Paving the Way for Asphalt Rubber

Jul 26, 2018, 20:45 PM
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July/August 2018

Asphalt rubber isn’t gaining much ground on U.S. public roads despite its benefits in road performance. What will it take for this recycled rubber product to pull ahead in the paving race?

By Megan Quinn

Asphalt-RubberDrive along I-17 in Arizona, I-78 in New Jersey, a toll road in Chicago, or the streets of Long Beach, Calif., and you’ll likely be driving on rubberized asphalt made with crumb rubber from recycled tires. Researchers say adding crumb rubber to asphalt results in safer, longer-lasting roads that cost less in the long run. This is a potentially sizable end market for recycled tires, keeping them out of landfills and providing good business for tire recyclers.

The material faces several speed bumps on the way to widespread implementation, however. While a few states, including California and Arizona, have made it a priority to use recycled tire rubber in public road-paving projects, most states have just a few pilot projects that are using or testing rubberized asphalt on selected roads. Getting states on board is a slow process because each state’s transportation department must approve its use and create specifications. In states where its use isn’t widespread, contractors sometimes have to acquire new paving machinery to accommodate it, which is a barrier when the contractors don’t think it’s worth the cost. On top of that, crumb rubber often costs more than a more common competing virgin additive, a synthetic polymer called styrene butadiene styrene, “and most state [transportation departments] will not voluntarily approve a more expensive product,” says Redmond Clark, president of Asphalt Plus (Barrington, Ill.), which provides crumb rubber designed for this use. Yet recyclers and rubberized asphalt companies say they’re making progress by demonstrating the efficacy of the product in the field and by advocating for this material on the state and federal levels. “It’s notable each time another state gets on board,” he says.

Rubber Asphalt’s Benefits

Using tire rubber in road pavement isn’t new—it’s a practice Arizona first used back in the 1960s, when Charles McDonald, an engineering supervisor in Phoenix, was looking for a better way to fix potholes and cracks in the pavement. He found that mixing crumb rubber in with asphalt helped the patches last longer. There’s a good reason the practice has caught on in the years since, says Doug Carlson, vice president of asphalt products for Liberty Tire Recycling (Pittsburgh). Tires are already designed to be tough, and those qualities translate easily into a road material. “It’s a low-cost way of getting high-cost technologies” into the road mixture, he says.

Rubberized asphalt improves road performance during adverse weather, adds Barry Takallou, president and CEO of CRM (Newport Beach, Calif.), a manufacturer of crumb rubber for rubberized asphalt. “When we design a pavement, we’d like to design it for four seasons” and the wear and tear associated with harsh weather. In hot temperatures, asphalt can melt slightly when tires drive over it, creating ruts in the pavement. This can be dangerous during rain or snow storms because water pools in the ruts, spraying windshields and creating visibility problems, or contributing to hydroplaning, he says. In the winter, pavement can crack or potholes can form when moisture seeps into the pavement, expanding and contracting when temperatures rise and fall. Crumb rubber is “not temperature-sensitive, and it’s 100-percent elastic,” so it can protect against both ruts and cracks, he says. The rubber also helps improve tire traction, and the semi-porous nature of the rubberized asphalt helps drainage, which can prevent spray from wet roadways, improving visibility, he says.

Tire rubber also makes roads quieter. In one road study conducted in Colorado Springs, Colo., the city’s roads containing rubberized asphalt were 4 to 5 decibels quieter than those without. A reduction of 6 dB or more would be the equivalent of building a sound wall, according to the Western Pavement Maintenance Association (Fair Oaks, Calif.).

According to the U.S. Tire Manufacturers Association, about 9.3 million tires were used for asphalt in 2015, which is about 4 percent of total recycled tires reused that year. Depending on the paving method, it takes between 500 and 2,000 scrap tires to pave each lane mile of pavement, meaning a one-mile section of a four-lane highway could require between 2,000 and 8,000 tires, according to the Rubber Pavements Association (Tempe, Ariz.). If every state used rubberized asphalt, the market could “very easily” use about half of the available ground tire rubber in the United States, Carlson says.

Mandates Versus Markets

Despite that potential, right now markets for rubberized asphalt vary dramatically across the country. On one end of the spectrum is California, which has about 22,000 miles of rubber roads, Takallou says. That’s in part because the state mandates the use of rubberized asphalt in road construction and maintenance. “Half of the [rubberized asphalt] market in the U.S. is in California,” Carlson says.

