Steady-state polarization response of chloride-induced macrocell corrosion systems in steel reinforced concrete — numerical and experimental investigations

Chloride-induced macrocell corrosion of steel is recognized as a frequent and harmful problem affecting reinforced concrete structures. For this specific corrosion mechanism, anodic and cathodic areas at steel-concrete interface are spatially separated. Thereby, at equilibrium, anodic and cathodic potentials are different due to electrical resistivity of concrete, which means there is a potential gradient and a macrocell corrosion current flowing in the concrete volume. Despite some available works on electrochemical modelling of free macrocell corrosion systems in reinforced concrete, the literature is very scarce regarding the response of such systems under polarization. Due to this lack of knowledge, the assessment of steel corrosion rate in reinforced concrete is still commonly based on the uniform corrosion assumption. In this paper, the detailed polarization response of the different components of macrocell systems is studied in steady-state condition on the basis of numerical simulations and the qualitative conclusions are validated by original experiments. Some important results are achieved, with potentially major consequences regarding the non-destructive evaluation of steel corrosion in reinforced concrete. In particular, the distribution of the polarizing current in the macrocell system is found to be dependent on the polarization nature (anodic or cathodic) and magnitude. Moreover, in case of chloride-induced macrocell systems, the apparent linear polarization range is actually much higher than usually assumed and significant differences are observed between anodic and cathodic responses.