"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."