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Evaluation of Shrinkage Cracking Potential of Concrete Used in Bridge Decks in Florida


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i Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy EVALUATION OF SHRINKAGE CRACKING POTENTIAL OF CONCRETE USED IN BRIDGE DECKS IN FLORIDA By Rajarajan Subramanian May 2006 Chair: Fazil T. Najafi Cochair: Mang Tia Major Department: Civil And Coastal Engineering A research study was done to evaluate the different concrete mixtures that have various different admixtures add ed for reducing the shrinkage in the concrete, and to make recommendations for concrete mix designs for improved resistance to shrinkage cracking in service. Also, an effective and convenient laboratory set up and procedure for evaluating concrete mixture s for their resistance to shrinkage cracking in service was developed as a result of this study. The results of the testing program indicated that the use of a shrinkage reducing admixture was effective in reducing the free shrinkage strains and shrinkage induced stresses of all the concrete mixtures tested, while the compressive strength, splitting tensile strength and elastic modulus of the concrete were not significantly affected. The addition of fly ash as a mineral admixture was found to be effective in reducing the free shrinkage strain and shrinkage induced stresses of all concrete mixtures. This research study presents a very promising testing and analysis method for evaluating the potential

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ii shrinkage induced stresses in concrete and its potential for shrinkage cracking in service. The developed Constrained Long Specimen (CLS) test method was used to evaluate the effects of a shrinkage reducing admixture on the potential shrinkage induced stresses of 15 different concrete mixes and their potential for shrinkage cracking in service. From the test data and the analysis results obtained from the 15 concrete mixes tested in this set of experiments, the developed Constrained Long Specimen method demonstrated that it provided reasonable asses sment of expected shrinkage induced stresses in the concrete. Due to the creep of concrete at early age, the shrinkage induced stress in the concrete is much lower than that estimated by multiplying the shrinkage strain by the elastic modulus of the concr ete. Using the CLS test method enables the creep component to be properly considered, and a realistic determination to be made of the expected induced shrinkage stresses in concrete in service. The results of the CLS tests on the 15 concrete mixes showe d the possible benefits of using a shrinkage reducing admixture in reducing the potential shrinkage cracking of concrete in service.

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PAGE 1

EVALUATION OF SHRINKAGE CRACKIN G POTENTIAL OF CONCRETE USED IN BRIDGE DECKS IN FLORIDA By RAJARAJAN SUBRAMANIAN A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2006

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Copyright 2006 by RAJARAJAN SUBRAMANIAN

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This document is dedicated to my parents Subramanian Balakrishnan and Udaya Subramanian

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iv ACKNOWLEDGMENTS I have immense pleasure in thanking the pe rsons and organizations that helped me over the course of time to bring my PhD thesis to the final form. My sincere thanks go to Dr. Fazil T Najafi, chair of my committee, for his valuable suppor t throughout my study at the University of Florida. I thank Dr. Mang Tia, the cochair of my committee, for his valuable advice and suggestions throughout th e research study and dissertation. The Florida Department of Transportation (F DOT) is gratefully acknowledged for providing the financial support, testing equipment, materi als and personnel that made this research possible. I would like to express my sin cere appreciation to my supervisory committee members Dr. Andrew J. Boyd, Dr. Ajay Sha nker and Mr. Peter Kopac (FHWA Research Engineer) for their invaluable guidance a nd support throughout my research at the University of Florida. I would also like to express my gratitude to Dr. Jonathan Earle for his continuous encouragement and support. Also, I would like to thank all my colleague s in the materials section in Civil And Coastal Engineering Department. Messr s. Chuck Broward and Danny Brown were acknowledged for their help w ith the setup of instrumenta tion to conduct the tests. The Florida Department of Transportati on personnel Messrs. Michael Bergin, Charles Ishee, Mario Paredes, Richard Delorenzo, Toby Dillow, Joseph Fitzgerald, and Craig Roberts are acknowledged for their help with the entire pr ocess of conducting the various tests. W. R. Grace & Co. is acknow ledged for providing the shrinkage-reducing admixture, water-reducing admixture and air-e ntraining admixture used in this study. Last, but certainly not least, I would like to thank my wife, my daughter, my parents, my

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v brother and his wife, my sister s and their husbands. They have been very patient and supportive.

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vi TABLE OF CONTENTS Page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES...............................................................................................................x LIST OF FIGURES..........................................................................................................xii ABSTRACT.......................................................................................................................xv CHAPTER 1 INTRODUCTION........................................................................................................1 1.1 Background............................................................................................................1 1.2 Problem Statement.................................................................................................2 1.3 Study Objectives....................................................................................................3 2 LITERATURE REVIEW.............................................................................................4 2.1 Introduction............................................................................................................4 2.2 Mechanism of Concrete Shrinkage and Cracking.................................................4 2.3 Types of shrinkages...............................................................................................5 2.4 Influence of Aggregates on Concrete Shrinkage...................................................7 2.5 Influence of Cement on Concrete Shrinkage.........................................................8 2.6 Influence of Water Cont ent on Concrete Shrinkage..............................................9 2.7 Influence of Specimen size a nd Shape on Concrete Shrinkage.............................9 2.8 Admixtures that affect Shrinkage........................................................................10 2.8.1 Mineral Admixtures..................................................................................10 2.8.1.1 Fly ash................................................................................................11 2.8.1.2 Silica fume.........................................................................................13 2.8.1.3 Silane..................................................................................................14 2.8.1.4 Onada Expan......................................................................................15 2.8.2 Chemical Admixtures...............................................................................15 3 MATERIALS..............................................................................................................19 3.1 Introduction..........................................................................................................19 3.2 Concrete Mixtures Evaluated..............................................................................19 3.3 Concrete Mixture Constituents............................................................................36 3.3.1 Water.........................................................................................................36

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vii3.3.2 Fine Aggregate..........................................................................................36 3.3.3 Coarse Aggregate......................................................................................37 3.3.4 Cement.......................................................................................................38 3.3.5 Fly Ash......................................................................................................39 3.3.6 Ground Blast-Furnace Slag.......................................................................39 3.3.7 Air-Entraining Admixture.........................................................................39 3.3.8 Water-Reduci ng Admixtures.....................................................................40 3.3.8.1 WRDA 64...............................................................................................40 3.3.8.2 Adva Flow (Super plasticizer)................................................................40 3.3.9 Shrinkage-Reducing Admixture................................................................40 3.4 Preparation of Concrete Mixtures........................................................................41 3.4.1 Mixing of Concrete....................................................................................41 3.4.2 Preparation of Concrete Specimens for Mechanical Tests........................43 3.4.3 Preparation of Concrete Specime ns for ASTM C157 Shrinkage Test......43 3.4.4 Preparation of Concrete Sp ecimens for Long Specimen Tests.................43 4 LABORATORY TESTING PROGRAM...................................................................44 4.1 Introduction..........................................................................................................44 4.2 Tests on Fresh Concrete.......................................................................................44 4.3 Tests on Hardened Concrete................................................................................44 4.3.1 Compressive Strength Test....................................................................45 4.3.2 Modulus of Elasticity Test.....................................................................46 4.3.3 Splitting Tensile Strength Test...............................................................49 4.3.4 Free Shrinkage Measurement (ASTM C157) Using LVDTs................50 4.3.4.1 Test Setup........................................................................................50 4.3.4.2 Test procedure.................................................................................54 4.3.5 Free Shrinkage Measured by Embedmen t Gage in the Long-Specimen Apparatus................................................................................................55 4.3.5.1 Test setup.........................................................................................55 4.3.5.2 Test procedure.................................................................................57 4.3.6 Free Shrinkage Measurement using Whittemore Gage in the LongSpecimen Apparatus..................................................................................58 4.3.6.1 Test setup.........................................................................................58 4.3.6.2 Test procedure.................................................................................59 4.3.7 Free Shrinkage Measurement Using Whittemore Gage on Cylindrical Specimens..................................................................................................60 4.3.7.1 Test setup.........................................................................................60 4.3.7.2 Test procedure.................................................................................60 4.3.8 Constrained Shrinkage Test Us ing the Long Specimen Apparatus...........64

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viii 5 DEVELOPMENT AND EVALUATION OF THE MODIFIED CONSTRAINED LONG SPECIMEN APPARATUS............................................................................65 5.1 Introduction..........................................................................................................65 5.2 Fundamentals of the Constrained Long Specimen Method.................................65 5.2.1 Original Design.........................................................................................65 5.2.1 Test Procedure...........................................................................................66 5.2.3 Method of Analysis...................................................................................67 5.3 First Refinement of Apparatus Us e of LVDT, Load Cell and Data Acquisition System.............................................................................................69 5.3.1 Changes Made to the Original Design.......................................................69 5.3.2 LVDTs for Measurement of Strain............................................................72 5.3.3 Load Cell for Measurement of Stress........................................................76 5.3.4 Data Acquisition System...........................................................................77 5.3.5 Modified Instrumentation for the LVDTs.................................................80 5.3.6 Calibration of the LVDT/Signal Conditioner System...............................81 5.4 Second Refinement of Apparatus Use of Lubricated Base Plate.....................83 5.5 Third Refinement of Apparatus Use of Embedment Strain Gages..................86 5.5.1 Embedment Strain Gage............................................................................86 5.5.2 Strain Gage Signal Conditioner.................................................................86 5.6 Fourth Refinement of Apparatus Ze roing of Strain in the Constrained Specimen.............................................................................................................89 6 RESULTS OF LABORATO RY TESTING PROGRAM..........................................92 6.1 Introduction..........................................................................................................92 6.2 Evaluation of Different Methods of Free Shrinkage Measurement....................92 6.2.1 Methods Evaluated....................................................................................92 6.2.2 Comparison of Test Results.......................................................................93 6.2.3 Observations on the Different Me thods of Shrinkage Measurement.......105 6.2.3.1 Whittemore gage on the long specimen........................................105 6.2.3.2 LVDT on the long specimen.........................................................105 6.2.3.3 Embedment gage in the long specimen.........................................105 6.2.3.4 Whittemore gage on a cylindrical specimen.................................106 6.2.3.5 ASTM C157 method using a LVDT.............................................106 6.2.4 Recommended method.............................................................................107 6.3 Evaluation of the Effects of a Shrinkage-Reducing Admixture........................107 6.3.1 Effects on Free Shrinkage.......................................................................107 6.3.2 Effects on Shrinkage-Induced Stress.......................................................112 6.3.3 Effects on Strengths and Elastic Modulus...............................................121 6.4 Evaluation of the Effects of Fl y Ash and Ground Blast Furnace Slag.............127

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ix 7 SUMMARY AND RECOMMENDATIONS...........................................................138 7.1 Development and Evaluation of the Modified Constrained Long Specimen Apparatus..........................................................................................................138 7.2 Evaluation of Different Methods of Free Shrinkage Measurement..................139 7.3 Evaluation of the Effects of a Shrinkage-Reducing Admixture.......................140 7.4 Evaluation of the Effects of Fl y Ash and Ground Blast Furnace Slag.............141 7.5 Recommendations..............................................................................................142 APPENDIX ORIGINAL READINGS.................................................................................................143 LIST OF REFERENCES.................................................................................................146 BIOGRAPHICAL SKETCH...........................................................................................151

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x LIST OF TABLES Table page 3-1. Mix Proportions for Mix 1......................................................................................21 3-2. Mix Proportions for Mix 2......................................................................................22 3-3. Mix Proportions for Mix 3......................................................................................23 3-4. Mix Proportions for Mix 4......................................................................................24 3-5. Mix Proportions for Mix 5......................................................................................25 3-6. Mix Proportions for Mix 6......................................................................................26 3-7. Mix Proportions for Mix 7......................................................................................27 3-8. Mix Proportions for Mix 8......................................................................................28 3-9. Mix Proportions for Mix 9......................................................................................29 3-10. Mix Proportions for Mix 10..................................................................................30 3-11. Mix Proportions for Mix 11..................................................................................31 3-12. Mix Proportions for Mix 12..................................................................................32 3-13. Mix Proportions for Mix 13..................................................................................33 3-14. Mix Proportions for Mix 14..................................................................................34 3-15. Mix Proportions for Mix 15..................................................................................35 3-15. Physical Propertie s of Fine Aggregate....................................................................37 3-17. Physical Properties of the Coarse Aggregate..........................................................38 3-18. Physical Properties of the Type I Cement Used......................................................38 3-19. Chemical Composition of the Type I Cement Used................................................38 3-20. Chemical Composition of the Class F Fly Ash Used..............................................39

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xi 3-21. Physical Properties of the Class F Fly Ash Used....................................................39 3-22. Chemical Composition of the Slag Used.................................................................39 6-1. Free Shrinkage Strains of the 15 Pairs of Concrete Mixtures as Measured by the Different Methods....................................................................................................95 6-2. Percentage Reduction in Free Shrinka ge Strains of the SRA Mixtures as Compared With the Standard Mixtures as Measured by the Embedment Strain Gages in the Long Specimens................................................................................108 6-3. Results of Constrained Long Specimen Test on the 15 Pairs of Concrete Mixtures113 6-4. Percentage Reduction of Computed Shrinkage-Induced Stresses of SRA Mixtures as Compared With the Standard Mixtures.............................................................120 6-5. Compressive Strength, Splitting Tensile Strength and Elastic Modulus of the 15 Pairs of Concrete Mixtures.....................................................................................122 6-6. Results of t-Tests on the Compressive Strength of the SRA Mixtures Versus the Standard Mixtures..................................................................................................128 6-7. Results of t-Tests on the Splitting Te nsile Strength of the SRA Mixtures Versus the Standard Mixtures............................................................................................129 6-8. Results of t-Test on the Modulus of Elasticity of the SRA Mixtures Versus the Standard Mixtures..................................................................................................130 6-9. The Statistical Ranges of Free Shrinkage Strains of the Concrete Mixtures With Different Mineral Admixtures................................................................................136 6-10. The Statistical Ranges of Computed Shrinkage-Induced Stresses of the Concrete Mixtures with Di fferent Mineral Admixtures.........................................137

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xii LIST OF FIGURES Figure page 3-1. Gradation chart for the fine aggregate (Goldhead silica sand)..................................36 3-2. Gradation chart for the coarse aggregate (#89 limestone).........................................37 3-3. Concrete mixer used..................................................................................................42 4-1. Set-up for compressive strength test..........................................................................45 4-2. Set-up for modulus of elasticity test..........................................................................47 4-2. Set-up for modulus of elasticity test..........................................................................47 4-3. Close-up view of elastic modulus test wet-up with a LVDT for strain measurement.............................................................................................................48 4-4. Set-up for splitting tensile strength test.....................................................................49 4-5. Mold for 3 3 11.25-in. (76 76 286-mm) shrinkage test specimen...............50 4-6 Set-up for ASTM C157 free shrinkage measurement using a LVDT........................52 4-7. Picture of several te st setups for free shrinkage measurement using LVDTs...........53 4-8. Schematics of test set-ups for meas urement of free shrinkage using LVDTs...........53 4-9. Schematics for test setup for fr ee shrinkage measurement using the long-specimen apparatus..........................................................................................55 4-10. Picture of two long-specimen molds.......................................................................56 4-11. Whittemore gage for measuring th e distance between two gage points..................58 4-12. Long concrete specimen with gage point studs installed........................................59 4-13. Gage-point positioning guide..................................................................................61 4-14. Gauge-position guide...............................................................................................62 4-15. Plastic cylinder mold inside gauge-position guide..................................................63 4-16. Concrete cylinders with gauge point studs installed on them..................................64 5-1. The original constrained long specimen apparatus [Tia et al., 1998]........................66 5-2. Schematics of the restrained long specimen under contraction.................................67

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xiii 5-3. Constrained long specime n apparatus using a LVDT...............................................70 5-4. Top and side views of the c onstrained long specimen apparatus..............................71 5-5. Side and top views of th e end collar block of the mold............................................71 5-6. Front and side views of the PVC side pieces for the constrained long specimen apparatus...................................................................................................................72 5-7. Aluminum bracket support for the gage studs that hold the LVDT and the core rod holders to the concrete specimen.......................................................................72 5-8. Cross-sectional view of an LVDT.............................................................................73 5-9. LVDT core displacement a nd the respective voltage change....................................74 5-10. LVDT holder and a portion of the rod that is connected to the other holder..........75 5-11. The holder for the rod that passes through the LVDT core.....................................75 5-12. The load cell attached to th e frame of the concrete specimen.................................77 5-13. Agilent 34970A data acquisition system unit..........................................................77 5-14-a. Setup for the constrained long specimen test with a LVDT ................................79 5-14-b. Setup for the constrained long speci men test with a LVDT and a loadcell. 5-15. A LVDT line powered LPC-2100 signal conditioner.............................................81 5-16. Individual constrained long concrete specimen connected to an LVDT, LVDT signal conditioner, DAS and the computer..............................................................82 5-17. A plot of LVDT/conditioner output versus displacement (micrometer reading).....................................................................................................................83 5-18. Set-up for calibration of LVDTs used in the long specimens.................................84 5-19. Use of wax paper to reduce fricti on between concrete and base plate....................85 5-20. Constrained long specimen appa ratus with a Teflon base plate..............................85 5-22. Schematics of the constrained long specimen apparatus using an embedment strain gage for strain measurement...........................................................................87 5-23. OMEGA OM2-163 Backplane 8-channel signal conditioner.................................88 5-24. Manual pulling of a test specimen to correct for specimen contraction..................91

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xiv 6-1. Free shrinkage strains as measured by Whittemore gage on the long specimens for six standard mixes............................................................................................100 6-2. Free shrinkage strains as measured by LVDT on the long specimens for six standard mixes........................................................................................................101 6-3. Free shrinkage strains as measured by embedment gages in the long specimens for six standard mixes............................................................................................102 6-4. Free shrinkage strains as measured by Whittemore gage on the cylinders for six standard mixes........................................................................................................103 6-5. Free shrinkage strains as measured by ASTM C157 Method for six standard mixes......................................................................................................................104 6-6. Comparison of free shrinkage strains of Standard and SRA mixtures at 3 days curing......................................................................................................................109 6-7. Comparison of free shrinkage strains of Standard and SRA mixtures at 7 days curing......................................................................................................................110 6-8. Comparison of free shrinkage strains of Standard and SRA mixtures at 14 days curing......................................................................................................................111 6-9. Comparison of computed shrinkageinduced stresses of Standard and SRA mixtures at 3 days curing.......................................................................................118 6-10. Comparison of computed shrinkage -induced stresses of Standard and SRA mixtures at 7 days curing.......................................................................................119

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xv Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy EVALUATION OF SHRINKAGE CRACKIN G POTENTIAL OF CONCRETE USED IN BRIDGE DECKS IN FLORIDA By Rajarajan Subramanian May 2006 Chair: Fazil T. Najafi Cochair: Mang Tia Major Department: Civil And Coastal Engineering A research study was done to evaluate the different concrete mi xtures that have various different admixtures added for reduc ing the shrinkage in the concrete, and to make recommendations for concrete mix desi gns for improved resistance to shrinkage cracking in service. Also, an effective and convenient la boratory set-up and procedure for evaluating concrete mixtures for their re sistance to shrinkage cracking in service was developed as a result of this study. The results of the testing program i ndicated that the use of a shrinkage-reducing admixture was effective in reducing the fr ee shrinkage strains and shrinkage-induced stresses of all the concrete mixtures test ed, while the compressi ve strength, splitting tensile strength and elastic modulus of the c oncrete were not significantly affected. The addition of fly ash as a mineral admixture wa s found to be effective in reducing the free shrinkage strain and shrinkage-i nduced stresses of all concrete mixtures. This research study presents a very promising testing and analysis method for evaluating the potential

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xvi shrinkage-induced stresses in concrete and it s potential for shrinkage cracking in service. The developed Constrained Long Specimen (CLS ) test method was used to evaluate the effects of a shrinkage-reducing admixture on the potential shrinkage -induced stresses of 15 different concrete mixes and their potential for shrinkage cracking in service. From the test data and the analysis results obtained from the 15 concre te mixes tested in this set of experiments, the developed Constraine d Long Specimen method demonstrated that it provided reasonable assessment of expected shri nkage-induced stresses in the concrete. Due to the creep of concrete at early age, the shrinkage-indu ced stress in the concrete is much lower than that estimated by multiply ing the shrinkage strain by the elastic modulus of the concrete. Using the CLS test method enables the creep component to be properly considered, and a rea listic determination to be ma de of the expected induced shrinkage stresses in concrete in service. The results of the CLS te sts on the 15 concrete mixes showed the possible benefits of usi ng a shrinkage-reducing admixture in reducing the potential shrinkage cracki ng of concrete in service.

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1 CHAPTER 1 INTRODUCTION 1.1 Background Shrinkage cracking of concrete bridge decks is a critical problem in Florida. Many concrete bridge decks have been observed to develop plastic shrinka ge cracks soon after construction. These cracks shorten the service lives of the decks and increase the cost for maintenance and repairs. In recent year s, the increasing use of High-performance concretes might have made this problem wors e. High-performance concretes, which are usually produced by using high cement conten t, are known to have higher free shrinkage and are thus more likely to develop shrinkage cracking. One of the possible solutions to this problem is to modify the concrete mix designs so that the concretes could be less suscepti ble to shrinkage cracking while maintaining their other high-performance properties. Howe ver, the tendency of c oncrete to shrinkage cracking is not a simple function of its free shri nkage. It is also affected by factors such as the constraint on the conc rete, rate of strength gain, temperature and the elastic modulus of the concrete. The creep of the concrete during its pl astic stage can also relieve some of the induced stress due to sh rinkage. Because the creep counteracts the shrinkage as a stress re laxation mechanism. All these fact ors need to be fully considered in evaluating a concrete mix for its resistance to shrinkage cracking. In a prior research project entitled D evelopment of a Laboratory Procedure for Evaluating Concrete Mixes for Resistance to Shrinkage Cracking in Service, sponsored by the FDOT, a testing and an alysis method was developed for evaluation of concrete

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2 mixes for resistance to shrinka ge cracking. The developed testing procedures included characterizing the tensile streng th and elastic modulus of th e concrete at early ages by means of the conventional strength tests, and characterizing the cree p, free shrinkage and elastic properties of the conc rete by means of a constrained long specimen apparatus, which was developed as part of this project done by Mang Tia and Tu-Ming Leung. Results from the above study show that the de veloped test method is very effective in measuring the pertinent properties of concrete that are related to shrinkage cracking, and is a very promising tool for evaluating the resi stance to shrinkage cracking of concrete in service. This testing and analysis met hod should be further evaluated, refined and implemented as a standard procedure for evaluating shrinkage cracking resistance of concrete used by FDOT. 1.2 Problem Statement Concrete shrinkage is of growing con cern when focusing on maintaining durable structures. Over time, the shrinkage i nduces cracking, which can severely reduce concrete life expectancy. These volume cha nges are often attributed to drying of the concrete over a long time period. At early ages the concrete is still moist and there are difficulties in measuring the fluid material. These difficulties have hindered comprehensive physical testing and understandin g of the factors influencing shrinkage. Shrinkage cracking is due to restrained sh rinkage, and also, it is affected by the constraints on the concrete, rate of strength gain, the aggregates, water, water to cement ratio, and temperature of concrete. There is a lack of proper equipment with a well defined standard procedure to measure th e restrained shrinkage in concrete.

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3 1.3 Study Objectives The main objectives of this research are as follows: 1. To develop an effective and convenien t laboratory setup and procedure for evaluating concrete mixtures for their resi stance to shrinkage cr acking in service of bridge decks in Florida. 2. To implement the developed tes ting and analysis method using the developed constrained long specimen apparatuses as a standardized t ool for evaluation of shrinkage cracking resistance of concrete in Florida. 3. To evaluate the different concrete mixtures that have various different admixtures added for reducing th e shrinkage in the concrete. 4. To make recommendations for modi fication of concrete mix designs, based on the evaluation of the different concrete mixtures that were used in bridge decks of Florida for improved resistance to shrinkage cracking in service. 5. To evaluate the different test methods on measuring the free shrinkages of concrete specimens.

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4 CHAPTER 2 LITERATURE REVIEW 2.1 Introduction This chapter presents a literature review on the basics of concrete shrinkage and the results of some studies on admixtures for reducing shrinkage in concrete. 2.2 Mechanism of Concrete Shrinkage and Cracking The portion of the concrete th at shrinks is the cement pa ste. Cement paste shrinks as it loses moisture due to the surface tension of water and the menisci that are formed in the pore spaces in the paste. The surface tens ion of water in partia lly filled pores pulls inward on the walls of the pore spaces. The c oncrete responds to thes e internal forces by shrinking. Tensile stresses develop when the concre te is prevented from shrinking freely. The combination of high tensile stresses with the low fracture resistan ce of concrete often results in cracking. Cracks reduce load carrying capacity and accel erate deterioration, resulting in increased main tenance costs and reduced se rvice life. Although free shrinkage measurements are useful in comp aring different mixture compositions, they do not provide sufficient information to determin e if the concrete will crack in service. Cracking is a complex phenomenon, which is dependent on several factors including free shrinkage, age-dependent material property development (e.g. Compressive strength), creep relaxation, shrinkage rate, and degree of restraint. Th e amount of shrinkage for any cement paste is primarily a function of the wa ter-to-cement ratio of the paste, but it may

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5 also be affected by cement type, cement fine ness, and any other ingredients which alter the pore size distribution. 2.3 Types of shrinkages The types of shrinkages can be categorized as plastic shrinkag e, drying shrinkage, autogenous shrinkage and carbonation shrinkage. Plastic Shrinkage The space between particles of fresh concrete is completely filled with water. When the water is removed from the paste by ex terior influences, such as evaporation at the surface, a complex series of menisci are formed. These in turn, generate negative capillary pressures, which will cause the volume of the paste to contract. Such contraction is called as plastic shrinkage. Th e magnitude of plastic shrinkage is affected by the amount of water lost from the surf ace of the concrete, which is influenced by temperature, ambient relative humidity, and wind velocity [Neville, 2000]. Drying Shrinkage Drying Shrinkage is defined as the time-dep endent strain due to moisture loss at constant temperature in the absence of an exte rnal load and takes place after the concrete has set. This shrinkage is due to loss of water from the concrete by evaporation. Water in hydrated cement or concrete can be loosely described as free (or excess) water located in capillary pores, physically adsorbed water on the surface of the CSH gels and chemically bonded water in the products of hydration of the cement [Gani, 1997]. Autogenous Shrinkage If no additional water beyond that added during mixing is provided during curing, concrete will begin to dry inte rnally, even if no moisture is lost to the surroundings as

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6 water is consumed by hydration. This phenom enon of drying internal ly is known as selfdesiccation and is manifested as autogenous shrinkage (or Chemical shrinkage). Carbonation Shrinkage Hardened cement paste will react ch emically with carbon dioxide. The atmospheric carbon dioxide is sufficient to ca use considerable reaction with cement paste over a long time period. However, this is accompanied by irreversible shrinkage, and hence it is called carbonation shrinkage [Mindess, Young and Darwin, 2003]. Water-related shrinkage (Plastic, Au togenous and Drying shrinkages) is a volumetric change caused by the movement a nd the loss of water (i .e., change in the internal pore pressure caus ed by drying or self-desiccation). Drying is driven by the environmental conditions in which the relative humidity of the concre te structure strives to bring into balance with the humidity of the surrounding environment. Water is squeezed out from the capillary pores resulti ng in the development of tensile stresses since the internal humidity attempts to make uniform with a lower environmental humidity. The cause of compressing the concrete matrix is the tensile stress that explains partially the phenomenon of drying shrinkage Water-related shrinkage is the most significant in thinner structures (with large surface area to volume ratio) due to the more rapid loss of water. Pavements, bridge decks, and slabs are examples of thin structures that may be susceptible to drying shrinka ge cracking [Bazant 1986; Bazant and Carol 1993; and Tazawa 1998]. This dissertation will focus on drying sh rinkage and conseque ntly, the following sections will be used to provi de a brief summary of the terms that are used to describe shrinkage of concrete. Also, the effects of ingredients and their phys ical characteristics

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7 on the shrinkage of concrete are discussed in this chapter. While plastic and carbonation shrinkage can occur in structures, this re search report will focus primarily on drying shrinkage. 2.4 Influence of Aggregates on Concrete Shrinkage Aggregates affect concrete deformati on through water demand, aggregate stiffness and volumetric proportion, and paste/aggregat e interaction [Han et al. 1994]. The primary source of shrinkage is the cement past e. Aggregates that require a lower water demand for workability will th erefore produce concretes with a lower cement content, which will result in lower shrinkage. Shape a nd texture of coarse aggregate play a role on the behavior of fresh and hardened concre te. Shape and texture affect the demand for sand. Flaky, elongated, angular, and rough part icles have high voids and require more sand to fill the voids and to provide a work able concrete, thus increasing the demand for water and thereby increasing shrinkage. Spherical or cu bical aggregates have less specific surface area than flat and elongated part icles. Consequently, spherical or cubical aggregates require less paste and less water for workability [Shilstone 1999]. For a given workability, flaky and elongated aggregates incr ease the demand for water, thus affecting strength of hardened concrete as well as in creasing the shrinkage in concrete. Spherical or cubical particles lead also to better pumpability and finishability as well as produce higher strengths and lower shrinkage than flaky and elongated aggregates [Shilstone 1990]. Aggregates with higher stiffn ess will give greater restra ining effects to shrinkage stresses and result in lower shrinkage in conc rete [Neville 1996]. Aggregates that shrink considerably upon drying usually have a low stif fness. This type of aggregate may also have a large water absorption value, which w ill result in a concrete with higher shrinkage

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8 [Troxell et al. 1996]. Aggregat es with low absorption tend to reduce shrinkage and creep [Washa 1998]. A concrete using a well-graded aggregate and with large maximum aggregate size requires less cement paste, thus decreasing bleeding, creep, and shrinkage [Washa 1998; Shilstone 1999]. However, it is to be noted that although an excess of coarse aggregate could decrease drying shrinkage, it will increas e the number of micro-cracks within the paste [Aitcin 1998]. In some parts of the world, high absorp tion aggregates exis t and use of these aggregates will increase the water content and may increase shrinkage. However, it should be noted that recently the use of high porosity light weight aggregate (LWA) has been proposed as one method to minimize aut ogenous shrinkage. In these works, the LWA is saturated to various degrees before casting and the aggregate acts as a water reservoir to supply water that counteracts the self-desiccati on of the paste [Van Breugel and deVries 1998; Bloom et al. 1999]. 2.5 Influence of Cement on Concrete Shrinkage Tazawa and Miyazawa [1997] found that cement composition has a greater influence on autogenous shrinkage than dr ying shrinkage. As compared with normal Portland cement, larger autogenous shrinka ge was observed for high early strength cement at an early age, and blast furnace sl ag cement at later ages. Less autogenous shrinkage was observed for moderate heat ce ment paste, and low heat Portland cement with a high C2S content. Autogenous shrinkage depends on the hydration of C3A and C4AF and it increases with an increase in these compounds. The use of an expansive cement was f ound to produce a large shrinkage reduction in the cement mortar, but negligible effect in the concrete in a study by [Saito et al.

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9 1991]. The aggregate was found to play an important role in the shrinkage of the concrete. It was found that at the begi nning of shrinkage, some cracks had already existed around the coarse aggregate particles us ed in the expansive cement concretes. The formation of cracks was found to lead to a pa rtial loss of restraint of coarse aggregate particles against drying shrinkage. 2.6 Influence of Water Content on Concrete Shrinkage The water content has a large influence on the drying shrinkage of cement paste and concrete. For a given w/ c ratio, concretes of a wet c onsistency have a higher paste content and have a greater amount of shrinka ge than a stiffer mixture [Troxell et al. 1996]. For a given proportion of cement and aggregate, concretes of a wet consistency have a higher water content and thus have a greater amount of shrinkage than a stiffer mixture. 2.7 Influence of Specimen Size a nd Shape on Concrete Shrinkage The size and shape of a concrete specimen definitely influence the rate of loss or gain of moisture under a given storage conditi on, and this can affect the rate of volume change as well as total expansion or contraction. Almudaiheem and Hansen [1987] observed th e shrinkage of concrete specimens of various sizes over a one-year period. The shri nkage decreased with increasing specimen size. The ultimate shrinkage of paste, mort ar, and concrete was found to be independent of specimen size and shape according to the dynamic shrinkage/weight loss curves. They concluded that the ultimate dr ying shrinkage may be estimated from the shrinkage versus drying time curves for small laboratory specimens of 1 1 11 in. (25 25 279 mm) with the same mixture proportions as the larger structural members.

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10 2.8 Admixtures that affect Shrinkage Admixtures are used for the purpose of improving some characteristic of the concrete. Admixtures are ingredients other than water, aggregates, hydraulic cement, and fibers that are added to the concrete ba tch immediately before or during mixing. A proper use of admixtures offers certain benefi cial effects to concre te, including improved quality, acceleration or retardation of setting time, enhanced frost and sulfate resistance, control of strength development, improved work ability, and enhanced finishability. It is estimated that 80% of concrete currently pr oduced in North America these days contains one or more types of admixtures. Admixtures vary widely in chemical composition, and many perform more than one function. Two basic types of admixtures are available: chemical and mineral. All admixtures to be used in concrete construc tion should meet specifica tions; tests should be made to evaluate how the admixture will affect the properties of the concrete to be made with the specified job materials, under th e anticipated ambient conditions, and by the anticipated constr uction procedures. This section will include admixtures that can be used to reduce the shrinkage in concrete. These admixtures include silica fu me, fly ash, Onada-Expan, and Silane. They are found to have reduced the shrinkag e of concrete in varying degrees. Shrinkage-reducing admixtures (SRA) are in cluded here in two sections: one under mineral admixtures and the other in chemi cal admixtures. They typically reduce the shrinkage strain in concrete specimens. 2.8.1 Mineral Admixtures Use of mineral admixtures make mixtur es more economical, reduce permeability, increase strength, and influence other concrete properties. Mineral admixtures (fly ash,

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11 silica fume [SF], and slags) are usually added to concrete in larger amounts to enhance the workability of fresh concrete; to improve resistance of concrete to thermal cracking, alkali-aggregate expansion, and sulfate a ttack; and to enable a reduction in cement content. Mineral admixtures affect the natu re of the hardened c oncrete through hydraulic or pozzolanic activity. Pozzolans are cementitious materials and include natural pozzolans (such as the volcanic ash used in Roman concrete), fly ash and silica fume. They can be used with Portland cement, or blended cement either individually or in combinations. 2.8.1.1 Fly Ash Fly ashes are finely divided residue resu lting from the combustion of ground or powdered coal. They are generally finer than cement and consist mainly of glassyspherical particles as well as residues of hematite and magnetite, char, and some crystalline phases formed during cooling. Use of fly ash in concrete started in the United States in the early 1930's. The first comp rehensive study was that described in 1937, by R. E. Davis at the University of Californ ia [Davis et al., 1937 ; Kobubu, 1968]. The major breakthrough in using fly ash in concrete was the construction of Hungry Horse Dam (Montana) in 1948, utilizing 120,000 metric tons of fly ash. This decision by the U.S. Bureau of Reclamation paved the way for using fly ash in concrete constructions. In addition to economic and ecological benefits, the use of fly ash in concrete improves its workability, reduces segregati on, bleeding, heat evolution and permeability, inhibits alkali-aggregate reaction, an d enhances sulfate resistance. One of the most important fields of app lication for fly ash is PCC pavement, where a large quantity of concrete is used and ec onomy is an important factor in concrete

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12 pavement construction. FHWA has been enc ouraging the use of fly ash in concrete. When the price of fly ash concrete is equal to, or less than, the pr ice of mixes with only portland cement, fly ash concretes are given preference if technica lly appropriate under FHWA guidelines [Adams 1988]. Two major classes of fly ash are specifi ed in ASTM C 618 on the basis of their chemical composition resulting from the type of coal burned; thes e are designated Class F and Class C. Class F is fly ash normally produced from burning anthracite or bituminous coal, and Class C is normally produced from the burning of subbituminous coal and lignite (as are found in some of the western states of the United States) [Halstead 1986]. Class C fly ash usually has cementiti ous properties in addition to pozzolanic properties due to free lime, whereas Class F is rarely cementitious when mixed with water alone. Fly ash (from Afsin-Elbistan Power plant, Turkey) used in mortar samples reduces the drying shrinkages by about 30 to 40% when compared with pure Portland cement mortar. The mortar samples containing 40% fly ash expanded instead of shrinking. Based on the strength and shrinkage measur ement results, it was concluded that the nonstandard Afsin-Elbistan fly ash could be utilized in cement-based materials as a mineral additive, particularly in concrete pavement, large industrial concrete floors, parking lot applications or ro ck bolt applications of rock engineering where shrinkage should be avoided. Based on the expansive pr operty of this fly ash, it may also be concluded that this fly ash may be utilized as cement reducing agent or in production of a shrinkage compensating cement. However, fu rther studies are needed to investigate long-term properties of the concrete made with this fly ash before it can be used as a

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13 mineral additive or in production of a shri nkage compensating cement [Duran et al. 2004]. Tangtermsirikul tested 0.56 1.56 6.24 in. (15 40 160 mm) prism specimens to measure length change due to drying shri nkage. The drying shrinkage tests were conducted in a controlled environment of 77 F (25 C) and 60% re lative humidity. Three types of Class C fly ash and one type of Cla ss F fly ash were used in the experiment. The class C fly ash had a smaller drying shrinkage than the ordinary cement paste mixtures. The addition of the fly ash reduced the wate r requirement of the mi xtures, thus reducing the shrinkage. The Class C fly ash also reduced the autogenous shrinkage due to chemical expansion of the concrete mixtur e [Tangtermsirikul et al. 1995]. The morphology, particle size distribution and surface characte ristics of fly ash used as a mineral admixture has a consid erable influence on th e water requirement, workability, and rate of streng th development of concrete [Mehta 1986]. Particle sizes range from less than 1 micron to 100 microns in diameter, with more than 50% under 20 microns. 2.8.1.2 Silica fume Silica fume is an industrial by-product with a particle size about 100 times finer than Portland cement [Mehta 1986]. Tazaw a and Yonekura [1991] examined shrinkage and creep of mortar and concrete. Drying shrinkage of concrete was tested using 3.9 3.9 15.6-in. (100 100 400-mm) prism specimens. The specimens were in a controlled environment of 68 F (20 C), 50% relative humidity. The drying shrinkage of the concrete mixtures with the silica fume was lower than that of the same type mixtures without the silica fume.

