London: Scientists claim to have discovered the secret behind the strength and longevity of the Great Wall of China -- sticky rice.
A team at Zhejiang University in China has found that the delicious "sweet rice" that is a mainstay of modern Asian cuisine was also a key ingredient in the mortar used to build
the Great Wall 1,500 years ago.
Their study also found that construction workers in ancient China mixed sticky rice soup with slaked lime and limestone to create a paste ideal for filling in gaps between
bricks and stone blocks.
The super-strong material was used to build the Great Wall, as well as quake-proof tombs, pagodas and city walls, some of which still exist today, say the scientists.
"Analytical study shows the ancient masonry mortar is a kind of special organic-inorganic composite material. The inorganic component is calcium 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," team leader Dr Bingjian Zhang was quoted by the British media as saying.
To determine whether sticky rice can aid in building repair, the scientists prepared lime mortars with varying amounts of sticky rice and tested their performance compared
to traditional lime mortar.
Dr Zhang said: "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."
The findings have been published in the `American Chemical Society` journal.