles. Bank et al. (2004) subjected sa turant unidirectional CFRP to 330 days of immersion in simulated ocean water at 65C according to ASTM D1141-90. Dielectric measurements for moisture absorption showed the adhesive absorb ed 1% water. Shear tests showed that the addition of sea water changed the failure m ode from fiber tear to adhesive failure. Conclusions of Previous CFRP Environmental Durability Research The combination of moisture with elevated temperatures has been found to damaging effects on the performance of CFRP bonded concrete. Submersi on in heated water has been found to increase the amount of water absorbed by the composite strip. As water infiltrates the composite it has been found to cause the epoxy pl asticization, which cause s a reduction in the 16

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flexural stiffness of CFRP bonded concrete. Sa ltwater exposure resulted in reduction of the mechanical properties of epoxy due to matrix pl asticization and has been shown to change the failure mode, which indicated a reduction in the bond strength 17

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CHAPTER 3 TEST SET-UP Before exposing any beam specimens to environmental exposure conditions, a pilot study was conducted by the University of Florida and the University of Wyoming. The intent of this pilot study was to discover a standard test pr ocedure that would produ ce easily interpretable results and could be accepted by state departments of transportation and manufactures. The test methods and results for the aforementioned pilot study can be f ound in Gartner (2007). At the conclusion of the pilot study it was found that the configurati on in Figure 3-1 would be appropriate for durability tests. A single layer of wet-layup or pre-cured composite was centered on the saw-cut. The saw cut assures expo sure to the CFRP at the location of maximum moment as a simulated crack. For the wet-layup a nd precured laminate systems the widths of the CFRP strips were 25 mm and 19 mm, respectively. Concrete Mix Design After discovering a workable concrete beam configuration a total of 268 beams were constructed in six batches of 75 beams at the Florida Department of Transportation State Materials Office (FDOT SMO) in Gainesville, FL. The six batches of concrete were designed to have a concrete 28-day compressi ve strength of 698.0 MPa to prom ote adhesive failure of the CFRP laminate and limit flexure-shear failure. The mix had a water/cem ent ratio of 0.35 (N/N) and a ratio of cement/fine aggregate/coarse aggr egate was 1:1.5:1.7 by weight. The cement used was Cemex Type I cement and WR Grace Daravair 1000 air entrainer was used to improve the workability due to the low water/cement ratio. WR Grace WRDA 60 and WR Grace ADVA 140 admixtures were used to retard the chemical reaction and improve workin g time and workability. Steel forms that held five beams each were used for construction. Steel forms were machined to give exact 102 mm x 102 mm. x 356 mm. dimensions for each beam and to ensure each 18

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specimen had smooth form edges that were free of defects. Additionally, 102 mm diameter by 203 mm tall cylinder forms was f illed in two lifts. Specimens were removed from their respective formwork 24 hours after construction and placed in the moist cure room at the FDOT SMO for 28 days. Three cylinders for each mix were tested with average compressive stresses ranging from 63.8 MPa to 71.9MPa. The average MOR for the concrete mixes ranged from 6.83 MPa to 7.52 MPa, Table 3-1. Epoxy Systems Both commercially available CFRP systems a nd epoxies formulated by the research team were used for this investigation. The juxta position between commercial and formulated epoxy results were expected to allow an unbiased sti ffness analysis of each commercial system, while providing a series of controls for the formulated system. Commercial Epoxy Systems Four unidirectional wet-layup CFRP systems and one unidirectional carbon laminate system were used to construct the epoxied sp ecimens. This secti on provides the general description of the commercial systems used along with the manufacturer listed mechanical properties and the procedures used to apply the system. Composite A Composite A was comprised of a high strength unidirectional carbon fiber fabric saturant with an epoxy resin. The epoxy resin was a twocomponent 100% solids, moisture tolerant, high strength and high modulus epoxy. The system was sealed with a protective coating that had high resistance to carbon dioxide, chlorides and salt s; low temperature crack -bridging abilities; and excellent UV light resistance. The material properties of each component of the composite system, as well as the constructed composite are give n in Table 3-2. 19

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Composite A was constructed in four layers. Fi rst, a small batch of two-part saturant was mixed per manufacturers recomm endations. The mixed saturant was then applied to the concrete surface in the desired areas using a nap ro ller, making sure all crevices were adequately filled. The first saturant coat was allowed to set for approximately 1-hour until a tacky consistency was reached. Another batch of saturant was then mixed and applied to the first layer using the same nap roller. Using a nap roller the saturant was then used to impregnate the precut 203 mm x 25.4 mm carbon fiber weave. The satura nt fibers were then placed on the concrete on top of the saturant layer as shown in Figure 3-2a and allowed to cure overnight. After curing a topcoat was applied in three layers to the surface of the composite until uniform covering occurred, Figure 3-2b. Composite B Composite B consisted of epoxy primer, epoxy putty, epoxy saturant, fiber weave, and protective top coat. The fiber was a high strength and non corrosi ve unidirectional carbon fiber weave. The primer was a low viscosity, 100% solids, polyamine cured epoxy. The putty was a 100% solids non-sag paste used to level small surf ace defects. The saturant was a 100% solids, low viscosity epoxy material used to encapsulate the fiber fabric. The top coat provided protection against UV radiation and mild abrasio n. Table 3-3 gives the material properties for the components of Composite B. The five components of Composite B were applied in a layered fashion. The primer, putty, and saturant were 2-part epoxi es made by hand mixing appropriate amounts of parts A and B per manufacturers recommendations. The primer was applied to the surface using the same placement technique as Composite A. After the primer reached a tacky consistency the putty was then applied over the prime coat 20

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with a spatula. Saturated fibers were then pla ced on the putty and rolled flat onto the putty layer to promote adhesion. The composite was allowed to cure overnight and then two layers of topcoat were applied to a uniform consistency with a brush. Composite C Composite C consisted of a pre-cured lami nate and epoxy putty. The laminate was a unidirectional pultruded carbon reinforced polymer. The putty used was a 100% solids, moisture tolerant, high modulus and strength structural epoxy paste adhesive that conformed to the current ASTM C-881 and AASHTO M-235 specifications. Ta ble 4-4 lists material properties for both components of composite C. The laminate came as a 12.2 m long and 50.0 mm wide strip. It was cut to 203 mm long strips with a razor. The strips were cut to a width of 19.1 mm and then cl eaned of any debris and grease before bonding. After mixing per manufacturers recommendati ons the putty was first smoothed with a uniform thickness onto the concrete substrate and the appropriate laminate face using a spatula. The laminate was placed on the concrete, putty side down and pressure was applied to the surface of the laminate to allow proper adhesion between the puttied substrates, see Figure 3-3. Formulated Epoxy System Composites D and E consisted of the same 2-pa rt epoxy resin and fiber fabric, but different mixing ratios. Composite D epoxy was mixed in the manufacturers specified proportions. This mixture allowed for equal number of reaction site s for both saturant components. Composite E used an altered ratio of the two parts of th e epoxy causing the number of reaction sites for the two parts to be different, resulti ng in un-reacted sites. The weight ratios of Part A to Part B for composites D and E were 1:0.345 and 1:0.439 respectively. 21

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Both composites D and E were installed using the same method described for composite A. The only difference between the installation procedur es is that composite D and E did not require a top coat to be placed after the saturated fa bric weave had been placed and cured. The completed beam specimens for composites D and E can be seen below in Figure 3-4. Exposure System Of the 268 beam specimens constructed for th is investigation a total of 214 beams were exposed to a variety of moisture environments to investigate the effects on the CFRP flexural stiffness. Table 3-5 summarizes the various ex posure environments. The following sections provide further detail of the exposur e conditions listed in Table 3-5. Fresh Water Exposure Conditions The fresh water exposure system consisted of numerous 114-L insula ted containers that maintained heat equilibrium. Each system was equipped with a pump and a heater connected to the coolers via 15.9 mm di ameter heater hose. Small household electric water heaters were us ed to heat the water while magnetic driven pumps circulated the water thr ough the containers and the heater s. The pumps ran continuously, while the heaters were self-regulating. The self-regulating heaters maintained consistent water temperatures with fluctuation of 1.5C of the sp ecified temperature. The flow rate in the water tanks was maintained by an adjustable one-way ball valve installed at th e inlet of each tank. Pictures of the activated systems are shown in Figure 3-5. The specimens were added 9-15 per tank and were positioned on their sides so the CFRP could be exposed directly to the moisture. The water was filled to completely cover the CFRP. The specimens were added at different times through a four-week period with exposure dates ranging from April 18th to May 4th 2006. 22

