WASHINGTON—Tires continue to be one of the most recycled items in the U.S., but an old refrain is growing older: The gap between scrap tire generation and scrap tire recycling is increasing.
As such, the advancement of opportunities for scrap tire technologies—specifically by growing scrap tire end markets—should be at the forefront for the federal government and consumers alike, according to John Sheerin, director of end-of-life tire programs for the U.S. Tire Manufacturers Association.
"We are certainly aiming for 100-percent of all scrap tires to be recycled," Sheerin said. "The market is changing. ... It is transforming and moving into the ground rubber area, which requires more processing for production of a highly specified product.
"What is nice is there already are ASTM standards for ground rubber. And that should lead to growth in these markets."
The amount of scrap tires generated in 2021 topped more than 5 million tons for the first time ever, according to the 2021 USTMA Scrap Tire Management Report, released late in 2022.
About 71 percent, or 195 million of the 274 million scrap tires generated, ultimately became ground rubber, tire-derived fuel or raw material for civil engineering projects (among numerous other end markets) in 2021.
This is down from 76 percent in 2019, and a high point of 96 percent in 2013.
"We see scrap tire recycling as a key part of our role in supporting a sustainable circular economy and we have been steadfast in our efforts to promote market expansion," said Anne Forristall Luke, president and CEO of the USTMA. "USTMA will continue its commitment to expand markets and help advance opportunities for scrap tire technologies through work with our value chain partners, federal and state policy makers, academia and NGOs."
For the first time since the USTMA Scrap Tire Management Report was issued in 2013, ground rubber led the disposition for scrap tires at about 28 percent, with slightly more volume (about 1.41 million tons) than the amount of tires that went toward tire-derived fuel (about 1.39 million tons, also representing about 28 percent of the end-use markets for scrap tires).
"We saw real growth between 2019 and 2021 in the mulch space," Sheerin said. "The market is transforming and becoming more sophisticated ... and we see this as a very good thing for the industry."
And TDF appears to be trending the other way, Sheerin said, with about half of the TDF from scrap tires going to cement kilns, about 40 percent to pulp and paper manufacturing and about 13 percent to electric utilities.
TDF dropped 15 percent since the previous report was issued in 2019.
"Market development is key to scrap tire recycling," he said. "It is a demand-and-pull thing. And historically, TDF for coal-fired plants has been strong, but they are decreasing.
"With the utility sector shrinking, there has been a decline in TDF."
Cement kilns were responsible for using the most scrap tires for TDF at 682,000 tons in 2021, a decrease of more than 16 percent against 2019 due to a drop in demand for cement.
Pulp and paper mills logged the second-highest amount of scrap tires for TDF at 524,000 tons, an increase of 9 percent over 2019.
Electric and utility boilers dropped more than 50 percent since 2019 in their use of scrap tires for TDF, consuming about 187,000 tons in 2021. As emission limits continue to tighten and coal-fired plants are shut down, the market for TDF will continue to decrease, according to the USTMA.
This puts rubber modified asphalt (RMA), which uses ground rubber, squarely in the spotlight, a material that can be "stripped up and used again."
"It can circle back through the economy over and over again," Sheerin said.
But even as the ground rubber market grows, due in part to the Bipartisan Infrastructure Act passed earlier last year, the 15th biennial scrap tire report shows a 13-percent hike in scrap tire generation against a 6-percent increase in end markets.
And still there is optimism from the USTMA.
Only batteries and cardboard are recycled at a higher rate than scrap tires, which continue to find end uses at a higher rate than glass, plastic, aluminum, metal and paper, according to the USTMA.
"We see real opportunities for growth in the RMA sector, in part because of the provisions of the infrastructure and jobs act and in part because of the inflation reduction act—both of these pieces of legislation provide plenty of opportunities to work with the federal government to update specifications and open the markets to this material," Sheerin said.
As well, tire-derived aggregate (TDA) has gained considerable interest for use in civil engineering projects.
TDA, which is more coarsely cut from scrap tires than ground rubber (for RMA), is used as a cost-effective fill material in stormwater infiltration galleries, where it serves to clean stormwater.
"TDA can be used as a lightweight fill for retention or drainage systems," Sheerin said. "And (it can be used) as a filtration media in galleries, which can improve stormwater quality as it trickles through."
