ABSTRACT
The highly alkaline environment in concrete results in the spontaneous formation of a stable, tightly adhering, thin protective iron oxide (passive) film on the steel reinforcement surface, which protects it from corrosion. However, the passivity provided to steel reinforcement by the alkaline environment of concrete may be lost if the pH of the concrete pore solution falls because of carbonation or if aggressive ions such as chlorides penetrate in sufficient concentration to the steel reinforcement surface. Leaching of alkalis from concrete also lowers the pH, which allows corrosion of the steel reinforcement. Stray electrical currents, most commonly from electrified traction systems and interference currents from cathodic protection systems can also breakdown the passive film, and cause corrosion of steel reinforced and prestressed concrete elements. Fundamental and key issues relating to passivity and the passive film and the mechanisms of corrosion of steel under these conditions are discussed.
