Granite Contracting is a full-service contractor providing earthmoving, concrete, utilities, stone base and paving services. With its business comprised of 70 percent commercial and 30 percent state/municipal work, the Concord, NC company expects to generate over $22 million in revenue this year. Fifty percent of the work Granite performs is tied to asphalt paving.
For Cosper and his paving crew, the drag strip project proved to be a good test of their paving skills. Knowing that any slight bump could wreak havoc on a race car driver?s ability to maintain control, paying close attention to the details was critical.
?Since we had the contract to place the stone base under the asphalt, we were able to achieve the correct slope and grade requirements (within +/- ¼ inch) from the very beginning by setting the stone with a laser grading control system,? Cosper says. ?Then with each lift we placed it was simply a matter of making some minor tweaks at the screed to further fine tune the slope and smoothness specs. We had to be particularly careful with the first 200 feet coming off the concrete pad to provide a smooth transition for the racers.?
To make sure the asphalt lined up perfectly level with the concrete at the transition point, Cosper?s crews fabricated steel rails to align the paver screed to the concrete on each mat placed, with each rail corresponding to the various thicknesses of the three lifts.
The Volvo PF6110 tracked paver the Granite crew used on the project is equipped with an auger system that is independent of the conveyor system. Each of the two auger and conveyor drives uses sonic sensors for more precise handling of material. The paver is powered by a 205-hp Cummins Tier III engine, generating a paving speed of 246 feet per minute. The operator station features a digital display that provides onboard diagnostic capabilities, and the dual control consoles rotate and pivot, as well as extend beyond the edge of the machine for improved visibility.
The technically advanced hydrostatic direct-traction drive system eliminates 70 percent of all mechanical drivetrain components. The continuous and flexible rubber tracks have larger, oscillating bogies that provide optimal ground contact and traction. A Blaw-Kote release agent spray system is integrated into the machine with push-button operation to keep the tracks clean.
The paver used on the drag strip project was equipped with a Volvo Omni 318 screed with front-mounted extensions. The screed is equipped with a variable vibration system for improved performance, reliability and operator control. This vibratory screed is electrically heated.
To achieve density and smoothness, the Granite paving crew used a Volvo DD118HF compactor. The 13.2-ton compactor, with its 78.7-inch wide drums, is a high-frequency machine designed for faster rolling speeds. The machine design provides excellent operator visibility of the material being compacted, and the patented impact spacing meter provides the operator with a visual reference for speed control to maintain proper impact spacing and consistent smoothness. The compactor is also equipped with eccentric rotation that automatically matches direction of travel, which improves smoothness, and SMART drum vibration that starts with the lead drum, then follows with the rear drum to increase compaction efficiency and avoid damage to cold material.
While Granite placed over 50,000 tons of hot mix on the entire drag strip project, the actual racing portion required just over 8,900 tons: 3,760 tons of binder base course, 2,820 tons of an intermediate binder course and 2,350 tons of the surface mix. Using dual grade controls with a non-contact ski, the Granite crew achieved superior ride smoothness profilograph results on the intermediate and surface mats.
?We started our first pull with a string line and non-contact 30-foot ski and we also constructed grade rails to properly position the screed depth to achieve a smooth transition from the concrete to the asphalt surface,? Cosper says. ?Our first pull was four 15-foot-wide lifts with no longitudinal joints falling in the wheel path. Then we pulled five 12-foot-wide lifts to place the second binder mat. Finally, we pulled four 15-foot-wide surface lifts, again to stagger the longitudinal joints and to make sure those joints didn?t fall directly on the wheel path (where the drivers travel the strip). With each lift we placed we were able to achieve the final grade, slope and smoothness specifications required.?