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Environmental Monitoring to Support Revised Steel Pile Corrosion Protection Specifications

The North Carolina Department of Transportation (NCDOT) has observed early failure of the protective coatings of steel piles supporting bridges throughout the state, with some bridges exhibiting signs of corrosion within 20 years of construction, much sooner than anticipated. This has been observed primarily at stream crossings, where the steel piles act as substructure elements which transfer load from the superstructure to the soil. The most severe instances of corrosion have been observed at locations which encounter wet-dry cycles. The early failure of protective coatings has been observed in bridges located NCDOT Divisions 2-9, which suggests that specific environmental factors which are prevalent in these regions may be responsible. The overall research objectives of this project are to determine the cause of the early corrosion observed in the steel pile foundations, to suggest policies which can help mitigate this issue in the future. To accomplish these objectives, the following research tasks will be conducted: (1) Perform long-term comprehensive water quality and environmental monitoring at a selected number of bridges sites throughout the state. (2) Review the effectiveness of commonly used coatings for corrosion protection, identify specifications for steel pile protection in corrosive environments and determine repair options for deteriorated piles through a detailed literature review. (3) Partner with NCDOT to develop new policies related to protective coatings for steel piles and/or classifying corrosive environments for steel piles. The research products which will results from these tasks include: (1) Summary of the field monitoring campaign, including data which impacts the corrosive environment. This includes, but is not limited to, measured values of water velocity, size and velocity of floating debris, open circuit corrosion potential, pH, concentrations of dissolved salts, chloride and sulfide concentration, and dissolved oxygen at each of the monitored locations. (2) Recommendations for classifying sites as “corrosive environments” consistent with the results of this research and observed instances of corrosion. (3) Recommendations for corrosion protection of steel piles in new bridges based on the performance of piles observed in the field, considering their corrosive environment.