Scientists have discovered the secret behind an ancient Chinese super-strong mortar¹ made from sticky rice, the delicious "sweet rice" that is a modern mainstay（中流砥柱） in Asian dishes. They also concluded that the mortar（灰泥） ― a paste used to bind² and fill gaps between bricks, stone blocks and other construction materials ― remains³ the best available material for restoring ancient buildings. Their article appears in the American Chemical Society (ACS) monthly journal, Accounts of Chemical Research. Bingjian Zhang, Ph.D., and colleagues note that construction workers in ancient China developed sticky rice mortar about 1,500 years ago by mixing sticky rice soup with the standard mortar ingredient（要素，原料） . That ingredient is slaked⁴ lime（熟石灰） , limestone⁵ that has been calcined（煅烧） , or heated to a high temperature, and then exposed to water. Sticky rice mortar probably was the world's first composite mortar, made with both organic and inorganic⁶ materials.

The mortar was stronger and more resistant⁷ to water than pure lime mortar, and what Zhang termed one of the greatest technological⁸ innovations of the time. Builders used the material to construct important buildings like tombs, pagodas⁹（宝塔） , and city walls, some of which still exist today. Some of the structures were strong enough to shrug¹⁰ off（不屑理睬） the effects of modern bulldozers（推土机） and powerful earthquakes.

Their research identified amylopectin（支链淀粉） , a type of polysaccharide（多糖） , or complex carbohydrate¹¹（复合糖） , found in rice and other starchy（含淀粉的） foods, as the "secret ingredient" that appears to be responsible for the mortar's legendary¹² strength.

"Analytical¹³ study shows that the ancient masonry¹⁴ mortar is a kind of special organic-inorganic composite material," the scientists explained. "The inorganic component¹⁵ is calcium¹⁶ carbonate, and the organic component is amylopectin, which comes from the sticky rice soup added to the mortar. Moreover, we found that amylopectin in the mortar acted as an inhibitor: The growth of the calcium carbonate crystal was controlled, and a compact microstructure was produced, which should be the cause of the good performance of this kind of organic-organic mortar."

To determine whether sticky rice can aid in building repair, the scientists prepared lime mortars¹⁷ with varying amounts of sticky rice and tested their performance compared to traditional lime mortar. "The test results of the modeling mortars shows that sticky rice-lime mortar has more stable physical properties, has greater mechanical strength, and is more compatible（兼容的，能共处的） , which make it a suitable restoration mortar for ancient masonry（石造工业） ," the article notes.