For at least 1,500 years, Chinese masons have mixed sticky rice soup into their mortar for extra strength. Chemists now know why

【英文文本】

Mmm, sticky rice. It’s a glutinous side dish that’s perfect for practicing your chopstick skills, for sopping up curry sauce and, amazingly, for building really strong pagodas.

The Chinese have been building with mortar made from sticky rice and limestone since the time of the Ming Dynasty. Now scientists have figured out this ancient secret, in a study in the journal Accounts of Chemical Research.

Mud is probably the oldest mortar used to hold together bricks or stones. About 5,000 years ago, China started producing lime for construction. At least 1,500 years ago Chinese masons discovered that mixing in sticky rice soup makes lime even stronger.

Some tombs and city walls that were reinforced with the stuff are still standing. They’ve survived earthquakes and even modern bulldozers. The key, say the chemists, is amylopectin, a component of starch that interacts with the calcium carbonate in limestone to form a mortar that’s more water-resistant and less prone to shrinkage than lime mortar alone.

And that’s true even today. In 2006 traditional sticky rice mortar was used to restore the Shouchang bridge, built some eight centuries ago. Because even for an ancient stone bridge, sometimes sticky rice hits the spot.