I'd rather hope that fly ash from burning fossil fuels such as coal, generating greenhouse gases and prompting global warming, rapidly becomes a thing of the past.

Great! How will people buy it? Will it be mixed in with cement, or supplied in separate bags? How much will be needed per Cubic Metre of concrete, how does it effect the strength of the set concrete and most importantly, what will it cost? Without answers to these and more questions, it's only of academic interest.

Right on CarolynFarstrider. I would have thought that something like pumice would also do the trick. it is readily available because there is a whole island of the stuff floating in the pacific ocean. Better still why don't we use tufa as the Romans, the inventors of concrete, did.

While fly ash will become increasingly scarce in Canada and the US, it'll be available from China, India, etc for many years to come.

I would think that crushed cement blocks would work as well.

I would hope that, rather than using fresh new fly ash, from an operating coal fire power plant, this process could use old stockpiled or landfilled fly ash, perhaps from some waste ponds. I suspect that there is billions cubic years of the stuff laying around, a century supply or more. As for China and India, making the fly ash a useful product will perhaps make them try harder to capture it. I suspect that fly ash in those countries now mostly just ... flies.

How come nobody ever mentions hempcrete which has tons of advantages over most concrete; number one being it filters the air from toxins, it's lighter, hemp is a weed that grows anywhere, and it's incredibly strong!

@ Signguy

While hempcrete has many positive qualities, its compressive strength is only 1/20 of residential grade concrete, which means it cannot be used to build foundations or load-bearing walls, and that limits its suitability for many construction purposes.

Have the spheres been purified? We don't want all that radioactivity and heavy metals in our concrete. Hopefully, fly ash will soon diminish in the environment. Coal is cheap, and isn't worth it.

Fly and restricted ashes are pooled for another 50 years before any digging need be done to access it. Meanwhile there is a ton of testing to be done! The people looking for 'bags' of it to be a practical thing can take my laugh, because there's nothing to do but file the DOE application paperwork, know a source (power plant, shipper using ash as dunnage, you drew it we got it,) and have a kiln of the type described. For engineers, it's a matter of taking a safety factor of 18 and considering hitting 10 (and buying instruments for your driver, who shouldn't be picking up lanthanide slag-ash unless you totes planned it. Talk about a hard case for automated driver tech!)
Looking forward to those hempcrete citations pointing out firmer, less shaggy points of performance.

>has that ash been purified?
No, just separated by DOE hazard class. It's kind of the point that the stuff is stuck in a bridge, footing, arch or caisson 120 years. Otherwise it's cake fill for mines, refined for urban cement, etc.