Researchers Discover Why Roman Concrete Was So Durable (mit.edu) 55
Researchers have spent decades trying to figure out how ancient Romans were able to make concrete that's survived for two millennia. "Now, a team of investigators from MIT, Harvard University, and laboratories in Italy and Switzerland, has made progress in this field, discovering ancient concrete-manufacturing strategies that incorporated several key self-healing functionalities," reports MIT News. From the report: For many years, researchers have assumed that the key to the ancient concrete's durability was based on one ingredient: pozzolanic material such as volcanic ash from the area of Pozzuoli, on the Bay of Naples. This specific kind of ash was even shipped all across the vast Roman empire to be used in construction, and was described as a key ingredient for concrete in accounts by architects and historians at the time. Under closer examination, these ancient samples also contain small, distinctive, millimeter-scale bright white mineral features, which have been long recognized as a ubiquitous component of Roman concretes. These white chunks, often referred to as "lime clasts," originate from lime, another key component of the ancient concrete mix.
Previously disregarded as merely evidence of sloppy mixing practices, or poor-quality raw materials, the new study suggests that these tiny lime clasts gave the concrete a previously unrecognized self-healing capability. [...] Upon further characterization of these lime clasts, using high-resolution multiscale imaging and chemical mapping techniques [...], the researchers gained new insights into the potential functionality of these lime clasts. Historically, it had been assumed that when lime was incorporated into Roman concrete, it was first combined with water to form a highly reactive paste-like material, in a process known as slaking. But this process alone could not account for the presence of the lime clasts. [MIT professor of civil and environmental engineering, Adam Masic] wondered: "Was it possible that the Romans might have actually directly used lime in its more reactive form, known as quicklime?"
Studying samples of this ancient concrete, he and his team determined that the white inclusions were, indeed, made out of various forms of calcium carbonate. And spectroscopic examination provided clues that these had been formed at extreme temperatures, as would be expected from the exothermic reaction produced by using quicklime instead of, or in addition to, the slaked lime in the mixture. Hot mixing, the team has now concluded, was actually the key to the super-durable nature. "The benefits of hot mixing are twofold," Masic says. "First, when the overall concrete is heated to high temperatures, it allows chemistries that are not possible if you only used slaked lime, producing high-temperature-associated compounds that would not otherwise form. Second, this increased temperature significantly reduces curing and setting times since all the reactions are accelerated, allowing for much faster construction."
During the hot mixing process, the lime clasts develop a characteristically brittle nanoparticulate architecture, creating an easily fractured and reactive calcium source, which, as the team proposed, could provide a critical self-healing functionality. As soon as tiny cracks start to form within the concrete, they can preferentially travel through the high-surface-area lime clasts. This material can then react with water, creating a calcium-saturated solution, which can recrystallize as calcium carbonate and quickly fill the crack, or react with pozzolanic materials to further strengthen the composite material. These reactions take place spontaneously and therefore automatically heal the cracks before they spread. Previous support for this hypothesis was found through the examination of other Roman concrete samples that exhibited calcite-filled cracks. According to MIT, the team is working to commercialize their modified cement material.
The findings have been published in the journal Science Advances.
Previously disregarded as merely evidence of sloppy mixing practices, or poor-quality raw materials, the new study suggests that these tiny lime clasts gave the concrete a previously unrecognized self-healing capability. [...] Upon further characterization of these lime clasts, using high-resolution multiscale imaging and chemical mapping techniques [...], the researchers gained new insights into the potential functionality of these lime clasts. Historically, it had been assumed that when lime was incorporated into Roman concrete, it was first combined with water to form a highly reactive paste-like material, in a process known as slaking. But this process alone could not account for the presence of the lime clasts. [MIT professor of civil and environmental engineering, Adam Masic] wondered: "Was it possible that the Romans might have actually directly used lime in its more reactive form, known as quicklime?"
