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.

Issue link: https://mp.epubxp.com/i/403882

Contents of this Issue

Navigation

Page 32 of 92

The ICCP design included an explor- atory investigative phase that included, among other things, locating anchors and studying bonding methods for the anchors, conducting trials for grout infill to deter- mine which grouting method facilitated the most current output from the anodes, and stray current testing. One of the greatest risks when using ICCP to protect an historic building is the inability to locate ancil- lary steel, Noyce says. He stresses that it's extremely important to understand where all the cramps and anchors would be and to ensure they are electrically continuous to the steel frame that the ICCP system is designed to protect. Typically, the cramps and anchors tend to corrode before the steel frame corrodes because they are closest to the exterior surface of the structure and are generally in joint lines where moisture and oxygen can penetrate first. Also, he adds, any piece of metal that is in the vicin- ity of a CP system can be affected by stray current. "We've proven many times in all instances that the anchors and cramps have to be bonded to the steel beam and be part of the CP system," he says, explaining that ions from the anode would pass through any unbonded anchor or cramp located between the anode and the steel beam and cause accelerated corrosion of that anchor or cramp with a corrosion rate that could be 1,000 times higher than what it would be without the stray current. "One thing we did not know at the time of investigation—and even during early construction—was how the steel shims were disassociated and discontinuous," Crevello says. She notes the structure needed to be fully scaffolded before it was possible to locate all the pieces of steel shimmed into the stonework and find very deep anchors, and even then the task was extremely challenging. The thick masonry cover, more than 11 in (279 mm) in some instances, made it difficult to differentiate between corroding anchors and voids in the mortar; and it also hindered traditional methods used to detect the steel, such as magnetometers and eddy current detection. Additionally, the anchors were not placed in the exact location from stone to stone, although they were all placed perpendicular to the horizontal steel. To locate the anchors, the team used ground penetrating radar (GPR), a nondestructive testing method that provided images of the masonry's subsurface by using radar pulses, along with visual identification using a borescope. Once the anchors were located, electrical continuity tests were performed. All steel components within 2 ft (0.6 m) of the anode zone were tested for continuity and bonded if necessary. Crevello comments that ~144 lug anchors and up to 200 ancillary anchors required bonding to the steel frame. The process for establishing a bond for each lug anchor involved drilling a core in the masonry; welding a connection to the anchor and shim and testing the connec- tion between the anchor and shim; creating A corrosion contractor installs MMO-coated titanium expanded mesh probe anodes in an interior joint of the entablature. Photo courtesy of Gina Crevello, Echem Consultants. Anodes are installed in the lower exterior joint of the repaired entablature. Great care was taken to avoid damaging the limestone masonry. Photo courtesy of Gina Crevello, Echem Consultants. FEATURE ARTICLE 30 NOVEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 11

Articles in this issue

Archives of this issue

view archives of Materials Performance - NOV 2014