The Guardian has an interesting article on why Roman concrete is so much better than modern concrete.
Yeah, sort of, but also, there’s a survivor-effect here; the surviving examples of Roman concrete are durable - and it’s why they survived.
If there were examples of shitty, not-very-durable Roman Concrete that crumbles away to nothing after a few years, we wouldn’t be able to point to them, because they crumbled away after a few years.
True, but there’s an awful lot of it. And you’re - paradoxically - also missing the point: the survivor effect is the effect that’s of interest in the article.
Volcanic ash: Pozzolana. I’ve been hearing about this stuff, and how it’s what makes Roman concrete so strong, since basically forever. So I don’t think that, per se, is the breaking news. But it’s certainly cool that they’re sciencing how this works in detail.
Note that the article is specifically about Roman underwater structures (such as piers and breakwaters) and how they become stronger over time, in a way that modern concrete doesn’t. Which, apparently, is due to prolonged exposure to seawater. This, then, doesn’t apply to all use of Roman concrete. The Colosseum, for instance, isn’t under water. (Or at least it wasn’t the last time I checked, although I don’t keep up with all the latest news on global warming.) And I think it’s pretty well understood already why it’s still around.
BTW, I don’t want to hijack this, but on a totally different note, I noticed this in the OP’s quote:
I think this is an attempt of poetically referring to the fall of the WRE, 476 AD (YMMV). And, BTW, now you all know my password, because I’m totally changing it to WRE476ADYMMV. Or maybe I could just get that as a vanity plate.
But this is not when the last centurion snuffed it. There was still an Eastern army around. However, the Roman army went through lots of reforms and changes, and I’m not sure how long the title of centurion was in use. I was totally planning to come in here and saying it was until a particular Thursday, the year so-and-so, but it turns out that I don’t actually know, and googling it isn’t really working so far. Was it around Justinian? Later? Or even earlier? Do we even know?
Please check in with me if you have the answer to this. Meanwhile, I return you to your regularly scheduled concrete thread.
I’m quite surprised they successfully used sea water.
Salt is a known problem in concrete. Craftsman style bungalows often used beach sand in the concrete for the foundation. Beach sand contains salt. That’s bad news. Crumbling foundations can be a costly fix. I’ve seen this come up numerous times on HGTV shows.
Obviously the Romans were successful with their methods.
Did they even, though? In the actual mix, I mean? IANAbuilder. How do you build stuff underwater?
For that matter, how do you build stuff on land? So, you’re building the Colosseum. You have some lime, some pozzolana and some water. Presumably you just mix it up, pour it into a mould? Where does the water come from? Out of the Tiber, or from an aqueduct?
If you’re building underwater, how do you get the concrete down there? Mix it up first? In that case, where does that water come from? Sea, river or aqueduct?
Concrete will set underwater. You just have to keep it from being washed away before it sets.
I imagine they used piles, in much the same manner as is used today.
How do you think they built Sea-Walls ? Or for that matter Harbour Moles such as the most famous at Stuart Tangier, and earlier the link to the Isle at Pharos ?
The wiki on Sea-Walls says:
*Seawall construction has existed since ancient times. In the 1st century BCE, Romans built a seawall / breakwater at Caesarea Maritima creating an artificial harbor (Sebastos Harbor). The construction used Pozzolana concrete which hardens in contact with sea water. Barges were constructed and filled with the concrete. They were floated into position and sunk. The resulting harbor / breakwater / sea wall is still in existence today - more than 2000 years later.
*
Caesar and his friends dodged all about the Med during the Civil War ferrying troops etc., which needed quick harbours and engineering ( I see he dropped a ship, dropped another on top and built a tower on that – which is easier to talk about than do ).
Belloc wrote a small essay on The Sea-Wall Of The Wash protecting the Fens from The German Ocean, probably less concrete used, but I’ve no idea what they did in the High Mediaeval and pre-Roman.
*Of these words, whose tradition is immemorial, the greatest, of course, are the sea-walls.
*
*Perhaps the river-walls came first, but the great bank which limited and protected the land against the sea is also older than any history.
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*It is called Roman, and relics of Rome have been found in it, but it has not the characteristic of Roman work. It runs upon no regular lines; its contour is curved and variable. It is surely far older than the Roman occupation. Earth, heaped and beaten hard, is the most enduring of things; the tumuli all over England have outlasted even the monoliths, and the great defensive mounds at Norwich and at Oxford are stronger and clearer cut than anything that the Middle Ages have left. This bank, which first made Fenland, still stands most conspicuous. You may follow it from the Nene above Sutton Bridge right over to Lynn River, and again northward from Sutton Bridge (or rather, from the ferry above it) right round outside Long Sutton and Holbeach, and by Forsdyke Bridge and outside_ Swyneshead; everywhere it encloses and protects the old parishes, and everywhere seaward of it the names of the fields mark the newest of endeavours.
