America's Bridges Are falling down. Victor Li says he knows a better way to build them. The civil and environmental engineering professor at the University of Michigan has invented a new kind of concrete that hardly ever cracks and, if it does, can repair itself. A typical American bridge is built to last 50 years (and then only if it gets frequent roadbed replacements). Today the average age of U.S. bridges is 42 years.
展开▼