Materials Performance

MAR 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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New control units were installed in a climate-controlled room above the wharves. Photo courtesy of Atef Cheaitani. 31 MATERIALS PERFORMANCE: VOL. 57, NO. 3 MARCH 2018 Protecting Concrete Wharves with Cathodic Protection "If you don't have concrete spalling or cracking, the only thing you can do is ham- mer testing to detect delamination by hear- ing a hollow sound. This is an indication that there is a problem in the concrete." Cheaitani explains. A detailed inspection at areas where delamination was suspected revealed that the gunite material encapsulating the rib- bon anode was fully sufficient to pass the CP current to the embedded steel reinforce- ment. The suspected delamination proved not to be associated with any corrosion of the steel reinforcement. Grout Acidification Where the ribbon anodes were installed in slots cut in the original unrepaired con- crete, there was missing grout and evidence of grout acidification at various locations in the splash and tidal zone areas. Cheaitani notes that the acidification of the grout was related to the encapsulation of the ribbon anodes in the cut slots. "The repair encap- sulation wasn't sufficient for areas sub- jected to tides and continuous water spray," he comments, noting that as the tide came in and wet the areas, there was minor shrinkage cracking over time between the grout and the original concrete. As the water penetrated the material surrounding the anode, acidification occurred. "At the time of installation, this problem wasn't really known," he adds. The system audit didn't determine any evidence of a correlation between grout acidification and a reduction of anode cur- rent density, Cheaitani says. The ribbon anode was operational while immersed in water. Based on the audit results, initiation of reinforcement corrosion and concrete deterioration was not observed in the tidal and splash zones because of grout acidifica- tion, which indicated that grout acidifica- tion had no impact on the ICCP system's performance. Water Damage Components with varying degrees of water damage were noted for many of the junction boxes and control units located at the abutment wall underneath the wharf. At the time of system installation, enclo- sures rated as IP67 were thought to be suffi- cient for providing protection to all compo- nents within the enclosures against moderate water exposure at high tide. However, ~50% of the control units and 50% of the junction boxes located at the abut- ment wall in an area with water exposure had some sort of water damage to termi- nals and electronics inside. The audit found, though, that 96 junction boxes located at the front crane beam and away from the water were in excellent condition. Overall, Cheaitani says, the perfor- mance of the original ICCP system since its commissioning was very satisfactory. Locating the control units underneath the wharf, which made them susceptible to water and moisture exposure and increased the failure rate for some system compo- nents, was the main drawback of the sys- tem that needed to be addressed. ICCP System Renovation The scope of the renovation work was to move the junction boxes and control units to locations above the wharves while maintaining and utilizing all embedded CP system components in the concrete (ribbon anodes, reference electrodes, and cabling). While developing the configuration for this task, Cheaitani explored increasing the size of the ICCP zones and reducing the number of circuits in the existing system. This could be possible because an analysis of system data showed a similar level of current requirements between similar zones in dif- ferent sections. In theory, he explains, smaller zones in a CP design provide more control of the CP current. Doing this, however, requires more cabling, reference electrodes, and power supply units. "After analyzing more than 15 years' worth of data, we noticed a big simi- larity in the level of current going to each zone within different sections, and because of this similarity we understood that small zones are not really necessary," he says. "There is no advantage to having local zones because they all use about the same amount of current." The guidelines he used to reduce the number of circuits was to combine zones that had similar steel den- sity, corrosion status, and exposure condi- tions, as well as maintain a similar voltage drop in current delivered via the cabling. The new design called for combining smaller circuits with the same exposure conditions and CP current requirements, merging certain zones in each section, and changing the system layout from a local dis- tributed system, where the power supply is distributed to the individual sites of the control units, to a global supervised system, where the power is supplied to all control units in one location above the wharf.

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