Experimental study and modelling of heat evolution of blended cements

Abstract

The advisability of controlling the temperature rise and fall in concrete at early age is well recognised, and the choice of an appropriate, low-heat cement with suitable heat of hydration characteristics can assist in this control. This is particularly pertinent with respect to water-retaining and massive concrete structures where the need to prevent early-age thermal cracking is paramount. Portland cement/ground granulated blast furnace slag (PC/ggbs) or PC/fly ash cements are often used in these structures due to their low heat hydration properties. This paper presents the results of isothermal conduction calorimetry tests carried out on PC/ggbs and PC/fly ash cements and describes a model that uses these results to simulate the heat evolution processes in hydration concrete sections at early ages. The tests covered a range up to 90% ggbs and up to 65% fly ash content by mass of cement, at temperatures from 5° to 60°C. For PC/ggbs cements, the total heat of hydration can be considered as a composition of three components, that is heats from an initial Portland cement reaction, a latent ggbs hydraulic reaction and co-reactivity effects of PC and ggbs; whereas for PC/fly ash cements, the initial PC reaction dominated with a small co-reactivity effect.