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14 Haque [1996] measured the drying shrinkage on 3.35 3.35 11.22-in. (85 85 285-mm) prism specimens. The addition of bot h 5 and 10% silica fume (by weight) in concrete mixtures resulted in a substa ntial reduction of drying shrinkage. A dozen high strength concrete prisms of size 3 3 11.25 in. (76 76 286 mm) were examined for assessing the drying shrink age strain that the silica fume concrete experienced [Alsayed 1998]. These prisms were monitored over a three-year time period. All of the mixtures were iden tical except for the admixture c ontent. Three mixtures were compared; the first had a superplasticiz er as the admixture, the second had a superplasticizer and 10% s ilica fume by weight, and the third mixture had a regular plasticizer and 10% silica fu me by weight. The specimens were submerged in water for seven days. Six specimens were then put in a laboratory-controlled environment, while the other six specimens were exposed to field conditions. By adding 10% silica fume, the shrinkage was reduced over time. The mixtur e with the superplasticizer and silica fume showed a reduction in shrinkage. Specimens w ith the normal plasticizer showed a larger drying shrinkage than those with the superplasticizer. The combined superplasticizer and silica fume mixtures showed a reduced dryi ng shrinkage rate in the first month. The addition of the silica fume helped to reduce the sensitivity of the concrete to curing conditions. After the first 90 days of expos ure, 75% to 80% of the drying shrinkage occurred depending on the curing conditions. 2.8.1.3 Silane Silane is an aqueous admixture, calle d aqueous amino vinyl silane. Silane treatment of silica fume and/or carbon fiber is highly eff ective for decreasing the drying shrinkage of cement paste. The increase of the hydrophilic char acter of fibers and

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15 particles after the treatment a nd the formation of chemical bonds between fibers/particles and cement are believed to be the main reason s for the observed decrease of the drying shrinkage. By adding silane-t reated carbon fibers and repl acing as-received silica fume by silane-treated silica fume, the shrinkage at 28 days is decreased by 32% [Yunsheng Xu 2001]. 2.8.1.4 Onada Expan ONADA EXPAN is an expansive additive currently used in Japan for concrete. This admixture expands when it is hydrat ed, without strength loss and hence reduces shrinkage in turn. It uses calcium silicate and glass interstitial substitute rather than CaO. This material is stable but it must be mo ist cured and requires longer mixing [Tazawa and Miyazawa 1995]. 2.8.2 Chemical Admixtures Chemical admixtures are added to concrete in very small amounts mainly for the entrainment of air, reduction of water or cemen t content, plasticization of fresh concrete mixtures, or control of setting time. Seven types of chemical admixtures are specified in ASTM C 494, and AASHTO M 194, depending on their purpose or purposes in PCC. Air entraining admixtures are specified in ASTM C 260 and AASHTO M 154. General and physical requirements for each type of admixture are included in the specifications. The use of chemical shrinkage-reduci ng admixture (SRA) in high-performance concrete was found to significantly reduce dr ying shrinkage and restrained shrinkage cracking in laboratory ring specimens. Cement paste shrinks as it loses moisture due to the surface tension of water and the menisci that are formed in the pore spaces in the paste. The surface tension of water in partia lly filled pores pulls inward on the walls of

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16 the pore spaces. The phenomenon of pulling the walls of the pore spaces is called shrinkage. The SRA works to reduce shrink age by reducing the surface tension of the water in all the filled spaces in the concrete. The following effects were observed when an organic SRA (shrinkage-reducing admixture) was added [Bentz et al. 2001]: 1. Comparing to distilled water, there is a significant reduction in the surface tension of a solution containing the SRA. 2. The drying rate of the cement pastes is reduced. 3. A significant decrease in autogenous shrinkage in low w/c ratio mortars cured under sealed conditions. There was no significant change in 28-d ay compressive strength of mortar specimens with the addition of an SRA, fo r w/c = 0.35 (8% silica fume) and cured under sealed conditions at 86 F (30 C). A shrinkage reducing admixture (SRA) has been suggested for use in reducing the rate of shrinkage in concrete at early-ag es when concrete is most vulnerable [Weiss 1999]. Tests were conducted on concrete with SRA added according to ASTM C 157-93 [Balogh 1996]. A larger percenta ge of decrease in shrinkage was noted in concretes with a lower w/c ratio. For concretes with a w/ c ratio of less than 0.60, the SRA reduced the 28-day shrinkage by 80% or more, and the 56day shrinkage was reduced by about 70%. The applied admixture dosage rate was 1.5% by weight of cement. For concretes with a w/c ratio of 0.68, the SRA reduced the 28and 56-day shrinkage by 37% and 36%, respectively. The SRA was tested with diffe rent cements, one with fly ash, one with fly

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17 ash and slag cement. The long-term (greater than one year) shrinkage reductions without moist-curing the concretes ranged from 25% to 38%, depending on the composition of the concrete mixtures. Concrete specimens were cured for 1 to 14 days, and tests were conducted to evaluate the drying shrinkage of concrete [Ber ke et al. 1997]. The specimens were stored at 37.4 F (3 C) and at 50% relative humidity. The concrete specimens having 2% SRA by weight of cement showed less shrinkage at early ages after controlled drying. For the same cement content, the drying shrinkage of the concrete increased as the w/c ratio increased for all the mixtures tested. The drying shrinkage was greatly reduced with the addition of the SRA. Drying shrinkage was significantly reduced with increased curing time. Longer curing periods reduced the sens itivity to changes in the w/c ratio with respect to shrinkage reduction. The shrinkage strain of conc retes using a silica fume slu rry, a superplasticizer and an SRA was studied [Folliard 1997]. The fresh c oncrete had a slump of 6 to 8 in. (150 to 200 mm). Concrete prisms of 3 3 11.25 in. (75 75 285 mm) were cast to measure free drying shrinkage. The use of a SRA re duced the drying shrinkage of the high strength concretes both with and without silica fume. The ring test was used to determine the restrained shrinkage. The restrained shrinkage was significan tly reduced when the SRA was used. The shrinkage reduction was more significant with the silica fume mixtures. The ring test was used to determine the rest rained shrinkage of concretes containing different SRAs by Shah, Karaguler, and Sari gaphuti [1992]. The specimens were placed in a controlled environment of 68 F (20 C) and at 40% relative humidity. Three

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18 different SRAs were used. Te sts were also conducted on 4 4 11.25-in. (100 100 285-mm) prism specimens. The SRAs were found to possibly decrease the compressive strength of the concrete. The addition of the SRA did reduce the amount of shrinkage. As the amount of SRA added increases, the shri nkage further decreases. The addition of SRA reduced the restrained shrinkage crack width. Free shrinkage was also measured on 3.9 3.9 15.6-in. (100 100 400-mm) prism specimens. The addition of SRA greatly improved the reduction of free sh rinkage. An equal amount of water was removed when the SRA was added. The addi tion of the SRA caused a delay in the restrained shrinkage cracking.

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19 CHAPTER 3 MATERIALS 3.1 Introduction This chapter describes the mix proportions and the mix ingredients of the concrete mixtures evaluated in this study. The method of preparation of th e concrete mixtures, fabrication of the test specimens and testi ng procedures used in this study are also presented. 3.2 Concrete Mixtures Evaluated Concrete mixtures were prepared in the la boratory and tested for their resistance to shrinkage cracking to evaluate (1) the effec tiveness of the shrinka ge test apparatuses used, (2) the shrinkage characte ristics of typical concretes us ed in bridge deck applications in Florida, and (3) the effects of a dding a shrinkage-reducing admixture. A typical mix design for a Florida Class IV concrete w ith a total cementitious materials content of 700 lb per cubic yard (lb/yd3), or 415.7 kg per cubic meter (kg/m3), of concrete was selected for use. Various percentages of fly ash and ground blast-furnace slag were incorporated into this basic mix design to fo rm six different mix designs to be evaluated in the laboratory testing program. Based on the six mix designs mentioned before, nine more mixes were developed by varying water cement ratios, resulting in a total of 15 pairs of mixtures that were used for this study. For each pair of the concrete mixture evaluated, two concrete mixes were prepared at the same time one with the addition of a shrinkage-reducing admixtur e (SRA) and one without.

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20 Tables 3-1 through 3-15 show the mix pr oportions for the 15 pairs of concrete mixtures evaluated in this study. The concre te mixes were numbered according to the order by which they were prepared and tested in this study. Mixes 1 and 13 had a cement content of 350 lb/ yd3 (207.8 kg/m3) and a slag content of 350 lb/yd3 (207.8 kg/m3) of concrete. Mixes 2 and 3 had a cement content of 210 lb/ yd3 (124.7 kg/m3) and a slag content of 490 lb/yd3 (291 kg/m3). Mixes 4, 7, 8 and 11 had a cement content of 560 lb/yd3 (332.5 kg/m3) and a fly ash content of 140 lb/yd3 (83.1 kg/m3). Mixes 5, 9, 10 and 14 had a cement content of 455 lb/yd3 (270.2 kg/m3) and a fly ash content of 245 lb/yd3 (145.5 kg/m3). Mixes 6 and 12 had a cement content of 210 lb/yd3 (124.7 kg/ m3), a fly ash content of 140 lb/yd3 (83.1 kg/m3) and a slag content of 350 lb/yd3 (207.8 kg/ m3). Mix 15 had a cement content of 700 lb/yd3 (415.7 kg/ m3), and no mineral admixture. The slump of the fresh concrete was targeted to be 8 1.5 inches (203 38 mm). The number of replicates of conc rete specimens used for different tests are provided in the Section 4.2 of Chapter 4.

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21 Table 3-1. Mix Proportions for Mix 1. Mix 1 Weight (pounds per cubic yard, lb/yd3) Standard SRA Ingredients Design BatchActual Batch Design Batch Actual Batch Cement 350 350 350 350 Fly ash Slag 350 350 350 350 Water 287 234 274 219 F.A. 1257 1252 1257 1252 C.A. 1513 1572 1513 1572 Air Entrainer 0.0625 0.0625 0.0625 0.0625 Admixture (WRDA 64) 0.875 0.875 0.875 0.875 Admixture (Adva 120) 1.313 1.313 1.313 1.313 Admixture (SRA) 12 12 Slump (in inches) 6.25 6.25 7.25 7.25 Air (%) 3.75 3.75 3 3 Workability Good Good Good Good W/C Ratio 0.41 0.33 0.41 0.33 Unit Weight (pcf) 139.1 139.2 139.1 139.1

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22 Table 3-2. Mix Proportions for Mix 2. Mix 2 Weight (lb/yd3) Standard SRA Ingredients Design BatchActual Batch Design Batch Actual Batch Cement 210 210 210 210 Fly ash Slag 490 490 490 490 Water 224 176 211 165 F.A. 1336 1331 1336 1331 C.A. 1583 1633 1583 1633 Air Entrainer 0.0625 0.0625 0.0625 0.0625 Admixture (WRDA 64) 0.875 0.875 0.875 0.875 Admixture (Adva 120) 2.063 2.063 2.063 2.063 Admixture (SRA) 12 12 Slump (in inches) 8 8 9.25 9.25 Air (%) 2.75 2.75 1.75 1.75 Workability Sticky Sticky Sticky Sticky W/C Ratio 0.32 0.25 0.32 0.25 Unit Weight (pcf) 142.3 142.2 142.3 142.3

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23 Table 3-3. Mix Proportions for Mix 3. Mix 3 Weight (lb/yd3) Standard SRA Ingredients Design BatchActual Batch Design Batch Actual Batch Cement 210 210 210 210 Fly ash Slag 490 490 490 490 Water 287 213 274 200 F.A. 1253 1248 1253 1253 C.A. 1507 1586 1507 1507 Air Entrainer 0.0625 0.0625 0.0625 0.0625 Admixture (WRDA 64) 0.875 0.875 0.875 0.875 Admixture (Adva 120) 1.313 1.313 1.313 1.313 Admixture (SRA) 12 12 Slump (in inches) 9 9 8.5 8.5 Air (%) 3.5 3.5 2.5 2.5 Workability Good Good Good Good W/C Ratio 0.41 0.30 0.39 0.29 Unit Weight (pcf) 138.8 138.8 138.3 135.5

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24 Table 3-4. Mix Proportions for Mix 4. Mix 4 Weight (lb/yd3) Standard SRA Ingredients Design BatchActual Batch Design Batch Actual Batch Cement 560 560 560 560 Fly ash 140 140 140 140 Slag Water 287 244 275 232 F.A. 1250 1246 1250 1246 C.A. 1486 1533 1486 1533 Air Entrainer 0.0625 0.0625 0.0625 0.0625 Admixture (WRDA 64) 1.75 1.75 1.75 1.75 Admixture (Adva 120) 2.188 2.188 2.188 2.188 Admixture (SRA) 12 12 Slump (in inches) 7.5 7.5 9 9 Air (%) 3.25 3.25 2.5 2.5 Workability Good Good Good Good W/C Ratio 0.41 0.35 0.39 0.33 Unit Weight (pcf) 137.9 137.9 137.4 137.4

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25 Table 3-5. Mix Proportions for Mix 5. Mix 5 Weight (lb/yd3) Standard SRA Ingredients Design BatchActual Batch Design Batch Actual Batch Cement 455 455 455 455 Fly ash 245 245 245 245 Slag Water 287 228 275 216 F.A. 1217 1213 1217 1213 C.A. 1469 1533 1469 1533 Air Entrainer 0.0625 0.0625 0.0625 0.0625 Admixture (WRDA 64) 1.75 1.75 1.75 1.75 Admixture (Adva 120) 2.188 2.188 2.188 2.188 Admixture (SRA) 12 12 Slump (in inches) 9.25 9.25 8.75 8.75 Air (%) 3.25 3.25 3.25 3.25 Workability Good Good Good Good W/C Ratio 0.41 0.33 0.41 0.33 Unit Weight (pcf) 136.0 136.1 136.0 136.1

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26 Table 3-6. Mix Proportions for Mix 6. Mix 6 Weight (lb/yd3) Standard SRA Ingredients Design BatchActual Batch Design Batch Actual Batch Cement 210 210 210 210 Fly ash 140 140 140 140 Slag 350 350 350 350 Water 289 246 275 232 F.A. 1240 1236 1240 1236 C.A. 1475 1522 1475 1522 Air Entrainer 0.0625 0.0625 0.0625 0.0625 Admixture (WRDA 64) 1.75 1.75 1.75 1.75 Admixture (Adva 120) 2.188 2.188 2.188 2.188 Admixture (SRA) 12 12 Slump (in inches) 9.25 9.25 9 9 Air (%) 1.75 1.75 2.75 2.75 Workability Good Good Good Good W/C Ratio 0.41 0.35 0.41 0.35 Unit Weight (pcf) 137.2 137.2 137.1 137.1

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27 Table 3-7. Mix Proportions for Mix 7. Mix 7 Weight (lb/yd3) Standard SRA Ingredients Design Batch Actual BatchDesign Batch Actual Batch Cement 560 560 560 560 Fly ash 140 140 140 140 Slag Water 254 235 242 223 F.A 1334 1330 1257 1330 C.A 1561 1554 1513 1554 Air Entrainer 0.0625 0.0625 0.0625 0.0625 Admixture (WRDA 64) 1.31 1.31 0.88 0.88 Admixture (Adva 120) 1.31 1.31 1.31 1.31 Admixture (SRA) 12 12 Slump (in inches) 8 8 9 9 Air (%) 2.75 2.75 3.25 3.25 Workability Good Good Good Good W/C Ratio 0.36 0.34 0.36 0.34 Unit Weight (pcf) 142.6 141.4 137.9 141.4

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28 Table 3-8. Mix Proportions for Mix 8. Mix 8 Weight (lb/yd3) Standard SRA Ingredients Design Batch Actual Batch Design Batch Actual Batch Cement 560 560 560 560 Fly ash 140 140 140 140 Slag Water 224 264 212 252 F.A 1453 1449 1455 1451 C.A 1453 1417 1455 1419 Air Entrainer 0.0625 0.0625 0.0625 0.0625 Admixture (WRDA 64) 0.88 0.88 0.88 0.88 Admixture (Adva 120) 2.06 2.06 2.06 2.06 Admixture (SRA) 12 12 Slump (in inches) 2.5 2.5 2.25 2.25 Air (%) 4.5 4.5 3.75 3.75 Workability Stiff Stiff Stiff Stiff W/C Ratio 0.32 0.38 0.32 0.38 Unit Weight (pcf) 141.9 141.9 142.0 142.0

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29 Table 3-9. Mix Proportions for Mix 9. Mix 9 Weight (lb/yd3) Standard SRA Ingredients Design BatchActual Batch Design Batch Actual Batch Cement 455 455 455 455 Fly ash 245 245 245 245 Slag Water 287 324 275 312 F.A. 1351 1347 1351 1347 C.A. 1351 1318 1351 1318 Air Entrainer 0.0625 0.0625 0.0625 0.0625 Admixture (WRDA 64) 0.88 0.88 0.88 0.88 Admixture (Adva 120) 1.31 1.31 1.31 1.31 Admixture (SRA) 12 12 Slump (in inches) 3.25 3.25 4.5 4.5 Air (%) 2.75 2.75 2.5 2.5 Workability O.K O.K O.K O.K W/C Ratio 0.41 0.46 0.41 0.46 Unit Weight (pcf) 136.6 136.6 136.6 136.6

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30 Table 3-10. Mix Proportions for Mix 10. Mix 10 Weight (lb/yd3) Standard SRA Ingredients Design BatchActual Batch Design Batch Actual Batch Cement 455 455 455 455 Fly ash 245 245 245 245 Slag Water 252 289 240 278 F.A 1265 1261 1265 1261 C.A 1513 1480 1513 1480 Air Entrainer 0.0625 0.0625 0.0625 0.0625 Admixture (WRDA 64) 0.88 0.88 0.88 0.88 Admixture (Adva 120) 1.31 1.31 1.31 1.31 Admixture (SRA) 12 12 Slump (in inches) 3.25 3.25 4.5 4.5 Air (%) 2.75 2.75 2.5 2.5 Workability O.K O.K O.K O.K W/C Ratio 0.36 0.41 0.36 0.41 Unit Weight (pcf) 138.2 138.2 138.1 138.2

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31 Table 3-11. Mix Proportions for Mix 11. Mix 11 Weight (lb/yd3) Standard SRA Ingredients Design BatchActual Batch Design Batch Actual Batch Cement 560 560 560 560 Fly ash 140 140 140 140 Slag Water 287 321 275 308 F.A. 1250 1246 1250 1246 C.A. 1486 1456 1486 1456 Air Entrainer 0.0625 0.0625 0.0625 0.0625 Admixture (WRDA 64) 1.75 1.75 1.75 1.75 Admixture (Adva 120) 2.188 2.188 2.188 2.188 Admixture (SRA) 12 12 Slump (in inches) 8.5 8.5 9 9 Air (%) 3 3 2.75 2.75 Workability Good Good Good Good W/C Ratio 0.41 0.46 0.41 0.46 Unit Weight (pcf) 137.9 137.9 137.9 137.9

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32 Table 3-12. Mix Proportions for Mix 12. Mix 12 Weight (lb/yd3)) Standard SRA Ingredients Design BatchActual Batch Design Batch Actual Batch Cement 210 210 210 210 Fly ash 140 140 140 140 Slag 350 350 350 350 Water 224 194 212 183 F.A. 1516 1511 1516 1511 C.A. 1376 1410 1376 1410 Air Entrainer 0.0625 0.0625 0.0625 0.0625 Admixture (WRDA 64) 1.75 1.75 1.75 1.75 Admixture (Adva 120) 2.188 2.188 2.188 2.188 Admixture (SRA) 12 12 Slump (in inches) 3 3 6.5 6.5 Air (%) 3.25 3.25 3 3 Workability Stiff Stiff Sticky Sticky W/C Ratio 0.32 0.28 0.32 0.28 Unit Weight (pcf) 141.3 141.3 141.3 141.3

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33 Table 3-13. Mix Proportions for Mix 13. Mix 13 Weight (lb/yd3) Standard SRA Ingredients Design Batch Actual BatchDesign Batch Actual Batch Cement 350 350 350 350 Fly ash Slag 350 350 350 350 Water 224 285 212 273 F.A. 1547 1543 1547 1543 C.A. 1405 1348 1405 1348 Air Entrainer 0.0625 0.0625 0.0625 0.0625 Admixture (WRDA 64) 1.75 1.75 1.75 1.75 Admixture (Adva 120) 2.188 2.188 2.188 2.188 Admixture (SRA) 12 12 Slump (in inches) 1.75 1.75 7 (Sheared off) 7 (Sheared off) Air (%) 3.75 3.75 3.25 3.25 Workability Stiff Stiff Stiff Stiff W/C Ratio 0.32 0.41 0.32 0.41 Unit Weight (pcf) 143.6 143.5 143.6 143.6

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34 Table 3-14. Mix Proportions for Mix 14. Mix 14 Weight (lb/yd3) Standard SRA Ingredients Design BatchActual Batch Design Batch Actual Batch Cement 455 455 455 455 Fly ash 245 245 245 245 Slag Water 224 209 212 197 F.A. 1502 1499 1502 1499 C.A. 1364 1383 1364 1383 Air Entrainer 0.0625 0.0625 0.0625 0.0625 Admixture (WRDA 64) 1.75 1.75 1.75 1.75 Admixture (Adva 120) 2.188 2.188 2.188 2.188 Admixture (SRA) 12 12 Slump (in inches) Sheared off Shear ed off Sheared off Sheared off Air (%) 3.5 3.5 4.5 4.5 Workability Stiff Stiff Stiff Stiff W/C Ratio 0.32 0.30 0.32 0.30 Unit Weight (pcf) 140.4 140.4 140.4 140.4

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35 Table 3-15. Mix Proportions for Mix 15. Mix 15 Weight (lb/yd3) Standard SRA Ingredients Design BatchActual Batch Design Batch Actual Batch Cement 700 700 700 700 Fly ash Slag Water 224 202 212 190 F.A. 1557 1553 1557 1553 C.A. 1415 1441 1415 1441 Air Entrainer 0.0625 0.0625 0.0625 0.0625 Admixture (WRDA 64) 0.875 0.875 0.875 0.875 Admixture (Adva 120) 1.313 1.313 1.313 1.313 Admixture (SRA) 12 12 Slump (in inches) 0.25 0.25 0.25 0.25 Air (%) 4.5 4.5 4 4 Workability Stiff Stiff Stiff Stiff W/C Ratio 0.32 0.29 0.32 0.29 Unit Weight (pcf) 144.3 144.3 144.3 144.3

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36 3.3 Concrete Mixture Constituents The mix constituents that were used in producing the concrete mixture are described in this section of the chapter. 3.3.1 Water Water used was obtained from the local city water supply system. 3.3.2 Fine Aggregate The silica sand mined from Mine 76-137 loca ted in Kueka, Florida, was used as fine aggregate for the concrete mixtures. The oven-dried silica sand was used for producing the concrete for this study. The gradation plot of the Kueka silica sand is displayed in Figure 3-1. The physical properties of fine aggregate are given in Table 3-16. Figure 3-1. Gradation chart for the fi ne aggregate (Goldhead silica sand) 0 20 40 60 80 100 120 #100#50#30#16#8#4 Sieve SizesPercentage Passing 20 40 60 80 100 120 Sieve Sizes #100 #50 #30 #16 #8 #4 0 Percentage Passing

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37 Table 3-16. Physical Proper ties of Fine Aggregate. Physical Property Value Bulk specific gravity 2.63 Bulk specific gravity SSD 2.68 Apparent specific gravity 2.64 Absorption 0.73% Fineness Modulus 2.30 3.3.3 Coarse Aggregate The coarse aggregate used was a #89 limestone obtained from Mine 08-0057 located in Brooksville, Florida. The coarse aggregate was used as-is at its natural moisture condition. The grada tion of the coarse aggregates is shown in Figure 3-2. Its physical properties are given in Table 3-17. Figure 3-2. Gradation chart for th e coarse aggregate (#89 limestone) 0 20 40 60 80 100 120 #50#16#8#4 3/8 1/2 Sieve SizesPercentage Passing 20 40 60 80 100 120 Sieve Sizes #50 #16 #8 #4 3/8 1/2 0 Percentage Passing

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38 Table 3-17. Physical Properti es of the Coarse Aggregate Physical Property Value Bulk Specific Gravity 2.23 Bulk Specific Gravity SSD 2.40 Apparent Specific Gravity 2.56 Absorption 4.55% 3.3.4 Cement Cemex Cement Company provided the T ype I Portland cement for use in the concrete mixtures that were used for this study. The physical characteristics and the chemical composition of the cement are show n in Tables 3-18 and 3-19, respectively. Table 3-18. Physical Properties of the Type I Cement Used Tests Specification Cement Spec. Limits Autoclave Expansion ASTM C151 0.01% <= 0.80% Fineness by Apparatus ASTM C204 402 m2 /kg >= 260.0 & <= 420.0 Loss on Ignition ASTM C114 1.50% <= 3.0% Time of setting (Initial) ASTM C226 125 min. >= 60 Time of setting (Final) ASTM C226 205 min. <= 600 3-day Compressive Strength Test ASTM C109 2400 psi >= 1740 7-day Compressive Strength Test ASTM C109 2930 psi >= 2760 Cement acid insoluble test ASTM C114 0.48% Insoluble <= 0.75 Table 3-19. Chemical Compositi on of the Type I Cement Used Constituents % SiO2 20.3 Al2O3 4.8 CaO 63.9 SO3 3.1 Na2O-K2O 0.5 MgO 2.0 Fe2O3 3.3 C3A 7.0 C3S 59.0 C2S 13.8 C4AF+C2F 15.8

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39 3.3.5 Fly Ash Class F fly ash, which was derived fro m the combustion of ground or powdered coal and met the requirements of ASTM C 618, was used for this project. Boral Company provided the fly ash for this project. The chemical composition of the fly ash is shown in Table 3-20. Its physical properties are shown in Table 3-21. Table 3-20. Chemical Compositi on of the Class F Fly Ash Used Chemical Value Sulfur Trioxide 0.3% Oxides of Si, Fe, Al 12.1% Table 3-21. Physical Properties of the Class F Fly Ash Used Property Fly ash Limits % Moisture 0.10% <= 3.0 Loss on Ignition 4.30% <= 6.0 3.3.6 Ground Blast-Furnace Slag The ground blast-furnace slag used in this project met the requirements of ASTM C 989. The slag used in this project was provided by Boral Company. The chemical composition of the slag used is shown in Table 3-22. Table 3-22. Chemical Com position of the Slag Used Chemical Value Sulfur Trioxide 1.70% Total Alkali as Na2O 0.7 3.3.7 Air-Entraining Admixture The air-entraining admixture used in th is study was Darex AEA (Supplied by W.R. Grace & Co.), which was an aqueous solution of a complex mixture of organic acid salts. It is specially formulated for use as an ai r-entraining admixture for concrete. It was supplied as ready-to-use admixture and did not require pre-mixing with water. The air-

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40 entraining admixture was used to improve the workability, and to reduce bleeding and segregation of the fresh concrete In this project, 0.1 lb of Darex was used for one cubic yard (0.059 kg/m3) of concrete. 3.3.8 Water-Reducing Admixtures Water-reducing admixtures were used in the concrete to reduce the demand of water in the mix. Two types of water-redu cing admixtures were used in the concrete mixtures for this project. They were WRDA 64 and Adva Flow (Supplied by W.R. Grace & Co) which are described in the following sections. 3.3.8.1 WRDA 64 WRDA 64 is a polymer-based aqueous solu tion of complex organic compounds. It is a ready-to-use low viscosity liquid which contains no calcium chlo ride. It can reduce the water demand of concrete by typically 8 to 10%. Sett ing times and water reduction are more consistent due to the presence of polymer components. It also performs especially well in concretes containing fly as h and other pozzolans. In this project, 1.75 lb of WRDA 64 was used per cubic yard (1.04 kg/m3) of concrete. 3.3.8.2 Adva Flow (Super plasticizer) Adva Flow Superplasticizer is a high range water-reducing admixture and does not have any chloride added. In this project, 2. 2 lb of Adva Flow was used per cubic yard (1.31 kg/m3) of concrete. 3.3.9 Shrinkage-Reducing Admixture The shrinkage-reducing admixture (SRA ) is a liquid admixture specially formulated for use in indoor slab-on-grade concrete construction. The trade name is Eclipse and it was supplied by W.R. Grace & Co. The SRA has no expansive agent, but acts chemically to dramatically reduce the pr imary internal forces that cause shrinkage

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41 and curling. The SRA at a dosage of 1.5 gal/yd3 (7.43 liter/m3) has been shown to reduce drying shrinkage, as measured by ASTM C 157, by as much as 80% at 28 days, and up to 50% at one year or beyond. It is a clear liquid admixture. In this project, 12 lb of the SRA was used per cubic yard (7.13 kg/m3) in the concrete mixtures that required the shrinkage-reducing admixture. 3.4 Preparation of Concrete Mixtures 3.4.1 Mixing of Concrete Fifteen pairs of concrete mi xtures were produced and test ed in this project. The concrete batches were mixed in two rotary dr um mixers of capacities of 3.5 cubic feet (ft3), or 0.098 cubic meters (m3), for relatively small mix and 6 ft3 (0.168 m3) according to the ASTM (American Society for Testing and Materials) require ment. The photo of the 6 ft3 (0.168 m3) mixer is shown in Figure 3-3. Th e surface of interi or portion of the drum was rinsed with a butter mix (i.e., the or iginal mix in small quantity) before mixing to avoid absorption of moisture from the mi x and to ensure the same mixing conditions for all mixes. The following procedures of mixing of concre te were followed in the preparation of each concrete mixture: 1. Place the coarse and fine aggregates in the mixer, and mix for about two minutes with one half of mixing water adde d to ensure uniform dispersion of the aggregates. 2. The SRA is added to the water th at is used in the concrete mixture 2. Add the cement, fly ash, slag, ai r entraining admixtur e, water-reducing admixtures and the remaining water into the mixer, and continue the mixing for an additional three minutes. Stop the mixer as ne eded to break loose the materials sticking

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42 to the mixer to facilitate thorough mixing. After mixing three minutes, follow with a 3minute rest period. 3. Continue the mixing for an additi onal two minutes after the rest period. 4. After the mix appears uniformly mixed, run the slump test on the fresh concrete. Add additional water-reducing admixtures if the slump is too low. While adding waterreducing admixtures, take care not to exceed the allowable dosages. Otherwise, the mixtures may become segregated and start bleeding. Figure 3-3. Concrete mixer used

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43 3.4.2 Preparation of Concrete Spe cimens for Mechanical Tests The following steps were followed in maki ng the concrete specimens for evaluation of mechanical properties: 1. After mixing is complete, fill each of the 4 8-in. (101.6 203.2-mm) cylindrical molds with the fresh concrete to one half of its height, and place the mold on a vibrating table for 30 seconds of vibration. 2. Fill the cylinder mold to overflowing, and place it on the vibrating table for an additional 30 seconds. 3. Finish the surface of the concrete specimen with a hand trowel, and cover the cylinder with a plastic sheet to prevent evaporation of water. 4. Remove the concrete specimens from the molds after 24 hours of curing, and put them in a standard moist room for prope r curing until the specific tests (compressive strength, modulus of elasticity and splitting tensile strength te sts) are to be performed at the specified curing times (such as 3, 7, 14 and 28 days). 3.4.3 Preparation of Concrete Specimens for ASTM C157 Shrinkage Test A portion of the fresh concrete was used to produce the 3 3 11.25-in. (76 76 286-mm) square prism specimens for the ASTM C157 Shrinkage Test. The procedures for making of these specimens are described in Section 4.3.4 of this report. 3.4.4 Preparation of Concrete Speci mens for Long Specimen Tests The rest of the fresh concrete from the mixer was used to make the long specimens for the constrained shrinkage test and the free shrinkage test. The procedures for making the long specimens for free shrinkage test are described in Section 4. 3.5, while those for the constrained shrinkage test are desc ribed in Chapter 5 of this report.

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44 CHAPTER 4 LABORATORY TESTING PROGRAM 4.1 Introduction This chapter describes the laboratory te sting program on the concretes to be evaluated for their resistance to shrinkage cracking in this study. It includes the description of the tests on fresh and hardened conc retes and the associated instrumentation. 4.2 Tests on Fresh Concrete The following tests were performed on the fresh concrete: 1. Slump test (ASTM C143); 2. Unit weight test (ASTM C138); 3. Air content by volumetric method (ASTM C173); and 4. Temperature measurement (ASTM C1064). 4.3 Tests on Hardened Concrete The following tests were run on the hardened concrete: 1. Compressive strength (ASTM C39) tests using 4 8-in. (101.6 203.2-mm) specimens at 3, 7, 14 and 28 days (3 replicates per condition). 2. Elastic modulus (ASTM C469) tests using 4 8-in. (101.6 203.2-mm) specimens at 3, 7, 14 and 28 days (2replicates per condition). 3. Splitting tensile strength test (ASTM C496) using 4 8-in. (101.6 203.2-mm) specimens at 3, 7 and 14 days (3 replicates). 4. Free shrinkage measurement (ASTM C157) using 3 3 11.25-in. (76 76 286-mm) specimens (3replicates).

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45 5. Free shrinkage measurement using the long specimen apparatus without the constraint, monitored continuously for a minimum of 14 days (2 replicates). 6. Constrained shrinkage test using the long specimen apparatus, monitored continuously for a minimum of 14 days (2 replicates). The equipment, instrumentation and pr ocedures for these tests on hardened concrete are described in the following section. 4.3.1 Compressive Strength Test The compressive strength test was run in accordance with ASTM Test Method C39. Figure 4-1 shows the set-up for the comp ressive strength test. The testing machine used was a servo-controlled compression te sting machine with a capacity of 500,000 lb (227,000 kg). All the tests were run with a rate of loadi ng ranging from 400 to 500 lb (1,780 to 2,225 N ) per second. Figure 4-1. Set-up for co mpressive strength test

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46 Three 4 8-in. (101.6 203.2-mm) cylindrical specimens per batch per curing condition were tested for the analysis. Befo re testing, the cylinde rs were ground by using a grinding stone so that two end surfaces ar e made even to support the applied load uniformly. Compressive strengths were determined at moist-curing times of 3, 7, 14 and 28 days. The compressive strength of the specimen was calculated using the following equation (Eq.): Compressive Strength, fc = P/A (Eq. 4.1) where P = ultimate load attained during the test in pounds (lb); and A = loading area in square inches (in2 ). Of the three replicate specimens per condi tion, one specimen was first tested to determine its ultimate compressive strength, so th at the modulus of elasticity test could be run at 40% of the ultimate strength of the conc rete. The modulus of elasticity test was then run on the other two repli cate specimens before they were tested for their compressive strength. 4.3.2 Modulus of Elasticity Test The modulus of elasticity test was run in accordance with ASTM Test Method C469. Cylindrical specimens of size 4 8 in. (101.6 203.2-mm), which were also used in the compressive strength test, were used for this test. Similar to the compressive strength test, the modulus of elasticity test was performed at curing times of 3, 7, 14 and 28 days. The test set-up is shown in Figure 4-2 and Figure 4-3.

