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What’s holding up China’s oldest buildings?

Scientists, reporting in an issue of *Accounts of Chemical Research*, have discovered the secret organic ingredient added to building mortar in China to create super strong walls that withstood even earthquakes: sticky rice.

In creating what amounts to the first organic-inorganic composite material, construction workers circa 1500 years ago utilized a unique feature of a polysaccharide chain from the sticky rice. This substance, amylopectin, is a complex carbohydrate which reduces the size of calcium carbonate crystals – CaCO3 from the lime – which in turn leads to smaller, more compact internal microstructures and therefore stronger mortar.

Besides discovering the secret compound responsible for these old buildings’ supreme strength, the researchers also tested newly manufactured sticky rice mortar against modern lime mortar, and found it had greater stability, mechanical strength, and was more compatible with the older buildings. Looks like the next restoration will have to proceed after the next pot of rice is done.

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