Michigan wants more roads paved using recycled tires.
Called “rubber-modified asphalt,” the state has used a mixture of ground rubber and asphalt to pave roads in 32 communities across the state. But the practice is not widespread, in part because the technology behind it has only recently improved. The time is ripe to expand its use, according to the Department of Environment, Great Lakes, and Energy.
Kirsten Clemens, who coordinates the department’s scrap tire program, said Michigan’s scrap tires are a valuable resource.
“Michigan itself generates one scrap tire a year per resident of the state,” she said. “Those tires are here.”
The scrap tire program began in 1990 amid concerns about large piles of tires in landfills. Scrap tire stacks can leach toxins into water and house mosquitoes carrying disease.
That problem has largely been remediated, according to a 2020 market report by the department.
Now, the program wants to pivot towards reusing scrap tires, not just managing them. A big part of that pivot is rubber-modified asphalt.
Using recycled rubber to bind asphalt mixtures isn’t new. The practice has been around since the 1960s and Michigan began testing it on roads in 1992. But early attempts ran into problems, such as early cracking, that stalled wider implementation.
Today, it’s a lot more feasible to mix recycled rubber with asphalt. It can be pulverized into a fine power “about the consistency of powdered sugar,” Clemens said.
Since 1992, Michigan has paved 300 lane miles of road with rubber-modified asphalt. Almost a quarter of those lane miles are being paved this year.
That’s a small fraction of Michigan’s more than 250,000 lane miles. The scrap tire program provides grants to agencies in charge of road paving at the city and county levels, but funding is scarce, Clemens said.
The program’s funds come from a small fee charged when a resident transfers their vehicle title. That money goes to market development grants, which focus on rubber-modified asphalt projects.
In 2023, the program awarded $2 million to seven projects in the state. Most of those projects were for rubber-modified paving, according to the department’s 2023 funding report.
Those grants incentivize municipalities to use a paving method that many state and local bodies still consider experimental, Clemens said.
“What we are seeing is that several of the grantees that we have funded in the past are now implementing this material on their own, without using grant funding,” she said.
The state wants to expand these opportunities to more Michigan communities, but some obstacles still remain.
Previous studies have shown that rubber-modified asphalt reduces road noise. It also lasts longer than conventional asphalt, even in colder climates like Michigan. It might produce fewer greenhouse gases, too.
However, those studies are outdated. New, comprehensive assessments of the technology are needed to bring more stakeholders on board, according to a state-of-knowledge report by the U.S. Tire Manufacturers Association.
Clemens is working with a committee of tire manufacturers and other state scrap tire programs to create an environmental impact assessment of rubber-modified asphalt. The study will investigate whether rubber-modified asphalt is “a sustainable and environmentally friendly” alternative to conventional asphalt, Clemens said.
The committee has applied for funding from the U.S. Environmental Protection Agency and is waiting to hear back. Clemens and the state are hopeful the study will encourage more municipalities to adopt the practice.
“We expect that this material is going to grow, which is so exciting,” she said.
