Autogenous shrinkage of slag-fly ash blends activated with hybrid sodium silicate and sodium sulfate at different curing temperatures

Abstract

This study investigates the effect of sodium sulfate concentration and curing temperature (20 °C and 40 °C) on the autogenous shrinkage of hybrid sodium silicate and sodium sulfate activated slag/fly ash systems (AASF). Regardless of the curing temperature, the main reaction products formed are C-A-S-H gels, and no formation of N-A-S-H type gels is observed in the studied AASF systems. Due to increase in rate of reaction and refinement of the pore structure, the autogenous shrinkage increased with increasing sodium sulfate concentration. At a high curing temperature (40 °C), the decrease in rate of autogenous shrinkage with time is primarily attributed to the suppression of the self-desiccation process due to decrease in reaction rate, and formation of a matrix with high elastic modulus or restrain effect at early ages. Furthermore, the increase in crystallinity of C-A-S-H gels is also responsible for a lower autogenous shrinkage in samples cured at 40 °C. Ettringite does not form to compensate the autogenous shrinkage at early hours.