|   Chicagoland
Speedway, Joliet, Illinois
Chicago Testing Laboratory provided construction
management and materials quality control services for Gallagher
Asphalt Corporation on the construction of the 1.5 mile tri-oval
at the Chicagoland Speedway in 2000. CTL and Gallagher conquered
the challenges of paving on slopes from 5 to 18 degrees, and
exceeded the requirements for pavement density and smoothness.
The project involved three layers of HMA. The base and level
binder courses used the same aggregates and gradation, with
the only difference being the asphalt binder—PG 76-22
for the base course, and PG 82-22 for the level binder. It
was discovered early-on during the paving operations that
both of these 3/4-inch nominal mixtures had a tender zone
that developed at a mix temperature of about 270°F, and
persisted until the mix temperature reached about 180°F.
The tender zone allowed for only one vibratory roller to operate
behind the initial static rollers spaced evenly across the
mat. The length of the compaction zone behind the paver was
about 350 feet. At that point, roller operations on the base
and level binder course had to cease for about an hour. Two
rollers were then employed to complete compaction.
The HMA surface mix was unique from many
aspects. The mixture aggregate gradation has 83 percent passing
the #4 (2.36 mm) sieve, which is much finer than even a typical
parking lot mixture. The coarse aggregate and half of the
fine aggregate consisted of air-cooled blast furnace (ACBF)
slag. The slag provides the high degree of friction required
on racetracks, but the material is also very absorptive. The
combination of absorptive aggregate and fine aggregate gradation
led to an HMA surface mixture with 7.5 percent asphalt binder—also
PG 82-22.
The final result is a super-smooth speedway
for both NASCAR and Indy car circuits that one driver described:
“In a word, Perfect.”
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