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Romans Invented Self-Repairing Concrete

Updated: May 28

Ancient Roman infrastructure puts many modern buildings to shame. While today’s concrete structures might only last a few decades, some long-lived concrete in Rome has survived for 2,000 years. For example, the Pantheon’s unreinforced concrete dome, completed around 125 C.E., remains intact to this day.

Pantheon's concrete dome, Rome
Pantheon's concrete dome | Unsplash

“The Pantheon would not exist without the concrete as it was in the Roman time,” says Admir Masic, a chemist at MIT.

Scientists have long wondered how the Romans achieved such an immense feat of engineering. In a new paper, published in the journal Science Advances, Masic and other researchers propose that the concrete mixed by Romans could repair cracks on its own.

While the finding reveals new insights on ancient Rome, it also provides a blueprint for improving modern concrete, scientists say.

Researchers took mortar samples from walls in the ancient city of Privernum, near Rome, to study its composition and found that the mortar contained small white chunks of calcium deposits, called lime clasts. Previously, researchers thought the chunks meant that Romans weren’t mixing the concrete well enough. But Masic wasn’t convinced.

The team theorized that these calcium deposits served an important purpose. They thought that as water entered cracks in the concrete, it could dissolve the chunks of calcium. Then, the dissolved chemicals could recrystallize or react with other materials, filling the cracks and strengthening the structure.

To test this, the team made concrete using a Roman recipe and a modern recipe. They then broke the concrete and let water pass through it for 30 days. Afterward, the modern concrete still let water pass through, but the Roman concrete did not, suggesting the cracks had been filled. Thus demonstrating that Roman engineers had solved a problem that had eluded modern techniques.

The new findings could, therefore, lead to more durable modern concrete.


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