However, as coal plants have shut down across the U.S., 21 of which in the last two decades, fly ash has become harder to source. Coal, which once reigned supreme by generating more than half of the country’s electricity, has seen its dominance steadily fade with the rise of cleaner energy sources, now accounting for just 15 percent of the power grid.
However, the resulting shortage has forced concrete makers to reduce fly ash content to around 8 percent, substituting it with more cement, which is not only pricier, but more polluting. That shift not only compromises the strength and longevity of concrete but also raises its carbon emissions.