*
Sadly that Sea Wall wiki doesn’t go into the wonders of French invented Tetrapods, which are also concrete, but pre-formed, and cover the coasts of Japan.
I hadn’t heard that the pozzolon concrete was especially good in salt water before. As mentioned above there is the survivor effect, and in addition as has been mentioned in other threads on the subject, the Romans over-built the shit out of everything. But a durable salt-water resistant concrete was a challenge until modern times. Without volcanic ash readily available it took centuries to develop Portland cement, made by heating and pulverizing stone into a new material which would reform hydraulically. The Romans had earlier on developed not just cement and concrete but waterproof grout, a necessity in containing water in tiled structures and long lasted wall mosaics. Despite all that technology they still made many structures from piling up stone and bricks using only simple lime based mortars. Not the fine lined mortar structures we think of in a brick wall either, mortar lines could be several inches thick, probably a time and effort saver when building stone structures that saved lots of chiseling of rocks to get uniform shapes. They did all this without much analytical technology, just hundreds of years of trial and error, much of which must have started before the rise of the empire. Still a big leap over the Egyptians who raised enormous monuments simply by stacking giant cut rocks one on top of another like simple toy building blocks. The sides of the pyramids were once mortared over but only traces of that material remain, although not many materials would have survived the erosion of wind blown sand.
Never heard of the Why Files, but they stopped last year and I would think this is from about 2008 at a guess ( no dates anywhere )
*King Herod’s imported Roman engineers, it seems, enlisted the sea to help them complete the world’s first modern harbor. Moreover, they had a formula for cement that could harden underwater, and may have incorporated into the design a sluicing system that created a current to cleanse the harbor of ship-stopping sediments, an engineering marvel not yet understood by today’s scientists.
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Work by University of Colorado historian Robert Hohlfelder and others has unmasked an ingenious system of breakwater construction. Large stone and concrete blocks were laid out in checkerboard fashion. Then the alternating hollows between the set and submerged blocks, all encased in a wooden framework, quickly filled with sand as a result of natural sea action. Finally, Hohlfelder says, the breakwater was “capped with rubble, concrete and paving stones to form continuous sea walls.”
And over-engineering is cool.
Is this true though? I thought all concrete gets harder with time.
Did the Romans have some kind of Viagra?
Vidi vici veni
Well, that’s what I’m asking. Look, I obviously know that underwater stuff exists. It wasn’t a rhetorical question. I’m just wondering about the engineering specifics of it.
Concrete hardens in contact with sea water, yeah? That’s fine. But how do you mix up the concrete? With sea water? Or other water? It’s just a very persnickety question, I suppose.
Cements used in construction can be characterized as being either hydraulic or non-hydraulic. Hydraulic cements (e.g., Portland cement) harden because of hydration, a chemical reaction between the anhydrous cement powder and water. Thus, they can harden underwater or when constantly exposed to wet weather. The chemical reaction results in hydrates that are not very water-soluble and so are quite durable in water. Non-hydraulic cements do not harden underwater; for example, slaked limes harden by reaction with atmospheric carbon dioxide.
Công thức tới thành công
And for my next trick… Smeaton hardened cement nearly a 100 years before Portland Cement was invented in 1824.
*Repeated structural failure of the Eddystone Lighthouse off the coast of Cornwall, England, led John Smeaton, a British engineer, to conduct experiments with mortars in both fresh and salt water. In 1756, these tests led to the discovery that cement made from limestone containing a considerable proportion of clay would harden under water.
*
[POST=20209186]“How long are concrete apartment buildings supposed to last?”[/POST]
[THREAD=669711]“Why do abandoned concrete buildings decay so fast?”[/THREAD]
Stranger
Check out the book Concrete Planet by Robert Courland. Lots of interesting information.
Italians
As a former structural engineer, I have to give this article somewhat of a :dubious:.
All concrete gets stronger over time. Personally, I worked on renovating a 50-year-old reinforced concrete tunnel. The original plans called for 3000 or 4000psi concrete. I don’t remember exactly how strong the cores we took tested at, but it was much higher than 4000psi, I think it was 7000-9000psi.
Concrete in seawater does tend to decay much faster, so I think the scholarly article may have some useful insights into concrete composition to inhibit saltwater decay.
And Roman concrete technology was indeed amazing. The Pantheon is still the world’s largest unreinforced concrete dome.