Role of CaO Reactivity in Controlling Fresh Properties and Long-Term Strength Development of CaO-Activated GGBFS Composites

This study systematically investigates the influence of CaO reactivity on the fresh-state rheological behavior and long-term mechanical performance of GGBFS binders. Four types of industrial quicklime, characterized by distinct slaking kinetics (tmax ranging from 9 to 36 min), were used as primary activators, with dosages of 5%, 9%, and 13% by binder mass. The results reveal that CaO reactivity significantly affects water demand, yield stress, and setting times, with extremely reactive quicklime inducing the greatest increases in water demand and plastic viscosity. Setting behavior was strongly dependent on both activator content and curing environment, with less reactive limes failing to induce setting under water immersion. Compressive strength development was largely unaffected by CaO reactivity up to 120 days, but at 720 days, higher CaO contents (≥9%) contributed to significant strength gains, likely due to carbonation-induced matrix densification. These findings demonstrate that controlling CaO reactivity and dosage is essential for optimizing the workability and durability of CaO-activated slag binders.