Alex, thanks for your question.

What is Fly Ash?

Fly ash is the solid residue derived from incineration processes and can be used as a substitute for Portland cement in concrete (and therefore a preconsumer recycled material), according to the LEED BD+C Reference Guide. Materials & Resources (MR) credit 4, Recycled Materials, cites fly ash as a supplementary cementitious material to be used in concrete and applicable for this credit. So you’re correct, fly ash is still used in the construction of green buildings (see Fly Ash Bricks).

And utilizing a material that would otherwise be considered manufacturing waste as a filler product for cement is obviously a sustainable design principle because it reduces waste.

Fly Ash on 60 Minutes

Now the 60 minutes program you’re referring to is, I assume, the story from October when 60 minutes correspondent Lesley Stahl interviewed Jim Roewer, one of the top lobbyists for the power industry. It was during this interview that Stahl learned about the “Kingston spill” in which a retention pool of a coal ash slurry failed and allowed a billion gallons to dump into the Emory River in Kingston, TN.

Coal ash contains many toxic metals, including arsenic, lead, mercury, selenium, cadmium and other toxic metals. Coal ash, if left unchecked, can leak into ground water and be extremely hazardous to breathe. So there’s no doubt this isn’t something most of us would feel comfortable having hang around our neighborhood.

Fly ash is one of the two residues generated in the combustion of coal (the other being bottom ash). Depending on the composition of the coal, components of fly ash can vary but typically fly ash includes substantial amounts of silicon dioxide and calcium oxide, making it an ideal additive to cementous processes. During the combustion of coal, fly ash is entrained in flue gases and was previously allowed to disperse into the atmosphere unchecked. Current environmental laws have significantly reduced fly ash emissions. As a result, the fly ash must be recycled or disposed of in landfills or ash ponds.

So while the 60 Minutes episode concentrated on coal ash (of which fly ash is one component of), the inclusion of fly ash alone in green building projects can – and is – still being debated among those in the green building community. Do the potentially hazardous elements of fly ash outweigh the benefits of utilizing it as a recycled material? And if the answer is yes, than what’s to be done with the fly ash? The bottom line is that much of the energy generated in the U.S. is from coal-powered plants, and that doesn’t look like it’s going to change in the near future and something has to be done with the waste. Again, I don’t have a definite black and white answer on this myself, so I’ll just leave things in the gray area for now (no pun intended) and allow you to sort out the decision for yourself.

Related Advice:

• Fly Ash Brick: What's the Best Way to Manufacture it?



• Fly Ash: Safer than Portland Cement?