Coal ash commonly used in engineering projects

Nov 22 - Sanford Herald (NC)

 

With Duke Energy planning to transfer up to 8 million tons of coal ash to Sanford , many Lee County residents wondered aloud at a recent board of commissioners meeting about the ways the material could be reused.

According to Duke Energy , the company recycled or reused about 67 percent of coal ash produced in 2013, mostly in engineered structural fills and concrete projects.

Coal ash comes in two different forms -- fly ash and bottom ash. Fly ash comes is a fine powder, which can be used in concrete projects like roads, buildings and bridges, and bottom ash can be used to replace sand or gravel for concrete blocks and pipe.

Duke Energy Communications Specialist Jennifer Jabon said the coal ash transported to the Sanford mine from the Riverbend and Sutton site will include both fly ash and bottom ash; both materials can be used for engineered structural fills like leveling work areas, filling in excavations and creating embankments.

Steve Abbott , North Carolina Department of Transportation communications supervisor, said more than 19,500 tons of fly ash was used in 2013 for projects that were contracted out. He said from NCDOT's experience, fly ash is safe when it is encapsulated in the concrete and provides multiple benefits.

"It's basically sealed so it saves us money," he said. "It's not a health risk at all, and it helps extend the lives of the bridges."

Abbott said the Federal Highway Administration encourages the use of fly ash in its concrete mixes because it provides a "more durable, less porous concrete," and the NCDOT requires the use of fly ash in all bridge decks from Raleigh and west of Raleigh .

"These are areas that must treat bridge decks more often with salt due to frozen precipitation," he said. "The particles of the fly ash are finer than cement particles and fill any holes, or voids, in the concrete, which helps protect the bridge decks from the salt."

Abbott said fly ash would be used in the upcoming Bonner Bridge and Pea Island Bridge projects because of the protection it provides from salt water. He said fly ash also is used on some roadway projects when certain stone is used because it helps provide a better bond.

According to the American Road and Transportation Builders Association , adding fly ash to concrete mixtures makes roads last longer and saves money because fly ash is estimated to cost 17 percent less than Portland cement, which is normally used in concrete production. Using fly ash also would replace some of the 1.6 billion tons of cement produced every year, which accounts for 7 percent of global carbon dioxide emissions, according to the organization.

Other transportation project uses of fly ash include use as filler in asphalt production, as a road base and as a soil modifier.

Scott Sewell , chief operating officer of Charah , a Kentucky -based power plant support services company working with Duke Energy on the project, said Charah uses the best practices, materials and technology for structural fill projects like the one in Sanford to provide assurances that its projects are safe and will protect the environment and public health.

He said in the Sanford project, the ash will be encapsulated in a series of synthetic liners with the top and bottom impermeable liners being heat welded with a layer of soil on top.

"This project will meet all state and federal standards for a structural fill, including groundwater monitoring and reporting, and will comply with the requirements set forth in the North Carolina Coal Ash Management Act," he said.

Despite assurances that the coal ash will be well contained, Lee County residents have expressed concerns about potential groundwater and air contamination.

Jabon said about 90 percent of fly ash contained common elements, such as silicon, iron and calcium, with less than 1 percent containing arsenic, selenium or mercury.

According to Duke Energy , while many of these trace elements also are found in foods and beverages, such as flour, juice and chicken, the company also performs regular toxicity tests, and more than 99 percent of the tests indicate the absence of toxicity.

"We are committed to the safe, economic beneficial reuse of coal ash," Jabon said.

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