Influence of chloride ion on depassivation of passive film on galvanized steel bars in concrete pore solution

This work aimed at studying the depassivation mechanism of the passive film on galvanized steel bar in concrete pore solution with different concentrations of chloride ion. The results showed that in a saturated Ca(OH)2 solution, the critical chloride values for the depassivation of the passive films formed on galvanized steel bars and zinc metal specimens were 0.2 M and 0.3 M respectively. When the Cl− concentration was lower than the critical value, the donor density of the passive film increased and thus the protective property reduced with increasing the concentration of chloride ion, which could be interpreted by the point defect model (PDM). The corrosion products formed on the galvanized steel surface could inhibit the further ingress of the chloride ions and enhance the protective property, while such effect was not obvious for the zinc metal.