In the 1960’s and 1970’s, weathering steel was commonly viewed as a “maintenance-free” cost-effective alternative for bridge superstructures, as the costs and environmental impacts associated with the maintenance/replacement of paint coatings would be theoretically eliminated. Weathering steel was first used for bridge applications in 1964, when weathering steel bridges were constructed in Michigan, Iowa and New Jersey. During the late 1970’s, Michigan evaluated many of their weathering steel bridges and found that the protective patina had not formed and the corrosion rates were not reduced. As a result, Michigan instituted a partial moratorium on weathering steel bridges in 1979. It focused on avoiding weathering steel in urban and industrial areas, as well as low-clearance, tunnel-like environments. In 1980, the moratorium was expanded to include all weathering steel bridges. However, by this time Michigan had already constructed approximately 500 bridges using weathering steel. After the Michigan moratorium, many states followed suit by limiting or eliminating weathering steel bridges going forward, often stopping short of banning their use outright. The most common reasons for the limitations were the problems reported by Michigan or other states, and/or similar conditions observed within their own state. By the mid-1980’s, approximately 2,000 weathering steel bridge structures had been constructed in the United States. A decade later, the number had only increased by approximately 300 structures, indicating that many agencies had reservations regarding their use. The perceived problems with the use of weathering steel for bridge structures resulted in the initiation of several research projects during the 1980’s and 1990’s. In the early 1980’s, a task group was formed with the support of the American Iron and Steel Institute (AISI) that included federal highway officials, state bridge engineers, and corrosion specialists. This task group performed a field investigation of approximately 49 bridges in seven states (Michigan, Illinois, Maryland, New York, North Carolina, Wisconsin, and New Jersey) in order to evaluate the performance of weathering steel bridges in different environments. This study found that the performance of most weathering steel bridges was either “good” or “good with moderate corrosion in some areas.” Approximately 12% of the bridges inspected had “heavy” corrosion in some areas and deicing salts were found to be a major contributor to the excessive corrosion.
The objectives of this project are summarized as follows:
Identify weathering steel bridge structures that are most vulnerable to chloride contamination, based on location, exposure, environment, and other factors. These bridges are more likely to exhibit unsatisfactory performance of the weathering steel patina.
Identify locations on an individual weathering steel bridge structure that are 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/or chloride test results.