Early age shrinkage and bond at interface between repair material and concrete substrate

EARLY AGE SHRINGKAGE AND BOND AT INTERFACE BETWEEN REPAIR MATERIAL AND CONCRETE SUBSTRATE KYAW MYINT LAY (B. E.) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHIOSOPHY DEPARTMENT OF CIVIL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2007 ACKNOWLEDGEMENTS I begin by expressing my gratitude to my supervisor, Associate Professor K. C. Gary Ong, for his guidance, advice, and patience throughout the course of this study. I will always be grateful for lessons learned under his tutelage. I would like to thank the staffs of the Concrete Technology and Structural Engineering Laboratory of the Department of Civil Engineering at the National University of Singapore for their kind assistance throughout the study. Finally, I express my deepest gratitude to my family for all their love, support, and encouragement throughout my life. Without their guidance and encouragement this work would not have been possible. Last but not least I would like to dedicate this work to my beloved wife, Mya Nandar, and our daughter, Cheryl Lee @ Mya Cherry, for their understanding, love and motivation throughout this study. i Table of Contents TABLE OF CONTENTS Pages TITLE PAGE ACKNOLEDGEMENTS i TABLE OF CONTENTS ii SUMMARY x LIST OF TABLES xii LIST OF FIGURES xiv CHAPER INTRODUCTION 1.1. Background 1.2. Mechanisms of early age shrinkage 1.2.1. Chemical shrinkage 1.2.2. Autogenous shrinkage 1.2.3. Settlement 1.2.4. Shrinkage due to moisture loss 1.2.5. Thermal effect 1.3. Very early age total shrinkage 1.4. ‘Time-zero’ for early age shrinkage measurement 1.5. Effect of very early age shrinkage in the concrete structure 10 1.6. Effect of early age shrinkage on composite concrete structure 11 1.6.1. Tensile stress in the composite concrete 12 1.6.2. Debonding at interface of the composite concrete 12 1.7. Objectives of the study 13 ii Table of Contents 1.8. Organization of thesis CHAPTER 14 IMAGE ANALYSIS TECHNIQUE 2.1. Introduction 16 2.2. Application of image analysis used in the monitoring of movements 16 2.2.1. Deflection and cracking measurements 17 2.2.2. Structural vibration measurement 17 2.2.3. In-plane deformation or displacement measurement 17 2.3. Image analysis technique and equipment used in current study 19 2.3.1. Target pins and high resolution camera 20 2.3.2. Procedures in the image analysis technique 21 2.3.3. Image analysis software 24 2.3.4. Analysis in XCAP software 24 2.3.5. Particle tracking 24 2.3.5.1.Segmentation and threshold 25 2.3.5.2. Analysis parameters in tracking the targets 26 2.3.6. Calculation of shrinkage 27 2.4. Accuracy of the image analysis technique 29 2.4.1. Accuracy testing on fixed targets 29 2.4.2. Accuracy testing on moving targets 30 2.4.2.1.Estimating a measurement uncertainty 34 2.4.2.2.Calculation of uncertainty in the calibration of the image analysis with dial gauge (using 4288 pixels) 35 2.4.2.3. Calculation of uncertainty in the calibration of the image analysis with dial gauge (using 12864 pixels) 37 iii Table of Contents 2.5. Effect of the software 39 2.6. Effect of image acquisition technique and targets 40 2.7. Effect of lens distortion 42 2.7.1. Effect of lens distortion on the image analysis technique 45 2.7.2. Effect of distortion with different focal length tested using fixed targets 47 2.7.3. Effect of distortion with different focal length tested on moving targets 49 2.7.4. Comparison of results obtained using the fixed targets and moving targets 51 2.7.5. Effect of lens distortion on the image analysis technique 52 2.8. Other factors 54 2.8.1. Effect of instability of camera mounting 54 2.8.2. Effect of leveling of camera and specimen 55 2.9. Summary CHAPTER 56 VERIFICATION OF IMAGE ANALYSIS TECHNIQUE WITH OTHER TECHNIQUES 3.1. Introduction 58 3.2. Methods of monitoring early age shrinkage 58 3.2.1. Transducer methods 59 3.2.2. Dilatometer method 61 3.2.3. Laser sensor methods 62 3.2.4. Embedded strain gauge method 64 3.2.5. Embedded fiber optic sensor methods 64 3.3. Methodology and materials 67 iv Table of Contents 3.3.1. Laser sensor method used in this study 67 3.3.2. Moisture loss and temperature rise measurement 68 3.3.3. Mix proportions and materials used 70 3.4. Behaviors of the concrete mixes at a very early age 71 3.4.1. Moisture loss and temperature rise 71 3.4.2. Very early age total shrinkage of concrete 73 3.4.3. Stiffening effect on very early age total shrinkage 75 3.5. Correlation