Effect of temperature on the hydration of Portland cement blended with siliceous fly ash

摘要

The effect of temperature on the hydration of Portland cement pastes blended with 50 wt.% of siliceous fly ash is investigated within a temperature range of 7 to 80℃ . The elevation of temperature accelerates both the hydration of OPC and fly ash. Due to the enhanced pozzolanic reaction of the fly ash, the change of the composition of the C-S-H and the pore solution towards lower Ca and higher Al and Si concentrations is shifted towards earlier hydration times. Above 50℃ , the reaction of fly ash also contributes to the formation of siliceous hydrogarnet At 80℃ , ettringite and AFm are destabilised and the released sulphate is partially incorporated into the C-S-H.The observed changes of the phase assemblage in dependence of the temperature are confirmed by thermodynamic modelling. The increasingly heterogeneous microstructure at elevated temperatures shows an increased density of the C-S-H and a higher coarse porosity.