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Ancient Chinese building secret revealed: sticky rice mortar

http://content.usatoday.com/communities/sciencefair/post/2010/06/ancient-chinese-building-secret-revealed---sticky-rice-mortar/1


Scientists in China have discovered the secret to a 1,500-year-old
super-strong ancient Chinese sticky rice mortar that is found in
buildings still standing today.

Sticky rice is the sweet, glutinous rice familiar to many Americans
from a dessert served in Thai restaurants in which it is paired with
coconut milk and mango. It is a popular ingredient in many Asian
ciuisines.

But only the Chinese appear to have discovered that when mixed with
slaked lime, it creates a composite organic/inorganic mortar of
legendary strength.

The key to this super-strong mortar is amylopectin, a type of
polysaccharide, or complex carbohydrate, found in the rice, report
Bingjian Zhang and colleagues from the Laboratory of Cultural Relic
Conservation Materials in the Department of Chemistry at Zhejiang
University in Hangzhou, China. Their paper is in this month's edition
the American Chemical Society journal, Accounts of Chemical Research.

In addition, amylopectin inhibited the growth of the calcium carbonate
crystals in the mortar, producing a compact microstructure that ages
well.

Ancient Chinese builders experimented with multiple organic compounds
to add to mortar, including egg whites, tung oil, fish oil and animal
blood. Historians believe these organic/inorganic mortars are one
reason why so many ancient Chinese buildings have survived. But sticky
rice mortar was the most widely used.

Zhang calls the sticky rice mortar one of the greatest technological
innovations of the time. It was stronger and more resistant to water
than pure lime mortar. It was used to build tombs, pagodas and city
walls, some of which still exist today and some of which have survived
multiple, powerful earthquakes.

The earliest record of sticky rice mortar is found in a book on
construction techniques from the Ming Dynasty, 1368 to 1644. But
archeological digs show that it was already a mature technology by the
South-North Dynasty, from 386 to 589 .

The scientists in Hangzhou made plain lime mortar and sticky rice
mortars to compare them. They found that the sticky rice mortar has
greater mechanical strength and could easily be used to restore
ancient stone work.