Dr. Eddy Dean Smith

TIRES LITERALLY DRIVE the U.S. military, as most military vehicles, from Humvees to planes, are equipped with tires. The Department of Defense's (DoD) great demand for tires has led to large piles of used scrap tires, which are reduced through public sell-offs and service contracts.

However, the amount of military tires sold to the public has decreased nearly 65 percent in the past five years, causing military tire handling costs to increase. To combat this, the DoD looked to the waste industry to solve the problem. The same scrap tire reuse options are available to the entire waste industry, it says.

Currently, 38 states ban the landfilling of whole tires. While the military diverts 100 percent of whole-tire waste, doing so is expensive. In fiscal year 2003, the military generated more than 14 million pounds of vehicular rubber scrap and incurred costs of $670,000 to remove rubber scrap. The DoD predicts annual removal costs could reach more than $1 million. So to eliminate stockpiles and reduce the cost of removing them, the military has implemented tire retreading programs, and has investigated diversion and recycling options successfully used by today's industry.

Retreading worn tires

Retreading involves removing worn tread from an undamaged used tire casing and replacing it with new tread. Compared to new tires, retreads require five less gallons of oil per tire to produce. Subsequently, the tire purchase price is 30 percent to 50 percent lower. Retreads are mostly used by the federal government and trucking, aircraft, construction and agriculture industries.

Deriving fuel from tires

Whole, shredded or chipped tires have been used as a supplement to conventional fossil fuels and biomass in the United States since the 1970s. Tire-derived fuel (TDF) is an attractive fuel for industrial processes because of its heating value range of 12,000 to 16,000 Btus per pound, favorable emissions test results, lower moisture content and its typically cheaper cost compared to coal. The TDF market used more than 115 million scrap tires in 2001 — accounting for 52 percent of total scrap tire use that year.

Despite TDF's advantages, burning scrap tires for fuel is perceived negatively by the public and is susceptible to regulatory changes because it involves incineration.

Ground rubber applications

Crumb rubber, which is tire rubber reduced to ½-inch pieces or smaller, is made from scrap tires or tire buffings from the retread process. The product may be used for rubber product production, construction of asphalt roads, and supplementing virgin stock in the manufacturing of new tires. Crumb rubber and civil engineering application markets are the second-largest scrap tire market after TDF, accounting for 33 percent of scrap tire use in 2001.

Civil engineering applications

Tires shredded to sizes between 2 and 12 inches may be used in lieu of dirt, clean fill, gravel, stone and sand in civil engineering projects. The small tire pieces also may be used in landfill construction to replace clean fill materials between geotextiles and under the final cover material.

Agricultural uses

Farmers can use whole scrap tires to hold down covers over haystacks, to control erosion and to protect structures from livestock damage.

Greater awareness of tire properties, the low cost of scrap tires, the environmental benefits from reducing the national scrap tire surplus, government subsidies and recent developments in processing equipment have led to a rapid growth of used tire end-markets. Civil engineering and crumb rubber markets alone used 73 million tires in 2001, up from 35 million tires in 1998. A one-mile stretch of two-lane road paved with rubber-modified asphalt comprises between 12,000 and 15,000 passenger tires, so all of the scrap tire applications have great potential for preventing pileups.

Dr. Eddy Dean Smith
U.S. Army Engineer Research and Development Center and Scott Leasure
National Defense Center for Environmental Excellence

Acknowledgement:

Funding for this effort has been provided under the National Defense Center for Environmental Excellence, which is operated under contract W74V8H-04-D-0005 by Concurrent Technologies Corporation. The views, opinions, and/or findings contained in this paper are those of the authors and should not be construed as an official Department of the Army position, policy, or decision unless so designated by other official documentation.