Coal ash jumped into the headlines this year when a pond maintained by Duke Energy spilled into the Dan River in North Carolina. It fouled the water supply, and brought national scrutiny to what sounded like a huge, and largely unregulated source of toxic waste.
The same week, to much less fanfare, the Environmental Protection Agency announced that it endorsed the practice of using coal ash to make concrete. As it turns out, environmentalists largely agree.
Engineers tend to be advocates. Steve Fleming is technical director for Chicago-based Prairie Materials, a large concrete supplier. And he is a fan of coal ash.
"We add it to our concrete to help with its performance," he says. "Both in its plastic state"— that is, when it’s wet, since coal ash makes concrete easier to work with — "and most important from my point of view, it helps the long-term performance of the concrete as well. It actually increases the strength, and makes the concrete last longer."
As an engineer, Fleming has long appreciated coal ash’s benefits. It took customers longer.
"When I first started, 18-19 years ago, I had a lot of customers who thought that fly-ash was not good," he says. "They said, 'It’s a waste product, and why are you putting it in my concrete?' Now, we have contractors who are requesting fly ash. If we ship them a straight cement mix, they’ll complain."
There are environmental advantages, too. Coal ash has toxins in it: arsenic, lead, mercury. Locking that stuff up in concrete seems safer than letting it sit in landfills or ponds that can contaminate groundwater.
The EPA endorsed using coal ash in concrete after comparing it to the toxins in Portland cement. Turns out, Portland cement is more toxic.
Portland cement is also much worse for the environment. "Portland cement production is one of the major greenhouse-gas sources worldwide," says Craig Benson, a professor of environmental engineering at the University of Wisconsin.
He explains: Making Portland cement involves applying heat to limestone — which is made of calcium, oxygen and carbon — to get lime: calcium and oxygen.
"That process liberates a lot of carbon dioxide," he says. "That goes right up in the atmosphere."
There are more benefits: Using coal ash means not using resources to dig up limestone. Or burning fuel to heat it up. And because fly ash makes concrete last longer, it also means not replacing the concrete as often.
All of which also means saving money. Benson did a study on that. "It was really remarkable," he says. "Just the economic impact is about $5 billion to our economy."
Lisa Evans, a lawyer for Earthjustice, is reluctant to declare herself a fan of using coal ash for concrete. She’d rather we stop burning coal. Failing that, however, she thinks concrete is a good idea.
"I think characterizing it as a 'win' would be accurate," she says. "If you’re going to make coal ash in the first place, locking it up in concrete is preferable to a lot of the other ways we use or dispose of coal ash."
But the consensus isn’t perfect. The EPA is currently deciding between two alternatives for regulating coal ash. Evans favors one that would regulate coal ash as hazardous waste, except for designated "beneficial re-uses" like concrete.
That proposal worries John Ward, a spokesman for the coal-ash recycling industry, who runs a group called Citizens for Recycling First. He thinks the exception would just cause confusion. "How can you call something hazardous on the property of the people who made it," he says, "and expect you to want to use it in your house?"
He thinks that potential confusion could make utilities reluctant to allow recyclers to take coal ash at all.