Insights into autogenous shrinkage of alkali-activated slag under elevated curing temperature

Abstract

This paper investigates the autogenous shrinkage of alkali-activated slag (AAS) under thermal curing using a tailored corrugated tube system. The results reveal that thermal curing decreases the total deformation of AAS mortar due to thermal expansion while increasing autogenous shrinkage. This enhanced autogenous shrinkage results from the interaction of multiple factors, with the dominant influences evolving over time. At early ages, thermal curing enhances autogenous shrinkage without intensifying internal humidity reduction, ascribed to improved silicate polymerisation. Afterwards, self-desiccation governs the autogenous shrinkage, initially constrained by increased early-age stiffness, reduced mesopore volume, and weakened viscous characteristics of AAS under thermal curing. However, the self-desiccation-induced autogenous shrinkage is intensified at later ages due to rapid pore refinement at elevated temperature, shifting the dominant shrinkage driving force from capillary pressure to surface-free energy. The findings of this study provide a foundation for improving the volumetric stability of AAS-based materials at elevated temperature.