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Tidal Zone Exposure With the cooperation of the FDOT, 29 beams were hung from five beams on the northeast fender system of the SR 206 bridge in Crescent B each, Fl as shown in Figure 3-6. Six concrete beams were hung from each fender beam using stai nless steel cable and clamps; a typical series of specimen installation is shown in Figure 3-7. Twelve months after real time coastal expos ure was initiated, 9 beam specimens (3 of composite A, B, and C) were selected at random to be tested in flexure. All specimens were retrieved by boat and upon arrival at fender system it was noted that the overall location and orientation of each beam specimen remained relatively unchanged. Additionally, it was observed that as a result of being exposed to tidal action all of the beams had experienced barnacle growth, Figure 3-8. The highest densi ties of barnacle growth were seen on the bottom and side surfaces of each beam specimen. Despit e the large number of barnacles present along the perimeter of each CFRP strip, the strips themselves experienced very l ittle barnacle growth. The 12 month samples were disconnected from their pre-fabricated wooden bases and placed into the boat one at a time by removing a series of pre-installed 1/8 nuts and screws. After being removed from the bridge supports, th e coastal specimens remained dry until reaching the testing destination. At the te sting location all remaining stainless steel support strands were removed with bolt cutters and the specimens were submerged into a room temperature, fresh water tank. After 24 hours of fresh water submersion, barnacles were removed from the concrete substrate with a scraper blade, Figure 3-9. Care was taken to avoid damaging the CFRP reinforcing strip. Immediatel y after removing the excess barnacles, beam specimens were returned to the room temperature, fresh water ta nk. After an additional 24 hours of fresh water submersion all nine specimens were tested in flexure. 23

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After 18 months of salt water submersion the remaining 20 beam specimens were removed from the coastal exposure location to be tested in flexure. At this time there was no noticeable change in the density of barnac les present on the surf ace of each concrete specimen compared to the 12 month coastal exposure specimens. The sa me cleaning and testing procedures as for the 12-month tests were used. Testing Procedure A specific testing procedure was used for all of this study to ensure that all beams were tested under similar moisture and loading conditi ons. After each beam completed its specified exposure period, specimens were transported from the University of Florida Coastal Lab to the testing location. During transportation a damp sheet and or group of damp rags were placed over the beam specimens to reduce moisture loss in e ach beam specimen. Upon arrival at the testing location specimens were immediately placed in a large metal tub filled with room temperature fresh water. Specimens remained submerged in the fresh water tank for a period of 24 hours, after which each specimen was carefully removed and allo wed to sit in the open air for 1 hour. The open air exposure allowed for the surface moisture to be evaporated without allowing any additional moisture to be removed from the CFRP bond surface or the concrete substrate. Additionally, the surface drying prevented any moistu re from dripping on any electronics used in this experiment. All specimens were tested with in one hour of surface drying to ensure little to no extra moisture evaporated from the CFRP or concrete. Each specimen was loaded using an Instron 3384 testing machine as shown in with the CFRP composite on the tensile face (not visible in figures) see Figur e 3-10. Previously installed and configured Partner software was used to cont rol the cross-head displacement. The load was applied at a displacement controll ed load rate of .254 mm/min. The load rate used for this 24

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procedure was applied to cause total specimen failure 1-2 minutes after reaching the half capacity of the beam. The Partner software r ecorded the load and cr osshead position throughout the entirety of the test. All testing data logged by the Part ner software was exported to a spreadsheet where the data was la ter interpreted and analyzed. 25

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Table 3-1. Twenty eight day compressi ve strength and modulus of rupture Mix Average 28-day cylinder strength (MPa) Average 28-day modulus of rupture (MPa) 1 68.0 7.10 2 67.6 7.31 3 63.8 7.52 4 65.0 7.24 5 71.9 7.52 6 68.2 6.83 26

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Table 3-2. Material prop erties for composite A Component Tensile Strength Tensile Modulus Elongation (MPa) (GPa) (%) Fiber Weave 3790 234 1.5 Epoxy Saturant 55.2 172 3.0 Composite 850 70.6 1.12 27

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Table 3-3. Material prop erties for Composite B Component Tensile Strength Tensile Modulus Elongation T g CTE (MPa) (GPa) % C 10-6/C Fiber Weave 3790 228 1.67 -.38 Epoxy Primer 17.2 0.72 2.0 77 35 Epoxy Putty 15.2 1.79 1.5 75 35 Epoxy Saturant 55.2 3.30 2.5 71 35 28

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Table 3-4 Material prop erties for Composite C Component Tensile Strength Tensile Modulus Elongation (MPa) (GPa) (%) Fiber Laminate 2800 165 1.69 Epoxy Putty 24.8 4.48 1.0 29

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Table 3-5. Summary of envi ronmental conditions used to weather the specimens Condition Solution Temp. (C) Approximate exposure times (months) UF location Wet Water 30 0.25, 0.5, 1, 3, 6, 12, 18 Coastal Lab 40 0.25, 0.5, 1, 3, 6, 12, 18 Coastal Lab 50 0.25, 0.5, 1, 3, 6, 12, 18 Coastal Lab 60 0.25, 0.5, 1, 3, 6, 12, 18 Coastal Lab Bridge Tidal exposure 20 12, 18 Crescent Beach Control none 20 as needed Coastal Lab 30

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356 mm As required 1 0 2 m m 203 mm 102 mm 305 mm 5 1 m m2.5 mm sawcut Figure 3-1. Final beam specimen configuration. 31

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A B Figure 3-2. Procedure to apply composite system A. A) Saturated fiber placement. B) Top coat placement. 32

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A B Figure 3-3. Construction techni que for composite C. A) Ap plying putty to concrete and laminate. B) Completed construction of laminate system. 33

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Figure 3-4. Completed constr uction of composites D and E 34

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A B Figure 3-5. University of Florida exposure tank set-up. A) Overa ll view. B) Typical piping for water circulation. 35

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Fender beams on the Northeast fender 5 4 3 2 1 Figure 3-6. Fender beams to be used to hang concrete beams 36

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Figure 3-7. Typical real time beam installation 37

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Figure 3-8. Typical specimen layout after coastal exposure 38

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Figure 3-9. Typical specimen afte r scraping and flexural testing 39

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Figure 3-10. Specimen loaded in testing apparatus 40

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CHAPTER 4 SUMMARY OF STRENGTH RESULTS Using the same testing data used for this stiffness investigat ion, a study was jointly conducted by the University of Florida and the Un iversity of Wyoming re garding the effects of moisture on the ultimate flexural capacity on be ams reinforced with composite systems A-E. This was done by defining the ratio in Equation 4-1. Control Max Exposed MaxP P_ Ratio Strength _P (4-1) in which is the ultimate flexural load (N) reached by the environmental exposed beam specimen and is the ultimate flexural load (N) reached by the control beam specimen. By calculating Strength_Ratio for each composite system a relative comparison of the strength loss due to moisture exposure could be calculated. Exposed Max _Control MaxP_CFRP System A: Water Immersion The University of Florida (UF) and the Univer sity of Wyoming (UW) beam test results of CFRP Composite System A in water immersi on at 30C, 40C, 50C and 60C are shown in Figure 4-1. Test results at 6 and 12 months indicate a significant loss of st rength due to environmental exposure. The majority of the strength loss oc curs within 14 days and further deterioration remains nearly constant for temperatures of 40C, 50C and 60C out to 540 days. CFRP System B: Water Immersion Beam test results of CFRP Composite System B after 18 months of different elevated temperature water immersions ar e shown in Figure 4-2. Figure 4-2 shows that the flexural strength decreases as the expos ure temperature increases and th e flexural stiffness remained relatively constant after 6 months of exposure. 41

