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 Sept. 28, 2011 with paving finishing on Oct. 22. The project was completed on Nov. 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.”