Hey Otto
I admitt i'm most curious what you intend to build

with it.
There any many substances with pozzolanic properties.
Some are wasteproducts that are much safer than coal ash and such. Coal ash contains heavy metals that might leach out or are unsafe during processing. To be avoided.
If you have no safe, legal and environmentally sound access to natural pozzolanes you could use ceramic waste products. The following links are a bit heavy to read but you could use the key words and key authors to locate information relevant to you. Are you familiar with google scholar? You could find this kind of publications in the library of technical and/or science colleges/universities.
http://www.ipcsit.com/vol28/025-CoimbatoreConferences-T003.pdf
http://waset.org/publications/9997569/a-review-on-the-usage-of-ceramic-wastes-in-concrete-production
http://www.ijettjournal.org/volume-9/number-6/IJETT-V9P253.pdf
I recommend that you don't use anything with fancy colouring (reds, yellows, greens and blues). Those colors are typically based on heavy metal pigments. For an environmental cleanup
project some years ago we found a cement plant liked bathroom ceramics (ceramic toilets, white ceramic tiles to name some) best because they usually contain few heavy metals in Europe. I DO NOT KNOW for sure this is also true in the us. The EPA or industrial associations
should have info on that.
If you use the stuff beware of the machinery requirements. Heavy duty crushers to produce the powder are just one thing. Dust prevention another.
Personal safety measures are also an issue, dust masks, cutproof gloves & protective eyewear (ceramic shards are SHARP) etc......
BTW it is a very good idea to use ceramics. They usually end up in a landfill, cost lots of
energy to mine, produce and dump. Re-ussing should save a lot of CO2.
So that's my 2cents.
Good luck
Erwin