High FRAP content generates savings

The Illinois Tollway is currently investing $180.2 million to reconstruct and widen a 16-mile section of the Jane Addams Memorial Tollway (I-90) near Rockford, IL between the Newburg Road Intersection north to Rockton Road just south of the Wisconsin border. Work to reconstruct and widen the interstate roadway to three lanes in each direction began last year as part of the Tollway's multi-billion dollar Congestion-Relief Program designed to rebuild and restore most of the 286-mile system.

With eastbound traffic now shifted to the westbound lanes of the divided roadway, general contractor Rockford Blacktop Construction Co. of Loves Park, IL, and subcontractor Rock Road Companies of Janesville, WI, have been working around the clock to reconstruct and widen the eastbound portion of the project. Advance work on the project was completed in 2007 and included shoulder resurfacing to accommodate the traffic load of two open lanes in each direction, construction of median crossovers, adjustments in existing guardrail and intermittent pavement repairs.

The section of interstate being reconstructed and widened carries the highest percentage of trucks in the entire Tollway System. On the east end of the project near Newburg Road, Average Daily Traffic numbers in 2007 were recorded at 29,000 vehicles in each direction.

On the west end of the project near Rockton Road, ADT numbers of 24,000 vehicles were recorded in 2007. To relieve the congestion of this section and provide a safer corridor, the Tollway's widening design from two to three travel lanes is being accomplished by changing the median from an open drainage ditch system to a closed drainage system with concrete median barrier wall.

The existing roadway is being recycled into either new asphalt pavement or new aggregate base. All aggregate base material recycling is being done on-site to save in trucking costs and reduce vehicle emissions.

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.