Effect of Simulated Concrete Pore Solution Chemistry, Chloride Ions, and Temperature on Passive Layer Formed on Steel Reinforcement

The nature of the passive film that forms on steel reinforcement bars has been found to be profoundly affected by the type of concrete pore solution, the chloride ion concentration in the solution, and variation in temperature. X-ray photoelectron spectroscopy, Raman spectroscopy, microscopy, and electrochemical studies have shown that changes in the nature of the passive film on the steel surface under different conditions can produce a wide variation in the corrosion and pitting tendency of reinforcing bars. A passive film formed in a lime-saturated solution exhibited polarization resistance values that were 1.5 times higher than the simulated concrete pore solution. The admittance value of the former film was approximately 1.75 times lower than that of the latter film. The capacitance of the film developed in the lime-saturated pore solution was also lower (28 nF) than the capacitance (34 nF) of the film formed in the lime-free solution. The presence of the chloride ions in the pore solution subtly changed the passive film before its complete breakdown. Variation in temperature of the test electrolyte was observed to significantly affect the nature of the passive film.