When concrete is manufactured, it can be instantaneously contaminated by chloride (Cl−) ions or later by their intrusion from the environment. This work aims to study the electrochemical behavior of the passive layer formed on the reinforcing steel surface in the presence of the same Cl− ion concentration, with and without passivation time. This will, undoubtedly, affect the corrosion threshold values thereafter.
Electrochemical polarizations were carried out in two concrete pore solutions. The surfaces of samples immersed for 255 days in saturated Ca(OH)2 solution were examined with optical and scanning electron microscopy and Raman microspectroscopy.
Cl− ion origins in reinforced concrete lead to different values of corrosion thresholds. The passive layer behaves like a physicochemical barrier, and corrosion occurs at higher NaCl concentration thresholds. The formed passive film on the steel surface shows differences in the chemical composition and the morphology. The results show a rich presence of hematite. Maghemite, lepidocrocite, akaganeite and goethite are also present in much lower concentrations. The Cl− ion presence in fresh concrete at the beginning of the manufacture harms the good formation and the good stability of these oxides, leading to corrosion initiation.
This study contributes to a better understanding of the passive layer role, not only in reducing the corrosion rate value but also in reconsidering new Cl− ion corrosion threshold values.
