Critical Criteria for Aluminum Culvert Durability in Wisconsin

Current Wisconsin Department of Transportation (WisDOT) policy severely limits the use of aluminum drainage structures (pipe and box culverts) based on the observation of corrosion from deicing salts that led to the failure of an aluminum culvert in Wisconsin in 1993. The research goals were to establish best practices for aluminum culvert use and formulate recommendations for updated aluminum culvert policy in Wisconsin. The research included a literature review of aluminum culvert material specification and durability, of expected environmental conditions in Wisconsin, of policies and specifications from U.S. federal agencies, WisDOT, and five other state departments of transportation, published research, and manufacturer literature; development and administration of an aluminum culvert stakeholder survey; field inspection and site environmental characterization of three aluminum culverts in Wisconsin; a review of aluminum culvert inventory and inspection data from WisDOT and FHWA; and identification of best practices for aluminum culvert use in Wisconsin with recommended updates to WisDOT policy. Based on natural environmental conditions in Wisconsin, aluminum culverts should provide 50 to 75 years or more of service life if installed in sites that meet generally accepted abrasion, pH, and resistivity limits. Infiltration of chloride-based deicing chemicals through soil fill and contact with aluminum leads to pitting corrosion that may lead to premature culvert failure. Best practices to prevent this mechanism include installing an impermeable isolation membrane within the backfill, testing and limiting the chloride content of the embedment backfill, and using free-draining backfill below the membrane and as embedment around the buried structure.