Carbonated steel slag as a dual-function additive for strength and sustainability enhancement of alkali-activated slag

This study investigates carbonated steel slag (CS) as a dual-function additive in NaOH-activated blast furnace slag (AAS) binders, aiming to enhance both mechanical performance and sustainability. Incorporating CS significantly improved compressive strength at all curing ages, with a ∼70 % increase at 28 days for 30 wt% substitution. Microstructural analyses revealed reduced capillary porosity and improved micromechanical properties of C–(A)–S–H. Environmental assessment further showed that CS reduced total CO 2 emissions and improved the environmental index by more than 35 %. Mechanistically, CS moderated early-age reaction kinetics through pH buffering, while supplying reactive CaCO 3 and silica gels that promoted sustained gel formation. These effects enhanced silicate polymerization and induced Na–Ca carbonate formation, yielding a denser and more stable hybrid gel network. Overall, CS not only improves strength and refines microstructure, but also acts as a CO 2 sink, offering a sustainable pathway for developing high-performance, low-carbon AAS binders.