In 1972, Illinois used 246,000 cubic yards of coal fly ash beneath 7,500 feet of expressway

More than five decades ago, civil engineers in northern Illinois carried out a major engineering experiment by using 246,000 cubic yards of coal fly ash beneath 7,500 feet of a major expressway embankment. The pioneering project, completed in 1972 near Waukegan along the US Route 41 corridor, was one of the earliest large-scale examples of recycling industrial waste for American highway construction. Long-term monitoring showed that the alternative fill performed very well, with no signs of structural settlement, frost heave or problems caused by rising groundwater. Detailed technical studies of the project were later published by the National Cooperative Highway Research Program in NCHRP Synthesis 199, titled Recycling and Use of Waste Materials and By-Products in Highway Construction. The Federal Highway Administration also included the project in its detailed user guidelines. The findings helped change how state transportation departments across North America viewed industrial byproducts. They showed that fine ash collected from coal-fired power plants could replace traditional soil and aggregate used as backfill.Engineering a major highway embankment with industrial wasteThe de...