Mechanism of corrosion protection in reinforced concrete marine structures
C. L. PAGE
Department of Civil Engineering, University of Strathclyde, Glasgow, UK
RECENT developments in concrete offshore structures have drawn attention to a disturbing ignorance of the mechanism by which steel corrosion is prevented when it is embedded in dense concrete1. The traditional view has been that the metal remains passivated owing to the high pH (approx 12.5) of the pore solution in concrete. It is, however, well known that relatively small concentrations of Cl- destroy the corrosion inhibitive properties of non-buffered alkalis and approx 700 p.p.m. of Cl- will depassivate steel in limewater at pH 12.5 (ref. 2). Since seawater contains concentrations of Cl- far in excess of this figure, and since penetration by these ions to the reinforcing bars in concrete takes place within a small fraction of the service life of a marine concrete structure3, corrosion might be expected to be a frequent problem. In practice, however, there are many examples of reinforced concrete structures which have remained durable in seawater for 30 yr and more. Such corrosion problems as have been reported are, in the majority of cases, associated only with areas immediately above the level of high tide, where the concrete is not maintained in a saturated condition.
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References
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