In Minnesota, the combination of traffic and extreme weather can turn small pavement problems into big potholes. To make progress in the seemingly unending task of pothole repair, U of M researchers are designing durable patches and repairs that are quick to apply and less costly for maintenance budgets.
“The goal of pothole repair is to mend the road surface in a way that lasts and is relatively inexpensive,” says Lawrence Zanko, a senior research fellow at the University of Minnesota Duluth’s Natural Resources Research Institute (NRRI). “Maintenance departments are realizing that the traditional method of ‘throw and go’ cold patch is quite ineffective and therefore costly in terms of both materials and labor.”
In a new report, researchers present two improved options for pothole repair that are ideally suited to Minnesota’s cold and wet conditions. The first approach is a fast-setting, taconite-based compound, which was found to be especially well-suited for rigid and relatively deep repairs in concrete pavements. The second approach uses a vehicle-based microwave heating system with taconite materials for in-place pothole and pavement repair; this technology proved very effective for repairing potholes in asphalt pavement at all temperatures, including very cold temperatures.
The research was part of a broader effort by the Minnesota Department of Transportation (MnDOT) to evaluate current practices, materials, and policies for pavement patching and repair. “There are more ways to patch than just sitting in the back of a truck and throwing bituminous mix into holes,” says Sue Lodahl, MnDOT assistant state maintenance engineer. “Some work better with concrete, some with bituminous. These taconite-based mixes can make durable patches.”
Full-depth replacement of potholes is expensive and time-consuming. Careful cleaning and filling with hot-mix asphalt can work, but in winter is impractical or even impossible. The new taconite options could help agencies overcome these obstacles.
“Because the microwave equipment heats the existing pavement to the point that the pavement itself becomes part of the repair, we get an excellent bond,” says Zanko, the study’s principal investigator. “This makes the technology superior to most other methods for repairing potholes in asphalt pavements, especially during the winter. Plus, we also demonstrated that an effective repair compound can be made almost entirely from inexpensive and easily-available recycled materials for a significant cost savings compared to typical repair compounds that rely on specialized asphalt formulations.”
To fully assess these technologies, the research team conducted comparative field-testing and in-place analysis of a variety of repair methods and materials. Many taconite-based repairs lasted three years, Zanko reports, and though some cracked, the repairs remained in place.
“Our findings indicate that these two repair options have the potential to save maintenance departments thousands of dollars in labor costs annually, reduce traffic disruption caused by the frequent repair of repeatedly failing patches, and add efficiency and longevity to repairs,” he says.
The final report includes two fact sheets on the new repair methods that maintenance agencies can use as part of their toolkit of options for repairing potholes and other pavement failures.
In addition, a new licensing agreement was recently finalized with a company interested in NRRI’s patented pothole/pavement repair compound. The agreement was in part influenced by work performed during the project, Zanko says.
In new work funded by the Minnesota Local Road Research Board, researchers will refine the taconite-based repair compound and develop and field-test a low-cost mechanized system that can efficiently mix and place the repair compound in larger quantities while minimizing or eliminating direct contact and hand-mixing by maintenance personnel, Zanko says.