An excavation in Pompeii has uncovered dried building materials that reveal the ingredients used by the Romans to create their famous strong, self-healing concrete.
A recent analysis of a 2000-year-old Pompeii archaeological site has revealed the clearest evidence yet of how the ancient Romans created their concrete incredibly durable.
The discoveries in Nature Communicationsconfirm that Roman builders used a method known as “hot mix“, a technique that, according to scientists, can explain why structures such as the Pantheon and aqueducts have survived earthquakes, volcanic eruptions and centuries of environmental wear and tear.
The archaeological site, which was discovered last year beneath layers of ash from the eruption that destroyed Pompeii in AD 79, contained neat piles of dried building materials. These materials offered a unprecedented insight into Roman building practicesincluding the ingredients used to create your long-lasting concrete.
A team of researchers led by MIT materials scientist, I admire Masicanalyzed the materials and found a volcanic ash mixtureknown as pozzolan, combined with quicklime, a substance that reacts intensely when exposed to water, producing high temperatures inside the mixture.
According to Masic, the internal heating of the concrete allowed chemical reactions that do not occur in conventional hydrated lime mixtures, in addition to accelerating construction, drastically reducing curing time, explains .
Crucially, the process also created lime fragments, or remaining pieces of quicklime, which researchers said gave Roman concrete its self-repairing properties. When cracks formed, they tended to migrate towards these fragments.
The water that entered the fissure triggered a chemical reaction that formed calcium carbonate, sealing the fracture and strengthening the structure over time.
Although scientists suspected that Roman concrete could be hot-mixed, the technique conflicted with instructions from the famous Roman architect Vitruvius, who described a hydrated lime method in his treatise On architecture1st century BC
However, the discovery at Pompeii resolved the ancient contradiction: the piles of dry materials contained quicklime and lime fragments already mixed with volcanic ash, being clear physical proof of the hot mixing process.
Microscopic analysis of the mortar from the archaeological site confirmed the characteristics of the hot mix, including fractured lime fragments, reaction ridges that connect the lime to the volcanic ash, and crystals that form within the pumice grains.
Isotopic analysis also monitored the chemical processes that allowed concrete to carbonate and strengthen over the centuries.
Modern concrete, although widely used, has no durability and emits significant amounts of carbon during production. Masic, who founded the company DMAT to explore modern applications, believes that adopting self-healing properties inspired by Roman concrete could considerably extend the useful life of current structures.
“We don’t want to copy Roman concrete,” he said. “We want to translate its principles, especially its regenerative capabilities, in modern materials.”