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CFRP System C: Water Immersion The flexural test results of CFRP Composite System C afte r 12 months of submersion in elevated temperature water baths are shown in Fi gure 4-3. Test results indicate that System C had lost all strength after 12 m onths of exposure and a visible CFRP material delamination and laminate expansion occurred. The 12 month testi ng results for composite C show a failure load ratio of 20% after one year; this corresponds to the flexural st rength of the saw-cut concrete beam without CFRP strips. Thus, all contribution of the CFRP laminate was lost after 12 months. Photographic evidence taken from each failed specimen shows that as submersion temperature increases, each laminate system s howed signs of decreasing fiber cohesion, see Figure 4-4. CFRP System D: Water Immersion System D beam tests show constant stre ngth ratios when submerged at elevated temperatures for 6, 12 and 18-months, Figure 4-5. The strength ratio of beam specimens is over 80% for all exposure conditions. Strength ratios of 0.90, 0.82, 0.81 and 0.80 were recorded for immersion temperatures of 30C, 40C, 50C, and 60C, respectively at 18 months. Temperature and time appear to have little effect on System D. The failure mode in the exposed System D specimens was consistently adhesive. CFRP System E: Water Immersion System E exhibited high strength ratios after submersion at elevated temperature, Figure 46 indicating little strength loss. The strength ratio w ith exposure time and temperature are seen below in Figure 4-6. Contrary to the general tr end that the strength ratio s decrease with exposure time, the flexural strength after 12 months exposur e was higher than the strength after 6 months of exposure. The strengths at 40C and 60C after 12 months have strength ra tios greater than 1. After 18 months of exposure, th e strength ratios were 1.05, 0.94, 0.95 and 0.96 at 30C, 40C, 42

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50C and 60C, respectively. 43

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Figure 4-1. Strength ratio for UF and UW CFRP system A for di fferent temperature submersion 44

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Figure 4-2. Strength ratio fo r CFRP system B for differe nt immersion temperatures 45

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Figure 4-3. Control flexural strength ratio for composite C 46

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A B C D E Figure 4-4. Failure modes for composite C at vari ous temperatures. A) Control exposure. B) Immersion at 30C. C) Immersion at 40C. D) Immersion at 50C. E) Immersion at 60C. 47

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Figure 4-5 Strength ratio for CFRP system D for different immersion temperatures 48

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Figure 4-6. Strength ratio for CFRP System E for different immersion temperatures 49

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CHAPTER 5 EFFECT OF ENVIRONMENT ON STIFFNESS This chapter covers the flexural stiffness be haviors of CFRP reinforced specimens placed in various moisture environments. It was disc overed through this analysis that concrete beams externally reinforced with CFRP experience th ree loading behaviors: uncracked, cracking load, and cracked. In order to investigate the eff ect of CFRP reinforcing on uncracked flexural stiffness, the uncracked flexural stiffness for the control specimens were compared against the uncracked flexural stiffness values for three slo tted, unreinforced beam specimens. Furthermore, the effect of environmental exposure on uncrack ed stiffness was examined by comparing the uncracked flexural stiffness values for the mo isture conditioned specimens with the uncracked flexural stiffness values of the control specimens. After the cracking load was reached, it was noticed that each beam specimen exhibited three types of stiffness behavior at cracking, which will be th oroughly discussed later in this chapter: bilinear (no noticeable load drop or deflection plateaus), slight stiffness reduction, and severe stiffness reduction. The number of occurrences of each be havior noticed at cracking will be compared to the type of environmental exposure. As loading increased past the cracking thresh old, it was noted that each beam specimen exhibited a post-cracking stiffness region before failure. In order to analyze the total reduction in flexural stiffness for each composite after crackin g, the post-cracking flexural stiffness for the control specimens was compared to the uncracked flexural stiffness for the control specimens. Furthermore, to investigate any additional losses in post-cracking stiffness created by environmental conditioning, the post-cracking stiffn ess of the control specimens were compared to post-cracking stiffness values of the environmentally conditioned specimens. 50

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Flexural Behavior During testing, the universal testing machine was set to apply load using a cross-head displacement rate of 0.254 mm/min. This load rate resulted in te st durations of 3 to 5 minutes from initiation to beam failure. The universal testing machine measured and recorded the applied load and the centerline deflection of each beam specimen. To remove the flexibility of the test machine from the measured deflections, a compliance test was run on a deep steel section with a high flexural stiffness ( 10 times greater than the CFRP reinforced beam specimens). The compliance test measured the total deflection of the universal testing machine over the typical load range noticed for the CFRP reinforced beam specimens. The calculated compliance deflections were then subtracted from the recorded beam data to calculate the centerline deflection of the beam specimens without contribu tions from the testing apparatus. After each test, the load vs. deflection data was plotted to analyze the stiffness behavior of each tested specimen. Figure 5-1 and Figure 5-2 show two t ypical compliance correcte d load vs. deflection plots. As additional loading was applied beyond the cracking threshold, a flexural crack typically appeared at the tip of the 51 mm saw cut a nd slowly grew to the compression face of each concrete beam specimen (Figure 53). A video recording taken dur ing one of the flexural tests showed that cracking does not become visible until approximately 30 seconds before the ultimate load capacity of the reinforced beam specimen was reached. Within approximately 10 seconds of failure, audible cracking was heard that coincided with visible cracks forming along each edge of the CFRP composite reinforcement on both sides of the saw-cut (Figure 5-4). The cracking of the epoxy surrounding th e composite strip was thought to be indicative of debonding between the composite and the concrete substrate immediately prior to collapse. 51

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As loading continued beyond cracking and appro ached failure, most (at least 85% of the specimens tested) of the beam specimens produced load-deflection curves with linear postcracking stiffness regions spanning until failure (F igure 5-1). The remainder of the specimens had post-cracking stiffness characterized by multiple small and abrupt stiffness reductions followed by short deflection spans (< 5% ultimate ) of increasing flexural stiffness until failure (Figure 5-2). To determine how environmental exposure might affect the flexural stiffness of each beam specimen, the three characterist ics of the load displacement curve previously discussed were selected for analysis: Uncracked stiffness Cracking point Post-cracking stiffness Regardless of the composite systems used after loading was initiated, the loaddisplacement was generally linear up to cracking. The linear un cracked stiffness region noted for each beam specimen typically ranged from 2200 N to 8000 N. After correcting the loaddeflection data for compliance, the uncracked flexural stiffness was determined by linear regression of the load-deflection plot betw een 50% and 90% of the cracking load. The aforementioned load range was selected to ensure that support and load po int settlement were not included in the uncracked stiffness. As loading surpassed the cracking point it wa s noticed that the load cell read negative strength gains for approximately 40% of the test ed specimens. Due to the large percentage of specimens experiencing load losses, the beam mech anics causing the load loss were investigated. As indicated earlier, characteristics of the cr acking point and post-crack ing stiffness varied among the specimens. Figure 5-5 shows three lo ad-deflection plots th at show the typical 52

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variation in behavior at cracking and immediately after the onset of cracking. This variation was categorized into three distinct cracking point behaviors based on the following key characteristics: Bilinear: characterized by a sudden transition from uncracked stiffness to a reduced and constant post-cracking stiffness. Slight stiffness reduction: characterized by a short plateau (< 10% total deflection at failure) or small load reduction (< 10% of cracking load) or both. Severe stiffness reduction: characterized by a large plateau (> 10% total deflection at failure) or large load reduction (> 10% of cracking load) or both. As flexural cracking occurred above the saw cut, the secti onal properties of the beam section were reduced creating a sudden loss in fle xural stiffness. Bilinear behavior was noticed in beam specimens that could immediately transfer stresses from the concrete to the composite strip. Slight stiffness and severe stiffness re duction behaviors occurred in beam specimens that needed additional loading for the composite strip to become fully engaged. The combination of reduced flexural stiffness due to cracking, and the additional load n eeded to engage the composite strip resulted in the noticed load drops. After the cracking load is reached, the tensi on load required to maintain equilibrium is carried entirely by the CFRP composite strip. As the load within the composite strip is increased, the performance characteristics of each composite system become increasingly important as little concrete is avai lable to assist the CFRP strip carry the tensile load. Due to this fact, the effects of moisture on the post-cracking stiffness for each CFRP system were analyzed. The load deflection plots showed that the ma jority of the specimens exhibited constant cracked stiffness as shown in Figure 5-1. The stiffness was calculated by a linear regression of 53