Arizona is another state with a well-established rubberized asphalt program. In 1989, years after Charles McDonald’s rubberized asphalt patching idea, the state began using the material to pave full lane miles, according to the Arizona Department of Transportation. It also funded a special $34 million noise abatement resurfacing project in 2013, which installed rubberized asphalt on 115 miles of Phoenix-area highways to reduce noise for nearby residents.

In other states, little or no crumb rubber goes into public roads. One reason is that the asphalt rubber industry must follow state DOT regulations for asphalt composition, and not every state has regulations allowing rubber, though some are slowly working on them, Clark says. “DOTs are a big holdup because you need to be in their specifications before it can be used in the public sector,” he says.

In Georgia, the state’s transportation department amended its road specifications in 2012 to allow recycled tire rubber as an alternative to conventional oil-based polymers. This change was notable, Clark says, because the state is the first to approve both the common “wet” paving method many rubberized asphalt contractors use and a “dry” paving method, which is written into few state specifications. This opens up the market for more companies that mix and sell a variety of rubberized asphalts, he says. (For more on the differences among wet, dry, and terminal RA paving processes, see “How It’s Made” on page 52.) Clark’s paving business relies solely on the dry process, so the Georgia specs are a big win for his business and the tire recyclers from which he sources rubber. “Georgia is really a leader in this. They have a million tons of [asphalt rubber mix] on the ground,” he says.

Takallou says state specifications, along with federal and state incentives that help fund rubberized road projects, are a major driver of rubberized asphalt. His business is based in California, where state regulations help him do steady business and grant programs help cities and counties pay for rubberized asphalt projects. Yet he worries that the rubberized asphalt industry is too reliant on mandates and incentives. “It’s a stick instead of a carrot” approach that can help temporarily—but once incentives run out, asphalt rubber projects that rely on such funding also could stop, he says. This problem extends beyond California, too, Clark says. “The markets for rubberized asphalt are being driven by mandate, not market,” which drives up the cost of rubber in states where there are mandates to use the material, he says.

Incentives are a good tool for introducing rubberized asphalt projects to places that lack them, or to fund pilot programs that could prove rubberized asphalt is worth the investment, says Billy Johnson, ISRI’s chief lobbyist. In 2010, ISRI helped develop language for a federal transportation bill that provided $13 million in funds for states to use alternative materials in road construction projects. The bill has since passed and become law, he says.

Incentives also can be helpful to cover rubberized asphalt’s up-front costs. Rubber asphalt roads typically cost about $15 more per ton than conventional roads, but prices can fluctuate based on where the paving is taking place, what method contractors use to mix the asphalt, and how available the materials are, Carlson says. Yet these roads are cheaper in the long run, according to a study from the California Department of Resources Recycling and Recovery. The “improved durability, reduced maintenance demand, and longer service life provided by [rubberized asphalt] materials should substantially reduce the overall life cycle costs and help offset the increase in initial cost,” the report says.

Bumps in the Road

Though rubberized asphalt lasts longer when installed properly, the asphalt rubber industry is still recovering from damage to its reputation resulting from projects undertaken due to the 1991 federal Intermodal Surface Transportation Efficiency Act. ISTEA directed state departments of transportation to use an increasing amount of crumb rubber in roadways as a condition of receiving federal highway funds. States tried pilot projects without really understanding the technology, and the results were “a disaster that set the industry back 20 years,” Clark says. One problem was that the formula some states used hadn’t been properly tested, and the rubberized asphalt clogged machinery and didn’t stay on the road.

Congress repealed the rubberized asphalt mandates in ISTEA after a few years, but the material’s bad reputation lingers. ISTEA showed that not all industry players were on the same page when it came to supporting rubberized asphalt efforts, Takallou says. Some states that weren’t already using crumb rubber thought the rubber was to blame, not the faulty formula. “As a civil engineer, we’re trained to say, ‘virgin material is better than recycled.’ But honestly, that’s a misunderstanding,” he says. “Agencies say they don’t want to put ‘trash’ in our roads. But crumb rubber is not trash.”

