Thermo‑hydro‑chemo‑mechanical coupled modeling of concrete under sulfate attack and freeze-thaw cycles

Concrete structures in mid- and high-latitude regions are often exposed to the combined effects of sulfate attack (SA) and freeze-thaw cycles (FTC). However, most models consider SA and FTC separately, lacking a comprehensive numerical framework for their coupled effects. This study developed a fully coupled numerical model based on crystallization-reaction kinetics and elastoplastic damage mechanics, incorporating latent heat, unsaturated transport, freeze-thaw hysteresis, and mechanical damage. Results show that the synergy between salt crystallization and frost heaving significantly accelerates deterioration. High sulfate concentrations increase both ion penetration and crystallization pressure. Early-stage damage is primarily governed by FTC and physical crystallization, while the standardized rapid freeze-thaw method fails to capture chemical sulfate attack in real service scenarios. Thermodynamic differences between sodium sulfate and sodium chloride at low temperatures lead to distinct impacts on damage evolution. This study provides a theoretical basis for durability assessment and design of concrete in cold sulfate-rich environments.