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Chloride extraction

Electrochemical chloride extraction (or ‘desalination’) systems have been developed to remove chloride ions from contaminated concrete to overcome the problem of chloride-induced corrosion. Extraction is achieved by applying an electrical field between the reinforcement and an externally mounted anode mesh. During the process chloride ions are transported towards the anode and out of the concrete. An outline of this process is shown in the Figure. Measurements of chloride levels at a range of depths at selected locations should be made before and on completion of the work to determine the reduction in chloride content.

Chloride extraction is a most useful system for bringing chloride levels down below the threshold level at which corrosion can be initiated. The removal of chloride from the concrete will normally re-establish the original properties and allows the concrete to continue in service without further concerns.

Where continuing environmental circumstances, such as marine concrete in a seawater splash zone, has caused the build-up of chloride, extraction will still be possible. However, it will obviously be beneficial to provide further protection to the concrete when the extraction process is complete to reduce the possibilities of re-contamination.

Chloride extraction is covered by the draft CEN/TS 14038, Electrochemical realkalization and chloride extraction treatments for reinforced concrete, Part 2: Chloride extraction.

Schematic of chloride extraction process

Acknowledgement: The Concrete Society

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