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Ancient Roman Concrete Has 'Self-Healing' Capabilities – Scientific American

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Mineral deposits called “lime clasts” found in ancient Roman concrete give the material self-healing capabilities that could help engineers develop more resilient modern concrete and reduce its associated emissions
It’s fair to say the ancient Romans knew a thing or two about infrastructure.
They were among the first to refine the basic elements of lime, shale, clay and aggregate rocks that we call concrete today; then, they poured billions of tons of it to build one of the greatest empires in human history — iconic relics of which still stand across modern Europe.
But did the Romans also hold a secret to help concrete structures such as the Pantheon and Colosseum endure more than 15 centuries of climate change?
Research led by the Massachusetts Institute of Technology has found evidence they did, and the discovery could have implications for reducing carbon emissions and creating modern climate-resilient infrastructure.
In a recent study published in the journal Science Advances, experts at MIT and Harvard University found that calcium-rich mineral deposits called “lime clasts,” commonly found in Roman-era concrete, gave buildings and structures “a previously unrecognized self-healing capability.”
Yet there’s nothing magic about it, according to the researchers, who describe the clasts as “white chunks” of rock that originate from lime and appear as “small, distinctive, millimeter-scale” features in Roman concrete.
Admir Masic, the study’s senior author and professor of civil and environmental engineering at MIT, said he had long been fascinated by the unusual deposits in the 2,000-year-old material, which are not found in modern concrete. In fact, such deposits are viewed as impurities by today’s concrete manufacturing standards.
“The idea that the presence of these lime clasts was simply attributed to low quality control always bothered me,” Masic said in a release. “If the Romans put so much effort into making an outstanding construction material, following all of the detailed recipes that had been optimized over the course of many centuries, why would they put so little effort into ensuring the production of a well-mixed final product? There has to be more to this story.”
And there was.
Aided by spectroscopic examinations and high-resolution, multiscale imaging and chemical mapping techniques, the researchers gained new insights into how lime clasts were used by Roman concrete-makers.
The team then produced samples of what’s called “hot-mixed concrete” using both Roman and modern methods. After the materials hardened, the scientists deliberately cracked the samples and ran water through the cracks.
For the sample using ancient mixing techniques, “the cracks had completely healed” within two weeks, and water no longer flowed through the material. The lime clasts had aided in a chemical process that resulted in “self-healing.” Meanwhile, an identical chunk of concrete without the lime-clast structure never healed, and the water just kept flowing through the sample.
The difference is that scientists believe the Roman process involved a highly chemically reactive form of lime called quicklime that aided in the self-healing process. That lime form is not used to make concrete today.
The findings have a relevance to today’s climate challenges, first by proving that an ancient method of producing concrete resulted in highly resilient infrastructure. Second, the development of more resilient concrete “could help reduce the environmental impact of cement production, which currently accounts for about 8 percent of global greenhouse gas emissions,” the researchers said.
In addition to MIT and Harvard, study contributors included experts from research institutions in Italy and Switzerland.
Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2023. E&E News provides essential news for energy and environment professionals.
Daniel Cusick covers climate change adaptation and resilience. He joined E&E News in 2003 and has filed news stories from South Florida to Northern Minnesota. He has reported from more than a half dozen hurricane recovery zones and documented climate change impacts, resilience and energy transitions in East Africa. He lives in Minneapolis.

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