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34 CHAPTER FIVE PROBLEMS ENCOUNTERED WITH CATHODIC PROTECTION SYSTEM APPLICATION Problems with cathodic protection system application have natives that are likely candidates for the particular project been experienced in all aspects of the application process, based on corrosion condition survey results. The latest in the from selection of the appropriate system through installation series is the Manual developed under an NCHRP study that to the regular monitoring and maintenance of the systems. documents a methodology for conducting corrosion condition Each phase of the application process is discussed in this evaluations and selecting alternatives based on its results (48). chapter to ascertain the areas in most need of improvement. In addition to determining the applicability of cathodic protection for a particular structure, it is also necessary that SELECTION OF A CATHODIC the corrosion condition data provide information on whether PROTECTION SYSTEM galvanic or impressed current cathodic protection will be The results of the survey conducted in this effort indicate that, required. The results of the survey indicate a trend toward in general, agencies do perform visual, crack, and delamina- the use of galvanic cathodic protection systems. Galvanic tion surveys during routine bridge inspection, which provides cathodic protection systems have a current delivery limit that them with information to determine if corrosion has been ini- is controlled by the type of anode and the environment and tiated in their structures and whether it needs attention. Once may not provide sufficient current in certain applications. corrosion-induced damage reaches a certain threshold, which At the start of the industry, in the 1970s, the E Log I test was is probably different for each state, a corrosion condition eval- used to determine the current requirement. Owing to equip- uation is performed that generally includes chloride ion con- ment and time requirements, this test is rarely used today. tent analysis and half-cell potential testing. Such data would Experienced practitioners use all or some combination of provide a good idea of susceptibility to future corrosion in chloride ion distribution, severity of the environmental expo- sound areas. If chloride ion distribution at the steel depth has sure, half-cell potential survey results, corrosion rate measure- either exceeded or is close to the threshold and the top layer ments, electrical conductivity measurements, and quantity of of the sound concrete has high levels of chloride ion concen- damage information to ascertain if galvanic or impressed cur- tration, the reinforced concrete element is a good candidate for rent systems will be required. Therefore, it is imperative that agencies either use in-house personnel with appropriate skill cathodic protection. However, judging from the response to sets or hire a consultant with the requisite qualifications and survey questions, it appears that the quantity of damage is experience to make the selection decision. considered by most agencies to be the determining factor. Although the quantity of damage is a good indicator of what is happening, waiting for a certain level of damage to occur DESIGN OF SYSTEM increases the total cost of repair. If instead of quantity of damage chloride ion content is used, the structures would Proper design of a cathodic protection system is paramount. be prioritized earlier for installation of a cathodic protection Good design guidelines and criteria will ensure that system system and would result in lower total cost of repair. designs meet some minimum standard. The available guide- lines and criteria for cathodic protection on reinforced con- Between 55% and 60% of the responding agencies have crete structures are not sufficient. At present the following some form of standards, procedures, protocols, or methodology two documents are available: for conducting corrosion condition evaluations, analyzing the data, and using the data to select alternatives for repair and reha- 1. NACE SP0290-2007 Standard Practice for "Impressed bilitation. This means that a good number of them either do not Current Cathodic Protection of Reinforcing Steel in need or do not have a standardized procedure for implementing Atmospherically Exposed Concrete Structures," devel- this or other technologies. It is reasonable to expect that the oped by the National Association of Corrosion Engi- standards, procedures, and protocols used by the agencies vary; neers, published in 2007. whereas some may be in need of an update, others may be the 2. Guide Specification for Cathodic Protection of Concrete state of the art. Several attempts have been made to develop a Bridge Decks, developed by a joint committee of protocol or a decision matrix that can be used to identify alter- AASHTO, AGC, and ARTBA, and was published 1994.
