High FRAP content generates savings

by Greg Udelhofen
Created: November 18, 2008

Illinois Tollway uses a high fractionated reclaimed asphalt pavement and ground tire rubber on 16-mile section of Jane Addams Memorial Tollway (I-90) rebuild and widening project.

The Illinois Tollway designed this project to use a high percentage of fractionated reclaimed asphalt pavement (FRAP) in its HMA and SMA (stone matrix asphalt) mixes.
The Illinois Tollway designed this project to use a high percentage of fractionated reclaimed asphalt pavement (FRAP) in its HMA and SMA (stone matrix asphalt) mixes.
Why did the Tollway choose asphalt? "All the work we do has a standard we need to address and through the research we do on a project, asphalt proved to be the best solution," says Paul Kovacs...
Why did the Tollway choose asphalt? "All the work we do has a standard we need to address and through the research we do on a project, asphalt proved to be the best solution," says Paul Kovacs, chief engineer for the project.
To avoid shoving of the mat, lighter vibratory rollers, operating in static mode, perform the initial compaction before the heavier tandem rollers began their roller patterns.
To avoid shoving of the mat, lighter vibratory rollers, operating in static mode, perform the initial compaction before the heavier tandem rollers began their roller patterns.

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.

Fortunately for the Tollway, the existing pavement milled off the roadway contained 100-percent crushed aggregate. The SMA design for the project allows for up to 15-percent fine aggregate RAP. Following test strips and construction of temporary travel lanes, it was determined that a Trap Rock aggregate would provide the best results for SMA mix containing 15-percent FRAP material. Mix designs being used on the main travel lanes of the project include:

On the 12-inch asphalt being placed over the rubblized concrete:
? 3 1/2-inch N50, IL-19, base course containing 40- to 50-percent FRAP with PG 58-28 AC
? 3 1/2-inch N90, IL-19, binder course containing 40-percent FRAP with PG 58-22 AC
? 3-inch N80 SMA/GTR binder course containing 15-percent fine-aggregate FRAP with PG 76-22 AC
? 2-inch N80 SMA/GTR surface course containing 15-percent fine-aggregate FRAP with PG 76-22 AC

On the 15-inch full-depth portions:
? 3-inch N50, IL-19, base course containing 40- to 50-percent FRAP with PG 58-28 AC
? 3 1/2-inch N70, IL-19, binder course containing 40-percent FRAP with PG 58-22 AC
? 3 1/2-inch N90, IL-19, binder course containing 25-percent FRAP with PG 58-22 AC
? 3-inch N80 SMA/GTR binder course containing 15-percent fine-aggregate FRAP with PG 76-22 AC
? 2-inch N80 SMA/GTR surface course containing 15-percent fine-aggregate FRAP with PG 76-22 AC

"We're projecting a $10-million savings by using a high RAP content in the mix designs for the project when it's completed," notes Paul Kovacs, Illinois Tollway's chief engineer.

When asked why the Tollway chose asphalt over concrete, Kovacs says the agency identified asphalt as the appropriate design for the project considering the volume of traffic, truck traffic in particular.

"All the work we do has a standard we need to address and through the research we do on a project, asphalt proved to be the best solution," Kovacs says.

And the Tollway's research in using a high FRAP content in design played a critical role in choosing a cost-effective solution to designing, constructing and maintaining a quality road structure.

"Based on the assumption we developed through the research work we developed in producing and constructing high-RAP roadways, and the extensive investigations we conducted to determine if this was the way to go, we concluded that it was the best approach and one that could save millions of dollars," adds Steve Gillen, materials manager for Illinois Tollway.

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.