Characterization of the Microstructure of Ordinary Portland Cement Paste Using Autogenous Shrinkage and Heat of Hydration Parameters

Abstract

The main objective of this study was to characterize the microstructure of Ordinary Portland Cement paste using autogenous shrinkage and heat of hydration parameters. The relevance of the research was the need to advance the knowledge on understanding the underlying mechanism of autogenous shrinkage and heat of hydration parameters and their influence on the evolution of cement paste microstructure. This will allow Engineers to develop performance based specifications to mitigate pre mature cracking due to autogenous shrinkage and heat of hydration. Though there are many types of cements manufactured and available in Kenya, this thesis focused on Ordinary Portland Cement paste. To limit scope and hence achieve a comprehensive research, the research was limited to cement paste and concrete mixes of water/cement (w/c) ratios of 0.35 and 0.45. Type K temperature probes and Extech Differential Temperature Data Logger were used to measure the heat of hydration of Ordinary Portland Cement paste. Strain gauge and MadgeTech Bridge/Strain data loggers were used to measure autogenous shrinkage-induced strain of hydrating Ordinary Portland Cement paste. A stereo microscope was used to evaluate the microstructure evolution of a hydrating Ordinary Portland Cement paste (as a function of pores formation and cracking). The research findings were that samples with lower w/c ratios recorded higher autogenous shrinkage, bigger pores and increased risk of cracking than the rest of the samples. It was also found that curing in saturated conditions ensures replacement and availability of more water for hydration of Ordinary Portland Cement paste. This reduces autogenous shrinkage. Availability of water for curing reduces the temperature due to cooling aided by the presence of water. It was recommended that further research is done to relate the development of pore structure with autogenous shrinkage. The effect of aggregates on autogenous shrinkage should be further studied. Evidence that autogenous shrinkage causes problems in concrete practice in this region should be sought.