Heat of hydration prediction for blended cements

Prediction and control of concrete temperature rise due to cement hydration is of great significance for mass concrete structures since large temperature gradients between the surface and the core of the structure can lead to cracking thus reducing durability of the structure. Cement replacement with supplementary cementitious materials (SCMs) is frequently used to reduce the concrete temperature rise. Several models have been proposed for predicting heat release of blended cements; however, none of them address incorporation of metakaolin into the mixture. Isothermal calorimetry measurements, based on statistical experimental design, were taken on pastes incorporating combinations of SCMs and chemical admixtures. The data were then used to develop equations to predict the total heat reduction with the incorporation of chemical admixtures and SCMs. Analysis of the calorimetry data indicated that chemical admixtures do not have a significant effect on heat evolution beyond 12 h. SCMs investigated in this study (fly ash, slag, silica fume and metakaolin), on the other hand, were found to have a significant effect at hydration ages of 12, 24, 48 and 72 h.