To allow water to flow beneath roads, engineers use culverts. Steel culverts, however, corrode over time, and their service lives depend on the properties of the soil that surrounds them.
To help engineers choose the appropriate steel pipe materials for culverts in different parts of the state, U of M researchers collected soil data and developed a series of steel pipe service-life maps for Minnesota. The project, funded by the Minnesota Local Road Research Board and the Minnesota Department of Transportation (MnDOT), will help agencies save on costs while developing longer-lasting infrastructure.
Two important soil properties affect steel culvert longevity: pH (a measure of the soil’s acidity and corrosiveness) and resistivity (a measure of how much the soil resists the flow of electricity, which is usually related to the cohesiveness of the soil but also to moisture and temperature).
Steel pipe differs in gage, or wall thickness, and in the coatings used to reduce corrosion (aluminum, zinc, or polymeric). Aluminum coating provides superior corrosion protection compared to the zinc coating of galvanized pipes, says Jeff Marr, associate director for engineering and facilities at the St. Anthony Falls Laboratory and the study’s principal investigator. It is also more expensive—but may still be the most cost-effective choice.
Marr’s team collected more than 560 soil resistivity and pH samples statewide during the summer of 2014. Roughly 50 to 90 sample sites were selected per MnDOT district, with samples taken from the embankments of state trunk and county highways. The researchers then used the data, along with other observations, to calculate the service-life estimates for different types of steel pipe.
“This project was eye-opening, showing that you can double the service lives of steel culverts just by changing the coating of the pipe at little extra expense,” says Andrea Hendrickson, state hydraulic engineer with MnDOT’s Office of Bridges and Structures.
MnDOT will use the results of this project to update its drainage manual and is sharing steel pipe service-life maps with MnDOT and county maintenance personnel.
To learn more, read the full article in the November issue of Catalyst.