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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. |
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