Published on September 24, 1997
COAL COMBUSTION PRODUCT MAKES FOR SOUND HIGHWAY REPAIRS
COLUMBUS, Ohio -- Researchers at Ohio State University have found that a byproduct of coal-burning power plants functions well for highway repairs.
The byproduct, an ash produced by power plants that burn sulfur-rich coal, is 27 times more stable than soil when used as a highway embankment material. It also shows promise as a low-cost surfacing material for roadways, and as a liner for livestock waste lagoons, wetlands and landfills.
Under current environmental regulations, power plants must remove much of the sulfur emissions that result from burning high-sulfur coal mined in the eastern United States. Scrubbing mixes calcium with the sulfur dioxide that forms when the coal is burned. Plants must then pay to haul the resulting ash to a landfill.
A large power plant can produce a couple million tons of this ash every year, said William E. Wolfe, associate professor of civil and environmental engineering and geodetic science. We wanted to look for alternate uses for this material since it exists in such large quantities.
Wolfe published the results of the research, which was sponsored by the Ohio Coal Development Office, in a recent issue of the journal Fuel.
In conjunction with the Ohio Department of Transportation (ODOT) District 5 of Jacksontown, Ohio, the Dravo Lime Company Research Center of Pittsburgh, and American Electric Power, the Ohio State researchers explored a practical application for the ash -- they used it to rebuild an embankment on State Route 83 in southeastern Ohio.
ODOT had been repairing this heavily-trafficked stretch of road two to three times a year, because loose soil beneath the highway was sliding downhill and the pavement was sinking.
The researchers rebuilt the embankment in three sections. In the first they packed soil under the highway -- the traditional method of repair. In the second they used an equal mix of soil and ash, and in the third they used only ash. The researchers then analyzed the stability of each section, and discovered that the ash was 27 times more stable than soil alone. The ash-soil mix was 15 times more stable than soil alone.
The ash functions like a weak concrete, so its much more stable than the original soil, said Wolfe. What that means is that this area simply isnt going to slip anymore, as long as environmental conditions around it dont change significantly.
The ash should last longer than the pavement on top will last, Wolfe continued. The ash has been there four years, and in all that time, it hasnt needed any repairs.
The researchers tested water around the embankment and could find no indication of metals leaching into the surrounding environment. Wolfe said the water they found near the embankment approached drinking water quality.
By chance, the researchers discovered a second application for the ash. When they rebuilt the embankment at the end of 1993, all asphalt companies were closed for the winter. ODOT normally covers such areas with gravel until spring. To see whether the ash would make a suitable road surface, the researchers covered half the area with gravel, and the other half with ash.
ODOT planned to pave the site as soon as the asphalt companies opened up, Said Wolfe. But the ash performed so well that they were able put off paving while they worked on other projects that were more critical. From mid-December until they paved the area in June, they had to go to the site four times to replenish the gravel, but they never had to replenish the ash.
All in all, ODOT saved about $80,000 by using the ash along that 1000-foot stretch of Route 83.
The Route 83 project utilized ash produced through a process called dry scrubbing, in which power plants remove sulfur from the coal in the furnace. Wet scrubbing, in which plants extract sulfur by running the furnace smoke through a watery solution, is much more common, so the researchers began to look for uses for this kind of ash.
This ash is weaker, and so wouldnt perform as well in highway repair. It must also dry in the sun, and so couldnt be deposited outside in the wintertime, as the other ash could.
Laboratory tests have shown that the wet-scrubbing ash resists the flow of water, so we are currently evaluating its performance a liner for livestock waste lagoons and artificial wetlands, said Tarunjit S. Butalia, research associate in civil and environmental engineering and geodetic science. Butalia said that the material may also form an excellent liner for landfills.
More information about this newest part of Wolfe and Butalias research is available from the project web site, http://www-ltap.eng.ohio-state.edu/liner/.
We want to find ways to use the material that will do more good than just dumping it in a landfill, said Butalia. We can save a power utility the cost of operating a landfill, and at the same time help other people save on construction cost. The cost of the material isnt any higher than the cost of hauling it. #
Written by Pam Frost, (614) 292-9475; Frost.firstname.lastname@example.org
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