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Paving the Chicagoland SpeedwayChicagoland Speedway, Joliet, Illinois

Chicago Testing Laboratory provided construction management and materials quality control services for Gallagher Asphalt Corporation on the construction and maintenance of the 1.5 mile tri-oval at the Chicagoland Speedway. 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.”