Sticky rice, which has been a staple of the Chinese diet for centuries, also played a huge role in the construction of their ultra-durable cities and walls. The glutinous side dish has been used since the Ming Dynasty to create a super-strong mortar that has helped keep ancient buildings intact and resisted earthquakes. Scientists recently discovered what it is about glutinous rice that creates the super-strength mortar, and have also determined that sticky rice mortar is best available material to restore ancient and historic buildings.
Around 1,500 years ago, the Chinese started adding sticky rice soup to their traditional lime mortar mixture, which dramatically increased the strength of the mortar. Important buildings like tombs, pagodas, and city walls were constructed using this composite mixture, and some of the buildings are still standing today even after earthquakes. Bingjian Zhang, Ph.D., and colleagues performed studies to hone in on the key ingredient in the sticky rice to determine why it made for such a strong mortar.
The results showed that the organic-inorganic compound was made possible by amylopectin, a type of polysaccharide, or complex carbohydrate, found in rice and other starchy foods. The amylopectin combines with the inorganic calcium carbonate from the lime to form a mortar that has more stable physical properties, greater mechanical strength, and is more compatible than normal lime mortar. After their tests on various mortar recipes, the scientists determined that the sticky rice mortar is the most suitable mortar for restoration of ancient buildings, which means its probably also appropriate for new construction as well.