Hydration behavior, silicate polymerization and mechanical performance of granulated blast furnace slag-desulfurization gypsum binders under different activation systems

The efficient activation of slag-desulfurization gypsum cementitious materials using low-carbon activators has become an important issue in the field of sustainable cement-based materials. This work investigated the effects of Portland cement, sodium metasilicate, and carbide slag on the hydration behavior, mechanical properties, pore structure, and silicate polymerization characteristics of slag-desulfurization gypsum systems. The total solid waste content (blast furnace slag + desulfurization gypsum) reaches 93 wt% of the binder, and a significant reduction in CO₂ emissions compared to ordinary Portland cement. Compressive and flexural strength tests, hydration heat analysis, X-ray diffraction (XRD), thermogravimetric analysis (TG-DTG), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and solid-state nuclear magnetic resonance (NMR) were conducted to reveal the activation mechanisms of different systems. The results show that sodium metasilicate and carbide slag significantly enhance the hydration activity of the slag system compared with Portland cement. Among the three activators, the carbide slag system exhibits the highest early reactivity at its optimal dosage of 1%, with a 72 h cumulative hydration heat approaching 900 J/g and a maximum 28 d compressive strength of 57.4 MPa. However, increasing the carbide slag dosage beyond 1% (e.g., to 3%) causes a marked strength retrogression, and similar non‑monotonic behavior occurs for all activators when their dosages exceed the respective optimal levels. Such over‑activation increases the proportion of low‑polymerized Q¹ structures and reduces the mean chain length and networking degree of silicate gels, resulting in deterioration of later‑age strength and structural stability. This work provides theoretical guidance for the efficient activation of slag‑desulfurization gypsum cementitious materials and the sustainable utilization of industrial solid wastes.