The Charlotte region’s bounty of Duke Energy coal ash leaves Henry Batten, president of the city’s largest ready-mix concrete company, with the richest of ironies.
Concrete Supply Co., whose product built the Duke Energy Center, has to import ash, a concrete ingredient, from South Carolina and other states.
“I don’t know why they haven’t made the decision to sell more ash,” Batten said. “It’s a material that’s in demand, and we need it.”
A bill that breezed through N.C. Senate committees last week orders Duke, after a Feb. 2 ash spill into the Dan River, to close its 33 ash ponds within 15 years. But legislators struggled with another question that Batten’s problem illustrates: What to do with 102 million tons of coal ash?
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“The plain fact is we just don’t have enough room to bury it all,” said Sen. Tom Apodaca, the Hendersonville Republican guiding the bill.
Duke says it’s eager to sell the material and is evaluating three or four new construction products that could be made with ash. But the scale of the disposal problem leads the company back to old solutions that seem unlikely to recycle much of its stockpile.
“It’s got to be a pretty large use, like concrete,” said Tony Mathis, Duke’s byproducts manager. “Economics is the primary driver.”
Duke sells about a quarter of the 1.8 million tons of ash it generates in the state each year to concrete makers. But that market is limited, and ash from some plants isn’t usable because it contains too much carbon, which makes weak concrete.
The Environmental Protection Agency endorses ash-made concrete, which is strong and durable. The potentially toxic metals in ash that could contaminate water are locked inside. Ash also replaces Portland cement, a concrete ingredient that releases massive amounts of planet-warming greenhouse gases as it is made.
The Duke coal plants closest to Charlotte, Allen and Marshall, generated more than 500,000 tons of ash in 2012-13, but sold less than 10 percent of it for concrete and other uses.
Duke says it might build a processing plant at the Marshall Steam Station, on Lake Norman, to reduce the carbon content in its ash and make it usable to buyers like Batten. Carbon-reduction is already done at Duke’s Roxboro plant.
The Marshall plant would process 300,000 tons of ash a year. Added to the 400,000 tons Duke already sells to concrete makers, it would roughly equal annual statewide demand by the concrete industry.
But that solution doesn’t eat into Duke’s backlog of pond ash. And it’s a step behind the ash-disposal pace of smaller utilities in South Carolina.
S.C. Electric & Gas is emptying its ponds and recycles 90 percent of its ash. The state-owned utility Santee Cooper expects to recycle all 11 million tons of fly ash from its seven ponds into concrete products.
“If this had been easy to do we would all have been doing this a long time ago,” said Santee Cooper spokeswoman Mollie Gore. “Why would you choose to maintain something on-site when you can turn it into a business opportunity?”
A Lexington, S.C., company, the SEFA Group, will reprocess 400,000 tons of ash a year at Santee Cooper’s Winyah plant with a patented technology that makes ash concrete-ready.
SEFA president Thomas Hendrix said larger utilities like Duke will have to combine ash processing with burying ash in lined landfills.
“We’re part of the solution, a good part of the solution, because no one questions that the best place for ash is entombed in concrete,” he said. “If we could pick up and do 102 million tons, I’d be tickled to death.”
Duke’s ‘worst possibility’
Duke uses 40 percent of the ash it produces as structural fill, tamped into place to level the ground at building sites.
The company wants to do more large structural fills, like the one underway at Asheville’s airport. The Senate bill requires that large fills have liners to protect groundwater, a step Duke says it has committed to take, but does not mandate them in small fills.
“The worst possibility is what the Senate bill allows, that is putting it in unlined structural fills,” said Frank Holleman of the Southern Environmental Law Center, which has sued Duke on behalf of advocacy groups.
The Senate’s plan allows Duke to drain the water from low-risk ponds and cap the ash but leave it in place. The measure calls for ash from higher-risk ponds to be buried in lined landfills.
Duke: We’ll sell ash
Some ash experts say the Dan River spill, which prompted both high-priority legislation and a federal grand jury investigation, should prompt interest into new uses for ash.
“What was uneconomical the day before the Dan River spill might be economical now,” said Brett Tempest, a UNC Charlotte assistant professor of civil and environmental engineering. “My concern is that we might re-landfill this ash before we fully explore options for reusing it.”
Tempest researches geopolymer concrete, which entirely replaces Portland cement with fly ash. The product strengthens in days instead of weeks or months, compared to traditional concrete. Tests show it’s more durable and less porous, making it an ideal material for projects such as coastal bridges that are pounded by saltwater.
The Senate legislation orders the N.C. Department of Transportation to assess increased use of ash-made concrete in road building. Each ten cubic yards of concrete would consume a ton of ash, the concrete industry says.
“You’d take this issue of ash off the table,” said Batten, whose company doesn’t work on roads. “They’d never put another pound in the ground.”
DOT requires ash in concrete for bridge projects from Raleigh westward because it resists road salt. But that amounted to only 19,500 tons of ash in its projects last year.
Tempest’s UNCC engineering colleague, John Daniels, works with chemicals called organosilanes that can make ash repel water. Rain-X for dirt, as Daniels calls it, could prevent leaching of metals in ash to groundwater.
“There’s no shortage of effort to create new products,” Daniels said. But viable applications will have to use large amounts of ash, he added.
Researchers at N.C. A&T University have come up with a strong, lightweight ash composite that resists water, fire and corrosion, according to news reports. Duke University scientists are working on extracting elements called rare earth metals, which are prized for use in electronic devices, from ash.
Duke Energy says it’s fielded dozens of pitches for new uses.
“We’re not looking to not sell the ash,” Mathis said. “We’re looking for opportunities to sell the ash.”