"It's not every day that you get to be present at the birth of a landmark," said Los Angeles Mayor Eric Garcetti. The 3,500-foot concrete 6th Street Viaduct is a Los Angeles icon. But the 80-year-old structure isn't holding up well. A chemical reaction in the concrete is causing the bridge to crack and break apart. Costly restorative methods have not worked, and the only option left was to rebuild.