[Busy Bee]

Originally Posted by ardecila

Fly ash from coal power plants has many of the same chemical properties as the volcanic ash the Romans used, and it's used in quite a few concrete pours these days.

But there are always trade-offs; in our cold climate, concrete actually needs air pockets inside to absorb the expansion of ice crystals from moisture in cold weather. It's a bad thing for it to be too dense. Pozzolanic concrete mixes (like Roman concrete or concrete with fly ash) are denser than traditional Portland cement mixes, and they could have bad spalling problems if exposed to freeze/thaw cycles. That's obviously not a problem in Italy...

Very interesting.