The effect of temperature on the hydration of composite cements containing limestone powder and fly ash

摘要

The effect of the curing temperature (5,20 and 40℃) on the degree of hydration, amount of bound water and calcium hydroxide, porosity and the development of mechanical properties was investigated on pastes and mortars prepared with fly ash (FA)-limestone (L) Portland composite cements. Increasing the curing temperature for ordinary Portland cement (OPC) leads to a more inhomogeneous distribution of hydration products, resulting in an increased coarse porosity and therefore a lower compressive strength after 7 days and longer. In contrast, the FA containing mortars showed higher compressive strength with increasing curing temperature up to 90 days. The reaction of the FA is increased at 40℃ and strongly retarded at 5℃. At 20 and 40℃, FA reduces the porosity at later ages. The replacement of 5% of the OPC or FA by L powder did not impair the strength at 5 and 20℃, but lowered strength slightly at 40℃ for the FA blended cements. The porosity appears to be the dominating factor regarding the compressive strength, independent of whether part of the OPC is replaced by FA and L powder or not.