Ductility and hydration mechanisms of innovative engineered/strain-hardening cementitious composites (ECC/SHCC) incorporating solid-waste-derived binder

For decarbonized and durable infrastructure, Engineered Cementitious Composites (ECC) must maintain tight crack control and strain-hardening behavior while drastically reducing clinker content. A promising approach is the use of solid-waste-based binder systems to lower carbon dioxide emissions. This study develops a gypsum-activated ternary solid-waste-derived binder composed of steel slag, blast-furnace slag, and desulfurization gypsum for zero-clinker ECC. The coupling between hydration and ductility under different curing humidity conditions is systematically quantified. The ECC exhibits a compressive strength of 45–65 MPa at 28 days. Meanwhile, it achieves stable multiple cracking with an average crack width of 53 μm and sustains a tensile strength of up to 5.61 MPa. When the curing humidity increases to 95%, the ECC demonstrates increased compressive strength; however, its tensile ductility decreases to 1.43% at 28 days. Isothermal calorimetry, XRD, SEM/EDS, and TGA results reveal that gypsum activation synergistically accelerates the hydration of slag and steel slag, leading to the formation of C–S–H and AFt phases. These hydration products densify the matrix and enhance fiber–matrix bonding. Adequate moisture promotes AFt accumulation and suppresses carbonation, whereas low humidity retards hydration. Overall, the findings demonstrate that waste-derived binders combined with humidity-controlled curing provide a simple and scalable strategy to produce low-carbon ECC with robust crack-width control and reliable strain-hardening, thereby advancing durable infrastructure with reduced clinker demand.