Coupled models to describe the combined diffusion-reaction behaviour of chloride and sulphate ions in cement-based systems

Abstract

This paper proposes coupled models to describe the combined chloride-sulphate diffusion–reaction behavior in cement-based systems, by taking into account their competitive nature. An experimental program was designed to determine the chloride and sulphate concentrations inside exposed specimens, when subjected to individual and combined attacks. Further, together with the coupled models, a durability-based limit state function is adopted to forecast the moment, at which chloride-induced corrosion and sulphate-induced cracking occur. A multiphase concrete system is considered, with coarse aggregates distributed stochastically. Both numerical and experimental results show that the chloride and sulphate ingress are mitigated in the combined case when compared to a system under individual exposure. However, between them, the presence of the other ion led to over 50% reduction in the chloride ingress as opposed to 30% drop for sulphate ingress. This study predicts that under combined exposure, the sulphate-induced cracking shall present a higher risk of failure much before the onset of corrosion in the embedded steel.