Electrochemical chloride extraction : influence of concrete surface on treatment.
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2002-10-01
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Edition:Interim report.
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Bridges and Structures;NTL-HIGHWAY/ROAD TRANSPORTATION-Construction and Maintenance;NTL-HIGHWAY/ROAD TRANSPORTATION-Materials;NTL-HIGHWAY/ROAD TRANSPORTATION-Pavement Management and Performance;
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Abstract:One bridge restoration technique available for reducing corrosion-induced concrete deterioration, which removes
chloride ions while simultaneously realkalizing the concrete adjacent to the steel, is electrochemical chloride extraction
(ECE). Studies have shown that ECE is capable of removing, in a single application, a significant portion of the chloride
ions fiom a reinforced concrete structure. Prior research has also shown that the quantity of chloride ions removed is
dependent on numerous factors including quantity and spacing of reinforcing steel, applied voltage, initial chloride
concentration, etc. In addition, investigations into chloride binding and competition between other ions as current carriers
have helped to clarify the probable mechanisms responsible for decreases in current efficiency with time during chloride
removal.
This portion of the investigation has focused on the influence of water-to-cement (wlc) ratio. In addition, an
investigation was conducted to identify the cause of decrease in efficiency during chloride removal. A clear relationship
between the w/c ratio and the chloride extraction rate was not evident. However, the investigation revealed that the
resistance of the concrete surface layer increases considerably during ECE, which effectively restricts the current flow, while
the resistance of the underlying layer of concrete either decreases orremains constant. It appears that the increased
resistance of the surface layer concrete is accompanied by the formation of a tightly adhering residue on the concrete surface.
Preliminary analysis of the surface formation indicates it contains calcium carbonate and calcium chloride.
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