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47 The test set-up consisted of a compression te sting machine, a digital key panel (for controlling the testing machine) and a laptop computer (for downloading the data from the test). The rate of loading adopted for this test was the same as that for the compressive strength test, and ranged from 400 to 500 lb (1,780 to 2,225 N) per second. The output from the load cell (in the testi ng machine) and the output from the LVDT (which was connected to the specimen to measure its ve rtical deformation) were connected to the laptop comput er via a USB connection. Figure 4-2. Set-up for modulus of elasticity test The software Virtual BenchLink Data Logge r was used to capture the output data from the LVDT and load cell and convert th em into a readable CSV (Comma Separated Variable) Microsoft Excel format. A close-up view of the LVDT used is shown in Figure 4-3. Figure 4-2. Set-up for modulus of elasticity test

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48 Figure 4-3. Close-up view of elas tic modulus test set-up with a LVDT for strain measurement Before Modulus of Elasticity test is run, one of the three cylinders was tested for ultimate compressive strength until breaking. On the remaining two cylinders, the Modulus of Elasticity Test was run at a stre ngth level of 40% of the ultimate compressive strength of the concrete. Af ter that, those two specimens fr om the Modulus of Elasticity test were tested for ultimate compressive strengths. The data from the first load cycle were disregarded. The data values from the last two cycles of loading were recorded and converted into CSV (comma separated variab le) format which is readable by the Excel

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49 spreadsheet. The modulus of elasticity was determined using regression analysis embedded in the Excel spreadsheet charts. 4.3.3 Splitting Tensile Strength Test The splitting tensile strength test was run in accordance with the procedures laid out in ASTM C496 method. Three 4 8-in. (101.6 203.2-mm) cylindrical specimens per condition were used for this test. The test set-up is shown in Figure 4-4. The splitting tensile strength of the specimen wa s calculated using the expression below: Splitting tensile strength, ft = 2P/ ld (Eq. 4.2) where P = maximum applied load; l = length of the cylindrical specimen; and d = diameter of the cylindrical specimen. Figure 4-4. Set-up for split ting tensile strength test

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50 4.3.4 Free Shrinkage Measurement (A STM C157) Using LVDTs Square prism specimens with dimensions of 3 3 11.25 in. (76 76 286 mm) were used in the free shrinkage test in accordance with ASTM C157 Method. Figure 4-5 shows a mold used to cast the shrinkage test specimens. Steel end plates with a hole at their centers were used to hold the contact po ints in place at each end of the specimen. 4.3.4.1 Test Setup A Lucas Schaevitz spring loaded model GCD-121-050 LVDT was used to monitor the vertical movement of the specimen. The LVDT had a travel range of 0.050 in. (1.27 mm) with a sensitivity of 200 V/in. (7.874 /mm). Thus over the travel range of 0.10 in. (2.54 mm), there would be a 20 V di fference in output voltage readings, i.e., 10 V to +10 V. The linearity range cited by th e manufacturer of 0.25% for the full range Figure 4-5. Mold for 3 3 11-in. (76 76 286-mm) shrinkage test specimen Figure 4-5 illustrates the mold for 3 3 11-in. (76 76 286-mm) shrinkage test specimen. The output produced readings with errors within 0.025 V, which translated into displacement measurement erro rs within .000125 in. (.00318 mm).

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51 These LVDTs are made of AISI 400 series st ainless steel. They are complete and ready-to-use displacement transducers with a sleeve bearing stru cture on one end that supports a spring-loaded shaft att ached to the core. The beari ng is threaded externally to facilitate mounting. By using a spring load ed LVDT, the need for core rods or core support structures is eliminated. All LVDTs ar e hermetically sealed to operate in harsh environments such as a moist room, and have an operating temperature range of 0F to 160F (17.8C to 71.1C) to facilitate testing of temperature effects. The data acquisition system used is an Agilent 34970A unit (by Agilent Technologies) with a HP 34901A (20-channel armature multiplexer) plug-in module. The data acquisition unit can be set up to take readings at specified time intervals and for a specified length of time. The HP 34901A multiplexer module can read up to 20 channels of AC or DC volta ges with a maximum capacity of 300 V. It has a switching speed of up to 60 channels per second. It also has a built-in thermocouple reference junction for use in temperature measurement by means of thermocouples. Thus, the Agilent 34970A data acquisition unit with one HP 34901A multiplexer module will be adequate for the job of recording load a nd displacement readings from 10 testing apparatuses. The Agilent 34970A unit can take up to three plug-in modules. Thus, if needed, it can be expanded to take up to 60 channels of output. The test setup for measuring the free shri nkage using a LVDT is shown in Figure 4-6. Figure 4-7 shows a pictur e of several test setups that were used simultaneously. Figure 4-8 shows the schematic s of these test setups

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52 Figure 4-6 Set-up for ASTM C157 free shrinkage measurement using a LVDT

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53 Figure 4-7. Picture of severa l test setups for free shrinkage measurement using LVDTs Figure 4-8. Schematics of test set-ups for measurement of free shrinkage using LVDTs

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54 The setup for the ASTM C157 free shrinka ge test consisted of a DC-powered LVDT connected to a shrinkage test frame that held the specimen. The output from the LVDT was connected to a Data Acquisition Sy stem (DAS). A laptop computer was used to download the data from the DAS. The da ta downloaded from the Data Acquisition System was in readable form with Micros oft Excel CSV (Comma Separated Variable) format. 4.3.4.2 Test Procedure The following steps were followed in conducting ASTM C157 free shrinkage test: 1. Cover the interior surfaces of the sp ecimen molds with transmission oil. 2. Set up the gage set points on the side s of the mold carefully, keeping them clean, and free of oil, grease and foreign matter. 3. After concrete mixing is done, place th e fresh concrete into the molds in two equal layers with each layer vibrated for 30 seconds by placing the molds over a vibrating table. 4. Cover the concrete samples with plastic sheets for one day. 5. After one day, remove the concrete samples from the molds and place them into the shrinkage test frames as shown in Figures 4-6 and 4-7. 6. Adjust the LVDT readings to zero by observing output displays in the DAS. It is somewhat difficult to set the LVDT reading to zero, because of its high sensitivity. Thus, just adjust it to as close to zero as possible. However, when obtaining the shrinkage value, the initial reading is subtracted from the readings taken at different days. 7. After the LVDT readings are set to zero (or close to zero), set the DAS to record readings every 15 minutes continuously.

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55 8. Download the readings from the DAS to a computer after 7 to 14 days, using the software Bench Link Data Logger. 4.3.5 Free Shrinkage Measured by Embedmen t Gage in the Long-Specimen Apparatus 4.3.5.1 Test Set-up The test setup for free shrinkage measur ement using the long-specimen apparatus consisted of a long-specimen mold, an embe dment strain gage, a Bridge-sensor (which was a strain indicator), a laptop computer, a data acquisition system and a temperature gage. The schematics for the test setup ar e shown in Figure 4-9. Figure 4-10 shows a picture of two long-specimen molds before the placement of concrete in them. Figure 4-9. Schematics for test setup with em bedment gauge for constrained shrinkage measurement using the long-specimen apparatus. An OMEGA OM2-8608 Backplane 8-channel signal conditioner was used to connect the embedment strain gages in a quart er bridge circuit and to amplify the output

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56 signals from the bridge circuits. The embedm ent strain gages used have a length of 4.68 in. (120 mm), a resistance of 120 Ohms and a ga ge factor of 2.0. An excitation voltage of 4V and a gain of 333.33 for the output signal were used. The outputs from the signal condition were connected to the data acquis ition system. The following equation relates the un-amplified voltage output to the measured strain: Strain = 4 (voltage output ) / (gage factor)( excitation voltage) = 4 (voltage output) / 2.0 (4V) = (voltage output in V) / 2 (Eq. 4.4) Figure 4-10. Picture of two long-specimen molds

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57 With a gain of 333.33 was used, the measur ed strain is related to the amplified voltage output as follows: Strain = (Amplified voltage output in V) / (2 333.33) Strain = (Amplified voltage output in V) / (666.67) (Eq. 4.5) 4.3.5.2 Test Procedure The following steps were followed for r unning the free shrinkage test using the long-specimen apparatus: 1. Assemble the side blocks and th e end blocks of the long-specimen molds together and fix them to the base plate firmly by using screws. 2. Coat the surfaces of the support base pl ate and the side blocks with a thin layer of transmission fluid to avoid friction be tween the concrete specimen and the bottom support plate and the side plates. 3. Configure the DAS to record the data for the test. The desired parameters such as the time interval for the DAS to scan the data, the unit for temperature, type of thermocouple, unit for voltages, etc., have to be set in the DAS by using the knobs and buttons in the front panel of the DAS. 4. Set the DAS unit to start scanning with a time interval of 15 minutes. 5. Place the fresh concrete into the mold in two equal layers, and tamp each layer with fingers for consolidation. After the fi rst layer is done, place the embedment gage in the concrete at the cente r of the mold. Then, apply the s econd layer of concrete on top of the gage. The gage should be placed about half an inch from the top of the mold. 6. Finish the surface of the specimen with a hand trowel. 7. Turn on the DAS to start recording data.

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58 8. After the concrete has set sufficiently, remove the side blocks so that the concrete specimen will have restraint on only the bottom portion, which has been coated with a thin layer of transmission oil to redu ce friction. Usually the side blocks can be removed within several hours to a days time. 9. Keep the specimen undisturbed fo r the entire duration of the test. 10. Download the data to a laptop computer at the desired times. Data from seven days may be downloaded at one time. The software Bench Link Data Logger can be used to download data from the DAS to the readable Excel CSV format files. 4.3.6 Free Shrinkage Measuremen t using Whittemore Gage in the Long Specimen Apparatus 4.3.6.1 Test Set-up In this test set-up, a pair of gage poi nt studs was embedded in the long concrete specimen at a distance of 10 inches (254 mm) apart from one another, and a Whittemore gage was used to measure the change in di stance between these two gage points due to shrinkage in the specimen. The Whittemore gage used is shown in Figure 4-11. The long concrete specimen with the two gage point studs installed is shown in Figure 4-12. Figure 4-11. Whittemore gage for measur ing the distance between two gage points

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59 Figure 4-12. Long concrete specimen with gage point studs installed 4.3.6.2 Test Procedure The following steps were followed in conducting the free shrinkage measurement using the Whittemore gage in the long specimen apparatus: 1. Assemble the side blocks and th e end blocks of the long-specimen molds together and fix them to the base plate firmly by using screws. 2. Coat the surfaces of the support base pl ate and the side blocks with a thin layer of transmission fluid to avoid friction be tween the concrete specimen and the bottom support plate and the side plates. 3. Place the fresh concrete into the mold in two equal layers, and tamp each layer with fingers for consolidation. After both layers are done, pr ess two gage st uds into the surface of the long concrete specimen, at the middle of the specimen and at a distance of 10 in. (254 mm) from one another. Make sure that the gage point studs are well pressed into the concrete so that after hardening, the Whittemore gage can be placed on top of the studs securely and the readings can be taken. 4. Finish the surface of the specimen with a hand trowel. Gage Point Studs

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60 5. After the concrete has set sufficiently, remove the side blocks so that the concrete specimen will have restraint on only the bottom portion, which has been coated with a thin layer of transmission oil to redu ce friction. Usually the side blocks can be removed within several hours to a days time. 6. After the concrete has hardened suffi ciently (usually afte r 24 hours of curing), take the first reading of the distance betw een the two gage points using the Whittemore gage. Take additional readings at the specified times as needed. 4.3.7 Free Shrinkage Measuremen t Using Whittemore Gage on Cylindrical Specimens 4.3.7.1 Test Setup In this method, 6 12-in. (152.4 304.8-mm) cylindrical concrete specimens are cast, and the free shrinkage of the concre te specimens is measured by means of a Whittemore gage. Three pairs of gage points with a gage distance of 10 in. (254 mm) are placed in each test concrete specimen. A Whittemore gage is used to measure the change in distance between the gage point s due to drying shrinkage. A gauge-point positioning guide, as shown in Figure 4-13, was used in positioning the gauge-points on the plastic cylinder mold. The guide can be placed around a 612-in. (152.4 304.8-mm) cylinder mold. By tightening the six screws on the guide, the precise locations for the three pairs of ga ge points, with a gage distance of 10 in. (254 mm), can be marked conveniently on the mold. Figure 4-14 shows a picture of the gauge-position guide. Figure 4-15 shows a pictur e of the plastic cylinder mold inside the gauge-position guide. 4.3.7.2 Test Procedure Figure 4-16 shows a picture of the conc rete cylinders with the gauge points

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61 attached on them after the molds have been removed. A Whittemore gauge was used to measure the change in the distance between the gage points as the concrete cylinder shrinks. The Whittemore gauge has a re solution of 0.0005 in. Three sets of measurements were taken from each specimen at each specified time. The original distances between the gauges are to be measur ed immediately after the plastic mold is removed. The shrinkage strain is taken as the average of the three readings from each specimen, and can be expressed as follows: Figure 4-13. Gage-point positioning guide

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62 Figure 4-14. Gauge-position guide

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63 Figure 4-15. Plastic cylinder mo ld inside gauge-position guide

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64 Figure 4-16. Concrete cylinders with gauge point studs installed on them 3 i0 sh i1 0(ll) 1 3l (Eq. 4.6) where li = measured distance between ith pair of gage points l0 = original distance between ith pair of gage points measured immediately after demolding. 4.3.8 Constrained Shrink age Test Using the Long Specimen Apparatus The test setup and procedure for the c onstrained shrinkage test went through numerous stages of development and refineme nt during the course of this study. The description of the test setups and procedures used in this study, and their evaluation are presented in Chapter 5 of this report. STUDS

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65 CHAPTER 5 DEVELOPMENT AND EVALUATION OF THE MODIFIED CONSTRAINED LONG SPECIMEN APPARATUS 5.1 Introduction This chapter presents the development a nd evaluation of the m odified constrained long specimen apparatus for evaluation of resi stance to shrinkage cracking of concrete. Based on the evaluation of the va rious designs that have been tried out, a final design was adopted for use in the laboratory testing program in this study. 5.2 Fundamentals of the Constrained Long Specimen Method 5.2.1 Original Design The constrained long specimen set-up had a dog-bone shaped mold with an overall length of 27.30 in. (700 mm). The actual portion of the mold that ho lds the concrete is 17.55 in. (450 mm) long and 1.56 1.56 in. (40 40 mm) in cross section. It has two flared ends each of which has a width of 4.29 in. (110 mm). One end is fixed to the bottom plate, and the other end was free to move Meanwhile, in order to give restraint to the free movement of concrete, it was clam ped with an end aluminum block through a proving ring so that the induced tensile force can be measured. This aluminum block was fixed to the bottom plate. When there is any shrinkage movement in the concrete specimen, the proving ring will get stretched because of its fixity to the end block and it will read a value equal to the tensile force th at is induced in the specimen. Figure 5-1 illustrates the design of the originally deve loped Constrained Long Specimen Apparatus.

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66 Figure 5-1. The original constrained l ong specimen apparatus [Tia et al., 1998] 5.2.1 Test Procedure The test procedure for the original co nstrained long specimen apparatus test consisted of the following steps: 1. Spread a thin layer of motor oil on the surface of the metal guide that is in contact with the concrete specimen. 2. Place the fresh concrete into mold. 3. Place the whole apparatus on a vibrating table for one minute. 4. Place two gage-point inserts which are attached under the metal guide (#9 in Figure 5-1) into the concrete specimen. 5. Place the entire apparatus again on the vibrating table for an additional minute. 6. Press the two gage point inserts into the concrete firmly with fingers to make sure that they are completely inside the conc rete mass. Two gage point inserts are used to hold the Whittemore gage to the concrete. 7. Finish the surface of the sp ecimen with a hand trowel.

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67 8. After 12 hours, remove the two side pieces of the mold, and remove the metal guide from the gage point inserts. 9. Attach the Whittemore gage to the two inserts with two screws. 10. Record the initial readings of both the proving ring and the Whittemore gage. 11. After the removal of the side pie ces and the attachment of the Whittemore gage, monitor the induced load by means of the proving ring, and the movement of the concrete specimen by means of the Whittemore gage for a period of 14 days. Though the concrete specimen was constrai ned from movement at the two ends, the Whittemore gage would usually measure a slight shortening of the concrete specimen. This could be explained by the movement of the proving ring as load was induced. Figure 5-2 shows how the movement of the proving ring ( PR) is equal to the movement of the constrained long specimen ( CL). Figure 5-2. Schematics of the restra ined long specimen under contraction 5.2.3 Method of Analysis The analysis part consists of several equations invol ving three different deformation components in the concrete specimen. Th e first component is the shortening due to Lg LT PR = CL

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68 shrinkage ( sh). The second component is the elas tic lengthening due to induced tensile stress ( E ). The third one is the creep due to the induced stresses ( CR ). These three components are related to the total movement of the specimen as follows: CL = sh E CR (Eq. 5.1) In terms of strains ( s), the relationship can be written as: CL = sh E CR (Eq. 5.2) The total strain in the constrained long specimen ( CL) can be calculated from the deformation read by the Whittemore gage ( g) as follows: Total Strain, CL = g/Lg (Eq. 5.3) where Lg = gage length = 10 in. (254 mm). The elastic strain ( E ) can be calculated from the induced stress ( E ) and the elastic modulus of the concre te (E) as follows: E = E / E = FPR / AE (Eq. 5.4) where FPR = force measured by the proving ring; and A = cross-sectional area of concrete specimen = 2.48 in2 (1600 mm2). The shrinkage strain ( sh) can be assumed to be equal to the free shrinkage strain measured by the length comparator. Fr om Equation 5.2, the creep strain ( CR) can be calculated from the other strains as follows: CR = sh E CL = sh (FPR/AE) g/Lg (Eq. 5.5) If a concrete member is fully constraine d from movement, the induced stress due to drying shrinkage can be expressed as: FC = ( sh CR) E (Eq. 5.6)

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69 where FC = induced stress in a fully constrained concrete. The free shrinkage strains as obtained fr om the free shrinkage measurements by means of the length comparator are used as the shrinkage strain ( sh), while the creep strains from the long constrained specimen test (as computed from Equation 5.5) are used as the creep strains, CR. The actual creep strain should be slightly more than the one experienced by the long constrained specimen, since the long constrained specimen is not fully constrained. Thus, using the creep st rains from the long cons trained specimen would result in a slightly higher (or more conserva tive) estimation of the induced stresses. When the computed expected shrinkage stress (FC) as computed by Equation 5.6 exceeds the expected tensile strength of the concrete (t ) at any particular time, the concrete will be likely to crack due to shrinkage stresses at that time. 5.3 First Refinement of Apparatus Use of LVDT, Load Cell and Data Acquisition System 5.3.1 Changes Made to the Original Design The constrained long specimen apparatus, which was previously developed for the FDOT by the University of Florida and descri bed in Section 5.2, was further refined by automating the data acquisition system process. The apparatus was refined by (1)replacing the Whittemore gage, which was used to measure the deformation of the specimen by a high-sensitivity Linear Variab le Differential Transformer (LVDT), and (2)replacing the proving ring, which was used to measure the induced force in the constrained long specimen by a load cell. A convenient and effective method of attaching an LVDT to the constrained long concrete specimen, and using the LVDT to measure the deformation of the specimen was designed and tested. After some comparative evaluation, an AC LVDT, instead of a DC LVDT was selected for use. An

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70 AC LVDT has two major advantages over a DC L VDT in this application. First, an AC LVDT is much lighter in weight. Sec ond, it has less noise and is more accurate. The selected AC LVDT is a CD375-025 by M acro Sensors. It has a stroke of .025 in. (0.635 mm), a weight of 0.1 oz (2 .8 grams) and gives an output of 10 mV per 0.001 in. (0.0254 mm) of deformation under the normal operating condition. Gage studs, brackets for holding the gage studs, and lig htweight holders for the LVDT body and LVDT core were designed, fabricated and te sted. Figure 5-3 shows the setup used for measuring the deformation of the constrai ned long specimen using an LVDT. When there is any shrinkage movement in the concre te specimen, the load cell will get stretched because of its fixity to the end block and it wi ll read a value equal to the tensile force that is induced in the specimen. The constr ained long specimen mold used a concrete specimen of a length of 21. 25 in. (539.75 mm) with 1.5 1.5 in. (38.1 38.1 mm) as cross-section. The end collar blocks have a width of 4.25 in. (111.95 mm) each. Figure 5-3. Constrained long sp ecimen apparatus using a LVDT A drawing of the top and the side views of the apparatus is shown in Figure 5-4. The long constrained concrete specimen with its dog bone sh ape has two ends of steel collars with a width of 4.25 in each. The steel collar blocks are shown in Figure 5-5. Figure 5-6 displays the front and side vi ews of the PVC side pieces for the Long

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71 Constrained Specimen apparatus. Figure 5-7 shows the aluminum bracket support for the gage studs that hold the LVDT and the core rod holders to the concrete specimen. Figure 5-4. Top and side views of th e constrained long specimen apparatus Figure 5-5. Side and top views of the end collar block of the mold

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72 Figure 5-6. Front and side views of the PVC side pieces for the constrained long specimen apparatus Figure 5-7. Aluminum bracket support for the gage studs that hold the LVDT and the core rod holders to the concrete specimen 5.3.2 LVDTs for Measurement of Strain An AC LVDT (Linear Variable Differentia l Transformer) is used to measure the displacement between two gage studs, which are placed on the concrete specimen at a spacing of 10 inches (mm) apart. An LVDT is an electromechanical device that produces an electrical output proportiona l to the displacement of a separate movable core. It consists of a primary coil and two secondary coils symmetrically spaced on a cylindrical form. A free-moving, rod shaped magnetic core inside the coil assembly provides a path

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73 for the magnetic flux linking the coils. The cross-sectional view of a typical LVDT is shown in Figure 5-8. Figure 5-8. Cross-sectio nal view of an LVDT The primary coil needs to be excited, in order to induce a voltage in the secondary coils. The excitation needs to be an alternating voltage, in the 400 Hz to 20 KHz range usually. Square, trapezoid and other wave sh apes can be used, but a sinusoidal shaped wave will yield the best results. The voltage that is applied to the primary coil produces a current whose magnitude depends on the impe dance of the primary coil at the chosen frequency. This current induces currents in the secondary coils of the LVDT. The amount of current induced in each secondary coil depends on the mutual inductance between the primary coil and each secondary coil. This mutual inductance, in turn, depends on the position of the co re, with relation to each se condary coil. The outputs of the LVDT are these two AC voltages, which can be added together to form one AC voltage. This voltage varies approximately linea rly with the axial position of the core. A typical LVDT signal conditioning electronics wi ll convert this AC voltage to DC voltage. When the primary coil is energized by an external AC source, voltages are induced in the two secondary coils. These are connected in series and in opposing direction so the

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74 two voltages are of opposite polarity. Therefore, the net output of th e transducer is the difference between these voltages, which is ze ro when the core is at the centre or null position. When the core is moved from the null position, the induced voltage in the coil toward which the core is moved increases, while the induced voltage in the opposite coil decreases. This action produces a differentia l voltage output that varies linearly with changes in core position. The phase of th is output voltage changes abruptly by 180 as the core is moved from one side of null to the other. Figur e 5-9 shows the core displacement and the respective voltage changes that occur in the coil. Figure 5-9. LVDT core displacemen t and the respective voltage change

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75 The LVDT used was a CD375-025 by Macr o Sensors and Figure 5-10 shows a close-up picture of the LVDT inside the LV DT holder. Figure 5-11 shows a close-up picture of the holder for the rod for the LVDT core. Figure 5-10. LVDT holder and a portion of the rod that is connected to the other holder Figure 5-11. The holder for the rod that passes through the LVDT core

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76 This LVDT has a stroke of .025 in. (0. 635 mm), a weight of 0.1 oz (2.8 grams) and gives an output of 10 mV per 0.001 in. (0 .0254 mm) of deformation under the normal operating condition. An AC voltage source is us ed to supply an excitation voltage of 3.0 RMS V at 2.5 kHz. The displacement (in inches) between the two gage points is computed from the RMS voltage output as: (Displacement in 0.001 in.) = (RMS voltage in mV) 0.1 The strain is then computed from the displacement as: Strain = Displacement / (Gage Length) = Displacement / (10 in. or 254 mm) 5.3.3 Load Cell for Meas urement of Stress A load cell was used to measure the fo rce experienced by the concrete specimen during a test. The load cell used was a LCCB-1K by Omega. It is a tension and compression S type load with a maximum capacity of 1000 lb (4450 N). The rated output is 3mV/V for the full load of 1000 lb ( 4450 N). A DC voltage source is used to supply an excitation volt age of 10 V. With the 10 V ex citation input, the load cell gives an output of 30 mV/1000 lb, or 0.03 mV/lb. The axial force in the concrete sample is computed from the DC output vol tage from the load cell as: (force in lb.) = (dc voltage in mV) 33.33 The stress in the concrete sample is then calculated from the force as: Stress = Force / (Cross-sectional area of concrete) = Force / (2.25 in2 or 1451.6 mm2) The load cell attached to the frame of the specimen is shown in Figure 5-12.

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77 Figure 5-12. The load cell attached to the frame of the concrete specimen 5.3.4 Data Acquisition System The output ends from the LVDT and the lo ad cell were connected to an automatic data acquisition system, an Agilent 34970A unit (by Agilent Technologies) with a HP 34901A (20-channel armature multiplexer) plug-in module. The Data Acquisition System unit is shown in Figure 5-13. The DAS unit can be set up to take readings at Figure 5-13. Agilent 34970A da ta acquisition system unit

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78 specified time intervals and for a specified length of time. Th e HP 34901A multiplexer module can read up to 20 channels of AC or DC voltages with a maximum capacity of 300 V. It has a switching speed of up to 60 ch annels per second. It also has a built-in thermocouple reference junction for use in temperature measurement by means of thermocouples. The Agilent 34970A unit can take up to three plug-in modules. The stored data can be downloaded to a personal computer via a RS232 cable connection. The data files are in CSV format and can be read readily by spreadsheet software such as Excel. After satisfactory performa nce was observed from a pr ototype of the developed constrained long specimen apparatus equippe d with a LVDT, a load cell and a data acquisition system, ten such apparatuses were constructed. Five of the ten apparatuses were equipped each with both a LVDT and a load cell, and were to be used to perform the constrained shrinkage test. The other fi ve apparatuses were equipped each with only a LVDT, and were to be used to perform the free shrinkage test. All the apparatuses were constructed to be identical to one another so that they coul d perform equally in measuring shrinkage. A load cell could be added easily to the apparatus if there was no load cell attached, prior to running the c onstraint shrinkage test. Sim ilarly, the load cell could be taken off easily from the apparatus to run th e free shrinkage test. The schematics of the set-up for the constrained shrinkage test us ing a LVDT and a load cell is shown in Figures 5-14-a and 5-14-b.

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79 Figure 5-14-a. Setup for the constrained long specimen test with a LVDT Figure 5-14-b. Setup for the constrained long specimen test with a LVDT and a Loadcell

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80 5.3.5 Modified Instrumentation for the LVDTs One major instrumentation problem was en countered when these ten apparatuses were evaluated. The problem was caused by th e fact that only one AC Voltage Function Generator was used to power all of the AC LVDTs. The AC LVDT requires an excitation voltage of 3 RMS V at a frequenc y 2.5 kHz. However, when one voltage function generator was used to power seve ral LVDTs at the same time, the function generator was not able to deliver the required voltage. In addition, interferences between the outputs from the different LVDTs were noted. The instrumentation for the LVDTs was subsequently modified to take care of this problem. Eleven LVDT signal conditioners (M odel LPC-2100 by Micro Sensors) were acquired. Each of these LVDT signal condi tioners was connected to each of the AC LVDTs (CD375-025 by Macro Sensors) to provide the needed excitation voltage of 3.0 RMS V at 2.4 kHz, to demodulate the AC output signal from the LVDT into a DC signal, and to amplify the DC signal before output ting it to the data acquisition system. According to the specificati on sheet, the LVDT signal conditioner had been calibrated such that a full stroke of the LVDT (.025 inch) would produce an output of 10.0 DC V from the signal conditioner. A LVDT signal conditioner is shown in Figure 5-15. According to this assumed calibration, th e displacement between the two gage points could be computed from the voltage output as follows: (Displacement in 0.001 inch) = (voltage in V) 2.5

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81 Figure 5-15. A LVDT line pow ered LPC-2100 signal conditioner 5.3.6 Calibration of the LVDT/Signal Conditioner System When the assumed calibration of the LVDT/signal conditioner system was used, the measured shrinkage from the long specime n apparatus appeared to be too low and erroneous. Thus, a special calib ration setup using a micrometer was built to calibrate the LVDT/signal conditioner system. It consisted mainly of a holder for the micrometer, a holder for the LVDT and a spring attachment for the extension rod for the core of the LVDT, to be aligned with the micrometer. The micrometer used had a range of 0.5 in. (12.7 mm) and a precision of 0.001 in. (0.0254 mm). Figure 5-16 shows the schematic of an individual constrained long specimen connected to the LVDT and other instrumentations.

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82 Figure 5-16. Individual constrained long c oncrete specimen connected to an LVDT, LVDT signal conditioner, DAS and the computer The calibration was set up so that the core was positioned near the center of the LVDT. The core was then moved through th e LVDT with the displacement read by the micrometer. The corresponding voltage output from the LVDT/conditioner was read by a digital voltmeter. A plot of the LVDT/c onditioner output versus displacement is shown in Figure 5-17. A picture of the calib ration setup is shown in Figure 5-18. Results of the calibration indicated that the previously assumed calibration of the LVDT/signal conditioner system was in error. The previously assumed calibration was that 1 V of output from the LVDT/signal c onditioner translated in to 0.0025 in. (0.0635 mm) of displacement. However, the results of the actual calibration indicated that 1 V of output from the LVDT/conditioner system should translate into 0.013 in. (0.3302 mm) of displacement (as shown from the plot in Figure 5-17). Equation for computation of displacement becomes: Displacement (in inches) = Output (in volts) 0.013 (Eq. 5.7)

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83 Figure 5-17. A plot of LVDT/conditioner outpu t versus displacement (micrometer reading) Equation for computation of strain becomes: Strain = Displacement / (Gage Length) = Displacement / (10 in. or 254 mm) = Output (in volts) 0.0013 (Eq. 5.8) 5.4 Second Refinement of Apparatus Use of Lubricated Base Plate Another observed problem w ith the constrained long specimen apparatus was that the long concrete specimen appeared to be sticking to the steel plate below it. A wax paper was placed over the steel base pl ate in an effort to reduce the friction between the concrete specimen and the base plate, as shown in Figure 5-19. However, the wax paper got soaked by the wet concrete and it worsened the problem further. This idea was thus abandoned. 1 3 4 6 7 9 Micrometer reading (inches) 0 Voltage (volts) Calibration of LVDT 8 5 2

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84 Figure 5-18. Set-up for calibration of LVDTs used in the long specimens LVDT Micrometer Rod carrying the core for LVDT Spring Loaded Portion of the Rod Rod carrying the core for LVDT Spring Loaded Portion of the R od Micrometer

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85 Figure 5-19. Use of wax paper to reduce friction between concrete and base plate Finally, a water-resistant and low-friction Te flon sheet was used as the base plate of the long constrained specimen apparatus to minimize the friction between the concrete specimen and its supporting base. Figure 5-20 shows a picture of the modified apparatus with the Teflon base plate. The use of Tefl on sheets as base plates appears to give good results, and was adopted in this study. Figure 5-20. Constrained long specimen apparatus with a Teflon base plate Wax Paper Teflon Sheet

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86 5.5 Third Refinement of Apparatus Use of Embedment Strain Gages 5.5.1 Embedment Strain Gage The constrained long specimen apparatus using LVDT for strain measurement had one drawback in that the LVDT could be placed on the specimen only after the concrete has attained sufficient strength. Thus, the shrinkage of the concrete in the very early age could not be measured. In order to monitor the shrinka ge of concrete at its very early age after placement, embedment strain gages were used for strain measurement. The embedment gage selected for this purpose was a 4.68-in. (120-mm) long embedment gage for concrete and mortar (KM-120-120H2-11 made by Soltec-Kyowa Inc). This strain gage has a resistance of 120 Ohms and a gage factor of 2.0. Figure 5-21 shows a picture of two long specimen molds with the embedment strain gages in them. Figure 5-21. Embedment strain ga ges inside the long specimen molds 5.5.2 Strain Gage Signal Conditioner An OMEGA OM2-163 Backplane 8-channe l signal conditioner was used to connect the embedment strain gages in a quart er bridge circuit and to amplify the output

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87 signals from the bridge circuits. OME GA OM2-163 is a complete signal conditioning system designed for single half, or full br idge transducers. Figure 5-22 shows the schematics of the setup of the constrained long specimen apparatus using an embedment strain gage for strain measurement. Fi gure 5-23 shows a picture of the OMEGA OM2163 Backplane 8-channel signal conditioner used. Figure 5-22. Schematics of the constr ained long specimen apparatus using an embedment strain gage for strain measurement Each embedment strain gage was connected to a channel of the signal conditioner in a quarter bridge configuration. An exci tation voltage of 4 V and a gain of 333.33 for the output signal were used. The outputs from the signal condition we re connected to the data acquisition system. The following equati on relates the un-amplified voltage output to the measured strain: Strain = 4 (Voltage output) / (Gage Factor)(Excitation Voltage) = 4 (Voltage output) / 2.0 (4V) = (Voltage output in V) / 2 (Eq. 5.9) With a gain of 333.33 used, the measured st rain is related to the amplified voltage output as follows:

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88 Strain = (Amplified voltage output in V) / (2 333.33) = (Amplified voltage output in V) / (666.67) (Eq. 5.10) Figure 5-23. OMEGA OM2-163 Backpl ane 8-channel signal conditioner The instrumentation for the embedment st rain gages was set up and tested. The amplified voltage outputs from the strain ga ge connections were connected to the data acquisition system and tested to be working pr operly. The internal wire connections are shown in figure 5-24.

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89 Figure 5-24 The internal connections of the Backplane signal conditioner The test results appeared to be correc t and this set-up was adopted for use to continue the testing of concrete fo r resistance to shrinkage cracking. The recording of shrinkage readings is started 16 2 hours after the concrete specimens were cast. 5.6 Fourth Refinement of Apparatus Zeroing of Strain in the Constrained Specimen From experimenting with testing of conc rete in the constrained long specimen apparatus, it was found that the apparatus was not able to provide complete restraint to

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90 the concrete specimen to keep it from contra cting during the constrai ned shrinkage test. Due to the contraction of the specimen during the test, a complete restrained condition was not achieved as intended. It was decided to provide the correcti on to the specimen contraction by manually pulling the specimen during the test such that th e strain in the specimen would be kept as close to zero as possible. The manual pulling of the test specimen was done by turning a nut on a threaded rod on the te st apparatus, which would result in pulling of the test specimen. Figure 5-25 shows how this was done. The strain reading from the strain gage was used as a guide on how much the specimen needed to be pulled. Every time the specimen was to be pulled for correction for contraction, the specimen would be pulle d until the strain was as close to zero as possible. Ideally, this pulling of specimen to zero out the strains in the test specimen should be done as often as possible and as ear ly as possible, so th at the strains would remain close to zero throughout the test. This manual method of correcting the contraction strains in the constr ained long specimen appeared to give acceptable results. Thus, this method was adopted for use in test ing the concrete mixtures in the laboratory testing program of this study

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91 Figure 5-25. Manual pulling of a test speci men to correct for specimen contraction

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CHAPTER 6 RESULTS OF LABORATORY TESTING PROGRAM 6.1 Introduction This chapter presents the results of th e laboratory testing program described in Chapter 4. It includes: (1) the evaluation of the five different methods for measurement of free shrinkage of concrete; (2) the eval uation of the effects of a shrinkage-reducing admixture on the compressive strength, splitt ing tensile strength, elastic modulus, free shrinkage and resistance to shrinkage cracki ng of concrete; and (3) the comparison of the resistance to shrinkage cracking of concre te containing fly ash with that containing ground blast-furnace slag as mineral admixture. 6.2 Evaluation of Different Methods of Free Shrinkage Measurement 6.2.1 Methods Evaluated Five different methods for measuring free sh rinkage of concrete were evaluated. These five methods were: 1. Shrinkage measurement using a Whittemore gage in the long specimen apparatus (as described in Section 4.3.6). 2. Shrinkage measurement using a LVDT in the long specimen apparatus (as described in Section 5.3.2). 3. Shrinkage measurement using an embedment gage in the long specimen apparatus (as described in Section 4.3.5).

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93 4. Shrinkage measurement using a Whittemore gage on a 6 in. 12-in. (152.4 304.8-mm) cylindrical specimen (as described in Section 4.3.7). 5. Shrinkage measurement using a LVDT on a 3 in. 3 in. 11.25-in. (76 76 286-mm) square prism specimen according to ASTM C157 procedure (as described in Section 4.3.4). 6.2.2 Comparison of Test Results Free shrinkage measurements using these fi ve different methods were made on the 15 pairs of concrete mixtures (with and without the addition of a shrinkage-reducing admixture) used in this study. The mix desi gns for these concrete mixtures are described in Tables 3.1 through 3.15 in Chapter 3. Ta ble 6-1 presents the results of these free shrinkage strain measurements in units of microstrain (10 6) using these five different methods along with their means and variances. From the comparison of the free shrinkage strain measurements using the different methods, it can be seen that strain meas urements using the embedment gage in the long specimen apparatus showed the best repeatability with th e lowest variance, with an overall average variance (s2) of 263, or an overall average standard deviation (s) of 16.2 microstrains. This was followed by the ASTM C157 method using LVDT with an overall average s2 of 662, or an overall average s of 25.7 microstrains. The strain measurements from the other three methods had much higher variances, with overall average s2 of 2987, 4695 and 5511, or overall average s of 54.7, 68.5 and 74.2 microstrains. The shrinkage strains as measured by th e ASTM C157 method and the Whittemore gage on the cylindrical specimens were much lowe r than those from the other three methods using the long specimens. This can be expl ained by the relatively larger size of the

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94 cylindrical concrete specimens and the square prism specimens, which have lower surface area per unit mass, and thus lower drying rates. The long specimens had a relatively lower thickness and higher surface ar ea per unit mass, and thus a higher drying rate. Among the three methods of measuri ng free shrinkage of the long specimens, the embedment gage method gave lower strain measurements than those by the Whittemore gage or the LVDT methods. This can be e xplained by the fact that the Whittemore gage points and the LVDT were attached to the surf ace of the specimen, which dried out faster than the inner part of the specimen wher e the embedment gage was placed. Figures 6-1 through 6-5 show plots of free shrinkage strains versus time as measured by the five different methods for the first six standard mixes (without SRA). It can be observed that the strains as measur ed by the embedment gage method (as shown in Figure 6-3) and the ASTM C157 method (a s shown in Figure 6-5) show that the shrinkage increases largely with time. These observations indicate that the data from these two methods appear to be more reasonable.

