Coupled reactive transport and poromechanics modelling of external sulfate attack in cementitious materials

External sulfate attack (ESA) is a leading cause of durability deterioration in concrete structures, primarily driven by expansion due to crystallization pressures associated with ettringite formation.This research develops a novel chemo-mechanical model to simulate degradation in cementitious materials under ESA conditions.The model integrates a pore-scale representation of the C-S-H gel, considering both reactive transport and poromechanical effects.Chemically, the model incorporates precipitation/dissolution kinetics and ionic adsorption/desorption at the C-S-H phase within a comprehensive reactive transport framework.Mechanically, a poromechanical model is coupled to the transport processes to capture local strain effects at the C-S-H gel scale.Three primary mechanisms contribute to the mechanical response: (i) the chemical reaction between monosulfate within the C-S-H phase and incoming sulfate ions, resulting in the eventual consumption of monosulfates, (ii) sulfate adsorption and subsequent desorption from the C-S-H surface, resulting in ettringite precipitation, and (iii) crystallization pressure exerted within the gel's interstitial porosity, driven by the equilibrium of sulfate ions in solution.The fully coupled chemo-mechanical model provides robust predictions of sulfate ion transport, capturing both the spatial and temporal evolution of sulfate adsorption in the C-S-H phase, while identifying zones with high sulfate concentrations.Additionally, the model reveals the influence of material parameters on chemo-mechanical interactions, offering valuable insights into their role in controlling mechanical expansion.The results show an encouraging correlation between predicted and experimental macroscopic strain values, validating the model's ability to simulate sulfate-induced degradation mechanisms in cementitious systems.