Effect of Chloride Concentration on the Pitting and Repassivation Potentials of Reinforcing Steel in Alkaline Solutions

Reinforcing steel bars (-12mm diameter and 150mm long) were used in cyclic polarization tests in saturated Ca(OH)z solution and simulated concrete pore solution (SPS) with various levels of sodium chloride addition. Below a limiting chloride level (-O.004M [Cl-] in Ca(OH)z solution and -0.4M [Cl-] in SPS solution), steel was not found to undergo pitting corrosion even if it was polarized to the oxygen evolution potential (-O.6V/SCE). At higher NaCl addition, pitting corrosion could often be initiated but the pitting potential was non-deterministic to a great extent. In Ca(OH)z solutio~ the average pitting potential was found to be strongly dependent on chloride concentration when [C1-]>0.008M. In SPS solution, the average pitting potential was almost independent of the chloride concentration when [C1-]>0.8M. The repassivation potential was found to be a strong fimction of the severity of corrosion attack that has occurred on the steel surface before repassivation, rather than a fbnction of the chloride content of the bulk solution. The pitting tendency in chloride-containing SPS and Ca(OH)z solutions was interpreted on a statistical basis. The threshold thus determined good agreement with other values reported in the literature.