Effect of nano-silica on mechanical properties and shrinkage of alkali-activated slag cementitious material

Alkali-activated slag cementitious material (AASCM) is a promising green building material that can effectively reduce carbon dioxide emission. Nano-silica (NS) can effectively improve the mechanical properties of cement-based materials and reduce their shrinkage; however, the effect of AASCM is unknown. Therefore, the rheology, workability, compressive strength, flexural strength, shrinkage and microstructure of NS-AASCM are investigated in this study, and the effects of the water-binder ratio (w/b) and NS content are considered. Results show that the rheological characteristics and workability of the NS-AASCM increases with the w/b and decreases as the NS content increases. Under the w/b of 0.55, 2% NS content increases the compressive and flexural strengths by 42.1% and 36.6%, respectively. The shrinkage of the AASCM increases with the w/b and NS content. The lower the w/b, the more significant is the effect of the NS content on the NS-AASCM shrinkage growth rate. SEM results show that the appropriate NS content improves the compactness of the AASCM gel matrix.