Reconstruction of Robert Bosch's Vehicle Dynamic Area (VDA) at the Flat Rock Proving Grounds in Ash Township, MI, provided another opportunity for Ajax Paving Industries to demonstrate its unique skills in precision track paving and design. The project included removal and reconstruction of the existing VDA and construction of a new 30-degree banked, high-speed parabolic (pavement curve is similar to inside a bowl) return road.
The existing VDA was constructed by Ajax in the early 1980s and was in dire need of upgrading. The newly designed 139,000-square-yard VDA pad called for installation of 12 inches of crushed limestone base and 5 inches of hot mix asphalt pavement. The wearing surface consisted of 1 1/2 inch HMA Superpave mixture specifically designed to achieve a surface coefficient of friction of 90mu.
Stringent ride quality specifications called for an International Roughness Index (IRI) of 30 measured both longitudinally and diagonally.
Another unique aspect of the project called for recycling another portion of the existing asphalt pavement, mixing it with on-site materials, and installing the reclaimed asphalt as "green" shoulders around the track. The recycling effort was and is part of Bosch's green initiative.
Ajax helped Bosch achieve that particular objective. And, since the paving contractor was involved in the project from design through construction, Bosch was assured the final product would be delivered at the highest quality.
Meeting the performance demands of the testing facility was top priority for Bosch in the design and construction of the VDA and return road, according to Gary Champine, manager of Bosch's Chassis Systems Control Product Division's test track facilities.
"Smoothness and the surface coefficient (friction characteristics) are critical when testing chassis control systems," Champine notes.
Bosch designs and manufactures antilock braking systems (ABS), traction control systems (TCS), electronic stability control (ESC) and sensors used in vehicle chassis control systems.
"We decided to go with a parabolic design on the banked return road to provide an optimal sensitivity testing of our sensors," Champine says. "The parabolic design has a way of fooling the sensors because of the curved surface vehicles have to travel over during testing at the facility. It's just another design element that allows us to test our products.
"It was also very important that we designed and built a test facility that would provide longevity while withstanding a variety of load requirements of different vehicles that would be used during testing," Champine adds. "Our sensors and chassis control systems our used on different vehicles (consumer and commercial) and we also lease the facility to other vehicle (component) manufacturers for testing purposes, so it was very important to design and build a top-notch and reliable testing facility."
Placing the pavement
A standard Michigan Department of Transportation mix design was specified for the project, with three lifts required to achieve the 5-inch-thick pavement. A 2-inch base course was placed over the aggregate, followed by 1 1/2-inch leveling course and a 1 1/2-inch wearing/surface course. All contained a PG 64-22 AC binder, with the wearing course modified to achieve the friction coefficient specified by the project design.
For the construction of the VDA pad, Ajax's paving crew placed each sequential lift diagonally across the previous lift to ensure longitudinal joints would be constructed with minimal ride smoothness degradation. Making runs without stopping were also imperative to minimize creating any smoothness deviations to the pavement surface.
"We paved continuously without stopping the paver to avoid any bumps or dips that could result from stopping the paver and allowing the screed to settle into the mat," explains Dave Marshall, project manager. "We used a material transfer device to maintain a continuous paving process and prevent trucks from bumping into the paver. We also paved in different directions with each lift to achieve additional smoothness results."