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the data from approximately 1332 N above the crack ing load until the first signs of stiffness loss noticed in the load deflection plot. This range was selected to ensure the longest possible deflection span without a ny contributions from the stiffness behavior at the cracking load. After linear regression was used to approximate cracked stiffness it was discovered that moisture has little effect on cracked stiffness. The data and an alysis used to formulate this conclusion will be discussed later in this chapter. For the specimens that exhibited non-linear cr acked stiffness behavior trial and error was initially used in an attempt to find a specific load and/or deflection range that would consistently produce acceptable linear regression results. Acceptable linear regressions results were required to visually match the average be havior of the cracked stiffness region see in the load deflection plots. Unfortunately, all attempts using trial a nd error were unsuccessful. Therefore, the cracked stiffness was determined by calculating a linear regression that calculat ed the slope between 300 lbs above the cracking load and the ultimate capac ity of each beam specimen, Figure 5-2. This range was selected because it calculated the most conservative flexural stiffness value without any contributions created from the stiffne ss reduction behaviors created by cracking. Analysis of Uncracked Stiffness Control Specimens Before evaluating the effect of environment on stiffness, the relative stiffness of the various repair systems was calcu lated. This was done by defining the ratio in Equation 5-1. ened Unstrength U CFRPU Ck k UR_ (5-1) in which is the average uncracked stiffness of the control CFRP strengthened specimen and is the average uncracked flexural sti ffness of 3 slotted and unstrengthened CFRPUk_ened Unstrength Uk_ 54

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concrete beams. The ratio URC provides a relative comparison of the contribution of the CFRP to the uncracked flexural stiffness of the concre te beam. The slotted and unrepaired concrete beams specimens were constructed from mixture #6 and tested at an age of approximately 23 months. Figure 5-6 shows the URC values at each testing period. For comparison, the theoretical flexural uncr acked stiffness was calculated using either tested or manufacturer provided material data fo r the composites and concrete and are shown in Table 5-1 along with the stiffness ratios from the control specimens. Details of the calculations are provided in Appendix A. As might be expe cted, the calculated values indicate that the composite reinforcement contributes very little to the overall stiffness of the beams (5% maximum). The measured URc values, however, show that the measured stiffnesses of the specimens are increased by over 100% is some cases. Furthermore, the stiffness values appear to decrease as the specimens age. It is not clear why the measured stiffnesses are so much greater than that of the calculated values. Based on th e large relative stiffne ss contribution provided by the concrete, these observed changes are likely something to do with changes in either the control specimen concrete or the exposed specimen concrete, or both. Heated Water Exposure This section explores the effect that heated water might have on the uncracked stiffness of composite systems A, B, C, D and E. This was done by defining the ra tio in Equation 5-2: Control CFRPU Water Heated CFRPk__ __ U Hk UR_ (5-2) in which is the average uncracked sti ffness of the CFRP strengthened specimen exposed to each immersion temperature and is the average uncracked stiffness of the CFRP strengthened specimen exposed to control conditions. The ratio URH Water Heated CFRPUk___Control CFRPUk__ 55

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provides a relative comparison of the uncracked flexural stiffness performance of each composite system after being immersed in heated water. Figure 5-7 shows how URH varies with temperature and time It should be noted that at 6 months of moisture exposure at varying temperatures all of the composite systems had stiffness ratios less than 1, (meaning the average exposed specimens had lower uncracked stiffness than that of the control mixtures). With a few ex ceptions, the uncracked stiffnesses increase with time. It is believed that this increase is due to the continued curing of the concrete under prolonged moisture exposure. The increased curi ng created by prolonged moisture exposure will improve the density of the interior of the conc rete which will increase the compressive strength and elastic modulus of the sp ecimen (Neville 1995) relative to that of the control. One exception to the general trend was that of composite C (Figure 5-7c). The uncracked stiffness appears to markedly decrease with increasing temperature. As the immersion temperature of the water was increased from 30C to 60C, the URH values dropped from 0.85 to 0.35. As related earlier, the strength results for this composite indicated an almost complete loss of strength after very short duration exposure. Loss of the contribution of composite, however, is not expected to cause a 65% loss in uncracked stiffness as indicated by the data. The contribution of the stiffness is thought to be relatively small compared to the concrete. Coastal Exposure The effects of coastal exposure on the flexural stiffness of the concrete beams reinforced with composite systems A, B, and C were eval uated. This was done by defining the ratio in Equation 5-3. Control CFRU Tidal CFRPU Tk k__ __UR (5-3) 56

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in which is the average uncracked stiffne ss of the CFRP strengthened specimen exposed to coastal conditions and is the average uncracked stiffness of the CFRP strengthened specimens. The ratio URT provides a relative comparison of the uncracked flexural stiffness performance of each composite system after being exposed to tidal conditions. The URT values for the coastal specimens can be seen belo w in Figure 5-8. Due to the fact that highest temperature ocean temperature recorded during th is investigation at Crescent Beach was 83F (28.3C), comparisons were only made between the specimens exposed to coastal and 30C heated immersion specimens. Tidal CFRPUk__Control CFRUk__With the exception of the 12 month coastal exposure specimens for composite A, the coastal specimens have lower URT values than the 30C heated immersion specimens. Neville 1995 reports when concrete specimens are continually wetted by sea water, with altering periods of drying (similar to the coastal exposure used in th is investigation), salt is left within the pores of the concrete. As the number of wetting cycles increases, the salt crys tals re-hydrate and grow exerting tensile forces within the concrete. The internal tensile forces created by expanding salt particles will create internal cracking and damage s that will reduce the mechanical properties of the concrete specimen. High levels of damage due to salt weathering were expected to occur around the saw cut of the beam, as salt was directly exposed to aggregate and interior pores of the beam specimen. Any damage noticed around the saw-cut of the concrete beam specimen will affect the elastic modulus of the concrete in the tensile zone, which will reduce the URT values of the beam specimen regardless of the composite system used. It is important to address that damage in the tensile zone of the concrete will influence the uncracked flexural stiffness and not the ultimate capacity of the CFRP reinforced spec imens. It will be discussed later that the 57

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ultimate capacity of the coasta l specimens is dominated by the level of debonding created between the composite strips and the concrete substrate. Analysis of Cracking Point Behavior This section presents the analysis of the postcracking stiffness behavior In particular, the behavior of the specimens during load testing immediately after cracking is examined. Recall that the results were generally characterized into bilinear, slight stiffness reduction, and severe stiffness reduction. The bilinear load displa cement exhibited no load drop at cracking while slight and severe stiffness reduction had small and significan t load drops after cracking, respectively. The magnitude of the load loss is controlled by a combination of the displacement control loading and sudden reduction in flexural s tiffness of the beam specimens at cracking. While it is understood that this behavior is an artifact of displacement control loading, it does provide insight into the behavior of the specimens and, in particular, the change in properties with exposure. Control Specimens Before evaluating the effect of environment on stiffness reduction behavior, the stiffness behavior at cracking point was determined for each composite system under control conditions. Figure 5-9 shows the variation in stiffness reducti on behavior among the speci mens at cracking. Figure 5-9. Stiffness re duction behavior at crac king for control specimens Figure 5-9 shows that the stiffness reduction behavior noticed at cracking by each beam specimen is dependent on the type of composite sy stem used for external reinforcing. It is theorized that the resulting stiffness losses reco rded for each specimen is created by two possible modes: corner cracking at th e saw cut line or debonding between the composite strip and the concrete substrate. Figure 5-10 illustrates corner cracking. This behavi or was noted on many of 58

