Photo/Illutration Samples of recycled concrete, produced by adding wood powder instead of cement, on Feb. 6, in Tokyo’s Chiyoda Ward (Roku Goda)

Researchers have developed an environmentally friendly method of recycling concrete waste by mixing in wood and other materials.

The new method makes it possible to “recycle concrete waste without using cement,” Yuya Sakai, a lecturer at the University of Tokyo’s Institute of Industrial Science, who led the research team, said at a news conference on Feb. 6.

“It will help reduce carbon dioxide and reuse wood building materials and plants that would otherwise be scrapped,” Sakai said.

Every year, 33 million tons of concrete waste, such as debris from demolished buildings and bridges, are generated in Japan.

In many cases, such concrete waste is pulverized and reused as sub-base gravel for road surfaces.

Some of the waste will be recycled into concrete by adding cement. However, since cement is produced by burning limestone at 1,500 degrees, the cost is high.

In the new method, researchers crushed concrete waste to a powder. Then they added wood powder and water into the mixture and applied pressure equivalent to five atmospheres at a temperature of 160 degrees.

The mixture became concrete again, without the use of cement.

The flexural strength of the recycled concrete exceeded regular concrete, researchers said.

Lignin, a chemical compound richly contained in plants, played a role as an adhesive bond and helped connect particles of the pounded concrete, according to the researchers.

The durability of the recycled concrete seemed inferior to regular concrete. However, researchers are confident that the recycled concrete can be sufficiently utilized for parking blocks and temporary facilities.

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