Jun 16, 2004

States achieve recycling success

Using concrete again saves transportation agencies like TxDOT time and money

For states across the country, the use of recycled concrete aggregate (RCA) is cutting down on the amount of solid waste ending up in landfills and saving transportation agencies both time and money. A recent review of RCA use conducted by the Federal Highway Administration (FHWA) found that the Texas Department of Transportation (TxDOT), for example, has been using RCA in portland cement concrete (PCC) highways and streets and as aggregate for new PCC pavement and base material for the past 10 years. Through training and information sessions for its districts, TxDOT worked to overcome an initial perception in the state that RCA was a substandard or waste material. Now the state saves on the time and expense of hauling aggregate from quarries, because RCA primarily is generated and reused within the same urban areas.
The Minnesota Department of Transportation (MnDOT), meanwhile, uses almost 100% of the concrete removed from its pavements as dense-graded aggregate base, with statewide use of RCA permitted by the MnDOT Standard Specifications for Construction. Minnesota has found that RCA used in base and sub-base material performs similarly to virgin aggregate. MnDOT is now conducting research to establish laboratory performance parameters for RCA used in aggregate for bases and sub-bases.
The California Department of Transportation (Caltrans) has found that even though the initial production cost of RCA may be higher than that of new aggregate, the location of RCA plants near project areas lowers the final cost of using RCA, primarily due to reduced hauling distance and overhead costs. The damage to highways from loaded trucks also is reduced. Caltrans’ current specifications allow the use of RCA in pavement supporting layers. The agency also is working with the concrete and aggregate industries to develop further applications for RCA.
Over the last 20 years, the Michigan Department of Transportation (MDOT) has used RCA in PCC projects on such roads as I-75, I-94 and I-95. Currently, MDOT is reconstructing U.S. 41 in Michigan’s Upper Peninsula using RCA as the base material. RCA also is being used as a base material on two projects in the Detroit area. Similar to Minnesota’s experiences, MDOT has found that RCA used in base and sub-base material can provide performance comparable to or better than using virgin aggregate. This is because of the cementitious action that can still occur within the compacted base, adding higher supporting strength for the highway.
The use of recycled materials in transportation applications, including RCA, will be covered in a workshop for 11 Northeastern states that the University of New Hampshire’s Recycled Materials Resource Center (RMRC), FHWA and the American Association of State Highway & Transportation Officials (AASHTO) Recycling Task Force will present Sept. 12-14, 2004, in Manchester, N.H. The event will bring together state highway agency materials engineers and environmental specialists, state environmental protection agency staff and FHWA division office personnel. The workshop is designed to give attendees a tool box of information so that they can develop their own recycling expertise in their state. It will focus on four particular recycled materials applications: (1) coal fly ash as a cementation replacement; (2) foamed bitumen for stabilized full-depth reclamation; (3) asphalt shingles in asphalt; and (4) recycled concrete aggregate as a base material. The sponsors intend for the workshop to serve as a blueprint for other similar regional workshops.

About the author

Harrington is an asphalt pavement engineer in FHWA’s Office of Pavement Technology and team leader of FHWA’s Recycling Team.