Mechanisms of inorganic salts on Ca(OH)2-activated ground granulated blast-furnace slag curing under different temperatures

Abstract

This study investigated in detail the coupling effects of curing temperatures (5, 20, and 35 °C) and additional activators (Na2SO4, Ca(NO2)2, NaCl, and Na2S2O3) on Ca(OH)2-activated granulated blast-furnace slag (GGBFS). The results show that the early strengths, hydration degree and microstructure of samples depend strongly on the curing temperature and the nature of activators. Activators influence considerably the initial pore solution composition and pH value, while low-pH values and high-Ca2+ activity suppress the dissolution of Ca(OH)2 and the reaction of GGBFS. Elevated temperatures mainly accelerate the hydration of GGBFS in all samples at early age. However, owing to the cross-over effect, there is a negative effect on the properties of the samples with added sodium salts in the middle and late stages of hydration. For samples in which Ca(NO2)2 was added, the early hydration is low owing to the common ion effect, and high temperature plays a facilitating role instead. Furthermore, the apparent activation energy of GGBFS hydration was also determined to explain the observation. Results show that the sample in which the additional activator was added was influenced considerably by the curing temperature, while samples in which Ca(NO2)2 was added were more sensitive to curing temperature changes.