AFP, published Monday 09 January 2023 at 21:51
How did Roman buildings, such as the aqueducts or the Pantheon in Rome, stand the test of time? This question has occupied experts for a long time.
American and European researchers believe they have finally discovered the secret of the longevity of these roughly 2,000-year-old architectural wonders: a concrete that can repair itself.
While some modern buildings fall into disrepair after just a few decades, scientists hope their discovery may help reduce the environmental and climate impact of concrete manufacturing, which produces significant greenhouse gas emissions.
Until now, the strength of Roman concrete has been attributed to one ingredient: volcanic ash from the Bay of Naples region of Italy, which was used in construction throughout the Roman Empire.
But the researchers turned their attention this time to the presence of a different feature: small shiny white pieces that come from lime, another ingredient used to shape concrete.
“Ever since I started working on Roman concrete, I have always been fascinated” by the presence of these pieces, said Admir Masic, co-author of this study published in the journal Science Advances and professor at the renowned Massachusetts Institute of Technology (MIT) , in the United States. “They don’t exist in modern concrete, so why were they in old?”
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.
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.
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.
In the future, the researchers want to try to bring this concrete with the modified composition onto the market.