Materials Performance

NOV 2014

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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a connection to the steel frame and testing the connection between the anchor, shim, and frame; and reinstating the drilled-out masonry core. The ancillary anchors were located, and then bonded by drilling a self- threaded TAPTITE † screw with a lead wire back to the steel frame. Great care had to be taken to avoid damaging the masonry, she adds, noting that the joint line for the reinstated core could be no larger than 0.125 in (3 mm). The entablature was grouted to ensure current flow to the interior steel. For the ICCP design, the rotunda was divided into four zones with six bays each. Each bay has a total of ~104 ft 2 (9.7 m 2 ) of steel. Because of the layout of the limestone masonry, joint lines where the system could be installed were limited. According to Noyce and Crevello, the anode system was installed within the two joints (the exterior and interior) of the frieze—the joints near the steel flanges—to ensure that the embedded beams, channels, and anchorage are all protected. The system incorporates more than 1,000 6-in (150-mm) ballasted MMO-coated titanium expanded mesh probe anodes. The maximum current output is 3.9 mA/m 2 per anode, which required significant derating for this monumental historic structure. All system components were embedded at least 2 in (51 mm) within the masonry joint so that future joint repointing will not disturb the wiring. Each bay is independently monitored with a reference electrode to guarantee proper current distribution throughout the rotunda, with a total of 24 monitoring cells within the system. Noyce comments that the current density chosen for the system, 0.3 mA/ft 2 , is extremely low by concrete CP standards; however, it is of paramount importance that a trickle of current be used to avoid any adverse effects to the masonry joints or limestone. "One of the things we have to be conscious about with historic buildings is the reaction of the anode, which is a hydrogen-producing reaction that can create acids," Crevello explains. "We have to be careful that we don't generate an acid reaction or acidification of the anode in historic buildings because—for reasons of historic integrity—we can't afford to dissolve the materials." To limit the effects of high current from any one anode and provide an even distribution of current, the anodes were placed close to one another, ~12-in (305-mm) apart on center; staggered between the exterior and interior joints; and derated. "We designed the hydrogen problem out of our system," she says. The external CP wires were brought through an open soffit space at the top of the rotunda, and all CP wires were attached to a designated junction box that was connected to the local power supply located at the base of the dome. Communication cables running from the local power supply were connected to the main controller in the rotunda's electrical room. The ICCP system was energized in October 2013, and the steel is polarizing as expected. Noyce emphasizes that the aim of this project was to preserve the historic fabric of the building's façade by minimizing damage to the limestone masonry, which could be done by preventing corrosion through CP—and that was in the forefront of their approach. In the architectural arena, he adds, this is still a very "forward-thinking" approach. Not all historic buildings are candidates for CP because of the complex nature of their geometries and detailing, he says, and it's crucial to understand whether CP will actually offer a corrosion solution for these structures. The initial corrosion analysis report for the Elks Veterans Memorial was submitted in August 2009 and the project contract was issued in March 2012. The design for the ICCP system was submitted in July 2012, construction commenced in the late fall of 2012, and the ICCP system was commis- sioned in October 2013. The project team, led by Harboe Architects, also included structural engineering firm TGRWA Engineers, archi- tectural engineering firm Architectural Consulting Engineers, masonry restoration contractor Mark 1, and corrosion consultant Electro Tech CP. For more information on the project, see CORROSION 2014 conference paper no. 4172, "Preserving a Memorial: The Use of Impressed Current Cathodic Protection on a Historic Steel Frame Rotunda," by G. Crevello and P. Noyce. † Trade name. 31 MATERIALS PERFORMANCE NOVEMBER 2014 NACE INTERNATIONAL: VOL. 53, NO. 11

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