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95Table 6-1. Free Shrinkage Strains of the 15 Pairs of Concrete Mixtures as Measured by the Different Methods Free Shrinkage Strains as Measured by Different Methods, in 106 Whittemore Gage on Long Specimen LVDT on Long Specimen Embedment Gage on Long Specimen Whittemore Gage on Cylinder LVDT on ASTM C157 Prism Time (Days) 1 2 s2 1 2 s2 1 2 s2 1 2 s2 1 2 3 s2 Mix 1 Standard 3 200 180 190 200 358312335106615514114896 42 68 55 356 53 84 67 68 240 7 330 305 318 313 377354366247 317283300563 43 93 68 1250 161200177179376 14 350 320 335 450 473452462214 4063543801340 12313512968 242298264268788 Mix 1 SRA 3 90 40 65 1250 14214275 71 73 6 40 20 30 200 23 15 19 19 15 7 180 240 210 1800 2382381831821830 52 13091 3003 87 80 86 84 12 14 230 250 240 200 343343264249257105 60 2201401280015814515315239 Mix 2 Standard 3 220 300 260 3200 3192422813005196182189104 25 53 39 378 67 83 12491 847 7 370 500 435 8450 461381421319932331632025 67 1331002113 189209242213715 14 380 520 450 9800 47846947443 404390397103 32 11372 3200 258276306280568 Mix 2 SRA 3 75 140 107 2113 80 11095 464 88 97 92 42 48 58 53 50 22 22 21 22 0 7 140 125 132 112 138171154529 17416016793 57 78 68 200 11971 10398 590 14 195 205 200 50 176192184135 24123323725 38 35 36 3 159108136134651 Mix 3 Standard 3 180 10 95 14450 3902923414810178149163409 43 38 40 13 30 77 53 1083 7 330 160 245 14450 5234734981208314332323163 58 70 64 78 1312011662425 14 380 160 270 24200 523540531133 376414395718 2181551861953 2213092653849 Mix 3 SRA 3 15 15 25 37 31 74 10786 97 230 20 25 22 13 54 33 28 38 193 7 171 171 143188166996 227210219144 20557 1311087878 79 57 71 149 14 380 380 218247233402 30729930332 2203482848128 140142114132236

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96Table 6-1 continued Free Shrinkage Strains as Measured by Different Methods, in 106 Whittemore Gage on Long Specimen LVDT on Long Specimen Embedment Gage on Long Specimen Whittemore Gage on Cylinder LVDT on ASTM C157 Prism Time (Days) 1 2 s2 1 2 s2 1 2 s2 1 2 s2 1 2 3 s2 Mix 4 Standard 3 8 50 29 903 1642331982355 132151142192 80 1701254050 42 68 37 49 282 7 260 129 194 8646 2833623233141 238262250289 140183161903 130162126139393 14 535 308 421 25878 3434283853620 302331317407 2333302814753 230268228242521 Mix 4 SRA 3 85 95 90 50 56 44 50 71 27 61 44 598 70 65 67 12 2 0 1 1 0 7 100 130 115 450 12511211876 96 125110433 77 1481132450 44 41 43 43 1 14 240 225 232 113 166199183561 165197181505 110153131903 1011011031021 Mix 5 Standard 3 100 125 113 312 1821161492190 122105114145 72 2751732067237 69 34 47 370 7 185 250 218 2113 3342522933363 2782302541123 18342030128203110151109123572 14 290 250 270 800 3523013271264 3432813121942 33851842816200204253200219876 Mix 5 SRA 3 110 35 72 2813 18 33 25 111 41 48 44 26 93 10 51 3403 10 13 8 10 6 7 210 110 160 5000 11365 89 1169 11112311762 1682752215778 41 44 43 43 2 14 340 225 282 6612 2881652267536 18118718421 2653403032813 96 10095 97 6 Mix 6 Standard 3 8 50 29 903 34 91 62 1675 47 43 45 10 150173161253 55 52 54 54 3 7 260 129 194 8646 20943332125099248231240147 3052032545253 1671701681682 14 535 308 421 25878 27458042747099336315326220 3533003261378 25827126126347 Mix 6 SRA 3 60 110 85 1250 16 16 16 0 16 9 13 29 2651331998778 7 50 11 23 563 7 135 215 175 3200 14493 1181302 1411401411 2833453141953 68 10 6 28 1206 14 165 290 228 7812 203163183832 21121721417 3254233744753 13071 7 70 3784

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97Table 6-1 continued Free Shrinkage Strains as Measured by Different Methods, in 106 Whittemore Gage on Long Specimen LVDT on Long Specimen Embedment Gage on Long Specimen Whittemore Gage on Cylinder LVDT on ASTM C157 Prism Time (Days) 1 2 s2 1 2 s2 1 2 s2 1 2 s2 1 2 3 s2 Mix 7 Standard 3 200 180 190 200 12592 108565 1051071062 42 68 55 356 42 54 37 44 77 7 330 305 318 313 26419322825602072052061 43 93 68 1250 110128103113163 Mix 7 SRA 3 10 29 19 178 24 26 25 2 40 20 30 200 5 9 8 7 4 7 70 10989 752 86 85 85 0 52 13091 3003 29 38 37 35 23 Mix 8 Standard 3 39 132 86 4356 11370 91 949 1051001039 30 50 40 200 96 89 80 88 63 7 174 152 163 247 222132177407519719119423 68 1531103612 16716214915988 Mix 8 SRA 3 75 140 107 2113 24 28 26 12 33 32 32 0 27 58 42 465 41 37 38 39 5 7 140 125 132 112 83 68 76 118 86 86 86 0 75 95 85 200 68 63 65 66 7 Mix 9 Standard 3 50 45 48 13 10083 91 137 65 70 68 13 27 18 22 38 9 16 10 12 16 7 160 185 173 313 275259267132 19920820442 62 82 72 200 77 84 75 79 19 Mix 9 SRA 3 13 12 12 1 21 23 22 4 28 12 20 113 1 2 1 1 0 7 75 10690 479 83 83 83 0 60 45 52 112 17 15 23 18 15 Mix 10 Standard 3 75 105 90 450 153119136576 83 76 79 28 22 32 27 50 56 51 50 52 10 7 180 135 158 1013 246199223111418618018317 45 57 51 78 1121151111135 Mix 10 SRA 3 33 1 17 522 22 8 15 93 30 33 31 3 23 21 18 20 4 7 22 58 40 646 70 40 55 448 75 80 77 12 44 42 41 42 3

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98Table 6-1 continued Free Shrinkage Strains as Measured by Different Methods, in 106 Whittemore Gage on Long Specimen LVDT on Long Specimen Embedment Gage on Long Specimen Whittemore Gage on Cylinder LVDT on ASTM C157 Prism Time (Days) 1 2 s2 1 2 s2 1 2 s2 1 2 s2 1 2 3 s2 Mix 11 Standard 3 70 15 43 1512 16647 1077162 96 10910284 15 27 21 78 46 14955 83 3279 7 150 220 185 2450 34261 2023944724025324787 80 95 87 113 1492551531853589 Mix 11 SRA 3 43 14 29 438 35 42 38 28 35 15 25 200 25 31 25 27 15 7 167124145947 11812812358 55 45 50 50 64 69 66 66 5 Mix 12 Standard 3 75 190 132 6612 33113323219525210173191666 135115125200 52 10860 73 906 7 690 350 520 57800 459249354219853362903131076 175150163313 1982111081723163 Mix 12 SRA 3 37 76 56 766 90 77 83 85 80 80 80 0 34 60 52 49 173 7 133165149525 16815916437 1101101100 11695 95 102154 Mix 13 Standard 3 90 180 135 4050 2672182421208 198226212392 45 92 69 1128 69 10312097 691 7 155 305 230 11250 4303663982026 371410390746 95 1531241653 24124124924425 Mix 13 SRA 3 12196 108304 93 79 86 102 55 35 45 200 26 17 52 32 321 7 234214224217 190176183106 11092 101168 10352 10386 888

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99Table 6-1 continued Free Shrinkage Strains as Measured by Different Methods, in 106 Whittemore Gage on Long Specimen LVDT on Long Specimen Embedment Gage on Long Specimen Whittemore Gage on Cylinder LVDT on ASTM C157 Prism Time (Days) 1 2 s2 1 2 s2 1 2 s2 1 2 s2 1 2 3 s2 Mix 14 Standard 3 65 65 14861 105 384498 90 94 28 27 5 16 253 26 26 34 29 25 7 130 130 19491 142 5349172151162 225 83 73 78 50 99 90 73 87 173 Mix 14 SRA 3 68 78 73 48 38 36 37 2 18 52 35 584 34 17 52 34 296 7 10999 104 50 86 82 84 11 65 78 72 89 146120138135173 Mix 15 Standard 3 155 155 137131134 22 156143149 87 30 10065 2450 52 60 69 60 74 7 185 185 156138147 163 238217228 222 65 12896 1953 11210311210925 Mix 15 SRA 3 94 99 97 11 77 74 75 4 50 35 42 113 17 17 26 20 25 7 139153146 92 127120124 20 90 75 82 112 34 34 34 34 0 Overall Average 147 5511 159 4695 137 263 96 2987 75 662

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100 Figure 6-1. Free shrinkage strains as measured by Whittemore gage on the long specimens for six standard mixes 0 100 200 300 400 500 600 3714 Time (days)Free shrinkage strains X 10-6 (Micro-strain) Mix-1 Mix-2 Mix-3 Mix-4 Mix-5 Mix-6

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101 Figure 6-2. Free shrinkage strains as measured by LVDT on the long specimens for six standard mixes 0 100 200 300 400 500 600 3714 Time (days)Free shrinakge strain X 10-6 (Micro-strain) Mix-1 Mix-2 Mix-3 Mix-4 Mix-5 Mix-6

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102 Figure 6-3. Free shrinkage strains as measured by embedment gages in the long specimens for six standard mixes 0 50 100 150 200 250 300 350 400 450 3714 Time (days)Free shrinkage strain X 10-6 (Micro-strain) Mix-1 Mix-2 Mix-3 Mix-4 Mix-5 Mix-6

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103 Figure 6-4. Free shrinkage strains as measured by Wh ittemore gage on the cylinders for six standard mixes 0 50 100 150 200 250 300 350 400 450 3714 Time (days)Free shrinkage strain X 10-6 (Micro-strain) Mix-1 Mix-2 Mix-3 Mix-4 Mix-5 Mix-6 250 300)

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104 Figure 6-5. Free shrinkage strains as measured by ASTM C157 Method for six standard mixes

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1056.2.3 Observations on the Different Methods of Shrinkage Measurement 6.2.3.1 Whittemore Gage on the Long Specimen This method has the advantage that the Wh ittemore gage is a simple mechanical gage that does not require any electronic system for it to work. It can be calibrated reliably with an invar bar before each measurement is made. The limitation of this method is that the Whittemore gage is a manual gage, and thus the strains cannot be monitored convenientl y. Another limitation is that it requires sufficient curing time before the gage points can be held securely by the concrete before readings can be taken with the Whittemore gage For the concrete mixes evaluated in this study, it required a minimum of 24 hours be fore readings could be started. 6.2.3.2 LVDT on the Long Specimen This method has the advantage that strain readings can be taken automatically and continuously throughout the test. The limitation of this method is that it re quires sufficient curing time before the gage studs (that hold the LVDT and the core rod holder) can be he ld securely by the concrete before the LVDT and the core rod holder can be attached and readings can be taken with the LVDT. For the concrete mi xes evaluated in this study, it required a minimum of 24 hours before readings could be started. 6.2.3.3 Embedment Gage in the Long Specimen This method has the advantage that strain readings can be taken automatically and continuously throughout the test. Since embe dment gage is embedded in the concrete from the very beginning, strain readings can be started at a very early age of the concrete. The disadvantage of this method is the re latively higher cost of the test, as the embedment gage is not reusable after each test.

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1066.2.3.4 Whittemore Gage on a Cylindrical Specimen This method has the advantage that the Wh ittemore gage is a simple mechanical gage that can be calibrated conveniently a nd reliably with an invar bar before each measurement is made. The limitation of this method is that the Whittemore gage is a manual gage, and thus the strains cannot be monitored convenientl y. Another limitation is that it requires sufficient curing time for the concrete to be able to hold the gage points securely before the molds can be removed and readings with th e Whittemore gage can be started. For the concrete mixes evaluated in this study, it re quired a minimum of 24 hours before readings could be started. 6.2.3.5 ASTM C157 Method using a LVDT The advantage of this method is that it is already a fairly we ll developed procedure for measurement of shrinkage strains of conc rete. With the use of a LVDT, the strains can be conveniently monito red throughout the test. The limitation of this method is that sufficient curing time is needed before the specimens can be taken out from the mold a nd strain readings can be started. For concrete mixes evaluated in this study, it re quired a minimum of 24 hours before readings could be started. Another limitation of this method is that, since it uses a different specimen size from that for the constraine d long specimen test, the free shrinkage measurements from this method cannot be applied directly to the constrained long specimen test without proper adjustments.

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1076.2.4 Recommended Method In consideration of the good repeatabili ty and reasonableness of the strain measurements, and that the strain measurements can be made from a very early age of the concrete, the embedment gage method was sele cted to be used for measurement of free shrinkage and for measurement of strain in the constrained long specimen test. 6.3 Evaluation of the Effects of a Shrinkage-Reducing Admixture 6.3.1 Effects on Free Shrinkage Table 6-2 lists the average free shrinkag e strains as measured by the embedment strain gages on the long specimens for the 15 pairs of concrete mixtures (with and without the addition of a shri nkage-reducing admixture), whic h were evaluated in this study. The percentage reduction in free shrinka ge strains of the mixtures containing SRA as compared with the standard mixtures (w ithout SRA) were comput ed and presented in this table. It can be seen that th e addition of SRA reduced the free shrinkage substantially for all mixes. The SRA, EclipseTM is a glycol based ether that reduces the surface tension of water. With the reduction in surface tension, the force pulling in on the walls of the pores is reduced, and the resu ltant shrinkage strain is reduced. The percentage reduction varies from 41 to 81% at 3 days, from 32 to 70% at 7 days, and from 23 to 43% at 14 days. The comparis on of free shrinkage strains between the standard and the SRA mixtures are plotted in Figures 6-6 thro ugh 6.8 for 3, 7 and 14 days of curing, respectively.

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108 Table 6-2. Percentage Re duction in Free Shrinkage Stra ins of the SRA Mixtures as Compared With the Standard Mixtures as Measured by the Embedment Strain Gages in the Long Specimens % Reduction in Free shrinkage strains of SRA Mixtures over Standard Curing time (days) Mix Type 3 7 14 Average Strain, 10-6 % Reduction Average Strain, 10-6 % Reduction Average Strain, 10-6 % Reduction Standard 148 51 300 39 380 32 1 SRA 73 183 257 Standard 189 51 320 48 397 40 2 SRA 92 167 237 Standard 163 41 323 32 395 23 3 SRA 97 219 303 Standard 142 69 250 56 317 43 4 SRA 44 110 181 Standard 114 61 254 54 312 41 5 SRA 44 117 184 Standard 45 72 240 41 326 34 6 SRA 13 141 214 Standard 106 76 206 59 N/A N/A 7 SRA 25 85 N/A N/A Standard 103 68 194 56 N/A N/A 8 SRA 32 86 N/A N/A Standard 68 68 204 59 N/A N/A 9 SRA 22 83 N/A N/A Standard 79 81 183 70 N/A N/A 10 SRA 15 55 N/A N/A Standard 102 62 247 50 N/A N/A 11 SRA 38 123 N/A N/A Standard 191 57 313 48 N/A N/A 12 SRA 83 164 N/A N/A Standard 212 59 390 53 N/A N/A 13 SRA 86 183 N/A N/A Standard 94 61 162 48 N/A N/A 14 SRA 37 84 N/A N/A Standard 149 50 228 46 N/A N/A 15 SRA 75 124 N/A N/A 62 51 36

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109 Figure 6-6. Comparison of free shrinka ge strains of Standard and Eclips e (SRA) mixtures at 3 days curing 0 50 100 150 200 250 1-S2-S3-S4-F5-F6-S+F7-F8-F9F10-F11-F12-S+F13-S14-F15-CMixes (S Slag, F Fly ash & C Cement)Shrinkage strain X 10-6 (Micro-strain) Std Ecl 300 350 400 450 strain)

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110 Figure 6-7. Comparison of free shrinka ge strains of Standard and Eclips e (SRA) mixtures at 7 days curing 300 350 400 450 r o-strain)

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111 Figure 6-8. Comparison of free shrinka ge strains of Standard and Eclips e (SRA) mixtures at 14 days curing

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1126.3.2 Effects on Shrinkage-Induced Stress The modified constrained long specimen test as described in Section 5.3 and with the refinements as described in Sections 5. 4, 5.5 and 5.6, was performed on the 15 pairs of concrete mixtures (with and without the addition of SRA). The analysis method as described in Section 5.2.3 was used to analy ze the test results and to compute the induced shrinkage stresses under a fully constrained cond ition. Table 6-3 presen ts the test results and the computed shrinkage-induced stresses for all the mixtures evaluated along with the splitting tensile strength of the concrete at the corresponding curi ng times. When the computed shrinkage-induced stress exceeds the tensile strength of the concrete at the corresponding curing time, it mean s that the concrete would have cracked due to drying shrinkage under a fully constrained condition. It can be seen from Table 6-3 that th e SRA mixtures had substantially lower computed induced shrinkage stresses than th eir corresponding standard mixtures. The results predict that 6 of the 15 standard mixt ures would have cracked within 3 days under a fully constrained condition, while none of the SRA mixtures would crack under a similar condition. The comparison of the shri nkage-induced stresses of the standard and SRA mixtures is shown in Figures 6-9 and 6-10 for the curing times of 3 and 7 days, respectively. Table 6-4 presents the percenta ge reduction of computed induced shrinkage stresses due to the addition of SRA. Th e percentage reduction ranges from 20 to 88% with an average of 62% at 3 days curing. The percentage reduction ranges from 14 to 66% with an average of 48% at 7 days curing. The percentage reduction ranges from 2 to 55% with an average of 27% at 14 days curing.

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113Table 6-3. Results of Constrained Long Specime n Test on the 15 Pairs of Concrete Mixtures Time (Days) E (psi) Specim. Stress, E (psi) Elastic Strain, E Free Shrinkage Strain, sh Total Specimen Strain, CL Creep Strain, CR Computed Shrinkage Stress, FC (psi) Splitting Tensile Strength (psi) Mix 1 Standard 3 4455155 103 0.000023 0.000222 0.000104 0.000094 569* 381 7 5150415 157 0.000030 0.000300 0.000194 0.000076 1151* 594 14 5535946 185 0.000033 0.000380 0.000204 0.000142 1314* 614 SRA 3 4731254 106 0.000022 0.000082 0.000026 0.000033 234 397 7 5404991 164 0.000030 0.000183 0.000043 0.000110 394 603 14 5716239 175 0.000031 0.000262 0.000072 0.000159 588 718 Mix 2 Standard 3 6427326 138 0.000022 0.000189 0.000084 0.000083 682* 376 7 7168223 194 0.000027 0.000320 0.000120 0.000172 1058* 617 14 7285077 192 0.000026 0.000397 0.000154 0.000217 1316* 695 SRA 3 6538004 23 0.000003 0.000092 0.000012 0.000077 95 395 7 6981284 60 0.000009 0.000167 0.000112 0.000047 813* 607 14 7068646 88 0.000012 0.000237 0.000171 0.000054 1290* 644 Mix 3 Standard 3 2905150 28 0.000010 0.000163 0.000115 0.000270 362 381 7 3427850 210 0.000061 0.000323 0.000204 0.000058 908* 594 14 4082624 236 0.000058 0.000395 0.000247 0.000090 1243* 614 SRA 3 3650126 10 0.000003 0.000097 0.000076 0.000018 288 397 7 4185281 138 0.000033 0.000219 0.000153 0.000033 779* 603 14 4193226 168 0.000040 0.000303 0.000215 0.000048 1069* 718

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114 Table 6-3 continued Time (days) E (psi) Specim. Stress, E (psi) Elastic Strain, E Free Shrinkage Strain, sh Total Specimen Strain, CL Creep Strain, CR Computed Shrinkage Stress, FC (psi) Splitting Tensile Strength (psi) Mix 4 Standard 3 3055865 51 0.000017 0.000142 0.000065 0.000060 249 376 7 3462333 108 0.000031 0.000250 0.000147 0.000072 618* 617 14 3901191 139 0.000036 0.000317 0.000195 0.000086 899* 695 SRA 3 3008550 79 0.000026 0.000044 0.000004 0.000013 92 395 7 3343896 151 0.000045 0.000110 0.000034 0.000031 267 607 14 3856788 167 0.000043 0.000181 0.000090 0.000047 507 644 Mix 5 Standard 3 2861518 59 0.000021 0.000114 0.000045 0.000048 187 381 7 3441955 154 0.000045 0.000254 0.000123 0.000087 575 594 14 3619022 180 0.000050 0.000312 0.000167 0.000095 783* 614 SRA 3 2869918 47 0.000016 0.000041 0.000010 0.000014 76 397 7 3336697 102 0.000030 0.000111 0.000057 0.000024 293 603 14 3568982 120 0.000034 0.000181 0.000128 0.000019 576 718 Mix 6 Standard 3 4455155 48 0.000011 0.000045 0.000003 0.000031 1314* 381 7 5150415 70 0.000014 0.000240 0.000132 0.000094 753* 594 14 5535946 76 0.000014 0.000326 0.000188 0.000124 1121* 614 SRA 3 5404263 57 0.000011 0.000013 0.000013 -0.000011 127 397 7 6250985 71 0.000011 0.000141 0.000140 -0.000011 947* 603 14 6457045 76 0.000012 0.000214 0.000225 -0.000023 1530* 718 Table 6-3 continued

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115Time (Days) E (psi) Specim. Stress, E (psi) Elastic Strain, E Free Shrinkage Strain, sh Total Specimen Strain, CL Creep Strain, CR Computed Shrinkage Stress, FC (psi) Splitting Tensile Strength (psi) Mix 7 Standard 3 3606318 51 0.000014 0.000106 0.000069 0.000023 300 381 7 3992038 130 0.000033 0.000206 0.000141 0.000032 696* 594 SRA 3 3388225 35 0.000010 0.000025 0.000008 0.000007 64 397 7 3785151 110 0.000029 0.000085 0.000042 0.000014 269 603 Mix 8 Standard 3 3684585 99 0.000027 0.000103 0.000067 0.000009 346 381 7 4046461 149 0.000037 0.000194 0.000128 0.000029 667* 594 SRA 3 4161028 48 0.000012 0.000032 0.000018 0.000003 122 397 7 4293893 89 0.000021 0.000086 0.000057 0.000008 334 603 Mix 9 Standard 3 2820558 51 0.000018 0.000068 0.000024 0.000026 118 381 7 3273363 130 0.000040 0.000204 0.000112 0.000052 497 594 SRA 3 2963033 35 0.000012 0.000022 0.000006 0.000004 53 397 7 3300901 110 0.000033 0.000083 0.000029 0.000021 204 603 Table 6-3 continued Time E Specim. Elastic Free Total Creep Computed Splitting

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116(Days) (psi) Stress, E (psi) Strain, E Shrinkage Strain, sh Specimen Strain, CL Strain, CR Shrinkage Stress, FC (psi) Tensile Strength (psi) Mix 10 Standard 3 3052549 89 0.000029 0.000080 0.000047 0.000004 233 381 7 3280739 154 0.000047 0.000184 0.000109 0.000028 512 594 SRA 3 3114178 55 0.000018 0.000018 0.000005 -0.000005 71 397 7 3298157 101 0.000031 0.000058 0.000035 -0.000007 216 603 Mix 11 Standard 3 3226966 149 0.000046 0.000102 0.000049 0.000007 306 381 7 3666718 158 0.000043 0.000247 0.000164 0.000040 758* 594 SRA 3 3189941 125 0.000039 0.000038 0.000001 -0.000002 127 397 7 3507181 128 0.000037 0.000123 0.000082 0.000004 417 603 Mix 12 Standard 3 3992077 134 0.000034 0.000193 0.000103 0.000055 549* 381 7 4239146 157 0.000037 0.000314 0.000199 0.000079 999* 594 SRA 3 3880440 104 0.000027 0.000083 0.000037 0.000019 246 397 7 4417371 118 0.000027 0.000164 0.000102 0.000035 568 603 Table 6-3 continued Time (Days) E (psi) Specim. Stress, E (psi) Elastic Strain, E Free Shrinkage Strain, sh Total Specimen Strain, CL Creep Strain, CR Computed Shrinkage Stress, FC (psi) Splitting Tensile Strength (psi) Mix 13 Standard

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1173 3861868 119 0.000031 0.000212 0.000138 0.000043 654* 381 7 4539476 139 0.000031 0.000390 0.000281 0.000079 1413* 594 SRA 3 4138054 107 0.000026 0.000086 0.000048 0.000013 304 397 7 4757098 132 0.000028 0.000183 0.000131 0.000025 754* 603 Mix 14 Standard 3 3842707 100 0.000026 0.000094 0.000068 0.000000 361 381 7 3886822 134 0.000034 0.000162 0.000120 0.000008 599* 594 SRA 3 3556466 93 0.000026 0.000037 0.000008 0.000002 122 397 7 4001058 119 0.000030 0.000084 0.000037 0.000017 269 603 Mix 15 Standard 3 4167444 101 0.000024 0.000149 0.000108 0.000017 552* 381 7 4962452 144 0.000029 0.000228 0.000160 0.000039 936* 594 SRA 3 4384647 111 0.000025 0.000075 0.000036 0.000014 266 397 7 4887643 155 0.000032 0.000124 0.000072 0.000020 508 603 300 400 500 600 700 800Stress (psi)

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118 Figure 6-9. Comparison of com puted shrinkage-induced stresses of Standard a nd Eclipse (SRA) mixtures at 3 days curing 400 600 800 1000 1200 1400 1600Stress (psi)

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119 Figure 6-10. Comparison of computed shri nkage-induced stresses of Standard and Ec lipse (SRA) mixtures at 7 days curing

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120 Table 6-4. Percentage Re duction of Computed Shrinkage-Induced Stresses of SRA Mixtures as Compared With the Standard Mixtures % Reduction of Computed Induced Shrinkage Stress of SRA Mixes Curing time (days) Mix Type 3 7 14 Stress (psi) % Reduction Stress (psi) % Reduction Stress (psi) % Reduction Standard 569 59 1151 66 1314 55 1 SRA 234 394 588 Standard 682 86 1058 23 1316 2 2 SRA 95 813 1290 Standard 362 20 908 14 1243 14 3 SRA 288 779 1069 Standard 249 63 618 57 899 44 4 SRA 92 267 507 Standard 187 52 575 46 783 23 5 SRA 90 312 600 Standard 665 88 440 43 673 26 6 SRA 83 250 497 Standard 300 79 696 61 N/A N/A 7 SRA 64 269 N/A N/A Standard 346 65 667 50 N/A N/A 8 SRA 122 334 N/A N/A Standard 118 55 497 59 N/A N/A 9 SRA 53 204 N/A N/A Standard 233 70 512 58 N/A N/A 10 SRA 71 216 N/A N/A Standard 306 58 758 45 N/A N/A 11 SRA 127 417 N/A N/A Standard 549 55 999 43 N/A N/A 12 SRA 246 568 N/A N/A Standard 654 53 1413 47 N/A N/A 13 SRA 304 754 N/A N/A Standard 361 66 599 55 N/A N/A 14 SRA 122 269 N/A N/A Standard 654 53 1413 47 N/A N/A 15 SRA 304 754 N/A N/A Mean 62 48 N/A 27

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1216.3.3 Effects on Strengths and Elastic Modulus The results of the compressive strength, splitting tensile strength and elastic modulus tests at 14 days on the 15 pairs of c oncrete mixtures evaluated in this study are presented in Table 6-5. It can be seen from these data that, in some mixes, the SRA mixtures appeared to have slightly higher st rengths and elastic modu li, while for the other mixes, the SRA mixtures appeared to have sl ightly lower strengths and elastic moduli. Were these observed differences statistically sign ificant, or were they due primarily to the variability of the test data? The Students ttest was used to answer this question. For each pair of concrete mixtures, the St udents t-test was performed to compare the means of each of these three mechanical properties from the SRA and the standard mixtures to determine if they were significan tly different from one another with respect to each of these three mechanical properties. For each t-test, the t statistic was calculated as follows: 12 0.5 12XX t 11 s nn (Eq. 6.1) where X1 and X2 are means of the samples from populations 1 and 2; n1 and n2 are sample sizes for the samples from popula tions 1 and 2; s is the square root of the pooled variance (s2 ) given by: 22 1122 2 12n1sn1s s nn2 (Eq. 6.2) where (s1)2 and (s2)2 are variances of the samples from populations 1 and 2.

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122 Table 6-5. Compressive St rength, Splitting Tensile Strength and Elastic Modulus of th e 15 Pairs of Concrete Mixtures Table 6-5 continued Mixes Time (days) E (Psi) Compressive Strength Splitting Tensile Strength (psi) E (psi) Compressive Strength (psi) Splitting Tensile Strength (psi) Mixes Time (days) 1 2 Average 1 2 3 Average 1 2 3 Average 3 4416855 4493455 4455155 48104470 50044761 461396428429 7 5308886 4991944 5150415 69507050 67906930 654577551594 Mix 1 (C-50, S-50), Standard (w/c 0.33) 14 5640288 5431603 5535946 77008160 77407867 614551676614 3 4584048 4878461 4731254 50304830 50204960 441423504456 7 5438242 5371741 5404991 70907120 74007203 640613557603 Mix 1 (C-50, S-50), SRA (w/c 0.33) 14 5642459 5790019 5716239 82208150 84108260 788696670718 3 6224478 6630175 6427326 67006440 65206553 493486495492 7 7063727 7272718 7168223 87108434 84308525 658636602632 Mix 2 (C-30, S-70), Standard (w/c 0.25) 14 7271631 7298524 7285077 93708760 85608897 694726680700 3 6445834 6169017 6307425 47104810 49604827 383366403384 7 6689849 6790581 6740215 65506650 68306677 506516513512 Mix 2 (C-30, S-70), SRA (w/c 0.25) 14 6838769 7231382 7035076 73607270 70707233 607599595600 3 2978144 2832156 2905150 42704310 41304237 314384365354 7 3386258 3469441 3427850 56955469 54425535 709657616661 Mix 3 (C-30, S-70), Standard (w/c 0.30) 14 4044965 4120283 4082624 74507570 75607527 773656667699 3 3618629 3681622 3650126 35903530 35703563 322360304329 7 4208640 4161921 4185281 53995620 55705530 565555499540 Mix 3 (C-30, S-70), SRA (w/c 0.29) 14 4181911 4204542 4193226 71706870 68706970 610651660640

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1231 2 Average 1 2 3 Average 1 2 3 Average 3 3138865 2972865 3055865 29102830 29702903 360403366376 7 3511892 3412774 3462333 66806750 65206650 604660587617 Mix 4 (C-80, F-20) Standard (w/c0.35) 14 3881511 3920872 3901191 78707910 81007960 766632688695 3 3044235 2906975 2975605 20002040 20602033 391400395395 7 3275018 3464325 3369671 64006250 63706340 571626623607 Mix 4 (C-80, F-20) SRA (w/c-0.33) 14 3792704 3740321 3766512 79007940 79207920 646656630644 3 3000886 2722150 2861518 34403460 34303443 376415439410 7 3390959 3492951 3441955 45004560 45304530 533590519547 Mix 5 (C-65, F-35) Standard (w/c-0.33) 14 3661683 3576361 3619022 55805540 56405587 566471542526 3 2880273 2859563 2869918 32303300 33203283 406436331391 7 3382939 3290456 3336697 47104520 45104580 489390491457 Mix 5 (C-65, F-35) SRA (w/c-0.33) 14 3616783 3521181 3568982 55405540 55505543 529487464494 3 2618982 2622861 2620921 24502410 23802413 381345372366 7 3120751 3162391 3141571 46904790 46204700 574496492521 Mix 6 (C-30, S-50 & F-20), Standard (w/c-0.35) 14 3514496 3510558 3512527 66696465 69036679 669726664686 3 2535208 2548807 2542007 22802210 24002297 376303284321 7 3349643 3362484 3356063 47204780 46904730 481542578534 Mix 6 (C-30, S-50 & F-20), SRA (w/c-0.35) 14 3495439 3537646 3516542 60306450 63656282 649588607615 Table 6-5 continued E (Psi) Compressive Strength Splitting Tensile Strength (psi) Mixes Time (days) 1 2 Average 1 2 3 Average 1 2 3 Average 3 3606318 3606318 3606318 44634439 44554452 465 467 467 467 7 4076555 3900563 3988559 58556324 60066061 644 499 539 561 Mix 7 (C-80, F-20), Standard (w/c 0.34) 14 4525851 4304663 4415257 75337509 72397427 581 478 606 555

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12428 4537320 4525331 4531325 80028328 82658198 576 684 551 604 3 3388225 3388225 3388225 35163548 35723545 376 366 354 365 7 3729430 3840872 3785151 51945417 53145308 493 447 557 499 14 3983873 3991834 3987853 63566197 63396297 552 514 523 530 Mix 7 (C-80, F-20) SRA (w/c 0.34) 28 4138115 4332631 4235373 76367422 75177525 616 598 676 630 3 3631600 3737570 3684585 47334781 47894767 483 512 516 504 7 4056772 4036149 4046461 65396491 66586563 611 634 611 618 14 4314802 4203692 4259247 74537557 73507453 718 718 704 713 Mix 8 (C-80, F-20), Standard (w/c 0.38) 28 4497366 4609553 4553460 81788399 83418306 1970205721002043 3 4019694 4260053 4139874 49644805 49324900 413 520 463 465 7 4281844 4305943 4293893 67226499 64516557 616 611 561 596 14 4728351 4441247 4584799 75257636 73667509 628 734 595 652 Mix 8 (C-80, F-20), SRA (w/c 0.38) 28 4724886 4831122 4778004 78818227 84028170 693 745 610 683 3 2847699 2793418 2820558 24262490 24982471 326 290 326 314 7 3230478 3316248 3273363 36513611 36113625 457 446 334 412 14 3446445 3625646 3536046 47894653 47974746 479 557 563 533 Mix 9 (C-65, F-35), Standard (w/c 0.46) 28 3599945 3822791 3711368 58785688 58235796 636 636 545 606 3 2997575 2928491 2963033 25382649 25612583 358 318 332 336 7 3223592 3378211 3300901 38023938 39853908 369 377 368 371 14 3607691 3715169 3661430 48284868 48524850 561 519 416 498 Mix 9 (C-65, F-35), SRA (w/c 0.46) 28 3864973 3711668 3788320 57275759 56645717 531 614 601 582 Table 6-5 continued E (psi) Compressive Strength (psi) Splitting Tensile Strength (psi) Mixes Time (days) 1 2 Average 1 2 3 Average 1 2 3 Average 3 2936739 3168360 3052549 26572792 29192789 360364328351 7 3295355 3266124 3280739 36513699 39063752 457461485468 14 3466569 3496266 3481417 45984765 47414701 523523463503 Mix 10 (C-65, F-35), Standard (w/c 0.41) 28 3702587 3719864 3711225 57595775 57435759 573602507561 Mix 10 (C-65, 3 3161160 3067196 3114178 26812705 28322739 360382378373

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1257 3240103 3356210 3298157 38663874 39303890 469497380449 14 3601638 3626390 3614014 50034860 49884950 507459581516 F-35), SRA (w/c 0.41) 28 3712301 3959791 3836046 58395950 61575982 403541499481 3 3258290 3195641 3226966 36913683 37473707 322326344330 7 3720572 3612864 3666718 55205409 53455425 464612447508 14 3862169 3827133 3844651 60646006 59796016 490555477507 Mix 11 (C-80, F-20) Standard (w/c 0.46) 28 4145363 4255670 4200516 71517199 72477199 542441537506 3 3143982 3235900 3189941 35243516 36753572 346439320368 7 3498332 3516031 3507181 49565051 49724993 490470562507 14 3610294 3660458 3635376 56885823 56115707 549542604565 Mix 11 (C-80, F-20), SRA (w/c 0.46) 28 3834219 3949312 3891766 71517366 68897135 667687688681 3 3550043 4434111 3992077 48444645 50194836 414414527451 7 4203387 4274906 4239146 66186411 66346555 577501560546 14 4369976 4487084 4428530 74857533 74537491 594543652596 Mix 12 (C-30, S-50 & F-20), Standard (w/c 0.28) 28 4591187 4564588 4577888 78038130 8225 3 4100167 3660713 3880440 38103922 39613898 362430360384 7 4442825 4391918 4417371 57275791 57595759 505505506506 14 4542769 4575835 4559302 63647016 66986692 593577614595 Mix 12 (C-30, S-50 & F-20), SRA (w/c 0.28) 28 4794909 4926751 4860830 72477207 71517202 524579553552 Table 6-5 continued E (Psi) Compressive Strength Splitting Tensile Strength Mixes Time (days) 1 2 Average 1 2 3 Average 1 2 3 Average 3 3735773 3987963 3861868 6189 6491 6523 6401 414507412444 7 4570450 4508502 4539476 8114 8193 8201 8169 556498659571 14 4747266 5123076 4935171 9259 9378 9514 9384 755671729718 Mix 13 (C-50, S-50), Standard (w/c 0.41) 28 4781950 5146989 4964470 9657 9736 9553 9649 911656867811 3 4111928 4164180 4138054 5497 5314 5417 5409 406410396404 7 4658387 4855809 4757098 7398 7278 7613 7430 483515576525 14 5001046 5001046 5001046 8543 8519 8710 8591 509562646572 Mix 13 (C-50, S-50), SRA (w/c 0.41) 28 5177606 5134069 5155838 9044 9148 9108 9100 789599629672 Mix 14 (C-65, 3 3858952 3826463 3842707 3475 3523 3378 3459 287383367346

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1267 3886822 2911755 3886822 4542 4470 4311 4441 467436453452 14 4423983 4366718 4395351 5505 5377 5170 5351 515533545531 F-35), Standard (w/c 0.30) 28 5580151 4812471 5196311 7239 7382 6928 7183 611509723615 3 3556466 3341947 3449206 3043 2954 2980 2993 313327331324 7 3965263 4036854 4001058 4176 4073 4120 4123 475416396429 14 4441069 4218399 4329734 5003 5338 4828 5056 481515561519 Mix 14 (C-65, F-35), SRA (w/c 0.30) 28 4592010 4711529 4651769 6618 6570 6284 6491 526508507514 3 3803863 4510687 4157275 7764 8082 7835 7894 618622702647 7 5039900 5039900 5039900 10047 9561 9713 9773 651722722698 14 5315464 5123516 5219490 11192 10595 10206 10664 769768611716 Mix 15 (C-100), Standard (w/c 0.29) 28 5322837 5471778 5397307 11089 11526 11574 11396 597692716668 3 4408573 4323830 4366202 6109 6173 6109 6130 528472585528 7 3366304 4917633 4917633 7692 7589 7772 7684 696679745707 14 5035781 5669101 5352441 9052 8480 8480 8670 627504532554 Mix 15 (C-100), SRA (w/c 0.29) 28 5234741 5439419 5337080 9076 9386 9593 9352 730678571660

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127 The null hypothesis that the two means were equal to one another was tested at an level of 5%. The t value for (n1 + n 2 2) degrees of freedom and level of 5% for a two-tail distribution was determined from the Students t distri bution table and was denoted as tCritical. If the computed t value was smaller than tCritical, the null hypothesis could not be rejected, and the two means were considered to be statistically not different from one another. Tables 6-6, 6-7 and 6-8 present the results of the Students ttest on the compressive strengths, splitting tensil e strength and elastic modulus of elasticity, respectively, of the SRA mixtures versus the standard mixtures It can be seen that for seven of the 15 pairs of mixtures evaluated, the compre ssive strength of SRA mixtures were not statistically different from t hose of Standard mixtures. Among the eight pairs that showed significant differences, seven pairs show ed that the Standard mixtures had higher compressive strengths than their correspondi ng SRA mixtures. The splitting tensile strengths of four SRA concrete mixtures were statistically significantly different from those of Standard mixtures. Among these four pairs, three pairs showed that the Standard mixtures had higher splitting tensile streng ths than their corresponding SRA mixtures. The modulus of elasticity values of four SRA concrete mixtures were statistically significantly different from those of Standard mixtures. Among th ese four pairs, two pairs showed that the Standard mixtures ha d higher modulus of elasticity than their corresponding SRA mixtures. Since these ttests rendered inconclusive results, it was decided to run Paired t-tests for evalua ting the impact of SRA on the mechanical properties (Compressive streng th, Splitting tensile strength a nd Modulus of Elasticity) of concrete mixtures.

