The semiconductor properties of the rebar passive film formed in the simulated pore solutions for different dosages of sodium hydroxide (NaOH) activated slag were investigated with free corrosion potential, Mott Schottky plots. The detrimental effect of different chloride ion concentrations on the passive film and the threshold chloride ion concentration were also studied. The rebar passive film formed in the simulated pore solutions of Ordinary Portland Cement (OCP) was tested for comparative purpose.The results indicated that the passive film formed in the simulated pore solutions of NaOH activated slag needs 18 d~26 d. When the dosage of NaOH is low (2% or 4%),the passive film has the characteristics of bipolar semiconductor structure (n-p).As the dosage of sodium hydroxide increases by 6%,8% and 10%,the passive film is changed to tripolar semiconductor structure (p-n-p).So the corrosion resistance of passive films is improved with the increasing dosage of NaOH.When the sodium hydroxide dosage is higher than 6%, the steel resistance to chlorine ion corrosion ability is better than the contrast group from Portland cement.The threshold chloride ion concentration is 0.11 mol/L when the dosage of sodium hydroxide is 10%, while the control sample formed from Portland cement is only 0.03 mol/L.
