ARCHEOLOGY – Researchers at MIT have highlighted an amazing feature of Roman construction. Their resistance would be linked to the use of quicklime.
The Roman monuments are finally revealing their secrets. American and European researchers believe they have discovered the secret of the longevity of ancient Rome’s ancient buildings, from the aqueducts to the Pantheon. How have these marvels of architecture so amazingly stood the test of time for almost 2000 years? Thanks to a concrete that can repair itself, the experts now say.
Until now, the strength of Roman concrete has been attributed to one ingredient: pozzolana, which is volcanic ash from the Bay of Naples region of Italy that was sent to major construction sites throughout the Roman Empire. But this time, the researchers turned their attention to the presence of a different feature: tiny shiny white pieces that come from lime, another ingredient used to shape concrete.
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“Ever since I started working on Roman concrete, I’ve always been fascinated by the presence of these pieces,” said 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 aren’t present in modern concrete, so why were they in old?” the researcher asked.
Experts used to think that these tiny pieces are the result of poor mixing of the mixture or poor quality raw materials. But by examining the concrete of a wall in the city of Privernum, Italy, using advanced imaging techniques, the researchers discovered that these small white chunks were actually calcium carbonate formed at very high temperatures. They came to the conclusion that the lime was not (or not only) incorporated by mixing it with water, as previously thought, but in the form of quicklime.
regenerative calcium
According to the researchers, it is this “hot mix” that gives this concrete its amazing strength. When cracks appear, rainwater that comes in contact with the concrete creates a calcium-saturated solution, which then recrystallizes into calcium carbonate, allowing the cracks to be filled.
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In order to test this hypothesis, the team of scientists used the same method to produce concrete samples, which they then deliberately broke open and poured over with water. Result: After two weeks, the concrete was completely repaired. Another sample made without quicklime remained cracked.
As modern buildings relentlessly decay after only a few decades, MIT scientists hope their discovery can help reduce the environmental and climate impact of concrete manufacturing, which produces significant greenhouse gas emissions. The researchers therefore hope to be able to bring this new “Roman-style” concrete to the market with a modified composition.