||Effects of Coarse Aggregates to the Electrical Resistivity of Concrete
||Department of Civil Engineering
||Van Kien Nguyen
In this study, the influences of coarse aggregate to the electrical resistivities of concrete were investigated. Specifically, types and sizes of the aggregates were targeted as the studied parameters. Commercially available granites and marbles with various sizes of 4.75, 9.5, 12.5, and 19mm were used in the concrete mixtures, and the resistivities at the age of 28 days were investigated. Polarization induced resistivity growth during the electrical measurement were considered and experimentally nullified, such that the real bulk resistivities of concrete specimens can be obtained for comparison. Concrete specimens were made by cement mortars and several degrees (amounts) of coarse aggregates; with a fixed size of coarse aggregates used in a single specimen. Cement mortars were mixed with the water/cement ratio of 0.4, and the cement/sand ratio was held constantly at 1:1. The microstructures of certain specimen samples were obtained by Scanning Electron Microscopy so as to estimate the porosity of cement pastes, which is the primary conductive portion of cementitious materials. This was done to validate the resistivity observation. The results show that the electrical resistivities of concrete made with crushed granites were quite close to those that made with crushed marbles. Moreover, the particle size of aggregates seems to have no significant influences to concrete resistivities while it is to concrete strengths. As a partial study of nondestructive testing technologies to the performance estimations of concrete, further studies were required and we have drew a few comments.
TABLE OF CONTENTS III
LIST OF TABLES VI
LIST OF FIGURES VIII
CHAPTER ONE INTRODUCTION 1
1.1 Background 1
1.2 Research Objective 3
1.3 Research Methods 3
CHAPTER TWO LITERATURE REVIEW 5
2.1 Resistivity Measurement 5
2.1.1 Theory 5
2.1.2 Polarization Effect in Cement-Based Materials 6
2.2 Effect of Raw Materials on Electrical Resistivity 10
2.2.1 Effect of Cement 10
2.2.2 Effect of Supplementary Cementing Materials 13
2.2.3 Effect of Aggregate 13
2.3 Interfacial Transition Zone 19
2.4 Electrical Conduction Mechanism of Concrete 23
2.5 Estimation of the Porosity of Portland Cements Pastes by Using SEM 23
CHAPTER THREE RAW MATERIALS AND EXPERIMENTAL METHODS 25
3.1 Raw Materials 25
3.1.1 Binder Materials 25
3.1.2 Aggregates 26
3.1.3 Water 26
3.1.4 Electrode 27
3.2 Experimental Apparatus 27
3.2.1 Specimen Mold 27
3.2.2 Electronic Balance 28
3.2.3 Grinding Machine 28
3.2.4 Instrument Used for Electrical Resistance Measurement 28
3.3 Experiment Methods 29
3.3.1 Mixing Details 29
3.3.2 Procedure of Casting Concrete Specimens 30
3.3.3 Electrical Resistance Measurement 30
CHAPTER FOUR RESEARCH RESULTS AND DISCUSSIONS 32
4.1 Experiment Results 32
4.1.1 Influence of coarse aggregate content on the electrical resistivity of concrete 32
4.1.2 Effect of Coarse Aggregate Size on the Electrical Resistivity of Concrete 34
4.1.3 Effect of the Coarse Aggregate Type on the Electrical Resistivity of Concrete 41
4.1.4 Porosity Surface Fraction of Cement Paste in Concrete 45
4.2 Discussion 54
CHAPTER FIVE CONCLUSION 56
Appendix A: The electrical resistivity of concrete specimens measured according to time. 60
Appendix B: BSE image and their corresponding black threshold image of cement paste 80
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