United States Department of Transportation
i
Assessment of weathering steel bridge performance in Iowa and development of inspection and maintenance techniques.
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2013-02-01
[PDF-10.25 MB]
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Bridges and Structures;NTL-HIGHWAY/ROAD TRANSPORTATION-Construction and Maintenance;
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Abstract:Weathering steel is commonly used as a cost-effective alternative for bridge superstructures, as the costs and environmental
impacts associated with the maintenance/replacement of paint coatings are theoretically eliminated. The performance of
weathering steel depends on the proper formation of a surface patina, which consists of a dense layer of corrosion product used to
protect the steel from further atmospheric corrosion. The development of the weathering steel patina may be hindered by
environmental factors such as humid environments, wetting/drying cycles, sheltering, exposure to de-icing chlorides, and design
details that permit water to pond on steel surfaces.
Weathering steel bridges constructed over or adjacent to other roadways could be subjected to sufficient salt spray that would
impede the development of an adequate patina. Addressing areas of corrosion on a weathering steel bridge superstructure where a
protective patina has not formed is often costly and negates the anticipated cost savings for this type of steel superstructure. Early
detection of weathering steel corrosion is important to extending the service life of the bridge structure; however, written
inspection procedures are not available for inspectors to evaluate the performance or quality of the patina. This project focused on
the evaluation of weathering steel bridge structures, including possible methods to assess the quality of the weathering steel patina
and to properly maintain the quality of the patina. The objectives of this project are summarized as follows:
Identify weathering steel bridge structures that would be most vulnerable to chloride contamination, based on location,
exposure, environment, and other factors.
Identify locations on an individual weathering steel bridge structure that would be most susceptible to chloride contamination,
such as below joints, splash/spray zones, and areas of ponding water or debris.
Identify possible testing methods and/or inspection techniques for inspectors to evaluate the quality of the weathering steel
patina at locations discussed above.
Identify possible methods to measure and evaluate the level of chloride contamination at the locations discussed above.
Evaluate the effectiveness of water washing on removing chlorides from the weathering steel patina.
Develop a general prioritization for the washing of bridge structures based on the structure’s location, environment,
inspection observations, patina evaluation findings, and chloride test results.
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