Effect of sunlight/ultraviolet exposure on the corrosion of fusion-bonded epoxy (FBE) coated steel rebars in concrete

Currently, highway/railway bridges are designed for the service life of more than 100 y. In such reinforced concrete structures, fusion-bonded epoxy (FBE) coated steel rebars are being used in anticipation of delayed initiation of reinforcement corrosion. However, the FBE steel rebars get exposed to sunlight/ultraviolet rays during prolonged storage and delayed/staged construction. This paper presents microanalytical and electrochemical data (Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersion x-ray diffraction, and electrochemical impedance spectroscopy) and shows the adverse effects of sunlight/UV exposure on the corrosion resistance of FBE-coated steel reinforcement in concrete construction. Based on tests on steel-mortar specimens, the mechanisms of UV-induced chemical changes, shrinkage, and cracking of FBE coating, and the resulting steel corrosion mechanisms are proposed. Also, the adverse effects of sunlight/UV exposure on chloride threshold and reduction in the service life of FBE-coated steel in cementitious systems are presented. The paper recommends to minimize the exposure of FBE-coated steel rebars to sunlight/UV rays to less than one month. © 2020 NACE International.