Corrosion of reinforcements in concrete – Examples, repairs, diagnosis and prevention

Two main mechanisms lead to the depassivation of reinforcement: the carbonation of concrete, which corresponds to the neutralization of its alkalinity by carbon dioxide in the air, and the action of chlorides from marine environments, de-icing salts, industry, etc. on reinforcement.

The main consequences of reinforcement corrosion are the formation of cracks and spalls, and the loss of load-bearing capacity. These disorders are a major problem for the client, with their impact on safety (of property and people), and loss of time and money (including the costs incurred by operating losses, as in parking lots, for example).

In the majority of cases, it is impossible for the client to anticipate the appearance of disorders, mainly for economic reasons.

A precise preliminary diagnosis is necessary whatever the repair technique adopted for a reinforced concrete structure suffering from corrosion problems.

Its objectives are as follows:

• identify the origin of the corrosion (carbonation, external or internal chlorides, other);

• assess spatial extent ;

• predict probable evolution, in time or space;

• estimate the consequences for the safety of the structure or people ;

• define the follow-up action to be taken, including the principle of repair solutions.

Diagnosis of the state of corrosion of a reinforced concrete structure is generally organized in two stages:

• the first consists of a global, non-destructive analysis to identify corroded areas and their extent;

• the second involves destructive testing, the main aim of which is to predict the residual service life of the structure in question.

The number and location of analyses and samples will be determined for representative areas, depending on the importance of the project in terms of size and strategy.

After the diagnostic stage, the methodology leading to the final choice of a repair process involves the following steps:

• definition of the basic principles of repair proper, with its objectives: to restore, avoid the appearance of new disorders, ensure good durability, without neglecting the aesthetic aspect which is of prime importance for certain monuments, not forgetting the associated structural reinforcements;

• the final choice of technique, including any preliminary studies or tests.

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