TDA has a larger void space, providing greater water volume capture when compared to gravel. This allows for flexibility in design of stormwater infiltration galleries without compromising stormwater capture capacity where space is limited, according to the USTMA.
TDA also can be used as weights along highway construction sites and as truck tire sidewalls, Sheerin said.
While ground rubber and TDF represented the majority of scrap tire dispositions from 2021 at about 56 percent combined, civil engineering accounted for about 6 percent, or about 276,000 tons of scrap tires, in 2021.
Roads, highways and airfield surfaces remain some of the most daunting and massive infrastructure undertakings.
As such, the USTMA is hitching its scrap tire end-use wagon to RMA, while keeping all options for end-use markets open, Sheerin said.
The overarching research completed in the last three years by the USTMA and other academic institutions shows that RMA extends pavement life, enhances ride quality and mitigates noise from tires and traffic, according to the USTMA in a "State of Knowledge of RMA" report released in May 2021.
RMA has not been universally adopted since then, according to Sheerin, though it is used in California, Kentucky and New York "to rebuild America's roadways with a resilient pavement solution."
"That is the No. 1 area we have focused on is RMA," Sheerin said. "RMA is substantially more processed (than TDA) and well-defined applications for RMA center around ground rubber that is the size of sugar grains. The fabric is removed and the steel is removed."
As RMA uses ground rubber, and the ground rubber market has increased by 29 percent since 2019, RMA appears to be the scrap tire end-use market with the most potential.
Molded and extruded products (also using ground rubber) increased by 25 percent and ate up 485,000 tons of scrap tires, according to the 2021 USTMA report. This includes an uptick in products like rubber mats and flooring.
Rubber mulch consumed 391,000 tons of end-of-life tires, an end-market increase of 54 percent over 2019. The USTMA attributes this rise to home renovations and facility improvements during COVID shutdowns.
Fine ground rubber, used in new tires, coating, sealants and other exports, took away another 79,000 tons of scrap tires for a more sustainable use.
And RMA consumed about 141,000 tons of scrap tires in 2021.
Sheerin noted that knowledge gaps remain with RMA.
Namely, most state highway agencies and contractors have "limited-to-no" experience with modern RMA products. As well, "almost none of the modern, advanced asphalt binder and mixture performance tests ... were developed with RMA in mind."
"I think the legislation should stimulate the use of RMA, at least where we would like to see more substantial use, where people and industries will become familiar and understand its cost and environmental benefits," Sheerin said. "Pavement engineers—who are typically very conservative—have given RMA a 40-year life cycle in some cases.
"To think, perpetual pavement and low maintenance ... and I think the biggest boon will be from these bills."
Sheerin added that TDA certainly "can fit in this space as well."
To fill in some of the knowledge gaps on RMA, the USTMA sent a Feb. 3, 2022, letter to U.S. Congressional leaders, urging them to adopt six policies that the USTMA believes will assist end-use markets for scrap tires.
While the use of RMA and TDA led the way in the letter, investing in stormwater runoff research and incentivizing the use of retreaded and low rolling resistance tires also were listed.
"There are some purchasing preferences available for retreaded tires to help in the marketplace, but the real struggle is that low cost imports are taking market share—and they are not retreadable," Sheerin said. "Retreads have to meet a certain standard and these do not. That is the primary driver in that space (causing the decline in scrap tires for retreading)."
In addition to reaching out to the federal government, the USTMA has partnered with the University of Missouri at Columbia to study RMA, a collaboration known as "The Ray," for Ray Anderson, the founder of a carpet company who foresaw the need for a circular economy.
"The Ray is an innovative demonstration, on the highway and in the lab, that resulted in a very detailed report that spelled out the status of RMA technology," Sheerin said of what ultimately became the State of Knowledge of RMA report released in May 2021. "The USTMA helped fund that study."
Sheerin said RMA goes back to the early 1960s in Arizona.
In the 1990s when the use of RMA finally was required on a mass scale, the market was not ready and its uses were never adopted.
"Experienced engineers might have said, 'we tried that' and moved on," he said. "There is truth to that statement, but the technology has caught up today, ready to expand and meet the needs of pavement engineers."
Luke said U.S. tire manufacturers are "a critical part of the American economy, and our members are committed to sustainable practices in every aspect of their businesses."
"As global leaders in manufacturing, our companies embrace a shared responsibility of helping to achieve a more sustainable society," she states in the February 2022 letter to elected officials.
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