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How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

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Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#51

Post by gus_massa »

matheusmoreira wrote: post #28
aiauthoritydev wrote: post #24

The whole promise of engineering is not to build a bridge that stands but to build a bridge that barely stands. It is not a good idea to build a bridge that last 500 years. You likely destroyed valuable resources to build one. Build a bridge that lasts 100 years and save those resources. In 100 years the technology to build bridges improves so much that it is lot easier to build a new one. At least in most countries…

Nobody is going to tear down old bridges and rebuild them at enormous costs just because technology changed. Some things can't or won't be redone and so it's worth it to build it to last and getting it right on the first try.

Usually you need wider bridges, so the old bridge needs a replacement or a second bridge on the side.

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#52

Post by toasty228 »

Mistletoe wrote: post #7

I’ve often wondered why every good sidewalk I see has a WPA stamp on it from the 1930s and the modern ones are all crumbled and uneven. https://share.gemini.google/5g0gxGyOmAPD

Don't you love it when gemini quotes an AI generated video with 83 views as a source of truth

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#53

Post by kergonath »

pinkmuffinere wrote: post #50
litoE wrote: post #20

Earlier quoted context omitted.

As I understand it, concrete has excellent resistance to compression but fails easily on traction, while steel bars are exactly the opposite. That is why you put rebar in concrete: the steel handles the traction loads and the concrete handles the compression. This works well because both materials have similar coefficients of thermal expansion, so as the temperature changes they both expand and contract at the same r…

> Wouldn't your beams start cracking at the bottom, where they are subject to traction? 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 experienc…

> 1. You are intending to ask about tension (which the rebar helps with), not traction (the force your tires exert against a road).

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.

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#54

Post by Animats »

bombela wrote: post #15

> It turns out that another chemical reaction, known as carbonation, might also contribute to Roman concrete’s longevity. 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 us…

Stainless steel rebar is a thing. It's expensive, but structures built with it last much longer. Washington State now has a policy that bridges over salt water will be built with stainless steel rebar. Stainless steel costs much more, but total project cost goes up less than 10%.

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_...

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#55

Post by Modified3019 »

mikepurvis wrote: post #26
litoE wrote: post #20

Earlier quoted context omitted.

As I understand it, concrete has excellent resistance to compression but fails easily on traction, while steel bars are exactly the opposite. That is why you put rebar in concrete: the steel handles the traction loads and the concrete handles the compression. This works well because both materials have similar coefficients of thermal expansion, so as the temperature changes they both expand and contract at the same r…

To build without tension you have to build structures that basically look like Roman structures [1]: a bunch of tightly spaces arches so that the entire thing is in compression, with no meaningful tension anywhere. 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 acknowled…

The “it’s built so everything is under compression” is great thing to bring up, but fyi your link is AI generated, filled with senseless repetition and “it’s not just x, it’s y”.

Looking it up on archive.org shows it was generated this year.

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#56

Post by ErroneousBosh »

Animats wrote: post #54
bombela wrote: post #15

> It turns out that another chemical reaction, known as carbonation, might also contribute to Roman concrete’s longevity. 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 us…

Stainless steel rebar is a thing. It's expensive, but structures built with it last much longer. Washington State now has a policy that bridges over salt water will be built with stainless steel rebar. Stainless steel costs much more, but total project cost goes up less than 10%. 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 hav…

> Stainless steel costs much more, but total project cost goes up less than 10%.

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.

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#57

Post by Cthulhu_ »

joshellington wrote: post #41

There must be a better format and distribution method than this. Ideologically a strong brand name and domain, yet ads every two sentences. Even with ad blocking, there is constant aggressive attempts at attention. 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 fu…

There is, the article links to a source, https://www.scientificamerican.com/article/how-a-1-900-year-..., which you need a $5/month subscription for.

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.

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#58

Post by modo_mario »

otherme123 wrote: post #37
dev_l1x_be wrote: post #34

Earlier quoted context omitted.

This is exactly what we did with houses, buildings. We had perfectly functional 100+ years old fully functional, gorgeous buildings and we replaced those with brutalist concrete/glass barely functional garbage.

In Europe we have plenty of old buildings. The good ones (i.e. made by very wealthy people) tend to be decent, with a skew towards huge living rooms but tiny rooms. The cheaper ones are a mess to mantain: cold in winter, hot in summer, expensive to renovate (it could be more expensive to renovate than to build a new one), bad to no isolation, in my region terribly humid, usually too dark with minuscule windows for mo…

>cold in winter >in my region terribly humid

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

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#59

Post by Cthulhu_ »

somenameforme wrote: post #42
TylerE wrote: post #17

Earlier quoted context omitted.

Survivorship bias in action.

I don't see how this would work because you're saying that the older sidewalks are scrapped and rebuilt when they hit a state of 'x' deterioration, so you only see > 'x' state ones. But how then could it be that newer sidewalks are allowed to fall below 'x' instead of also just being scrapped and rebuilt?

Politics, money allocation, taxation, etc. The US had a golden age last century and is now in decline. It can still bounce back but it needs a political and legal revolution, in this particular case, it needs to tax the wealthy and spend it on municipal improvements.

But that's socialism / liberalism and apparently that's terrorism now.

Re: How Has Roman Concrete Lasted for Millennia? 1,900-Year-Old Latrine Offers Clues

#60

Post by modo_mario »

demosthanos wrote: post #6

Related, Grady Hillhouse on the myth of Roman concrete. > 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 c…

The same is said for why we don't build classical buildings anymore and trend towards more featureless stuff... and it's also mostly bullshit with plenty of counterexamples.

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

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