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The Mystery of Ancient "Self-Healing" Roman Concrete May Have Finally Been Solved

Now we know why their structures last so long.
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We all know cracks in the sidewalk. We’ve seen bridges only a few decades old need massive refurbishment. Concrete today is regularly reinforced with steel beams for added strength and durability. Why then, has much concrete from Ancient Rome stood the test of time? Why do their aqueducts still span rivers, and why does the famous dome of the Pantheon still stand after thousands of years? It is a mystery which has long plagued archaeologists.

And now, they might at last have found an answer.

Ancient Roman concrete is incredibly durable, in part because it has properties that some describe as “self healing. Whereas other concrete cracks and crumbs under stress or due to wear, Roman concrete has the mysterious ability to heal tiny fissures in its structure.

Scientists have recently determined that this might be due to the way the Romans added lime (or quicklime) to their gravel aggregate in a hot kiln, creating tiny flecks of lime class in the final concrete. These flecks act as healing agents when rainwater seeps into any fissures, reacting with the water to create calcium which then crystallizes in the cracks.

For years, the lime flecks were thought to be a flaw in the concrete, but it turns out that it is part of the reason this substance is as strong and long-lasting as it is.

The study was done at MIT and Harvard, and recently published in the journal Science Advances.

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