Reinforcement corrosion in concrete — Mechanism

From an early age, reinforced concrete structures are subjected to mechanical stresses (loads, various external or internal stresses, including wind, temperature variations, etc.) and environmental stresses (atmosphere, sea water, etc.).

Their durability is essentially linked to the specific behavior of the concrete material. It constantly reacts with the environment: water exchanges, chemical reactions, the action of carbon dioxide (natural aging). This can lead to disorders.

Reinforcement corrosion is the most frequent of these phenomena, and is likely to require major, and therefore costly, repairs.

Initially, steel is protected both by a passivation layer, due to the alkalinity of the environment, and by the quality of the concrete coating. However, carbonation and chlorides lead to depassivation of the reinforcement. This results in the appearance of oxides, sometimes of an expansive nature, leading to the destruction of the embedding concrete, and ultimately to the loss of mechanical properties of the structures.

Prevention is therefore essential. A good understanding of the mechanisms involved is essential for better maintenance, diagnosis and repair.

The aims of this article and the two others that complete the study of the subject ( [COR 408] "Corrosion of reinforcement in concrete – Examples and actions", [COR 409] "Corrosion of reinforcement in concrete – Approaches"), are as follows:

• describe the phenomena leading to rebar corrosion and its consequences (formation of splinters, spalls, element failure, etc.);

• present case studies.