SHRINKAGE CRACKING POTENTIAL & PETROGRAPHIC ANALYSES OF CONCRETE WITH MgO EXPANSIVE ADMIXTURE ABSTRACT OF THE THESIS SHRINKAGE CRACKING POTENTIAL & PETROGRAPHIC ANALYSES OF CONCRETE WITH MgO EXPANSIVE ADMIXTURE   Shrinkage cracking is one of the main engineering problems that reduce the durability of concrete infrastructure. MgO expansive admixture is a technology designed to diminish shrinkage cracking in various applications of concrete, to decrease the cost of maintenance and project timeline as well as to increase the service life of the material. Ordinary portland cement (OPC) concrete with MgO expansive admixture is tested by two sets of restrained ring instruments standardized by ASTM C1581 and AASHTO PP-34. Results of restrained ring tests of plain and MgO concrete specimens with 0.42 w/c showed that 5% addition of MgO expansive admixture to the OPC delayed shrinkage cracking in concrete. Petrographic analyses of plain and MgO concrete showed that fewer shrinkage microcracks are observed in the MgO concrete specimens. SEM/EDS analyses showed that hydrated MgO expands in concrete and reduces shrinkage microcracks. Fresh properties of MgO concrete showed insignificant difference from that of plain concrete while MgO admixture reduced the slump of concrete predominantly.       TABLE OF CONTENTS LIST OF FIGURES……………………………………………………………………………………………………. vi LIST OF TABLES…………………………………………………………………………………………………….. xi ACKNOWLEDGEMENTS……………………………………………………………………………………….. xii CHAPTER 1: INTRODUCTION………………………………………………………………………………….. 1 1.1.PROBLEM STATEMENT………………………………………………………………………………….. 1 1.2.RESEARCH OBJECTIVE AND SCOPE……………………………………………………………… 2 1.3.THESIS ORGANIZATION ……………………………………………………………………………….. 2 CHAPTER 2: LITERATURE REVIEW………………………………………………………………………… 4 2.1.INTRODUCTION……………………………………………………………………………………………… 4 2.2.CONCRETE SHRINKAGE………………………………………………………………………………… 6 2.2.1.Plastic Shrinkage………………………………………………………………………………………….. 7 2.2.2.Autogenous Shrinkage………………………………………………………………………………….. 7 2.2.3.Drying Shrinkage…………………………………………………………………………………………. 7 2.3.MGO EXPANSIVE ADMIXTURE …………………………………………………………………….. 8 CHAPTER 3: MATERIALS AND MIXTURE DESIGN………………………………………………. 26 3.1.INTRODUCTION……………………………………………………………………………………………. 26 3.2.MATERIALS………………………………………………………………………………………………….. 26 3.3.MIXTURE PROPORTIONS……………………………………………………………………………… 28 3.4.MIXING PROCEDURE …………………………………………………………………………………… 29 CHAPTER 4: PROPERTIES OF FRESH CONCRETE………………………………………………… 31 4.1.INTRODUCTION……………………………………………………………………………………………. 31 4.2.TEMPERATURE…………………………………………………………………………………………….. 31 4.3.AIR CONTENT……………………………………………………………………………………………….. 32 4.4.UNIT WEIGHT……………………………………………………………………………………………….. 33 4.5.SLUMP…………………………………………………………………………………………………………… 34 4.6.TIME OF SETTING…………………………………………………………………………………………. 35 4.7.COMPRESSIVE STRENGTH ………………………………………………………………………….. 41 CHAPTER 5: RESTRAINED RING TEST………………………………………………………………….. 45 5.1.INTRODUCTION……………………………………………………………………………………………. 45 5.2. RESTRAINED RING TEST…………………………………………………………………………….. 45 5.2.1.Restrained Ring Test Background………………………………………………………………… 45 5.2.2.ASTM C 1581 Ring Test Set-up…………………………………………………………………… 46 5.2.3.AASHTO P-34 Ring Test Set-up………………………………………………………………….. 47 5.2.4.Restrained Ring Test Procedure……………………………………………………………………. 48 5.2.5.Results of the Restrained Ring Test ……………………………………………………………… 53 CHAPTER 6: PETROGRAPHIC ANALYSES…………………………………………………………….. 57 6.1.INTRODUCTION……………………………………………………………………………………………. 57 6.2.THIN SECTION SAMPLE PREPARATION………………………………………………………. 62 6.3.THIN SECTION CONCRETE SPECIMENS………………………………………………………. 67 6.4.CONCRETE MICROSCOPY……………………………………………………………………………. 72 6.4.1.Fluorescence Microscopy…………………………………………………………………………….. 72 6.4.2.Polarized Light Microscopy…………………………………………………………………………. 76 6.5.RESULTS OF PETROGRAPHIC ANALYSES…………………………………………………… 83 6.5.1.Results of Fluorescence Microscopy…………………………………………………………….. 83 6.5.2.Results of Polarized Light Microscopy …………………………………………………………. 86 CHAPTER 7: SCANNING ELECTRON MICROSCOPY…………………………………………….. 91 7.1.INTRODUCTION……………………………………………………………………………………………. 91 5.2.SEM AND EDS RESULTS OF PLAIN CONCRETE SPECIMEN………………………… 94 5.3.SEM AND EDS RESULTS OF MGO CONCRETE SPECIMEN …………………………. 97 CHAPTER 8: SUMMARY AND CONCLUSION………………………………………………………. 100 REFERENCES……………………………………………………………………………………………………….. 103 APPENDIX A: MIXTURE PROPORTIONS OF CONCRETE BATCHES…………………… 107 APPENDIX B: RESULTS OF FLUORESCENCE MICROSCOPY……………………………… 108 APPENDIX C: SEM/EDS RESULTS OF PLAIN CONCRETE…………………………………… 133 APPENDIX D: SEM/EDS RESULTS OF MgO CONCRETE……………………………………… 140

