Consisting of 2,047 lane miles connecting four interstates and serving 12 counties, the Illinois Tollway serves Northern Illinois. It operates under user fees, and with 1.4 million vehicles using the Tollway daily, essentially all funding for projects is made through user payments. Emphasizing a focus on recycling and reducing materials, warm mix asphalt (WMA) has been chosen as the specified material for all major Tollway construction projects where asphalt is required.
Six small warm mix projects have been completed on the Tollway to date with the majority of those projects completed in 2010. Currently, the Tollway has five major rehabilitation projects being completed using warm mix including two projects on the Reagan Memorial Tollway (I-88) and three on the central Tri-State Tollway (I-294). There are also five other smaller rehabilitation projects being completed on the Tollway using warm mix asphalt. With all of the warm mix projects, the Tollway has seen a total production of 750,000 tons of WMA in 2012. The agency is using MWV's Evotherm warm mix asphalt additive on all the projects.
Several years of research were completed prior to the Tollway announcing warm mix as the new standard specification for all high-volume construction projects. “We spent four years researching warm mix asphalt before deciding that it should be specified in current projects,” says Steve Gillen, materials manager for the Tollway. “We had to prove to ourselves that we had enough evidence warm mix would not cause construction problems or reduce the life of our pavements.”
A variety of situations were included for the testing of warm mix leading to successful results. “We started completing research in 2008 through several universities,” says Paul Kovacs, chief engineer with the Tollway. “There were several test bed projects used in 2010. They were isolated patches of asphalt a few hundred feet long used for research projects with the University of Illinois. We’ve had great results on everything to make the decision to specify warm mix. After the research and tests we felt confident that warm mix produces the same quality material as hot mix.”
Reasons to specify WMA
The Tollway’s decision to specify warm mix in all major construction projects provided several benefits.
“It’s helping prove we incorporate green technologies in our construction,” Kovacs says. “It further demonstrates our commitment to sustainability and minimizing the impact of our work on the environment.”
With a great focus on reducing asphalt plant emissions and recycling materials, warm mix offers an opportunity to employ a material with a lower environmental impact. “Most of our recent work did a great job by recycling material to use as the base for new pavements,” Kovacs says. “Warm mix asphalt further allows for an increase in use of reclaimed asphalt pavement because of reduced oxidation of the asphalt binder during production. There also isn’t as much of an odor with WMA as there is with hot mix asphalt.”
In addition it offers cost benefits to all parties involved in the projects. “Many contractors were pushing for the specification of warm mix due to oil prices,” Gillen says. “Producing large quantities of warm mix will save a few dollars at the plant.”
Another benefit to specifying warm mix in all Tollway projects is the opportunity to work longer in the season — a much desired opportunity in the Midwest. “Warm mix allows crews to complete work later in the season,” Kovacs says. “In an area where weather and cold temperatures limit road work, it is helpful to have a new technique that gives us greater flexibility in getting our work done.”
Additional benefits include the ability to open lanes sooner, minimize rutting issues and improve density during compaction. With all of these new opportunities, the Tollway is still able to produce a quality final product.