United States Department of Transportation
i
Evaluation of Rocky Point Viaduct Concrete Beam : Final Report
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2000-06-01
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[PDF-6.91 MB]
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Bridges and Structures;NTL-HIGHWAY/ROAD TRANSPORTATION-Materials;
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Abstract:This study was intended to determine why it was necessary to replace the Rocky Point Viaduct after a period of service that was much shorter than that of many other reinforced concrete bridges on the Oregon coast; to identify construction practices that may have contributed to its early failure; and to identify evaluation methods that are most effective for characterizing bridge condition. A 14.3 m (47 foot) section of concrete Beam A1 and bridge deck between the north abutment and pier 1 was removed from the seaward side of the Viaduct for evaluation of: (1) concrete properties; (2) reinforcing bar (rebar) corrosion; and (3) chloride migration in the concrete.
The harsh environment at the site was an important factor in the premature failure of the Viaduct. This led to substantial salt penetration of the concrete to the depth of the shear stirrups and square rebar. The severity of chloride penetration of the concrete was such that neither the original concrete cover nor subsequent efforts to repair the structure and prevent further corrosion could mitigate its effects on rebar corrosion. Efforts at preventing further corrosion damage (corrosion resistant coatings on the rebar, coal tar and linseed oil barrier coatings) were ineffective.
The study concludes that bridge construction practices should consider, in addition to quality concrete and adequate cover, the aggressiveness of the site environment, including meteorological conditions and washing and sheltering that affect chloride deposition. Assessment of site environmental conditions would be a useful to bridge design to assure a structure would achieve the desired service life. Such an assessment recognizes that a wide range of microclimates exist on the Oregon coast. Chloride profiles for coastal bridges and a knowledge of corrosion initiation threshold chloride levels provide solid evidence supporting the selection by Oregon DOT of stainless steel rebar and microsilica (high-performance) concrete for use in new bridge construction on the Oregon coast. 99 p.
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