Effect of heat curing treatment on the drying shrinkage behavior and microstructure characteristics of mortar incorporating different content ground granulated blast-furnace slag

The effect of heat curing treatment that samples cured from room temperature to an elevated temperature of 60 °C for 24 h on the mass loss, drying shrinkage and microstructure of mortar incorporating ground granulated blast-furnace slag (GGBS) as cement replacement at 0%, 20%, 40% and 60% by weight was experimentally investigated in this study. The results show that the heat-treated mortar exhibits lower mass loss compared to the untreated mortar. In addition, when the content of GGBS is 0% or 20%, the heat-treated mortar has a lower drying shrinkage than that of untreated mortar. However, when the content of GGBS is 40% or 60%, the result is the opposite. Moreover, for the heat-treated and untreated mortar, there is an optimal replacement content of about 40% GGBS to restrain drying shrinkage. For the mortar incorporating 0% or 20% GGBS, infrared spectrum (IR) and nuclear magnetic resonance (NMR) analysis reveal that the heat curing treatment mainly leads to a higher degree of silicon polymerization in C-S-H gel and consequently affects the drying shrinkage. For the mortar incorporating 40% or 60% GGBS, scanning electron microscopy (SEM), chemical bound water and mercury intrusion porosimetry (MIP) analysis show that heat curing treatment mainly increases the amount of C-S-H gel and mesopore (<50 nm) of mortar and consequently affects the drying shrinkage.