Long-term effectiveness of cathodic protection systems on highway structures Publication No.

Based on extensive study, FHWA researchers conclude that cathodic protection--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 applying an external source of current to counteract the internal corrosion current produced in reinforced concrete components. During cathodic protection, current flows from an auxiliary anode material through the electrolyte (concrete) to the surface of the reinforcing steel.

Assorted materials in different configurations are used as auxiliary anodes for cathodic protection, resulting in various types of systems. The selection of the anode material and its configuration is paramount to the success of the system. The primary objective of this 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.

In this study, researchers looked at 20 highway structures (19 bridges and 1 tunnel) protected by one or more cathodic protection systems. The structures, located in 11 States and 1 Canadian Province, were protected by a total of 19 impressed-current and 5 galvanic systems. FHWA selected most of the structures based on previous studies performed tinder the Strategic Highway Research Program; the current study was funded under the continuation of that 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, resulting in poor performance. If these systems had been operated at higher output currents, their performances would have been rated higher.