Influence and mechanism of anhydrite on the sulfuric acid resistance of full-solid waste high-belite calcium sulfoaluminate cement

This study investigates the influence and underlying mechanism of anhydrite on the sulfuric acid resistance of full-solid waste high-belite calcium sulfoaluminate cement (WHBCSA). Sulfuric acid solutions with concentrations of 0.05 %, 0.5 % and 5 % were prepared as corrosion media. The sulfuric acid resistance of WHBCSA with 0, 5 %, 10 % and 15 % anhydrite contents were comprehensively analyzed through visual appearance, mass change, compressive strength, corrosion depth and area of specimens, as well as pH value change of corrosion media. XRD-Rietveld refinement, TGA, selective extraction technique, MIP, and SEM-EDS analysis were employed to examine the phase composition, pore structure, microstructure during hydration and sulfuric acid attack processes. Additionally, an acid neutralizing capacity test for GGBS and ettringite was conducted. The results revealed that anhydrite promoted the dissolution of GGBS and the formation of ettringite, densifying the pore structure and improving the microstructure, thereby enhancing the strength. Nevertheless, the sulfuric acid resistance of WHBCSA exhibited an inverse correlation with anhydrite content. Mechanistic analysis demonstrated that GGBS provided effective pH buffering capacity (neutralizing up to 6.441 mmol H⁺/g), thereby decelerating the reaction kinetics between sulfuric acid and hydration products. Notably, the GGBS itself does not participate in the formation of cementitious structures, and its consumption has a much smaller impact on strength than hydration products’ consumption. These findings provide new insights into the dual role of anhydrite in regulating both mechanical development and chemical durability of CSA-based cementitious systems containing GGBS.