Producing an Environmentally Friendly Pavement

CDOT worked with Arrow Road Construction & Healy Asphalt Co. to produce a mix that combines RAS, RAP and GTR in an SMA for its $1 million Magnificent Mile Project

Bag House Dust Silos Slat Sil 10821529

Arrow Road Construction Company was founded in 1925 and is headquartered in Mt. Prospect, IL. Its affiliate company, Healy Asphalt Co. LLC, manufactures high-quality, competitively priced products for both its own public and private construction projects. Arrow Road Construction specializes in all aspects of commercial paving, including both large and small jobs.
Recently, Arrow Road was tapped by the City of Chicago to help with its $1 million Magnificent Mile project. This section of roadway, which covers North Michigan Avenue from the Chicago River to Oak Street, is home to high-end shopping and historic buildings, including the Chicago Water Tower.

In addition to being one of the most famous shopping stretches in the world, Chicago was getting ready to host the NATO 2012 Summit and wanted to give this section of roadway a facelift. The section of road was not in very good condition, and with budget and time limitations, the Chicago Department of Transportation (CDOT) needed to find a solution. Working with engineering and materials testing firm S.T.A.T.E. Testing LLC, CDOT developed an alternative mix to the typical dense-graded Superpave mix that it would traditionally use for a resurfacing project.

The Magnificent Mile mix

The environmentally friendly pavement created for the project combined recycled asphalt shingles (RAS), reclaimed asphalt pavement (RAP) and ground tire rubber (GTR) in a stone matrix asphalt (SMA).

SMA pavements are designed to stand up to heavy truck traffic and to resist rutting because of the aggregate structure of the mixture. The 12-block area that was being resurfaced has several bus routes, so SMA was a good choice for the heavy traffic load.

"One of the reasons an SMA was chosen was the accelerated time frame of the project," explains John Healy, president of Arrow Road Construction. "This section of road has a lot of pedestrian, cab and car traffic, but it also has a lot of bus routes. Typically, we would put in 10-inch concrete bus pads, but CDOT wanted to find an effective cost alternative due to the time constraints. The 2-inch SMA would provide the same stability and longevity as the concrete bus pad."

Mt. Prospect facility

The Arrow Mt. Prospect asphalt production facility sits on a total of 11 acres northwest of O'Hare International Airport. While Arrow operates three asphalt plants in total, the Mt. Prospect facility was chosen to produce the Magnificent Mile mix because geographically it was the closest asphalt production facility to the project.

The Arrow Mt. Prospect facility has a 500-tph Gencor counterflow drum mixer, six 300-ton silos, seven cold feed bins, two RAP and one RAS bin, and it produces about 450,000 tons of mix per year. The plant is capable of producing warm mix as well. About 90% of its mix is produced for the Illinois Department of Transportation (IDOT), Illinois Tollway and other municipalities and 10% is used for private work.

One feature of the Mt. Prospect facility that was attractive for this project was its two dust silos with multiple size vane feeders which correctly portion the right amount of mineral filler into the mix.

"SMA requires a fair amount of mineral filler," says Healy. "We had worked on an SMA project on the Eisenhower (I-290), and installed a secondary dust silo. That came in handy for this project."

Test strips & quality control

Several test strips featuring the SMA mix were placed at the Arrow Mt. Prospect facility. Because of the tight time restrictions of the project, Healy says this was the best way to ensure the mix was performing to spec before being placed on Michigan Ave.

"The mix was produced, placed and tested at the plant," he says. "One time, we would have high air voids, the next low air voids. We learned we had to produce the mix at higher temperatures because it was so stiff. Because of the amount of coarse aggregate, we had to make it stiffer so it wouldn't segregate."

The mix design was developed by S.T.A.T.E. Testing LLC in coordination with CDOT and Arrow Road Construction. The SMA mix consisted of:

• 74% Quartzite aggregate for strength and a high level of friction;

• 15% FRAP, which made up most of the fine aggregate in the mix. The FRAP was processed on-site at the Mt. Prospect facility to a less than 3/8-inch sieve;

• 7.5% RAS, which was also sized to a less than 3/8-inch sieve;

• 3.3% GTR modified asphalt binder

The base liquid asphalt for the project was PG 58-28, but when blended with the GTR, the effective final binder grade was equivalent to a polymer-modified PG 70-28. Of the 6% binder in the mix, about 1% was contributed by the RAP and 2% by the RAS.

"There was no need for fibers in the mix because the GTR prevented any drain down," says Healy.

As with many projects, quality control testing was required by spec. "Every 1,200 tons, we did a quality test," says Healy. "The City of Chicago also did testing, and our results had to match with the city's results."

The accelerated paving schedule started on September 28, 2011 with paving finishing on October 22. The project was completed on November 14, just in time for the Magnificent Mile Lights Festival parade.

The National Asphalt Pavement Association (NAPA) recognized the autumn 2011 repaving of North Michigan Avenue, Chicago’s Magnificent Mile, as an outstanding example of breaking new ground in developing environmentally responsible pavements. The Chicago Department of Transportation (CDOT) Commissioner Gabe Klein accepted the NAPA Environmental Leadership Award on behalf of Mayor Rahm Emanuel last summer during NAPA's Midyear Meeting in Chicago.

In all, the repaving job used rubber from 2,200 tires, discarded shingles from about 130 houses, and 24 truckloads of reclaimed asphalt pavement. According to an analysis using the Project Emissions Estimator software developed at Michigan Technological University, the use of RAP and RAS reduced carbon dioxide equivalent emissions by 24 percent for the project compared to having used all-virgin materials.

"Based on performance, we feel it's an effective design," says Healy. "The plan is to rebuild Michigan Ave. in its entirety in the 10 years. This pavement will get them there."


Companies in this article