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the failed specimens after testing. It was not confirmed, however, whether the cracks formed at the cracking load or formed as failure was imminent. Figure 5-10 also illustrates how the cracking behavior (and cracked stiffness, as well) might vary depending on the size of the wedge. As the wedge becomes larger the effective moment of inertia (Ie) of the reinforced beam is reduced. Due to the fact that the flexural stiffness of the beam specimens is proportional to Ie, it can be theorized that specimens exhibiting bilinear or slight stiffness reduction be havior will have smaller concrete wedges than specimens exhibiting severe stiffness reducti on behavior. Figure 5-11 shows examples of spalling concrete on Composites C, D, and E Alternatively, Figure 5-12 shows how debondi ng might similarly reduce the effective moment of inertia of the beam. As with the conc rete corner spall, it is suggested that a short length of the CFRP on one side of the crack debonds when the beam cracks. For specimens exhibiting large debonding lengths at cracking, the am ount of composite available to provide reinforcement is reduced, which results in reduced flexural stiffness behavior. Therefore, specimens that exhibit slight or severe stiffn ess reduction behavior have more debonding at their cracking loads than specimens exhibiting bilinear cracking behavior. It was noticed that all of the failed specimens exhibited concrete wedge fa ilures on one side of th e saw cut and partial debonding on the other. Quantitative measurements of the bond length, however, are not available. As seen in Figure 5-9 the majority of cont rol specimens reinforced with composite C exhibit bilinear behavior at cr acking, while composite systems D and E primarily exhibit slight reduction and severe reduction beha vior, respectively. If the de gree of concrete wedge damage created during failure is related to stiffness re duction behavior then the control specimens for 59

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composite C should have smaller concrete wedge si zes than the other com posite systems. Figure 5-10 shows that the size of the concrete fa ilure wedges remain re latively unchanged with composite type. Due to this fact it is believed that debonding governs the stiffness behavior at cracking. Debonding of the FRP composite can be thought of as the formation and extension of a mode II crack along the bond line of the epoxy. In itiation of the cracki ng, growth rate and extension of the crack is a functi on of the geometry of the initia tion site and perhaps the fracture toughness of the epoxy adhesive. Figure 5-13 show s the theorized loadin g behavior and crack propagation that resulted in the mode II failures seen in the tested specimens. Previous research conduced by Au and Buyukoz turk (2006) suggests than when unexposed beams with laminate reinforcement are loaded concrete delamination is often the primary mode of failure. It was discovered that after load ing a crack formed that sheared off around the initiation site (Achintha and Burgoyne 2008). The crack then kinked into the concrete near the epoxy/concrete interface and propagated parallel to the concrete/epoxy interface leading to a concrete delaminated failure. This failure mode is nearly identical to the failure modes recently discussed, however, the crack propagation found in this study did not kink into the concrete. Figure 5-11 shows that the unexposed specimens for composite systems C, D and E failed along the epoxy/concrete bond surface. Au and B uyukizturk (2006) report the 28 day compressive strength of their concrete at 32.4 MPa, while the 28 day compressive st rength for the concrete used in this investigation was listed as approxi mately 69.0 MPa. It is speculated that the concrete used in this investigation was strong er than the bond line epoxy and thus the mode II crack extension occurred at th e weaker bond line epoxy layer. 60

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Research conducted on the pullout capacity of epoxy bonded anchors provides another possible mechanism of the aforementioned adhe sive failure noticed for the tested beam specimens. McVay et al (1996) discovered at low load levels the shear stress on the bonded anchor could be modeled with a hyperbolic ta ngent function (Equation 5-4) where the shear stress was concentrated at the top and decreased with depth. )tanh(ef oh d uN (5-4) Where Nu is the predicted ultimate strength of the bond, is the bond stress (MPa), do is the hole diameter (mm), is the stiffness characterization of the adhesive anchor system (mm-1), and hef is the embedment depth of the anchor (mm). At higher load levels, it was noticed that as the shear stresses in the epoxy increased, the shear stresses transformed from the hyperbolic tangent function to a more uniform stress distribution along the length of the anchor. Applying these fi ndings to the composite beam specimens used for this analysis, the speculate d shear stress distributi ons along the composite strip are shown in Figure 5-14. McVay et al (1996) noted that all of their anchor specimens exhibited a cone shaped concrete chunk at the surface of th eir tested specimens. It is possible that mechanics causing the cone failure are also producing the wedge failure shown in Figure 5-11. The occurrence of the uniform stress distribution along the end of the compos ite strip also appears to be probable as the video of the failed beam specimens reveals that the end of the composite strip away from the sawcut experiences debonding failure at the sa me time. Once the high uniform bond stress surpasses the capacity of the bonding epoxy the entire composite strip separates from the concrete substrate. 61

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Heated Water Exposure After compiling all of the s tiffness reduction behaviors due to heated water exposure at cracking, the data revealed that stiffness reductio n behavior at cracking wa s directly affected by increasing the immersion temperature. The effect of moisture on composite systems D and E can be seen below in Figure 5-15 and Figure 5-16. However, the effects of Sika (Composite A) and Degussa (Composite B) epoxy on CFRP specimens exposed to heated water can not be concluded on with any confidence due to th e limited number of Composite A and B samples exposed to elevated water temperatures. Both Figure 5-15 and Figure 5-16 show an increasing trend for wet lay-up composite systems to experience reduced stiffness reduction be havior at cracki ng. One explanation for this behavior is that water absorpti on decreases the debonding lengths of the specimens at cracking. It is speculated that the smaller load drops for composites D and E exposed to elevated temperatures was related to the changing behavi ors in mechanical properties of the composite system. It is speculated that the increasing e xposure temperature softens the saturant epoxy, but also improves the fracture toughness. The in creased fracture toughness created by moisture exposure prevents cracks from forming at the in itiation site or reduces the crack extension created by mode II fracture. This occurrence is believed to be the cause of the decreasing stiffness reduction behavior noti ced in Figure 5-15 and Figure 5-16. When exposed to high elevated temperatures (> 40C) specimens externally reinforced with CFRP system C experienced in terfacial failure of the carbon la minate strip, see Figure 5-17. The interfacial failure exhibited by Composite C results in the lack of post-cracking strength previously discussed in this chap ter. In order for interfacial fa ilure to occur the saturant epoxy added during laminate fabrication must weaken to a level where it can long hold the fibers 62

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together resulting in the separation of the fibe rs themselves and not debonding of composite system. Coastal Exposure Figure 5-18 shows the effect of tidal exposure on composite specimens A, B, and C. The plots show that that tidal exposure caused a move toward severe stiffness reduction rather than toward bilinear behavior as was cause d by the heated water exposure. Figure 5-18 shows that the number of compos ite A specimens that exhibited severe stiffness more than doubled. Most of the expos ed and control composite B specimens exhibited slight stiffness reduction with nearly 25% of the exposed specim ens exhibiting severe stiffness reduction. The difference in cracking point beha vior may be related to the difference in epoxy stiffness. Recall that composite B epoxy is nearly twice as stiff as composite A stiffness. Composite C experienced slight stiffness reduction behavior, while only 25% of the control specimens exhibit similar stiffness behavior at cracking. The fact that Composite C was installed as a pre-fabricated laminate with no protective coat ing a low initial epoxy to carbon fiber ratio explains the drastic influence that salt intrusion has on post-cracking stiffness behavior. Without the addition of a protective top coating, the effects of the physical mechanism that caused the increase in debonding length fo r composites A and B was more prevalent in composite system C. As a direct result of tidal exposure the beam specimens were exposed to salt water and were continuously in wet/dry cycling. Either of these occurren ces and/or a combination of the two actions is causing the changes in the bonding/saturant epoxy. It is specula ted that as a result of tidal exposure composite systems A, B, and C experience decreased fr acture toughness in the bonding epoxy. One explanation is that the chan ge in post-cracking behavior created by tidal exposure is a direct result of the salt water affecting the bond st rength of the coastal beam 63

