How did Roman constructions, say the aqueducts or the Pantheon in Rome, stand the test of time so well? Experts have long plagued this question.
American and European researchers believe they have finally discovered the secret to the longevity of these architectural marvels, which are nearly 2,000 years old: concrete that is able to repair itself.
While some modern buildings fall into disrepair after only a few decades, these scientists hope their discovery will help reduce the environmental and climate impact of concrete production, which generates significant greenhouse gas emissions.
Until now, the strength of Roman concrete was attributed to a single ingredient: volcanic ash from the Gulf of Naples region in Italy, which was sent throughout the Roman Empire for use in construction.
But this time the researchers focused their attention on the presence of another property: small, shiny white chunks, coming from lime, another ingredient used in designing concrete.
Admir Masic, co-author of this study published in the journal Science Advances and a professor at the prestigious Massachusetts Institute of Technology (MIT), said in a press release. “They are not present in modern concrete, so why were they in the old?”
Experts previously believed that these small pieces were the result of poor mixing of the batter, or poor quality raw materials.
But by examining the concrete using advanced imaging techniques of the city wall of Prefernum in Italy, researchers discovered that these tiny white chunks were actually calcium carbonate, formed at very high temperatures.
They concluded that the lime was not (or not only) combined 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 hardness.
In fact, when cracks appear, the contact of rainwater with concrete produces a solution saturated with calcium, which then turns into calcium carbonate, making it possible to fill the cracks.
To verify this hypothesis, the team of scientists made samples of concrete using the same process, which they deliberately broke and poured water on. Result: after two weeks, the concrete was completely fixed. Another sample produced without quicklime remained cracked.
In the future, the researchers want to try to commercialize this concrete with the modified composition.
