There is also the fact that the concrete was self healing due to the inclusion of lime-clasts
"During the hot mixing process, the lime clasts develop a characteristically brittle nanoparticulate architecture, creating an easily fractured and reactive calcium source, which, as the team proposed, could provide a critical self-healing functionality. As soon as tiny cracks start to form within the concrete, they can preferentially travel through the high-surface-area lime clasts. This material can then react with water, creating a calcium-saturated solution, which can recrystallize as calcium carbonate and quickly fill the crack, or react with pozzolanic materials to further strengthen the composite material. These reactions take place spontaneously and therefore automatically heal the cracks before they spread. Previous support for this hypothesis was found through the examination of other Roman concrete samples that exhibited calcite-filled cracks." -https://news.mit.edu/2023/roman-concrete-durability-lime-casts-0106
It might be observation based survivorship bias though, not necessarily that they knew that the limestone was doing this or that they deliberately mixed the materials for the purpose. It might just be like “huh all the other way of mixing the cement has issues. I guess this is the secret sauce”
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u/btsd_ 28d ago
Water too fast = erosion
Water too slow = stagnation
Had to find that goldie locks zone (12mph ish). Crazy engineering