Sulfate resistance of sulfate-alkali activated cementitious materials

Abstract This study investigates the influence of desulfurized gypsum (DSG) on the sulfate resistance of alkali-activated materials (AAMs), including alkali-activated slag (AAS) and hybrid alkali-activated cement (HAC). The sulfate resistance and microstructural evolution of AAMs were systematically evaluated with respect to DSG content and type. Specimens were subjected to accelerated corrosion via exposure to a sulfate environment (5 wt% Na 2 SO 4 solution) combined with 150 dry-wet cycles. The results demonstrate that DSG content significantly influences sulfate resistance of AAMs: sulfate resistance ability improves at 10% and 15% DSG but deteriorates at 5% or 20%. XRD and SEM-EDS analyses were conducted to elucidate the underlying mechanisms. It was observed that during sulfate attack, the increased formation of ettringite and hydrotalcite-like phases fills microcracks in the AAM matrix, producing a denser microstructure and enhanced corrosion resistance. However, when DSG content exceeds 15%, excessive crystal growth leads to additional cracking, thereby reducing corrosion resistance. Furthermore, the chemical stability of hydration products and the inhibitory effects of the chemical environment further contribute to the enhanced sulfate resistance of alkali-sulfur composite activated cementitious materials.