Performance of corrosion inhibitors and epoxy coatings in cracked reinforced concrete subjected to a marine environment

Corrosion of embedded steel in concrete caused by chloride penetration is one of the major problems in structures exposed to harsh environments. Some of the most common corrosion protection methods are the improvement of the concrete in the form of High Performance Concrete (HPC), the use of Corrosion Inhibitors (CI) or the application of Fusion Bonded Epoxy Coatings (FBEC) to the reinforcing bars. Although considerable research has been carried out on the performance of these corrosion prevention methods, there are still many uncertainties about their performance, especially in cracked concrete and further research on the subject is needed. To provide a better understanding of the effect of calcium nitrite based corrosion inhibitor and epoxy coating rebars on the corrosion process of reinforced concrete, an extensive experimental program was carried out. Small-scale concrete slabs containing steel reinforcement were cast in concrete with a cover depth of 20 mm. The slabs were subjected to a simulated marine environment and a natural marine exposure. The effect of Calcium Nitrite Based Corrosion Inhibitor (CNI) and width of crack on the corrosion process of steel reinforcing bars in High Performance Concrete were investigated. A 34 full factorial design was developed considering water to cement ratio, fly ash percent, calcium nitrite based corrosion inhibitor content and crack width as factors. The responses were corrosion potential, corrosion current density, surface areas of corrosion, pit depth, chloride content and tensile strength of the reinforcing bars. It was found that CNI alone has, in general, no effect in decreasing corrosion, and that the crack condition of the specimens strongly affects the corrosion process in silica fume concrete. A significant effect of crack width on corrosion of ordinary portland cement concrete was also found but at early ages and as the time passes by this effect disappears. Furthermore, a non-detrimental effect of CNI on corrosion of specimens containing fly ash was detected. The study of seven types of epoxy coatings subjected to a simulated environment and testing of a structure built in 1984 and subjected to deicers during the winter revealed that epoxy coatings do not provide total protection to the steel reinforcing bars. However, coated bars significantly extend the corrosion initiation period as compared to uncoated bars for structures subjected to a very aggressive chloride environment.