Researchers at Missouri University of Science and Technology believe that increasing the amount of fly ash in concrete up to 70 percent can result in excellent concrete in terms of both strength and durability. And it could prevent millions of tons of the waste product from ending up in landfills.
“Traditional specifications limit the amount of fly ash to 35 or 40 percent cement replacement,” says Jeffery Volz, assistant professor of civil, architectural and environmental engineering at Missouri S&T in a university press release. “Recent studies have shown that higher cement replacement percentages – even up to 70 percent – can result in excellent concrete in terms of both strength and durability.”
Fly ash is commonly used as a concrete additive, but increasing the amount used will cut CO2 emissions, but it also brings its own set of challenges.
“Construction workers might refuse to work with it,” Volz says. “And there’s also the issue of at what point is it not a hazardous material when used for beneficial reuse. Is it once it is added to the ready mix truck, which means it is a hazardous waste in the silo at the ready mix plant? Or is it once the concrete hardens, which means it’s a hazardous waste up to that point?”
The EPA supports adding fly ash to concrete, however the agency is considering designating fly ash as a hazardous waste. And although it has been proven that adding fly ash to concrete renders is chemically altered and unable to leach toxic material, a hazardous waste label would make it more difficult to garner wide acceptance.
Volz is working with the Missouri Department of Transportation to develop guidelines for the proper application of high-volume fly ash concrete in infrastructure components.