Causes for the corrosion of concrete steel in reinforced concrete

For cathodic corrosion protection of steel reinforcement in concrete, significant progress has been made in recent years in the development of sacrificial anodes. Under normal climatic conditions, the steel reinforcement is sufficiently protected from corrosion by the natural alkalinity of concrete (pH > 12.5) . This pH value results in passivation of the steel surface which inhibits corrosion. Unfavourable environmental conditions are frequently causes of corrosion damage which require extensive repair work throughout the world.
Spalling of the concrete cover is caused by the corrosion products forming on the steel reinforcement which may be five times the volume of the original uncorroded steel. Various environmental conditions (temperature, moisture), but also concrete-specific causes (cement type, water-cement ratio, additives) have a significant influence on the durability of the passivation of the steel reinforcement.
Corrosion mechanisms in concrete are carbonation and chloride contamination (chloride content exceeding the critical value in concrete).
It is just in marine environments that the ingress of chloride ions by salt water is a frequent cause of corrosion of the steel reinforcement in concrete. This is also true for traffic structures and industrial plants which are contaminated by chloride ions.