The technologies for u· ing many wa te materials including indutrial, dome tic, and mining/metallurgical wa tes were developed by the Federal Highway Administration during the 1970s. tudie on fly ash, bonom ah incinerator residue, sulfate wa te·, dige ted sewage sludge, coal mine refus wa te rubber. and cement manufacturing wastes have been completed. Materials in estigaced were stabilized with various binder including lime. lime-Dy a. h·, asphalt cement, and portland cement. Both laboratory evaluations and field tests wer performed. Many of the sy tem. evaluated developed strength and other physical properties adequate for use in embankments, subbases, and bases. Some materials (eg, fused incinerator re idue) were technically adequate for use in bituminous concrete-wearing surfaces. While the emphasis of the research was on engineering behavior, assessments of economic and environmental factors were made in some cases. Information generated should be of interest and of use today wh n more and more emphasis is being pla ed on saving the envi. ronment from further desecration.

The FHWA has had an interest in waste and by-product utilization since the mid 1950s. Early work concentrated on the properties and utilization of various fly ashes and fly ashcontaining systems (1, 2). In the early 1970s, several events gave impetus to the development of a comprehensive research program on waste and by-product utilization in highway construction. First, the president, in his 1970 Environmental Message, stated the need to encourage more recycling and requested the Council on Environmental Quality to develop proposals in this area. Second, the Oil Embargo of 1973 demonstrated the need to conserve energy and to develop alternative materials to supplement or replace asphalt cement. Finally, a large by-product utilization demonstration project at Dulles International Airport was sponsored by FHWA (3, 4) that demonstrated that many by-product materials had potential for use as paving binder and aggregate supplements or replacements. On the basis of those and other events (eg, the Clean Air Act of 1970) the FHWA developed a research program entitled" Use of Waste Materials for Highways." FHWA's research program was designed to evaluate a wide spectrum of by-products that, in general, were technically promising as aggregate or binder supplements or replacements. Economics and environmental concerns were also considered. In some cases, materials with little or no potential for use as a highway material (eg, sewage sludge) were evaluated to address an immediate, critical, and specific highway problem.