Influence of Clinker Replacement and Curing Temperature on Hydration Kinetics, Strength Development, and Phase Assemblage of Fly Ash–Blended Cements

Abstract

The influence of clinker replacement on temperature sensitivity of fly ash–blended cements was investigated at three realistic temperatures. Blends were prepared by replacing clinker with fly ash or quartz at two replacement levels of 30% and 45%. The rate of hydration of slow-reacting clinker phases, especially belite, reduced in fly ash systems at higher temperatures. At lower replacement levels, this reduction in clinker hydration is compensated by an increase in the pozzolanic activity. However, in high-volume fly ash blends, apart from reduced clinker hydration, and the reduction in pozzolanic reaction due to lower portlandite precipitation, it leads to lower strength development at later ages at higher temperature. While the same level of quartz replacement does not influence belite hydration, it indicates that the main hydration product, calcium silicate hydrate (C-S-H), formed at 50°C in fly ash blends might be different from that of ordinary portland cement (OPC) or quartz blends, and influences the further hydration of clinker.