Scientists discovered that ancient Chinese structures, including a section of the Great Wall of China, had a special ingredient in the extremely strong mortar: sticky rice.
The American Chemical Society (ACS) published a report last week in the Accounts of Chemical Research which said that Chinese workers mixed in sticky rice into their mortar paste approximately 1,500 years ago. The report noted that the sticky rice mortar was combined with “slaked lime” or “limestone that has been calcined,” and was likely one of the first composite mortars ever created.
Dr. Zhang Bingjiang, one of the scientists who made the discovery, said that the sticky rice mortar was stronger and more water-resistant than previous versions, making it “one of the greatest technological innovations of the time.”
Sections of the Great Wall were built using the sticky rice mortar 600 years ago, reports The Telegraph.
Other than the Great Wall, pagodas, tombs, temples, and city walls were constructed with the mortar and many are still standing in the present day, notes the ACS report.
Some of the structures are still strong enough to “shrug off” damage caused by bulldozers and earthquakes over the years, the report said.
After closely examining the mortar, they found amylopectin, a complex carbohydrate found in rice and other carbohydrates.
“Analytical study shows that the ancient masonry mortar is a kind of special organic-inorganic composite material,” scientists explained in the report. ”The inorganic component is calcium carbonate, and the organic component is amylopectin, which comes from the sticky rice soup added to the mortar.”
The scientists tested their hypothesis, mixing sticky rice with mortar paste and prepared lime mortar bricks at varying sizes.
“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, which make it a suitable restoration mortar for ancient masonry,” notes the article.