Study on effect of chloride ions on corrosion behavior of reinforcing steel in simulated polluted concrete pore solutions by scanning micro-reference electrode technique

[Display omitted] •Reinforcing steel passivity was detected by scanning reference electrode technique.•Chloride threshold level for the steel corrosion was determined.•Pitting occurred preferentially at MnS inclusion locations on the steel surface.•Chloride ions were adsorbed preferentially at MnS inclusion locations. Chloride ion (Cl-) attack is a main reason for localized corrosion of reinforcing steel in concrete. Study on the effect of Cl- on corrosion behavior of the steel is of importance for corrosion protection. In this study, reinforcing steel (Q235 carbon steel) passivity in simulated polluted concrete pore solutions at pH 11.50 with different Cl- concentrations was studied by a scanning micro-reference electrode technique, combined with polarization curve and electrochemical impedance spectroscopy measurements and an electron probe method. The results indicated that the steel remained passive in the solution without Cl-. The steel passivity might be destroyed by the Cl- attack, and the pitting corrosion took place. The chloride threshold level for localized corrosion of the steel in the solution was 0.010 to 0.020 M Cl-. Pitting corrosion occurred preferentially at MnS inclusion locations, and the Cl- was adsorbed at these locations resulting in depassivation of the steel surface.