pompeii still stands because ancient romans used self-healing concrete that lasts for decades

"In 2023, MIT Associate Professor Admir Masic and his team published a paper explaining how Roman concrete was made, describing a method called hot-mixing. In this process, lime fragments are mixed dry with volcanic ash and other materials, and water is added only at the end. When water touches the dry mix, it creates heat, which traps the lime inside the concrete as small white pieces. These pieces can later dissolve and fill cracks, giving the concrete the ability to repair itself."

"In the recent discovery, the team found out that the ancient Roman architect Vitruvius wrote a book about architecture, where he said Romans added water to the lime first to make a paste, then mixed it with other materials. This was different from what the MIT professor found in the lab, and because Vitruvius is so important in history, Admir Masic felt unsure about contradicting him."

"Professor Admir Masic and his university collaborators collected samples from dry material piles, unfinished walls, finished walls, and repair sections during their visit at Pompeii in pursuit of restudying the site's self-healing concrete. They found lime clasts in the concrete, just like in the earlier study, but they also came across unreacted quicklime fragments inside the dry material pile, showing that the Romans mixed the lime dry and proving that hot-mixing was us"

Hot-mixing combines lime fragments dry with volcanic ash and other materials, with water added only at the end. When water contacts the dry mix, heat generation traps lime as small white clasts that can later dissolve and fill cracks, enabling self-repair. An ancient architectural source described a contrasting wet-paste method, creating a historical discrepancy. A well-preserved Pompeii construction site offered raw material piles, tools, and walls at multiple construction stages for direct sampling. Samples from dry piles, unfinished and finished walls, and repair sections contained unreacted quicklime fragments, confirming dry hot-mixing in Roman construction.

Read at designboom | architecture & design magazine