| "One beauty of engineering is solving several problems at once. A one-shot solution can turn something costly into economic benefit." |
How do you dismantle a cake into its constituent components after it has been baked, and why would you want to? You would if the cake was really just an analogy for the 279 million automotive tires generated in the U.S. each year. A team of researchers at the college has been working on what to do with mass quantities of industrial by-products and post-consumer refuse like tires. They are researching uses for tires that can take advantage of the high-value resources that go into them.
"Tires have excellent properties," said Professor of Civil and Environmental Engineering Tuncer B. Edil. "Their high carbon content makes them a good absorber of volatile organic compounds. It's a shame to burn such a valuable resource."
Because stockpiles of tires are a breeding ground for mosquitoes that transmit encephalitis, and because tire piles sometimes catch fire resulting in enormous pollution and hazardous waste, the state legislature funded the Waste Tire Program. Since 1988, almost all of Wisconsin's 20 million used tires have been incinerated to generate power, according to Wisconsin Department of Natural Resources' Waste Tire Program manager Paul Koziar.
Ninety-five percent of new used tires are now burned, the remaining five percent are used in other products.
"We sort of got rid of what was here by using the low-cost technology that was available. We're probably deep sixing a lot of high-quality steel and other valuable material, but fuel sets the price for what you can do," Koziar said. "Now it's up to the engineers to develop technological advances that can take us beyond burning."
Tires are particularly wasteful of landfill space due to their large voids. Ironically, one of the uses Edil and Associate Professor Jae (Jim) K. Park have found for shredded tires is as a reactive barrier on the bottom and top layers of landfills. As leachate passes through the tires on the bottom and vapors rise through the top, carbon in the tires traps volatile organic compound. Since landfills are covered each day, using tire chips could save soil and control gases.
Edil and Civil and Environmental Engineering Associate Professors Craig H. Benson and Peter J. Bosscher have also been working with shredded tires as a light-weight fill material in highway embankments and retaining walls. In areas with soft ground, some reinforcing fills can sink and fail under their own weight. But tire chips, when properly mixed and compressed with sand, create a fill that is lighter and just as strong as sand alone.
Associate Professor Peter J. Bosscher inspects a tire "chip" atop a mountain of shredded tires. The tires are finding new usefulness as reactive layers in landfills and as support for weak soils. |
More recently, Edil's team has been researching uses for class F type flyash. Flyash is a byproduct of coal combustion. Class C flyash is sold to concrete producers for use as an additive to concrete, as is true class F flyash. But older combustion systems at power plants produce "off spec" class F flyash that is not suitable for the same use.
"Some class F flyash has a high carbon content which is not good for concrete," said Edil. "So all of this flyash has to be landfilled which is costly to utilities."
Edil and Benson found that if class F flyash is mixed with a little class C flyash, it has low permeability and is suitable for lining the bottoms of landfills. Because it has high carbon content, it also absorbs volatile organic compounds.
"Clay is normally used as landfill liners, but is not always available in different geographic regions," Edil said. "Plus mining clay does some environmental damage."
Wisconsin Power and Light combustion by-product coordinator Randy Pollek said WP&L must dispose of 50,000 tons of class F flyash per year.
"There are very few approved uses for this kind of ash at this point. This is one more potential use for an ash that is not in demand now," Pollek said. "Both Edil and Benson have been very willing to work with us. They aren't afraid to get their hands dirty. They really get involved."
Flyash and foundry sand each represent 10 percent of all material landfilled in Wisconsin, according to commodities consultant Elizabeth Olenbush. Olenbush works for the Wisconsin Solid Waste Research Council. Part of the council's work involves finding and funding research that applies directly to removing specific materials from the waste stream. Each year, the council produces a list of 30 priority materials targeted for removal.
"That's where applied research and real-world partners are extremely important," said Olenbush. "We need to see results. Part of the reason Edil and Benson get funding is because they have relationships with the National Transportation Safety Board and the Federal Highway Administration. That improves the chances that their research results will actually be put into use."
Benson and Edil have just started to study spent foundry sand as another potential candidate for capping landfills.
Foundries mix sand with clay to form molds. After the molds wear out, the sand is landfilled. Because it has enough clay in it, the researchers believe it will have low permeability. And while clay is reactive to environmental changes, sand is not. The mixture is mostly sand and so the team hopes it will be resistant to frost action. These properties may also make the material suitable for beefing up the base material under highways.
"One beauty of engineering is solving several problems at once," Edil said. "A one shot solution can turn something costly into economic benefit."
--By Jim Beal--
| For further information, please contact: |
Tuncer B. Edil, 608/262-3491
edil@engr.wisc.edu
Copyright 1997 The Board of Regents of the University of Wisconsin System
Content by perspective@engr.wisc.edu
Markup by webmaster@engr.wisc.edu
Date last modified: Wednesday, 19-Mar-1997 12:00:00 CST
Date created: 19-Mar-1997
