Chloride Penetration into Offshore Concrete and Corrosion Risks

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Title: Chloride Penetration into Offshore Concrete and Corrosion Risks

Author(s): G. De Wind and P. Stroeven

Publication: Special Publication

Volume: 100

Issue:

Appears on pages(s): 1679-1690

Keywords: chlorides; concrete durability; corrosion; cover; diffusion; offshore structures; oxygen; reinforcing steels; saturation; General

Date: 4/1/1987

Abstract:
The oxygen flux through concrete saturated with water has been calculated by means of the theoretically determined diffusion constant. Presuming oxygen diffusion to be the rate-controlling step, it is concluded, based on this flux, that the corrosion of reinforcement in the underwater zone is negligible. This holds also if the chloride concentration at the surface of the embedded steel exceeds the 0.4 percent by weight of cement level. The calculations are confirmed by analyses carried out on a 35-year-old concrete sea structure that is, until now, the most extensively examined one. In the splash zone of the structure, the chloride concentrations at the surfaces of the reinforcements far exceed the 0.4 percent level. In this zone there is corrosion only in places where depth of cover or quality of concrete are inadequate. Calculation of the oxygen fluxes with the help of diffusion coefficients, taken from the literature, shows that the corrosive attack would be too severe even at a relative humidity of 90 percent. This indicates that the durability of offshore concretes in the splash zone iscontrolled by a thin layer of material saturated with water.