Upcycling industrial waste into zero-clinker alkali-activated binders for low-carbon construction

Global decarbonization requires alternative binder that eliminates the high CO₂ burden of Portland cement. This study develops a zero-clinker, cement-free alkali-activated binder produced from two by-products: calcium carbide residue (CCR) and rice husk ash (RHA). Solid sodium silicate and NaOH were incorporated into the dry mixture to provide silica and alkali activators, enabling water-based mixing without calcination. The synergistic availability of Ca²⁺ from CCR and silica from RHA promotes nucleation and calcium silicate hydrate (C-S-H) formation, resulting in a continuous reaction product under mild heat-assisted curing. Microstructural analysis shows a compact C-S-H matrix, while RHA-rich formulations exhibit reduced mass loss at 450°C, indicating enhanced high-temperature stability. Although the strength (∼16 MPa) is suitable for non-structural applications, the system demonstrates a viable pathway for valorizing industrial wastes into functional, low-emission binders. This work supports circular economy strategies and contributes to the development of low-carbon construction materials.