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A portion of the 24-inch-thick runways from Stapleton International Airport sits in a heap after Recycled Materials Co. Inc. demolished it as part of a demolition project

The U.S. Green Building Council estimates that buildings account for 30% of all raw materials used and 30% of all waste generated. So it's no surprise that efforts are being made to find ways to reuse “waste” construction materials in new projects.

While concrete producers have been at the forefront of using industrial waste materials (fly ash and slag) in their mixes, they haven't been as receptive to reusing construction waste. But this is about to change.

Recycled concrete aggregate (RCA) is gaining acceptance from many engineers. The U.S. Federal Highway Administration (FHWA) is currently preparing an updated technical advisory on using RCA as aggregate for new concrete. The document is being reviewed within the agency. Suneel Vanikar, FHWA's PCC Team Leader, is spearheading the project. FHWA's last printed report was a national review on using RCA, which is available from the Recycled Materials Resource Center at FHWA's Web site at www.fhwa.dot.gov.

Several states are also actively promoting RCA. For example, the State of California passed some recycling requirements for RCA within the last year.

But RCA isn't restricted to paving projects. According to engineers at the Portland Cement Association, the Leadership in Energy and Environmental Design (LEED) Green Building Rating System recognizes recycled concrete in its point system. Credit 4 (Materials and Resources) states, “Specify a minimum of 25% of building materials that contain in aggregate a minimum weighted average of 20% post-consumer recycled content material, or a minimum weighted average of 40% post-industrial recycled content material.”

Using recycled aggregates instead of extracted aggregates would qualify as post-consumer. Because concrete is an assembly, its recycled content should be calculated as a percentage of recycled material on a mass basis.

Credit can also be obtained for Construction Waste Management. It is awarded based on diverting at least 50% by mass of construction, demolition, and land clearing waste from landfill disposal. Concrete is a relatively heavy construction material and is frequently recycled into aggregate for road bases or construction fill.

With all of this interest, producers can expect RCA to become an important aggregate source. Just as important, producers may wish to get involved early and set up operations to create their own material. RCA can be a big business. For a variety of reasons, some producers are taking a close look at the ways hardened concrete can be crushed for RCA.

Runway projects

There are several good examples. Denver-based Recycled Materials Co. Inc. (RMCI) has been a leader in producing RCA. Having finished removing the 24-inch thick runways from the former Stapleton International Airport, the aggregate producer has moved operations to a new project in California.

The project at El Toro Marine Corps Air Station near Irvine is complex. It involves removing and recycling more than 3.5 million tons of concrete and asphalt. The developer stipulated that none of the material could leave the 3000-acre site and affect the surrounding community.