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Bridge Collapse - Many Hurt

Bridge Collapses - Many Hurt

Epoxy-Coated Rebars not Effective in Prestressed Concrete

In May of this year the future of a pedestrian bridge was reported in ENR. It occurred at the Lowe's Motor Speedway in Charlotte, NC. Over 100 fans were injured, some critically. Forensic engineers investigating the accident found that the steel strands at the mid-point of one prestressed concrete double tee had rusted completely through, which caused it to snap under approximately one-sixth of its design load.

Epoxy-coated strands cannot be used in prestressed concrete. The use of a corrosion inhibitor would have prevented this accident. For safety, corrosion inhibitors should be used in all prestressed concrete that will be exposed to the elements.

When the Allegan Street Parking Ramp and Plaza in Lansing MI had to be restored, a corrosion inhibitor was used with high quality concrete. The designers felt that using epoxy-coated reinforcing steel in a non-prestressed condition would likely result in significantly wider slab cracking. This was reported in the Concrete Repair Bulletin, March/April, 2000.

In February 2000, the results of field tests on bridge decks in Virginia were reported in Concrete International. In the 1970s short term laboratory tests showed that epoxy-coated rebars could prevent corrosion of steel in concrete. However, in 1988 through 1993 serious corrosion problems were found with five major bridge structures in Florida after a short service life (5 to 7 years for the Long Key Bridge). Because of these findings, bridges and piers were studied in Virginia. It was found that epoxy coatings loose their bond to steel in concrete bridge decks in less than 15 years and in less than 8 years in concrete piles. It is highly probable that the debonding takes place before the salt reaches the rebars. If the epoxy to steel bond is significantly reduced or the epoxy is not bonded to the steel, the epoxy-coated rebar will provide the least, or possibly no additional, corrosion protection service life extension.

The authors stated that past and present epoxy-coated rebar prescription-based specifications do not address the condition of the reduction in epoxy bond to steel in moist concrete environments nor the corrosion protection efficiency of epoxy-coated rebars with debonded coatings.

Hasan and Ramirez studied the effects of static and repeated loadings on concrete bridge decks and slabs reinforced with epoxy-coated bars. Their work was reported in the Transportation Research Circular, No. 403, March 1993 on page 46. Their findings indicate the average concrete crack width is larger in specimens with epoxy-coated reinforcement than in companion specimens with uncoated reinforcement.

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