between image analysis and laser sensor techniques 76 3.6. Correlation between image analysis and Demec measurement 81 3.7. Factors affecting very early age shrinkage monitored using the image analysis technique 82 3.7.1. Settlement of the targets and its effect 82 3.7.2. Effect of expansion of the specimen 85 3.7.3. Effect of specimen size 89 2.7.3.1.Shrinkage in the longitudinal direction 89 2.7.3.2.Shrinkage in the transverse direction 90 2.7.3.3.Effect of specimen size on mortar specimen 92 2.7.3.4.Shrinkage in the diagonal direction 94 3.8. Summary CHAPTER 96 EFFECT OF WATER AND SUPERPLASTICIZER ON VERY EARLY AGE TOTAL SHRINKAGE 4.1. Introduction 99 4.2. Early age shrinkage of concrete in literature 99 4.3. Materials and mix proportions 100 v Table of Contents 4.3.1. Aggregates 100 4.3.2. High range water reducing admixture 101 4.3.3. Mixture proportions 102 4.4. Experimental Procedure 102 4.5. Results and Discussions on D series Mixes 103 4.5.1. Compressive strength and setting time 103 4.5.2. Moisture loss and temperature rise 104 4.5.3. Effect of moisture loss on very early age total shrinkage 106 4.5.4. Effect of moisture loss on very early age shrinkage (starting from initial setting time of concrete) 108 4.5.5. Effect of W/C ratio on very early age total shrinkage 112 4.6. Results and discussions on A series mixes 115 4.6.1. Compressive strength and setting time 115 4.6.2. Moisture loss and temperature rise 116 4.6.3. Effect of W/C very early age total shrinkage of concrete 117 4.7. Effect of setting time on very early age total shrinkage of concrete 119 4.8. Modeling of very early age shrinkage 122 4.8.1. Empirical model for very early age shrinkage (before initial setting time) 123 4.8.2. Empirical models for very early age shrinkage (after initial setting time) 127 4.9. Effect of amount of water added on the very early age total shrinkage of construction grout 132 4.9.1. Specimen preparation and testing procedure 133 4.9.2. Effect of amount of mixing water 134 vi Table of Contents 4.9.3. Expansion before and after setting time 4.10. Summary CHAPTER 135 136 EFFECT OF SILICA FUME AND SHRINKAGE REDUCING ADMIXTURE ON VERY EARLY AGE TOTAL SHRINKAGE 5.1. Introduction 137 5.1.1. Effect of silica fume on very early age properties of concrete 137 5.1.2. Effect of shrinkage reducing admixture on very early age properties of concrete 139 5.2. Materials and mix proportions 140 5.2.1.1. Silica fume (SF) 140 5.2.1.2. Shrinkage reduction admixture (SRA) 140 5.2.1.3.Mix proportions 140 5.3. Results and discussions 5.3.1. Setting time 142 5.3.2. Temperature development 144 5.3.3. Moisture loss 146 5.3.4. Effect of silica fume on very early age total shrinkage (Series A mixes) 148 5.3.5. Effect of silica fume on very early age total shrinkage (Series D mixes) 153 5.3.6. Empirical model for very early age shrinkage of concrete with silica fume replacement before initial setting time 156 5.3.7. Empirical models for very early age shrinkage of concrete with silica fume replacement after initial setting time 160 5.3.8. Effect of SRA on early age total shrinkage of concrete 162 5.4. Summary 168 vii Table of Contents CHAPTER EARLY AGE DIFFERENTIAL SHRINKAGE AND BOND STRENGTH DEVELOPMENT IN COMPOSITE CONCRETE 6.1. Introduction 170 6.1.1. Early age differential shrinkage in composite concrete 170 6.1.2. Effect of early age shrinkage on bond strength 172 6.1.3. Effect of moisture condition of substrate on bond strength 172 6.2. Experimental Program 174 6.2.1. Material and mix proportions 174 6.2.2. Composite specimen used 175 6.2.3. Specimen preparation and shrinkage monitoring 177 6.2.4. Bond strength measuring method 178 6.2.4.1. Existing bond strength test methods 178 6.2.4.2. Shear bond test method used in this study 180 6.3. Results and discussions on differential shrinkage of composite specimen 181 6.3.1. Properties of concrete 181 6.3.2. Drying shrinkage of monolithic specimen 184 6.3.3. Absorption and expansion of substrate concrete 185 6.3.4. Effect of moisture condition of substrate on restraint shrinkage 188 6.3.4.1. Very early age restraint shrinkage of composite specimen 188 6.3.4.2. Effect of moisture condition of substrate on the very early age restraint shrinkage of composite specimen (during the first 24 hour after adding water to the new concrete) 195 6.3.4.3. Effect of moisture condition of substrate on the early age restraint shrinkage of composite specimen (from day to 90 days after adding water to new concrete) 199 