More than 40 different mixes of concrete were used for the San Francisco-Oakland Bay Bridge in California. Each mix contained between 25% and 50% of recylced materials, which made them greener than traditional concrete. This helped slash about 60 million pounds of carbon dioxide emissions, according to Jeff Davis, vice president and general manager of Central Concrete Supply Co. "In the last four, five years, Caltrans was extremely aggressive and proactive," Davis said. "And through that, we were designing concrete for this job that was cutting-edge as far as low [carbon dioxide]."