American Recycler, February 2009 - Innovative uses for scrap tires on the rise

In the old days, most tires were dumped in landfills and the most visible recycling was as fenders for boats and docks (if you didn’t mind black streaks on a white hull).

Now about 45 percent of the approximately 400 million tires scrapped annually are used for tire derived fuel (TDF) and are co-fired with other fuels. This is the economic backbone of the scrap tire industry. The majority of the remaining scrap tires are shredded into tire derived aggregates (TDA) or ground into crumb rubber for use in products such as molded rubber goods, new passenger tires, truck tire retread compounds, hoses, brake linings, coatings, sealants, rubberized asphalt, outdoor playground and track surfacing, and wire-free colored nuggets for playground safety and landscaping mulch.

What scrap tire companies want, and are constantly seeking are new and more profitable ways to use raw materials. Products derived from ground rubber hold the promise for bigger profits.

Jeff Kendall, CEO of Liberty Tire Recycling, one of the country’s largest tire recyclers, sees potential for several of his company’s products. “In-fill for artificial turf and mulch for playground and gardens have been growth areas for us. Last year and this year, the playground market showed us record results. In playgrounds, our mulch products are much better than wood because they have more give to it. Our product is surprisingly good looking, lasts a long time and is increasingly being accepted commercially as decorative mulch.” Kendall also sees tremendous potential for more crumb rubber going into asphalt. “It’s a use that is untapped in most places around the county. There’s no reason why it shouldn’t become enormous, and I think it will.”

Doug Carlson, executive director of the Rubber Pavement Association agrees that the future of rubberized asphalt is promising. “It is working extremely well – out-performing traditional asphalt considerably in both durability and maintenance costs. Moreover, when properly formulated it can significantly reduce road noise and can provide better skid resistance for improved safety. After decades of test paving and evaluations, the New Jersey Department of Transportation has three sizable rubberized asphalt projects planned for next summer. “New Jersey appears to be on-track to use the friction course material widely throughout their system for the safety enhancement,” Carlson noted.

As the Obama administration considers new national infrastructure investments, rubberized asphalt could play an important role due to its cost-to-value durability, noise reduction and safety characteristics.

When products made from recycled tires are introduced there are often initial doubts about their efficacy, safety and health. One area of public concern has been the use of recycled tire rubber for outdoor playgrounds, track surfacing and landscaping mulch.

The Handbook for Public Playground Safety published by the U.S. Consumer Product Safety Council states that over 200,000 children are hospitalized each year from playground injuries and over 80 percent are the result of children falling from equipment. Ask parents if they would rather have their kid fall onto asphalt, concrete or dirt or onto an adequate rubberized surface or rubber nuggets and guess the answer. But when it comes to the toxicity of recycled tire products, dangers of ingestion, contact with skin and general environmental impact – questions remain.

California’s Integrated Waste Management Board (CIWMB) wants answers and commissioned the state’s Office of Environmental Health Hazard Assessment (OEHHA) to conduct a study in 2007. Jordan Scott, a public information officer with CIWMB summarized the findings, “What they came back with is that there is nothing substantial that was a public health risk. They found there was little to no impact on health, or any sort of health risk on ingestion.”

Obviously, they did not have the children eat handfuls of recycled tire crumbs but rather conducted a gastric digestion experiment. They took 22 chemicals released by tire shreds and incubated them for 21 hours in a solution and under conditions simulating the gastric environment. Then, assuming a young child ate ten grams of tire shreds, OEHHA compared the levels of the released chemicals to health-based screening values. The results: all exposures were at or below screening values and suggested a low risk of non-cancer health effects. Five of the chemicals released by tire shreds were carcinogens. If these chemicals were ingested once in a lifetime, the cancer risk would be 3.7 in one hundred million, well below what is generally considered an acceptable cancer risk. They also conducted tests for hand-to-surface-to-mouth, skin sensitization and leaching from rain experiments and found a low risk of ill health effects.

CIWMB promotes markets for tire-derived products through statewide outreach, business and technical assistance, and grant and loan programs to qualified public and private entities. Programs are funded by a $1.75 fee charged for each new tire and the money goes towards reducing old tires going into in landfills or illegal stockpiles.

