As far as uses for power plant coal ash goes, the "fly ash" is collected and I believe that is what is used in concrete blocks. Fly ash is what is caught and kept out of the smokestack emissions.
As far as the "clinker".... the heavier stuff that falls out of the bottom of the furnace... at the plant I delivered coal to, it was "pumped" out into a big settling basin a little ways from the plant. The roads in the plant complex were covered with it. Nice smooth roads, for sure.

They shipped fly ash out via covered hopper. The clinker... I never saw it going anywhere. It was black like coal. The fly ash was a light tan color, the consistency of baby powder.

An important tip to remember is that many cement plants are still consumers of coal. I closely watch two cement plants in Arizona, both located on the same short line which also derives a lot of passenger excursion business. They bring in coal to burn as a heat source for heating the limestone they crush as one of the base ingredients for their cement, and the ash from the coal becomes another feed into the cement production. Some of the inbound cars are also fly ash from utilities as well. I start to wonder how these plants will survive without power plants sending them ash............

Clinker at many plants goes into a clinker grinder and is then I believe is sold off as "black beauty" blasting abrasive.

I have a feeling most of the regulations for coal ash are really written for a different type of ash than what you're going to see coming out of a steam locomotive. I think most of it is fly ash that the regulations are handling and not the lumpy stuff found in an ash pan of a locomotive.
A while ago TVA had a big pond of the stuff burst and cause massive issues that likely led to a lot of new regulations on handling power plant ash. But keep in mind that stuff is nothing like what's in a locomotive. https://en.wikipedia.org/wiki/Kingston_ ... urry_spill

One of the other interesting byproducts of a modern power plant that most people don't know of is gypsum wallboard. They invented a new process where they spray I believe calcium (carbonate?) into the flue gas emissions which soaks up the sulfur and creates calcium sulfate which they use to make drywall. I don't know if they're also able to mix in some of the fly ash too into the drywall. I recall being at, at least one of those facilities being installed on a power plant out in Nebraska, and think I recall seeing another similar facility around southern Illinois or maybe Missouri and I know a lot more were going all around the country around the 2008 time frame.

The plant had a massive rail yard just to service the drywall plant in addition to all the train cars coming in with coal. So next time you're at Home Depot and looking at all that drywall just think that it most likely is a big old pile of industrial waste!

Ever think that humans might just be God's effort to make a product out of 'protoplasm waste'?

"Soylent Green" IS PEOPLE!!!!