Cathodic Protection for Life Extension of Existing Reinforced Concrete Bridge Elements (2009) / Chapter Skim
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Pages 34-41
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From page 34... ...
SELECTION OF A CATHODIC PROTECTION SYSTEM The results of the survey conducted in this effort indicate that, in general, agencies do perform visual, crack, and delamination surveys during routine bridge inspection, which provides them with information to determine if corrosion has been initiated in their structures and whether it needs attention. Once corrosion-induced damage reaches a certain threshold, which is probably different for each state, a corrosion condition evaluation is performed that generally includes chloride ion content analysis and half-cell potential testing.
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From page 35... ...
Not only might the performance and durability of the anode material be considered but its applicability to the subject project could be evaluated. In an interview, the Manager of DP-34 Cathodic Protection for Reinforced Concrete Bridge Decks stated that after FHWA involvement in the cathodic protection industry was reduced in 1989, many agencies had not yet acquired sufficient expertise in the technology and became dependent on vendors and material suppliers for all aspects of the use of the technology.
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From page 36... ...
In another example, an impressed current cathodic protection system on a bridge deck or decks in New Jersey failed to provide corrosion control because the designers had not included the impact of corrugated metallic forms present at the bottom of the bridge deck(s)
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From page 37... ...
In some instances, the agencies did not appreciate Reason No. of Respondents Cathodic protection system did not work at all Cathodic protection did not stop corrosion and concrete repairs were required after cathodic protection installation within the first 5 years 0 Cathodic protection components failed and could not be maintained 7 Monitoring and maintenance was a significant burden 13 The agency does not have the resources to monitor and maintain the cathodic protection system 7 The technology is not well understood by the agency 3 The consultants are not well versed in the technology to recommend it to the agency 1 Applicators and contractors that do business with the agency do not have any experience with the technology 2 Experience of other agencies suggest cathodic protection is too complicated, does not work, is too expensive, and requires significant monitoring and maintenance 1 Agency staff with experience in cathodic protection has retired or have been promoted and new staff have no experience with cathodic protection 2 Cost of cathodic protection was relatively higher then other options 10 3rehtO Note: Table based on results of Question 31 of the survey.
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From page 38... ...
All anodes have some performance and durability limitations; for example: • Conductive polymer material used as secondary anodes is susceptible to acid attack, • Conductive paint can weather within 5 to 10 years depending on the exposure conditions, • Mixed metal oxide anodes when operated above 10 mA/ft2 of anode surface area can generate chlorine, which can result in acid attack of the concrete, • Zinc anodes can passivate in certain environments, • Ceramic anodes can have low contact resistance and if the gasses are not vented properly can result in acid attack, • Adhesive in the zinc foil anodes can dissolve and loss of bond can occur if water infiltrates, • Coke breeze systems can suffer from high resistance due to loss of coke around anodes and corrosion of wire connectors, and • Arc sprayed zinc and aluminum–zinc–indium alloy may experience bond problems, etc. 38 Therefore, anode materials and the configurations in which they are used must be selected, designed, and installed in accordance with the best practice and the system operated within safe operating ranges.
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From page 39... ...
In one instance, it was found that homeless people living under a bridge had cut the conduit and wires for the cathodic protection system in an effort to obtain power for their heaters and television sets. North Carolina installed five different types of impressed cathodic protection systems, the mixed metal oxide mesh, conductive paint, conductive polymer, conductive coke breeze, and aluminum–zinc–indium alloy, on five different bents and all of them failed within one year.
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From page 40... ...
Many of the problems and failures of cathodic protection systems discussed previously are symptomatic of the evolution of anode materials and the process of learning the material interactions and limitations. With the exception of the conductive coke asphalt, ferex anode, and the zinc foil anode, all other anodes are still successfully being used.
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From page 41... ...
These numbers also provide insight into the marketplace in terms of monopoly and lack of competition. When agencies were questioned as to which factors will encourage the application of cathodic protection technology, reduction in cost was cited by the greatest number of agencies.
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