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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16 NOVEMBER 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 11 MATERIAL MATTERS Continued f rom page 15 Inspecting piles is a very expensive and time-consuming pro- cess, where you have to dig up the soil and expose the piles." Abu-Yosef believes the corrosion can be traced back to defects with the initial coat- ing, which was dam- aged through the pile- driving process and not detected during inspections. "Unfortunately, the coating that was applied at Leo Frigo failed during installa- tion," Abu-Yosef says. "That is a major differ- ence between current construction practices The most severe corrosion was found in a 4-ft (1.2-m) long area located near the water line and between the fly ash and clay layers. Image courtesy of Ali Abu-Yosef, Pivot Engineers. and those utilized during the construc- tion of Leo Frigo. The coating industry has encountered the issues of coating fail- ures in a piling process, so there have been drastic improvements in the design and technolog y of the coatings." He notes the bridge would have had a chance to survive if the coating applied on the pile remained intact and was not damaged during installation. "What hap- pens now, if engineers are designing a bridge and they know that the soil is cor- rosive, they would have two options," Abu-Yosef continues. "Either cover the pile with a corrosion-inhibiting coating that can form a physical barrier, which would isolate the pile from the corrosive soil, or accept that corrosion will happen and conservatively increase the design thickness of the pile. If the structural analysis determines that a certain thick- ness is needed to carry the design loads, the designer would artif icially increase the required thickness. By doing so, the engineer accepts that corrosion will con- tinue to happen, but [the bridge] can still carry the load. Some engineers rely on galvanized coating as means to mitigate loss in piles sections. In extreme cases, if the site is very corrosive, there could also be soil replacement options." To return the bridge to service, the engineering team grouped the 51 bridge piers into three different tiers based on the investigation's f indings. Tier 1 piers needed immediate repairs. On piers in Tier 2, signif icantly lower levels of pile corrosion damage were observed, and soils showed characteristics that were potentially corrosive but much less severe than the soil attributes for Tier 1 piers. As such, Tier 2 piers did not represent an immediate safety concern, but further monitoring was deemed necessary to determine the capability for longer-term corrosion. Meanwhile, Tier 3 piers were considered unlikely to experience severe pile corrosion. Visual inspections of exposed piles indicated ty pical condi- tions and no need for further investigation. In all, f ive piers—all near failed Pier 22 and the unique soil combination of f ly ash and clay—were assigned to Tier 1 for immediate repair; 17 were categorized as

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