Coal power plants across the US are closing, and concrete producers may need to find a replacement for the coal waste product of fly ash. Experts say ground glass pozzolans could serve as a replacement, but the process for recycling glass poses challenges.



In the spring of 2020 New York changed forever, and not just because of COVID. On March 14, 2020, the last coal power plant in New York State closed in Niagara County, marking a permanent shift away from fossil fuel power and towards more sustainable options.
New York is not the first state to move away from coal, and it will not be the last.

This quiet event is having ripple effects in unexpected ways, such as putting a nail in the coffin of the states’ concrete infrastructure supply chain. Coal power plants not only produce electrical power but also fly ash, a by-product of coal combustion that is used in concrete every day.

The concrete industry first adopted fly ash in the 1920s as a way to lower costs and improve the strength and longevity of the concrete. It has since been incorporated into most states’ DOT standards. It is a required part of concrete mix designs due to its ability to enhance the strength and durability of critical structures such as bridges.

Now, due to extensive plant closures, this required material is becoming impossible to source. By the end of 2027, most of the northeastern and western states will have essentially no locally produced fly ash for their concrete infrastructure.

Slag is a by-product of steel foundries that also has been used in concrete for decades. Fly ash (in some circumstances) can be traded out for slag, offering a potential solution for some infrastructure projects. However, steel foundries in the U.S. have been closing since the rise of Chinese steel manufacturing in the 1980s.

In 2021 the United States Geological Survey (USGS) reported: “during 2020, domestic GGBFS [slag] remained in limited supply because granulation cooling was available at only two active U.S. blast furnaces.” This means there are only two places in the country that produce slag; the rest of the U.S. supply is supplemented by countries that have ample steel production.