Long-Term Effects of Electrochemical Chloride Extraction on Laboratory Specimens and Concrete Bridge Components
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2011-09-01
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Abstract:Electrochemical chloride extraction (ECE) is a process that extracts chloride ions from chloride-contaminated reinforced concrete structures by applying an electrical current between the embedded steel and an external anode. ECE is becoming increasingly popular as a rehabilitation option for chloride-contaminated reinforced concrete structures to mitigate ongoing corrosion of embedded steel.
In 1987, section 128 of the Surface Transportation and Uniform Relocation Assistance Act initiated the Strategic Highway Research Program (SHRP). The structures portion of SHRP evaluated ECE technology in detail and determined its feasibility through a laboratory study. Additionally, it performed four field validation studies from 1987 to 1992. The laboratory portion of the study affirmed the feasibility of ECE application, and three of the four field validation studies were successful. Although sufficient levels of chloride ions remained in the structure after the application of ECE, researchers found that the distribution of chloride ions in concrete and the production of hydroxyl ions at the concrete-steel interface could significantly delay the initiation of corrosion and provide an extension in service life. A long-term evaluation of ECE-treated laboratory concrete slabs was considered necessary to evaluate the remigration of chloride ions with time and to study the impact of the higher levels of hydroxyl ions at the concrete-steel interface in delaying the initiation of corrosion. Although the SHRP study clearly established the feasibility of extracting sufficient amounts of chloride ions from concrete bridge elements, it was not designed to ascertain the long-term effectiveness of the technology in mitigating corrosion. The primary goal of this study was to monitor 10 SHRP concrete laboratory specimens and 3 SHRP field validation sites for 5 years to determine the long-term effectiveness of ECE.
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