Mechanistic modeling for coupled chloride-sulfate attack in cement-based materials

Concrete infrastructures in marine and saline environments are vulnerable to simultaneous chloride and sulfate attacks, compounded by calcium leaching. To address this complex degradation process, we developed a multiion transport-chemo-thermo-damage (TCTD) model. This model captures the intricate interactions among multiion diffusion, chemical reactions, pore evolution, thermodynamic effects, mechanical damage, and calcium leaching. Validation against multiple independent third-party experimental data confirms the model's reliability and accuracy. Based on this validated model, we analyzed the instantaneous spatiotemporal variations in phase concentrations and porosity, quantifying the primary factors affecting ion transport and concrete degradation. This analysis provides a clear understanding of the individual and combined impacts of these factors. The results indicate that coupled chloride-sulfate attack mitigates individual sulfate and chloride attacks in the short term, while calcium leaching promotes significant gypsum and ettringite formation near the concrete surface. Higher water-to-cement ratios, increased aluminate content, and elevated temperatures are found to exacerbate degradation by accelerating diffusion and reaction rates. Calcium leaching and pore evolution have a much greater effect on coupled chloride sulfate attack than chemical activity coefficients. This research enhances the understanding of coupled ion attacks and aids in optimizing the durability design and predicting the longevity of concrete structures in aggressive environments.