Marine Exposure of Concrete Under Selected South African Conditions


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Title: Marine Exposure of Concrete Under Selected South African Conditions

Author(s): James R. Mackechnie and Mark G. Alexander

Publication: Special Publication

Volume: 163


Appears on pages(s): 201-214

Keywords: chlorides; concrete durability; diffusion; exposure; fly ash; portland cement; slags; underwater structures; Materials Research

Date: 8/1/1996

The marine environment provides a severe durability test for reinforced concrete structures with premature deterioration often being associated with steel corrosion. The rate of chloride ingress from the sea through the concrete cover is of primary importance since the depassivation of steel and subsequent corrosion are largely controlled by the chloride concentration at the reinforcement. Accurate service-life predictions are made by defining the material, assessing the severity of exposure, and monitoring the durability performance in that environment. Concrete, therefore, needs to be characterized in terms of early age properties that control the diffusion of chlorides through the cover concrete. These characterized values may then be related to long-term characteristics which determine durability for different environmental conditions. Early age tests should only be used as indicators of potential durability once suitable relationships have been established with the durability performance of concrete under marine conditions. Results from a research program are presented, in which concrete specimens were initially characterized at 28 days before being exposed to four marine environments in South Africa. The concrete was tested using a newly developed chloride conductivity test which determined the chloride resistance of concrete using an accelerated technique. Chloride contents were measured after 24 months of exposure and the diffusion coefficients were related to the initial characterization values. Results indicated that the severity of exposure has a major influence on the relative rate of chloride ingress into the concrete. The chloride conductivity test was found to be a useful indicator of chloride resistance, but the results are specific to the type of concrete being tested. Comparisons of potential durability of concretes based solely on the results of rapid chloride tests at early ages may be misleading and should be used with caution.