The secret behind Roman concrete has finally been revealed

The Colosseum, Pantheon, Arles Amphitheatre, many aqueducts – all of these are structures from the Ancient Roman Empire, built two thousand-plus years ago, that are still standing today. And while the modern world has known about the ultra-durable material used in their construction for ages (Roman concrete), researchers had no idea how it was actually created…until now.

According to a new peer-reviewed study published in Science Advances, the strength of Roman concrete can be attributed to a special mixing process called “hot mixing,” which allows buildings made with the material to literally repair themselves.

🧑‍🔬 How the discovery went down: Scientists from MIT and Harvard were first alerted to the concept of hot mixing after noticing millimeter-wide bright white calcium deposits in the ancient Roman concrete samples they were studying – and seriously doubting the previous explanation for it.

Researchers had long believed the existence of those deposits meant the concrete-makers were using poor mixing practices… which didn’t sit right with the study’s authors. “It was really difficult to believe that ancient Roman [engineers] would not do a good job, because they really made careful effort when choosing and processing materials,” MIT chemist Admir Masic told CNN.

• After performing an analysis, the scientists discovered these calcium deposits were the result of an advanced technique they dubbed “hot mixing.”
• And what’s more, this technique appears to have held the hidden key to Roman structures’ self-healing properties all along.

🤔 How, you ask?... When water enters cracks in the concrete, the chunks of calcium are dissolved and later recrystallize, filling the cracks and strengthening the structure. That’s right – Roman concrete is water-activated, just like your favorite cocoa butter oatmeal bath bomb.