Roman concrete was made lime cement (calcium dioxide); which cures via carbonation (hardens with carbon oxide). And adding pozzolan to lime makes it hydrolic (hardens with water). Is it surprising that it can still carbonate some? Modern concrete has steel which rust and crack concrete. You can use fiberglass rebar for longevity, or build without rebar even, but that is more costly and and less efficient.
Epoxy coated rebar looked promising for a while, but it's on the way out. Water gets in at cuts and joints. So all field joints have to have field patching.
There is a great comparison. Two piers were built in the 1940s, side by side, one with carbon steel rebar, one with stainless steel rebar.[1] Go look.
[1] https://worldstainless.org/wp-content/uploads/2025/02/ref19_...
[1] https://worldstainless.org/wp-content/uploads/2025/02/ref19_...
I think people are often surprised how little materials cost affects the total cost of a job.
I'm having this argument at work, where I want some more expensive cabling installed in a bunch of offices across Scotland so it doesn't need to be done again in another ten year's time, but "that stuff is so expensive, do we really need it?" is what I'm running up against.
So as it turns out today I'm giving them a breakdown of the cost of the job. Guess what the expensive bits are?
Did you guess "wages for two guys, hotel rooms for two guys, 800 miles of diesel, and a couple of ferry tickets?"
Well, you're way ahead of today's crowd then.
This is what's interesting with AI pricing at the moment - it has gone from "a fraction of the equivalent labour cost" and so people have tried to cut staff, and is moving to "on par with labour cost" and all the calculations change.
But it turns out that's pretty inconvenient; we really like doing dozens of feet of span for highway overpasses, building floors, and everything else. So we put rebar in all the concrete and just acknowledge that that means it has an absolute maximum lifespan of a century or two, and will certainly not last for millennia the way pure concrete in pure compression can.
Looking it up on archive.org shows it was generated this year.
No, steel is better in both ways, ten times over. It's just more expensive, concrete is a "filler" to cheap out construction.
If you think about it, all engineering is about cheaping out things. It's pretty easy to build awesome projects having unlimited budget.
You have a few mistakes here. I’m not trying to demean you, but I’m going to number them just for clarity, as it can get confusing when there are many misunderstandings.
1. You are intending to ask about tension (which the rebar helps with), not traction (the force your tires exert against a road).
2. Tension is not only experienced at the bottom of beams, the location with the most tension will depend on the geometry. For a vertical beam, I think tension will probably be pretty even through the whole beam in most “normal” designs and loading configurations. But it will really depend on the geometry and on the loads being applied.
3. I think when you say concrete beams you’re meaning columns (apologies if I’m wrong about this). Concrete columns are remarkably good at holding up without rebar, because they experience almost exclusively compression! And indeed, ancient Roman designs did not use rebar at all :). It’s certainly possible.
I don’t know if it is the case here, but it is a common mistake for some non-native English speakers. In some languages traction is a false friend.
Maybe this is the clue as to why our concrete crumbles after 100 years: it's not economically efficient to make it last longer?
1) Quicklime/Slakedlime (Calcium Oxide, CaO)
2) Lime (Calcium Hydroxide, CaOH2)
3) Limestone (Calcium Carbonate, CaCO3)
To keep it simple, typically you start with Quicklime (CaO) and after construction you end up with some mix of all three and after hundreds of years, the masonry transitions to mostly Limestone with microscopic traces of the other two. The slow transition of the lime cycle upon exposure of the masonry to both air and water (rain) ends up making the structure "self healing" and "stronger over time".
Fun fact! Lime putty is anti-mold even in humid conditions because upon exposure to moisture, CaOH2 + H20 becomes too basic for mold to grow on.
Cement/Concrete (based on Portland cement) is water proof but Lime by itself is not. But Roman Concrete, made from Lime and mixing with ash or broken pottery or ceramics makes it water proof [2]. I beleive Roman concrete was used whenever contact with water was expected. Both concrete and Roman concrete have the same underlying chemistry (Pozzolanic reaction) to make them water proof [3].
The fascinating thing is that Lime is everywhere in ancient masonry. Lime is more breathable, workable and sustainable. The only thing is, it requires maintainance, which is why Portland cement has taken over the world.
Modern cement/concrete is amazing for large structures. I hope Lime makes a comeback soon at least partly as putty and for building smaller homes.
