I was referring to the knowledge of how to make long lasting concrete, not necessarily specifically how the Romans did it, but I guess I could've been clearer.
The answer is still no, we don't know how to make long lasting concrete with modern techniques either apparently. Hence the research.
Especially steel-reinforced concrete, the lifespan is only 50-100 years. The only exceptions are massive structures like dams that will probably last a couple millennia.
Right but the thing is neither did the Romans. The only reason roman concrete lasted so long is it didn't use steel reinforcement. All of the structures we have from them are carefully designed to only use compression.
