There’s undwater concrete landmarks from Roman times. They must have known how to make good concrete. Probably the blood.
I’ve read much of a doc analyzing Roman concrete. Evidently it is better than much of ours. Evidently it has to do in large part to some of the type of particles involved as well as the cement mix. But it was barely on the edge of my knowledge so I wouldn’t swear to it. The bottom line was, we now know how to reproduce it when we didn’t for a long time.