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Federal Highway Administration > Publications > Focus > April 2004 > Recycled Concrete Study Identifies Current Uses, Best Practices
April 2004Publication Number: FHWA-HRT-04-024

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Recycled Concrete Study Identifies Current Uses, Best Practices

The Federal Highway Administration’s (FHWA) Pavement Recycling Team recently completed a year-long review of recycled concrete aggregate (RCA) state-of-the-practice use by five State transportation departments. “The review’s goal was to identify the current state of use and then transfer that knowledge to other State highway agencies,” says Jason Harrington of FHWA.

The Texas Department of Transportation (TxDOT) has been using RCA in portland cement concrete highways and streets and as a base material for the past 10 years and has found that it provides engineering, economic, and environmental benefits. In addition to eliminating the need for solid waste to go to landfills, RCA primarily is generated and used within the same urban areas. In Houston, for example, the total amount of concrete rubble generated is being consumed as RCA. This saves time and money when compared to hauling aggregrate from quarries.

TxDOT’s use of RCA in new concrete initially created problems with mix workability, with contractors having difficulty in maintaining a consistent and uniform saturated surface dry condition. This hurdle was overcome through the implementation of a process control program that heightened awareness of the need to water RCA stockpiles and to conduct more frequent testing of the aggregate for moisture content.

Through training and information sessions for its districts, TxDOT has also worked to overcome the initial general perception in the State that RCA is a waste product and thus substandard material.

Among the recommendations found by the FHWA study for using RCA is that compaction of RCA in a base should be in a saturated state to aid in the migration of fines throughout the mix. It is also recommended that steel wheel rollers be used to compact RCA, as minor amounts of steel present in the material can interfere with rubber-tired equipment.

Since 1983, the Michigan Department of Transportation (MDOT) has used RCA in numerous road projects. Currently, US-41 in Michigan’s Upper Peninsula is being reconstructed using RCA as the base material. RCA is also being used as a base material on two projects in the Detroit area. MDOT’s experience has shown that RCA used in base and subbase material can provide performance comparable to or better than using virgin aggregate. This is due to the cementitious action that can still occur within the compacted base, adding higher supporting strength for the highway.

MDOT has also found that incorporating RCA can reduce costs. Using RCA for the US-41 reconstruction project has resulted in savings of $114,000, for example.

MDOT notes that quality control and quality assurance procedures are vital when using RCA. Among the areas MDOT is looking to gain additional experience in are RCA’s effect on drainage systems and documentation of RCA’s long-term performance as a base material.

The Virginia Department of Transportation’s (VDOT) use of RCA has been limited to date. In one application, VDOT used RCA in the subbase aggregate for a $140 million reconstruction of a section of Interstate 66 in Fairfax and Prince William counties. Portable concrete crushing equipment was set up in the work zone at a closed truck weighing station. This eliminated the need to truck aggregate to the construction zone.

The University of New Hampshire’s Recycled Materials Resource Center (RMRC), in conjunction with the AASHTO Recycling Task Force and the FHWA Recycling Team, will present a workshop on the beneficial use of recycled materials in transportation applications from September 12–14, 2004, in Manchester, New Hampshire. The workshop will bring together State highway agency materials engineers and environmental specialists, State environmental protection agency staff, and FHWA Division Office personnel from 11 northeastern States to discuss the use of recycled materials in the highway environment. "The workshop will be structured to give attendees a tool box of information so as to allow them to develop their own recycling expertise in their State,” says Jason Harrington of FHWA. “We hope this will provide a pattern for other regional workshops that will teach participants about the uses of various recycled materials that are sound both environmentally and in an engineering sense.”

The RMRC workshop 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.

For more information about the workshop, contact Taylor Eighmy at RMRC, 603-862-1065 (email: t.eighmy@rmrc.unh.edu).

For in depth technical knowledge of asphalt pavement recycling methods, sign up for the National Highway Institute (NHI) course, Asphalt Pavement Recycling Technologies (Course No. 131050A). The course was developed by FHWA, the Asphalt Recycling and Reclamation Association, and the National Center for Asphalt Technology. Among the topics covered are performance of recycled mixes, selection of pavement for recycling, structural design of recycled pavements, recycling strategies, and the economics of recycling.

Upon completion of the course, participants will be able to:

  • Describe the various methods (hot and cold) of recycling pavements.
  • Determine when asphalt recycling is a viable pavement rehabilitation alternative.
  • Select the most appropriate asphalt recycling method or technique.
  • Identify materials and mix design for recycled pavements.
  • Specify equipment, construction methods, and quality control/quality assurance procedures involved in recycling.
  • Demonstrate design methods for hot and cold recycled pavements.

The 2-day course is intended for State and local highway officials, administrators, pavement design engineers and technicians, and construction engineers and inspectors involved in the recycling of asphalt pavements. The cost is $270 per participant.

To schedule the course, contact Danielle Mathis-Lee at NHI, 703-235-0528 (email: danielle.mathis-lee@fhwa.dot.gov). For technical information about the course, contact Jason Harrington at FHWA, 202-366-1576 (email: jason.harrington@fhwa.dot.gov).

The Minnesota Department of Transportation (Mn/DOT) uses almost 100 percent of the concrete removed from its pavements as dense graded aggregate base, with Statewide use of RCA permitted by the Mn/DOT Standard Specifications for Construction. Minnesota has observed that RCA used in base and subbase material performs similarly to virgin aggregate. Research is now underway to establish laboratory performance parameters for RCA used in aggregate for bases and subbases.

The California Department of Transportation’s (Caltrans) current specifications allow use of RCA in pavement supporting layers. Caltrans is working with the concrete and aggregate industries to develop further applications of RCA. 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 and overhead costs. This also saves time and reduces the damage to highways from loaded trucks.

Summaries of the Texas, Michigan, Virginia, Minnesota, and California RCA reviews can be found online at www.fhwa.dot.gov/pavement/recycle.htm. An overall summary report is due to be released later this year. FHWA is also working with the American Association of State Highway and Transportation Officials (AASHTO), U.S. Environmental Protection Agency, and the American Concrete Institute to develop guidance information on how States can use recycled concrete in highway applications. To learn more about the State RCA reviews or the guidance information being developed, contact Jason Harrington at FHWA, 202-366-1576 (email: jason.harrington@fhwa.dot.gov).

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Updated: 04/07/2011

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