Hydration kinetics of AAS at different CaO/SiO 2 ratios
Teresa Liberto, Pierre Carmona, Benedetta Costa, Christiane Rößler, Thomas Sowoidnich, Mohamed Abubakar Ali, Agathe Robisson, Michael HaistAbstract
This study investigates the hydration kinetics of alkali‐activated slag (AAS) at varying CaO/SiO 2 ratios. A one‐part formulation using solid activators (Ca(OH) 2 and Na 2 CO 3 ) was adopted to reduce CO 2 emissions and improve handling safety. Four compositions with CaO/SiO 2 ratios from 0.5 to 1.5 were prepared by adjusting Ca(OH) 2 and colloidal SiO 2 (Ludox®) contents. A multi‐technique approach characterized hydration from initial water contact through long‐term hardening: SAOS rheology, NMR, isothermal calorimetry, SEM, chemical speciation, in‐situ and ex‐situ XRD, and mechanical testing up to 56 days. Results reveal strong composition‐dependent effects on cohesion, structural build‐up, heat release, and water interactions. Low CaO/SiO 2 ratios (0.5) show rapid structuration driven by nanosilica water uptake, producing silica‐rich phases with limited strength (∼1.6 MPa at 28 days). Higher ratios (1.1) exhibit faster hydration, progressive C–(A)–S–H formation, and significantly improved strength (∼10 MPa at 28 days). This integrated approach establishes composition‐property relationships in AAS, supporting optimized mix design and promoting AAS as sustainable, low‐CO 2 cement alternatives.