Good News for Fly Ash

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by Bill Palmer

fly ash

Fly ash is a very fine-particulate material that looks and feels like talcum powder and can be a tan to gray color, depending on its source. It is classified as a pozzolan and with its high silica content is used by concrete producers as a component in the range of 10 to 25% of the cementitious portion of concrete mixtures (iv). Fly ash forms calcium silica hydrate (cementitious material) in addition to that produced by hydration of portland cement.

How many of you believe that we are running out of high quality fly ash? According to Rafic Minkara, president of Headwaters Resources, none of us should raise our hand because he insists there is plenty. But he also notes that the use of fly ash in concrete has been declining slightly, at least in part due to uncertainty over whether the Environmental Protection Agency will declare fly ash a hazardous waste. Perhaps that will change though following a recent report from the U.S. Environmental Protection Agency that states very directly that fly ash used in concrete is safe—better than safe since it consumes a byproduct that would otherwise end up in a landfill and reduces cement manufacturing which generates greenhouse gases.

“Environmental releases of constituents of potential concern from coal combustion residuals fly ash concrete and FGD gypsum wallboard during use by the consumer are comparable to or lower than those from analogous non-CCR products, or are at or below relevant regulatory and health-based benchmarks for human and ecological receptors,” the EPA said in its report. “EPA supports the beneficial use of coal fly ash in concrete and FGD gypsum in wallboard.” Click here to read the full report.

This is a significant endorsement from the EPA. Thanks to the leadership of the American Coal Ash Association and its executive director Tom Adams, this should dissipate the cloud that has been hanging over fly ash for the last several years. From the concrete industry’s viewpoint, this is much more than simply an environmental coup; more important to us is the improvement fly ash imparts to concrete properties. Even a small percentage of cement replacement results in concrete with lower permeability, less susceptibility to alkali-silica reactivity, lower heat of hydration, and a smaller carbon footprint. EPA has committed to finalizing the fly ash rules by the end of 2014 and it looks likely now that we will see more fly ash use in the coming years.

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