The extra grip on roadways provided by high-friction surface treatments (HFST) improves safety by helping drivers maintain better control of their vehicles, preventing skids and reducing braking distances at high-risk areas such as sharp curves and busy intersections. However, the industry-standard road treatment, calcined bauxite, is typically imported and expensive—and requires an energy-intensive production process. One possible homegrown alternative is taconite rock from Minnesota’s Mesabi Iron Range—one of the hardest natural materials available for use as a roadway friction aggregate.
In a new project sponsored by the Minnesota Department of Transportation and the Local Road Research Board (LRRB), researchers from the UMN’s Department of Civil, Environmental and Geo- Engineering (CEGE) and the University of Minnesota Duluth’s Civil & Environmental Engineering Department and Natural Resources Research Institute (NRRI) set out to determine whether this local mining byproduct could perform as well as the expensive import. The study was conceived by Larry Zanko, former senior research program manager with the NRRI, and Victor Lund, traffic engineer with St. Louis County’s public works department. CEGE professor and CTS scholar Mihai Marasteanu took over as the study’s lead after Zanko’s retirement.
“We wanted to test the power of this local HFST alternative in real-world conditions and see how [the two treatments] would compare side-by-side on Minnesota roads with daily traffic, climate variations, and maintenance operations like snowplowing,” says Marasteanu.
The team established pavement test sections on a low-volume, two-lane road near Duluth, Minnesota, comparing calcined bauxite and taconite against a traditional chipseal control. For four years, the team monitored the sections to see how the materials held up under the stress of Minnesota winters and regular traffic.
The results showed that taconite held its own, staying within 6 percent of bauxite’s friction performance during the study. Additionally, the taconite sections provided a massive safety jump—averaging 40 to 50 percent higher friction than standard pavement—and showed no signs of losing grip after years of snowplowing and daily traffic.
“Results suggest taconite could offer comparable safety benefits while reducing environmental impacts and providing potential cost reductions,” says Lund, while noting that further research is needed for more performance comparisons with calcined bauxite.
The environmental benefits of taconite are as significant as its safety performance. While bauxite must be heated to 3,000 degrees Fahrenheit and shipped across oceans, taconite aggregate is produced through simple drying and screening here in Minnesota. A life-cycle assessment revealed that taconite has a much lower impact on ecosystems and natural resources compared to the synthetic alternative.
“The most significant benefit may be the productive use of a Minnesota mining byproduct as a source of high-quality friction aggregate that would have otherwise been disposed of,” Marasteanu says. Although cost was not analyzed as part of the study, taconite’s availability in Minnesota suggests it would be less expensive than manufactured and imported calcined bauxite, he adds.
Based on the success of this initial study, researchers are looking at next steps for the local material. They recommend referring to taconite as an “enhanced friction treatment” (EFT), as the HFST classification is technically tied to the chemical specifications of bauxite. And future research should focus on taconite installations in higher-stress environments, including on high-volume curves, steep vertical grades, and routes with high truck volumes, to see if this Iron Range grit can become the new standard for pavement safety on Minnesota’s roads.
—Megan Tsai, contributing writer
