Effects of Alkali Slag Activator on Formation and Damage of Passive Film on Steel Bars

Electrochemical impedance spectroscopy was adopted to characterize the passivation and depassivation behavior of ordinary steel bars and corrosion resistant steel bars in four kinds of alkali activator solutions of sodium hydroxide, sodium silicate, sodium sulfate and sodium carbonate. And saturated calcium hydroxide solution was used as a simulated pore solution in ordinary concrete for comparative study. The results show that the formation process and destruction process of steel bar passive films were highly relied on the type and pH value of activator. The steel bar passive film forming in Na₂SiO₃ solution was the most stable passive film and had the best ability to resist chloride corrosion. The steel bars self-corroded in Na₂SO₄ solution. Compared with ordinary steel bars, corrosion resistant steel bars can form passive film more quickly and had better corrosion resistance.