Can we duplicate roman concrete even now? Last I heard, it was a matter of debate. But I also remember reading, that the addition of volcanic ash strengthens the concrete immensely, and increases its usefule life by some large factor - so perhaps it has been done.
...and that gets me wondering how Roman concrete was invented. I am picturing some government contractor short on his delivery order - “Well, mix some of this dang ash in it. We got enough of that lying around, what with Vesuvius and all...”
They are very hard; very strong; very stable; very sharp ~ you must wear heavy gloves to handle them.
I think the only mortar for which the recipe was lost during the Early Middle Ages was that for hydraulic or marine cement. It sets up under water.
Every now and then you'll see this on DISCOVER where they're looking over an old fortress or castle in Europe and they mention that the mortar seams are almost invisible.
Actually it wasn’t concrete per se we couldn’t duplicate but concrete that would set up under water. The Romans were able to build many things we couldn’t later duplicate because we had no concrete that would set up under water. It was only quite recently(as time is reckoned)that we were able to make concrete that would set up under water. Al Capone, and other mobsters, used it quite extensively I understand.
I believe so. It's called internally cured concrete.