for National Geographic News
Its not quite as advanced as Terminator technology. But a new concrete that can heal its own wounds may soon bring futuristic protection to bridges and roads.
Traditional concrete is brittle and is easily fractured during an earthquake or by overuse.
By contrast, the new concrete composite can bend into a U-shape without breaking. When strained, the material forms hairline cracks, which auto-seal after a few days of light rain.
Dry material exposed by the cracks reacts with rainwater and carbon dioxide in the air to form "scars" of calcium carbonate, a strong compound found naturally in seashells, said study co-author Victor Li of the University of Michigan in Ann Arbor.
The flexible material is just as strong after it heals, the study authors report.
For the past 15 years Li, along with colleagues such as study leader and visiting scholar Yingzi Yang, has been developing next-generation concrete for various applications.
Similar self-healing concrete has already been used inside the core of Osaka, Japan's tallest residential building, a 60-story structure, Li noted.
The material was also used in a bridge built in 2006 over Interstate 94 in Michigan, where it eliminated the need for traditional expansion joints. These "toothed" metal slats allow normal concrete to expand and contract without bending, but they can create significant road noise as vehicles rattle over them.
"One of the big attractions, apart from reducing maintenance requirements, is the fact that [the new concrete] is very quiet" without expansion joints, Li said.
Self-healing concrete is now being considered for use in irrigation channels in Montana.
Although it costs three times as much as traditional concrete, the material is a cost-saver in the long run, due to its reduced maintenance needs and energy demands, Li said.
Builders using the bendable concrete, for example, don't need to buy and install devices that counter seismic activity.
"The initial building cost actually becomes lower," Li said.
Findings published online March 4 in the journal Cement and Concrete Research.
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