Effect of modulus and dosage of waterglass on early age shrinkage of sodium silicate activated slag paste

In recent years, alkali-activated slag (AAS) as an alternative low-carbon emission and high strength cementitious material has received increased attention. However, high shrinkage and crack tendency of AAS limit its wider industrial applications. Although considerable researches have already been carried out on Portland cement (PC) based systems, the information and understanding on the early age shrinkage of AAS is still limited. On the other hand, early age shrinkage occurs mainly due to a high rate of water evaporation from the surface of fresh concrete. Therefore, this study seeks to explore the potential of two sodium silicate activated slag mixtures variables, namely, waterglass moduli and activator content, on moisture loss and early age shrinkage properties of AAS. A control AAS mix was formulated with water glass (silica modulus of 1.5) as an activator at the dosage of 4% (Na2O equivalent) by mass of slag and fixed waterbinder ratio (w/b) of 0.4. Two mixtures with modulus of 0.75 and activator dosage of 6% were compared in this study. The most significant findings to emerge from this study is that, AAS paste with moduli of 0.75 and activator content of 4% showed lower amount of early age shrinkage. However, further study still needs to be carried out in order to establish a better understanding of the current results.