Numerical Study on Chloride Ingress in Cement-Based Coating Systems and Service Life Assessment

Chloride-induced corrosion is a critical issue for RC structures. Cement-based coatings can be used to protect concrete structures with unsatisfactory quality against chloride ingress. To evaluate the effectiveness of the coatings to extend the service life of coated concrete structures, the evolution of the chloride profile in the coated concrete structures should be determined. This paper investigated the mechanism of chloride ingress into coated concrete structures (i.e., coatings made of cement paste and concrete substrate). A numerical tool is proposed for calculating the chloride profiles in the coated concrete structures. A parametric study investigated the influence of several factors on the chloride ingress: the water:cement (w:c) ratio of the coating, the thickness of the coating, and early or late application of the coating. A preliminary cost analysis of coating materials was carried out. The results showed that the effectiveness of the coatings increased with coating thickness at a drastic increase of material cost; the effectiveness of the coatings increased with the decrease of the w:c ratio at a moderate increase of material cost. In order to extend the service life of the substrate, a coating with a low w:c ratio is recommended, and the coating thickness should be designed depending on the requirements. Moreover, the exposure history of the substrate before application of the coating also has an influence on the effectiveness of the coating. To protect an existing concrete structure exposed to a chloride environment against rapid chloride ingress, it is preferable to apply a coating as early as possible, because the effectiveness of the coating is reduced by late application.