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Creative Thinking May Help Retire Old Landfill Problem

Engineers in the College of Engineering may help transform scrap tires from a waste-disposal headache to a quality construction material. Professors Tuncer B. Edil, Peter J. Bosscher, Jae (Jim) K. Park and Craig H. Benson recently completed six years of studies on using scrap tires in highway construction and environmental remediation. They say the results should encourage state environmental and transportation agencies to use the materials in pilot projects. Among the uses explored: using tire chips as fill in highway sound barriers; as reinforcement material underneath new highways; and as mixtures with sand and soil to produce more stable surfaces for construction. Another series of studies found that shredded scrap tires could be useful filter of contaminants from landfill runoff and waste water treatment. The Environmental Protection Agency estimates the United States has five billion scrap tires piled up around the country. The number continues to grow at a rate of 250 million tires per year. By federal law, scrap tires cannot be placed in landfills, so they end up in vast stockpiles on waste management grounds.

Mountain of old tires

Peter J. Bosscher, associate professor of civil and environmental engineering, inspects a tire "chip" atop a mountain of used tires and shredded tire material. Tires such as these were shredded and used as the base for a sound barrier along Highway 172 in Green Bay, Wisconsin. The mound of tire chips was then covered with soil and foliage, providing protection from traffic noise while maintaining a natural-appearing landscape. (large image)

"The relevant question here is, how do you get rid of billions?" says Bosscher. "Any alternative use has to emphasize quantity. And if we could find a way to use them routinely in highway construction, we could empty the stockpile in five to 10 years."

Bosscher and Edil used a stretch of road east of Madison as a test site for roadbed material augmented with tire chips. They measured how the road held up under the weight of extensive car and truck traffic.

The studies have generally found that tire chips make a cheap and effective fill material for roads, while not adversely affecting ground water quality.

Edil says the best use of tire chips would be as a supplement to gravel and sand in places where the ground needs reinforcement, such as in land of marginal building value or in soils too soft to build on.

Edil says tire chips are already being used with some success on rural roads in Minnesota and Colorado.

"The issue is not just substituting one cheap and available material with another, but getting a superior material for what you're trying to accomplish," Edil says.

Tests of shredded tires as pollution filters also produced promising results. Park led projects that found tire chips have the ability to absorb organic compounds that might leach from landfill sites. They also had "great potential" in soaking up volatile organic compounds during waste water treatment.

The researchers have produced a report that they hope will guide state agencies and companies in using scrap tires in construction. The next step, however, has to come from agencies willing to develop projects.

Funding for the research has come from the state Department of Transportation, the state Department of Natural Resources, the Environmental Protection Agency and the Solid Waste Management Council.

Currently, about 17 percent of all waste tires are burned as an alternative fuel source in power plants and other industries, such as cement plants. Burning tires is growing in popularity as a solution, but Bosscher sees only valuable material going up in smoke.

"Why waste something as fuel that clearly has a greater engineering value?" he says. "We reuse the steel from cars, we can do the same for tires".