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128 Table 6-6. Results of t-Te sts on the Compressive Streng th at 14 days of the SRA Mixtures Versus the Standard Mixtures Mix Admixture & w/c Type Sample size Mean tCalculated tCritical for 95% Confidence Significantly Different? Standard 3 7867 1 S-50 & 0.33 SRA 3 8260 -0.215 2.776 No Standard 3 8897 2 S-70 & 0.25 SRA 3 7233 6.443 2.776 Yes Standard 3 7527 3 S-70 & 0.30 SRA 3 6970 5.201 2.776 Yes Standard 3 7960 4 F-20 & 0.33 SRA 3 7920 0.561 2.776 No Standard 3 5587 5 F-35 & 0.33 SRA 3 5543 1.482 2.776 No Standard 3 6679 6 S-50 & F20 & 0.35 SRA 3 6282 2.210 2.776 No Standard 3 7427 7 F-20 & 0.34 SRA 3 6297 10.562 2.776 Yes Standard 3 7453 8 F-20 & 0.38 SRA 3 7509 -0.560 2.776 No Standard 3 4746 9 F-35 & 0.46 SRA 3 4850 -2.164 2.776 No Standard 3 4701 10 F-35 & 0.41 SRA 3 4950 -3.613 2.776 Yes Standard 3 6016 11 F-20 & 0.46 SRA 3 5707 4.630 2.776 Yes Standard 3 7491 12 S-50 & F20 & 0.28 SRA 3 6692 4.211 2.776 Yes Standard 3 9384 13 S-50 & 0.41 SRA 3 8591 8.350 2.776 Yes Standard 3 5351 14 F-35 & 0.30 SRA 3 5056 1.652 2.776 No Standard 3 10664 15 C-100 & 0.29 SRA 3 8670 5.791 2.776 Yes

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129 Table 6-7. Results of t-Tests on the Splitti ng Tensile Strength at 14 days of the SRA Mixtures Versus the Standard Mixtures Mix Admixture & w/c Type Sample size Mean tCalculated tCritical for 95% Confidence Significantly Different? Standard 3 583 1 S-50 & 0.33 SRA 3 742 -3.503 2.776 Yes Standard 3 710 2 S-70 & 0.25 SRA 3 603 8.020 2.776 Yes Standard 3 715 3 S-70 & 0.30 SRA 3 631 1.654 2.776 No Standard 3 699 4 F-20 & 0.33 SRA 3 651 0.873 2.776 No Standard 3 518 5 F-35 & 0.33 SRA 3 508 0.230 2.776 No Standard 3 698 6 S-50 & F20 & 0.35 SRA 3 619 2.310 2.776 No Standard 3 530 7 F-20 & 0.34 SRA 3 533 -0.081 2.776 No Standard 3 718 8 F-20 & 0.38 SRA 3 681 0.860 2.776 No Standard 3 518 9 F-35 & 0.46 SRA 3 540 -0.612 2.776 No Standard 3 523 10 F-35 & 0.41 SRA 3 483 2.041 2.776 No Standard 3 522 11 F-20 & 0.46 SRA 3 546 -0.870 2.776 No Standard 3 568 12 S-50 & F20 & 0.28 SRA 3 585 -0.760 2.776 No Standard 3 713 13 S-50 & 0.41 SRA 3 535 4.372 2.776 Yes Standard 3 524 14 F-35 & 0.30 SRA 3 498 1.661 2.776 No Standard 3 769 15 C-100 & 0.29 SRA 3 565 4.040 2.776 Yes

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130 Table 6-8. Results of t-Test on the Modulus of Elasticity at 14 days of the SRA Mixtures Versus the Standard Mixtures Mix Admixture & w/c Type Sample size Mean tCalculated tCritical for 95% Confidence Significantly Different Standard 2 5535946 1 S-50 & 0.33 SRA 2 5716239 -1.730 2.776 No Standard 2 7285077 2 S-70 & 0.25 SRA 2 7035076 1.562 2.776 No Standard 2 4082624 3 S-70 & 0.30 SRA 2 4193226 -3.440 2.776 Yes Standard 2 3901191 4 F-20 & 0.33 SRA 2 3766512 5.031 2.776 Yes Standard 2 3619022 5 F-35 & 0.33 SRA 2 3568982 0.963 2.776 No Standard 2 3512527 6 S-50 & F-20 & 0.35 SRA 2 3516542 -0.230 2.776 No Standard 2 4415257 7 F-20 & 0.34 SRA 2 3987853 4.730 2.776 Yes Standard 2 4259247 8 F-20 & 0.38 SRA 2 4584799 -2.594 2.776 No Standard 2 3536046 9 F-35 & 0.46 SRA 2 3661430 -1.470 2.776 No Standard 2 3481417 10 F-35 & 0.41 SRA 2 3614014 -8.401 2.776 Yes Standard 2 3844651 11 F-20 & 0.46 SRA 2 3635376 8.380 2.776 Yes Standard 2 4428530 12 S-50 & F-20 & 0.28 SRA 2 4559302 -2.630 2.776 No Standard 2 4935171 13 S-50 & 0.41 SRA 2 5001046 -0.431 2.776 No Standard 2 4395351 14 F-35 & 0.30 SRA 2 4329734 0.702 2.776 No Standard 2 5219490 15 C-100 & 0.29 SRA 2 5352441 -0.490 2.776 No Table 6-9 shows the results of the Pair ed t-test run on the compressive strength values of SRA and Standard mixtures to evalua te if there is no differences exist between the two pairs of the mixtures. The paired t-te st shows that there is significant difference exists between the compressive strengths of SRA mixtures and the Standard mixtures.

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131 Table 6-9 The paired t-test results for the Compressive Strength at 14 days The methodology for paired t-tests is as follows: Paired t-tests were run on 14 days propertie s for all 15 pairs of mixtures to examine if they were statistically di fferent from each other (Standard to SRA group) with respect to the mechanical properties that were examined. Compressive Strength (psi) Mixes 14 days Std SRA difference, di (di davg)2 1 7867 8260 -393 764689 2 8897 7233 1663 1397600 3 7527 6970 557 5706 4 7960 7920 40 194597 5 5587 5543 43 191668 6 6679 6282 397 7022 7 7427 6297 1130 420784 8 7453 7509 -56 288169 9 4746 4850 -103 341688 10 4701 4950 -249 533447 11 6016 5707 309 29629 12 7491 6692 798 100473 13 9384 8591 793 97139 14 5351 5056 294 34899 15 10664 8670 1994 2288587 davg = 481 6696097 n = 15 Sd = 692 Two-tailed test TCalculated = 2.69 At 0.05, TCritical = 2.145 Significant difference exists between Std and SRA Mixes

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132 For each pair t-test, the t stat istic was calculated as follows: davg tcalculated = Sd n Where davg is the average of the differences be tween the mechanical properties of Standard and SRA mixtures. Sd is the Standard Deviation of the pr operty values of Standard and SRA mixes n is the number of samples in either Standard or SRA group. Sd = sum(di davg)2 (n-1) The null hypothesis that the two means were equal to one another was tested at an level of 5%. The t value for n-1 degrees of freedom and level of 5% for a two-tail distribution was determined from the Student s t distribution tabl e and was denoted as tCritical. If the computed t value, tCalculated was smaller than tCritical, the null hypothesis could not be rejected, and the two means were considered to be statistically not different from one another. The table 6-10 illustrates that there is no significant difference exists between the SRA and Standard mixtures on their splitting tensile strengths. Also, table 6-11 shows that there is no significant difference exists between the SRA and Standard mixtures on their modulus of elasticity. However, the paired t-test for compressive strength, implies that there is difference existing between SRA and Standard mixtures. Further research is necessary to examine

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133 the possibility of using SRA as an shrinkage reducing admixture since it impacts the compressive strength of the concrete mixture. Table 6-10 The paired t-test results for the Splitting Te nsile Strength at 14 days Splitting Tensile Strength (psi) Mixes 14 days Std SRA di (di davg)2 1 614718 -104 19600 2 700600 100 4096 3 699640 59 529 4 695644 51 225 5 526494 32 16 6 686615 71 1225 7 555530 25 121 8 713652 61 625 9 533498 35 1 10 503516 -13 2401 11 473565 -92 16384 12 596595 1 1225 13 718572 146 12100 14 531498 33 9 15 689554 135 9801 davg = 36 68358 n = 15 Sd = 70 TCalculated = 2.00 At 0.05, TCritical = 2.145 No Significant difference between Std and SRA Mixes

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134 Table 6-11 The paired t-te st results for the Modulus of Elasticity at 14 days Modulus of Elasticity (psi) Mixes 14 days Std SRA di (di davg)2 1 5535946 5716239 -180293.41 43172227073 2 7285077 7035076 250001.63 49513265723 3 4082624 4193226 -110602.13 19068294332 4 3901191 3766512 134678.91 11490348920 5 3619022 3568982 50040.105 508693747 6 3512527 3516542 -4014.95 992301339 7 4415257 3987853 427403.895 159934430808 8 4259247 4584799 -325552.05 124635769349 9 3536046 3661430 -125384.4 23369317887 10 3481417 3614014 -132596.6 25626395565 11 3797122 3929110 -131988.2433 25431991193 12 4428530 4559302 -130771.53 25045403037 13 4935171 5001046 -65875 8716251093 14 4395351 4329734 65616.6 1453952960 15 5219490 5352441 -132950.8 25739923441 davg = 27486 544698566468 n = 15 Sd = 197249 TCalculated = 0.54 At 0.05, TCritical = 2.145 No Significant difference between Std and SRA Mixes

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1356.4 Evaluation of the Effects of Fly Ash and Ground Blast Furnace Slag The mix designs of all the 15 pairs of conc rete mixtures evaluated in the laboratory testing program are presented in Section 3.2. All the concrete mixtures had a fixed cementitious materials content of 700 lb/yd3 (415.7 kg/m3) of concrete. The composition of the mixtures varied mainly by the type and amount of mineral admixtures. The mixtures can be divided into four categories. The first category includes eight mixtures containing fly ash as a mineral admixture. Of these eight fly ash mixtures, four (Mixes 4, 7, 8 and 11) contained 20% fly ash, and four (Mixes 5, 9, 10 and 14) contained 35% fly ash. The second category includes the four mixtures containing ground blast furnace slag as a mineral admixture. Of these four slag mixtures, two (Mixes 1 & 13) contained 50% slag, and two (Mixes 2 &3) contained 70% slag. The third category includes two mixtures (Mixes 6 & 12) containing both fl y ash (20%) and slag (50%) as mineral admixtures. The fourth category is the refe rence mixture (Mix 15) containing no mineral admixture. The effects of the mineral admixtures on fr ee shrinkage of concrete were evaluated by comparing the free shrinkage strains of these four categories of concrete. Table 6-12

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136 shows the comparison of the means and the ra nges of the free shrinkage strains among the concrete in these four categ ories. It can be seen that the concrete mixtures containing fly ash had the lowest free shrinkage strains at both 3 days and 7 days curing, for both the standard mixes and the SRA mixes. The conc rete mixtures containing slag generally had the highest free shrinkage strains among the four categories of concrete evaluated. The concrete mixtures containing both slag and fly ash generally had about the same free shrinkage strains as those of the concrete containing no mineral admixture. These two categories of mixes had relatively lower free shrinkage strains as compared with the concrete containing slag, and relatively higher free shrinkage strains as compared with the concrete containing fly ash. Table 6-12. The Statistical Ranges of Free Sh rinkage Strains of the Concrete Mixtures With Different Mineral Admixtures Ranges of Free Shrinkage Strains in Microstrains 3 days 7 days Admixtures Highest Lowest MeanRangeHighest Lowest MeanRange Standard Fly ash 142 68 101 74 254 162 213 92 Slag 222 163 197 58 390 300 333 90 Fly ash + Slag 193 45 119 148 314 240 277 75 None N/A N/A 149 N/A N/A N/A 228 N/A SRA Fly ash 44 18 32 26 123 58 93 65 Slag 97 82 89 15 219 167 188 52 Fly ash + Slag 83 13 48 71 164 141 152 23 None N/A N/A 75 N/A N/A N/A 124 N/A Table 6-13 shows the comparison of the m eans and the ranges of the computed shrinkage-induced stresses among the four categories of concrete It can be seen that the concrete mixtures containing fly ash had th e lowest shrinkage-induced stresses at both 3 days and 7 days curing, for both the standard mixes and the SRA mixes. The concrete

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137 mixtures in the other three categories did not show any clear rankings among themselves with regards to the shrinkage-induced stresses. Table 6-13. The Statistical Ranges of Co mputed Shrinkage-Induced Stresses of the Concrete Mixtures with Di fferent Mineral Admixtures Ranges of computed shrinkage-induced stress in psi 3 days 7 days Admixtures Highest Lowest Mean Range Highest Lowest Mean Range Standard Fly ash 361 118 262 243 758 497 615 261 Slag 682 362 567 320 1413 908 1133 505 Fly ash + Slag 1314 549 932 766 999 753 876 247 None N/A N/A 552 N/A N/A N/A 936 N/A SRA Fly ash 127 53 91 74 417 204 284 212 Slag 304 95 230 209 813 394 685 419 Fly ash + Slag 246 127 187 118 947 568 757 380 None N/A N/A 266 N/A N/A N/A 508 N/A

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138 CHAPTER 7 SUMMARY AND RECOMMENDATIONS 7.1 Development and Evaluation of the Modified Constrained Long Specimen Apparatus The constrained long specimen apparatus, which was previously developed for the FDOT by the University of Florida for evalua tion of resistance to shrinkage cracking of concrete, was further refined and evaluated in this study. Four main refinements were made to the test appa ratus and procedure. First, the long constrained specimen appa ratus was refined by, (1) replacing the Whittemore gage, which was used to measure the deformation of the specimen, by a high-sensitivity Linear Variab le Differential Transformer (LVDT); and (2) replacing the proving ring, which was used to measure th e induced force in the constrained long specimen, by a load cell. The outputs from the LVDT and the load cell were connected to an automatic data acquisition system, which can be set up to take readings at specified time intervals and for a specified length of time. One observed problem with the constraine d long specimen apparatus was that the long concrete specimen appeared to be sticking to the steel plate below it. The second refinement to the apparatus was made to address this problem. A water-resistant and low-friction Teflon sheet was used as the ba se plate of the long constrained specimen apparatus to minimize the friction between the concrete specimen and its supporting base. The use of Teflon sheets as base plates app eared to give good results, and was adopted. The constrained long specimen apparatus using LVDT for strain measurement had one drawback in that the LVDT could not be placed on the specimen until after the concrete has attained sufficient strength. Thus, the shrinkage of the concrete in the very

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139 early age could not be measured. The third refi nement was made to address this issue. In order to monitor the shrinkage of concrete at its very early age after placement, an embedment strain gage was used in place of the LVDT for strain measurement in the long specimen apparatus. The use of the em bedment strain gages for strain measurement gave satisfactory performance, and thus was adopted. Another observed problem was that the l ong specimen apparatus was not able to provide complete restraint to the concrete spec imen to keep it from contracting during the constrained shrinkage test. Due to the c ontraction of the specimen during the test, a complete restrained condition was not achieved as intended. A modification to the test procedure was made to provide the correcti on to the specimen c ontraction by manually pulling the specimen (by turning a nut on a threaded rod on the test apparatus) during the test such that the strain in the specimen woul d be kept as close to zero as possible. The strain reading from the strain gage was used as a guide on how much the specimen needed to be pulled. This manual method of correcting the contra ction strains in the constrained long specimen appeared to give acceptable results. Thus, this method was adopted for use in the laboratory te sting program of this study. 7.2 Evaluation of Different Methods of Free Shrinkage Measurement Five different methods for measuring free sh rinkage of concrete were evaluated. These five methods were: (1) Whittemore gage in the long specimen apparatus; (2) LVDT in the long specimen apparatus; (3) embedment strain gage in the long specimen apparatus; (4) Whittemore gage on a 6 12-in. (152.4 304.8-mm) cylindrical specimen; and (5) LVDT on a 3 3 11.25-in. (76 76 286-mm) square prism specimen according to ASTM C157 procedure.

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140 Free shrinkage measurements using these fi ve different methods were made on the 15 pairs of concrete mixtures (with and without the addition of a shrinkage-reducing admixture) used in this study. From th e comparison of the free shrinkage strain measurements using the different methods, th e strain measurements using the embedment strain gage in the long specimen apparatus show ed the best repeatabil ity with the lowest variance. The embedment strain gage met hod also has the advantage that the strain measurements can be made from a very early age of the concrete. Thus, the embedment gage method was used for measurement of fr ee shrinkage and for measurement of strain in the constrained long speci men test in this study. 7.3 Evaluation of the Effects of a Shrinkage-Reducing Admixture Fifteen pairs of concrete mixtures (with and without the addition of a shrinkagereducing admixture, SRA) were evaluated for their free shrinkage, resistance to shrinkage cracking, compressive strength, splitting tensile strength and modulus of elasticity. The results from the free shrinkage test indicat e that the addition of SRA reduced the free shrinkage substantially for all mixes. The pe rcentage reduction varies from 41 to 81% at 3 days, from 32 to 70% at 7 days, and from 23 to 43% at 14 days. The results from the constrained long speci men test indicate that the SRA mixtures had substantially lower computed induced shrinkage stresses than their corresponding standard mixtures. The results predict that 6 of the 15 standard mixtures would have cracked within 3 days under a fully cons trained condition, wh ile none of the SRA mixtures would have cracked under a simila r condition. The percentage reduction of computed induced shrinkage stresses due to the addition of SRA ranges from 20 to 88% with an average of 62% at 3 days curing. The percentage reduction ranges from 14 to

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141 66% with an average of 48% at 7 days curing. The percentage reduction ranges from 2 to 55% with an average of 27% at 14 days curing. The results of Students t-te st for 14 days compressive st rength indicate that the SRA mixtures are significantly di fferent from the Standard mixtures. However, for all 15 pairs of mixtures evaluated, the splitting tens ile strength and modulus of elasticity of the SRA mixtures at 14 days were not significantly different fr om those of the standard mixtures. 7.4 Evaluation of the Effects of Fly Ash and Ground Blast Furnace Slag The mixtures evaluated in this study can be divided into four cat egories. The first category includes eight mixtures containing 20 to 35% fly ash as a mineral admixture. The second category includes the four mixt ures containing 50 to 70% ground blast furnace slag. The third category includes two mixtures containing both fly ash (20%) and slag (50%) as mineral admixtures. The fourth category is the reference mixture containing no mineral admixture. Among the four categories of concrete eval uated, the concrete mixtures containing fly ash showed the lowest free shrinkage strain s. The concrete mixtures containing slag generally had the highest free sh rinkage strains. The concre te mixtures containing both slag and fly ash generally had about the sa me free shrinkage strains as those of the concrete containing no mineral admixture. The concrete containing fly ash also showed the lowest shrinkage-induced stresses. The concrete mixtures in the other three categories did not show any clear rankings among themselves with regards to the shrinka ge-induced stresses. All these obs ervations indicate that addition of fly ash appeared to improve the resistance to shrinkage cracking

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142 of concrete. The results also indicate that the addition of ground blast furnace slag did not appear to improve the resistance to shrinkage cracking of concrete. 7.5 Recommendations The following recommendations are made based on the results of this study: 1. The addition of a shrinkage-reducing admixture should be considered in the design of a concrete mixture for increa sed resistance to shrinkage cracking. 2. The addition of fly ash as a minera l admixture should be considered in the design of a concrete mixture for incr eased resistance to shrinkage cracking. 3. While the developed modified cons trained long specimen apparatus was shown to be effective in evaluating the free shrinka ge and resistance to shrinkage cracking of concrete in this study, the test procedure was somewhat laborious and time consuming due to the need to manually correct for the cont raction strains in the long specimen. It is recommended that the apparatus be further refined such that the correction for the contraction strains can be done automatically rather than manually. It is recommended that a computer controlled servo-hydraulic ac tuator be used to pu ll the long specimen to correct for the possible c ontraction strains automatically. The outputs from the embedment strain gage in the long specimen can be read into the computer, which in turn can use this information to control the move ment of the actuator to correction for the contraction strains in the constrained long specimen.

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143 APPENDIX ORIGINAL READINGS The samples of original readings are provided in the form of tables in this section. The sample reading from the readings obtai ned directly from Da ta Acquisition Systems when LVDTs and Embedded gages were used are presented. The tables in the first page, second page and the third page represent th e readings for the LVDTs, Load-Cell and Large LVDTs respectively. The numbers on the first row of each table indicates the module number as well as channel number in the DAS (Data Acquisi tion System). For example 101 means that the first 1 represen ts the module one and 01 represents the channel number 1 in the DAS. The Time stam p gives the real time shown on the display panel of the DAS. VDC means the DC Voltage. 101(Time stamp) 101(Seconds)101(VDC)102(Time stamp) 102(Seconds) 102(VDC) 03:59.2 0.136 1.64E-01 03:59.4 0.305 7.49E-01 18:59.1 900.003 1.63E-01 18:59.1 900.054 7.25E-01 33:59.1 1800.003 1.59E-01 33:59.1 1800.054 7.40E-01 48:59.1 2700.003 1.56E-01 48:59.1 2700.054 7.25E-01 03:59.1 3600.003 1.59E-01 03:59.1 3600.054 7.23E-01 18:59.1 4500.003 1.51E-01 18:59.1 4500.054 7.33E-01 03:59.1 7200.003 1.55E-01 03:59.1 7200.054 7.17E-01 18:59.1 8100.003 1.80E-01 18:59.1 8100.054 7.66E-01 33:59.1 9000.003 1.94E-01 33:59.1 9000.054 7.83E-01 48:59.1 9900.003 2.09E-01 48:59.1 9900.054 7.96E-01 03:59.1 10800.003 2.17E-01 03:59.1 10800.054 8.04E-01 18:59.1 11700.003 2.26E-01 18:59.1 11700.054 8.08E-01 33:59.1 12600.003 2.13E-01 33:59.1 12600.054 7.76E-01 48:59.1 13500.003 1.98E-01 48:59.1 13500.054 7.59E-01 03:59.1 14400.003 1.85E-01 03:59.1 14400.054 7.52E-01 18:59.1 15300.003 1.74E-01 18:59.1 15300.054 7.45E-01 33:59.1 16200.003 1.75E-01 33:59.1 16200.054 7.41E-01 48:59.1 17100.003 1.72E-01 48:59.1 17100.054 7.43E-01 03:59.1 18000.003 1.77E-01 03:59.1 18000.054 7.42E-01

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144 111(Time stamp) 111(Seconds) 111(VDC) 112(Time stamp) 112(Seconds) 112(VDC) 03:59.9 0.836 -5.42E-03 03:59.9 0.887 -2.08E-03 18:59.6 900.512 -5.41E-03 18:59.6 900.562 -2.01E-03 33:59.6 1800.511 -5.31E-03 33:59.6 1800.562 -1.85E-03 48:59.6 2700.511 -5.23E-03 48:59.6 2700.561 -1.74E-03 03:59.6 3600.511 -5.18E-03 03:59.6 3600.561 -1.63E-03 18:59.6 4500.511 -5.15E-03 18:59.6 4500.562 -1.57E-03 03:59.6 7200.511 -5.11E-03 03:59.6 7200.561 -1.49E-03 18:59.6 8100.511 -5.14E-03 18:59.6 8100.562 -1.54E-03 33:59.6 9000.511 -5.18E-03 33:59.6 9000.562 -1.60E-03 48:59.6 9900.511 -5.20E-03 48:59.6 9900.562 -1.66E-03 03:59.6 10800.511 -5.23E-03 03:59.6 10800.561 -1.71E-03 18:59.6 11700.511 -5.25E-03 18:59.6 11700.562 -1.75E-03 33:59.6 12600.51 -5.24E-03 33:59.6 12600.561 -1.76E-03 8:59.6 13500.51 -5.21E-03 48:59.6 13500.561 -1.73E-03 03:59.6 14400.511 -5.19E-03 03:59.6 14400.562 -1.71E-03 18:59.6 15300.51 -5.18E-03 18:59.6 15300.561 -1.70E-03 33:59.6 16200.511 -5.17E-03 33:59.6 16200.562 -1.69E-03 48:59.6 17100.511 -5.16E-03 48:59.6 17100.562 -1.69E-03 03:59.6 18000.511 -5.16E-03 03:59.6 18000.562 -1.68E-03 18:59.6 18900.511 -5.19E-03 18:59.6 18900.562 -1.72E-03 33:59.6 19800.512 -5.21E-03 33:59.6 19800.562 -1.76E-03 48:59.6 20700.511 -5.23E-03 48:59.6 20700.561 -1.79E-03 03:59.6 21600.511 -5.26E-03 03:59.6 21600.562 -1.83E-03 18:59.6 22500.511 -5.28E-03 18:59.6 22500.561 -1.87E-03 33:59.6 23400.511 -5.30E-03 33:59.6 23400.562 -1.90E-03 48:59.6 24300.51 -5.28E-03 48:59.6 24300.561 -1.89E-03 03:59.6 25200.511 -5.22E-03 03:59.6 25200.562 -1.83E-03

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145 211(Time stamp) 211(Seconds) 211(VDC) 212(Time stamp) 212(Seconds) 212(VDC) 04:01.32.211-5.56E-01 04:01.32.262 -6.08E-01 19:00.5901.469-5.59E-01 19:00.6901.52 -6.11E-01 34:00.61801.544-5.62E-0134: 00.61801.595 -6.14E-01 49:00.52701.468-5.64E-0149: 00.62701.519 -6.17E-01 04:00.53601.469-5.66E-0104: 00.63601.519 -6.19E-01 49:00.56301.463-5.71E-0149: 00.66301.514 -6.23E-01 04:00.57201.465-5.71E-0104: 00.67201.515 -6.23E-01 19:00.68101.577-5.67E-0119: 00.78101.628 -6.18E-01 34:00.59001.466-5.62E-0134: 00.69001.516 -6.13E-01 49:00.79901.612-5.57E-0149: 00.79901.663 -6.08E-01 04:00.510801.46-5.53E-01 04:00.610801.51 -6.03E-01 19:00.511701.46-5.49E-01 19:00.611701.52 -5.98E-01 34:00.512601.46-5.46E-01 34:00.612601.52 -5.95E-01 49:00.513501.46-5.47E-01 49:00.613501.51 -5.97E-01 04:00.514401.46-5.48E-01 04:00.614401.52 -5.98E-01 19:00.515301.46-5.49E-01 19:00.615301.51 -6.00E-01 34:00.516201.46-5.50E-01 34:00.616201.51 -6.00E-01 49:00.517101.46-5.52E-01 49:00.617101.52 -6.01E-01 04:00.518001.46-5.53E-01 04:00.618001.52 -6.02E-01 19:00.618901.58-5.51E-01 19:00.718901.63 -5.99E-01 34:00.619801.54-5.49E-01 34:00.619801.59 -5.97E-01 49:00.520701.47-5.47E-01 49:00.620701.52 -5.96E-01 04:00.521601.46-5.44E-01 04:00.621601.52 -5.92E-01 19:00.522501.46-5.41E-01 19:00.622501.52 -5.89E-01 34:00.523401.46-5.39E-01 34:00.623401.52 -5.86E-01 49:00.524301.46-5.38E-01 49:00.624301.52 -5.86E-01 04:00.525201.47-5.43E-01 04:00.625201.52 -5.92E-01 19:00.526101.46-5.48E-01 19:00.626101.51 -5.96E-01 34:00.527001.46-5.49E-01 34:00.627001.51 -5.95E-01 49:00.527901.47-5.47E-01 49:00.627901.52 -5.92E-01 04:00.528801.46-5.46E-01 04:00.628801.51 -5.90E-01 19:00.529701.47-5.44E-01 19:00.629701.52 -5.89E-01 34:00.530601.46-5.43E-01 34:00.630601.51 -5.88E-01 49:00.531501.47-5.43E-01 49:00.631501.52 -5.88E-01 04:00.532401.46-5.45E-01 04:00.632401.51 -5.92E-01

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146 LIST OF REFERENCES Adams, T. H. 1988. Marketing of fly ash conc rete. In MSU seminar: Fly ash applications to concrete (January), 1.10, 5.10. East Lansing: Michigan State University Aitcin, P. C. 1998. High Performa nce Concrete. E & FN Spon, London. Almudaiheem, J. A., and Hansen, W. 1987. Effect of specimen size and shape on drying shrinkage. ACI Materials Journal, Vol. 84, No. 2, pp. 130-135. Alsayed, S. H. 1998. Influence of superpla sticizer, plasticizer, and silica fume on the drying shrinkage of high strength concrete subjected to hot-dry field conditions. Cement and Concrete Research, Vol. 28, No. 10, pp. 1405-1415. Balogh, A. 1996. New admixture combats c oncrete shrinkage. Aberdeens Concrete Construction, Vol. 41, No. 75, pp. 1051-5526. Bazant, Z. P., and Carol, I., eds. 1993. Proceedings. Fifth International RILEM Symposium on Creep and Shri nkage of Concrete, September 6-9, pp. 27 31. Barcelona Spain. Bazant, Z. P., ed. 1986. Proceedings. Fourth RILEM International Symposium on Creep and Shrinkage of Concrete: Math ematical Modeling, August 26-29, pp. 120 126. Northwestern University. Bentz D. P., Geikerb, M. R., and Hansenb, K. K. 2001. Shrinkage-reducing admixtures and early-age desiccation in cement pastes and mortars. Cement and Concrete Research, Vol. 31, pp. 1075-1085. Berke, N. S., Dallaire, M. C., Hicks, M. C ., and Kerkar, A. 1997. New developments in shrinkage-reducing admixtures, superplastic izers and other chemical admixtures in concrete. Proceedings. Fifth CANMET/ ACI International Conference, Rome, Italy, pp. 115-123. Bernader, S., and Emborg, M. 1995. Risk of cracking in massive concrete structures, new developments and experiences. Proceedings. International Symposium Thermal Cracking in Concrete at Early Ages, Munich, Germany, edited by R. Springenschmidt.

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147 Bloom, R., and Bentur, A. 1995. Free a nd restrained shrinkage for normal and high strength concretes. ACI Materials Journal, Vol. 92, No. 2, pp. 211-217. Boral Materials Technologies, Inc., 2003 Bora l_Class_F_Fly ash. Brochure issued by Boral Materials Technologies, Inc., Found in the website http://www.boralmti.com/ProductSh eets/Boral_Class_F_Fly_Ash.pdf Viewed on 5/5/2005 Davis, R. E., R. W. Carlson, J. W. Kelly, and A. G. Davis. 1937. Properties of cements and concretes containing fly ash. Proceed ings, American Conc rete Institute 33:577612. Duran, A. C., Kilic, A., and Sevim, U. K. 2004. Strength and sh rinkage properties of mortar containing a nonstandard high-calci um fly ash. Cement and Concrete Research, Vol. 34, pp. 99-102. Emborg, M. 1989. Thermal stresses in concrete structures at early ages. Ph.D. Thesis. Lulea University, Sweden. Folliard, K. J., and Berke, N. S. 1997. Properties of high-performance concrete containing shrinkage-reducing admixture. Ce ment and Concrete Research, Vol. 27, No. 9, pp. 1357-1364. Gani M.S.J. 1997. Cement and Concrete. Chapman and Hall Publishers. Chapter 9 pp.112. Halstead, W. J. 1986. Use of fly ash in concrete. NCHRP 127 (O ctober). Washington: Transportation Research Board, National Research Council. Han, N., and Walraven, J. C. 1996. Creep and shrinkage of high-st rength concrete at early and normal ages. Adva nces in Technology, pp. 73-94. Haque, M. N. 1996. Strength developmen t and drying shrinkage of high strength concretes. Cement and Concrete Composites, Vol. 18, No. 5, pp. 333-342. Kohubu, M. 1968. Fly ash and fly ash cement. In Proceedings, Fifth international symposium on the chemistry of cement Tokyo: Cement Association of Japan. Part IV, pp. 75-105. Kraai, P. P. 1985. Proposed test to dete rmine the cracking potential due to drying shrinkage of concrete. Concrete Construction, Vol. 30, No. 9, pp. 775-778. Lyman, G. C. 1934. Growth and Movement in Portland Cement Concrete. Oxford, University Press, London, U. K., pp. 1-139.

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148 Malhotra V. M. 2004. Properties of the hi gh-volume fly ash concre te, and its role in sustainability of cement and concrete Proceedings. Recent Advances in Cementitious Materials sponsored by Univer sity of Wisconsin at Milwaukee Center for By-Products Utilization, March 19-20. Mehta, P. K. 1986. Concrete: Structures Properties and Materi als, Prentice-Hall, Englewood Cliffs, N. J., Chapters 6 and 8. Mehta, P. K., and Monteiro, P. J. 1993. C oncrete: Structures, Prope rties, and Materials, 2nd Edition. Prentice-Hall Englewood Cliffs, N.J. Mindess Sidney, J. Francis Young and David Darwin, 2003. Concrete, 4th Edition, Prentice Hall, Upper Saddle River, NY. Chapter 16, pp. 417 432. Mindess, S., and Young, J. F. 1981. Concre te. Prentice-Hall, Englewood Cliffs, N.J., 671 pp. Neville, A. M. 2000. Properties of Concrete, 4th Edition. Addison Wesley Longman, Essex, England. Persson, B. 1998. Self-desiccation and its im portance on concrete technology. Nordic Concrete Research, Vol. 21, pp. 120129. http://lu-research.lub.lu.se/php/gateway.php?who=lr&method=getf ile&file=archive/00014056/ Powers, T. C., and Brownyard T. L. 1948. Studies on the physical properties of hardened Portland cement paste. PCA Bulletin 22, Chicago, Illinois. Saito, M., Kawamura, M., and Arakawa, S. 1991. Role of aggregate in the shrinkage of ordinary Portland and expansive cement concrete. Cement and Concrete Composites, Vol. 13, No. 2, pp. 115-121. Schaels, C. A., and Hover, K. C. 1988. Influence of mix propor tions and construction operations on plastic shrinkage cracking in th in slabs. ACI Material Journal, Vol. 85, Nov-Dec, pp. 495-504. Shah, S. P., Karaguler, M. E., and Sarigaphuti, M. 1992. Effects of shrinkage reducing admixtures on restrained shrinkage cracki ng of concrete. ACI Materials Journal, Vol. 89, No. 3, pp. 291295. Shilstone, J. M. 1999. The aggregate: Th e most important valu e-adding component in concrete. Proceedings. Seventh Annual International Center for Aggregates Research Symposium, Austin, Texas. Shilstone, Sr., J. M. 1990. Concrete mixt ure optimization. Concrete International: Design and Construction, Vol. 12, No. 6, June, pp. 33-39.

