What is the secret of ancient Chinese super-strong mortar?

Washington, May 31 (IANS) What is the secret of an ancient Chinese super-strong mortar made from sticky rice?

Scientists have concluded that the mortar – a paste used to bind and fill gaps between bricks, stone blocks and other construction materials – remains the best available material for restoring ancient buildings.

Bingjian Zhang, professor of physical chemistry at Zhejiang University, China 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.

That ingredient is slaked lime, limestone that has been calcined, 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 inorganic materials.

The mortar was stronger and more resistant to water than pure lime mortar, and what Zhang termed one of the greatest technological innovations of the time.

Builders used the material to construct important buildings like tombs, pagodas, and city walls, some of which still exist today. Some of the structures were strong enough to shrug off the effects of modern bulldozers and powerful earthquakes.

Their research identified amylopectin, a type of polysaccharide, or complex carbohydrate, found in rice and other starchy foods, as the ‘secret ingredient’ that appears to be responsible for the mortar’s legendary strength, said a release of the American Chemical Society (ACS).

‘Analytical study shows that the ancient masonry mortar is a kind of special organic-inorganic composite material,’ the scientists explained.

‘The inorganic component is calcium carbonate, and the organic component is amylopectin, which comes from the sticky rice soup added to the mortar,’ scientists added.

These findings appear in the ACS monthly journal, Accounts of Chemical Research.