The long-term corrosion of mild steel in depassivated concrete: Localizing the oxygen reduction sites in corrosion products by isotopic tracer method

Over a long period (>10 years), the prediction of iron/mild steel corrosion in concrete requires the use of a mechanistic approach. For that purpose, a key point of the mechanisms involved is the localization of the oxygen reduction sites within the thick corrosion layers, which may greatly influence the nature of the rate-limiting step. In this context, iron rebars (originally covered with concrete) were sampled from a 50-year-old historical building and submitted to isotopic tracers methods (O-18) combined with structural Raman microspectroscopy analyses on transverse sections. By this method, the authors demonstrate that the oxygen reduction sites are strongly impacted by the presence of a conductive phase (magnetite) in contact with the metallic substrate.