Materials Performance

NOV 2017

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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14 NOVEMBER 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 11 Unique Corrosion Mechanisms Behind Leo Frigo Bridge Failure A unique environment consist- ing of f ly ash, clay, and water led to a rare combination of corrosion mechanisms on the piers of the Leo Frigo Memorial Bridge in Green Bay, Wisconsin, according to a structural engineering consultant involved with the repair work. The four-lane bridge into Green Bay was closed on September 25, 2013, after a bridge inspector with the Wisconsin Department of Transportation (WisDOT) (Madison, Wisconsin) found that a 400-ft (121.9-m) section across all four lanes of the bridge was sagging by almost 2 ft (0.61 m). The bridge, which carries Interstate 43 over the Fox River and into Green Bay, was shut down for months by WisDOT for a full investigation and repair process. A li Abu-Yosef, currently a project engineer with structural engineering consultancy Pivot Engineers (Austin, Texas), was one of the engineers brought in to survey the unique problem. "Our team was retained as corrosion consultants at the time," Abu-Yosef explains. "It was one of my f irst projects out of school for my Ph.D. They wanted me to investigate the corrosion mecha- nisms on the bridge that led to the failure. After repairs were completed, we were assigned with the development of a moni- toring program." The bridge is held up by 51 piers, each supported by vertical steel H-piles that extend 100 ft (30.5 m) into the ground. Pier 22 on the bridge had sunk 22 in (559 mm) on one side and 27 in (686 mm) on the other. In its investigation, WisDOT first inspected the underside of the bridge and found no obvious signs of damage. How- ever, subsurface exploration determined that severe corrosion of the steel piles in the foundation that supports Pier 22 was the reason for the vertical displacement, the investigative report noted. 1 As part of the subsurface exploration, test holes were excavated at 20 out of the 51 piers, and laboratory tests were per- formed on soil and water samples to determine foundation conditions. Robotic survey instruments were also installed to monitor for any additional pier displacement. According to WisDOT, the results showed that several factors contributed to a highly unusual environment, which caused severe corrosion of the steel pile foundation supporting Pier 22. A corro- sive environment was created by the pres- ence of a moist, porous, low-resistivity f ly ash f ill that contained high levels of chlo- rides and sulfates. Additionally, a dense clay layer was present below the f ly ash, which led to different oxygen and chemi- cal concentrations within the f ill layers. This sparked a process known as acceler- ated low water corrosion (A LWC). Bacte- ria were also found at many of the piers, suggesting the presence of microbiologi- cally inf luenced corrosion (MIC). The MIC led to localized pitting of steel piling on several of the piers. "The MIC was quite severe," Abu-Yosef says. "On other projects like pipelines, what you'll see is localized pits that are about three inches by three inches [762 by MATERIAL MATTERS

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