Minnesota road crews may soon have a better way to battle potholes, as U of M researchers work to further refine an innovative, quick pothole repair method for both concrete and asphalt pavements. The new repair method is based on a plentiful Minnesota material—taconite—that can be applied fairly quickly and shows promise as a cost-competitive, long-term solution for potholes.
“A fast, durable pothole repair that can be conducted in cold or wet weather remains an elusive and prized technology,” says Lawrence Zanko, a senior research fellow with the U of M’s Duluth Natural Resources Research Institute. “We have been working to develop a rapid patch using the readily available, iron-containing materials of northern Minnesota taconite mining.”
In the project, funded by the Minnesota Local Road Research Board, Zanko’s team continued to improve taconite repair methods to simplify mixing procedures, avoid the need for expensive and large specialized equipment, and speed up patching activity.
This project builds on a 2016 effort funded by MnDOT that found taconite mixtures and microwave machinery could make potholes repairs in roughly 15 minutes that last for 6 to 12 months. Goals of the recent study included improving the earlier non-microwave taconite pothole patch methods, conducting field testing, and examining inexpensive mixing equipment that would be easy to use in the field.
Taconite pothole repairs were tested on local roads, state roads, parking lots, and an airport taxiway; researchers revisited all repair sites to inspect repair performance periodically. The method to place the taconite patches was also improved during this project. Previous taconite patching mixtures required mixing two packaged dry ingredients by hand with a liquid activator in a 5-gallon bucket; the new mixture is just two ingredients and can be blended in a special 15-gallon mixing barrel known as a “Mega Hippo.”
“A big success with this project was working with three different entities—the Minnesota Department of Transportation, the City of Duluth, and the Duluth Airport Authority—each having its own needs,” Zanko says. “We’re continuing to focus on making the repair compound and mixing method easier to use and work even better.”
Researchers found that the improved taconite repairs set well in both asphalt and concrete and performed well for a year or more of observation. The method seems to be more durable than typical “throw-and-go” and cold-mix options for pothole repair, offering local agencies an asphalt- and cement-free option that uses plentiful local materials and costs less than mastic or hot-mix asphalt repairs.
The mixture was found to set more slowly in cold temperatures than warm, and better in deep repairs than in shallow. Fieldwork identified operating temperatures that allowed taconite patches to be placed in cool to cold (subfreezing) fall conditions—and site repairs were drivable in 30 minutes.
Next, researchers will further refine mixing methods and application to increase the material quantities workable by local crews and speed up repair activities. Researchers aim for repairs that can accept traffic in 10 to 15 minutes or less under moderate to warm temperature conditions. “This highlights the importance of having an efficient mixing and placement system that is a good match for the repair product’s quicker set time,” Zanko says.
“This research looks promising, but it’s early,” says Perry Collins, MnDOT assistant district engineer in MnDOT District 1. “Time will tell how it will perform in comparison to a hot-mix operation or mastic.”