In 2002, CIWMB started its Rubberized Asphalt Concrete (RAC) grant program to encourage municipalities, cities and counties to use RAC. And, it’s working – thus far they have granted nearly $25 million to help build RAC roads and kept several million tires out of landfills. Due to increasing demand, more companies are producing and paving with RAC. California studies have shown that using RAC, rather than traditional materials, builds longer lasting roads because it resists wear and cracking. It also provides a safer driving surface, especially in wet conditions, holds the color of road markings better for increased visibility, creates a quieter driving surface and saves on maintenance costs, often upwards of $50,000 over the life of the road. And, RAC recycles 2,000 tires for every lane mile paved.

California has serious landslide and mudslide problems due to much of the state’s geology and topography. These include steep hills of soil, weak rocks formations and the presence of springs. Add earthquakes, floods and slopes denuded by forest fires and very dangerous conditions can exist that threaten life, limb and property – and utility and transportation infrastructure, both vital during emergencies.

Tire derived aggregates are gaining momentum throughout California. Some of the more common uses include embankment fills, landslide stabilization, retaining wall backfill and vibration mitigation for light rail lines. “We just did a project in Sonoma County where we have a lot of landslides, especially during the winter months, to stabilize and repair a 130-foot section of landslide-damaged road. They removed the saturated soil and replaced it with 1,500 tons of tire shreds in two layers buried under the soil. The water runs right through it, no longer saturates the soil and there is no longer a landslide problem in that area,” said CIWMB’s Jordan Scott. With a number of successful TDA projects under its belt and nearly 2.5 million tires diverted from landfills CIWMB is hoping to have a TDA grant program established next year similar to the one for RAC.”

TDAs have often been overlooked for other civil engineering applications. In the early 1990s, projects using TDAs were often experimental and discouraged by random project fires and the general lack of knowledge about their engineering properties. That changed in 2004 when the American Society of Testing Materials re-approved ASTM D 6270, Standard Practice for Use of Scrap Tires in Civil Engineering Applications. It provided data that answered many of the doubts, concerns and uncertainties about using scrap tires for engineering projects.

Shortly thereafter, states began to take a serious look at TDA for sanitary landfill applications. In Iowa, for instance, the Department of Natural Resources had Barker Lemar Engineering Consultants, Inc., a Des Moines engineering consulting firm, create a 134-page Scrap Tire Workshop Manual to educate government employees and landfill operators. It’s a comprehensive and impressive document that covers the physical characteristics of TDA as well as landfill applications. It’s well worth reading. To download a copy: www.iowadnr.com/waste/recycling/tires/files/manual.pdf.

TDA is now well accepted by sanitary landfills across the country. It is used for leachate collection systems, alternate daily cover and methane collection systems. While useful applications for TDA exist, it is a low profit-per-ton market, but as demand increases profits are likely to rise.

Aside from landfills, TDA may have a future in other civil engineering projects. Why not? It’s an excellent solution – lightweight (one-third to one-half lighter than soil) durable, compressible, has effective porosity and is a good insulator for backfilling foundations.

Matt Nieswender, senior project manager at Barker Lemar, is looking for new ways to employ TDA. “When you begin to look at the thermal properties of tire chips it begins to open your eyes. They have excellent insulating properties. That’s why some standards do not want the chips piled too deeply, because they can catch fire. Why do they catch fire? Because small amounts of heat, caused by oxidation or other mechanisms, can be trapped by the insulating properties of the aggregate. We continue to look for civil applications that can effectively use tire chips as insulation, including geothermal applications. Engineered properly, TDA can insulate warm and cool return lines near the surface, reducing energy loss and reducing reliance on virgin raw materials.”

Pipes for horizontal heat and cooling pumps are buried just below the frost line and well above the water table. Besides being able to absorb vibration and stress, TDA has a thermal conductivity approximately eight times lower than typical granular soils and has been shown to reduce frost penetration by up to 25 percent.

TDA is not classified by ASTM as a hazardous waste and meets their recommended use for above the water table installations. Furthermore, a five-year study conducted jointly by the University of Maine and the University of Texas at Austin concluded that TDA placed below the water table appears to have a negligible off-site effect on water quality.