CHARLOTTE, N.C. -- You’ve heard one man’s trash is another man’s treasure?
Well, Duke Energy’s 100 million tons of coal ash is a valuable source of raw material, according to environmental engineers at the University of North Carolina, Charlotte.
Engineers envision the prospect of “mining” coal ash dumps as a cleaner, greener alternative to the mining and production of Portland cement.
Portland cement is a key ingredient in making concrete, produced by mining limestone or similar stone and heating it in bulk to high temperatures to change its chemical makeup – a carbon intensive process.
“So if we can start thinking of the [coal] ash ponds as a quarry we can use to produce the cement that we use to produce concrete for our infrastructure, that would be a huge boon,” said Brett Tempest, assistant professor of civil and environmental engineering at UNCC.
“Portland cement production is one of the most carbon intensive processes we have in the world.”
Tempest and his colleagues are experimenting with concrete made with no Portland cement at all, but with 25-percent unprocessed coal ash coupled with gravel, sand and water. The resulting “geopolymer concrete” can be used as a building material for bridge decks, beams, girders and walls. Dr. Tempest describes the geopolymer as not so much of a discovery, but as a rediscovery of an ancient process.
“There’s some evidence the pyramids at Giza are made out of exactly this material.”
Precast sections of concrete to produce roads might even cut the time it takes to complete resurfacing or road construction on major interstates like I-85 or 485. Are you hearing this commuters? Clean up coal ash dumps and get rid of orange barrels and long commutes? Where do we sign?
Not so fast.
“These things can’t be done immediately,” said Dr. John E. Daniels, the interim chair of UNCC’s department of civil and environmental engineering.
But, he says, “Maybe there are a lot more things we can do other than storing it in a pond or putting it in a landfill.”
Dr. Daniels says that the economics of coal ash shifted in North Carolina after the Dan River spill, and some alternatives for coal ash may now be more viable.
“There's a number of ways we can use ash in light of the new economic reality and realities of liability as well,” he said.
So alternatives for coal ash are not limited to taking it out of one hole in the ground and trucking it to be dumped in another.
The options will vary depending on location according to Dr. Daniels – but in the years it takes to move 22 million tons of coal ash from the Marshall Steam Station on Lake Norman (Duke’s largest) new alternatives may become economically viable.