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149 Springenschmidt, R., Gierlinger, E., and Ker nozycki, W. 1985. Thermal stress in mass concrete: A new testing method and th e influence of different cements. Proceedings. The 15th International Congr ess for Large Dams, Lausanne, R4, pp. 57-72. Swamy, R. N., and Stavardes, H. 1979. In fluence of fiber reinforcement on restrained shrinkage cracking. ACI Journal, Vol. 76, No. 3, pp. 443-460. Tangtermsirikul, S., Sudsangium, T., and Nim ityongsakul, P. 1995. Class C fly ash as a shrinkage reducer for cement paste. Proceedings. Fifth CANMET/ACI International Conference on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, June 4-9, Milwaukee, Wisconsin, Vol. 1, pp. 385-401. Tazawa, E., and Miyazawa, S. 1995. Influe nce of cement and admixture on autogenous shrinkage of cement paste. Cement Concrete Research, Vol. 25, No. 2, pp. 281287. Tazawa, E., and Miyazawa, S. 1997. Effect of self-desiccation on volume change and flexural strength of cement paste and mortar Proceedings. International Research Seminar on Self-Desiccation and Its Importa nce on Concrete Technology, held in Lund, Sweden. Tazawa, E., and Miyazawa, S. 1997. Influence of constituents and composition on autogenous shrinkage of cementitious material s. Magazine of Concrete Research, Vol. 49, No. 178, pp. 15-22. Tazawa, E., and Yonekura, A. 1986. Drying shrinkage and creep of concrete with condensed silica fume. Proceedings. Th e 2nd International C onference on the Use of Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Madrid, Vol. 2, pp. 903-921. Tazawa, E., ed. 1998. Autoshrink-98. Proceedings. International Workshop on Autogenous Shrinkage of Concrete, Japan Concrete Institute, Hiroshima, Japan June 13-14, 358 pp. Tia Mang, Tu-Ming Leung and Daniel Darku. 1998. Development of a Laboratory Procedure for Evaluating Concrete Mixes for Resistance to Shrinkage Cracking in Service. U.F. Project No. 4910450456012. Tia Mang, Tu-Ming Leung, Daniel Darku and Michael J. Bergin. 1999. An Effective Laboratory Procedure For Evaluating Concre te Mixes For Resistance to Shrinkage Cracking in Service. Proceedings. Wo rld Engineering Congress and Exhibition, Kuala Lumpur, Malaysia. July, 1999. pp. 215-220. Troxell, G., Harmer, D., and Kelly, J. 1996. Composition and Properties of Concrete, 2nd edition. McGraw-Hill, New York, pp. 290-320.

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150 Van Breugel, K., and de Vries, J. 1998. Mixture optimization of low water/cement ratio high strength concretes in view of aut ogenous shrinkage. Proceedings. International Symposium on High Performan ce and Reactive Powder Concrete, Sherbrooke, Canada, pp. 365-382. Washa, G. W. 1998. Volume Changes, Chapter 9, Concrete Construction Handbook,4th edition. Dobrowolski, J., ed. McGraw-Hill, New York. Weiss, W. J. 1999. Prediction of early-age shrinkage cracking in concrete elements. Ph.D. Thesis. Northwestern University, Evanston, IL. Wiegrink, K., Marikunte, S., and Shah, S. P. 1996. Shrinkage cracking of high strength concrete. ACI Materials Journal, Vol. 93, No. 5, pp. 409-415. Yunsheng, Xu, D.D.L. Chung. 2000. Reducin g the drying shrinkage of cement paste by admixture surface treatments. Cement and Concrete Research, vol. 30, pp. 241245. Yunsheng, Xu, D.D.L. Chung. 2001. Silane-tr eated carbon fiber for reinforcing cement. Carbon, Vol. 39, Nov., pp. 1995-2001.

PAGE 167

151 BIOGRAPHICAL SKETCH Rajarajan Subramanian graduated with his b achelors degree in civil and structural engineering from Annamalai University, India, in the year 1982. He started his career as as a Lecturer in the Civil Engineering Depart ment at Annamalai University. After nine years, he moved to the United States to do his masters degree in civil engineering with a specialization in transportation engineering. He graduated w ith a masters degree in civil engineering at the Univers ity of Florida in 1993. After a brief stint in India (for about one year), as a Senior Lecturer in a private engineering college, he went to Malaysia to work as a Senior Lecturer in a private engineering college. He spent three years teaching civil engineering courses to undergraduate students and again he moved back to the United States for doing his PhD in civil engineering at the University of Florida.


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EVALUATION OF SHRINKAGE CRACKING POTENTIAL OF CONCRETE USED
IN BRIDGE DECKS IN FLORIDA















By

RAJARAJAN SUBRAMANIAN


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA


2006

































Copyright 2006

by

RAJARAJAN SUBRAMANIAN

































This document is dedicated to my parents Subramanian Balakrishnan and Udaya
Subramanian













ACKNOWLEDGMENTS

I have immense pleasure in thanking the persons and organizations that helped me

over the course of time to bring my PhD thesis to the final form. My sincere thanks go to

Dr. Fazil T Najafi, chair of my committee, for his valuable support throughout my study

at the University of Florida. I thank Dr. Mang Tia, the cochair of my committee, for his

valuable advice and suggestions throughout the research study and dissertation. The

Florida Department of Transportation (FDOT) is gratefully acknowledged for providing

the financial support, testing equipment, materials and personnel that made this research

possible. I would like to express my sincere appreciation to my supervisory committee

members Dr. Andrew J. Boyd, Dr. Ajay Shanker and Mr. Peter Kopac (FHWA Research

Engineer) for their invaluable guidance and support throughout my research at the

University of Florida. I would also like to express my gratitude to Dr. Jonathan Earle for

his continuous encouragement and support.

Also, I would like to thank all my colleagues in the materials section in Civil And

Coastal Engineering Department. Messrs. Chuck Broward and Danny Brown were

acknowledged for their help with the setup of instrumentation to conduct the tests.

The Florida Department of Transportation personnel Messrs. Michael Bergin,

Charles Ishee, Mario Paredes, Richard Delorenzo, Toby Dillow, Joseph Fitzgerald, and

Craig Roberts are acknowledged for their help with the entire process of conducting the

various tests. W. R. Grace & Co. is acknowledged for providing the shrinkage-reducing

admixture, water-reducing admixture and air-entraining admixture used in this study.

Last, but certainly not least, I would like to thank my wife, my daughter, my parents, my












brother and his wife, my sisters and their husbands. They have been very patient and

supportive.















TABLE OF CONTENTS

Page

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

LIST OF TABLES ............... .. ...... ........ .. ........ .......... .......... .... ....

L IST O F F IG U R E S .... ...... ................................................ .. .. ..... .............. xii

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

CHAPTER

1 IN T R O D U C T IO N ................. .................................. .... ....... .. ............. .

1.1 B background ................................................................ .......1
1.2 Problem Statem ent .................................................... .... .. ........ ..
1.3 Study Objectives ............ ........ ...... ................. .................... .. .3

2 LITER A TU RE R EV IEW ............................................................. ....................... 4

2 .1 Introduction ................................ .. ........................... ............ ... .4
2.2 Mechanism of Concrete Shrinkage and Cracking ...............................................4
2.3 Types of shrinkage ...................... ...... ............ ........ ........ .. ............ .5
2.4 Influence of Aggregates on Concrete Shrinkage...................... ................7
2.5 Influence of Cement on Concrete Shrinkage .................................................8
2.6 Influence of Water Content on Concrete Shrinkage ................ ...................
2.7 Influence of Specimen size and Shape on Concrete Shrinkage...........................9
2.8 Admixtures that affect Shrinkage ......................... ........... ............. 10
2.8.1 M ineral A dm ixtures...................... .. .. .......... .. ...................... ...........10
2.8.1.1 Fly ash ...................... ...................... ..................................11
2 .8.1.2 Silica fum e ...................... .......................... .... ........................... 13
2 .8 .1 .3 S ila n e ............................................................................................ 1 4
2.8.1.4 O nada E xpan ...................... ....... ........ ..............................15
2.8.2 Chemical Admixtures ................................................................. 15

3 M A TER IA L S ...................... ............... ......................................... 19

3.1 Introduction ...................................................................... .. ........ .................. 19
3.2 Concrete M ixtures Evaluated ................................... ...............19
3.3 Concrete Mixture Constituents .......................... .......... .........36
3 .3 .1 W a te r ................................................................................................... 3 6















3.3.2 Fine A ggregate .................................... .................. ......... 36
3 .3 .3 C oarse A ggreg ate ........................................................... .....................37
3 .3 .4 C em ent ............................................................... ............. 38
3.3.5 Fly A sh ...........................................................39
3.3.6 G round B last-Furnace Slag ............................................ ............... 39
3.3.7 A ir-Entraining A dm ixture ........................................ ...... ............... 39
3.3.8 W ater-Reducing Admixtures ............... ............................................. 40
3.3.8.1 W R D A 64 .............................. ....................... ........... .. ............. 40
3.3.8.2 A dva Flow (Super plasticizer).......... ................................................ 40
3.3.9 Shrinkage-Reducing Admixture..................................... ............... 40
3.4 Preparation of Concrete M ixtures.................................... ........................ 41
3.4.1 M ixing of Concrete.............................. ......... .................................41
3.4.2 Preparation of Concrete Specimens for Mechanical Tests........................43
3.4.3 Preparation of Concrete Specimens for ASTM C157 Shrinkage Test......43
3.4.4 Preparation of Concrete Specimens for Long Specimen Tests ................43

4 LABORATORY TESTING PROGRAM................................................................44

4 .1 Intro du action ...................................... ............................................ 4 4
4 .2 T ests on F resh C oncrete............................................................ .....................44
4.3 Tests on H ardened C oncrete.................................................................... ..... 44
4.3.1 Compressive Strength Test ..........................................................45
4.3.2 M odulus of Elasticity Test .............. .............................................. 46
4.3.3 Splitting Tensile Strength Test.......................... ............................... 49
4.3.4 Free Shrinkage Measurement (ASTM C157) Using LVDTs ................50
4.3.4.1 Test Setup ................................... ........................ .... ..... 50
4 .3.4 .2 T est procedure .................. ......................... ........ ................. .... 54
4.3.5 Free Shrinkage Measured by Embedment Gage in the Long-Specimen
A p p aratu s ................................................................................. 5 5
4.3.5.1 Test setup ............................................................ ............... 55
4.3.5.2 Test procedure ............... ............................... ........... ...... ..... 57
4.3.6 Free Shrinkage Measurement using Whittemore Gage in the Long-
Specim en A pparatus ............................................................................ 58
4 .3 .6 .1 T est setu p .......................................... ................ 5 8
4.3.6.2 Test procedure ........................................... .... .. .............. .. ....... 59
4.3.7 Free Shrinkage Measurement Using Whittemore Gage on Cylindrical
S p e cim en s ................................................. ................ 6 0
4 .3 .7 .1 T est setu p .......................................... ................ 6 0
4 .3.7.2 T est procedure ....................... ........ ....... ...... ... ......... ..........60
4.3.8 Constrained Shrinkage Test Using the Long Specimen Apparatus...........64















5 DEVELOPMENT AND EVALUATION OF THE MODIFIED CONSTRAINED
LON G SPECIM EN A PPAR A TU S ................................................. .....................65

5 .1 Intro du action ......... .. ........ .. ... ....... .......... ................... ............... 6 5
5.2 Fundamentals of the Constrained Long Specimen Method..............................65
5 .2 .1 O rig in al D esig n ............................................................... ................ .. 6 5
5.2.1 Test Procedure ... .... ..... ..... .............................. .... .... ....... 66
5.2.3 M ethod of A analysis ................................................................................67
5.3 First Refinement of Apparatus Use of LVDT, Load Cell and Data
A acquisition System ................ .. ............................ ............ ........ .... 69
5.3.1 Changes M ade to the Original Design.................................. ... ......69
5.3.2 LVDTs for M easurement of Strain............... ...........................................72
5.3.3 Load Cell for M easurement of Stress......... ................... ..................... 76
5.3.4 Data Acquisition System ...................... ............................ 77
5.3.5 Modified Instrumentation for the LVDTs ...........................................80
5.3.6 Calibration of the LVDT/Signal Conditioner System ...............................81
5.4 Second Refinement of Apparatus Use of Lubricated Base Plate ...................83
5.5 Third Refinement of Apparatus Use of Embedment Strain Gages................86
5.5.1 Embedment Strain Gage...........................................................86
5.5.2 Strain Gage Signal Conditioner.................... ... ................. 86
5.6 Fourth Refinement of Apparatus Zeroing of Strain in the Constrained
S p ecim en ...................... .. .. ......... .. .. ......... ..................................8 9

6 RESULTS OF LABORATORY TESTING PROGRAM .......................................92

6 .1 In tro d u ctio n .............................................. ....... .......................................... 9 2
6.2 Evaluation of Different Methods of Free Shrinkage Measurement....................92
6.2.1 M ethods Evaluated ............................................................................. 92
6.2.2 Comparison of Test Results...................... ..................93
6.2.3 Observations on the Different Methods of Shrinkage Measurement....... 105
6.2.3.1 Whittemore gage on the long specimen ............ ... .................105
6.2.3.2 LVDT on the long specimen .............................. ................... 105
6.2.3.3 Embedment gage in the long specimen ................ ....... ........ 105
6.2.3.4 Whittemore gage on a cylindrical specimen ..............................106
6.2.3.5 ASTM C157 method using a LVDT ...............................106
6.2.4 R ecom m ended m ethod....................... .............. ............... ....107
6.3 Evaluation of the Effects of a Shrinkage-Reducing Admixture ........................107
6.3.1 Effects on Free Shrinkage ............................................ ............... 107
6.3.2 Effects on Shrinkage-Induced Stress...................................................... 112
6.3.3 Effects on Strengths and Elastic M odulus.............................................121
6.4 Evaluation of the Effects of Fly Ash and Ground Blast Furnace Slag ...........127















7 SUMMARY AND RECOMMENDATIONS.................... .................... 138

7.1 Development and Evaluation of the Modified Constrained Long Specimen
A apparatus .................. ............... ....................... ................. ..... 138
7.2 Evaluation of Different Methods of Free Shrinkage Measurement................139
7.3 Evaluation of the Effects of a Shrinkage-Reducing Admixture ..................140
7.4 Evaluation of the Effects of Fly Ash and Ground Blast Furnace Slag ...........141
7 .5 R ecom m en nation s................................................................... ..................... 142

APPENDIX

O R IG IN A L R E A D IN G S ..................................................................... .....................143

L IST O F R E FE R E N C E S ........................................................................ ................... 146

BIOGRAPHICAL SKETCH ........................................................... ........151
















LIST OF TABLES


Table

3-1. Mix Proportions for Mix -

3-2. Mix Proportions for Mix -

3-3. Mix Proportions for Mix -

3-4. Mix Proportions for Mix -

3-5. Mix Proportions for Mix -

3-6. Mix Proportions for Mix -

3-7. Mix Proportions for Mix -

3-8. Mix Proportions for Mix -

3-9. Mix Proportions for Mix -

3-10. Mix Proportions for Mix

3-11. Mix Proportions for Mix

3-12. Mix Proportions for Mix

3-13. Mix Proportions for Mix

3-14. Mix Proportions for Mix

3-15. Mix Proportions for Mix


3-15.

3-17.

3-18.

3-19.

3-20.


page

1 .............................................................. ....... ..... 2 1

2 .............................................................. ....... ..... .2 2

3 .............................................................. ....... ...... 2 3

4 .............................................................. ....... ..... .2 4

5 .............................................................. ....... ..... .2 5

6 .............................................................. ....... ..... .2 6

7 ....................................... ............ ..... .2 7

8 .............................................................. ....... ..... .2 8

9 .............................................................. ....... ..... .2 9

- 1 0 ..................................................... 3 0

- 1 1 ..................................................... 3 1

- 1 2 ..................................................... 3 2

- 1 3 ..................................................... 3 3

- 1 4 ..................................................... 3 4

- 1 5 ..................................................... 3 5


Physical Properties of Fine Aggregate .... .................... ..............37

Physical Properties of the Coarse Aggregate ............................... ...... ............ ...38

Physical Properties of the Type I Cement Used................................................ 38

Chemical Composition of the Type I Cement Used............................. .............38

Chemical Composition of the Class F Fly Ash Used.............................................39









3-21. Physical Properties of the Class F Fly Ash Used ......................................... 39

3-22. Chemical Composition of the Slag Used.................................... ............... 39

6-1. Free Shrinkage Strains of the 15 Pairs of Concrete Mixtures as Measured by the
D different M methods ...................... .... ................ ................... .... ....... 95

6-2. Percentage Reduction in Free Shrinkage Strains of the SRA Mixtures as
Compared With the Standard Mixtures as Measured by the Embedment Strain
G ages in the L ong Specim ens ..................................................... .....................108

6-3. Results of Constrained Long Specimen Test on the 15 Pairs of Concrete Mixturesl 13

6-4. Percentage Reduction of Computed Shrinkage-Induced Stresses of SRA Mixtures
as Compared W ith the Standard M ixtures .................................. ............... 120

6-5. Compressive Strength, Splitting Tensile Strength and Elastic Modulus of the 15
Pairs of Concrete M ixtures ......................................................... ............... 122

6-6. Results oft-Tests on the Compressive Strength of the SRA Mixtures Versus the
Standard M fixtures ...................... ...................... ..................... .. .... .. 128

6-7. Results oft-Tests on the Splitting Tensile Strength of the SRA Mixtures Versus
the Standard M fixtures ................................................. ............................... 129

6-8. Results oft-Test on the Modulus of Elasticity of the SRA Mixtures Versus the
Standard M fixtures ...................... ...................... ..................... .. .... .. 130

6-9. The Statistical Ranges of Free Shrinkage Strains of the Concrete Mixtures With
D different M ineral A dm ixtures ..................................................... ...... ......... 136

6-10. The Statistical Ranges of Computed Shrinkage-Induced Stresses of the
Concrete Mixtures with Different Mineral Admixtures ................. ...............137









LIST OF FIGURES


Figure pg

3-1. Gradation chart for the fine aggregate (Goldhead silica sand)............... ...............36

3-2. Gradation chart for the coarse aggregate (#89 limestone).............................37

3-3. C concrete m ixer used ............................................................... .... ... .... ..42

4-1. Set-up for com pressive strength test.................................... ........................ 45

4-2. Set-up for m odulus of elasticity test................................... ..................... .. .......... 47

4-2. Set-up for m odulus of elasticity test................................... ..................... .. .......... 47

4-3. Close-up view of elastic modulus test wet-up with a LVDT for strain
m easu rem en t................................................... ................ 4 8

4-4. Set-up for splitting tensile strength test ............................................ ...............49

4-5. Mold for 3 x 3 x 11.25-in. (76 x 76 x 286-mm) shrinkage test specimen ...............50

4-6 Set-up for ASTM C157 free shrinkage measurement using a LVDT........................ 52

4-7. Picture of several test setups for free shrinkage measurement using LVDTs ...........53

4-8. Schematics of test set-ups for measurement of free shrinkage using LVDTs...........53

4-9. Schematics for test setup for free shrinkage measurement using the
long-specim en apparatus. ...... ........................... .......................................55

4-10. Picture of two long-specimen molds .............. ........... .................................. 56

4-11. Whittemore gage for measuring the distance between two gage points..................58

4-12. Long concrete specimen with gage point studs installed .....................................59

4-13. G age-point positioning guide ............................................................................ 61

4-14. G auge-position guide............................................. .................. ............... 62

4-15. Plastic cylinder mold inside gauge-position guide...............................................63

4-16. Concrete cylinders with gauge point studs installed on them ................................64

5-1. The original constrained long specimen apparatus [Tia et al., 1998].....................66

5-2. Schematics of the restrained long specimen under contraction ..............................67









5-3. Constrained long specimen apparatus using a LVDT ............................................70

5-4. Top and side views of the constrained long specimen apparatus.............................71

5-5. Side and top views of the end collar block of the mold ................. .................71

5-6. Front and side views of the PVC side pieces for the constrained long specimen
apparatus ............................................................. .... ..... ........ 72

5-7. Aluminum bracket support for the gage studs that hold the LVDT and the core
rod holders to the concrete specim en ............................................ ............... 72

5-8. Cross-sectional view of an LVDT ................................ ........................ ......... 73

5-9. LVDT core displacement and the respective voltage change.................................74

5-10. LVDT holder and a portion of the rod that is connected to the other holder ..........75

5-11. The holder for the rod that passes through the LVDT core................................75

5-12. The load cell attached to the frame of the concrete specimen.............................77

5-13. Agilent 34970A data acquisition system unit ......................................................77

5-14-a. Setup for the constrained long specimen test with a LVDT .............................79

5-14-b. Setup for the constrained long specimen test with a LVDT and a loadcell .......79

5-15. A LVDT line powered LPC-2100 signal conditioner ..........................................81

5-16. Individual constrained long concrete specimen connected to an LVDT, LVDT
signal conditioner, DAS and the computer ................................... .................82

5-17. A plot of LVDT/conditioner output versus displacement (micrometer
reading g ) ............... ...................................... ............................ 83

5-18. Set-up for calibration of LVDTs used in the long specimens .............................84

5-19. Use of wax paper to reduce friction between concrete and base plate ..................85

5-20. Constrained long specimen apparatus with a Teflon base plate.............................85

5-22. Schematics of the constrained long specimen apparatus using an embedment
strain gage for strain measurement....................... ... ........................... 87

5-23. OMEGA OM2-163 Backplane 8-channel signal conditioner ...............................88

5-24. Manual pulling of a test specimen to correct for specimen contraction..................91









6-1. Free shrinkage strains as measured by Whittemore gage on the long specimens
for six stan d ard m ix es ................................................................. .................... 10 0

6-2. Free shrinkage strains as measured by LVDT on the long specimens for six
stan d ard m ix es ................................................. ................ 10 1

6-3. Free shrinkage strains as measured by embedment gages in the long specimens
for six standard m ixes ...................... .... ................... ...... .. ...............102

6-4. Free shrinkage strains as measured by Whittemore gage on the cylinders for six
stan d ard m ix es ................................................. ................ 10 3

6-5. Free shrinkage strains as measured by ASTM C157 Method for six standard
m ix e s ........................................................................... 1 0 4

6-6. Comparison of free shrinkage strains of Standard and SRA mixtures at 3 days
cu rin g ...................................... .................................................. 1 0 9

6-7. Comparison of free shrinkage strains of Standard and SRA mixtures at 7 days
cu rin g ...................................... .................................................. 1 1 0

6-8. Comparison of free shrinkage strains of Standard and SRA mixtures at 14 days
curing ..................................... ................................... ............... 111

6-9. Comparison of computed shrinkage-induced stresses of Standard and SRA
m ixtures at 3 days curing ...........................................................................118

6-10. Comparison of computed shrinkage-induced stresses of Standard and SRA
m ixtures at 7 days curing ...........................................................................119















Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

EVALUATION OF SHRINKAGE CRACKING POTENTIAL OF CONCRETE USED
IN BRIDGE DECKS IN FLORIDA

By

Rajarajan Subramanian

May 2006

Chair: Fazil T. Najafi
Cochair: Mang Tia
Major Department: Civil And Coastal Engineering

A research study was done to evaluate the different concrete mixtures that have

various different admixtures added for reducing the shrinkage in the concrete, and to

make recommendations for concrete mix designs for improved resistance to shrinkage

cracking in service. Also, an effective and convenient laboratory set-up and procedure

for evaluating concrete mixtures for their resistance to shrinkage cracking in service was

developed as a result of this study.

The results of the testing program indicated that the use of a shrinkage-reducing

admixture was effective in reducing the free shrinkage strains and shrinkage-induced

stresses of all the concrete mixtures tested, while the compressive strength, splitting

tensile strength and elastic modulus of the concrete were not significantly affected. The

addition of fly ash as a mineral admixture was found to be effective in reducing the free

shrinkage strain and shrinkage-induced stresses of all concrete mixtures. This research

study presents a very promising testing and analysis method for evaluating the potential









shrinkage-induced stresses in concrete and its potential for shrinkage cracking in service.

The developed Constrained Long Specimen (CLS) test method was used to evaluate the

effects of a shrinkage-reducing admixture on the potential shrinkage-induced stresses of

15 different concrete mixes and their potential for shrinkage cracking in service. From

the test data and the analysis results obtained from the 15 concrete mixes tested in this set

of experiments, the developed Constrained Long Specimen method demonstrated that it

provided reasonable assessment of expected shrinkage-induced stresses in the concrete.

Due to the creep of concrete at early age, the shrinkage-induced stress in the concrete is

much lower than that estimated by multiplying the shrinkage strain by the elastic

modulus of the concrete. Using the CLS test method enables the creep component to be

properly considered, and a realistic determination to be made of the expected induced

shrinkage stresses in concrete in service. The results of the CLS tests on the 15 concrete

mixes showed the possible benefits of using a shrinkage-reducing admixture in reducing

the potential shrinkage cracking of concrete in service.














CHAPTER 1
INTRODUCTION

1.1 Background

Shrinkage cracking of concrete bridge decks is a critical problem in Florida. Many

concrete bridge decks have been observed to develop plastic shrinkage cracks soon after

construction. These cracks shorten the service lives of the decks and increase the cost for

maintenance and repairs. In recent years, the increasing use of High-performance

concretes might have made this problem worse. High-performance concretes, which are

usually produced by using high cement content, are known to have higher free shrinkage

and are thus more likely to develop shrinkage cracking.

One of the possible solutions to this problem is to modify the concrete mix designs

so that the concretes could be less susceptible to shrinkage cracking while maintaining

their other high-performance properties. However, the tendency of concrete to shrinkage

cracking is not a simple function of its free shrinkage. It is also affected by factors such

as the constraint on the concrete, rate of strength gain, temperature and the elastic

modulus of the concrete. The creep of the concrete during its plastic stage can also

relieve some of the induced stress due to shrinkage. Because the creep counteracts the

shrinkage as a stress relaxation mechanism. All these factors need to be fully considered

in evaluating a concrete mix for its resistance to shrinkage cracking.

In a prior research project entitled "Development of a Laboratory Procedure for

Evaluating Concrete Mixes for Resistance to Shrinkage Cracking in Service," sponsored

by the FDOT, a testing and analysis method was developed for evaluation of concrete









mixes for resistance to shrinkage cracking. The developed testing procedures included

characterizing the tensile strength and elastic modulus of the concrete at early ages by

means of the conventional strength tests, and characterizing the creep, free shrinkage and

elastic properties of the concrete by means of a constrained long specimen apparatus,

which was developed as part of this project done by Mang Tia and Tu-Ming Leung.

Results from the above study show that the developed test method is very effective in

measuring the pertinent properties of concrete that are related to shrinkage cracking, and

is a very promising tool for evaluating the resistance to shrinkage cracking of concrete in

service. This testing and analysis method should be further evaluated, refined and

implemented as a standard procedure for evaluating shrinkage cracking resistance of

concrete used by FDOT.

1.2 Problem Statement

Concrete shrinkage is of growing concern when focusing on maintaining durable

structures. Over time, the shrinkage induces cracking, which can severely reduce

concrete life expectancy. These volume changes are often attributed to drying of the

concrete over a long time period. At early ages, the concrete is still moist and there are

difficulties in measuring the fluid material. These difficulties have hindered

comprehensive physical testing and understanding of the factors influencing shrinkage.

Shrinkage cracking is due to restrained shrinkage, and also, it is affected by the

constraints on the concrete, rate of strength gain, the aggregates, water, water to cement

ratio, and temperature of concrete. There is a lack of proper equipment with a well

defined standard procedure to measure the restrained shrinkage in concrete.









1.3 Study Objectives


The main objectives of this research are as follows:

1. To develop an effective and convenient laboratory setup and procedure for
evaluating concrete mixtures for their resistance to shrinkage cracking in service of
bridge decks in Florida.


2. To implement the developed testing and analysis method using the
developed constrained long specimen apparatuses as a standardized tool for evaluation of
shrinkage cracking resistance of concrete in Florida.


3. To evaluate the different concrete mixtures that have various different
admixtures added for reducing the shrinkage in the concrete.


4. To make recommendations for modification of concrete mix designs,
based on the evaluation of the different concrete mixtures that were used in bridge decks
of Florida for improved resistance to shrinkage cracking in service.


5. To evaluate the different test methods on measuring the free shrinkages of
concrete specimens.














CHAPTER 2
LITERATURE REVIEW

2.1 Introduction

This chapter presents a literature review on the basics of concrete shrinkage and the

results of some studies on admixtures for reducing shrinkage in concrete.

2.2 Mechanism of Concrete Shrinkage and Cracking

The portion of the concrete that shrinks is the cement paste. Cement paste shrinks

as it loses moisture due to the surface tension of water and the menisci that are formed in

the pore spaces in the paste. The surface tension of water in partially filled pores pulls

inward on the walls of the pore spaces. The concrete responds to these internal forces by

shrinking.

Tensile stresses develop when the concrete is prevented from shrinking freely.

The combination of high tensile stresses with the low fracture resistance of concrete often

results in cracking. Cracks reduce load carrying capacity and accelerate deterioration,

resulting in increased maintenance costs and reduced service life. Although free

shrinkage measurements are useful in comparing different mixture compositions, they do

not provide sufficient information to determine if the concrete will crack in service.

Cracking is a complex phenomenon, which is dependent on several factors including free

shrinkage, age-dependent material property development (e.g. Compressive strength),

creep relaxation, shrinkage rate, and degree of restraint. The amount of shrinkage for any

cement paste is primarily a function of the water-to-cement ratio of the paste, but it may









also be affected by cement type, cement fineness, and any other ingredients which alter

the pore size distribution.

2.3 Types of shrinkages

The types of shrinkages can be categorized as plastic shrinkage, drying shrinkage,

autogenous shrinkage and carbonation shrinkage.

Plastic Shrinkage

The space between particles of fresh concrete is completely filled with water.

When the water is removed from the paste by exterior influences, such as evaporation at

the surface, a complex series of menisci are formed. These in turn, generate negative

capillary pressures, which will cause the volume of the paste to contract. Such

contraction is called as plastic shrinkage. The magnitude of plastic shrinkage is affected

by the amount of water lost from the surface of the concrete, which is influenced by

temperature, ambient relative humidity, and wind velocity [Neville, 2000].

Drying Shrinkage

Drying Shrinkage is defined as the time-dependent strain due to moisture loss at

constant temperature in the absence of an external load and takes place after the concrete

has set. This shrinkage is due to loss of water from the concrete by evaporation. Water

in hydrated cement or concrete can be loosely described as free (or excess) water located

in capillary pores, physically adsorbed water on the surface of the CSH gels and

chemically bonded water in the products of hydration of the cement [Gani, 1997].



Autogenous Shrinkage

If no additional water beyond that added during mixing is provided during curing,

concrete will begin to dry internally, even if no moisture is lost to the surroundings as









water is consumed by hydration. This phenomenon of drying internally is known as self-

desiccation and is manifested as autogenous shrinkage (or Chemical shrinkage).

Carbonation Shrinkage

Hardened cement paste will react chemically with carbon dioxide. The

atmospheric carbon dioxide is sufficient to cause considerable reaction with cement paste

over a long time period. However, this is accompanied by irreversible shrinkage, and

hence it is called carbonation shrinkage [Mindess, Young and Darwin, 2003].

Water-related shrinkage (Plastic, Autogenous and Drying shrinkages) is a

volumetric change caused by the movement and the loss of water (i.e., change in the

internal pore pressure caused by drying or self-desiccation). Drying is driven by the

environmental conditions in which the relative humidity of the concrete structure strives

to bring into balance with the humidity of the surrounding environment. Water is

squeezed out from the capillary pores resulting in the development of tensile stresses

since the internal humidity attempts to make uniform with a lower environmental

humidity. The cause of compressing the concrete matrix is the tensile stress that explains

partially the phenomenon of drying shrinkage. Water-related shrinkage is the most

significant in thinner structures (with large surface area to volume ratio) due to the more

rapid loss of water. Pavements, bridge decks, and slabs are examples of thin structures

that may be susceptible to drying shrinkage cracking [Bazant 1986; Bazant and Carol

1993; and Tazawa 1998].

This dissertation will focus on drying shrinkage and consequently, the following

sections will be used to provide a brief summary of the terms that are used to describe

shrinkage of concrete. Also, the effects of ingredients and their physical characteristics









on the shrinkage of concrete are discussed in this chapter. While plastic and carbonation

shrinkage can occur in structures, this research report will focus primarily on drying

shrinkage.

2.4 Influence of Aggregates on Concrete Shrinkage

Aggregates affect concrete deformation through water demand, aggregate stiffness

and volumetric proportion, and paste/aggregate interaction [Han et al. 1994]. The

primary source of shrinkage is the cement paste. Aggregates that require a lower water

demand for workability will therefore produce concretes with a lower cement content,

which will result in lower shrinkage. Shape and texture of coarse aggregate play a role

on the behavior of fresh and hardened concrete. Shape and texture affect the demand for

sand. Flaky, elongated, angular, and rough particles have high voids and require more

sand to fill the voids and to provide a workable concrete, thus increasing the demand for

water and thereby increasing shrinkage. Spherical or cubical aggregates have less

specific surface area than flat and elongated particles. Consequently, spherical or cubical

aggregates require less paste and less water for workability [Shilstone 1999]. For a given

workability, flaky and elongated aggregates increase the demand for water, thus affecting

strength of hardened concrete as well as increasing the shrinkage in concrete. Spherical

or cubical particles lead also to better pumpability and finishability as well as produce

higher strengths and lower shrinkage than flaky and elongated aggregates [Shilstone

1990].

Aggregates with higher stiffness will give greater restraining effects to shrinkage

stresses and result in lower shrinkage in concrete [Neville 1996]. Aggregates that shrink

considerably upon drying usually have a low stiffness. This type of aggregate may also

have a large water absorption value, which will result in a concrete with higher shrinkage









[Troxell et al. 1996]. Aggregates with low absorption tend to reduce shrinkage and creep

[Washa 1998].

A concrete using a well-graded aggregate and with large maximum aggregate size

requires less cement paste, thus decreasing bleeding, creep, and shrinkage [Washa 1998;

Shilstone 1999]. However, it is to be noted that although an excess of coarse aggregate

could decrease drying shrinkage, it will increase the number of micro-cracks within the

paste [Aitcin 1998].

In some parts of the world, high absorption aggregates exist and use of these

aggregates will increase the water content and may increase shrinkage. However, it

should be noted that recently the use of high porosity lightweight aggregate (LWA) has

been proposed as one method to minimize autogenous shrinkage. In these works, the

LWA is saturated to various degrees before casting and the aggregate acts as a water

reservoir to supply water that counteracts the self-desiccation of the paste [Van Breugel

and deVries 1998; Bloom et al. 1999].

2.5 Influence of Cement on Concrete Shrinkage

Tazawa and Miyazawa [1997] found that cement composition has a greater

influence on autogenous shrinkage than drying shrinkage. As compared with normal

Portland cement, larger autogenous shrinkage was observed for high early strength

cement at an early age, and blast furnace slag cement at later ages. Less autogenous

shrinkage was observed for moderate heat cement paste, and low heat Portland cement

with a high C2S content. Autogenous shrinkage depends on the hydration of C3A and

C4AF and it increases with an increase in these compounds.

The use of an expansive cement was found to produce a large shrinkage reduction

in the cement mortar, but negligible effect in the concrete in a study by [Saito et al.









1991]. The aggregate was found to play an important role in the shrinkage of the

concrete. It was found that at the beginning of shrinkage, some cracks had already

existed around the coarse aggregate particles used in the expansive cement concretes. The

formation of cracks was found to lead to a partial loss of restraint of coarse aggregate

particles against drying shrinkage.

2.6 Influence of Water Content on Concrete Shrinkage

The water content has a large influence on the drying shrinkage of cement paste

and concrete. For a given w/c ratio, concretes of a wet consistency have a higher paste

content and have a greater amount of shrinkage than a stiffer mixture [Troxell et al.

1996]. For a given proportion of cement and aggregate, concretes of a wet consistency

have a higher water content and thus have a greater amount of shrinkage than a stiffer

mixture.

2.7 Influence of Specimen Size and Shape on Concrete Shrinkage

The size and shape of a concrete specimen definitely influence the rate of loss or

gain of moisture under a given storage condition, and this can affect the rate of volume

change as well as total expansion or contraction.

Almudaiheem and Hansen [1987] observed the shrinkage of concrete specimens of

various sizes over a one-year period. The shrinkage decreased with increasing specimen

size. The ultimate shrinkage of paste, mortar, and concrete was found to be independent

of specimen size and shape according to the dynamic shrinkage/weight loss curves. They

concluded that the ultimate drying shrinkage may be estimated from the shrinkage versus

drying time curves for small laboratory specimens of 1 x 1 x 11 in. (25 x 25 x 279 mm)

with the same mixture proportions as the larger structural members.









2.8 Admixtures that affect Shrinkage

Admixtures are used for the purpose of improving some characteristic of the

concrete. Admixtures are ingredients other than water, aggregates, hydraulic cement, and

fibers that are added to the concrete batch immediately before or during mixing. A

proper use of admixtures offers certain beneficial effects to concrete, including improved

quality, acceleration or retardation of setting time, enhanced frost and sulfate resistance,

control of strength development, improved workability, and enhanced finishability. It is

estimated that 80% of concrete currently produced in North America these days contains

one or more types of admixtures.

