The secret of the resistance of Roman concrete finally lifted!

 Antiquity has not finished giving us lessons. Scientists have finally unraveled the mystery of the composition of Roman concrete, capable of self-repair!

Bridges, aqueducts, Roman theaters have survived until us. And it's no coincidence that the concrete the Romans used still holds up 2,000 years later. Scientists, who have been looking for its secret for years, have just discovered how this concrete repairs itself. It is not a modern invention, as is often believed.

Concrete, a set of mineral aggregates aggregated by a binder such as cement or clay, is a material that would have appeared in the 2nd century BC. AD to take off in the 30s AD. It was thought that the superior quality of Roman concrete was due to pozzolana, a volcanic rock collected in the region of Pozzuoli, west of Naples, which, mixed with volcanic ash and lime, gave a mineral more elastic and able to fill faults. But no one understood the ability of this concrete to self-repair.

Quicklime

A team from MIT (Massachusetts Institute of Technology) and Swiss and Italian researchers have just shown that the exceptional resistance of the Roman material is actually due to the presence of quicklime. They took samples from the ancient wall of the city of Priverno, in Italy (Lazio), and thanks to a sophisticated imaging technique they were able to precisely define the composition of Roman concrete, in particular by studying closely the small shards whites present in the material: the lime clasts, in calcium carbonate, could only form because quicklime was used in the mixture. Rain or sea water that comes into contact with these clasts creates a saturated solution of calcium, which crystallizes into calcium carbonate.

It is this chemical reaction that closes the cracks. The researchers repeated the experiment. They prepared a concrete with quicklime, cracked it, and poured water on it: the cracks were filled in two weeks, unlike a piece of concrete prepared with inactivated lime. The team is now working on the commercialization of its discovery.