Deterioration of Enamel and Epoxy Coated Steel Rebar in 3.5 wt.% NaCl Solution

Abstract

Reinforcing steel bars coated with pure enamel and fusion-bonded epoxy (FBE) were immersed in 3.5 wt.% NaCl solution for a period of 84 days. Predetermined damage of the coatings was created with a standard impact tester to study the coating resistance to potential damage caused during transportation and construction. Open-circuit potential and electrochemical impedance spectroscopy (EIS) tests were used to investigate deterioration processes of the two coating systems. An equivalent electrical circuit model was established to extract corrosion-indicative dielectric properties of enamel and FBE coatings from the EIS data. The change of coating capacitance over time was represented by a diffusion-controlled process. In comparison with the FBE coating with the same extent of damage, the enamel coating corroded sooner due to its thinner layer and porous microstructure, but deteriorated more slowly due to its robust bond with the steel substrate.