One of the first studies aimed at the evaluation of weathering steel bridges was conducted by the American Iron and Steel Institute (AISI, 1982). At that time, the Michigan Department of Transportation had placed a moratorium on the use of all non-painted weathering steel. This action was due to the observation that many bridges in the state were developing excessive corrosion. This was especially true of: (1) bridges in urban, industrial locations where it was thought that the heavy application of deicing salts in combination with industrial and automotive pollution were creating an extremely corrosive environment and, (2) overpass bridges with less than 20 ft. under-clearance and retaining walls near the shoulders, often referred to as a depressed roadway. For bridges in depressed roadways, the salt-spray caused by traffic underneath the bridge collects on the girders, resulting in a regular application of a highly corrosive solution directly to the bridge superstructure. As a result of the Michigan moratorium, AISI organized a formal evaluation of weathering steel bridges including the inspection of 49 bridges in seven states (Illinois, Maryland, Michigan, New York, North Carolina, Wisconsin, and New Jersey) to determine if the problems observed in Michigan were indicative of a general problem or were unique to that state/area (AISI 1982). The bridges were selected for inspection based on two criteria: site characteristics and level of salt use. The site characteristic of a particular bridge was classified as being in one of four categories: (1) urban or industrial grade separation, (2) rural grade separation, (3) stream or railroad crossing, or (4) depressed roadway condition. Bridges were also categorized as having heavy, light, or no salt use. Bridges were then selected with the goal of having several bridges in each combination of categories. Therefore, when these problems are controlled or eliminated, weathering steel bridges are an attractive alternative that can provide substantial cost savings to bridge owners. While the initial material cost of weathering steel is more expensive than that of traditional (non-weathering) steels, considering the cost of painting causes weathering steel to be a cost-effective alternative. In addition to the cost savings offered, implementation of weathering steel provides environmental benefits such as preventing the release of volatile organic compounds into the atmosphere during maintenance painting as well as eliminating concerns with containment and disposal of removed paint. This paper will provide an overview of a comprehensive assessment of the performance of the weathering steel bridge inventory in West Virginia. It will present findings from an evaluation that was used to categorize locations and site conditions that may lead to less than favourable performance of weathering steel bridges, if applicable. It will also present recommendations regarding detailing procedures to be incorporated with weathering steel bridges.
A588 weathering steel is formed by alloying additional elements (2% or less of various combinations of copper, phosphorus, chromium, silicon, and/or nickel) with traditional steels (A36 or A572), which cause the corrosion resistance of the steel to be significantly increased. The behaviour of weathering steel exposed to appropriate environments is fundamentally different from that of traditional steel in that in contrast to the formation of iron oxide (rust) that occurs when traditional steels are exposed to atmospheric conditions, weathering steel forms a protective oxide coating that reduces the rate of corrosion of the steel. However, this protective oxide coating will form only if the weathering steel is not subjected to extended period of moisture. Additionally, proper detailing of the structure is critical to maintain the integrity of the protective coating. Additionally, environmental factors may adversely affect the ability of weathering steel to develop a protective oxide coating, particularly the presence of excessive levels of chlorides and sulfur dioxides. Of these, chlorides are typically more of concern in the United States because sulfur dioxide levels from pollution are generally not high 361-2 enough to have a detrimental effect on weathering steel. Chlorides are of great concern however; chloride contamination may result from runoff of deicing salts applied to roadways or proximity of the structure to marine environments having high atmospheric chloride levels. While concerns associated with the impacts of a marine environment are not an issue with this study, in some cases the WVDOH makes heavy use of deicing salts in winter roadway maintenance operations.