The effect of concrete pore solution composition on the quality of passive oxide films on black steel reinforcement

The effect of concrete pore solution composition on the protective properties of the oxide films that form on black reinforcing steel has been experimentally investigated using anodic polarization and electrochemical impedance spectroscopy (EIS). The tests were conducted on oxide films grown in saturated calcium hydroxide solutions that included different representative amounts of NaOH, KOH, and Ca(SO4), which are compounds that are commonly observed in most ordinary portland cement concrete types. The results of both anodic polarization and EIS tests show that pore solution composition has an effect on the protective properties of the passive oxide films and, in particular, sulfate ions (SO4)2-(SO4)2- have been shown to have a negative influence on the film quality.