Rubber Modified Asphalt Proves Good for Roads and the Environment

By Robin Hartman

Pavement Restorations, Inc. applies a layer of RMA chip seal to Helm Schoolhouse Road in Marion County. Gravel is fed into the back of the orange gravel spreader, moved to the front where it is applied on top of the sprayed-on coating of RMA prior to being driven on. The driver of the dump truck must steer the truck in reverse as it is pulled by the gravel spreader backwards.
Photo by Byron Bland, Recycling and Local Assistance Branch.

Nearly 300 million waste tires are generated each year in the U.S.; four million in Kentucky alone.

For years, economically viable options for tire disposal remained a challenge for producers and consumers. Scrap tires take hundreds of years to decompose and consume precious space in landfills. These tires collect water and provide an ideal breeding ground for mosquitos, creating a health issue.

Luckily, nearly 80 percent of tires produced in the U.S. today are recycled. The majority are mixed with coal  or other fuels and burned at very high temperatures to produce energy. Roughly 26 percent – the second highest percentage – are ground into fine particles and used as an additive in things like rubber modified asphalt (RMA), according to Popular Mechanics.

Since the 1960s, RMA has grown in popularity because of  the product’s durability and noise reduction. But the process of adding ground tires to asphalt isn’t as simple as one might think.

The reinforcing steel wires and fiber in tires must be separated and the rubber ground into very fine, clean particles. The right balance and timing of adding the powder-like substance to the asphalt can make a significant difference in the quality of the product.

Once fiber and metal are removed, waste tires are ground for future uses, such as rubber mulch, rubber modified asphalt, rubber walking trails and playgrounds, etc. At Liberty Tire, one of the primary operators, and crumb rubber producers in the state.
Photo by John Brown, Recycling and Local Assistance Branch.

Rubber can be used as part of an aggregate or filler, wet or dry, that’s then shipped to the asphalt plant, or added directly to the liquid asphalt at the plant prior to delivery at the paving site. The process can be time-consuming and adds to the cost of the asphalt.

Even so, Kentucky’s Division of Waste Management (DWM) sees a growth potential for RMA.

Since 2016, the agency has been helping local governments fund road resurfacing projects using RMA.

Grants are available through Kentucky’s Waste Tire Trust Fund, financed by a $2 fee on each new tire purchased. The program has been a testing ground, a type of partnership with governments willing to utilize RMA on a 1-2 mile portion of roadway and conventional asphalt on a road of similar length and condition. An independent engineering company then performs asphalt testing on both and DWM monitors the two sections for a five-year period, evaluating durability and performance.

Green County has had success using the product.

“I am very impressed with the RMA program thus far,” said Green County Judge-Executive John Frank. “We have applied RMA on two roads here in Green County and applied the rubber-modified chip/seal to one road. Both products are holding up very well and we are extremely pleased with both.”

The RMA roads seem to be quieter and are not fading as conventional asphalt does, Frank said.

“The public seems to really like both products as well. We do plan to apply (more) of the RMA in the future. In my opinion, this program is an excellent use of recycled tires and definitely needs to continue if at all possible.”

Byron Bland, an environmental scientist with the division, said the results of the initial evaluation period are promising across the state.

“We’ve learned a lot,” Bland said. “We initially only required one layer of chip seal and found we needed to require more than that. We’ve experience flooding, unexpected truck traffic due to newly paved roads and extreme weather conditions that impacted the condition of the road.”

Overall, Bland said, they’ve found significant benefits to using RMA.

A demonstration by a vendor for the Dry Process of the RMA.

Research and empirical studies demonstrate that the longevity of RMA is superior to traditional asphalt and it provides a quieter, smoother ride. Improved technology and confirmation that the product really does meet expectations, Bland said, could contribute to continued demand.

Add to that the obvious benefit of recycling thousands of waste tires each year and the process is a win-win.

The Division of Waste Management has awarded 23 grants totaling more than $1.7 million since 2016. Although the pandemic decreased the number of applicants last year, 20 applications were received for 2021 projects, nearly all of which are from new grant applicants.

The Lexington-Fayette Urban County Government utilized the grant in 2019 to resurface Southland Drive from Nicholasville Road to the railroad overpass using RMA.

“We were excited to try RMA for many reasons,” said Lexington-Fayette Urban County Government’s Director of Streets and Roads Robert Allen, “but the sustainability of using a waste product along with anecdotal speculation about less noise pollution and reduced rock salt needed during the winter really encouraged us to try something that has been available but until now, not in use in Lexington.”

The Division of Waste Management takes applications in the spring. Potential project sites are visited and scored based on geographic location, visibility, existing road conditions and whether the applicant has participated in the program before.

“We want to try to spread the funds across the state and make sure it’s a route that will benefit a significant number of motorists,” Bryon said. “And there can’t be any major changes to the roadway for five years,” to allow for the engineering study.

Applicants can either choose a two-mile project using chip seal (a treatment that combines one or more layers of asphalt with one or more layers of fine aggregate), or a one-mile project using asphalt overlay (a new layer of asphalt applied over an existing asphalt surface).

Each year, approximately 3,000 tires are recycled through the program.

The significance of the RMA program isn’t in the number of tires used or the number of miles paved, says Recycling and Local Assistance Branch Manager Gary Logsdon.

“Right now, the benefit is that we’re helping provide another market for Kentucky’s waste tire processing facilities, which will support the future of RMA.”

The agency is looking at alternative program models that may encourage increased use of RMA, Logsdon said. If the demand increases, the cost would decrease for everyone involved and provide a durable, recycled product.

The division works with counties to conduct waste tire collection events every four years, provides $4,000 per year for independent county cleanups and administers a tire-derived products program where recycled tires are used for poured-in-place surfacing, park benches and other products.

Combined, the programs provide $2-3 million each year toward waste tire collection and recycling and have contributed to the removal of more than 22 million tires.

“Nationally, Kentucky is ahead of the game,” Logsdon said. “We have a great partnership with the Transportation Cabinet, and coupled with our other tire recycling and removal programs, we’ve seen a significant decrease in the number of waste tires across the state.”

For more information on Kentucky’s waste tire program, visit here.

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