ARCHEOLOGY – Researchers at MIT have highlighted an astonishing property of Roman constructions. Their resistance would be linked to the use of quicklime.
The Roman monuments finally reveal their mysteries. American and European researchers think they have discovered the secret of longevity ancient buildings of ancient Rome, from the aqueducts to the Pantheon. How have these marvels of architecture so prodigiously resisted time for almost 2000 years? Thanks to a concrete capable of repairing itself, now say the experts.
Until now, the solidity of Roman concrete was attributed to one ingredient: pozzolan, which corresponds to the volcanic ash of the Bay of Naples region, in Italy, which was sent all over the Roman Empire for major construction sites. But this time the researchers focused their attention on the presence of another characteristic: tiny shiny white pieces, coming from lime, another ingredient used for the design of concrete.
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“Since I started working on Roman concrete, I have always been fascinated by the presence of these pieces”said in a press release Admir Masic, co-author of a study published in the scientific journal Science Advances and professor at the Massachusetts Institute of Technology (MIT), USA. “They are not present in modern concrete, so why were they in the old?”, asked the researcher.
Experts previously thought that these tiny pieces were the result of poor mixing of the mixture, or poor quality raw materials. But by examining, using advanced imaging techniques, the concrete of a wall of the city of Privernum in Italy, the researchers discovered that these small white pieces were in fact calcium carbonate, formed at very high temperatures. They concluded that the lime was not (or not only) incorporated by being mixed with water, as previously thought, but in the form of quicklime.
According to the researchers, this is “hot mix” which gives this concrete its astonishing solidity. Indeed, when cracks appear, rainwater coming into contact with the concrete produces a solution saturated with calcium, which then recrystallizes into calcium carbonate, thus making it possible to fill the cracks.
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To verify this hypothesis, the team of scientists made samples of concrete using the same process, which they then deliberately cracked and on which they poured water. Result: After two weeks, the concrete was completely repaired. Another sample produced without quicklime remained cracked.
As modern buildings relentlessly crumble after just a few decades, MIT scientists hope their discovery can help reduce the environmental and climate impact of concrete production, which generates significant greenhouse gas emissions. . The researchers thus hope to market this new “Roman-style” concrete, with a modified composition.
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