[1] https://en.wikipedia.org/wiki/Lime_(material)
[2] https://en.wikipedia.org/wiki/Roman_concrete
[3] https://en.wikipedia.org/wiki/Pozzolanic_activity#Reaction
(Sorry, I'm a bit of a nerd. But I am sure you can cope with that.)
There are also coated and non-metallic rebars.
> The miracle of modern chemistry has given us a wide variety of admixtures like superplasticizers to improve the characteristics of concrete beyond a Roman engineer’s wildest dreams. So why does it seem that our concrete doesn’t last nearly as long as it should? It’s a complicated question, but one answer is economics. There’s a famous quote that says “Anyone can design a bridge that stands. It takes an engineer to build one that barely stands.” Just like the sculptors job is to chip away all the parts of the marble that don’t look like the subject, a structural engineer’s job is to take away all the extraneous parts of a structure that aren’t necessary to meet the design requirements. And lifespan is just one of the many criteria engineers must consider when designing concrete structures. Most infrastructure is paid for by taxes, and the cost of building to Roman standards is rarely impossible, but often beyond what the public would consider reasonable.
https://practical.engineering/blog/2019/3/9/was-roman-concre...
A large part of why Roman concrete lasted longer than ours tends to is that we suffer from a shortage of narcissistic emperors with the means to wield entire economies towards their own immortality.
Truth is it's often just a bit cheaper so we trend that way under capitalism, we change styles faster and have come to subconsciously accept shorter lifespans and the kind of things you can build more practical for cars, large overhangs, etc
Would you pay 10x more to have something that lasts 100x or even 1000x longer? The upfront cost is higher, but the TCO is ultimately lower. IMHO it's ultimately a form of planned obsolescence. This becomes even more obvious when plenty of expense is spent just on "engineering" to deliberately reduce lifespan.
First, we can’t summon infinite money to pay for things. Paying 10X more per bridge means we can build 1/10th as many bridges or we have to start stealing from other budgets.
Second, we don’t know what the needs will be for the bridge in that location 100 or 1000 years from now. It could need to be torn down to be widened. Maybe we’re all riding around in electric vehicles that coordinate perfectly with each other and the bridge isn’t needed for cross traffic any more. We don’t know.
not recently
Turns out algae is hard to kill, especially when you feed the reflecting pool from a tidal basin.
This hasn't even been true for 200 years lol
This type of concrete does not give us any more flexibility in the future to rebuild or upgrade because doing anything to it could turn it into an environmental and public health hazard
With roman buildings that last 2000 thousand years we are looking at survivor bias. Near me there are some roman ruins from a (cheap and small) public bath that are barely distiguishable from a pile of bricks. The are some nearby pre-roman ruins in better shape.
You need to actually reduce draft a bit (often old houses like mine tend to accumulate flaws that the elderly living there before didn't fix anymore.) and use a heating sources that matches.
Having a fireplace is fine. It could overheat the house whilst also keeping air dryer and it's essentially renewable (compared to the alternatives and houses made of more plastic insulation than anything else) if you don't mind air quality dip in winter.
That said i can see how that's no longer an option in places that have drastically increased their population
https://www.listennotes.com/podcasts/the-conversation/keepin...
I propose the communal brain rot is less to do with short form video, and more to do with the everyday experience of trying to read something enlightening, tickle your curiosity - and be just absolutely fucking hammered with autoplay interstitials and 720x90 and 300x250 bullshit.
I'm sure hidden in the links is a link to the paper, which you can pay to get the no-nonsense study.
This is the third or fourth degree of scientific reporting; first is the paper, second is a news report, third is adult pop sci magazines, fourth is youth pop sci magazines. Pick your poison / preference.
In fact, that institution is non profit and publicly funded, so what gives...
Anyhow reading the piece with Brave showed me no ads whatsoever.
The folk of the 1930s were entirely capable of making poor quality concrete that barely lasted 30 years (source, my father, born 1935, still alive despite having mixed many a batch of concrete and having laboured).
The reason you don't see that walking about is that poor quality 1930s concrete was replace 50+ years ago.
But that's socialism / liberalism and apparently that's terrorism now.
[1] - https://usafacts.org/answers/how-much-does-the-us-federal-go...
Edit: if you were an expert in this field and that link saved you from typing, and you mentioned you could confirm every word, that’d make sense - I think those Flash models were tested as being as reliable as a coin flip in some hallucination test scenarios, so linking it’s like… eh do I wanna read potentially-only-plausible history?