Admixtures vary widely in chemical composition, and many perform more than

one function. Two basic types of admixtures are available: chemical and mineral. All

admixtures to be used in concrete construction should meet specifications; tests should be

made to evaluate how the admixture will affect the properties of the concrete to be made

with the specified job materials, under the anticipated ambient conditions, and by the

anticipated construction procedures.

This section will include admixtures that can be used to reduce the shrinkage in

concrete. These admixtures include silica fume, fly ash, Onada-Expan, and Silane. They

are found to have reduced the shrinkage of concrete in varying degrees.

Shrinkage-reducing admixtures (SRA) are included here in two sections: one under

mineral admixtures and the other in chemical admixtures. They typically reduce the

shrinkage strain in concrete specimens.

2.8.1 Mineral Admixtures

Use of mineral admixtures make mixtures more economical, reduce permeability,

increase strength, and influence other concrete properties. Mineral admixtures (fly ash,









silica fume [SF], and slags) are usually added to concrete in larger amounts to enhance

the workability of fresh concrete; to improve resistance of concrete to thermal cracking,

alkali-aggregate expansion, and sulfate attack; and to enable a reduction in cement

content. Mineral admixtures affect the nature of the hardened concrete through hydraulic

or pozzolanic activity. Pozzolans are cementitious materials and include natural

pozzolans (such as the volcanic ash used in Roman concrete), fly ash and silica fume.

They can be used with Portland cement, or blended cement either individually or in

combinations.



2.8.1.1 Fly Ash

Fly ashes are finely divided residue resulting from the combustion of ground or

powdered coal. They are generally finer than cement and consist mainly of glassy-

spherical particles as well as residues of hematite and magnetite, char, and some

crystalline phases formed during cooling. Use of fly ash in concrete started in the United

States in the early 1930's. The first comprehensive study was that described in 1937, by

R. E. Davis at the University of California [Davis et al., 1937; Kobubu, 1968]. The major

breakthrough in using fly ash in concrete was the construction of Hungry Horse Dam

(Montana) in 1948, utilizing 120,000 metric tons of fly ash. This decision by the U.S.

Bureau of Reclamation paved the way for using fly ash in concrete constructions.

In addition to economic and ecological benefits, the use of fly ash in concrete

improves its workability, reduces segregation, bleeding, heat evolution and permeability,

inhibits alkali-aggregate reaction, and enhances sulfate resistance.

One of the most important fields of application for fly ash is PCC pavement, where

a large quantity of concrete is used and economy is an important factor in concrete









pavement construction. FHWA has been encouraging the use of fly ash in concrete.

When the price of fly ash concrete is equal to, or less than, the price of mixes with only

portland cement, fly ash concretes are given preference if technically appropriate under

FHWA guidelines [Adams 1988].

Two major classes of fly ash are specified in ASTM C 618 on the basis of their

chemical composition resulting from the type of coal burned; these are designated Class

F and Class C. Class F is fly ash normally produced from burning anthracite or

bituminous coal, and Class C is normally produced from the burning of subbituminous

coal and lignite (as are found in some of the western states of the United States) [Halstead

1986]. Class C fly ash usually has cementitious properties in addition to pozzolanic

properties due to free lime, whereas Class F is rarely cementitious when mixed with

water alone.

Fly ash (from Afsin-Elbistan Power plant, Turkey) used in mortar samples reduces

the drying shrinkages by about 30 to 40% when compared with pure Portland cement

mortar. The mortar samples containing 40% fly ash expanded instead of shrinking.

Based on the strength and shrinkage measurement results, it was concluded that the

nonstandard Afsin-Elbistan fly ash could be utilized in cement-based materials as a

mineral additive, particularly in concrete pavement, large industrial concrete floors,

parking lot applications or rock bolt applications of rock engineering where shrinkage

should be avoided. Based on the expansive property of this fly ash, it may also be

concluded that this fly ash may be utilized as cement reducing agent or in production of a

shrinkage compensating cement. However, further studies are needed to investigate

long-term properties of the concrete made with this fly ash before it can be used as a









mineral additive or in production of a shrinkage compensating cement [Duran et al.

2004].

Tangtermsirikul tested 0.56 x 1.56 x 6.24 in. (15 x 40 x 160 mm) prism specimens

to measure length change due to drying shrinkage. The drying shrinkage tests were

conducted in a controlled environment of 770 F (250 C) and 60% relative humidity. Three

types of Class C fly ash and one type of Class F fly ash were used in the experiment. The

class C fly ash had a smaller drying shrinkage than the ordinary cement paste mixtures.

The addition of the fly ash reduced the water requirement of the mixtures, thus reducing

the shrinkage. The Class C fly ash also reduced the autogenous shrinkage due to chemical

expansion of the concrete mixture [Tangtermsirikul et al. 1995].

The morphology, particle size distribution and surface characteristics of fly ash

used as a mineral admixture has a considerable influence on the water requirement,

workability, and rate of strength development of concrete [Mehta 1986]. Particle sizes

range from less than 1 micron to 100 microns in diameter, with more than 50% under 20

microns.

2.8.1.2 Silica fume

Silica fume is an industrial by-product with a particle size about 100 times finer

than Portland cement [Mehta 1986]. Tazawa and Yonekura [1991] examined shrinkage

and creep of mortar and concrete. Drying shrinkage of concrete was tested using 3.9 x

3.9 x 15.6-in. (100 x 100 x 400-mm) prism specimens. The specimens were in a

controlled environment of 680 F (200 C), 50% relative humidity. The drying shrinkage of

the concrete mixtures with the silica fume was lower than that of the same type mixtures

without the silica fume.









Haque [1996] measured the drying shrinkage on 3.35 x 3.35 x 11.22-in. (85 x 85 x

285-mm) prism specimens. The addition of both 5 and 10% silica fume (by weight) in

concrete mixtures resulted in a substantial reduction of drying shrinkage.

A dozen high strength concrete prisms of size 3 x 3 x 11.25 in. (76 x 76 x 286 mm)

were examined for assessing the drying shrinkage strain that the silica fume concrete

experienced [Alsayed 1998]. These prisms were monitored over a three-year time period.

All of the mixtures were identical except for the admixture content. Three mixtures were

compared; the first had a superplasticizer as the admixture, the second had a

superplasticizer and 10% silica fume by weight, and the third mixture had a regular

plasticizer and 10% silica fume by weight. The specimens were submerged in water for

seven days. Six specimens were then put in a laboratory-controlled environment, while

the other six specimens were exposed to field conditions. By adding 10% silica fume, the

shrinkage was reduced over time. The mixture with the superplasticizer and silica fume

showed a reduction in shrinkage. Specimens with the normal plasticizer showed a larger

drying shrinkage than those with the superplasticizer. The combined superplasticizer and

silica fume mixtures showed a reduced drying shrinkage rate in the first month. The

addition of the silica fume helped to reduce the sensitivity of the concrete to curing

conditions. After the first 90 days of exposure, 75% to 80% of the drying shrinkage

occurred depending on the curing conditions.

2.8.1.3 Silane

Silane is an aqueous admixture, called aqueous amino vinyl silane. Silane

treatment of silica fume and/or carbon fiber is highly effective for decreasing the drying

shrinkage of cement paste. The increase of the hydrophilic character of fibers and









particles after the treatment and the formation of chemical bonds between fibers/particles

and cement are believed to be the main reasons for the observed decrease of the drying

shrinkage. By adding silane-treated carbon fibers and replacing as-received silica fume

by silane-treated silica fume, the shrinkage at 28 days is decreased by 32% [Yunsheng

Xu 2001].

2.8.1.4 Onada Expan

ONADA EXPANTM is an expansive additive currently used in Japan for concrete.

This admixture expands when it is hydrated, without strength loss and hence reduces

shrinkage in turn. It uses calcium silicate and glass interstitial substitute rather than CaO.

This material is stable but it must be moist cured and requires longer mixing [Tazawa and

Miyazawa 1995].

2.8.2 Chemical Admixtures

Chemical admixtures are added to concrete in very small amounts mainly for the

entrainment of air, reduction of water or cement content, plasticization of fresh concrete

mixtures, or control of setting time.

Seven types of chemical admixtures are specified in ASTM C 494, and AASHTO

M 194, depending on their purpose or purposes in PCC. Air entraining admixtures are

specified in ASTM C 260 and AASHTO M 154. General and physical requirements for

each type of admixture are included in the specifications.

The use of chemical shrinkage-reducing admixture (SRA) in high-performance

concrete was found to significantly reduce drying shrinkage and restrained shrinkage

cracking in laboratory ring specimens. Cement paste shrinks as it loses moisture due to

the surface tension of water and the menisci that are formed in the pore spaces in the

paste. The surface tension of water in partially filled pores pulls inward on the walls of









the pore spaces. The phenomenon of pulling the walls of the pore spaces is called

shrinkage. The SRA works to reduce shrinkage by reducing the surface tension of the

water in all the filled spaces in the concrete.

The following effects were observed when an organic SRA (shrinkage-reducing

admixture) was added [Bentz et al. 2001]:

1. Comparing to distilled water, there is a significant reduction in the surface

tension of a solution containing the SRA.

2. The drying rate of the cement pastes is reduced.

3. A significant decrease in autogenous shrinkage in low w/c ratio mortars

cured under sealed conditions.

There was no significant change in 28-day compressive strength of mortar

specimens with the addition of an SRA, for w/c = 0.35 (8% silica fume) and cured under

sealed conditions at 860 F (300 C).

A shrinkage reducing admixture (SRA) has been suggested for use in reducing the

rate of shrinkage in concrete at early-ages when concrete is most vulnerable [Weiss

1999].

Tests were conducted on concrete with SRA added according to ASTM C 157-93

[Balogh 1996]. A larger percentage of decrease in shrinkage was noted in concretes with

a lower w/c ratio. For concretes with a w/c ratio of less than 0.60, the SRA reduced the

28-day shrinkage by 80% or more, and the 56-day shrinkage was reduced by about 70%.

The applied admixture dosage rate was 1.5% by weight of cement. For concretes with a

w/c ratio of 0.68, the SRA reduced the 28- and 56-day shrinkage by 37% and 36%,

respectively. The SRA was tested with different cements, one with fly ash, one with fly









ash and slag cement. The long-term (greater than one year) shrinkage reductions without

moist-curing the concretes ranged from 25% to 38%, depending on the composition of

the concrete mixtures.

Concrete specimens were cured for 1 to 14 days, and tests were conducted to

evaluate the drying shrinkage of concrete [Berke et al. 1997]. The specimens were stored

at 37.40 F (30 C) and at 50% relative humidity. The concrete specimens having 2% SRA

by weight of cement showed less shrinkage at early ages after controlled drying. For the

same cement content, the drying shrinkage of the concrete increased as the w/c ratio

increased for all the mixtures tested. The drying shrinkage was greatly reduced with the

addition of the SRA. Drying shrinkage was significantly reduced with increased curing

time. Longer curing periods reduced the sensitivity to changes in the w/c ratio with

respect to shrinkage reduction.

The shrinkage strain of concretes using a silica fume slurry, a superplasticizer and

an SRA was studied [Folliard 1997]. The fresh concrete had a slump of 6 to 8 in. (150 to

200 mm). Concrete prisms of 3 x 3 x 11.25 in. (75 x 75 x 285 mm) were cast to measure

free drying shrinkage. The use of a SRA reduced the drying shrinkage of the high

strength concretes both with and without silica fume. The ring test was used to determine

the restrained shrinkage. The restrained shrinkage was significantly reduced when the

SRA was used. The shrinkage reduction was more significant with the silica fume

mixtures.

The ring test was used to determine the restrained shrinkage of concretes containing

different SRAs by Shah, Karaguler, and Sarigaphuti [1992]. The specimens were placed

in a controlled environment of 680 F (200 C) and at 40% relative humidity. Three









different SRAs were used. Tests were also conducted on 4 x 4 x 11.25-in. (100 x 100 x

285-mm) prism specimens. The SRAs were found to possibly decrease the compressive

strength of the concrete. The addition of the SRA did reduce the amount of shrinkage. As

the amount of SRA added increases, the shrinkage further decreases. The addition of

SRA reduced the restrained shrinkage crack width. Free shrinkage was also measured on

3.9 x 3.9 x 15.6-in. (100 x 100 x 400-mm) prism specimens. The addition of SRA

greatly improved the reduction of free shrinkage. An equal amount of water was

removed when the SRA was added. The addition of the SRA caused a delay in the

restrained shrinkage cracking.














CHAPTER 3
MATERIALS



3.1 Introduction

This chapter describes the mix proportions and the mix ingredients of the concrete

mixtures evaluated in this study. The method of preparation of the concrete mixtures,

fabrication of the test specimens and testing procedures used in this study are also

presented.

3.2 Concrete Mixtures Evaluated

Concrete mixtures were prepared in the laboratory and tested for their resistance to

shrinkage cracking to evaluate (1) the effectiveness of the shrinkage test apparatuses

used, (2) the shrinkage characteristics of typical concretes used in bridge deck applica-

tions in Florida, and (3) the effects of adding a shrinkage-reducing admixture. A typical

mix design for a Florida Class IV concrete with a total cementitious materials content of

700 lb per cubic yard (lb/yd3), or 415.7 kg per cubic meter (kg/m3), of concrete was

selected for use. Various percentages of fly ash and ground blast-furnace slag were

incorporated into this basic mix design to form six different mix designs to be evaluated

in the laboratory testing program. Based on the six mix designs mentioned before, nine

more mixes were developed by varying water cement ratios, resulting in a total of 15

pairs of mixtures that were used for this study. For each pair of the concrete mixture

evaluated, two concrete mixes were prepared at the same time one with the addition of

a shrinkage-reducing admixture (SRA) and one without.









Tables 3-1 through 3-15 show the mix proportions for the 15 pairs of concrete

mixtures evaluated in this study. The concrete mixes were numbered according to the

order by which they were prepared and tested in this study. Mixes 1 and 13 had a cement

content of 350 lb/ yd3 (207.8 kg/m3) and a slag content of 350 lb/yd3 (207.8 kg/m3) of

concrete. Mixes 2 and 3 had a cement content of 210 lb/ yd3 (124.7 kg/m3) and a slag

content of 490 lb/yd3 (291 kg/m3). Mixes 4, 7, 8 and 11 had a cement content of 560

lb/yd3 (332.5 kg/m3) and a fly ash content of 140 lb/yd3 (83.1 kg/m3). Mixes 5, 9, 10 and

14 had a cement content of 455 lb/yd3 (270.2 kg/m3) and a fly ash content of 245 lb/yd3

(145.5 kg/m3). Mixes 6 and 12 had a cement content of 210 lb/yd3 (124.7 kg/ m3), a fly

ash content of 140 lb/yd3 (83.1 kg/m3) and a slag content of 350 lb/yd3 (207.8 kg/ m3).

Mix 15 had a cement content of 700 lb/yd3 (415.7 kg/ m3), and no mineral admixture.

The slump of the fresh concrete was targeted to be 8 1.5 inches (203 + 38 mm). The

number of replicates of concrete specimens used for different tests are provided in the

Section 4.2 of Chapter 4.










Table 3-1. Mix Proportions for Mix 1.
Mix- 1
Weight
(pounds per cubic yard, lb/yd3)
Ingredients
Ingr s Standard SRA
Design Batch Actual Batch Design Batch Actual Batch
Cement 350 350 350 350
Fly ash -
Slag 350 350 350 350
Water 287 234 274 219
F.A. 1257 1252 1257 1252
C.A. 1513 1572 1513 1572
Air Entrainer 0.0625 0.0625 0.0625 0.0625
Admixture (WRDA
64) 0.875 0.875 0.875 0.875
Admixture (Adva 120) 1.313 1.313 1.313 1.313
Admixture (SRA) 12 12
Slump (in inches) 6.25 6.25 7.25 7.25
Air (%) 3.75 3.75 3 3
Workability Good Good Good Good
W/C Ratio 0.41 0.33 0.41 0.33
Unit Weight (pcf) 139.1 139.2 139.1 139.1









Table 3-2. Mix Proportions for Mix 2.
Mix 2
Weight
(lb/yd3)
Ingredients ---
Dein Standard SRA
Design Batch Actual Batch Design Batch Actual Batch
Cement 210 210 210 210
Fly ash -
Slag 490 490 490 490
Water 224 176 211 165
F.A. 1336 1331 1336 1331
C.A. 1583 1633 1583 1633
Air Entrainer 0.0625 0.0625 0.0625 0.0625
Admixture (WRDA
64) 0.875 0.875 0.875 0.875
Admixture (Adva
120) 2.063 2.063 2.063 2.063
Admixture (SRA) 12 12
Slump (in inches) 8 8 9.25 9.25
Air (%) 2.75 2.75 1.75 1.75
Workability Sticky Sticky Sticky Sticky
W/C Ratio 0.32 0.25 0.32 0.25
Unit Weight (pcf) 142.3 142.2 142.3 142.3










Table 3-3. Mix Proportions for Mix 3.
Mix 3
Weight
(lb/yd3)
Ingredients -- '
Ingr s Standard SRA
Design Batch Actual Batch Design Batch Actual Batch
Cement 210 210 210 210
Fly ash
Slag 490 490 490 490
Water 287 213 274 200
F.A. 1253 1248 1253 1253
C.A. 1507 1586 1507 1507
Air Entrainer 0.0625 0.0625 0.0625 0.0625
Admixture (WRDA
64) 0.875 0.875 0.875 0.875
Admixture (Adva 120) 1.313 1.313 1.313 1.313
Admixture (SRA) 12 12
Slump (in inches) 9 9 8.5 8.5
Air (%) 3.5 3.5 2.5 2.5
Workability Good Good Good Good
W/C Ratio 0.41 0.30 0.39 0.29
Unit Weight (pcf) 138.8 138.8 138.3 135.5










Table 3-4. Mix Proportions for Mix 4.
Mix 4
Weight
(lb/yd3)
Ingredients -
Ingr s Standard SRA
Design Batch Actual Batch Design Batch Actual Batch
Cement 560 560 560 560
Fly ash 140 140 140 140
Slag
Water 287 244 275 232
F.A. 1250 1246 1250 1246
C.A. 1486 1533 1486 1533
Air Entrainer 0.0625 0.0625 0.0625 0.0625
Admixture (WRDA 64) 1.75 1.75 1.75 1.75
Admixture (Adva 120) 2.188 2.188 2.188 2.188
Admixture (SRA) 12 12

Slump (in inches) 7.5 7.5 9 9
Air (%) 3.25 3.25 2.5 2.5
Workability Good Good Good Good
W/C Ratio 0.41 0.35 0.39 0.33
Unit Weight (pcf) 137.9 137.9 137.4 137.4










Table 3-5. Mix Proportions for Mix 5.
Mix 5
Weight
(lb/yd3)
Ingredients --
Ingr s Standard SRA
Design Batch Actual Batch Design Batch Actual Batch
Cement 455 455 455 455
Fly ash 245 245 245 245
Slag ____ _
Water 287 228 275 216
F.A. 1217 1213 1217 1213
C.A. 1469 1533 1469 1533
Air Entrainer 0.0625 0.0625 0.0625 0.0625
Admixture (WRDA 64) 1.75 1.75 1.75 1.75
Admixture (Adva 120) 2.188 2.188 2.188 2.188
Admixture (SRA) 12 12

Slump (in inches) 9.25 9.25 8.75 8.75
Air (%) 3.25 3.25 3.25 3.25
Workability Good Good Good Good
W/C Ratio 0.41 0.33 0.41 0.33
Unit Weight (pcf) 136.0 136.1 136.0 136.1










Table 3-6. Mix Proportions for Mix 6.
Mix 6
Weight
(lb/yd3)
Ingredients --
Ingr s Standard SRA
Design Batch Actual Batch Design Batch Actual Batch
Cement 210 210 210 210
Fly ash 140 140 140 140
Slag 350 350 350 350
Water 289 246 275 232
F.A. 1240 1236 1240 1236
C.A. 1475 1522 1475 1522
Air Entrainer 0.0625 0.0625 0.0625 0.0625
Admixture (WRDA
64) 1.75 1.75 1.75 1.75
Admixture (Adva 120) 2.188 2.188 2.188 2.188
Admixture (SRA) 12 12
Slump (in inches) 9.25 9.25 9 9
Air (%) 1.75 1.75 2.75 2.75
Workability Good Good Good Good
W/C Ratio 0.41 0.35 0.41 0.35
Unit Weight (pcf) 137.2 137.2 137.1 137.1










Table 3-7. Mix Proportions for Mix 7.
Mix 7
Weight
(lb/yd3)
Ingredients --
Dein Standard SRA
Design Batch Actual Batch Design Batch Actual Batch
Cement 560 560 560 560
Fly ash 140 140 140 140
Slag -
Water 254 235 242 223
F.A 1334 1330 1257 1330
C.A 1561 1554 1513 1554
Air Entrainer 0.0625 0.0625 0.0625 0.0625
Admixture (WRDA
64) 1.31 1.31 0.88 0.88
Admixture (Adva 120) 1.31 1.31 1.31 1.31
Admixture (SRA) 12 12

Slump (in inches) 8 8 9 9
Air (%) 2.75 2.75 3.25 3.25
Workability Good Good Good Good
W/C Ratio 0.36 0.34 0.36 0.34
Unit Weight (pcf) 142.6 141.4 137.9 141.4










Table 3-8. Mix Proportions for Mix 8.
Mix 8
Weight
(lb/yd3)
Ingredients --*
Ingr s Standard SRA
Design Batch Actual Batch Design Batch Actual Batch
Cement 560 560 560 560
Fly ash 140 140 140 140
Slag
Water 224 264 212 252
F.A 1453 1449 1455 1451
C.A 1453 1417 1455 1419
Air Entrainer 0.0625 0.0625 0.0625 0.0625
Admixture (WRDA
64) 0.88 0.88 0.88 0.88
Admixture (Adva 120) 2.06 2.06 2.06 2.06
Admixture (SRA) 12 12
Slump (in inches) 2.5 2.5 2.25 2.25
Air (%) 4.5 4.5 3.75 3.75
Workability Stiff Stiff Stiff Stiff
W/C Ratio 0.32 0.38 0.32 0.38
Unit Weight (pcf) 141.9 141.9 142.0 142.0










Table 3-9. Mix Proportions for Mix 9.
Mix 9
Weight
(lb/yd3)
Ingredients -- '
Ingr s Standard SRA
Design Batch Actual Batch Design Batch Actual Batch
Cement 455 455 455 455
Fly ash 245 245 245 245
Slag
Water 287 324 275 312
F.A. 1351 1347 1351 1347
C.A. 1351 1318 1351 1318
Air Entrainer 0.0625 0.0625 0.0625 0.0625
Admixture (WRDA
64) 0.88 0.88 0.88 0.88
Admixture (Adva 120) 1.31 1.31 1.31 1.31
Admixture (SRA) 12 12
Slump (in inches) 3.25 3.25 4.5 4.5
Air (%) 2.75 2.75 2.5 2.5
Workability O.K O.K O.K O.K
W/C Ratio 0.41 0.46 0.41 0.46
Unit Weight (pcf) 136.6 136.6 136.6 136.6










Table 3-10. Mix Proportions for Mix 10.
Mix 10
Weight
(lb/yd3)
Ingredients -- '
Ingr s Standard SRA
Design Batch Actual Batch Design Batch Actual Batch
Cement 455 455 455 455
Fly ash 245 245 245 245
Slag
Water 252 289 240 278
F.A 1265 1261 1265 1261
C.A 1513 1480 1513 1480
Air Entrainer 0.0625 0.0625 0.0625 0.0625
Admixture (WRDA
64) 0.88 0.88 0.88 0.88
Admixture (Adva 120) 1.31 1.31 1.31 1.31
Admixture (SRA) 12 12
Slump (in inches) 3.25 3.25 4.5 4.5
Air (%) 2.75 2.75 2.5 2.5
Workability O.K O.K O.K O.K
W/C Ratio 0.36 0.41 0.36 0.41
Unit Weight (pcf) 138.2 138.2 138.1 138.2










Table 3-11. Mix Proportions for Mix 11.
Mix 11
Weight
(lb/yd3)
Ingredients -- '
Ingr s Standard SRA
Design Batch Actual Batch Design Batch Actual Batch
Cement 560 560 560 560
Fly ash 140 140 140 140
Slag
Water 287 321 275 308
F.A. 1250 1246 1250 1246
C.A. 1486 1456 1486 1456
Air Entrainer 0.0625 0.0625 0.0625 0.0625
Admixture (WRDA
64) 1.75 1.75 1.75 1.75
Admixture (Adva 120) 2.188 2.188 2.188 2.188
Admixture (SRA) 12 12
Slump (in inches) 8.5 8.5 9 9
Air (%) 3 3 2.75 2.75
Workability Good Good Good Good
W/C Ratio 0.41 0.46 0.41 0.46
Unit Weight (pcf) 137.9 137.9 137.9 137.9










Table 3-12. Mix Proportions for Mix 12.
Mix- 12
Weight
(lb/yd3))
Ingredients --n-
Ingr s Standard SRA
Design Batch Actual Batch Design Batch Actual Batch
Cement 210 210 210 210
Fly ash 140 140 140 140
Slag 350 350 350 350
Water 224 194 212 183
F.A. 1516 1511 1516 1511
C.A. 1376 1410 1376 1410
Air Entrainer 0.0625 0.0625 0.0625 0.0625
Admixture (WRDA
64) 1.75 1.75 1.75 1.75
Admixture (Adva 120) 2.188 2.188 2.188 2.188
Admixture (SRA) 12 12
Slump (in inches) 3 3 6.5 6.5
Air (%) 3.25 3.25 3 3
Workability Stiff Stiff Sticky Sticky
W/C Ratio 0.32 0.28 0.32 0.28
Unit Weight (pcf) 141.3 141.3 141.3 141.3










Table 3-13. Mix Proportions for Mix 13.
Mix 13
Weight
(lb/yd3)
Ingredients ---
Ingr s Standard SRA
Design Batch Actual Batch Design Batch Actual Batch
Cement 350 350 350 350
Fly ash
Slag 350 350 350 350
Water 224 285 212 273
F.A. 1547 1543 1547 1543
C.A. 1405 1348 1405 1348
Air Entrainer 0.0625 0.0625 0.0625 0.0625
Admixture (WRDA
64) 1.75 1.75 1.75 1.75
Admixture (Adva
120) 2.188 2.188 2.188 2.188
Admixture (SRA) 12 12

Slump (in inches) 1.75 1.75 7 (Sheared off) 7 (Sheared off)
Air (%) 3.75 3.75 3.25 3.25
Workability Stiff Stiff Stiff Stiff
W/C Ratio 0.32 0.41 0.32 0.41
Unit Weight (pcf) 143.6 143.5 143.6 143.6










Table 3-14. Mix Proportions for Mix 14.
Mix- 14
Weight
(lb/yd3)
Ingredients -- '
Ingr s Standard SRA
Design Batch Actual Batch Design Batch Actual Batch
Cement 455 455 455 455
Fly ash 245 245 245 245
Slag
Water 224 209 212 197
F.A. 1502 1499 1502 1499
C.A. 1364 1383 1364 1383
Air Entrainer 0.0625 0.0625 0.0625 0.0625
Admixture (WRDA
64) 1.75 1.75 1.75 1.75
Admixture (Adva 120) 2.188 2.188 2.188 2.188
Admixture (SRA) 12 12
Slump (in inches) Sheared off Sheared off Sheared off Sheared off
Air (%) 3.5 3.5 4.5 4.5
Workability Stiff Stiff Stiff Stiff
W/C Ratio 0.32 0.30 0.32 0.30
Unit Weight (pcf) 140.4 140.4 140.4 140.4










Table 3-15. Mix Proportions for Mix 15.
Mix 15
Weight
(lb/yd3)
Ingredients -- '
Ingr s Standard SRA
Design Batch Actual Batch Design Batch Actual Batch
Cement 700 700 700 700
Fly ash
Slag
Water 224 202 212 190
F.A. 1557 1553 1557 1553
C.A. 1415 1441 1415 1441
Air Entrainer 0.0625 0.0625 0.0625 0.0625
Admixture (WRDA
64) 0.875 0.875 0.875 0.875
Admixture (Adva 120) 1.313 1.313 1.313 1.313
Admixture (SRA) 12 12
Slump (in inches) 0.25 0.25 0.25 0.25
Air (%) 4.5 4.5 4 4
Workability Stiff Stiff Stiff Stiff
W/C Ratio 0.32 0.29 0.32 0.29
Unit Weight (pcf) 144.3 144.3 144.3 144.3










3.3 Concrete Mixture Constituents

The mix constituents that were used in producing the concrete mixture are

described in this section of the chapter.

3.3.1 Water

Water used was obtained from the local city water supply system.

3.3.2 Fine Aggregate

The silica sand mined from Mine 76-137 located in Kueka, Florida, was used as

fine aggregate for the concrete mixtures. The oven-dried silica sand was used for

producing the concrete for this study. The gradation plot of the Kueka silica sand is

displayed in Figure 3-1. The physical properties of fine aggregate are given in

Table 3-16.


120


100-----


80


S60
0)

0 40


20



#100 #50 #30 #16 #8 #4
Sieve Sizes

Figure 3-1. Gradation chart for the fine aggregate (Goldhead silica sand)










Table 3-16. Physical Properties of Fine Aggregate.


Physical Property Value
Bulk specific gravity 2.63
Bulk specific gravity SSD 2.68
Apparent specific gravity 2.64
Absorption 0.73%
Fineness Modulus 2.30


3.3.3 Coarse Aggregate

The coarse aggregate used was a #89 limestone obtained from Mine 08-0057

located in Brooksville, Florida. The coarse aggregate was used as-is at its natural

moisture condition. The gradation of the coarse aggregates is shown in Figure 3-2. Its

physical properties are given in Table 3-17.

120


100


80
V)

a 60


S40


10



#50 #16 #8 #4 3/8 1/2

Sieve Sizes

Figure 3-2. Gradation chart for the coarse aggregate (#89 limestone)









Table 3-17. Physical Properties of the Coarse Aggregate
Physical Property Value
Bulk Specific Gravity 2.23
Bulk Specific Gravity SSD 2.40
Apparent Specific Gravity 2.56
Absorption 4.55%


3.3.4 Cement

Cemex Cement Company provided the Type I Portland cement for use in the

concrete mixtures that were used for this study. The physical characteristics and the

chemical composition of the cement are shown in Tables 3-18 and 3-19, respectively.

Table 3-18. Physical Properties of the Type I Cement Used

Tests Specification Cement Spec. Limits

Autoclave Expansion ASTM C151 0.01% <= 0.80%
>= 260.0 &
Fineness by Apparatus ASTM C204 402 m2 /kg <= 420.0
Loss on Ignition ASTM C114 1.50% <= 3.0%
Time of setting (Initial) ASTM C226 125 min. >= 60
Time of setting (Final) ASTM C226 205 min. <= 600
3-day Compressive Strength Test ASTM C109 2400 psi >= 1740
7-day Compressive Strength Test ASTM C109 2930 psi >= 2760
Cement acid insoluble test ASTM C114 0.48% Insoluble <= 0.75


Table 3-19 Chemical Com I


Cement Used


Constituents %
Si02 20.3
A1203 4.8
CaO 63.9
SO3 3.1
Na20-K20 0.5
MgO 2.0
Fe203 3.3
C3A 7.0
C3S 59.0
C2S 13.8
C4AF+C2F 15.8


-~~-~-. -~









3.3.5 Fly Ash

Class F fly ash, which was derived from the combustion of ground or powdered

coal and met the requirements of ASTM C 618, was used for this project. Boral

Company provided the fly ash for this project. The chemical composition of the fly ash

is shown in Table 3-20. Its physical properties are shown in Table 3-21.

Table 3-20. Chemical Composition of the Class F Fly Ash Used
Chemical Value
Sulfur Trioxide 0.3%
Oxides of Si, Fe, Al 12.1%


Table 3-21. Physical Properties of the Class F Fly Ash Used
Property Fly ash Limits
% Moisture 0.10% <= 3.0
Loss on Ignition 4.30% <= 6.0

3.3.6 Ground Blast-Furnace Slag

The ground blast-furnace slag used in this project met the requirements of ASTM C

989. The slag used in this project was provided by Boral Company. The chemical

composition of the slag used is shown in Table 3-22.

Table 3-22. Chemical Composition of the Slag Used
Chemical Value
Sulfur Trioxide 1.70%
Total Alkali as Na20 0.7


3.3.7 Air-Entraining Admixture

The air-entraining admixture used in this study was Darex AEA (Supplied by W.R.

Grace & Co.), which was an aqueous solution of a complex mixture of organic acid salts.

It is specially formulated for use as an air-entraining admixture for concrete. It was

supplied as ready-to-use admixture and did not require pre-mixing with water. The air-









entraining admixture was used to improve the workability, and to reduce bleeding and

segregation of the fresh concrete. In this project, 0.1 lb of Darex was used for one cubic

yard (0.059 kg/m3) of concrete.

3.3.8 Water-Reducing Admixtures

Water-reducing admixtures were used in the concrete to reduce the demand of

water in the mix. Two types of water-reducing admixtures were used in the concrete

mixtures for this project. They were WRDA 64 and Adva Flow (Supplied by W.R. Grace

& Co) which are described in the following sections.

3.3.8.1 WRDA 64

WRDA 64 is a polymer-based aqueous solution of complex organic compounds. It

is a ready-to-use low viscosity liquid which contains no calcium chloride. It can reduce

the water demand of concrete by typically 8 to 10%. Setting times and water reduction

are more consistent due to the presence of polymer components. It also performs

especially well in concretes containing fly ash and other pozzolans. In this project, 1.75

lb of WRDA 64 was used per cubic yard (1.04 kg/m3) of concrete.

3.3.8.2 Adva Flow (Super plasticizer)

Adva Flow Superplasticizer is a high range water-reducing admixture and does not

have any chloride added. In this project, 2.2 lb of Adva Flow was used per cubic yard

(1.31 kg/m3) of concrete.

3.3.9 Shrinkage-Reducing Admixture

The shrinkage-reducing admixture (SRA) is a liquid admixture specially

formulated for use in indoor slab-on-grade concrete construction. The trade name is

Eclipse and it was supplied by W.R. Grace & Co. The SRA has no expansive agent, but

acts chemically to dramatically reduce the primary internal forces that cause shrinkage









and curling. The SRA at a dosage of 1.5 gal/yd3 (7.43 liter/m3) has been shown to reduce

drying shrinkage, as measured by ASTM C 157, by as much as 80% at 28 days, and up to

50% at one year or beyond. It is a clear liquid admixture. In this project, 12 lb of the

SRA was used per cubic yard (7.13 kg/m3) in the concrete mixtures that required the

shrinkage-reducing admixture.

3.4 Preparation of Concrete Mixtures

3.4.1 Mixing of Concrete

Fifteen pairs of concrete mixtures were produced and tested in this project. The

concrete batches were mixed in two rotary drum mixers of capacities of 3.5 cubic feet

(ft3), or 0.098 cubic meters (m3), for relatively small mix and 6 ft3 (0.168 m3) according

to the ASTM (American Society for Testing and Materials) requirement. The photo of

the 6 ft3 (0.168 m3) mixer is shown in Figure 3-3. The surface of interior portion of the

drum was rinsed with a butter mix (i.e., the original mix in small quantity) before mixing

to avoid absorption of moisture from the mix and to ensure the same mixing conditions

for all mixes.

The following procedures of mixing of concrete were followed in the preparation of

each concrete mixture:

1. Place the coarse and fine aggregates in the mixer, and mix for about two

minutes with one half of mixing water added to ensure uniform dispersion of the

aggregates.

2. The SRA is added to the water that is used in the concrete mixture

2. Add the cement, fly ash, slag, air entraining admixture, water-reducing

admixtures and the remaining water into the mixer, and continue the mixing for an

additional three minutes. Stop the mixer as needed to break loose the materials sticking









to the mixer to facilitate thorough mixing. After mixing three minutes, follow with a 3-

minute rest period.

3. Continue the mixing for an additional two minutes after the rest period.

4. After the mix appears uniformly mixed, run the slump test on the fresh concrete.

Add additional water-reducing admixtures if the slump is too low. While adding water-

reducing admixtures, take care not to exceed the allowable dosages. Otherwise, the

mixtures may become segregated and start bleeding.


Figure 3-3. Concrete mixer used









3.4.2 Preparation of Concrete Specimens for Mechanical Tests

The following steps were followed in making the concrete specimens for evaluation

of mechanical properties:

1. After mixing is complete, fill each of the 4 x 8-in. (101.6 x 203.2-mm)

cylindrical molds with the fresh concrete to one half of its height, and place the mold on a

vibrating table for 30 seconds of vibration.

2. Fill the cylinder mold to overflowing, and place it on the vibrating table for an

additional 30 seconds.

3. Finish the surface of the concrete specimen with a hand trowel, and cover the

cylinder with a plastic sheet to prevent evaporation of water.

4. Remove the concrete specimens from the molds after 24 hours of curing, and

put them in a standard moist room for proper curing until the specific tests compressivee

strength, modulus of elasticity and splitting tensile strength tests) are to be performed at

the specified curing times (such as 3, 7, 14 and 28 days).

3.4.3 Preparation of Concrete Specimens for ASTM C157 Shrinkage Test

A portion of the fresh concrete was used to produce the 3 x 3 x 11.25-in. (76 x 76 x

286-mm) square prism specimens for the ASTM C157 Shrinkage Test. The procedures

for making of these specimens are described in Section 4.3.4 of this report.

