roman concrete being "rediscovered" for the 17th time is beginning to become a pet peeve for me, especially now that I've actually learned about the real history of roman concrete and how at literally no point in history between then and now has the recipe ever actually been lost. like we've known the recipe for it all along. we didn't always understand the mechanism behind its strength, but we already figured the fundamentals of it out decades ago, not like last year

[edit: I should also have mentioned the "self-healing" thing; roman concrete can withstand minor cracking and recover some of its strength over time, in the presence of water. it basically redissolves slightly and then fuses together due to having, essentially, what function as unactivated cement inclusions. it's not just that it's strong enough to last 2000 years, it has other significant properties that give it longevity. still, I first heard about the quicklime thing years ago, and afaik it wasn't actually a properly new discovery even then. and you can't combine the self-healing with rebar, so it has to be unreinforced]

roman concrete is just expensive and requires specific materials only found on the italian peninsula, and basically nobody is building roman-style permanent monumental structures (and most failures in concrete buildings are actually caused by rust, the concrete could last much longer if used by itself and in compression-only strain) so people use portland cement instead.

portland cement is extremely cheap and works well enough and usually already lasts longer than the rest of the building, and its properties are easily controlled with additives. also, roman concrete takes way longer to cure and become fully load-bearing than portland cement, and unreinforced concrete structures are massive and heavy. plus we can drain an area for underwater construction nowadays, the romans didn't have that option and needed concrete that could cure underwater

of course portland cement is also one of the biggest CO2 emitters so we can't just carry on like this forever, so it's a bit like plastic in that respect: it's a wonder material that we're highly dependent on that if we keep on using will destroy our ecosystem. but tbh I just don't think roman concrete is the solution, at least for 95%+ of our current concrete use