Studying samples of this ancient concrete, he and his team determined that the white inclusions were, indeed, made out of various forms of calcium carbonate. And spectroscopic examination provided clues that these had been formed at extreme temperatures, as would be expected from the exothermic reaction produced by using quicklime instead of, or in addition to, the slaked lime in the mixture. Hot mixing, the team has now concluded, was actually the key to the super-durable nature. "The benefits of hot mixing are twofold," Masic says. "First, when the overall concrete is heated to high temperatures, it allows chemistries that are not possible if you only used slaked lime, producing high-temperature-associated compounds that would not otherwise form. Second, this increased temperature significantly reduces curing and setting times since all the reactions are accelerated, allowing for much faster construction."
During the hot mixing process, the lime clasts develop a characteristically brittle nanoparticulate architecture, creating an easily fractured and reactive calcium source, which, as the team proposed, could provide a critical self-healing functionality. As soon as tiny cracks start to form within the concrete, they can preferentially travel through the high-surface-area lime clasts. This material can then react with water, creating a calcium-saturated solution, which can recrystallize as calcium carbonate and quickly fill the crack, or react with pozzolanic materials to further strengthen the composite material. These reactions take place spontaneously and therefore automatically heal the cracks before they spread. Previous support for this hypothesis was found through the examination of other Roman concrete samples that exhibited calcite-filled cracks. According to MIT, the team is working to commercialize their modified cement material.
The findings have been published in the journal Science Advances.
Oatmeal (Score:2)
I remember something about oats being a secret of strong concrete in a similar study
Missing from the summary (Score:5, Informative)
Missing from the summary:
Previous support for this hypothesis was found through the examination of other Roman concrete samples that exhibited calcite-filled cracks.
To prove that this was indeed the mechanism responsible for the durability of the Roman concrete, the team produced samples of hot-mixed concrete that incorporated both ancient and modern formulations, deliberately cracked them, and then ran water through the cracks. Sure enough: Within two weeks the cracks had completely healed and the water could no longer flow. An identical chunk of concrete made without quicklime never healed, and the water just kept flowing through the sample. As a result of these successful tests, the team is working to commercialize this modified cement material.
The search for the secret to long-lasting Roman concrete has indeed been going on for many years. I'm glad they finally found some of the secrets of the formula.
Re: Missing from the summary (Score:2)
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They won't get a patent, they would just sell the product.
Re: Missing from the summary (Score:2)
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But if the concrete lasts for two millenia, their repeat sales figures will plummet!
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Easy. "A Method for Producing Long-Lasting Concrete Using the Internet!"
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"Where's a good roman engineer when you need one?"
In Rome.
Re:Missing from the summary (Score:5, Funny)
Obligatory...
"What have the Romans ever done for US?"
Re:Missing from the summary (Score:5, Funny)
And give a concrete example, please...
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Nice to see Pliny the Elder referenced in the Science Advances paper
as a scholar who helped draft the specific instructions for construction sites.
Aside: I see now that the Hoover Dam used some kind of "hot mix" concrete --
it's supposed to last 1,000 years, maybe even longer than Lake Mead.
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Can someone explain the self-healing property? I understand the hot mixing and the other benefits, but I don't understand how they've concluded that the concrete can self-heal.
Re:Oatmeal (Score:5, Interesting)
After pouring, there are remaining granules of quicklime in the concrete, called free lime. If cracks develop, the humidity entering will react with the free lime turn into lime plaster, which takes a much larger volume and blocks the crack. The calcite-filled cracks reported by the article are examples of this type of reaction. The interesting thing is also that this reaction seems to prevent further deterioration, compared to iron expansion from corrosion which will hasten the degradation of reinforced concrete.
Re: Oatmeal (Score:2)
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coated rebar is bad. you have to prevent damage during construction and old age makes the epoxy brittle. Any cracks mean moisture will start corrosion and the coating will accelerate corrosion at that point. Better to spread it over the whole surface with no coating. The chemistry of the two in contact actually has the concrete slow the process but not when coated. Coated is on the way out.
Glass rebar is weaker and I bet the resin also weakens with age. A benefit to rebar is that it is malleable which g
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Stainless won't help anyway, if it's in constant water contact then most types of it rust in the absence of a sacrificial anode.