viii Table of Contents 6.3.4.4. Effect of moisture condition of substrate on the early age restraint shrinkage of composite specimen (from 0.5 hours to 90 days after adding water to new concrete) 201 6.3.5. Effect of age of substrate on the early age differential shrinkage of composite specimen 207 6.3.6. Effect of the silica fume and SRA on the early age differential shrinkage of the composite specimen 211 6.4. Results and discussions on bond strength development in composite specimen 215 6.4.1. Effect of moisture condition of substrate on shear bond strength of composite specimen 215 6.4.2. Effect of age of substrate on shear bond strength of composite specimen 225 6.4.3. Effect of silica fume and SRA on shear bond strength of composite specimen 227 6.5. Summary CHAPTER 231 CONCLUSIONS 7.1. Conclusions 234 RECOMMENDATIONS FOR FURTHER STUDY 238 REFERENCES 240 ix Conclusions 6. Very early age differential shrinkage of composite concrete specimens was presented. The effect of the moisture condition of the substrate prior to casting of the new concrete layer, and the effect of age of substrate was studied. The results showed that the rate of shrinkage increased with decreasing moisture content in the substrate concrete. This could be attributed to the higher rate of moisture absorption by the substrate possibly generating restraint forces in the newly cast concrete layer. The results also showed clearly the presence of differential shrinkage occurring within the new concrete layer, with higher shrinkage strains at locations at a distance 45 mm away from the interface to very low values at the interface in all specimens tested. It was also observed that the specimen with higher moisture absorption registered higher shear bond strength at the interface. 237 Recommendations for Further Study Recommendations for Further Study 1. Compared with the accuracy of the other methods used in this study, the accuracy of the image analysis method is less accurate. With improvement in imaging devices and imaging software the accuracy of the image analysis method could be improved further. Further research should be carried out to improve the accuracy of the image analysis method. 2. A modified test method should be developed to study the effect differential shrinkage with respect to the depth of the specimen. The test specimen geometry could be modified. Using different depth of the specimens, the effect of moisture loss on the very early age shrinkage could be clearer. 3. Based on the magnitude of shrinkage strains registered alone, early age shrinkage has the potential to cause cracks during the plastic stage if the concrete is restrained. However, only free shrinkage of concrete was monitored in this study. Further restrained shrinkage tests using a full range of test parameters are needed to estimate the potential of cracking of concrete at a very early age. 4. Although Chapters & provided a description of material properties and their influence on very early age shrinkage of concrete, the overall number of mixtures investigated is relatively small. More tests should be performed on determining the role of other additives, such as slag, fly ash, non reactive powders and fibers on very early age total shrinkage. It would be informative to replace part of the cement with non reactive powder such as granite powder to distinguish between the effects of filler, pozzolanic reaction, and bleeding. More information can be obtained through tests involving various mixtures and curing conditions help for 238 Recommendations for Further Study better shrinkage models so that the very early age shrinkage of concrete of a wider range of material composition and curing conditions can be formulated. 5. In this study, only a few configurations of composite specimens were tested to demonstrate differential shrinkage of composite specimens. Further tests are required to achieve a better understanding of differential shrinkage with respect to specimen geometry and exposure conditions. Different thicknesses of new concrete layers are recommended to study the restraint generated from the substrate concrete. 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P., (2003) “Effect of water to cementitious material ratio and silica fume on the autogenous shrinkage of concrete,” Cement and Concrete Research, V. 33, pp. 1687-1694. 252 [...]