Corrosion initiation mechanisms and service life estimation of concrete systems with fusion-bonded-epoxy (FBE) coated steel exposed to chlorides

摘要

This paper evaluates the suitability of various techniques such as half-cell potential, macrocell corrosion, linear polarization resistance, and electrochemical impedance spectroscopy (EIS) to detect corrosion initiation of fusion-bonded-epoxy (FBE) coated steel rebars in concrete. It was found that EIS is the best technique for this purpose. Then, a new test method (named as "es-ACT" test) using EIS is developed to detect the initiation of corrosion and determine chloride threshold at the coating-steel interface, which was not a practice in the literature. Also, the reduction in the resistance of the FBE coating was monitored and a a 4-stage degradation process and corrosion initiation process are identified and discussed using SEM, EDAX, and statistical analysis of the change in the polarization resistance of steel (from repeated EIS tests - Nyquist/Bode plots). Then, a new method that uses the properties of epoxy coating, steelcoating interface, and concrete cover to estimate the service life of reinforced concrete systems with FBE coated rebars is demonstrated. Modifications to the existing specifications to achieve target service life are also proposed. (C) 2021 Elsevier Ltd. All rights reserved.