Effect of various alkalis on hydration properties of alkali-activated slag cements

The effect of sodium silicate (NS system) and sodium hydroxide (NH system) on hydration properties of alkali-activated slag (AAS) cements is investigated, and more attention has been paid to the hydration kinetics in this paper. The increase of Na2O dosage tends to promote higher early strength of the cements, but lower strength gain at later, while increasing SiO2 dosage leads to improve both early and later strength. The hydration of the two AAS cements proceeds through three processes after induction period finished, namely nucleation and crystal growth (NG), phase boundary reaction (I), and diffusion (D). With the increased Na2O dosage and decreased SiO2 dosage, the NG and I processes are shortened. The hydration rate during NG and I processes is also accelerated. CSH gel is the main hydrates of all AAS cements, but the activator type and content have impact on the minor hydration products.