I wonder if you could solve the rebar corrosion problem with such a solution, though? Or maybe you could make a weathering steel rebar, and pre-weather it before the pour?
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I would sure think so, but you'd need constant water contact between the anode-- which you'd have to replace eventually and if the anode expands when it rusts then you crack up the concrete like the rebar does. If you coat it-- then you'd have galvanized but I've never seen that until lately. don't know why it is new... but you have problems at cut ends like epoxy rebar. Galvanized eventually rusts after the zinc 'anode' rusts away. Pre-weathered rebar is worse but negligible; I've hardly seen rust free re
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Reading the comments in the Ars Technica erticle, someone mentioned "basalt rebar", so I googled it.
The basalt rebar manufacturer heats their mined basalt raw material to either a paste or fully liquid, then extrudes it to form reinforcing bar ("rebar").
They claim that the extrusion process causes formation of microscopic fibers (sizes measured in microns, I think) that give the resulting rebar its tensile strength. It's not steel so there's no problem with rust.
Re:Oatmeal (Score:5, Interesting)
I was fairly well amazed myself at the whole idea of self-healing concrete, because that's usually one of the things that's worst about it. For example, the worst parts of the CA-101 are the concrete sections. I thought it was fairly well explained in TFS, though...
So not only do the lime clasts [wikipedia.org] self-react with water to form calcium carbonate [wikipedia.org] deposits that seal the crack, but the concrete also contained siliceous and/or aluminous materials which react chemically with calcium hydroxide [wikipedia.org] to form strong bonds between the broken pieces. The presence of Pozzolans in Roman concrete itself has been known since ca. 30-20 BCE [wikipedia.org], but I guess it wasn't known that they gave self-healing, only strength.
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Chinese mortar, as used at least 1800 years ago, was pretty strong, showing concrete-like properties at times, and a core ingredient was sticky rice soup that was mixed with slaked lime.
So finely ground oatmeal boiled into a soup could very well have been used if you didn't have volcanic ash.
Re:Oatmeal (Score:5, Informative)
These are currently used on water tanks, better quality swimming pools and other structures Or if you want high strength high speed curing you can go something like CTS mortar mix https://www.ctscement.com/prod... [ctscement.com] which actually has the property of heating up while curing. Note add Xypex for waterproofing
What is interesting is that the roman method may bring down the cost however calcium tends to leach in swimming pools delaminating the surface and causing other issues and requires the use of chemicals like cal-stop https://ozpoolsupplies.com.au/... [ozpoolsupplies.com.au]
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Re: Oatmeal (Score:2)
The mafia. No joke.
Re: Oatmeal (Score:2)
Asphalt is self healing and basically industrial waste from oil refineries, so cheap. It doesn't take patches very well so it is perpetually in need of repair. What you save on materials you pay for in labor.
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I can't find a reference to that anywhere.
Millennia? Bah. (Score:3, Funny)
Did they KNOW how and or why? (Score:2)
Did the Romans understand that the ingredients had this self-healing effect on the concrete, or did they simply realize that by adding certain compounds, they got better results? They couldn't attest to the longevity because they didn't have the evidence that we have, namely the fact that many structures lasted over two millennia.
Were their technological advances well-understood, but lost to history? Or were their successful techniques purely empirical and simply passed down, but not fully understood?
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They knew because the aliens told them so.
But more realistically, yea, this article (like so many these days) seems right full of bullshit.
Re: Did they KNOW how and or why? (Score:5, Insightful)
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MS-Windows
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They might have noticed that the concrete didn't leak as much.
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The Romans were nutball-level crazy about record keeping. I imagine that even without modern chemistry, their records of what worked better versus what did not would produce improvement in their processes over time.
Re:Did they KNOW how and or why? (Score:4, Insightful)
Did the Romans understand that the ingredients had this self-healing effect on the concrete, or did they simply realize that by adding certain compounds, they got better results? They couldn't attest to the longevity because they didn't have the evidence that we have, namely the fact that many structures lasted over two millennia.