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specimens. The addition of seawater on CFRP composites results in little loss in tensile properties but causes a reduction in bond strength (El-Hawary 2000). If the bonding strength of the composite system is reduced due to salt water infiltration, then it can be speculated that the coastal exposures cause increased mode II crack extension. The increased mode II crack extension will result in larger debonding lengths that will translate to increased stiffness reductions behavior at the cracking load. Analysis of Post-C racking Stiffness Control Specimens After the cracking load is reached, the tension required to maintain equilibrium is carried entirely by the CFRP composite strip. Conse quently, the measured post-cracking stiffness will be affected by the FRP composite much more than that of the uncracked stiffness. As the load within the composite strip is increased, the pe rformance characteristics of each composite system contribute significantly to the flexur al response of the beam. This section explores the effect of CFRP reinforcement on cracked flexural stiffn ess. This was done by defining the ratio in Equation 5-5. CFRPU CFRPC Ck k CR_ (5-5) in which is the average cracked stiffness of th e control CFRP strengthened specimens and is the average uncracked stiffness of the control CFRP strengthened specimen. The ratio CRC provides a relative comparison of the cracked flexural stiffness performance of each composite system. The CRC values for all exposure durations and composite systems are shown below in Figure 5-19. CFRPCk_CFRP Uk_The data presented in Figure 5-19 shows each composite system provides varying CRc values. Through the use of the design methods laid out in ACI440.2R-02, the theoretical CRc 64

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values for each composite system were calculated at an applied load of 12.2 kN to verify the measured CRc values. Figure 5-19 shows th e measured and analytical CRc values for composite systems A-E. It is important to note that the tensile properties fo r composite E were not calculated, so it assumed that the results ar e similar to the other composite systems. Figure 5-19 shows that the CRc values provided by the composite systems were measured lower than the analytical CRc values. This is likely the result the loss of stiffness caused by debonding or plastic deformation in areas of high bond stress. Neither of these behaviors are accounted for in the predicted values. Conse quently, lower tested stiffnessses would be expected. The CRc values shown in Figure 5-19 represent the reduction of stiffness experienced by each composite system after cracking. Unlike the URC values reported earlier, CRc values do show a relationship with the fi ber to epoxy ratio used during the fabrication of the composite systems. Figure 5-19 shows co mposite D and E having lower CRc values than composite A and B. As previously discussed, due to the addition of the topcoats composites A and B have lower fiber to epoxy ratios than composites A and B. In order to determine the cause of the CRc behavior, strength behavior of the composite systems used for the study conducted by the Univ ersity of Florida a nd the University of Wyoming was investigated. The ultimate flexural capacities of the cont rol specimens are seen below in Figure 5-20. With the exception of composite system C th e ultimate flexural capacities noticed in Figure 5-20, appear to echo the CRc values shown in Figure 5-19. The lower than expected ultimate flexural capacities for composite C can be explained by the decreased bonding area used for the laminate system. The carbon fabric shee ts were cut to widths of 25.4 mm, while the 65

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laminate system was cut to widths of 19.1 mm. The smaller dimensions of the laminate strip provided a smaller area to provide bonding betw een the laminate and the concrete, which reduced its ultimate capacity. During the UF and UW investigation it was hypothesized that sp ecimens with higher ultimate flexural capacities experience redu ced debonding lengths between the CFRP composite strips and the concrete substrate. The relationship between flexural capacity and debonding helps explain the mechanisms that cause each composite system to experience different CRc values. By increasing the debonding length between the CFRP com posite strip and the concrete substrate, the composite strip loses its ability to transfer load to the concrete beam which will decrease the flexural stiffness of the beam specimen. Heated Water Exposure As previously discussed during the uncracked flexural stiffness analysis, water immersion has been found to produce lower flexural stiffness values than the control specimens due to the fiber/matrix plasticization created from water imme rsion. This section ex plores the effect of moisture on cracked flexural stiffness of CFRP reinforcement. This was done by defining the ratio in Equation 5-6. CFRPC Water Heated CFRPk k_ __C HCR_ (5-6) in which is the average cracked stiffness of the CFRP strengthened specimens exposed to various imme rsion temperatures and is the average uncracked stiffness of the control CFRP strengthened specimen. The ratio CRH provides a relative comparison of post cracking stiffness lost created from moisture exposure. The calculated CRH values for all immersion temperatures and for composite system s A, B, D and E are se en below in Figure 5-21 and Figure 5-22. Water Heated ChRPCk___CFRPUk_ 66

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Figure 5-21 shows that composite systems A and B experience little variation in CRH values due to moisture immersion. The relative lack of change between the control and exposed specimens is supported by the findings of Karbhari and Engineer 1996, which found flexural stiffness losses of approximately 5% for wet la y-up due to moisture exposure. Comparing the CRH show in Figure 5-21, with the URH values previously shown in Figure 5-7 it is noticed that both stiffness ratios produce values of nearly 1. 0 for the majority of moisture exposures. This indicates that moisture exposure ex hibits little relative change in the cracked flexural stiffness characteristics for composite systems A and B. Figure 5-22 shows at 6 months of water immersion both com posite systems D and E show CRH values of approximately 1.0 or greater. This indicates that when exposed to moisture, specimens constructed with composite systems D and E experience increased flexural stiffness performance after cracking. The in crease in flexural stiffness is contrary to findings previously discussed for the URH values shown in Figure 5-7. Because cracked flexural stiffness values fo r composite systems D and E remain relatively constant after being immersed at elevated temper atures; it is believed that composite systems D and E do not experience any changes in debonding beha vior from moisture immersion. Earlier it was discussed that the specimens with smalle r debonding lengths are lik ely to exhibit higher ultimate flexural strength values. Therefor e, in order to estimate the level of debonding experienced by composite systems D and E the % of control strengths for each composite were compared. The % of control strengths for comp osites D and E are shown below in Table 5-2 and Table 5-3. After analyzing the % control st rength values shown in Table 5-2 and Table 5-3 it appears that neither composite D nor E experience si gnificant increase in debonding length due to 67

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moisture immersion. Composite E even shows i ndications that moisture exposure for composite E decreases debonding length as several immersi on temperatures produce % control strength values greater than 100%. Unfortunately, during the data collection for this analysis no efforts were made to address changes in debonding length due to moisture exposure. Therefore, the chemical and mechanical interactions that relate composite debonding with moisture exposure can not be speculated upon. Coastal Exposure The effects of tidal zone exposure were also used to investigate th e post-cracking stiffness performance of composite systems A, B and C. This section explores the relative loss in stiffness created by coastal exposure. This was done by defining the ra tio in Equation 5-7. CFRPC Tidal CFRPC Tk k CR_ __ (5-7) in which is the average cracked stiffness of the CFRP strengthened specimens exposed to tidal exposure and is the average uncracked stiffness of the control CFRP strengthened specimen. The ratio CRT provides a relative comparison of post cracking stiffness lost created from tidal exposure. The CRT results are presented in Figure 5-23. Tidal ChRPC__kCFRPUk_The strength analysis conducted by UF and UW discovered that tidal exposure could potentially increase the flexural capacities of beams externally reinforced with CFRP composites. Earlier it was theorized that the addition of salt water causes deterioration in concrete but has little effect on the post-cracking performance of composite systems A and B due to the addition of the protective t op coatings applied during fabricati on. In order to verify this relationship the load deflection plots for the control and coastal specimens were juxtaposed. Typical load deflection behaviors for composite B specimens exposed to coastal and control conditions can be seen below in Figure 5-24. 68

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Figure 5-24 shows that after cracking both of the coastal and c ontrol exposed beam specimens show similar cracked flexural stiffness values and ultimate flexural capacities. Currently, there is no available re search that concludes the add ition of salt and or moisture on CFRP composites will cause increas ed bonding strength of the impregnating epoxy. Due to this fact and the similar ultimate capacities noticed in Figure 5-24 it can be concluded that coastal exposure has no significant effect on the debonding length or cracked flexur al stiffness of CFRP composite systems A and B. After being exposed to tidal exposures, composite system C has CRT values of 0.85 and 0.74 at exposure durations of 12 and 18 months, respectively. The loss in stiffness for composite C specimens placed in marine environment is th ought to be caused by increased fiber/matrix degradation created from salt e xposure. While the addition of barnacle acted as a sealant, composite C was fabricated with a high fiber: epoxy ratio (little satu rant epoxy) and no top coating which allowed moisture and salt to de grade the interior bond ing adhesive of the laminate. The protective effect of the barnacles on composite C can be seen in the failure mode of composite C specimens exposed to each moistu re environment: control, heated, and coastal (Figure 5-25). All composite C specimens placed within the tidal zone all exhibited debonding failure between the CFRP reinforcing laminate and the concrete substrate. Other instances of debonding failure for composite C were only noticed for the cont rol specimens. Figure 5-25c shows that before failure, the entire laminate strip was fully engaged in tension without failing interfacia lly, which explains why the crack ed stiffness values could be calculated for the coastal expos ure specimens and not for the heated immersion specimens. 69

