A scientific and archaeological discovery Pompeii provides a definitive twist to one of the most fascinating debates in Roman engineering: how exactly they made the concrete that endured for two millennia, from aqueducts to enormous domes. He Roman concrete was … the basis of the story architectural revolution of Rome, allowing the construction of buildings, bridges and aqueducts, many of which have come down to us in an extraordinary state of preservation. For decades, modern engineering has admired and envied this durability, unable to reproduce materials with such resistance to the elements and the passage of centuries.
The answer about How exactly was this concrete made? comes from Massachusetts Institute of Technology (MIT). The team led by the professor Admir Masicworld expert in ancient materials, was able to analyze for the first time an authentic Roman construction site perfectly preserved by the eruption of Vesuvius in 79 AD. C. It is like a time capsule with materials, abandoned tools and a half-raised wall. Masic has been studying the chemical composition of this material for almost a decade. Already in 2023, his team published a first work in which it hypothesized that the longevity of Roman concrete was not only due to volcanic ash, as was believed, but to a different process. The real secret, the researchers then claimed, lay in the “hot mixing”. Now the discovery of Pompeii, published by the magazine ‘Nature’offers the first direct evidence that confirms this proposition.
The hot mixing process means that the Romans They combined lime fragments with volcanic ash and other dry ingredients before adding water. When water is added to this dry mixture, an exothermic reaction is generated which releases heat. As the concrete set, this process trapped and preserved the highly reactive lime in the form of small, white, gravel-like particles. These fragments, known as lime chipsare the heart of the Roman superpower. When cracks form in concrete over time, the clasts are exposed to water (rain or humidity) and “redissolve and fill the cracks, giving them self-healing properties”, that is, the ability to spontaneously seal small cracks.
This hypothesis contradicts the architect Vitruvius in his work “De architectura”, written in the 1st century BC.
However, this technical hypothesis, as convincing as it was, clashed with the most influential architectural book of antiquity. The Roman architect Vitruviusin his work “Of architecture”written in the 1st century BC. C., claimed that the Romans added water to lime to create a paste-like material, then mixed it with other ingredients. The contradiction was obvious and opened an intense debate within the scientific community.
Professor Masic, despite his findings, recognized the cultural and intellectual weight of the tradition: “Given my great respect for Vitruvius, it was difficult for me to suggest that his description could be inaccurate,” explains Masic. “The writings of Vitruvius played a central role in sparking my interest in ancient Roman architecture, and the results of my research contradicted these important historical texts.”
The definitive proof is a site from Pompeii, which offers a sort of time capsule
The definitive test to resolve this technical and historical debate came from the most unexpected place: an old active construction site in Pompeii. The site, abandoned and buried with extraordinary fidelity by the eruption of 79 AD. C., offered a time capsule containing materials and tools as they were left at the time of the disaster.
Archaeologists were able to document piles of pre-mixed dry materials, a wall under construction, completed buttresses and mortar repairs. For the MIT researchers, it was a irreplaceable opportunity. “We were fortunate to be able to open this time capsule of a construction site and find piles of materials ready to be used in building the wall,” says Masic.
The site offers the clearest evidence yet that the Romans used hot mixing. Scientists not only found the lime clasts in the finished concrete: the most decisive was the discovery of intact premixed quicklime fragments with other ingredients in a pile of dry raw materials. This discovery showed that the first step was to dry mix the crushed quicklime with volcanic ash, including pumice, and then add the water, thereby triggering the thermal reaction.
The team, including the first author, Ellie Vasermanused stable isotope studies to differentiate quicklime from the slaked lime described by Vitruvius. “The results revealed that the Romans prepared their binder by taking calcined limestone (quicklime), grinding it to a certain size, dry mixing it with volcanic ash, and finally adding water to create a cementitious matrix,” says Masic.
Discovery has crucial implications for modern construction
Additionally, analysis of the volcanic components revealed that over time, the pumice particles reacted chemically with the surrounding pore solution, creating new mineral deposits that further strengthened the concrete. This confirms the vision of Roman concrete as a material in constant chemical and evolutionary evolution. capable of rebuilding itself over time.
The MIT research is not just a historical anecdote; has crucial implications for modern construction. Today’s cement is known for its relatively rapid degradation and high carbon footprint, a problem that Roman technology could help solve. “This matter can regenerate over thousands of years, it’s responsive and very dynamic. It has survived earthquakes and volcanoes. “It has withstood under the sea and the degradation of the elements,” says Masic, who founded the company DMAT to take real-world lessons from ancient Rome and create modern, sustainable materials.
The best technology of the future could be hidden in the ancient city of Pompeii
The key is not to copy, but to learn of the philosophy of materials. “We just want to translate a few sentences from this book of knowledge into our modern construction practices,” explains the professor. The goal is to incorporate the matrix’s ability to fill pores through recrystallization processes, a natural mechanism that allowed the Roman “opus caementicium” to survive two thousand years.
Concerning the conflict with Vitruvius, Masic is conciliatory and suggests that the architect may have been misunderstood or that his slaked lime method was only one of those used in the Empire. Recall that Vitruvius also mentions latent heat during mixing, a detail which, in light of the Pompeii discovery, could suggest that he was fully aware of the now experimentally confirmed process.
The work, funded by the MIT Research Support Committee (RSC) and the MIT Concrete Sustainability Center, demonstrates that the best technology of the future It could be hidden, beneath the ashes of history, in the ancient Roman city of Pompeii.
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