... the material, temperature, relative humidity of the environment, and the size of the specimen Detail mechanism of very early age shrinkage will be discussed in the following sections 1.2 Mechanisms of early age shrinkage Studies on very early age shrinkage of concrete have identified some mechanisms which induce or influence shrinkage at a very early age as, (1) Chemical Shrinkage (2) Autogenous Shrinkage. .. the shrinkage during the first day, while the concrete is setting and starting to harden (Holt, 2000) Long term shrinkage refers to the shrinkage of the concrete at an age of after 24 hours Shrinkage occurring after 24 hours is easy to monitor as the concrete specimen is demolded and standardized shrinkage measurements method can be used In this study “very early age shrinkage is used to denoted shrinkage. .. system Key words: bond strength, differential shrinkage, early age shrinkage, evaporation, image analysis, shrinkage, shrinkage reducing admixture and silica fume xi List of Tables LIST OF TABLES Pages Table 2.1 – Parameters used in the tests for lens distortion test 47 Table 3.1 – Comparison of methods used for measuring of shrinkage at an early age 66 Table 3.2 – Mix proportion of concrete 71 Table... concretes which are more sensitive to cracking immediately after setting, there is more interest in the early age shrinkage of cementitious material Due to difficulties associated with the fixing and placing of targets for use with a number of shrinkage monitoring devices on fresh concrete, that has not set, information about very early age shrinkage was not well documented in the literature Very early. .. shrinkage to be monitored starting before the setting time of concrete At such very early ages the concrete is still soft and there are difficulties in the monitoring of shrinkage of a semi-solid material These difficulties 1 Introduction have hindered comprehensive the physical testing and understanding of the factors influencing very early age shrinkage (Holt, 2004) The amount of very early age shrinkage. .. early age of concrete, the research extended to investigate the differential shrinkage of composite specimens comprising concrete substrate and freshly cast repair material Finally, the effect of differential shrinkage of composite on the bond strength development at the interface was measured That test result will help to define a proper strategy to improve the bond strength, for a more durable repair. .. vertical shrinkage due to hydration of the paste would also induce settlement of the paste during the very early age In literature, the volume shrinkage before the setting of the paste was attributed to the vertical shrinkage and no horizontal shrinkage was assumed to have occurred In a study, Holt E E (2001) demonstrated a comparison between the vertical shrinkage (settlement) and horizontal shrinkage. .. volumetric autogenous shrinkage was calculated using simple equations, then correlated the volumetric chemical shrinkage and autogenous shrinkage The results showed that a large amount of horizontal shrinkage was registered in some specimens even before the setting time However, she could not demonstrate the very early age shrinkage quantitatively during that period due to the limitations of the measurement... hydration of cement Thermal expansion refers to the volume changes that occur when concrete undergoes temperature fluctuations During the early ages, concrete temperature is a function of the heat of hydration and climatic conditions The heat generated due to hydration results in a temperature rise in the concrete as a function of 7 Introduction the thermal conductivity and specific heat of the paste and. .. paste at a constant temperature has been called as chemical shrinkage, bulk chemical shrinkage, chemical volume change, self desiccation shrinkage, autogenous deformation, autogenous shrinkage, autogenous volume change, endogenous shrinkage, and indigenous shrinkage 3 Introduction In this thesis, the term total chemical shrinkage was used to describe the reduction in the absolute volume of the hydrated . total shrinkage 8 1.4. ‘Time-zero’ for early age shrinkage measurement 9 1.5. Effect of very early age shrinkage in the concrete structure 10 1.6. Effect of early age shrinkage on composite concrete. EARLY AGE SHRINGKAGE AND BOND AT INTERFACE BETWEEN REPAIR MATERIAL AND CONCRETE SUBSTRATE KYAW MYINT LAY (B. E.) A THESIS SUBMITTED. CHAPTER 4 EFFECT OF WATER AND SUPERPLASTICIZER ON VERY EARLY AGE TOTAL SHRINKAGE 4.1. Introduction 99 4.2. Early age shrinkage of concrete in literature 99 4.3. Materials and mix proportions