Studies have found all kinds of natural materials mixed into structures from long ago: fruit extracts, milk, cheese curd, beer, even dung and urine. In this way, the Mayan plaster was able to mimic sturdy natural structures like seashells and sea urchin spines - and borrow some of their toughness, Rodriguez-Navarro said. When scientists zoomed in, they saw that bits of organic material from the tree juice got incorporated into the plaster’s molecular structure. When researchers tested out the recipe-collecting bark, putting the chunks in water and adding the resulting tree “juice” into the material-they found the resulting plaster was especially durable against physical and chemical damage. The masons suggested using extracts from local chukum and jiote trees in the lime mix. And according to a study published earlier this year, the secret to these structures’ longevity might lie in the trees that sprout among them. “The concrete was so well designed that it sustains itself.” Tree “juice”Īt Copan, a Maya site in Honduras, intricate lime sculptures and temples remain intact even after more than 1,000 years exposed to a hot, humid environment. The ability to keep adapting over time “is truly the genius of the material,” Jackson said. This naturally reactive material changes over time as it interacts with the elements, Jackson said, allowing it to seal cracks that develop. The builders would gather volcanic rocks left behind after eruptions to mix into their concrete. Marie Jackson, a geologist at the University of Utah, has a different take. Her research has found that the key could be in the specific volcanic materials used by the Romans. That water activates the leftover pockets of lime, sparking up new chemical reactions that can fill in the damaged sections. When cracks form, water is able to seep into the concrete, Masic explained. Instead, after analyzing concrete samples from Privernum, an ancient city outside of Rome, the scientists found that the chunks could fuel the material’s “self-healing” abilities. Researchers used to think these chunks were a sign that the Romans weren’t mixing up their materials well enough. In a study published earlier this year, Admir Masic, a civil and environmental engineer at the Massachusetts Institute of Technology, proposed that this power comes from chunks of lime that are studded throughout the Roman material instead of being mixed in evenly. Exactly how is not yet clear, but scientists are starting to find clues. Now, scientists think they’ve found a key reason why some Roman concrete has held up structures for thousands of years: The ancient material has an unusual power to repair itself. The ancient builders mixed materials like burnt limestone and volcanic sand with water and gravel, creating chemical reactions to bind everything together. Then, chunks of material like rock and gravel are added, and the cement paste binds them into a concrete mass.Īccording to records from ancient architects like Vitruvius, the Roman process was similar. That cement is mixed with water to create a chemically reactive paste. Most modern concrete starts with Portland cement, a powder made by heating limestone and clay to super-high temperatures and grinding them up. Even in harbors, where seawater has been battering structures for ages, you’ll find concrete “basically the way it was when it was poured 2,000 years ago,” said John Oleson, an archaeologist at the University of Victoria in Canada.
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