GREENSBORO — In what would be one of the great ironies of modern science, roadside utility poles someday might be made of coal ash dredged from the storage ponds that have so plagued Duke Energy and other power companies nationwide.
Researchers at N.C. A&T are continuing their work with the power-plant pollutant and have settled on large structural pieces, ranging from the cross arms on utility poles to building blocks for retaining walls, as the most promising market for safely re-using coal ash in manufactured products.
They favor that end use for the controversial waste product because it requires large amounts of relatively inexpensive ash and because their unique blending of ash with polyurethane outperforms materials currently in use, said Kunigal Shivakumar, director of the university Center for Composite Materials Research where late-stage testing is underway.
“These are products that can be made as good as any other material, plus they have added benefits like fire- and insect-resistance,” said Shivakumar, who has overseen the research funded by state government to find ways of recycling the powdery substance that remains after pulverized coal is burned to make electricity.
Shivakumar and his research colleague Wade Brown say they are in discussion with several potential manufacturers as they move into the last stage of testing to verify the weather resistance of their new substance.
None of the discussions are far enough along to make public yet, they say.
One of the best aspects of the research is its focus on the coal ash equivalent of Public Enemy No. 1, the gunk that has lain submerged for years in storage ponds “with all the fish swimming around above it,” as Brown puts it.
Fly ash fresh from the smokestacks of coal-fired power plants has long been known as a valuable ingredient in concrete, so much that some suppliers actually import it from as far away as India.
But making use of the mixed forms of coal ash under the ponds is another matter. In times past, utilities commonly dispensed with the ash underwater as an out-of-sight, out-of-mind technique to prevent it from being blown away as an air pollutant.
Billions of tons of submerged ash have accumulated over the decades nationwide in ponds that became highly controversial in recent years as a source of water pollution.
The issue came to a head in North Carolina more than three years ago when a drainage pipe burst under one such pond at the retired Dan River Steam Station near Eden, spewing up to 30,000 tons of ash into the river that gave the shuttered plant its name.
“We are experimenting with that kind of ash because that is where the problem is,” Shivakumar said of the ash from storage ponds. “We don’t want to compete with the concrete industry.”
The cross arms on utility poles, possibly the poles themselves and such other construction pieces as building blocks, beams, columns and fence posts emerged as top, potential uses of reclaimed ash over the last year.
Shivakumar’s lab joined forces with Brown after A&T researchers discovered that the Mooresville chemist had developed a patented process they needed to use in fusing the ash successfully with polyurethane. Now Brown works at A&T as a professor of practice.
In their initial work, the researchers also developed an industrial foam using coal ash and polyurethane, but they abandoned that as a major focus of their current efforts because it only needed small amounts of ash that wouldn’t make a dent in the state’s overabundant supply.
The research sprang from a two-year grant of $400,000 that the center received in 2014 after state Sen. Trudy Wade (R-Greensboro) contacted the laboratory to ask whether its specialists might be able to help find beneficial uses for the waste product.
During the last year, A&T researchers have verified that their hybrid creation will not leak pollutants from the coal ash, does not catch fire readily and can be strengthened with plasticized ribbing that works like rebar in concrete.
Heavy structural products are made of 65 percent or more of ash, the two researchers say. The material also is sturdy, can be made flexible and shows great promise in withstanding long-term exposure to sunlight and heat, they add.
Proving that the material would not leach pollutants when in contact with water was critical. They did it by submerging a block of the ash-polyurethane mixture in a tank full of circulating water for more than a year and periodically sending test vials of tank water to the state Department of Environmental Quality to check for potentially harmful chemicals such as arsenic, antimony and selenium.
Not a trace, even when exposed to water that is more acidic than normal, Brown said.
“It doesn’t make a difference, it just doesn’t leach,” he said, referring to the chemical process in which a substance releases some pollutants.
The most recent test, started in the last month, uses an “Accelerated Weather Tester” to check the durability of A&T ash composite against everything from intense ultra-violet light to morning dew.
The next four months of testing inside the machine will simulate what the new material would have to withstand over the next 25 years.
Knowing such details up front will be important as the university seeks the right collaborators to produce the ash-based compound in commercial quantities, Brown said.
“These are the kinds of questions that a major industrial client would ask when they first come in,” Brown said.
The idea of using a waste product from electricity produced decades ago in utility cross arms supporting lines that pulse with today’s live current puts smiles on the researchers’ faces.
Imagine building a retaining wall to protect a lake, creek or river from runoff and the wall is made of blocks manufactured from ash that once threatened water quality.
“I think this is such a unique way of using a resource usually thought of as a negative and turning it into an asset,” said Robin Coger, dean of the College of Engineering that includes the composite materials program.
The researchers beg to differ with the popular perception that coal ash is a nuisance byproduct with few beneficial qualities and that it must, as many environmentalists urge, be buried in lined landfills for perpetuity.
“This,” Shivakumar said, “is a valuable material.”
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