Concrete is essentially everywhere for a reason. It's relatively easy to make and the materials that go into it are pretty common, so no one is really bereft of concrete resources. And it's useful - it can handle a lot of force squashing it, resists fire, can be poured into a mold, etc.
It's also environmentally damaging - the creation of concrete every year puts out 7% of the world's annual CO2 emissions, which is an absolutely huge amount - for comparison, every car in the world is about 35% (though they both pale in comparison with burning coal for energy). Much of the world's concrete is used by China for things like the Three Gorges Dam - which is a solid concrete structure with a span of 2,335 meters (a little less than 1.5 miles). Holy crap, right?
But concrete's environmental damage is a little strange, because according to this paper, we could make a lighter-but-still-strong concrete out of fly ash - one of the left overs from the coal industry. Fly ash could replace cement, which is the main source of carbon dioxide emissions in the concrete-making process, to not only lower carbon dioxide emissions but also remove a source of toxic waste that was loudly demonstrated to the world a few months ago. Super neat, right?
I don't know what the catch is. I'd like to think that it's primarily because most industrial companies are still fixated on a linear production model (raw materials make the product, the product is thrown away at the end) rather than the much more environmentally-friendly, common sense circular cycle, where industrial outputs ranging from by-products like fly ash to waste heat are used as inputs for another nearby industry.
The point being, if you're not really going out of your way to look into circular supply systems or recycling materials - and power plants aren't going out of their way to advertise their ponds and piles of semi-toxic fly ash and coal remnants - then it stands to reason that fly ash recycling isn't done very much. That's my gut feeling, but I honestly don't know. It could also be purity of materials.
Even though my own analysis is a little hamstrung by my lack of materials engineering knowledge, I bring up the subject because it's interesting, and because I like the idea of a circular production model. Nature, after all, heartily embraces a circular cycles - including your own body. Fun fact: it's very likely that not a single molecule in you - including brain cells - is more than nine years old. And if anything has stood the test of time, it's biological life - organisms have survived and flourished on this Earth for over three billion years. Even animals and plants as we know them have been around for many, many times the tenure of the human race.
Just sayin' that we could learn from nature, that's all.
Also: without any further evidence of negatives (they do recycle fly ash, just not at any significant level), fly ash concrete sounds like the way to go.