IDOT/ICT Lay Groundwork for Sustainable Pavements

The U.S. EPA estimates that 170 million tons of construction and demolition debris are generated every year, with asphalt shingles accounting for about 15% of that total. Fortunately, the recovery rate of asphalt shingles has almost doubled in the past decade, and much has been learned about how to successfully incorporate recycled asphalt shingles (RAS) and recycled asphalt pavement (RAP) into hot-mix asphalt (HMA). Benefits of using recycled materials in HMA are the following: 

  • Less use of virgin materials (aggregate and petroleum-based binder)
  • Reduced energy consumption and emissions resulting from use of fewer virgin materials during plant production of asphalt mixtures, as well as lower overall emissions because of the decreased need to transport construction materials
  • Less byproduct and waste materials in landfills
  • Greater economic competitiveness of asphalt pavement

Several studies have been conducted throughout the United States to evaluate the effect of using RAS in asphalt mixtures.   One of the reasons RAS became the focus of many studies is that it contains a high percentage of asphalt binder (18% to 30%) that can replace a high percentage of the HMA virgin asphalt binder—the expensive part of the HMA—and thereby help reduce the cost.   In addition, RAS is widely available in the United States.   It comes from two main sources:  The first source is shingles rejected by the manufacturer, which are called manufacturer waste scrap shingles; they provide a small amount of shingles for recycling and use in asphalt mixtures.   The second source is shingles removed during re-roofing, called
tear-off scrap shingles, which are a more plentiful source.  Approximately 11 million tons of roof shingles are disposed of in landfills every year throughout the United States.   The use of RAS (both manufacturer’s waste and tear-offs) increased from 702,000 tons in 2009 to
1.10 million tons in 2010, a 57% increase.

The Illinois Department of Transportation (IDOT) is working diligently to ensure that its pavements are sustainable by including more recycled materials—as long as the pavement maintains or exceeds its expected durability and performance and is still cost effective. Currently, IDOT’s Bureau of Materials and Physical Research has a special provision in its specifications that allows RAS to be used alone or in conjunction with RAP up to a specified maximum asphalt binder replacement depending on the mix type.  Whether used alone or in conjunction with RAP, the RAS is limited to a maximum of 5% of the total mix by weight, which translates into a 20 to 30% asphalt binder replacement. However, because of recent success in laboratory testing and field demonstration projects, guidelines may be changing soon.

The Illinois Center for Transportation (ICT), IDOT’s research partner at the University of Illinois at Urbana-Champaign, is conducting several pavement sustainability studies—both with IDOT and other organizations such as the Illinois State Toll Highway Authority.  Imad L. Al-Qadi, ICT Director and Founder Professor of Engineering in the Department of Civil and Environmental Engineering at the University of Illinois at Urbana-Champaign, notes, “Pavement sustainability is a key focus for transportation agencies and the industry as a whole.   ICT researchers are taking a lead on various projects to preserve our natural resources while keeping economic competiveness.”

IDOT Aims for “Total Recycle Asphalt”

In late 2012, IDOT in conjunction with the Reliable Ogden LLC asphalt plant in Chicago successfully demonstrated the most environmentally-friendly HMA ever developed in Illinois—and perhaps the United States.   Dubbed “Total Recycle Asphalt,” this HMA surface mixture is composed of more than 97% reclaimed and recycled materials.   The Total Recycle Asphalt project was based on research conducted at IDOT’s Bureau of Materials and Physical Research and District 1 Materials labs.

The components for Total Recycled Asphalt include RAP from pavement millings, crushed concrete salvaged from public works projects, steel slag byproduct and RAS.  No virgin aggregate is required for the mix.   Additionally, only a small percentage of new liquid asphalt is required in mix production.   New liquid asphalt that has a soft grade counters the relatively stiff and aged asphalt from RAP and RAS.   It also enhances pavement durability and reduces potential premature failure caused by pavement stiffness.

For the past several months, IDOT’s Region One Materials lab in Schaumburg has been making trial mixes and testing different combinations of reclaimed materials, but working with Reliable Ogden was necessary to determine whether the combinations worked on a larger scale.   As IDOT Region One Materials Engineer Abdul Z. Dahhan explains, “Making a mix in a lab is one thing, but successful and consistent production through an asphalt plant is another. We are very pleased with the mix the plant produced.” Although initial comparisons show little difference between Total Recycle Asphalt and traditional asphalt, Total Recycle Asphalt is going through a series of rigorous tests to determine its long-term durability.   Samples have been sent to IDOT’s Bureau of Materials and Physical Research lab in Springfield and ICT’s lab in Rantoul.   Testing of the mix is expected to be completed in time to allow possible use of Total Recycle Asphalt in several IDOT projects during the 2013 construction season.

As Secretary of IDOT Ann L. Schneider concludes, “We recycle over a million tons of reclaimed materials into our highways annually as a matter of everyday practice.  This latest effort with Total Recycle Asphalt is proudly taking Illinois to the next level in environmental sustainability, and others are sure to follow.”

ICT Sustainability Efforts

ICT researchers are also taking a lead on various projects that preserve our natural resources while remaining economically sound.   For the past several years, ICT researchers Imad Al-Qadi, Bill Buttlar, Hasan Ozer, Jeff Roesler, Yanfeng Ouyang, Rahim Benekohal, Erol Tutumluer and others have collaborated with several agencies to effectively integrate recycled materials into asphalt mixtures and concrete, investigate the feasibility of using windmills at Interstate highway rest areas, and use LED in traffic lights, to name a few projects.

In 2012, IDOT and ICT completed a multi-year study on the effective use RAP.   The study concluded that accurate volumetric characterization of mixes is key to determining the effect of RAP on mixes and in recommending the appropriate asphalt binder type to use with various amounts of RAP.   Currently, ICT is working with IDOT to increase RAS content in asphalt mixtures.

ICT recently completed an Illinois Tollway project on the effect of short-term curing of stone mastic warm mixes with RAP/RAS on pavement performance, and it is working with the O’Hare Modernization Project to develop effective RAP/RAS warm-mix asphalt designs for applications around the airfield and road network at O’Hare.   ICT, with the support of the Illinois State Toll Highway Authority, also led an effort to add black rock (coarse-fraction RAP) to concrete pavements and apply it in two-lift pavement construction, which was demonstrated on an I-88 project this past fall.   With IDOT, ICT also is investigating the use of marginal aggregates and recycled concrete in pavements.

ICT researchers Imad Al-Qadi working along with his colleagues, Bill Buttlar, Hasan Ozer, Jeff Roesler and Erol Tutumluer, is the co-principal investigators of the Federal Highway Administration’s sustainable pavements program.   Al-Qadi serves as facilitator of a team of diverse researchers from several groups and universities.   The team is developing a reference document about practices, methods and techniques for the design, construction, preservation and maintenance of sustainable pavement systems.  ICT researchers are also developing a framework for a life-cycle assessment tool for the Illinois Tollway Authority as part of team involving Advanced Research Associates, theRightEnvironment, and the CTL Group.

Full reports on all completed ICT and IDOT studies on creating sustainable pavements are available on the ICT website.  For more information on these or other ICT studies, contact

IDOT and ICT will continue to work together to ensure that Illinois is at the forefront of sustainable pavement technology.  As David Lippert, Chief of IDOT’S Bureau of Materials and Physical Research, states, “It is our goal to build and maintain a safe transportation system that is more environmentally friendly, cost effective and high performing.  We are working toward state-of-the-art sustainability approaches while improving the performance expected of our highways.”