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35 The NACE standard is the more recent document and pro- turers, which may not always be considered from an indepen- vides broad guidelines as to what might be considered during dent source. For many of the newer materials, very little infor- design and relies on professional experienced personnel to mation from independent sources is available. A well-defined make the decisions. The AASHTO document does go into test method or guidelines for evaluating anode materials and design detail for each type of system; however, many of the their various configurations is required. The evaluation of the newer systems are not included and some of the included sys- anode materials and configurations might be done by the agen- tems are no longer used. Neither of the documents provides cies themselves or by independent research and testing groups. a basic template for project specifications that might be used At present, the primary indicator of success used by many as a basis by designers. Only six agencies from among those sales groups is the number of applications of the particular that responded to the survey have a standard for design and/ material and its acceptance by other agencies. Often, there are or construction specifications governing the use of cathodic no hard data or sufficient length of operation to ascertain the protection on reinforced concrete bridge elements. Another performance and the long-term durability of the material. document that is presently being developed by NACE is a Therefore, this method of acceptance of an anode material Recommended Practice for Sacrificial Cathodic Protection based on sales figures can be flawed. Not only might the per- of Reinforcing Steel in Atmospherically Exposed Concrete formance and durability of the anode material be considered Structures. The Europeans in 2000 have recently published but its applicability to the subject project could be evaluated. the standard EN 12696:2000 for implementation of cathodic protection technology. The state of Missouri identified the In an interview, the Manager of DP-34 Cathodic Protection need for a new guide specification and suggested that if one for Reinforced Concrete Bridge Decks stated that after FHWA could be provided that the DOTs could ratify the use of involvement in the cathodic protection industry was reduced in NACE standards and recommended practices. 1989, many agencies had not yet acquired sufficient expertise in the technology and became dependent on vendors and mate- Once a decision has been made as to which type of cathodic rial suppliers for all aspects of the use of the technology. He protection system is to be used, the anode material and con- stated that "It was a free for all and many materials which were figuration needs to be selected. Based on the results of the not ready for use were pushed into the marketplace." He also survey, it is clear that for a majority of the agencies, agency indicated that the lack of competition in the industry is a prob- staff designs these systems. Some agencies are assisted by lem. He presented the example of the ferex anode. As soon as a consultant, although fewer require a consultant to design the material was identified as having good properties to serve the system with assistance from either a NACE-certified as an anode material, the sales and marketing teams pushed the Cathodic Protection Specialist or the material manufacturer material on numerous bridge structures (at least 50) without or supplier. Even for agencies that have a well-established verifying the performance or the durability of the material and experienced staff to handle cathodic protection issues, in concrete. Almost of all of these systems failed. Missouri good information on all materials and configurations may not reported them failing between 0 to 5 years, California reported be available and when a need arises for a material or config- that they failed between 6 to 10 years, and in South Dakota uration other than what they have previously used, they must the systems failed immediately after installation. A consultant rely on information from material manufacturers and suppli- involved in the use of this system believes that the ferex anode ers. Information from material manufacturers and suppliers failed because it becomes brittle in concrete, subsequently can be valuable; however, the agency must have the exper- cracks and the inner copper core becomes exposed. The cop- tise to evaluate that information. FDOT stated that "many per core is not a satisfactory anode material and it corrodes agencies are reluctant to accept the technology because there rapidly at the application of current and the anode quickly have been too many overzealous sales representatives and fails. Missouri concurred with this observation and stated they do not have in-house expertise to evaluate the proposed that this anode material was not suited for use in concrete. systems." Texas reported that they do not have the requisite The manager of DP-34 believes that some of the newer anode skill sets and "all we really know is what the sales people materials making their way into the marketplace may have tell us." A consultant stated that designers allow "material or similar problems. other commercial considerations to push design." That would only be possible if the designer is not an independent party Even when well-established anode materials and configu- and has commercial interests in the materials or supplies rations are selected, the design parameters need to be properly for cathodic protection systems. Some earlier specifications established. The present design protocols only require the required that the designer not have any vested interest in the design to limit the voltage drop along the anode material; they manufacture or supply of cathodic protection materials. do not provide any mechanism for or require the calculation or estimation of other system parameters. Mathematical mod- When the first applications of cathodic protection started, els are currently available for such calculations and estima- FHWA and local DOTs were performing research and exper- tions (49). The design of the cathodic protection system on the imenting with various anode materials and configurations. As Benjamin Franklin Bridge in Philadelphia did not properly funding for such research dried up, users depended more on estimate the system requirements. The overall resistance of information provided by the material suppliers and manufac- the system came out to be too high and the rectifiers specified