【英语时差8,16】自动复原的混凝土（在线收听）

Have you ever been driving down a pothole filled street, thinking, "I wish the city, someone, anyone would fix the roads!" Soon, roads and streets may be able to fix themselves. Researchers at the University of Michigan have developed a type of concrete that heals itself when it cracks. Regular concrete is like ceramic when it breaks. It really breaks, opening a wide chasm that requires serious mending. Self healing concrete behaves more like metal. It bends without breaking thanks to special fibers holding it together. Bending or stressing the new concrete creates hairline fractures instead of gaping holes. All it takes to mend the tiny fissures is exposure to water and carbon dioxide. Chemicals in the concrete mix with water and carbon dioxide to form a healing scar. In the lab, the concrete was able to heal itself back to nearly full strength after a slab was stretched to three times its normal size. Self healing concrete could help cut costs for rebuilding not only new roads but also bridges and other structures that use the material. You won’t find self healing concrete on roads just yet. The researchers are working on bringing it to market in the next few years. And when it’s ready for widespread use, self healing concrete could make potholes a thing of the past.