The Pantheon, in Rome, is thought to be almost 2,000 years old. (getyourguide.com)A number of publications have run stories describing the recent discovery of how the ancient Romans made their concrete structures last so long. For example, the dome of the Pantheon, in Rome, survives intact to this day. It is still the world’s largest dome of unreinforced concrete. And Roman aqueducts remain standing, some still transporting water slightly downhill over long distances.
Researchers found that Roman concrete contained small white chunks of lime known as lime clasts, which were treated with slaked lime to produce quicklime, which had the quality of curing and setting more quickly, thus reducing production times. But longstanding theory was that the existence of lime clasts in the concrete at many Roman sites was the result error arising from poor quality control. Researcher Admir Masic of MIT thought this might be a bit off. He told Michelle Starr of Science Alert:
The idea that the presence of these lime clasts was simply attributed to low quality control always bothered me. If the Romans put so much effort into making an outstanding construction material, following all of the detailed recipes that had been optimized over the course of many centuries, why would they put so little effort into ensuring the production of a well-mixed final product? There has to be more to this story.
After further research, his team at MIT discovered the lime clasts were a feature rather than a bug. The lime clasts also have the property of naturally expanding to fill and repair cracks that emerge in concrete over time.
At first I didn’t think this should be of any interest to me. Is it surprising that the Romans had construction methods superior to those of our own age of fake expertise? Hardly. The Romans were real people, with serious ideas on how things were and how they should be. But it occurred to me that this was exactly why we should care how they made concrete.
The key is in Masic’s use of the phrase “detailed recipes that had been optimized over the course of many centuries.” What today is “optimized” over the course of many centuries? Not much. The iPhone? After 14 model series, they still drive us crazy with their ineptitude. No. Instead of trial and error leading over time to higher quality of materials and production techniques, we seek rapid eyeblink advancements, usually assisted digitally, without the long slog of productive endeavor. To sneer at the past and its products is the big idea now. Quality control? What a concept! Planned obsolescence is more like it these days.
You can see this most directly in works of architecture. In architecture, as this discovery shows, the Romans got the big things and the little things right. Their buildings incorporated standards to ensure consistent beauty, and their concrete hardened more quickly. Pop quiz: Which is the big thing and which is the little thing? Answer: It was a trick question. Both are vital to ensuring quality. Frank Gehry’s mickled up pieces of paper don’t quite cut the mustard. Extra credit: Will today’s construction managers incorporate the techniques of Rome in modern concrete manufacture? Will they even bother to make themselves aware of these “advances”?
The aqueduct at the Pont du Gard, near Nimes, France, or 12 miles from its source. (USGS.gov)
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I would like to add a bit to this article. FIrst it is my opinion that today’s concrete only lasts a few decades because of the use of plain steel rebar to reinforce it. That crap begins to rust before it is even used and continues to rust inside the concrete eventually bursting the concrete. I think that road salt aggravates the problem. Second, I could swear I read an old article that stated that one of the reasons that Roman concrete was so strong was that it used a special type of volcanic ash in the mix, but I could be wrong about this.
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A quote mentioning the volcanic ash in a CNN article: “Their findings suggest that the lime clasts can dissolve into cracks and recrystallize after exposure to water, healing cracks created by weathering before they spread. The researchers said this self-healing potential could pave the way to producing more long-lasting, and thus more sustainable, modern concrete. Such a move would reduce concrete’s carbon footprint, which accounts for up to 8% of global greenhouse gas emissions, according to the study.
For many years, researchers had thought that volcanic ash from the area of Pozzuoli, on the Bay of Naples, was what made Roman concrete so strong. This kind of ash was transported 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. ”
https://www.cnn.com/style/article/roman-concrete-mystery-ingredient-scn/index.html
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rest of quote “Masic said that both components are important, but lime was overlooked in the past. “
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Great item, David. Having traveled to both the Pont Du Gard and the Pantheon?.. I’ve long marveled at Roman building technique, but to your broader point, we seem incapable of thinking ahead. Sadly its “now, or never”.
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Yes, Michael, so sad, and it shows up in so many ways.
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Roman concrete, archeological evidence points to utilization of volcanic ash and ground cinders.
Modern concrete industry does the same…. GGBFS
Or ground granulated Blast furnace slag
Volcano ash is time consuming to obtain for concrete. But… we have a substitute.
When steel is poured, the leftover bits which contain lots of silica and iron oxide leftovers are melted again, mixed and rapidly cooled to a glass, then ground into a powder. Mixed with cement it binds better, fewer air pockets. Recently it’s use in New replacement span Interstate 35 bridge.
https://i.imgur.io/lH3iwxH_d.webp?maxwidth=640&shape=thumb&fidelity=medium
It’s exceptionally tough and will last 200 years. While Parthenon lasted 2000, bear mind, Parthenon doesn’t carry road traffic.
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Is fly ash from coal-burning power plants used in concrete? I don’t know if it is, but was wondering what is done with this waste product
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It is. In fact t one the reasons of industry would kill for to pull heavy metals out to get the low metallicity ash residue. Since its oxide and glass components it’s water bonding properties are impeccable.
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