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While portions of the original concrete roadway (approximately 60 percent of the roadway is being totally reconstructed) are being removed and crushed to maintain clearance under bridge structures, some of the concrete roadway is being rubblized and left in place.

When the project is completed by the end of 2009, it's projected that 650,000 toms of asphalt will be used to construct a 12-inch overlay of the rubblized concrete, as well as build a full-depth 15-inch perpetual pavement of the areas that were completely reconstructed, along with and the additional new travel lanes and shoulders.

Addressing rising costs
Like many other road agencies across the country, the Illinois Tollway is utilizing construction designs and implementation practices to maximize its budget constraints. With ever-increasing costs of construction and materials like liquid asphalt, which hit $800-plus per ton this past summer, the Tollway designed the project to use a high percentage of fractionated reclaimed asphalt pavement (FRAP) in its HMA and SMA (stone matrix asphalt) mixes. Research and application of the high-FRAP mixes took place in 2007 with advance work to construct shoulders to carry heavy traffic during the reconstruction and widening project. Applied Research Associates developed the pavement type, and the Tollway and its consultant developed the mix design to be used for the project, with higher levels of FRAP content being used in the bottom lifts and decreasing FRAP content in subsequent lifts. But the design also allowed for sand-sized RAP to be used in the top two SMA lifts, which also included ground tire rubber (GTR) instead of a fiber filler to help maintain an open graded friction course (OGFC) design.

The Tollway uses the Illinois Department of Transportation (IDOT) Superpave mix design specifications, which allows for up to 25 percent RAP content on dense-graded base courses and up to 15 percent on intermediate binder dense-graded courses. The Tollway's research, however, allowed for up to 40 percent of FRAP in the intermediate dense-graded binder courses developed and placed by the two paving contractors working on the project.

The only concern the road agency had regarding the use of FRAP in its SMA design has been the quality of aggregate. An SMA design requires aggregate with an angular design to create a stone-on-stone matrix to ensure a rigid structural composition when compacted. That's what provides its anti-rutting characteristic on heavily traveled roadways.