United States Department of Transportation
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Use of Electrochemical Chloride Extraction and Associated Repairs to Extend the Beneficial Life of Reinforced Concrete Substructures
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2016-05-01
[PDF-7.73 MB]
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Abstract:One of the biggest causes of bridge deterioration is corrosion of the reinforcement in concrete structures. Therefore, repair techniques that mitigate corrosion and extend the service life of reinforced concrete are of great value to the Virginia Department of Transportation (VDOT). One such technique is electrochemical chloride extraction (ECE), which is a temporary in situ restoration method for removing chlorides from reinforced concrete structures that are deteriorating because of corrosion. The results of this study are based on historical and current data gathered during the evaluation of substructure elements in Virginia, i.e., the 5th Street Extended Bridge in Albemarle County and two I-95 bridges in Richmond, and on information from the literature about the earliest bridge substructure treated with ECE, i.e., the Burlington Bay Skyway in Burlington, Ontario, Canada,. Early ECE work on the Burlington Bay Skyway showed favorable results upon reassessment of the treated area after 9 years. With regard to the ECE-treated structures in Virginia, the study determined that if additional service life beyond that provided by ECE alone is desired, the structure must be protected against the reintroduction of chlorides to the repaired elements. Further, the use of ECE techniques should be accompanied by repair or removal of overhead deck expansion joints that exposed the concrete elements to salt-laden water and application of a waterproofing sealer such as silane, methacrylate, or epoxy to the substructure elements. ECE provided an additional 15 to 20 years of service life when a post-treatment silane sealer was also applied. The study also found that in the project specification, the criterion used for determining when to terminate ECE is often the amount of charge passed but difficulties in the field might result in unforeseen construction delays as a result of the attempt to meet this criterion. Therefore, contracts should specify that chloride concentration at the level of the reinforcing bar can be used as an alternative criterion for determining when the ECE is complete, particularly when treatment times become excessive. Specifications should also require that all ECE connections to the steel be completely removed or embedded after completion of the treatment and a highly resistive cementitious repair material should be used to patch any holes. Another valuable outcome from this study was the discussion on how combining electrochemical techniques, such as cathodic protection and ECE, could theoretically provide additional life beyond that provided by the use of one of these techniques alone. This study gathered baseline data to assess this option. The two I-95 bridges in Richmond, one over Hermitage Road and the other over Overbrook Road, should allow a comparison of how much galvanic anode cathodic protection can extend service life beyond that of ECE treatment alone. The study recommends that VDOT’s Structure and Bridge Division incorporate the lessons learned from assessing the restoration of the substructures of the 5th Street Extended Bridge and the two I-95 bridges. In addition, the Virginia Transportation Research Council should continue to monitor the I-95 bridges to determine the value of combining different electrochemical mitigation techniques to extend service life.
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