Unmasking the degradation of epoxy coating on the surface of steel subjected to stress in simulated concrete pore solution

The performance of epoxy-coated steel falls short of expectation under the co-existence of mechanical loading and corrosive media, leading to the premature failure of reinforced concrete structures in marine environment. To comprehensively understand the degradation of epoxy coating on the steel surface subjected to stress, an experimental setup in which the electrochemical measurements and the application of stress (both tension and compression) can be conducted simultaneously is used. Electrochemical measurements such as electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) are performed to evaluate the electrochemical properties of epoxy-coated steel system. Characterization techniques including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) are employed. Results indicate that tensile stress induces cracks perpendicular to the loading direction in the epoxy coating, which facilitate the water uptake and chloride penetration into the coating. Lowlevel compression generates wrinkling-induced defects while higher value of compression (i.e., yield-level) causes severe delamination at coating/steel substrate interface. The effect of stress on the coating performance is necessary to be considered in marine reinforced concrete structures.