CHAPTER 1: INTRODUCTION

1.1.PROBLEM STATEMENT

Concrete is the most commonly used construction material that is susceptible to undergo shrinkage cracking and reduction of durability leading to significant financial costs to the construction industry. Mitigation, repair and prevention measures against shrinkage cracks are costly and increase the price of concrete projects. Shorter joint spacing extends the construction timeline and produces maintenance costs before the expected lifecycle of the structure. Secondary effects of cracking such as corrosion, ASR, freeze-thaw damage, infiltration of chemicals reduces lifecycle expectancy of the concrete structures. Additionally, construction of mass concrete tends to be affected by thermal shrinkage cracking due to the high rate of heat generation during concrete operations. Precooling of raw materials and post-cooling of concrete increases the cost of a project with an uncertainty to mitigate thermal cracking and excessive delays in the construction timeline. Reducing the factors that lead to cracking of concrete is the key to lower maintenance costs, expedite the time of completion and extend the service life of construction projects. MgO expansive admixture is designed to provide the characteristics of expansion at a rate that closely compensates for shrinkage of concrete and reduce the capillary surface tension of the concrete pore water. It is applied in all types of cement-based mixes, highly-restrained structures, mass concrete, concrete structures exposed to de-icing such as bridge decks, parking lots and marine structures, concrete floors to control shrinkage cracking and curling and to extend joint spacing. It is expected to significantly reduce shrinkage cracking caused by drying and autogenous shrinkage, improve durability, decrease curling, allow for lesser usage of control joints and shorten infiltration of water, salt, and aggressive chemicals by reducing cracks. Therefore, identifying these effects and defining the potential of cracking of concrete mixes with MgO expansive admixture accurately are vital in controlling shrinkage cracking.

1.2.RESEARCH OBJECTIVE AND SCOPE

The primary purpose of this research is to define and compare the cracking potential of concrete with MgO expansive admixture to ordinary portland cement (OPC) concrete. Basic properties to be investigated include restrained shrinkage, compressive strength, time of setting, and fresh properties of concrete. Total of two mixtures of OPC concrete and OPC with 5% MgO expansive admixture concrete were tested. Water to cement ratio was 0.42 for both of the mixtures. Furthermore, the microstructural characteristics of two concrete mixtures were compared. Petrographic thin sections of both plain and MgO concrete cured for different ages were prepared and tested for fluorescence microscopy, polarized light microscopy, scanning electron microscopy, and energy dispersive spectroscopy to analyze the microstructural differences of plain concrete and MgO concrete and the effect of MgO expansive admixture on the cement matrix and the drying shrinkage cracking potential of concrete.

1.3.THESIS ORGANIZATION

This thesis consists of 8 chapters as the following: Chapter 1 covers the introduction consisting of the problem statement, research objective and scope, and thesis organization. Chapter 2 covers general background and literature review on definition and types of concrete shrinkage and literature review of MgO expansive admixture. Chapter 3 covers materials, concrete design and mixing procedure of plain and MgO concrete. Chapter 4 covers tests of fresh properties of plain and MgO concrete specimens. Chapter 5 covers background, operation and test results of the restrained ring set-up. Chapter 6 covers sample preparation and test results of petrographic analyses. Chapter 7 covers scanning electron microscopy and energy dispersive spectroscopy results of plain and MgO concrete specimens. Chapter 8 covers conclusions. SHRINKAGE CRACKING POTENTIAL & PETROGRAPHIC ANALYSES OF CONCRETE WITH MgO EXPANSIVE ADMIXTURE