Were their technological advances well-understood, but lost to history? Or were their successful techniques purely empirical and simply passed down, but not fully understood?
Modern concrete is formulated by (presumably) chemical engineers, then the formula is followed to create the specific mix needed for a project.
It's great if you want to know exactly how the material forming your building is going to perform, but only a relatively small group of people actually get to innovate.
In Roman times, I'm guessing every builder would have to mix their own concrete, and since there wasn't the kinds of certifications we have now each builder would have their own special formula. Over a few hundred years that leads to a lot of trained and motivated people doing a lot of experimentation*.
I'm sure they had some kind of theories as to why certain things worked and others didn't, but ultimately their process would be well refined, but highly empirical.
* There's probably a survivability bias at work as well, for all these formulations that have lasted 2000+ years there's probably a bunch that didn't last 20 years, but those ones would have got rebuilt.
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I'm sure they had some kind of theories as to why certain things worked and others didn't, but ultimately their process would be well refined, but highly empirical.
Wait. Did you just say that some of things the Romans did were "highly empirical"?
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...well, he's not WRONG, is he?
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The Romans built their empire on standardization [smithsonianmag.com]. They had a real hard-on for bureaucracy. Ugh, it was a real PITA to find information on roman standardization through a flurry of shit on roman battle standards.
Re: Did they KNOW how and or why? (Score:2)
Even in Roman antiquity, concrete buildings are a lot more expensive to build, so concrete generally got used only for "monumental" buildings. Once the empire collapsed, so did market demand for monumental buildings that required it. After a century or two, so few people bothered to master concrete construction, it became almost impossible to find anyone CAPABLE of competent concrete construction... which further accelerated its demise, because by that point, not even the Church could find skilled concrete
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The example in the summary, with cracks filling in within two weeks, is something the Romans could have discovered in two weeks. If I were to make a wild guess, the material being waterproof was likely what they were after in the first place. The Romans liked their aqueducts.
Huh? (Score:2)
Previously disregarded as merely evidence of sloppy mixing practices, or poor-quality raw materials, the new study suggests that these tiny lime clasts gave the concrete a previously unrecognized self-healing capability.
What? Seriously, who disregarded it?
"Was it possible that the Romans might have actually directly used lime in its more reactive form, known as quicklime?"
Uh, yeah they did. How do you become an MIT professor without knowing this? It's literally in the recipe. Reference: https://digitalcommons.unl.edu... [unl.edu]
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did you read the article you posted or this one?
from yours With Cato’s recipe, which Vitruvius was attempting to
explain, the limestone is now known as calcium carbonate
and varying hydrates thereof: Ca(CO 3) x H 2O, where “x” is
one to four. When kilned, this substance loses water and car-
bon dioxide. The two-thirds that remain are CaO, calcium
oxide. This com pound, synonymously named burnt lime,
caustic lime, quicklime, and in Latin, calx, slakes violently
in water—as Vitruvius knew
Quick lime... (Score:4, Interesting)
Silly Billy Romans Forgort to trademark\copyright (Score:2)
other reasons have been proposed before (Score:2)
Even the summary mentions that (Score:2)
Even the summary mentions that.
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As mentioned in this very article summary: "For many years, researchers have assumed that the key to the ancient concrete's durability was based on one ingredient: pozzolanic material such as volcanic ash..."
Every Bit of Concrete You See--Was Baked (Score:2)
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Atmospheric CO2 would best be considered as an "investment", and we should have been measuring industrial processes by their return on that investment. Sometimes a product or result is worth a given expenditure, oftentimes not.
One serious problem with CO2 production is basically the same as many externalities: The failure to require those who induce these externalities and profit from them, to pay for them.
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https://cleantechnica.com/2022... [cleantechnica.com]
i literally thanks to you (Score:1)
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shrinkage cracks (Score:2)
I understand that rather than a hot mix, some pours add ice into the mix-water to slow initial curing to prevent cracks from forming in the first place [researchgate.net]
Also I believe that when huge structures are poured (like dams) special concrete formulations are used to reduce exothermic temperatures generated during curing