Facelift for the Future

Asphalt technology and old-fashioned
planning combine for successful I-75 rebuild

By Dave Morningstar

I-75 is the major north-south route through Detroit, and the stretch between 8-Mile Road on the Wayne County border and 12-Mile Road in Oakland County is one of the most heavily traveled roadways in Michigan. Right in the middle of that 4-mile stretch is a major, triple-deck interchange with I-696, another high-volume freeway linking I-94 on the east side of Detroit with I-96 on the west.

Opened in 1971, the I-75 freeway supported sustained growth in the affluent Oakland County communities along its path as both a commuter route and a commercial artery for the truck traffic that served the many industrial facilities in that part of southeastern Michigan. But by the turn of the century, it was badly in need of extensive rebuilding to repair the damage caused by millions upon millions of cars and trucks over the years.

“This isn’t just any road,” says Paul Graney, Ajax Paving Industries, Inc., Project Manager for the rebuild. “Anything you do on I-75 is going to impact tens of thousands of people and businesses every day. The trick is to get things done in ways that minimize those impacts while still delivering a quality product at a reasonable cost. Making that happen took a lot of careful planning with the Michigan Department of Transportation (MDOT) and the subcontractors we selected to work on the job.”

The project involved removing an existing asphalt overlay down to the original concrete roadway, which was then patched or replaced as necessary and repaved in two courses, or lifts, with a modern “gap-graded Superpave” asphalt wearing surface over a 4E30 asphalt leveling course. It sounds simple, but the reality was much more complex.

Timing Is Everything

“This was a ‘lane-rental’ job,” Graney explains, “which means we had to pay MDOT an hourly rate whenever we shut down the road to work on it. It’s really just a different way of implementing a performance bonus that rewards the contractor for efficiency, but it does tend to focus your attention very sharply on planning and scheduling issues.”

The job was completed in four phases between July 2005 and June 2006. Each phase included either the northbound or southbound lanes between the I-696 interchange and 8-Mile Road or 12-Mile Road.

Under the terms of the contract, Ajax was allowed to shut down one lane at no charge, but if two lanes were shut, the “rental” was $1,200 per hour per lane mile. Shutting down the whole roadway carried a “rental” of $1,500 per hour per lane mile. The estimated “rental” costs were included in the contract bid, and Ajax was allowed to keep any “rentals” that were not used, up to a prescribed amount. In addition, the contract allowed “free” lane closures between 9 p.m. and 5 a.m. on weeknights but prohibited lane closures during weekdays.

“Realistically, that meant we had to do the job on weekends because you just can’t get enough done between 9 p.m. and 5 a.m. to make it worthwhile,” Graney says. “And all things considered, the most efficient way to approach a weekend schedule is to simply shut down the whole road while you’re working on it, even though you have to pay the lane rentals.”

Ajax implemented this process in every case, except for the southbound segment between 12-Mile Road and the I-696 interchange. “We had to keep one lane open there because MDOT determined that 12-Mile simply could not handle the amount of traffic we would be diverting onto it if we closed southbound I-75 completely. So we shut down the road at 9 p.m. on Friday and worked around the clock until it reopened at 5 a.m. on Monday for the start of the weekday morning rush. That meant our crews were working 12- to 14-hour shifts, and all of our subcontractors had to operate on the same schedule.”

Complex Project, Complex Materials

The first step of the process was removing the existing asphalt overlay to expose the concrete pavement underneath. That was the assignment given to Jim Tinkey, Milling Operations Manager for L&L Construction.

“Meeting Ajax’s schedule required a lot of ‘iron’ on the jobsite,” Tinkey recalls. “We used four large Roadtec RX-900 milling machines on the project, and most of the time, all four of them were running at the same time. Each of those machines can remove about 240 tons of asphalt per hour, and that translates into about 1,500 square yards of pavement. That’s a big commitment of resources, but we worked closely with Ajax to develop the schedule, and the whole project went very smoothly. It was actually pretty boring, which is a very good thing.”

Tinkey admits that some glitches on a job this size are expected. “But nothing broke down, the trucks didn’t get caught in traffic very often, and most of the time we just showed up and got to work,” he says. “I’m not sure how Ajax arranged it, but even the weather cooperated for the most part.”

Once Tinkey’s crews had removed the asphalt, other subcontractors went to work patching the existing concrete pavement, cleaning the sewers and other structures, raising drains and manholes flush with the new wearing course, and preparing everything for the new pavement.

“After all the preliminary work was done, we laid a 2-inch-thick leveling course of 4E30 asphalt,” Graney says. “We used 24,000 tons of that material on the 4 miles of roadway we replaced. Then we applied a 2-inch wearing course of gap-graded Superpave to finish the roadway. That represented another 28,700 tons. We also excavated and rebuilt the shoulders on both sides. That accounted for another 11,000 tons of 3C and 4C asphalt.”

According to Graney, between 10 and 15 percent of the asphalt used on the job was recycled from the material Tinkey’s crews milled off. Much of what’s left over will be recycled on other jobs, as well.

The Latest Asphalt Technology

Gap-graded Superpave asphalt is a relatively new material that combines European and American technology to produce a road surface that is highly resistant to rutting under high-traffic conditions. Ajax has considerable experience with this material, which they have used on several major freeway projects in Michigan over the past few years.

The European technology is called “Stone Matrix Asphalt,” or SMA, which is based on the use of hard, durable aggregates that are fractured into cubical shapes and carefully controlled sizes. These aggregates are then held together with an exact quantity of durable, moisture-resistant asphalt cement calculated to provide stone-on-stone contact between the aggregates.

American Superpave technology is more focused on the liquid asphalt cement or binder aspect of the mix, which typically includes both polymers and fibers to enhance performance. The fibers are used to help hold the binder in place to extend the life of the matrix. Aggregate size and geometry are also closely controlled but not to the same extent as in SMA mixes. Superpave materials are also placed with high-frequency vibratory roller/compactors.

SMA is extremely rut resistant, but it is also more costly than typical Superpave materials and more difficult to place. Gap-graded Superpave combines both technologies to produce a surface with outstanding rut resistance. In actual use, it has exhibited rut resistance equal to or, in some cases, superior to SMA.

Gap-graded Superpave is also quieter than regular Superpave materials and offers superior water-handling capabilities. Because of the air voids in the matrix, water tends not to collect on the surface, which reduces tire splash and improves drainage.

“Gap-graded Superpave is a more difficult material to work with,” Graney says. “You have to monitor the rollers very carefully because too much vibration will fracture the aggregate and too little will leave excessive voids. The rolling pattern is more ‘delicate’ and demanding, and hand work is difficult because the mix is a lot stiffer. Basically, you have to get it right the first time because it’s not very forgiving. “Fortunately, we have had quite a bit of experience with this material over the last few years, and our crews know how to work with it. There is no substitute for that kind of experience when you’re using advanced materials like this.”

In 2003, MDOT’s Pavement Committee recommended the use of gap-graded Superpave as the top course mixture for all projects using E30 and E50 Superpave mixes. “But at the moment, we are certainly among the most experienced users of this material in the state, and that was an important factor in this job,” Graney adds.

After nearly a year of effort, including 16 nonstop weekends, the I-75 rebuild wrapped up on June 30, 2006, on time and on budget. To the tens of thousands of commuters and truckers who depend on I-75 for their livelihoods, it means smooth travel on one of Michigan’s most important roads.