Fly ash imparts some beneficial properties to concrete, including reduced permeability, better finishability, and a reduction in the potential for alkali-silica reactivity. And, of course, it reduces the cement consumption and therefore makes the concrete more acceptable from a sustainability viewpoint. But I’ve wondered many times whether there is enough fly ash if all concrete was to use higher percentages. It was only a few years ago that there were ash shortages in some parts of the country.
But a recent article in Ash at Work, the magazine of the American Coal Ash Association provides a definitive answer. The author, Danny Gray executive vice president of Charah Solutions, looking at where the ash industry will go over the next 50 years, states that even with the gradual reduction in the number of coal-fired plants, there is plenty of fly ash today and well into the future. “While the supply of fly ash produced from traditional power plants will moderate as a result of plant closings, adequate levels of fly ash will continue to be available to meet market needs.”
One factor that makes this true is that ash disposal has become a very controversial issue for power generators. Pollution control agencies and environmental groups are putting increased pressure on power producers to find beneficial uses for ash instead of disposal and concrete is the best option. Some power plants are even altering the way they burn coal in order to produce higher quality ash.
Fly ash in the future might also be mined from older impoundments and landfills and processed, what’s called beneficiation, to make it more compatible to use in concrete. As the demand increases for use in concrete, and as the public requires removal of the material from leaking disposal sites, ash that once could not meet the specifications for use in concrete will become acceptable. “Use of alternative SCMs will include more blends with natural pozzolans, GGBFS, ground glass, and possibly imported fly ash,” writes Gray.
Of course, this also means that fly ash will become more expensive and begin to approach the price of portland cement. But everything comes with a price tag and protecting the planet gets more expensive and more imperative all the time.