My limited understanding trying to find out more about pozzolanic concrete (planning for my house extension in about a handful of years) is that those who study

My limited understanding trying to find out more about pozzolanic concrete (planning for my house extension in about a handful of years) is that those who study this stuff believe it stood up by itself like when used in the aqueducts with plenty of strength and durability, without constant immersion in salt water. Don't know if someone has drilled a core sample into those aqueducts to try to determine if salt water was used to mix that Roman concrete, though; would be interesting to find out. What drew attention to it was that modern concrete immersed in seawater, even without rebar, doesn't appear to have the same durability as ancient Roman concrete. Don't know how much of this is attributable to survivorship bias, though; would be unfortunate if all this attention turns out to be over a tiny fraction of a percent of ruins that happened to survive.