With a vast supply of used tires—approximately 300 million tires are generated every year, and a further 1 billion tires are currently stockpiled throughout the United States—and funding from various state agencies to help companies develop end markets, opportunities to tap into scrap tires as a raw material should be burgeoning.
However, many end markets have been slow to take off, with the exception of the largest market for this material: tire-derived fuel. This market has not been immune to the current economic environment, however, and a number of consumers of TDF have closed.
A report by the Rubber Manufacturers Association (RMA), Washington, D.C., notes that 1.43 million tons of scrap tires were used as tire-derived fuel in 2011. However, between 2009 and 2011, this market declined by more than 31 percent. The drop can be attributed in part to the recession that curtailed overall manufacturing, according to the RMA.
With states still limited by tighter budgets, the use of crumb rubber in asphalt could be poised for growth as it provides cost advantages relative to traditional material.
Far from a new end market, rubberized asphalt concrete (RAC) has been around for nearly 50 years, though it has had a bit of a checkered past.
In a white paper titled “Asphalt-Rubber 45 Years of Progress,” author George Way, chief engineer of the consulting company Consulpav International, Walnut Creek, Calif., notes that the American Society of Testing and Materials (ASTM), West Conshohocken, Pa., defines asphalt rubber (AR) as “a blend of asphalt cement, reclaimed tire rubber and certain additives in which the rubber component is at least 15 percent by weight of the total blend and has reacted in the hot asphalt cement sufficiently to cause swelling of the rubber particles.”
The use of crumb rubber from tires as a binder in asphalt may present some opportunities for scrap tire processors, though presently the application represents a small portion of the overall consuming markets for ground scrap tires. According to the most recent figures from the RMA, approximately 11 percent of the ground rubber produced from scrap tires goes into asphalt production, far less than the 31 percent used to make molded and extruded products.
What has many advocates of RAC enthusiastic is its growing acceptance by departments of transportation in various states. The RMA notes that rubber use in asphalt has grown from roughly 91,000 tons in 2005 to 165,000 tons in 2011.
Initially, the Arizona Department of Transportation began using rubberized asphalt as a “pavement preservation” strategy on major highways throughout the state. In the mid-1960s, the city of Phoenix pioneered the use of the product when it was incorporated into the “chip seal” program for city streets.
The use of scrap rubber in asphalt can be further narrowed to its first proponent, Charles MacDonald, a materials engineer for the city of Phoenix. MacDonald, in a search for a way to maintain pavements that were in poor condition, blended rubber from scrap tires with asphalt.
While Arizona has been the leader in using rubberized asphalt, states such as California, Florida, Texas, South Carolina, Nevada and New Mexico also are using a growing amount of asphalt rubber. Even states in the Midwest and Northeast are embracing the material.
Despite RAC’s failure to take hold on a widespread basis in the early 1990s, more recently there appears to be interest in incorporating crumb rubber into asphalt. The swing has been driven by significant shortages of styrene-butadiene rubber (SBR), which crumb rubber from scrap tires can replace.
Reflecting the opportunities afforded with using scrap tires to produce rubberized asphalt, the U.S. Environmental Protection Agency (EPA) recently held a webinar where the agency brought together a number of tire recycling experts to sketch out the prognosis for this end market.
Serji Amirkhanian, director of research and development at Phoenix Industries, a Las Vegas-based development firm, was among the presenters. He appears enthusiastic about the future of this end market. “I wish I was younger,” Amirkhanian says. “It is the best time to be in the business. There are so many opportunities with more states taking an interest in the process.”
Why the optimism?
For supporters, the most obvious reason is that more states are mandating their transporation departments to use more rubberized asphalt for road and highway projects. While there have been reservations about substituting SBS polymers with crumb rubber from scrap tires as a binding agent for asphalt, the economics are starting to make sense for contractors.
In a Bind
The use of crumb rubber as a binder to make asphalt started to peak the curiosity of potential consumers around five years ago, when many contractors were finding a serious shortage of SBS. “Paving jobs couldn’t get the material,” says Mark Belshe with the Tempe, Ariz.-based Rubber Pavements Association, another webinar presenter.
Doug Carlson, vice president of asphalt products for Liberty Tire Recycling, Pittsburgh, concurs that a shortage of SBS has helped to galvanize attention on the use of crumb rubber as a binder. “Many paving projects had to stop because they couldn’t get the SBS for their asphalt,” he says. “Another step was to find an alternative, in this case crumb rubber from scrap tires.”
With the SBS shortage, more state transportation departments have begun re-examining the use of rubberized asphalt for their projects. Initially, states in the South and Southwest were where most of this activity was taking place. However, supporters of rubberized asphalt say more state transportation agencies in the Midwest and Northeast are now seeking the material for their paving projects.
While supporters of using crumb rubber from scrap tires in asphalt see a considerable upside to the practice, they say that much of the remaining trepidation has to do with the failure to execute on earlier calls for the use scrap tires in asphalt. The Intermodal Surface Transportation Act of 1990 mandated increased use of asphalt that contains crumb rubber from scrap tires. Despite the mandate, the federal government failed to provide funding to support this move. Therefore, state transportation agencies failed to follow this directive, and the mandate eventually was rescinded.
For budget-conscious government agencies, the higher upfront cost associated with using rubberized asphalt has been one of the biggest obstacles. However, tests show that rubberized asphalt has a longer life cycle, which has eliminated many of the cost concerns.
Additionally, the cost of crumb rubber—roughly 20 cents per pound—is far lower than the cost of SBS, which can range from $1.50 to $2 per pound. Even factoring in the need to use three times as much crumb rubber as SBS to meet quality specifications, the price differential still favors using recycled crumb rubber from tires.
In raw dollars, Carlson says a project requiring 1,000 tons of binder would require 30 tons of SBS at a cost of $120,000, while 90 tons of RTR would cost $90,000, a savings of $30,000.
During the EPA webinar, Michael Blumenthal, vice president of the RMA, noted that environmental benefits can be realized by using recycled crumb rubber in asphalt, as it creates almost seven times less carbon emissions than traditional asphalt. He added that production of traditional asphalt yields 840 kilograms of carbon dioxide per metric ton, while the weighted average carbon footprint for making RAC is 124 kilograms of carbon dioxide per metric ton.
Asphalt rubber typically contains 80 percent asphalt and 20 percent tire rubber, though the proportion is declining, says Belshe. He estimates that RAC now uses 10 to 12 percent crumb rubber produced from scrap tires.
The Georgia Department of Transportation (DOT) announced that in light of the successful use of recycled tire rubber in asphalt in 2012 the agency plans to collaborate with construction companies in 2013 that expect to use millions of pounds of recycled rubber derived from scrap tires.
In a statement, the Georgia DOT notes that rubberized asphalt saves money by requiring less pavement thickness to withstand the same amount of traffic as conventional asphalt as well as by replacing higher-cost oil-based polymers.
The future may look bright for many advocates of rubberized asphalt, but even the biggest supporters acknowledge a number of hurdles and issues that still need to be dealt with. One issue that will continue to restrain further use of RAC is the long testing period that transportation agencies require before accepting rubberized asphalt in projects. Belshe says state transportation agencies are always concerned about the quality and effectiveness of the product. “It is not a fast process,” he adds.
As a result, while 28 million pounds of used tires were used in asphalt applications in 2007 to 2008, Carlson estimates that 36 million pounds of rubber from scrap tires are presently used.
Despite the slow growth, Carlson says RAC has huge potential, as a number of states are looking to increase their use, which will grow the overall demand for scrap tires needed as raw material.
The author is senior editor of Recycling Today and can be contacted via email at firstname.lastname@example.org.