Concrete corrosion or carbonating is chemical reaction, which runs off in each concrete. In the pore solution of the concrete solved is converted by the carbonating approx. (OH) 2 (Portlandit) into CaCO3 (limestone). The following Teilreaktionen run off:

Solve the crystalline Portlandit

Approx. (OH) _2 \ rightarrow Ca^ {2+} +2OH^

Solve from CO2 in the alkaline pore water

CO_2 + H_2O \ rightarrow H_2CO_3

Neutralization of approx. (OH) 2 by H2CO3

Approx. (OH) _2 + H_2CO_3 \ rightarrow CaCO_3 + 2H_2O

Consequence of the reaction is the decrease of the pH value of the pore solution of on the average 12.5 on under 9. At pH values above 10 a passivation layer on the surface of the reinforcing steel embedded in the concrete, which protects the steel durably against armouring corrosion, forms. If the pH value in the concrete sinks, the danger of damage connected with armouring corrosion exists.

The speed of the concrete corrosion depends on the following factors:

Exposition of the concrete - dry one stresses carbonatisieren in interiors or at weather-protected locations faster as if stress, which are exposed to the free weathering.

The old concrete - the carbonating speed is reduced with increasing concrete age after the root time law. due to this connection statements can be met to carbonating progress.

Porosity of the concrete - due to the larger surface carbonatisieren porous stress faster than seals stress.

By spraying with 1prozentiger to ethanolischer phenolphthalein solution the carbonating progress at the fresh concrete location of fracture can be visualized. At pH values between 8,2 and 9,8 takes place a color change of colorless (neutrally) too violet (alkalinely).

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