Calorimetric Study of Cement Blends Containing Fly Ash, Silica Fume, and Slag at Elevated Temperatures

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Abstract
The hydration behavior of blended cements containing fly ash, silica fume, and granulated blast furnace slag over the temperature range of 10 to 55°C was studied by isothermal calorimetry. The rates of heat evolution during the first 24 h of hydration were examined. The results were analyzed to determine the kinetics of hydration of portland and blended cements. Relationships between the reactivities of these blended cements and the curing temperature were established. The results show that the rates of hydration reactions increased with an increase in temperature in all instances. Comparison among the blends containing fly ash, silica fume, and slag was made to establish activation energies for the hydration reactions. Arrhenius activation energy Ea values obtained were 39.0, 26.7, 30.4, and 49.3 KJ/mol for portland cement, fly ash, silica fume, and slag blended cements, respectively. The relatively constant Ea values for the blended cements may be related to diffusionally controlled hydration of the mineral admixtures.

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