Microstructural and durability assessment of carbonated calcium silicate cement under sulfate attack

This study evaluates the microstructural and durability performance of carbonated calcium silicate cement (CSC) under external sulfate attack in Na₂SO₄ and MgSO₄ solutions across water-to-cement (W/C) ratios of 0.35, 0.4 and 0.45. The investigation included XRD, TGA, FT-IR, SEM, MIP, compressive strength testing, and expansion strain measurements over 18 months. Results showed that MgSO₄-exposed samples exhibited significant expansion strain and moderate phase alterations, including gypsum formation and calcium carbonate dissolution, particularly in samples with a W/C ratio of 0.45. In contrast, Na₂SO₄-exposed samples maintained expansion strains within the 0.1 % critical limit. Despite sulfate exposure, strength remained unaffected or slightly improved under all conditions, attributed to microstructural densification from gypsum crystallization within interconnected pores and additional C–S–H formation on CaCO₃ surfaces from hydration of belite and rankinite. CSC demonstrated excellent sulfate resistance, maintaining expansion strains within acceptable limits, except for W/C 0.45 samples exposed to MgSO₄. These findings highlight CSC potential as a durable, eco-friendly cement in sulfate-rich environments.