Long-term Effectiveness of Cathodic Protection Systems on Highway Structures

00962820529731142003PDFTech ReportFHWA-RD-01-096Anodic materialsBridgesCathodic protectionElectric currentPerformanceReinforced concrete pavementsService lifeTunnelsNorth AmericaUnited States. Federal Highway AdministrationSohanghpurwala, AAScannell, W. T.Turner-Fairbank Highway Research CenterUnited States. Federal Highway AdministrationNTL-HIGHWAY/ROAD TRANSPORTATION-Bridges and StructuresNTL-HIGHWAY/ROAD TRANSPORTATION-DesignNTL-HIGHWAY/ROAD TRANSPORTATION-HIGHWAY/ROAD TRANSPORTATIONFederal Highway AdministrationThe Federal Highway Administration (FHWA) has concluded, on the basis of extensive research, that cathodic protection (CP), the technology used to mitigate corrosion of metals embedded in concrete, is the only rehabilitation technique that has proven to stop corrosion in salt-contaminated bridge decks regardless of the chloride content of the concrete. This technology is based on the principle of applying an external source of current to counteract the internal corrosion current produced in reinforced concrete components. During CP, current flows from an auxiliary anode material through the electrolyte (concrete) to the surface of the reinforcing steel. Various materials in various configurations are used as auxiliary anodes for CP, resulting in various types of CP systems. The selection of the anode material and its configuration is paramount to the success of the system. The primary objective of the 5-year study was to determine the effectiveness of various materials and configurations when used as auxiliary anodes on highway structures during a long-term evaluation. Twenty highway structures (19 bridges and 1 tunnel) protected by one or more CP system(s) were included in this study. The structures were located in 11 States and 1 Canadian Province. These structures were protected by a total of 19 impressed current and 5 galvanic CP systems. Most of the structures were selected by FHWA based on previous studies performed under the Strategic Highway Research Program (SHRP); this study was funded under the continuation of the SHRP program. The findings of the study summarize the protection provided by the systems evaluated and estimate the expected service life for the anode materials in similar environments. On some structures, the systems were operated at insufficient output current and this resulted in poor performance. If these systems had been operated at higher output currents, their performance would have been rated higher