Even at (especially at?) Greenbuild, you can find greenwashing. 'Course, that's a subjective term, and some of it is more egregious than others. But one of the first booths I happened upon Wednesday morning was promoting the coal industry. As I've said before, is there anyone, anywhere, who favors coal in any form expect "left in the ground," apart from people who are economically tied to it? These folks — perfectly nice folks, who have kids to feed and mortgages to pay, etc. — weren't promoting coal burning, of course, they were touting fly ash, a byproduct that can be added in the the formulation of concrete. There's definitely a valid case to be made for fly ash. What it displaces is Portland cement, whose production is incredibly energy intense. (Little-known fact: Not only is it incredibly energy intense, but the process is designed to separate carbon from limestone, making it a double-negative.) The concrete needs less water, and what is created is less permeable. And, the fly ash doesn't end up dumped. But still. You only get fly ash if you burn coal. No one would burn coal just to create the ash, so the only way to get this great additive is to foul the atmosphere. Just two tabletops down from the fly ash crowd was the slag crowd, and this was a new one for me. Slag, many people will already know, is a byproduct of steel-making, and it's comparable, though different, to fly ash. My two new slag buddies told me you can use up to 90 percent slag as a cement substitute, although only in certain applications, because it cools much more slowly. It's also stronger with slag, the said. One important difference between slag and fly ash is that though steel-making is still a dirty, energy-intense industrial process, it will still be around long after we've moved beyond coal power. Second little-known fact: The only other significant industrial byproduct used in concrete is silica fume. My two slag buddies told me that.