Roman aqueducts built more than 2,000 years ago are still in operation. The Pantheon in Rome remains the largest dome made of unreinforced concrete in the world, with a diameter of 43.3 meters. At the same time, it is not unusual to see structures less than a decade old collapsing. Understanding why Roman structures remain standing has been the subject of studies by many researchers around the world. Why, even in hostile environments such as coastlines or seismic zones, do these structures remain intact? Is there some miraculous material or method that has been lost in history? An international group of researchers led by the Massachusetts Institute of Technology (MIT) has shed light on these questions, discovering that these structures had a previously overlooked capacity for self-healing, and the potentially huge environmental impact it can have, to create more durable concrete structures in the future.
The conclusions were reached through microscopic analysis, using X-ray technologies, of a sample of Roman concrete on the wall of the ancient city of Privernum, near Rome. This highlighted what we already knew about the composition of Roman concrete: volcanic tuff and other coarse aggregates, bound together by a mortar based on lime and pozzolana (a material found in volcanic ash, named after the town of Pozzuoli, in the vicinity of Vesuvius). The analysis also highlighted tiny white minerals, called "lime clasts," which had been noted previously but were attributed to a sloppy mixing process or low-quality raw materials. What this new study suggests is that it is these harmless white lumps that give concrete a previously unrecognized capacity for self-healing.
