Contributions of fly ash and ground granulated blast-furnace slag to the early hydration heat of composite binder at different curing temperatures

Hydration heat evolutions and non-evaporable water contents of binders and reaction degrees of fly ash and ground granulated blast-furnace slag (GGBS) were tested to investigate the contributions of fly ash and GGBS to the early hydration heat of composite binders at 25°C and 50°C. Results show that fly ash makes a very small contribution to the early hydration heat of composite binder at 25°C, but GGBS makes a considerable contribution at 25°C. Elevated temperature enhances the contributions of both fly ash and GGBS to the early hydration heat of composite binder significantly. The promoting effect of elevated temperature on the hydration heat and non-evaporable water content of GGBS binder is greater than that of fly ash binder. The reaction heat per unit mass of GGBS is only 16·7% higher than that of fly ash. The main reason for the difference of hydration heats between GGBS binder and fly ash binder is that GGBS shows much higher hydraulic activity than fly ash.