3.4.4 Preparation of Concrete Specimens for Long Specimen Tests

The rest of the fresh concrete from the mixer was used to make the long specimens

for the constrained shrinkage test and the free shrinkage test. The procedures for making

the long specimens for free shrinkage test are described in Section 4.3.5, while those for

the constrained shrinkage test are described in Chapter 5 of this report.














CHAPTER 4
LABORATORY TESTING PROGRAM

4.1 Introduction

This chapter describes the laboratory testing program on the concretes to be

evaluated for their resistance to shrinkage cracking in this study. It includes the descrip-

tion of the tests on fresh and hardened concretes and the associated instrumentation.

4.2 Tests on Fresh Concrete

The following tests were performed on the fresh concrete:

1. Slump test (ASTM C143);

2. Unit weight test (ASTM C138);

3. Air content by volumetric method (ASTM C173); and

4. Temperature measurement (ASTM C1064).

4.3 Tests on Hardened Concrete

The following tests were run on the hardened concrete:

1. Compressive strength (ASTM C39) tests using 4 x 8-in. (101.6 x 203.2-mm)

specimens at 3, 7, 14 and 28 days (3 replicates per condition).

2. Elastic modulus (ASTM C469) tests using 4 x 8-in. (101.6 x 203.2-mm)

specimens at 3, 7, 14 and 28 days (2 replicates per condition).

3. Splitting tensile strength test (ASTM C496) using 4 x 8-in. (101.6 x 203.2-mm)

specimens at 3, 7 and 14 days (3 replicates).

4. Free shrinkage measurement (ASTM C157) using 3 x 3 x 11.25-in. (76 x 76 x

286-mm) specimens (3 replicates).









5. Free shrinkage measurement using the long specimen apparatus without the

constraint, monitored continuously for a minimum of 14 days (2 replicates).

6. Constrained shrinkage test using the long specimen apparatus, monitored

continuously for a minimum of 14 days (2 replicates).

The equipment, instrumentation and procedures for these tests on hardened

concrete are described in the following section.

4.3.1 Compressive Strength Test

The compressive strength test was run in accordance with ASTM Test Method

C39. Figure 4-1 shows the set-up for the compressive strength test. The testing machine

used was a servo-controlled compression testing machine with a capacity of 500,000 lb

(227,000 kg). All the tests were run with a rate of loading ranging from 400 to 500 lb

(1,780 to 2,225 N) per second.


Figure 4-1. Set-up for compressive strength test









Three 4 x 8-in. (101.6 x 203.2-mm) cylindrical specimens per batch per curing

condition were tested for the analysis. Before testing, the cylinders were ground by using

a grinding stone so that two end surfaces are made even to support the applied load

uniformly.

Compressive strengths were determined at moist-curing times of 3, 7, 14 and 28

days. The compressive strength of the specimen was calculated using the following

equation (Eq.):

Compressive Strength, f, = P/A (Eq. 4.1)

where

P = ultimate load attained during the test in pounds (lb); and

A = loading area in square inches (in2 ).

Of the three replicate specimens per condition, one specimen was first tested to

determine its ultimate compressive strength, so that the modulus of elasticity test could be

run at 40% of the ultimate strength of the concrete. The modulus of elasticity test was

then run on the other two replicate specimens before they were tested for their compres-

sive strength.

4.3.2 Modulus of Elasticity Test

The modulus of elasticity test was run in accordance with ASTM Test Method

C469. Cylindrical specimens of size 4 x 8 in. (101.6 x 203.2-mm), which were also used

in the compressive strength test, were used for this test. Similar to the compressive

strength test, the modulus of elasticity test was performed at curing times of 3, 7, 14 and

28 days. The test set-up is shown in Figure 4-2 and Figure 4-3.









The test set-up consisted of a compression testing machine, a digital key panel (for

controlling the testing machine) and a laptop computer (for downloading the data from

the test). The rate of loading adopted for this test was the same as that for the

compressive strength test, and ranged from 400 to 500 lb (1,780 to 2,225 N) per second.

The output from the load cell (in the testing machine) and the output from the LVDT

(which was connected to the specimen to measure its vertical deformation) were

connected to the laptop computer via a USB connection.



I
ESTf" M- -- .
1 EST MAR .

NOWL,*


I


TEST MARK


6 /1:58 PM


S 5pM' ~'


Figure 4-2. Set-up for modulus of elasticity test








































Figure 4-3. Close-up view of elastic modulus test set-up with a
LVDT for strain measurement



Before Modulus of Elasticity test is run, one of the three cylinders was tested for

ultimate compressive strength until breaking. On the remaining two cylinders, the

Modulus of Elasticity Test was run at a strength level of 40% of the ultimate compressive

strength of the concrete. After that, those two specimens from the Modulus of Elasticity

test were tested for ultimate compressive strengths. The data from the first load cycle

were disregarded. The data values from the last two cycles of loading were recorded and

converted into CSV (comma separated variable) format which is readable by the Excel


i ,!










spreadsheet. The modulus of elasticity was determined using regression analysis

embedded in the Excel spreadsheet charts.

4.3.3 Splitting Tensile Strength Test

The splitting tensile strength test was run in accordance with the procedures laid

out in ASTM C496 method. Three 4 x 8-in. (101.6 x 203.2-mm) cylindrical specimens

per condition were used for this test. The test set-up is shown in Figure 4-4. The

splitting tensile strength of the specimen was calculated using the expression below:

Splitting tensile strength, ft = 2P/7ld (Eq. 4.2)

where

P = maximum applied load;

1 = length of the cylindrical specimen; and

d = diameter of the cylindrical specimen.

















Figure 4-4. Set-up for splitting tensile strength test






Figure 4-4. Set-up for splitting tensile strength test









4.3.4 Free Shrinkage Measurement (ASTM C157) Using LVDTs

Square prism specimens with dimensions of 3 x 3 x 11.25 in. (76 x 76 x 286 mm)

were used in the free shrinkage test in accordance with ASTM C157 Method. Figure 4-5

shows a mold used to cast the shrinkage test specimens. Steel end plates with a hole at

their centers were used to hold the contact points in place at each end of the specimen.

4.3.4.1 Test Setup

A Lucas Schaevitz spring loaded model GCD-121-050 LVDT was used to monitor

the vertical movement of the specimen. The LVDT had a travel range of 0.050 in.

(1.27 mm) with a sensitivity of 200 V/in. (7.874 /mm). Thus, over the travel range of

0.10 in. (2.54 mm), there would be a 20 V difference in output voltage readings, i.e., -10

V to +10 V. The linearity range cited by the manufacturer of 0.25% for the full range


















Figure 4-5. Mold for 3 x 3 x 11-in. (76 x 76 x 286-mm) shrinkage test specimen



Figure 4-5 illustrates the mold for 3 x 3 x 11-in. (76 x 76 x 286-mm) shrinkage test

specimen. The output produced readings with errors within 0.025 V, which translated

into displacement measurement errors within .000125 in. (.00318 mm).









These LVDTs are made of AISI 400 series stainless steel. They are complete and

ready-to-use displacement transducers with a sleeve bearing structure on one end that

supports a spring-loaded shaft attached to the core. The bearing is threaded externally to

facilitate mounting. By using a spring loaded LVDT, the need for core rods or core

support structures is eliminated. All LVDTs are hermetically sealed to operate in harsh

environments such as a moist room, and have an operating temperature range of 00 F to

160 F (-17.80 C to 71.10 C) to facilitate testing of temperature effects.

The data acquisition system used is an Agilent 34970A unit (by Agilent

Technologies) with a HP 34901A (20-channel armature multiplexer) plug-in module.

The data acquisition unit can be set up to take readings at specified time intervals and for

a specified length of time. The HP 34901A multiplexer module can read up to 20

channels of AC or DC voltages with a maximum capacity of 300 V. It has a switching

speed of up to 60 channels per second. It also has a built-in thermocouple reference

junction for use in temperature measurement by means of thermocouples. Thus, the

Agilent 34970A data acquisition unit with one HP 34901A multiplexer module will be

adequate for the job of recording load and displacement readings from 10 testing

apparatuses. The Agilent 34970A unit can take up to three plug-in modules. Thus, if

needed, it can be expanded to take up to 60 channels of output.

The test setup for measuring the free shrinkage using a LVDT is shown in Figure

4-6. Figure 4-7 shows a picture of several test setups that were used simultaneously.

Figure 4-8 shows the schematics of these test setups































































Figure 4-6 Set-up for ASTM C157 free shrinkage measurement using a LVDT


_ __








































Picture of several test setups for free shrinkage measurement using LVDTs


LVDT VODT











Specimens


LVDT


LV(DT









Frl


Specimens


IVDT ILVDT









Frane Fracmn
Specimens


Figure 4-8. Schematics of test set-ups for measurement of free shrinkage using LVDTs


Figure 4-7.


Ccnpit r

Plug-in-Wbdules

F4_ 1 AS









The setup for the ASTM C157 free shrinkage test consisted of a DC-powered

LVDT connected to a shrinkage test frame that held the specimen. The output from the

LVDT was connected to a Data Acquisition System (DAS). A laptop computer was used

to download the data from the DAS. The data downloaded from the Data Acquisition

System was in readable form with Microsoft Excel CSV (Comma Separated Variable)

format.

4.3.4.2 Test Procedure

The following steps were followed in conducting ASTM C157 free shrinkage test:

1. Cover the interior surfaces of the specimen molds with transmission oil.

2. Set up the gage set points on the sides of the mold carefully, keeping them

clean, and free of oil, grease and foreign matter.

3. After concrete mixing is done, place the fresh concrete into the molds in two

equal layers with each layer vibrated for 30 seconds by placing the molds over a vibrating

table.

4. Cover the concrete samples with plastic sheets for one day.

5. After one day, remove the concrete samples from the molds and place them into

the shrinkage test frames as shown in Figures 4-6 and 4-7.

6. Adjust the LVDT readings to zero by observing output displays in the DAS. It

is somewhat difficult to set the LVDT reading to zero, because of its high sensitivity.

Thus, just adjust it to as close to zero as possible. However, when obtaining the

shrinkage value, the initial reading is subtracted from the readings taken at different days.

7. After the LVDT readings are set to zero (or close to zero), set the DAS to record

readings every 15 minutes continuously.










8. Download the readings from the DAS to a computer after 7 to 14 days, using the

software "Bench Link Data Logger."

4.3.5 Free Shrinkage Measured by Embedment Gage in the Long-Specimen
Apparatus

4.3.5.1 Test Set-up

The test setup for free shrinkage measurement using the long-specimen apparatus

consisted of a long-specimen mold, an embedment strain gage, a Bridge-sensor (which

was a strain indicator), a laptop computer, a data acquisition system and a temperature

gage. The schematics for the test setup are shown in Figure 4-9. Figure 4-10 shows a

picture of two long-specimen molds before the placement of concrete in them.


Excitation
Voltage
Terminal
Block


I / Embedment train Gage L...___ U I
Load
Cell

Figure 4-9. Schematics for test setup with embedment gauge for constrained shrinkage
measurement using the long-specimen apparatus.

An OMEGA OM2-8608 Backplane 8-channel signal conditioner was used to

connect the embedment strain gages in a quarter bridge circuit and to amplify the output









signals from the bridge circuits. The embedment strain gages used have a length of 4.68

in. (120 mm), a resistance of 120 Ohms and a gage factor of 2.0. An excitation voltage of

4 V and a gain of 333.33 for the output signal were used. The outputs from the signal

condition were connected to the data acquisition system. The following equation relates

the un-amplified voltage output to the measured strain:

Strain = 4 (voltage output) / (gage factor)(excitation voltage)

= 4 (voltage output) / 2.0 (4V)

= (voltage output in V) / 2 (Eq. 4.4)


Figure 4-10. Picture of two long-specimen molds









With a gain of 333.33 was used, the measured strain is related to the amplified

voltage output as follows:

Strain = (Amplified voltage output in V) / (2 x 333.33)

Strain = (Amplified voltage output in V) / (666.67) (Eq. 4.5)



4.3.5.2 Test Procedure

The following steps were followed for running the free shrinkage test using the

long-specimen apparatus:

1. Assemble the side blocks and the end blocks of the long-specimen molds

together and fix them to the base plate firmly by using screws.

2. Coat the surfaces of the support base plate and the side blocks with a thin layer

of transmission fluid to avoid friction between the concrete specimen and the bottom

support plate and the side plates.

3. Configure the DAS to record the data for the test. The desired parameters such

as the time interval for the DAS to scan the data, the unit for temperature, type of

thermocouple, unit for voltages, etc., have to be set in the DAS by using the knobs and

buttons in the front panel of the DAS.

4. Set the DAS unit to start scanning with a time interval of 15 minutes.

5. Place the fresh concrete into the mold in two equal layers, and tamp each layer

with fingers for consolidation. After the first layer is done, place the embedment gage in

the concrete at the center of the mold. Then, apply the second layer of concrete on top of

the gage. The gage should be placed about half an inch from the top of the mold.

6. Finish the surface of the specimen with a hand trowel.

7. Turn on the DAS to start recording data.









8. After the concrete has set sufficiently, remove the side blocks so that the

concrete specimen will have restraint on only the bottom portion, which has been coated

with a thin layer of transmission oil to reduce friction. Usually the side blocks can be

removed within several hours to a day's time.

9. Keep the specimen undisturbed for the entire duration of the test.

10. Download the data to a laptop computer at the desired times. Data from seven

days may be downloaded at one time. The software "Bench Link Data Logger" can be

used to download data from the DAS to the readable Excel CSV format files.

4.3.6 Free Shrinkage Measurement using Whittemore Gage
in the Long Specimen Apparatus

4.3.6.1 Test Set-up

In this test set-up, a pair of gage point studs was embedded in the long concrete

specimen at a distance of 10 inches (254 mm) apart from one another, and a Whittemore

gage was used to measure the change in distance between these two gage points due to

shrinkage in the specimen. The Whittemore gage used is shown in Figure 4-11. The

long concrete specimen with the two gage point studs installed is shown in Figure 4-12.


Figure 4-11. Whittemore gage for measuring the distance between two gage points














F Z:TUO


Figure 4-12. Long concrete specimen with gage point studs installed

4.3.6.2 Test Procedure

The following steps were followed in conducting the free shrinkage measurement

using the Whittemore gage in the long specimen apparatus:

1. Assemble the side blocks and the end blocks of the long-specimen molds

together and fix them to the base plate firmly by using screws.

2. Coat the surfaces of the support base plate and the side blocks with a thin layer

of transmission fluid to avoid friction between the concrete specimen and the bottom

support plate and the side plates.

3. Place the fresh concrete into the mold in two equal layers, and tamp each layer

with fingers for consolidation. After both layers are done, press two gage studs into the

surface of the long concrete specimen, at the middle of the specimen and at a distance of

10 in. (254 mm) from one another. Make sure that the gage point studs are well pressed

into the concrete so that after hardening, the Whittemore gage can be placed on top of the

studs securely and the readings can be taken.

4. Finish the surface of the specimen with a hand trowel.


lllLrl"1LllllllL111(111111111
ir

Fia~
i,









5. After the concrete has set sufficiently, remove the side blocks so that the

concrete specimen will have restraint on only the bottom portion, which has been coated

with a thin layer of transmission oil to reduce friction. Usually the side blocks can be

removed within several hours to a day's time.

6. After the concrete has hardened sufficiently (usually after 24 hours of curing),

take the first reading of the distance between the two gage points using the Whittemore

gage. Take additional readings at the specified times as needed.

4.3.7 Free Shrinkage Measurement Using Whittemore Gage
on Cylindrical Specimens

4.3.7.1 Test Setup

In this method, 6 x 12-in. (152.4 x 304.8-mm) cylindrical concrete specimens are

cast, and the free shrinkage of the concrete specimens is measured by means of a

Whittemore gage. Three pairs of gage points with a gage distance of 10 in. (254 mm) are

placed in each test concrete specimen. A Whittemore gage is used to measure the change

in distance between the gage points due to drying shrinkage.

A gauge-point positioning guide, as shown in Figure 4-13, was used in positioning

the gauge-points on the plastic cylinder mold. The guide can be placed around a

6 x 12-in. (152.4 x 304.8-mm) cylinder mold. By tightening the six screws on the guide,

the precise locations for the three pairs of gage points, with a gage distance of 10 in. (254

mm), can be marked conveniently on the mold. Figure 4-14 shows a picture of the

gauge-position guide. Figure 4-15 shows a picture of the plastic cylinder mold inside the

gauge-position guide.

4.3.7.2 Test Procedure

Figure 4-16 shows a picture of the concrete cylinders with the gauge points









attached on them after the molds have been removed. A Whittemore gauge was used to

measure the change in the distance between the gage points as the concrete cylinder

shrinks. The Whittemore gauge has a resolution of 0.0005 in. Three sets of

measurements were taken from each specimen at each specified time. The original

distances between the gauges are to be measured immediately after the plastic mold is

removed. The shrinkage strain is taken as the average of the three readings from each

specimen, and can be expressed as follows:


Figure 4-13. Gage-point positioning guide


























































Figure 4-14. Gauge-position guide
























































Figure 4-15. Plastic cylinder mold inside gauge-position guide




























j STI'IDS








Figure 4-16. Concrete cylinders with gauge point studs installed on them


h -1) (Eq. 4.6)
i3 10
3 i=1i

where

ii = measured distance between ith pair of gage points

10 = original distance between ith pair of gage points measured immediately

after demolding.

4.3.8 Constrained Shrinkage Test Using the Long Specimen Apparatus

The test setup and procedure for the constrained shrinkage test went through

numerous stages of development and refinement during the course of this study. The

description of the test setups and procedures used in this study, and their evaluation are

presented in Chapter 5 of this report.














CHAPTER 5
DEVELOPMENT AND EVALUATION OF THE MODIFIED
CONSTRAINED LONG SPECIMEN APPARATUS

5.1 Introduction

This chapter presents the development and evaluation of the modified constrained

long specimen apparatus for evaluation of resistance to shrinkage cracking of concrete.

Based on the evaluation of the various designs that have been tried out, a final design was

adopted for use in the laboratory testing program in this study.

5.2 Fundamentals of the Constrained Long Specimen Method

5.2.1 Original Design

The constrained long specimen set-up had a dog-bone shaped mold with an overall

length of 27.30 in. (700 mm). The actual portion of the mold that holds the concrete is

17.55 in. (450 mm) long and 1.56 x 1.56 in. (40 x 40 mm) in cross section. It has two

flared ends each of which has a width of 4.29 in. (110 mm). One end is fixed to the

bottom plate, and the other end was free to move. Meanwhile, in order to give restraint to

the free movement of concrete, it was clamped with an end aluminum block through a

proving ring so that the induced tensile force can be measured. This aluminum block was

fixed to the bottom plate. When there is any shrinkage movement in the concrete

specimen, the proving ring will get stretched because of its fixity to the end block and it

will read a value equal to the tensile force that is induced in the specimen. Figure 5-1

illustrates the design of the originally developed Constrained Long Specimen Apparatus.










1. Fixed Grip 4, Syndwelic Rails 7. Scevw Assembly
2. Side of Mold 5. Prowng Rin8 8. Gage Poirit InU
3. Mo'mble Grip 6. Grip 9. Metal Gude for Gauge PLUrn











700 m




700 mm

Figure 5-1. The original constrained long specimen apparatus [Tia et al., 1998]

5.2.1 Test Procedure

The test procedure for the original constrained long specimen apparatus test

consisted of the following steps:

1. Spread a thin layer of motor oil on the surface of the metal guide that is in

contact with the concrete specimen.

2. Place the fresh concrete into mold.

3. Place the whole apparatus on a vibrating table for one minute.

4. Place two gage-point inserts which are attached under the metal guide (#9 in

Figure 5-1) into the concrete specimen.

5. Place the entire apparatus again on the vibrating table for an additional minute.

6. Press the two gage point inserts into the concrete firmly with fingers to make

sure that they are completely inside the concrete mass. Two gage point inserts are used

to hold the Whittemore gage to the concrete.

7. Finish the surface of the specimen with a hand trowel.









8. After 12 hours, remove the two side pieces of the mold, and remove the metal

guide from the gage point inserts.

9. Attach the Whittemore gage to the two inserts with two screws.

10. Record the initial readings of both the proving ring and the Whittemore gage.

11. After the removal of the side pieces and the attachment of the Whittemore

gage, monitor the induced load by means of the proving ring, and the movement of the

concrete specimen by means of the Whittemore gage for a period of 14 days.

Though the concrete specimen was constrained from movement at the two ends, the

Whittemore gage would usually measure a slight shortening of the concrete specimen.

This could be explained by the movement of the proving ring as load was induced.

Figure 5-2 shows how the movement of the proving ring (6PR) is equal to the movement

of the constrained long specimen (6cL).

6PR = 6CL











L9
----, .-----1
%."- .- ._









LT

Figure 5-2. Schematics of the restrained long specimen under contraction

5.2.3 Method of Analysis

The analysis part consists of several equations involving three different deforma-

tion components in the concrete specimen. The first component is the shortening due to









shrinkage (6sh). The second component is the elastic lengthening due to induced tensile

stress (bE). The third one is the creep due to the induced stresses (SCR). These three

components are related to the total movement of the specimen as follows:

6CL = 6sh 6E 6CR (Eq. 5.1)

In terms of strains (C's), the relationship can be written as:

SCL = Esh EE ECR (Eq. 5.2)

The total strain in the constrained long specimen (ECL) can be calculated from the

deformation read by the Whittemore gage (Sg) as follows:

Total Strain, ECL = 6g/Lg (Eq. 5.3)

where Lg = gage length = 10 in. (254 mm).

The elastic strain (CE) can be calculated from the induced stress (oE) and the elastic

modulus of the concrete (E) as follows:

EE = E/E = FPR/AE (Eq. 5.4)

where FPR = force measured by the proving ring; and

A = cross-sectional area of concrete specimen = 2.48 in2 (1600 mm2).

The shrinkage strain (Esh) can be assumed to be equal to the free shrinkage strain

measured by the length comparator. From Equation 5.2, the creep strain (ECR) can be

calculated from the other strains as follows:

SCR = Esh EE ECL

= Esh (FPR/AE) g/Lg (Eq. 5.5)

If a concrete member is fully constrained from movement, the induced stress due to

drying shrinkage can be expressed as:

(OFC = (Esh ECR) E (Eq. 5.6)









where DFC = induced stress in a fully constrained concrete.

The free shrinkage strains as obtained from the free shrinkage measurements by

means of the length comparator are used as the shrinkage strain (Psh), while the creep

strains from the long constrained specimen test (as computed from Equation 5.5) are used

as the creep strains, SCR. The actual creep strain should be slightly more than the one

experienced by the long constrained specimen, since the long constrained specimen is not

fully constrained. Thus, using the creep strains from the long constrained specimen would

result in a slightly higher (or more conservative) estimation of the induced stresses.

When the computed expected shrinkage stress (@FC) as computed by Equation 5.6

exceeds the expected tensile strength of the concrete (Ot) at any particular time, the

concrete will be likely to crack due to shrinkage stresses at that time.

5.3 First Refinement of Apparatus Use of LVDT,
Load Cell and Data Acquisition System

5.3.1 Changes Made to the Original Design

The constrained long specimen apparatus, which was previously developed for the

FDOT by the University of Florida and described in Section 5.2, was further refined by

automating the data acquisition system process. The apparatus was refined by

(1) replacing the Whittemore gage, which was used to measure the deformation of the

specimen by a high-sensitivity Linear Variable Differential Transformer (LVDT), and

(2) replacing the proving ring, which was used to measure the induced force in the

constrained long specimen by a load cell. A convenient and effective method of

attaching an LVDT to the constrained long concrete specimen, and using the LVDT to

measure the deformation of the specimen was designed and tested. After some

comparative evaluation, an AC LVDT, instead of a DC LVDT was selected for use. An









AC LVDT has two major advantages over a DC LVDT in this application. First, an AC

LVDT is much lighter in weight. Second, it has less noise and is more accurate.

The selected AC LVDT is a CD375-025 by Macro Sensors. It has a stroke of

+0.025 in. (0.635 mm), a weight of 0.1 oz (2.8 grams) and gives an output of 10 mV per

0.001 in. (0.0254 mm) of deformation under the normal operating condition. Gage studs,

brackets for holding the gage studs, and lightweight holders for the LVDT body and

LVDT core were designed, fabricated and tested. Figure 5-3 shows the setup used for

measuring the deformation of the constrained long specimen using an LVDT. When

there is any shrinkage movement in the concrete specimen, the load cell will get stretched

because of its fixity to the end block and it will read a value equal to the tensile force that

is induced in the specimen. The constrained long specimen mold used a concrete

specimen of a length of 21.25 in. (539.75 mm) with 1.5 x 1.5 in. (38.1 x 38.1 mm) as

cross-section. The end collar blocks have a width of 4.25 in. (111.95 mm) each.


..... :: .. ... .







Figure 5-3. Constrained long specimen apparatus using a LVDT

A drawing of the top and the side views of the apparatus is shown in Figure 5-4.

The long constrained concrete specimen with its dog bone shape has two ends of steel

collars with a width of 4.25 in. each. The steel collar blocks are shown in Figure 5-5.

Figure 5-6 displays the front and side views of the PVC side pieces for the Long







71


Constrained Specimen apparatus. Figure 5-7 shows the aluminum bracket support for the

gage studs that hold the LVDT and the core rod holders to the concrete specimen.


i I ROD clEa d.fa)
CUNCRE TE
5T I _EST LAIID RO-1/2' dle-ZO\ DRILLED O.LE
.i -- C--E.. P LL thrc./inm ,7656 o


4 E 3.25;

as.-:' o o
So
,r *. 10 15 2,* L.7"' .5


1.5 :
Qsj
i


Figure 5-4. Top and side views of the constrained long specimen apparatus


1.5'
.750'


SIDE VIE'


0.5'
0.375'


DRILLED
HOLE

-DIA-20 n
THREADS/INCH) U







W TOP VIEW


Figure 5-5. Side and top views of the end collar block of the mold











3 HOLES @6625' i/4' d)


II j il I I


i5' 6,625"
L5[' 15. 25

Figure 5-6. Front and side views of the PVC side pieces for the
constrained long specimen apparatus


750


750"
:--


1.035'


DRILLED HDLE
- (1/4' dic for- 1/4
DRILLED
DRILLED


I LI .251T HOLE
(1 /4' dia)
.45 0.3"
Figure 5-7. Aluminum bracket support for the gage studs that hold the LVDT and
the core rod holders to the concrete specimen

5.3.2 LVDTs for Measurement of Strain

An AC LVDT (Linear Variable Differential Transformer) is used to measure the

displacement between two gage studs, which are placed on the concrete specimen at a

spacing of 10 inches (mm) apart. An LVDT is an electromechanical device that produces

an electrical output proportional to the displacement of a separate movable core. It

consists of a primary coil and two secondary coils symmetrically spaced on a cylindrical

form. A free-moving, rod shaped magnetic core inside the coil assembly provides a path


.2"'



2,50'









for the magnetic flux linking the coils. The cross-sectional view of a typical LVDT is

shown in Figure 5-8.








S\ Core


Sncondnary Primary Secondary
Coll Coil Coll



Figure 5-8. Cross-sectional view of an LVDT

The primary coil needs to be excited, in order to induce a voltage in the secondary

coils. The excitation needs to be an alternating voltage, in the 400 Hz to 20 KHz range

usually. Square, trapezoid and other wave shapes can be used, but a sinusoidal shaped

wave will yield the best results. The voltage that is applied to the primary coil produces a

current whose magnitude depends on the impedance of the primary coil at the chosen

frequency. This current induces currents in the secondary coils of the LVDT. The

amount of current induced in each secondary coil depends on the mutual inductance

between the primary coil and each secondary coil. This mutual inductance, in turn,

depends on the position of the core, with relation to each secondary coil. The outputs of

the LVDT are these two AC voltages, which can be added together to form one AC

voltage. This voltage varies approximately linearly with the axial position of the core. A

typical LVDT signal conditioning electronics will convert this AC voltage to DC voltage.

When the primary coil is energized by an external AC source, voltages are induced

in the two secondary coils. These are connected in series and in opposing direction so the








two voltages are of opposite polarity. Therefore, the net output of the transducer is the

difference between these voltages, which is zero when the core is at the centre or null

position. When the core is moved from the null position, the induced voltage in the coil

toward which the core is moved increases, while the induced voltage in the opposite coil

decreases. This action produces a differential voltage output that varies linearly with

changes in core position. The phase of this output voltage changes abruptly by 1800 as

the core is moved from one side of null to the other. Figure 5-9 shows the core

displacement and the respective voltage changes that occur in the coil.


IMr ut.1UhI


Oil painlo

core D=aonuknt


Figure 5-9. LVDT core displacement and the respective voltage change


S.t.I.1











The LVDT used was a CD375-025 by Macro Sensors and Figure 5-10 shows a


close-up picture of the LVDT inside the LVDT holder. Figure 5-11 shows a close-up


picture of the holder for the rod for the LVDT core.


n ..: .2 2 ': .':.- --
_I .;.; ..**'M -; -
F.. .. .. a d .




Figure 5-10. LVDT holder and a portion of the rod that is connected to the other holder


a;.'-'. \ r




":.. ***,- :

-, .,. / *,*
S-a .,:: .?"


Figure 5-11. The holder for the rod that passes through the LVDT core









This LVDT has a stroke of +0.025 in. (0.635 mm), a weight of 0.1 oz (2.8 grams)

and gives an output of 10 mV per 0.001 in. (0.0254 mm) of deformation under the normal

operating condition. An AC voltage source is used to supply an excitation voltage of 3.0

RMS V at 2.5 kHz. The displacement (in inches) between the two gage points is

computed from the RMS voltage output as:

(Displacement in 0.001 in.) = (RMS voltage in mV) x 0.1

The strain is then computed from the displacement as:

Strain = Displacement / (Gage Length) = Displacement / (10 in. or 254 mm)

5.3.3 Load Cell for Measurement of Stress

A load cell was used to measure the force experienced by the concrete specimen

during a test. The load cell used was a LCCB-1K by Omega. It is a tension and

compression "S" type load with a maximum capacity of 1000 lb (4450 N). The rated

output is 3mV/V for the full load of 1000 lb (4450 N). A DC voltage source is used to

supply an excitation voltage of 10 V. With the 10 V excitation input, the load cell gives

an output of 30 mV/1000 lb, or 0.03 mV/lb. The axial force in the concrete sample is

computed from the DC output voltage from the load cell as:

(force in lb.) = (dc voltage in mV) x 33.33

The stress in the concrete sample is then calculated from the force as:

Stress = Force / (Cross-sectional area of concrete)

= Force / (2.25 in2 or 1451.6 mm2)

The load cell attached to the frame of the specimen is shown in Figure 5-12.







77





---















Figure 5-12. The load cell attached to the frame of the concrete specimen

5.3.4 Data Acquisition System

The output ends from the LVDT and the load cell were connected to an automatic

data acquisition system, an Agilent 34970A unit (by Agilent Technologies) with a HP

34901A (20-channel armature multiplexer) plug-in module. The Data Acquisition

System unit is shown in Figure 5-13. The DAS unit can be set up to take readings at

MullHe ront panel: tafa-oWlentet
saef-guldg nenua
-il-a rollnno if lnfllantlh


('/ digit l122tiint-r nal l
D.MM mrnda-i I I IunclonJDr rthoiu
ea1ina1 al na1l orsianing
-'%


melKrr hlo ,Jata r.*rff
pM t I i1 I urOea


HLrLO elrm Imts an Kea inp ut Ba' lae.Ued M reGlm clou rFI paeng
chinneLplus 4TeTLo lnn cuip$ l canr and dmnetslriTn l'aora

Figure 5-13. Agilent 34970A data acquisition system unit


I 1 1111~1









specified time intervals and for a specified length of time. The HP 34901A multiplexer

module can read up to 20 channels of AC or DC voltages with a maximum capacity of

300 V. It has a switching speed of up to 60 channels per second. It also has a built-in

thermocouple reference junction for use in temperature measurement by means of

thermocouples.

The Agilent 34970A unit can take up to three plug-in modules. The stored data can

be downloaded to a personal computer via a RS232 cable connection. The data files are

in CSV format and can be read readily by spreadsheet software such as Excel.

After satisfactory performance was observed from a prototype of the developed

constrained long specimen apparatus equipped with a LVDT, a load cell and a data

acquisition system, ten such apparatuses were constructed. Five of the ten apparatuses

were equipped each with both a LVDT and a load cell, and were to be used to perform

the constrained shrinkage test. The other five apparatuses were equipped each with only

a LVDT, and were to be used to perform the free shrinkage test. All the apparatuses were

constructed to be identical to one another so that they could perform equally in measuring

shrinkage. A load cell could be added easily to the apparatus if there was no load cell

attached, prior to running the constraint shrinkage test. Similarly, the load cell could be

taken off easily from the apparatus to run the free shrinkage test. The schematics of the

set-up for the constrained shrinkage test using a LVDT and a load cell is shown in

Figures 5-14-a and 5-14-b.









DAS Module


LVDT


Figure 5-14-a. Setup for the constrained long specimen test with a LVDT



DAS Module


DC Voltage Source Supplying
10V of Excitation Voltage


LVDT


Load Cell


Figure 5-14-b. Setup for the constrained long specimen test with a LVDT and a Loadcell









5.3.5 Modified Instrumentation for the LVDTs

One major instrumentation problem was encountered when these ten apparatuses

were evaluated. The problem was caused by the fact that only one AC Voltage Function

Generator was used to power all of the AC LVDTs. The AC LVDT requires an

excitation voltage of 3 RMS V at a frequency 2.5 kHz. However, when one voltage

function generator was used to power several LVDTs at the same time, the function

generator was not able to deliver the required voltage. In addition, interference between

the outputs from the different LVDTs were noted. The instrumentation for the LVDTs

was subsequently modified to take care of this problem.

Eleven LVDT signal conditioners (Model LPC-2100 by Micro Sensors) were

acquired. Each of these LVDT signal conditioners was connected to each of the AC

LVDTs (CD375-025 by Macro Sensors) to provide the needed excitation voltage of 3.0

RMS V at 2.4 kHz, to demodulate the AC output signal from the LVDT into a DC signal,

and to amplify the DC signal before outputting it to the data acquisition system.

According to the specification sheet, the LVDT signal conditioner had been calibrated

such that a full stroke of the LVDT (+0.025 inch) would produce an output of +10.0 DC

V from the signal conditioner. A LVDT signal conditioner is shown in Figure 5-15.

According to this assumed calibration, the displacement between the two gage points

could be computed from the voltage output as follows:

(Displacement in 0.001 inch) = (voltage in V) x 2.5
























Figure 5-15. A LVDT line powered LPC-2100 signal conditioner



5.3.6 Calibration of the LVDT/Signal Conditioner System

When the assumed calibration of the LVDT/signal conditioner system was used,

the measured shrinkage from the long specimen apparatus appeared to be too low and

erroneous. Thus, a special calibration setup using a micrometer was built to calibrate the

LVDT/signal conditioner system. It consisted mainly of a holder for the micrometer, a

holder for the LVDT and a spring attachment for the extension rod for the core of the

LVDT, to be aligned with the micrometer. The micrometer used had a range of 0.5 in.

(12.7 mm) and a precision of 0.001 in. (0.0254 mm). Figure 5-16 shows the schematic of

an individual constrained long specimen connected to the LVDT and other

instrumentations.










DAS with
Plug-in-Modules


Temperature Gage Ce


Figure 5-16. Individual constrained long concrete specimen connected to an LVDT,
LVDT signal conditioner, DAS and the computer

The calibration was set up so that the core was positioned near the center of the

LVDT. The core was then moved through the LVDT with the displacement read by the

micrometer. The corresponding voltage output from the LVDT/conditioner was read by

a digital voltmeter. A plot of the LVDT/conditioner output versus displacement is shown

in Figure 5-17. A picture of the calibration setup is shown in Figure 5-18.

Results of the calibration indicated that the previously assumed calibration of the

LVDT/signal conditioner system was in error. The previously assumed calibration was

that 1 V of output from the LVDT/signal conditioner translated into 0.0025 in. (0.0635

mm) of displacement. However, the results of the actual calibration indicated that 1 V of

output from the LVDT/conditioner system should translate into 0.013 in. (0.3302 mm) of

displacement (as shown from the plot in Figure 5-17).

Equation for computation of displacement becomes:

Displacement (in inches) = Output (in volts) x 0.013 (Eq. 5.7)










Calibration of LVDT
9

8

7

6

















Figure 5-17. A plot ofLVDT/conditioner output versus displacement (micrometer
s 5


0 3-

2






Micrometer reading (inches)

Figure 5-17. A plot of LVDT/conditioner output versus displacement (micrometer
reading)

Equation for computation of strain becomes:

Strain = Displacement / (Gage Length) = Displacement / (10 in. or 254 mm)

= Output (in volts) x 0.0013 (Eq. 5.8)


5.4 Second Refinement of Apparatus Use of Lubricated Base Plate

Another observed problem with the constrained long specimen apparatus was that

the long concrete specimen appeared to be sticking to the steel plate below it.

A wax paper was placed over the steel base plate in an effort to reduce the friction

between the concrete specimen and the base plate, as shown in Figure 5-19. However,

the wax paper got soaked by the wet concrete and it worsened the problem further. This

idea was thus abandoned.












Micromeler


h I-1'


Spring Loaded
Rod carrying Ihe Podion of Ihe
coire for LVDT Rod


- I:


LVDT


Rod carrying Ihe Spring Loaded
core for LVDT Portion of Ihe
Rod


I Micioinelei


Figure 5-18. Set-up for calibration of LVDTs used in the long specimens