TOKYO, Dec 28 (Reuters) - Flexible concrete that becomes stronger after it cracks is being used in Japanese buildings to protect against earthquakes.

Developed by construction firm Kajima Corp, it contains polymer fibres the thickness of a human hair, commonly used in tyres, that hold it together and prevent cracks from spreading.

Instead, the concrete bends and can bear an even stronger load after it cracks, the company said, making buildings stronger if they are jolted by one of Japan’s many quakes.

“It will be totally fine even if a giant earthquake hits,” said Tetsushi Kanda, a senior engineer at Kajima.

He said it stretches 100 times more than regular concrete.

Japan, which prides itself on its quake-resistant engineering standards, was traumatised by the destruction of concrete elevated highways and buildings in a magnitude 7.3 tremor in the western city of Kobe in 1995 that killed more than 6,400 people.

Kajima said in such an earthquake its bendable concrete would have no visible cracks and would retain its strength. So far, two new high-rise buildings using it have been built in Japan and up to 100 buildings and infrastructures have been reinforced with it. The product, which took over 10 years develop, was introduced around 2003 but holds only 0.1 percent of Japan’s concrete market, Kanda said, partly because it costs 10 times more than regular concrete.

“We’re working to find a way to fully utilise the capability of this material while bringing down the price,” Kanda said.

Japan, situated on the “Ring of Fire” arc of volcanoes and oceanic trenches around the Pacific Ocean, accounts for about 20 percent of the world’s earthquakes of magnitude 6 or greater.

(Reporting by Yoko Kubota, Editing by Michael Watson)

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