Enhanced durability of steel reinforcement protected by an epoxy/Al composite coating in chloride-contaminated concrete pore solution

Chloride-induced corrosion of embedded steel reinforcement is a major cause of premature deterioration and catastrophic failure of coastal bridges, resulting in significant economic losses and safety hazards. In this study, a composite coating system consisting of a 100 µm arc thermal sprayed aluminum (Al) layer and a 40 µm epoxy topcoat applied by nylon brush was developed to enhance corrosion protection. The corrosion performance of the coating system was evaluated in simulated concrete pore solution i.e. alkaline containing 3.5 wt.% NaCl under prolonged exposure conditions. Electrochemical measurements revealed that the epoxy/Al composite coating provided superior protection compared to the Al-only coating. The epoxy layer acted as an effective barrier against aggressive ions, while the Al layer offered sacrificial protection, resulting in a synergistic corrosion resistance mechanism. Although localized corrosion of the Al layer was began after prolonged exposure due to chloride penetration through micro/nano-defects in the epoxy layer, the subsequent formation of insoluble Al corrosion products filled these defects. After 51 days of exposure, the corrosion rates of the Al-only and composite coatings were 42.4 and 0.44 µm/year, respectively. The application of 40 µm epoxy layer over Al coating reduces corrosion rate by more than 96 times.