Understanding the degradation mechanisms of cement-based systems in combined chloride-sulfate attack

Chemical aggressions from the environment, such as salt ions, can damage reinforced concrete structures before they reach their service life. These deterioration mechanisms are coupled. The current research on cementitious material’s durability has thus gradually shifted to the field of durability damage caused by the combined action of multiple factors. The research in this study concerns the case of combined chloride-sulfate attacks to provide a better understanding of the coupling phenomena by studying the mutual effect of the chloride and sulfate ions on the materials. The effect of the type of cement and curing duration on the chloride-sulfate attack is also investigated. Experimental results based on different investigation techniques (ICP, XRD, NMR, etc.) clearly show the competition between chloride and sulfate ions, and how the physico-chemical involved mechanisms completely change with respect to the cases of an exposure to a single type of ion.