Hydration behavior and phase evolution of low-activity granulated blast furnace slag under mechanical-chemical activation

Low-activity granulated blast furnace slag (GBFS) has inherent limitations, including low chemical reactivity, sluggish hydration kinetics, and insufficient early-age strength development, which constrain its utilization as a cementitious material. To clarify the correlation between the activation treatment and the reactivity of GBFS, mechanical and composite activation techniques were employed to systematically investigate the amorphous phase evolution, hydration behavior, and mechanical properties of GBFS. A co-grinding approach involving solid activators and GBFS was adopted to effectively stimulate the latent reactivity of low-activity GBFS. Microscopic characterization techniques were utilized to investigate the amorphous phase evolution, hydration behavior, and product formation. The results revealed that co-grinding GBFS with 6% CaO for 4 min increased the 28 d compressive strength to 45.79 MPa and the 28 d activity index to 96.37%. CaO promoted GBFS hydration and facilitated the formation of C-(A)-S-H gels, thereby enhancing the compactness of the microstructure. These findings demonstrate the efficient activation of low-activity GBFS.