A simple mimic.

ing at the University of Arizona. Saadatmanesh developed the material, called CarbonWrap, about six years ago and now sells it through CarbonWrap Solutions. The polymer is made of woven filaments of glass, carbon and Kevlar, which are placed in a resin matrix. Its tensile strength—the force required to pull it apart—is about 200 tons per square inch, 10 times stronger than steel. The fiber costs $16 a pound and is attached to the bridge girders with a special epoxy. Patching a small girder crack would only cost about $200, including labor; doubling the layers increases the strength by about 30 percent. “You don’t need to drill holes,” which can further weaken a structure, Saadatmanesh says. “Instead of taking eight hours” for a traditional patch, he adds, “you can do this in half an hour.” In laboratory testing, Saadatmanesh says that CarbonWrap has held through the equivalent of about 10 million trips by a 35-ton truck. It resists corrosion, an important consideration given the galvanic currents that can be generated between metallic components on a bridge, and has withstood a pH 2.5 solution for two years. Steel would melt in just a few hours in such an acidic bath. CarbonWrap has shored up water pipes and light poles, but it has yet to patch bridges—engineers are conservative by nature. “It takes a while to adopt a new thing,” explains Taichiro Okazaki, a civil engineer at the University of Minnesota who is heading a team of researchers to examine the Minneapolis collapse. “New materials have to be very reliable, and it takes many years to develop trust.” Bridge engineers have begun talking to Saadatmanesh’s company, and Okazaki suggests that the first applications for CarbonWrap might be on small, lightly trafficked bridges, such as those found on golf courses. Such novel materials may play a crucial role in addressing the nation’s aging infrastructure, although ultimately they cannot replace commitments to timely inspections, better designs and new bridges.