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Table 5-1. Measured vs calculated URc values for all composite systems Composite System Measured URc at 6 months Measured URc at 12 months Measured URc at 18 months Calculated URc A 1.27 1.15 1.02 B 1.17 0.96 1.02 C 2.16 1.97 1.43 1.05 D 1.88 1.83 1.17 1.01 E 2.59 1.62 0.98 ~1.01 70

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Table 5-2. Percent control strengths at va rious immersion temperatures for composite D Exposure duration (months) 30C 30C 50C 60C 6 97 99 97 84 12 97 92 80 89 18 90 82 81 80 71

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Table 5-3. Percent control strengths at va rious immersion temperatures for composite E Exposure duration (months) 30C 30C 50C 60C 6 96 90 92 94 12 103 116 96 116 18 105 94 95 96 72

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0 2000 4000 6000 8000 10000 12000 0.000.250.500.75 Deflection (mm)Load (N) Uncracked Stiffness Cracking Point Post-Cracking Stiffness Figure 5-1. Typical load defl ection curve with bilinear uncracked and post-cracking behavior 73

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0 2000 4000 6000 8000 10000 12000 00.250.50.75 Deflection (mm)Load (N) Uncracked Stiffness Cracking Point Post-Cracking Stiffness Figure 5-2. Typical load defl ection curve with linear uncracked stiffness and approximated postcracking stiffness 74

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A B Figure 5-3. Typical flex ural crack propagation. A) After cracking. B) Just before failure 75

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Figure 5-4. Typical debonding damage observed for wet lay-up systems just before failure 76

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0 2000 4000 6000 8000 10000 12000 0.000.200.400.60 Deflection (mm)Load (N) Bilinear Slight Stiffness Reduction Severe Stiffness Reduction Figure 5-5. Typical plots for the th ree stiffness behaviors at cracking 77

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0.00 0.50 1.00 1.50 2.00 2.50 3.000 6 121824Exposure Time (Months)URc Composite A Composite B Composite C Composite D Composite E Figure 5-6. URC values at all exposure lengths 78

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0.00 0.25 0.50 0.75 1.00 1.25 1.50 0 6 12 18 24Exposure Time (Months)URH 30 C 40 C 50 C 60 C A 0.00 0.25 0.50 0.75 1.00 1.25 1.500 6 121824Exposure Time (Months)URH 30 C 40 C 50 C 60 C 6 12 1 8 B 0.00 0.25 0.50 0.75 1.00 1.25 1.500 6 12 18 24Exposure Time (Months)URH 30 C 40 C 50 C 60 C C 0.00 0.25 0.50 0.75 1.00 1.25 1.500 6 12 18 24Exposure Time (Months)URH 30 C 40 C 50 C 60 C D 0.00 0.25 0.50 0.75 1.00 1.25 1.50 0 6 12 18 24Exposure Time (Months)URH 30 C 40 C 50 C 60 C D Figure 5-7. Relative effect of heated water exposure on uncracked stiffnesses of CFRP systems. A) Composite A. B) Composite B. C) Composite C. D) Composite D. E) Composite E. 79

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0.00 0.25 0.50 0.75 1.00 1.25 1.500 6 12 18 24Exposure Time (Months)URT Composite A Composite B Composite C Figure 5-8. Effect of prolonged coastal exposure for composites A, B, and C on stiffness ratio 80

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0% 25% 50% 75% 100% 125%12345Composite System% of Occurences Bilinear Slight Stiffness Reductions Severe Stiffness Reductions A B C D E Figure 5-9. Stiffness re duction behavior at crac king for control specimens 81

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Small Concrete Wedge Flexure Crack A Large Concrete Wedge Flexure Crack B Figure 5-10. Illustration showi ng typical corner cracking for b eam specimens. A) Exhibiting bilinear. B) Slight stiffness reduction behavior at cracking. 82

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A B C Figure 5-11. Typical corner cracking behavior for control specimens. A) Composite C. B) composite D. C) composite E. 83

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Debonding At Cracking Point Flexure Crack A Debonding At Cracking Point Flexure Crack B Figure 5-12. Illustration of debonding in beam sp ecimens. A) Producing bilinear behavior. B) Severe stiffness reduction behavior. 84

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Flaw or initiation siteMode II Crack Extension Figure 5-13. Illustration showing mode II cr ack extension for half of a beam specimen 85

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Bond lengthB o n d s t r e s s Low load stress distribution High load stress distribution Figure 5-14. Stress distribu tion along composite strip fo r a half beam specimen 86

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0% 25% 50% 75% 100% 125%12345Temperature (oC)% of Occurences Bilinear Slight Stiffness Reduction Severe Stiffness Reduction 30 40 50 60 Control Figure 5-15. Stiffness reduction frequencies for composite D for all exposed specimens 87

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0% 25% 50% 75% 100% 125%12345Temperature (oC)% of Occurences Bilinear Slight Stiffness Reduction Severe Stiffness Reduction 30 40 50 60 Control Figure 5-16. Stiffness reduction frequencies for composite E for all exposed specimens 88

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Figure 5-17. Typical interfacial failure mode for composite C 89

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0% 25% 50% 75% 100% 125%12Temperature (oC)% of Occurences Bilinear Slight Stiffness Reduction Severe Stiffness Reduction Coastal Control A 0% 25% 50% 75% 100% 125%12Temperature (oC)% of Occurences Bilinear Slight Stiffness Reduction Severe Stiffness Reduction Coastal Control B 0% 25% 50% 75% 100% 125%12Temperature (oC)% of Occurences Bilinear Slight Stiffness Reduction Severe Stiffness Reduction Coastal Control C Figure 5-18. Stiffness reduction frequency cause d by tidal exposure. A) Composite A. B) Composite B. C) Composite C. 90

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0.00 0.25 0.50 0.75 1.000 6 12 18 24Testing date (months)CRC Composite A Composite B Composite C Composite D Composite E Calculated CRc range for all composite systems Figure 5-19. Cracked stiffness ratios at all testing dates for control specimens 91

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0 200 400 600 800 1000 1200 0 6 12 18 24Testing date (months)Ultimate flexural capacity (N) Composite A Composite B Composite C Composite D Composite E Figure 5-20. Ultimate flexural capacities for all of the control specimens 92

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0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 0 6 12 18 24Exposure Time (Months)CRH 30 C 40 C 50 C 60 C A 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 0 6 12 18 24Exposure Time (Months)CRH 30 C 40 C 50 C 60 C B Figure 5-21. Cracked stiffness ratio for the CFRP systems. A) Composite A. B) Composite B. 93

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0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.750 6 12 18 24Exposure Time (Months)CRH 30 C 40 C 50 C 60 C A 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.000 6 12 18 24Exposure Time (Months)CRH 30 C 40 C 50 C 60 C B Figure 5-22. Cracked stiffness ratio for the CFRP systems. A) Composite C. B) Composite D. 94

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0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.750 6 12 18 24Exposure Time (Months)CRT Composite A Composite B Composite C Figure 5-23. Cracked stiffness ratio performance with exposure time 95

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After Cracking y = 18476x + 2655.8 R2 = 0.9981 Before Cracking y = 48403x 661.44 R2 = 0.99810 2000 4000 6000 8000 10000 12000 14000 16000 18000 0.000.250.500.751.001.25 Deflection (mm)Load (N) A After Cracking y = 17807x 93.829 R2 = 0.9963 Before Cracking y = 29549x 507.04 R2 = 0.9920 2000 4000 6000 8000 10000 12000 14000 16000 18000 0.000.250.500.751.001.25 Deflection (mm)Load (N)B Figure 5-24. Typical load deflec tion plot for composite B. A) Control exposure. B) Coastal exposure. 96

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A B C Figure 5-25. Failure modes for composite C in vari ous exposure systems. A) Control specimen. B) Tidal exposure environment. C) Heated water environment. 97

