Hot Mix Asphalt Technology - January/February 2008 - (Page 35)

RAP T warded Research he Illinois Tollway is well underway with its multi-billion-dollar Congestion-Relief Program, which will rebuild and restore nearly the entire 274-mile system, add lanes to many miles of existing road, provide congestion relief by converting mainline toll plazas to non-stop open road tolling, and extending I-355 12.5 miles south from I-55 to I-80 to accommodate the needs of growing area communities. Since the program’s launch in 2005, the Tollway has faced the same challenges posed to other transportation agencies: managing increasing costs of construction and materials within current program budgets. One avenue the Tollway is researching is increasing RAP utilization in its HMA and SMA mixtures, without sacrificing the quality and long-term durability of its roadways. The Illinois Tollway will rebuild and widen 14 miles of the Jane Addams Memorial Tollway (I-90) near Rockford, Ill., during 2008 and 2009. The project’s design is nearly complete, and advance work is in progress to prepare for mainline work. The advance work involves utility work, strengthening shoulder pavements to carry mainline traffic, and constructing median crossovers and emergency pull-offs. It is within this advance work that the Tollway has begun its “higher RAP” research. Il inois Tollway Congestion-Relief Program wil research fractionated RAP and higher RAP use during a threeyear, $210 mil ion Rebuild and Widen Project on I-90 Asphalt overlay of rubblized concrete The existing pavement on I-90 consists of an asphalt overlay of concrete pavement. The new pavement will consist of a rubblized concrete base, which will support 12 inches of HMA pavement. The roadway also will be widened, with the added lane consisting of a 15-inch HMA pavement supported by a 12-inch aggregate base. The Tollway’s pavement design consultant, Applied Research Associates, developed the pavement structure, beginning with a 4-inch “rich bottom” base, then using progressively-stronger densegraded mixtures in the middle of the structure, and capping it off with two lifts of stone-matrix asphalt (SMA). The Tollway’s research involves incorporating the process of fractionating RAP (FRAP), to increase the use of RAP in the lower HMA courses, to introduce the use of sandsized RAP with high quantities of residual asphalt in the two layers of SMA, and to provide improved control of the mix properties and performance for all of the high-RAP HMA mixtures produced. The Tollway has recently adopted the Illinois Department of Transportation’s (IDOT) Superpave mix design process. IDOT’s maximum allowable RAP for dense-graded mixtures ranges from 10 to 25 percent depending on the application, with up to 50 percent allowed for the HMA subbase mixture. The Tollway is researching higher allowable RAP levels for dense-graded HMA: up to 40 percent in binder courses, and up to 25 percent in shoulder surface courses. One caveat is included in the use of the higher RAP percentages: the RAP must be fractionated into at least two sizes, to ensure that the control of the RAP materials will be at a level sufficient to achieve consistency in the produced mixture. One new step for Illinois is the use of RAP in SMA. A key concern when incorporating RAP into SMA is the properties of the RAP aggregates. To assure the performance of SMA, both the coarse and fine aggregates need to be crushed, angular materials. A benefit for the Tollway in the search for RAP containing these qualities is that previous specifications required mainline Tollway HMA to use 100 percent crushed aggregates. The Tollway has a readily available source for high-quality crushed aggregate RAP in its existing mainline pavements. The Tollway’s current “RAP in SMA” research allows the use of up to 15 percent fine aggregate RAP material passing the #4 (4.75 mm) sieve. With the availability of mainline RAP containing 100 percent crushed aggregates, the Tollway contractors have the materials available to include the fine aggregate RAP in its SMA mixtures. The prime contractor for the I-90 advance work is Rockford Blacktop Construction Company of Loves Park, Ill. It has included a subcontract with Rock Road Companies of Janesville, Hot Mix Asphalt Technology – JANUARY/FEBRUARY 2008 • 35

Table of Contents Feed for the Digital Edition of Hot Mix Asphalt Technology - January/February 2008

Hot Mix Asphalt Technology - January/February 2008 Contents Chairman's Commentary President's Perspective A Conversation with the New NCAT Director NCAT Test Track: Real-Time Testing for Real-World Results Warm Mix: The Lights are Green Illinois Tollway Tests RAP in Fast Forwarded Research Big Creek Teams with TxDOT to Pave Using Innovative Asphalt Mix Diamond Achievement Commendation Issues a Call for Quality Calendar of Events CONEXPO-CON/AGG Product Review Index of Advertisers Advertisers.com

Hot Mix Asphalt Technology - January/February 2008

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