The Chelsea facility, which dates to 1952, has approximately 95 miles of track that course through and around some of the 3,850 acres. In total, 80,000 tons of asphalt will be installed over the base course in four 1.5-inch lifts.

By Diane Calabrese

An egg is elliptical. A bowl is parabolic. Parabolic forms are fascinating to mathematicians, but they have many real-world applications.

The parabolic shape has a way of focusing energy and is used in devices such as antennae, microphones, and mirrored-trough solar energy collectors. But the shape lends itself to other uses, as well.

Imagine driving around the inside of a big bowl at high speeds. That’s the general idea of the parabolic test track at DaimlerChrysler’s Chelsea Proving Grounds just south of Interstate 94 near Chelsea, Michigan.

Test drivers endure a few Gs as they zoom around the track, thanks to the centrifugal G-force that builds with acceleration. But the point is not to test the driver’s gravity endurance but to test
the vehicle — from its brakes to integrity.

The Chelsea facility, which dates to 1952, has approximately 95 miles of track that course through and around some of the 3,850 acres. Over the years, drivers have nicknamed it the Chelsea Oval, or just the Oval. Although it is not an oval by geometric definition, the affectionate moniker derives from the familiarity car and truck aficionados have with the parabolic track.

The Oval is getting a complete makeover this year, and Ajax Paving Industries, Inc., is the prime contractor for the project. “The project began on March 19, 2007, and will be completed by August 15, 2007,” says Brad Hillard, Project Manager for Ajax.

Shape Matters

“The entire project is a challenge,” Hillard says. “The physical design of the track is one of the most challenging in the world as far as height and percentage and degrees of slope.”

Getting it all done according to nonnegotiable specifications takes the usual determination and dedication and just a bit more. The new track, for instance, is going to be relocated, but only a bit. Precision and attention to detail become key.

“There is a slight shift of the centerline of the track that amounts to about seven and one-half feet,” says Clarence Jones, Estimating Manager for Ajax. Jones is working closely with Hillard on the project.

The track alone requires special attention, and expectations from the owner are high, so errors are out of the question. “For the majority of the length of the track, it is transitioning its shape, which provides for numerous engineering and construction difficulties,” Hillard says. “This contract has very stringent material and construction specifications.”

Team Effort

“All in all, this project is challenging to engineer, build, and pave,” Hillard says. “However, these are all anticipated challenges, and there couldn’t be a better team assembled to conquer them.”

Gauging the thickness of the surface layer as it is installed requires a specially designed parabolic screed, such as the Vögele 4M Parabolic Screed.

With a value of $12 million to Ajax, the 150-day contract will result in approximately 28-lane miles of installation work. Among those working as subcontractors to Ajax on the project are five Michigan firms: Dan’s Excavating, Inc., Slagter Construction Company, Harry Fox, Inc., Michigan Highway Contracting, Inc., and P.K. Contracting, Inc. The owners, the Chrysler Group and its parent company, DaimlerChrysler AG, also have their representatives engaged in the project. Wilcox Associates, Inc., headquartered in Cadillac, Michigan, is the engineering-design firm for the effort.

Renewal

Although this is not the first time the Oval has been refurbished, it is the first time it has been taken out of service during the reconstruction. The work began with the removal of the existing track, a task that Dan’s completed during the first month.

Much of the material removed will see service again in the new track. “The existing track was broken using a tractor-towed, triangle-shaped breaker,” Hillard says. “It was then removed and loaded into trucks using an excavator.”

The trucks carried salvaged material to a stockpile near an onsite crusher operated by Western Michigan Recycled Aggregates, LLC. Old concrete is being crushed for reuse as a base course with a 7-inch thickness. Sand beneath the original base also is being retained and reused. “It is tested to ensure that it has the proper gradations,” Hillard says.

“If it does not meet the contract standard, it is removed, and new sand is brought in,” Hillard says. Only uncontaminated sand, or that free from admixture with other materials, will become part of the new track.

In total, 80,000 tons of asphalt will be installed over the base course in four 1.5-inch lifts. The installed asphalt will be 13A for the base and 36A for the wearing course. Depending on the wearing course asphalt installed, the track will have a particular friction, or resistance, to the tires. Friction coefficient affects braking distance and maneuverability, or steering. To enable DaimlerChrysler to achieve the friction aspect it wants, Ajax is helping with tests.

“Ajax will provide two different polymer-modified mixes in test strips on the track,” Hillard says. After friction testing, the owner will “direct us as to which 36A mixture they want us to use on the remainder of the track.”

Improvements

With the decision to deconstruct and reconstruct the track came opportunities for enhancement. The new track will be two lanes wider than the old one. It will have guardrails and a drainage ditch system.

Yet the testing at the track will still focus on the same things: melding safety and speed. The idea is to ensure any vehicle tested at the grounds is safe at the speed it is designed to travel, though there have been trials at the Oval that far exceed the driving speed on common roads. The track also allows for
sustained speed testing, which determines what happens to a vehicle if it travels at the same speed without deceleration or acceleration.

By its nature, a parabolic track allows extended movement at one speed. Get into the top lane at 140 mph and the angle of the track puts sufficient centrifugal force on the vehicle at certain speeds that act as a counterbalance to gravity. In theory, at a certain, consistent speed, it is possible to keep circling without steering.

Equipment

Gauging the thickness of the surface layer as it is installed requires a specially designed parabolic screed. “We purchased a computerized parabolic screed from a contractor in Mexico,” Hillard says.

Then there is the matter of towing the screed. “We purchased a paver that will properly tow the screed from the German manufacturer Vögele,” Hillard says. The screed being used is the Vögele 4M Parabolic Screed, Jones says. The track paver is the Vögele Super 2100.

Building a track with a parabolic profile takes considerable effort. It can all work on the engineer’s drawing board, but if the compacting part of the installation process is not done properly and there are differences in depth — even tiny ones — the flaws could push a vehicle out of its self-sustained path.

Managing the compaction of the substrate and at the same time installing a concave surface takes sophisticated equipment. The Super 2100 has large auger blades so that the mix can be spread quickly. Adjustment of the auger on the machine is entirely automated, and a powerful hydraulic system responds to simple touch button cues and changes the auger height to match desired depth.

Quality

The use of the new equipment will make the job easier. That is important, because on this project, a compressed timeline and rigid parameters are both in play.

“Ajax is responsible for quality control testing on all asphalt placed in order to ensure it meets project requirements,” Jones says. Ride requirements established by the owner will be met.

At the Oval site, Hillard is responsible for controlling construction activity, which includes overlapping and
interlocking tasks. He monitors subcontractors, develops and maintains schedules and budgets, and acts as a liaison between the owner, the engineer, and the subcontractors. He also monitors costs and writes the invoices to collect for the work performed.

Importance

To Sylvan Township, Chelsea Proving Grounds is a significant enterprise. Some 750 people work there. It contributes almost $1 million in taxes to its home municipality; the employees also add to the tax revenue and activity that keeps the area thriving.

A 12-foot fence conceals the activity at the test facility from the public, a necessity in a sector as competitive as the automotive industry. The grounds also include straight-aways and a skid-traction test area where drivers can test brake and tire performance with wheels on the same surface or two different surfaces, as well as on wet or icy pavement. The Oval also is one of Chrysler Group’s crash-test sites.

The overhaul at the Chelsea Oval is an extensive project that involves hard work, precision, and efficiency. The desired result is a job well done on a facility that puts safer cars and trucks on the road.