Relationship Between Pore Structure Change and Freeze–Thaw Resistance of Blast Furnace Slag Cements Under Repeated Dry–Wet Cycles

Abstract

In cold climates, the durability of construction materials against freeze-thaw cycles is critical for ensuring long-term structural safety. To minimize environmental impact, blast furnace slag cement, incorporating varying proportions of blast-furnace slag fines, is increasingly being adopted as a sustainable alternative to ordinary cement. While the freeze-thaw resistance of such materials has been widely studied, their performance after repeated dry-wet cycling, which simulates moisture fluctuations that can occur in typical environments, has not been thoroughly investigated. This study evaluates the freeze-thaw resistance of blast furnace slag cement with different blast-furnace slag replacement ratios following repeated dry-wet exposure. The influence of entrained air, introduced via an air-entraining agent, was also examined. Freeze-thaw resistance was assessed using the RILEM CIF method, and microstructural characteristics were analyzed via mercury intrusion porosimetry. Results showed that, even though capillary pores became coarser with AE addition, the presence of adequate entrained air mitigated frost damage. In specimens without AE, increasing blast-furnace slag content improved resistance by reducing the prevalence of capillary voids formed during dry-wet cycling. These findings suggest that the microstructural changes induced by blast-furnace slag and AE agents play a crucial role in enhancing the frost durability of blast furnace slag cement under cyclic environmental stress.