Comparative research on the effect of various mineral admixtures on the early hydration process of cement

Abstract

Selection of mineral admixtures (MAs) was an effective way to reduce the rapid heat release of mass concrete at early ages, avoiding the cracks caused by the thermal stress. Herein, fly ash (FA), steel slag (SS) and ground granulated blast-furnace slag (GGBS) was used to replace cement with the dosage of 40%, and the early hydration process and microstructure evolution of specimens were investigated by hydration heat (HH), hydration temperature (HT), XRD, TGA and SEM. The experimental results indicated that the use of various MAs reduced the 3 d HH by 20–33%, owing to the reduction of cement content. The highest HT for cement-FA paste was decreased from 54 ℃ in cement paste to 37.0 ℃, whereas that for cement-SS paste and cement-GGBS paste was decreased to 38.4 ℃ and 39.8℃, especially including a constant temperature period at 15.62–18.14 h and 12.67–14.50 h. It was demonstrated that the reactivity of FA was greatly lower than that of SS and GGBS at early ages. Moreover, the early hydration degree of cement was increased by the dilution and nucleation effects, whereas the compressive strength of paste was reduced by 24–53% at 3 d. However, the compressive strength of cement-GGBS paste at 28 d was equivalent to that of cement paste, resulting from the continuous hydration of GGBS. These results provided the selection basis for MAs in mass concrete.