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42 CHAPTER SIX LONG-TERM CATHODIC PROTECTION SYSTEM PERFORMANCE To date, more than 500 bridge structures in North America have moved beyond research and experimentation and have have had cathodic protection systems installed. Many of become mainstream systems is also included. the early systems were experimental and their design, installa- tion, and operation for a certain period have been docu- mented. To obtain a good understanding of the long-term IMPRESSED CURRENT CATHODIC performance, a history of performance for at least half or PROTECTION SYSTEMS more of its projected service life should be available. This Slotted Non-Overlay--Conductive would allow one to reasonably ascertain if the claims made Polymer Backfill with regard to extension in service life are realistic. As there are various types of cathodic protection systems, the long- One of the largest slotted conductive polymer non-overlay term performance is dependent on the materials and compo- cathodic protection systems was installed on the bridge car- nents used. When reviewing the performance of cathodic rying I-64 in Charleston, West Virginia, which was energized protection systems, it is important to ascertain the impact in 1985. This system was still operational at the time of this of design and the installation quality on its performance. report and although the system has undergone repairs, no Cathodic protection systems of the same type on various concrete repairs have been required since the start of opera- different installations have provided a varied performance tion. This system was monitored under the FHWA-54 pro- and sometimes performance has been limited by inadequate gram and monitoring and maintenance appeared to be a design, improper installation, or inadequate monitoring and major problem for the owners. A consultant was hired to maintenance. monitor and maintain the system and it had a documented history of satisfactory operation until 2005 when it was last In 1995, as a continuation of SHRP, the FHWA initiated monitored. The anode material in a few slots experienced an effort (FHWA-54) to monitor for 5 years the performance acid attack and the conductive polymer material had failed. of various different types of cathodic protection systems on The primary anode, platinum niobium wire, and the secondary highway structures that were operational at that time and/or anode, carbon fiber, were exposed to the traffic and were were just installed. Various materials in various configura- damaged. These were repaired after approximately 7 years of tions had been used as anodes resulting in various different operation. The West Virginia system uses platinum as the types of cathodic protection systems. The selection of the primary anode in the longitudinal slots and carbon fibers in anode material and its configuration is paramount to the suc- the transverse slots. This system does not have an overlay cess of the system. The primary objective of this study was to and the conductive polymer in the slots is exposed to loading determine the effectiveness of various materials and config- from vehicular traffic. urations when used as anodes on highway structures through a long-term evaluation. In this effort, a total of 20 highway Missouri has the largest inventory of slotted cathodic pro- structures (19 bridges and one tunnel) protected by one or tection systems. Its oldest system has been in operation for more types of cathodic protection system(s) were included. 23 years. Of its 161 bridge deck systems, 38 are mixed metal The structures were located in 11 states and 1 Canadian oxide titanium systems, 8 have platinum and carbon wire, province. These structures were protected by a total of 19 and the remainder of the systems uses platinum wire as the impressed current and 5 galvanic cathodic protection sys- anode material. It should be noted that all slotted systems in tems. There were 9 different types of anode materials and Missouri have an overlay. Only 10 slotted bridge deck sys- configurations used in impressed current and 3 different tems have asphalt overlay; all others have a concrete overlay. types of anode materials and configurations used in galvanic The cathodic protection systems on the bridge decks prevent cathodic protection systems. The length of time the systems corrosion of the embedded reinforcement and its electric had been in operation at the end of the program varied from field also forces the chloride ions to migrate away from the 1 to 15 years. The results of this effort were published in reinforcement toward the positive anode material, thereby 2000 (27). The findings of this report are briefly reviewed reducing the chloride ion content in the deck concrete. along with the response of various public agencies to the sur- Recently, when the bridge decks with cathodic protection vey conducted in this effort. Where possible, information on systems had to be widened, the chloride ion distributions in long-term performance available in literature for systems that the decks were evaluated. When the chloride content at the