The ancient Romans were known for their exceptional engineering and building skills, with their iconic aqueducts standing as a testament to their expertise. These enduring structures were made possible by a unique material known as pozzolanic concrete, which played a key role in their incredible strength and longevity.
Among the most famous Roman structures is the Pantheon, a nearly 2,000-year-old building that still holds the record for the world's largest dome made of unreinforced concrete. The secret to the durability of these structures has long been attributed to the composition of their concrete-pozzolana, a volcanic ash found in the Italian city of Pozzuoli, mixed with lime. When combined with water, these materials form a remarkably strong concrete.
However, recent research has revealed that the story behind Roman concrete is more complex than previously believed. In 2023, an international team of researchers led by the Massachusetts Institute of Technology (MIT) discovered that not only were the materials used in Roman concrete slightly different from earlier assumptions, but the techniques for mixing them were also unique.
"Ever since I first began working with ancient Roman concrete, I've always been fascinated by these features," MIT professor of civil and environmental engineering Admir Masic said in a news release. "These are not found in modern concrete formulations, so why are they present in these ancient materials?"
Previously disregarded as merely evidence of sloppy mixing practices, or poor-quality raw materials, the new study suggests that these tiny lime clasts gave the concrete a previously unrecognized self-healing capability. "The idea that the presence of these lime clasts was simply attributed to low quality control always bothered me," says Masic.
"If the Romans put so much effort into making an outstanding construction material, following all of the detailed recipes that had been optimized over the course of many centuries, why would they put so little effort into ensuring the production of a well-mixed final product? There has to be more to this story."
