Thaindian News

June 3, 2010 (Pen Men at Work): The scientists in China appear to have discovered the secret to a 1500 year old super-strong sticky-rice mortar that is found in buildings still standing today.

Sticky rice is the gelatinous, sweet rice, popular to many Americans from a dessert served in Thai restaurants, paired with coconut, milk and mango. It is also a very popular ingredient in Asian cuisine.

Scientists have discovered that when this sticky rice is mixed with slaked lime, it produces a composite organic/inorganic mortar with immense strength. They also concluded that the paste was used to bid and fill gaps between bricks, stone blocks and other construction materials, remains the best for restoring ancient buildings.

The article has been appeared in the American Chemical Society (ACS) monthly journal, Accounts of chemical research.

Bingjian Zhang along with his colleagues from the Laboratory of Cultural Relic Conservation Materials in the Department of Chemistry at Zhejiang University in Hangzhou, China, noted that construction workers in China had developed this mortar by mixing sticky rice soup with standard mortar ingredients. That ingredient is slaked lime, limestone that has been calcified or heated to a high temperature and exposed to water. Sticky rice happens to be world’s first composite mortar, made with both organic and inorganic materials.

The mortar was more resistant to water than pure lime and has been termed as one of the greatest technological inventions of the time. The material was used to construct important buildings like tombs, pagodas and city walls, which were strong enough to shrug off the effects of modern bulldozers and earthquake. Some of them still exist today.

The research has found that the key to this super-strong mortar is amylopectin, a type of polysaccharide found in rice. In addition, this amylopectin inhibited the growth of calcium carbonate crystals in the mortar, thus creating a compact microstructure that ages well.

To determine the building repair aid of sticky rice, scientists experimented with multiple organic compounds to add to the mortar. That includes egg whites, Tung oil, fish oil and animal blood. Then tested it and compared it to the more traditional lime mortar. But the result showed that the sticky-rice lime mortar has more stable physical properties, mechanical strength, and is more compatible which has made it a perfect restoration mortar.

Historians believe that the mortar is the reason for the survival of so many ancient Chinese buildings. The earliest record of sticky-rice has been found in a construction techniques book from Ming Dynasty, 1368 to 1644. But archeological explorers show that it was an already mature technology of the South-North Dynasty from 386-589.