A sustainable solution

Illinois Tollway's current multi-billion dollar Congestion-Relief Program, which will rebuild and expand the entire 274-mile system, is a massive undertaking that will not only improve safety and traffic flow, but one that clearly demonstrates the research benefits of constructing more sustainable and economical hot-mix asphalt pavements and overlays.

Local HMA industry contractors/supplies, other transportation agencies and universities encouraged the Tollway to research ways to construct more economically sustainable HMA pavements and overlays to be used in the rebuilding and expansion of the system.

With the ever-rising cost of materials (particularly that of liquid asphalt cement binder) and the reduced supply of some materials (particularly that of high-quality virgin aggregates), the Tollway's research efforts focused on increasing the use of reclaimed asphalt pavement (RAP) in the construction of the improved system.

On one particular project, the $180.2-million reconstruction and widening of a 16-mile section of the Jane Addams Memorial Tollway (I-90) near Rockford, IL, project engineers expect to save approximately $10 million by designing asphalt mixes with a high RAP content.

The HMA industry, as well as the contractors working on the project, worked with the Tollway to research the sustainable solution with little expense to the road agency.

The HMA industry and the contractors working on the project invested in the technology to separate or fractionate RAP (FRAP) in order to control the quality of RAP material being put back into the new high-RAP mixes being used to reconstruct the roadway. This allowed the Tollway to increase its RAP specifications from the Illinois Department of Transportation's Superpave mix design, which allows from 10 to 25 percent RAP in dense-graded base/binder course application, to a dense-graded base course mix design containing 50 percent RAP, a dense-graded binder course mix design containing 40 percent RAP and a shoulder mix design containing 25 percent RAP. Research efforts also determined that 15 percent fine aggregate RAP could also be used on the project's stone matrix asphalt/ground tire rubber binder course and SMA/GTR open-graded friction course.

The success of the current I-90 project, which will be completed by the end of 2009, has proved to the Illinois Tollway that economical quality pavements can be constructed, and all future projects will be constructed using the same sustainable solution its HMA industry partners are capable of providing.

It clearly demonstrates what can be accomplished with a collaborative effort to seek out new cost-effective solutions to building and maintaining a quality road infrastructure. The sustainable solution makes sense and the HMA industry should continue to help its road agency customers experience the benefits.

Greg Udelhofen, Editor

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