One major flaw of ISTEA’s mandate was that not enough research went into making the correct mixes. Today, it can take years for DOTs to research and request tests of different recipes and methods. This stalls progress and leaves recyclers and asphalt and paving companies waiting in the wings. But Clark says he can’t blame transportation officials who want to make sure they’re investing in the best material instead of an expensive mishap.

It also can take time and effort to convince paving companies to invest in equipment suited to the standard the state approves. Pavers can use the same equipment to apply dry-process rubberized asphalt and traditional asphalt to the road, but they must buy additional machinery for the mixing process, such as a machine that meters out crumb rubber in a precise measurement, Clark says. This equipment can cost thousands of dollars, and if the company is operating in a state where demand for rubberized road material is low, it might decide it’s not worth the investment, Carlson says.

Advocacy and Next Steps

One group often left out of the high-level conversations about rubberized asphalt use are tire recyclers, especially smaller ones, Takallou says. But he urges them to get involved. “One of the big problems is education,” and tire recyclers know their product best and can clear up misconceptions, he says.

Clark agrees. Tire recyclers can “have extended conversations with their local environmental agencies in their state and with their department of transportation. They can be direct advocates who arm DOTs with information” about the benefits of recycling tires into roads. These officials ultimately control the budget for such projects, Carlson adds, and “a lot of times, the DOT only sees the price tag.”

Georgia’s asphalt standard change is an example of successful advocacy by tire recyclers, Carlson and Clark say. Executives from Liberty Tire brought the issue to Georgia state Rep. Randy Nix in 2011, who worked with GDOT to amend the agency’s road specifications to allow the use of rubberized asphalt. Illinois also is working on updating its standards to accommodate rubber, and several other states are actively working to incorporate the dry process into their standards. “Soon, another group of states will jump in, then another,” Clark says.

In February, President Trump unveiled a new $200 billion federal infrastructure plan aimed at fixing U.S. infrastructure by leveraging local tax dollars and private investment. Johnson says this could create an opportunity to encourage states to start using rubberized asphalt and other recycled materials when building new infrastructure. “With any new infrastructure package, ISRI advocates that recyclable materials should be used whenever possible,” he says.

ISRI’s Tire Division recently created a committee to develop a strategy to advance the use of rubberized asphalt in the states, says Chair Kyle Eastman. The goal is to have discussions with the Federal Highway Administration and state DOTs that will remove obstacles that are preventing rubberized asphalt from being used regularly on highways and streets across the country. The country is slowly getting there, mile by mile, Clark adds, but the goal is an important one. “We can’t keep throwing tires away.”


Megan Quinn is reporter/writer for Scrap.



(Sidebar Content)

How It’s Made

While conventional asphalt road surfaces are made with asphalt—the black, sticky stuff—and a mix of aggregates, rubberized asphalt also contains finely ground rubber, called crumb rubber. The size of the crumb, the amount added to the asphalt, and the method for mixing and melting the material varies by production process. Producers typically make rubberized asphalt using one of three processes: wet, dry, or terminal. “All of these techniques work—and work well,” says Redmond Clark, president of Asphalt Plus (Barrington, Ill.), which offers dry mix paving services.

In the wet process, which is the most common, producers use mobile mixing equipment to combine asphalt with crumb rubber. About 15 to 20 percent of that mix will be crumb rubber, but the formula could change based on what’s needed for the project, says Doug Carlson, vice president of asphalt products for Liberty Tire Recycling (Pittsburgh). The asphalt and crumb rubber melt together as it is stirred “like a milkshake” for about an hour at 350 degrees F, creating a viscous binder much thicker than traditional asphalt binder. The paving company adds aggregate to this “hot mix,” which it then spreads on the road. While the wet process is done right on the paving site, the terminal-blend process adds the crumb rubber to the asphalt at the asphalt refinery and uses a smaller crumb size. Terminal-blend binders typically contain 10 percent or less crumb rubber, but some projects have successfully used up to 15 to 20 percent, according to CalRecycle. In the dry process, which is becoming more common, the contractor adds crumb rubber to the dry aggregate instead of to the wet binder.


Asphalt rubber isn’t gaining much ground on U.S. public roads despite its benefits in road performance. What will it take for this recycled rubber product to pull ahead in the paving race?

  • 2018
  • Jul_Aug

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