Effect of curing regimes on composition and microstructure of blended pastes: Insight into later-age hydration mechanism

Understanding the hydration of composite binders is essential for decarbonizing the cement industry. This study investigated the microstructure and composition of pastes with either fly ash or slag after different long-term curing. Results show that the elevated temperature slightly reduces the capillary pore volume and internal RH of sealed samples. Water curing largely enhances hydration of fly ash and slag after the first week, forming later-age products in surface zone with stabilized Mc and Hc. This increases both gel and capillary pore volumes. C-A-S-H in water-cured pastes has a longer mean chain length and extremely lower alkali uptake than that in sealed curing. Modelling results indicate that nucleation ceases in sealed pastes once thermodynamic limitations are reached due to self-desiccation. Even with adequate water, late-stage hydration remains kinetically constrained due to the slow nucleation and growth rate near the unhydrated surface, with diffusion likely being one of rate-controlling factors.