Researchers dig up secrets of 'self-healing' Roman concrete
How have Rome's ancient aqueducts and architectural marvels such as the Pantheon, which features the world's largest unreinforced concrete dome, endured the test of time? Researchers at the Massachusetts Institute of Technology (MIT) and other institutions believe they have uncovered the mystery of the durability of the 2,000-year-old structures - self-healing concrete.
The secret lies in an ingredient of the ancient concrete used by the Romans that the researchers, whose findings are published in the latest edition of the journal Science Advances, said has been overlooked in previous studies.
The durability of the concrete used by the Romans has most frequently been attributed to the use of volcanic ash from Pozzuoli on the Bay of Naples, which was shipped across the Roman empire for construction.
But the researchers focused their attention on another component of the ancient concrete mix, small white chunks called "lime clasts."
"Ever since I first began working with ancient Roman concrete, I've always been fascinated by these features," said MIT professor of civil and environmental engineering Admir Masic, an author of the study.
"These are not found in modern concrete formulations, so why are they present in these ancient materials?" The researchers said the lime clasts had been thought to be the result of "sloppy mixing practices" or poor-quality raw materials.
But they are in fact what gives the ancient 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," said Masic.
"If the Romans put so much effort into making an outstanding construction material... why would they put so little...