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As for the use of ground tire rubber (GTR) in the SMA mixtures, Gillen says the purpose is to hold the SMA mix together without the use of a fiber additive. Designing a safe and durable friction wearing course was an important consideration, and the Tollway's research efforts concluded that could be accomplished with GTR modified asphalt. Additional Tollway research shows that an open graded friction course mix with a GTR modifier provides quieter noise levels with excellent friction values and no flushing.

Project challenges
With the paving contractors on board with the Tollway's high-RAP design, both Rockford Blacktop and Rock Road invested substantially in the equipment to fractionate RAP and incorporate that material along with the GTR into the mixes they produce for project, the only significant challenge the road agency has faced is maintaining safe traffic flow through the project. It's the Tollway's policy not to reduce travel during construction while still providing contractors with 24-hour access to the project.

This has been accomplished by shifting all traffic to one side of the median, allowing contractors to work safely around-the-clock to complete the project as quickly as possible. Kovacs says the project would have cost considerably more and taken a lot longer if the Tollway tried to maintain traffic on both sides of the median.

Both Rockford Blacktop and Rock Road utilized high-speed mobile screeners to process HMA grindings into small piles of sized or fractionated RAP. During the 2007 advance work, the contractors and the Illinois Tollway used the temporary pavement work to test the FRAP processing procedure in the production and placement of mixes with much higher RAP quantity as compared to current Illinois DOT mixes. The high-speed FRAP processors used by both Rockford Blacktop and Rock Road were loaned to the contractors through the Astec Corporation during the test production phase.

For the contractors, initial work with production and placement of the SMA mixes did require some adjustments, according to George Malek and Joe Lindemier, resident engineer and assistant resident engineer respectively for V3, the project's engineering firm. During initial production, the crumb rubber additive was clogging screens in the tanks where it was being mixed with the AC. That was solved by removing the screens.