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: Indigenous Terror 
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
@someonetellmetosleep there's a ton of interesting research on net-zero or even carbon-negative manufacture of cement. which I think is exciting given that, as you point out, this is currently responsible for 5-8% of our annual carbon emissions
here's a current survey paper covering a huge range of directions that people are exploring: https://www.sciencedirect.com/science/article/pii/S2352710224031462
one that I (not an expert) think is particularly interesting is "carbonation curing", which puts extra CO2 into the cement. that makes it a CO2 storage technique, and also increases the strength and durability of the concrete, which in turn may mean less concrete is needed
another effort I think is neat has discovered that combining the process for recycling concrete with the process for recycling steel allows producing both without new carbon emissions: https://www.eng.cam.ac.uk/news/cambridge-engineers-invent-world-s-first-zero-emissions-cement
@jamey @someonetellmetosleep Cement manufacturers are going to complain that those recipes are more expensive. To which I can only say: imagine how rich you'll be if you figure out how to do it more cheaply.
@someonetellmetosleep And making quicklime produces a lot of CO2 as well.
@someonetellmetosleep I'm glad I'm not the only one.
I almost wrote this rant when I saw the article from a couple years recirculating again.
@someonetellmetosleep I suspect the rust problem could be solved if we just used somewhat more expensive metals for rebar—which is there to provide tension and compress the concrete. As usual, pick any two of cheap, fast, durable.
@cstross you can also reinforce concrete with methods that aren't rebar at all; I've heard that fiberglass reinforcement works pretty well for instance, but iirc it's fairly expensive for the amount of strength it adds relative to steel rebar
@someonetellmetosleep Yeah. It's 100% about cost. This is how we get shitty infrastructure: we try to build it on the cheap.
I was just reading Vitruvius and he’s so specific about how the good concrete is made. He tried! I was wondering if repeated “rediscovery” was what was happening. @someonetellmetosleep
@someonetellmetosleep The fact that the Romans built in a way that used gravity to keep concrete in tension while we often use steel under tension is a huge, massive engineering difference.
That said, we aren't even 150 years into our experience with concrete construction. We are just now learning the cost of failure from cheaply built construction.
Given the suddenness of these failures and consequences, as well as the difficulties in inspection, I'd not be suprised if we start seeing radical changes in design philosophies in the medium term.