Shrinkage behaviour, early hydration and hardened properties of sodium silicate activated slag incorporated with gypsum and cement

As a novel low carbon cementitious material, alkali-activated slag (AAS) attracted many researchers’ interests, not only because of its environmental benefits, but also some superior properties than Portland cement (PC). Due to different chemical reactions of AAS, gypsum, a commonly used expansive agent in PC, exhibits a different behaviour in AAS. This paper reports the investigation on the shrinkage behaviour of sodium silicate activated slag (SSAS) incorporated with gypsum and PC. In addition, the early properties, including setting time and early hydration products, were determined by Vicat apparatus, XRD and TG. The hardened properties, namely flexural and compressive strength, were investigated as well. The results showed that, by incorporating gypsum and PC, the drying shrinkage of SSAS could be significantly reduced because of the formation of expansive sulfate-rich and calcium-rich hydration products in terms of ettringite and Portlandite. The initial setting was delayed by blending PC, although adding gypsum accelerated the hydration of SSAS. The addition of gypsum and blend with 20% PC slightly increased flexural and compressive strengths of SSAS at 7 days and 28 days.