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CHAPTER 6 CONCLUSIONS Concrete beams strengthened w ith externally bonded CFRP reinforcement were immersed in heated water and exposed to seawater in a tidal zone. The heated water system included full immersion of the specimens in wa ter at elevated temperatures of (30C, 40C, 50C and 60C) The beams were 356 mm x 102 mm x 102 mm and were saw-cut to half their depth and midlength. Following exposure the beams were testi ng under three-point bending to failure. This research focused on the three different stiffne ss regions that were obs erved before failure: uncracked stiffness, stiffness reduction at the cracking load, and post-cr acking stiffness. The effects of moisture on these stiffness regi ons were found to be dependant on type of environmental exposure duration, length of exposure, and the composite system as reinforcement. Generally, the most drastic chan ges in stiffness were noticed in the laminate CFRP (composite C), while the wet lay-up CFRP specimens remained relatively unchanged after moisture exposure (composites A, B, D, and E). The magnitude of uncracked stiffness for the control specimens is related to the fiber to epoxy ratio of the CFRP composite strip. Control specimen s with high fiber to epoxy ratios (Composite C) will produce higher uncracked flexural stiffness than specimens with low fiber to epoxy ratios (Composites A and B) High immersion temperatures (> 40C) cause hi gh levels of deterioration in the saturant epoxy for composite C. Specimens with composite C reinforcement exhibited little postcracking behavior performance due to inte rfacial failure of the composite strip. The magnitude of stiffness reduction noticed at cracking is dependant on the level of debonding between the composite strip and the composite. Exposure to elevated water temperatures has been found to decrease sti ffness reductions at cracking, while tidal exposure has been found to produce increasi ng stiffness reduction at cracking. The relationship between exposure enviro nment and debonding length is still under investigation. Cracked flexural stiffness is relatively unaffected by moisture exposure for beam specimens installed with wet lay-up CFRP reinforcement (composite A, B, D and E). 98

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APPENDIX UNCRACKED FLEXURAL BEHAVIOR The theoretical uncracked stiffness for each specimen was calculated modifying the centerline deflection equation for a simply supported beam subjected to a concentrated load at mid-span, see Equation A-1. Where P = Applied load (N), E = Modulus of Elasticity (N), I = Moment of Inertia (mm4), and L = Length (mm). 348 L IEP (A-1) The moment of inertia calculated above uses th e full section properties of the beam (102 mm x 102 mm x 305 mm). Additionally the effect of CFRP compos ite systems on the transformed beam section were neglected in the uncracked sti ffness sectional properties due to the small cross sectional area of the composite system compared to cross section of the beam specimen. The theoretical uncracked flexural stiffness derived from beam theory for the tested specimens was found to be 467 kN/mm. As previously discussed, the concrete beams s ections used in this investigation had a 51 mm long sawcut at beam centerline with a width of 2.54 mm. The flexural stiffness of a typical sawcut beam specimen was calculated by using the principal of virtual work. The theoretical uncracked flexural stiffness calculated from vi rtual work was 15% less (397 kN/mm) than the prismatic beam specimen. In an effort to reduce the theoretical beam stiffness for each specimen, a shear deflection analysis was conducted to determine if shear ac tion in the beam resulte d in any significant deflection behavior. According to Timoshenko beam theory th e total deflection for a beam undergoing shear and flexur al deflections is shown in Equation A-2. 312 1 48 AG f IE LPs FLEXURE SHEAR(A-2) 99

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Where fs = Form factor for shear (fs = 6/5 for rectangular cross sections), G = Modulus of Elasticity in Shear (N), a nd A = Cross sectional Area (mm2). After plugging in all of sectional properties used for this analysis, the equation above simplifies to Equation A-3. I E LPFLEXURE SHEAR 33.1348 (A-3) After manipulating the above equation to solve for P/ Shear+Flexure researchers discovered that the theoretical flexural stiffness for prismatic beam section was reduced to 351 kN/mm while the corrected uncracked stiffness for the saw cut beam specimens equals 298 kN/mm. Unfortunately, the compliance corrected deflectio n data produced flexur al stiffness values well below the theoretical approximation. Th e cause of error between the corrected and theoretical stiffness values was investigated by using a linear pot to measure the centerline deflection of a non-externally reinforced b eam specimen during loading. A compliance calculation was also run using the linear pot to measure the centerline deflection of the beam. After subtracting the compliance linear pot data from the concrete linear pot data, researchers produced results on par with the beam theory met hod previously discussed. The source of error using the test machine data remains unsolved, howe ver, this investigation recommends all future investigations use LVDTs to measure deflection of beam specimens. 100

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LIST OF REFERENCES Achintha, P., Burgoyne. C., 2008. Fracture m echanics of plate debonding, Journal of Composites for Construction, American Soci ety of Civil Engineers, New York, pp. 396404 ACI Committee 440, 2004. Test methods fo r Fiber-Reinforced Polymers (CFRPs) for Reinforcing or Strengthening Concrete Structures (ACI 440. 3R-04), American Concrete Institute, Farmington Hills, MI, pp 1-40. Au, C., and Buyukozturk, O., 2006. "Peel and shear fracture characterization of debonding in CFRP plated concrete affected by moisture", Journal of Composites for Construction edited by C. Bakis, American Society of Civil Engineers, New York, pp 35-47. Banks, W. M., Pethrick, R. A., Armstrong, G. S., Crane, R. L., and Hayward, D., 2004. Dielectric and mechanical stud ies of the durability of adhe sively bonded CFRP structures subjected to aging in various solvents, Proceedings of the I MECH E Part L Journal of Materials:Design and Applications Professional Engineering Publishing, V. 218, pp. 273281. El-Hawary, M,, Al-Khaiat, H., and Fereig, S., 2000. "Performance of epoxy-repaired concrete in a marine environment", Cement and Concrete Research edited by K. Scrivener, Elsevier Science, New York, V. 30, pp. 259-266. Ferrier, E., and Hamelin, P., 2002. Effect of Wa ter Absorption on the Durability of Carbon CFRP Reinforcement, Proceedings CDCC Durability of Fibre Reinforced Polyer Composites for Construction edited by B. Benmokrane and E. El-Salakawy, University of Sherbrooke, Quebec, pp. 99-112. Gartner, A., 2007. Development of a flexural bon d strength test to determine environmental degradation of carbon fiber-reinforced polymer (CFRP) composites bond ed to concrete, ME thesis, Department of Civil and Coasta l Engineering, University of Florida, Gainesville. pp 50-100. Hulatt, J., Holloway, L., and Thorne, A., 2002."P reliminary investigations on the environmental effects on new heavyweight fabrics for use in civil engineering," Composites Part B: Engineering, Elsevier Science, New York, V. 33, pp. 407. Karbhari, V. M., Engineer, M., 1996. Effect of Environmental Exposure on the External Strengthening of Concrete with Com posites Short Term Bond Durability, Journal of Reinforced Plastics and Composites edited by S. Springer, Sage Publications, Thousand Oaks, V. 15, pp. 1194-1215. McVay, M.C., Cook, R., and Krishnamurthy, K. (1996). Pullout simulation of post installed chemically bonded concrete anchors, Journal of Structural Engineering edited by S. Kunnath, American Society of Civil E ngineers, New York, V. 122, 1016-1024. 101

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NCHRP Report 514 "Bonded Repair and Retrofit of Concrete Stru ctures Using CFRP Composites, Recommended Construction Spec ifications and Process Control Manual", Transportation Research Board, Washington, DC, 2004. Neville, A. M., 1995 Properties of Concrete, Pearson Education, 102

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103 BIOGRAPHICAL SKETCH Nathaniel Allen Van Etten was born to Jack and Theresa Van Etten in Santa Barbara, California in 1983. He was raised and primarily educated in th e small coastal town of Ojai, located in Southern California. In August of 2002, he began attendi ng the University of California. It was there that he found his calling in structural engineering. After receiving his Bachelor of Science in May 2006, he traveled to the Un iversity of Florida to pursue a graduate degree in structural engineering. In August of 2008, he anticipate s receiving the degree of Master of Engineering from the University of Florida. Upon graduation, he plans on continuing his love for structural engineering by working as a building engineer with Walter P. Moore.