Effect of Strain Levels on the Corrosion Resistance of an Enamel-Coated Steel Rebar

Abstract

The effect of strain levels on the corrosion resistance of an enamel-coated steel rebar is experimentally investigated in this study. Enamel coating was applied on the surface of a steel rebar by using the wet process. A strain gauge was attached on the surface of the coated steel rebar to record the strain levels and a plastic container was mounted for electrochemical corrosion tests. A stress-corrosion test set-up was designed to conduct corrosion and tensile tests simultaneously. The strain levels considered include 0 µε, 300 µε, 600 µε, 900 µε and 1200 µε, and the electrochemical techniques employed include open circuit potential, linear polarization resistance and electrochemical impedance spectroscopy. The microstructure of the enamel coating was also examined with scanning electron microscopy. Results show that the enamel coating has a thickness of ~150 µm, and there are some air bubbles in the coating. The average corrosion current density of the uncoated steel rebar decreases from 18.64 µA/cm2 to 14.39 µA/cm2 in NaCl solution due to the generation of corrosion products. The corrosion current density of the enamel-coated steel rebar gradually increases from 0.49 µA/cm2 when the strain is zero to 0.65 µA/cm2 as strain reaches 1200 µε, which is almost 40 times lower than that of the uncoated steel rebar. Impedance spectrum results show that the corrosion resistance of enamel coating decreases with an increase in the tensile strain level; however, it still protects steel rebar from corrosion to some degree.