Ground rubber applications growing

For years, tire derived rubber has been used to manufacture numerous recycled rubber products. By mechanically shredding tires and then magnetically separating the steel from bead and tread wires, high quality rubber granules are liberated for further use.

According to John Sheerin, director of U.S. Tire Manufacturers Association’s (USTMA) End-of-Life Tire Programs, ground rubber applications have been growing recently, including mats of all types, loose fill and poured in place playground surfaces, landscaping mulch and infrastructure applications like sign bases, car stops, and weights.

The USTMA Scrap Tire Management Report for 2021 illustrates that ground rubber uses have increased. More specifically, the report shows that the ground rubber market increased by 29 percent since 2019, making it the largest scrap tire market, consuming roughly 28 percent of all scrap tires in the following areas:

• Molded and extruded products – Products like rubber mats and flooring increased by 25 percent and consumed 485 thousand tons.
• Rubber mulch – Increased by 54 percent and consumed 391 thousand tons. Home and facility improvement activities during Covid shutdowns are credited in part for this.
• Rubber modified asphalt –Consumed slightly less than the 2019 report showed with 141 thousand tons of scrap tires. Covid interruptions to construction funding and market development impeded the growth of this promising market.
• Fine ground rubber – A material used in new tires, coating, sealants and exports consumed another 79 thousand tons of scrap tires.“Unfortunately, scrap tire markets as a whole have not grown quickly enough to absorb the increased generation,” Sheerin said. “Even though the markets for scrap tires have shifted and changed, further development of these markets is needed to keep pace with annual generation.”

Since scrap tire management is primarily the responsibility of state governments, Sheerin said it is important for states to have robust scrap tire management programs that generate revenue streams to fund research that develops and assesses existing and emerging markets and addresses scrap tire abatement. “USTMA continues to work closely with states to encourage the adoption of effective elements of state scrap tire programs identified in the our 2021 report document,” he said.

Bjornulf Ostvik, chief executive officer of Ecogensus, said the recycled rubber market is dominated by the recycled tires market (tires are already a separated waste stream.) The general consensus is that the generation of scrap tires (some 300 million tires per year in the U.S.) is outpacing the demand for recycled rubber.

“This, of course, has reverberating effects on other recovered rubber waste,” Ostvik said. “Historically, waste-to-energy applications represented a significant pathway for scrap tires but demand has been declining. There is increased focus now on asphalt and general roadway applications (e.g., as an aggregate), as well as other conventional applications such as playgrounds, running tracks, landscapes, and small projects such as decks, ramps and patios.”

An ongoing evolution

Although rubber recycling has been readily embraced by various industries over the years, rubber recycling has become more consistent and high-quality materials are now expected.

As Sheerin explained, mechanical shredding is the industry standard, but cryogenic grinding is also used to produce finely ground material.

“We have seen a shift towards ground rubber applications and away from what was historically the largest market – tire derived fuel,” Sheerin said. “This is because solid fuel combustion has been declining, while new and better ground rubber markets have grown. The mulch market has grown significantly, and the rubber modified asphalt market is poised for growth as well.”

With the passing of the Bipartisan Infrastructure Law (BIL), USTMA has been focused on expanding opportunities to grow scrap tire markets that offer sustainable infrastructure solutions. USTMA continues to support the use of scrap tires in rubber modified asphalt (RMA) and tire derived aggregate in civil engineering projects. In USTMA’s recent 2023 legislative priorities letter, the USTMA explained that RMA increases pavement service life and reduces road maintenance activities, leading to significant cost savings compared to traditional asphalt. It reduces CO2 emissions by 32 percent, lowering energy consumption over the lifetime of pavement as compared to traditional asphalt. RMA also provides performance and safety benefits by increasing skid resistance, reducing road noise and reducing road spray in wet conditions.

Given RMA’s proven economic, environmental and performance benefits, USTMA urged Congress to:

• IdentifyRMAasapreferredpavement material for federal projects;

• Support funding for research to further study RMA use benefits, including supplementing preliminary findings of reductions in environmental impact when using RMA.

The USTMA letter also addressed the use of Tire Derived Aggregate (TDA), large shreds of scrap tires that can be used as cost-effective infill material for roadside embankments, retaining walls and stormwater infiltration galleries.

As the USTMA pointed out, TDA reduces costs compared to traditional mined minerals like gravel, since the lightweight recycled material costs less to transport. “It provides improved drainage in stormwater infiltration galleries due to its larger void space compared to gravel, potentially capturing greater water volume with a smaller gallery footprint,” the legislative letter stated. “Studies show TDA use in infiltration galleries can reduce metals loading in stormwater. TDA used under railroad tracks also has proven effective and cost-efficient in mitigating ground vibrations from rail lines, a significant benefit to neighboring communities. For these compelling benefits, USTMA urges Congress to fund research and demonstration projects using TDA in federal, state and local construction projects.”