Steel-Concrete Interface Influence on Chloride Threshold for Corrosion – Empirical Reinforcement to Theory

Reinforcement corrosion is a common cause for reinforced concrete structure deterioration. One of the main causes for reinforcement corrosion is chloride ingress to the concrete. Published work hints a relationship between the susceptibility to chloride induced corrosion, referred as the chloride threshold, which is the chloride concentration at corrosion initiation, and the interface between the concrete and the rebar, known as interfacial transition zone (ITZ). This paper presents an investigation of the relationship between the chloride threshold for chloride-induced corrosion and the properties of the ITZ around embedded rebar was investigated using 16 different concrete mixes. ITZ properties were extracted using automated image analysis. The chloride threshold was found to decrease with the distance between the rebar surface and the concrete solids. In the case of horizontal rebar, the chloride threshold decreases with ITZ thickness as well. These results agree with the theory of concentration polarization in localized corrosion and may explain the variety of chloride threshold values reported in the literature.

Keywords: Concrete; Chloride threshold; Rebar; Corrosion; Interfacial transition zone

Abbreviations: BSE: Back Scattered Electron Microscopy; CCCL: Chloride Corrosion Concentration Limit or Chloride Threshold; EIS: Electrochemical Impedance Spectroscopy; HRWR: High Range Water Reducer; ITZ: Interfacial Transition Zone; RC: Reinforced Concrete