For most road crews, repairing potholes is an essential and highly visible duty. Choosing the best or most cost-effective pothole repair method, however, has remained a complicated puzzle.
“Selecting the appropriate patching method and materials varies depending on several factors, including the size of the pothole and its location on the roadway,” says Manik Barman, an assistant professor with the University of Minnesota Duluth (UMD) Department of Civil Engineering. “Patching methods and materials also face seasonal challenges in Minnesota when asphalt plants shut down for the winter, turning cold-weather repairs into short-term fixes.”
To help solve this puzzle, the Minnesota Department of Transportation (MnDOT) funded research to help road crews choose patching methods that match specific repair conditions. UMD researchers explored patching tools, materials, and methods to identify which ones were most appropriate for specific pothole conditions, road locations, and time of year. They also evaluated the effectiveness of different methods based on durability, road safety, ride quality, and driver satisfaction.
“We wanted to develop a decision tree for choosing the right pothole repair method that could be laminated for use in the field,” says Susan Lodahl, assistant state maintenance engineer with the MnDOT Office of Maintenance.
Researchers began by reviewing existing literature to identify the four repair methods best suited to Minnesota: cold mix, hot recycled asphalt, mastic material, and mill-and-fill with hot-mix asphalt. Next, they identified five sites near Duluth, where they oversaw 20 pothole repairs. Investigators then monitored these repairs for two years to assess the methods and their best applications. Their findings include:
- Cold-mix asphalt patch should only be used for temporary fixes in small to medium potholes. The material is not designed to be structurally sound for depths beyond two inches.
- Virgin hot-mix asphalt during the regular season is the most acceptable option for filling milled areas. This option can be used in any situation—mill-and-fill or established potholes.
- Mastic, although expensive, is the best option for repairing small potholes as well as longitudinal joints.
Using the findings from this study, researchers developed decision trees in both flowchart and flash card form to help road crews choose the most suitable method for each repair. They also compiled best practice guidelines for patching method selection, placement, compaction practices, and moisture control to provide further guidance.
“The decision trees and best practices we developed can be easily combined into a patching guide that, with laminated flash cards, can be distributed to MnDOT road crews throughout the state and will also be invaluable to our local public agencies in Minnesota and beyond,” Barman says.