Widening Interstate 75

GDOT Leading Effort to Widen Interstate in Southern Georgia

By Scott Judy

Like most interstate highways in the Southeast, Interstate 75 in southern Georgia is in great need of additional capacity, and the Georgia Department of Transportation is in the midst of reconstructing the highway from State Road 133 in Valdosta to the Crisp/Dooly county line.

GDOT has divided the project into eight individual contracts. Overall, it will consist of widening the congested highway to six lanes, resurfacing existing pavement, installing a median barrier and raising existing overpass bridges to provide a minimum vertical clearance.

Douglas Asphalt Co. of Douglas, Ga., won two of the first three contracts awarded, for a total of nearly 30 mi.

The two contracts included a $54 million, roughly 15-mi. segment stretching across Crisp and Turner counties, and a 14.5-mi. section in Lowndes County totaling roughly $75 million. The Crisp/Turner project, now nearly complete, started in July 2001. The Lowndes County contract started in May 2002 and is scheduled for completion in March.

Crisp/Turner: Straightforward

Since the existing roadway on the first project in Crisp and Turner counties was mostly asphalt, the job here was to mill off the existing friction course, inlay with a new layer of asphalt and then widen.

The sections of new roadway are built upon a 12-in. graded aggregate base, with 12.25 in. of new Superpave asphalt. Scott Chambers, area engineer with GDOT, said this new pavement was usually placed in seven lifts, with four different mix types: 6 in. of a 25 mm aggregate mix, 4 in. of a 19 mm mix, 1.50 in. of a 12.5 mm stone matrix asphalt (SMA) and 1.25 in. of new friction course.

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According to GDOT, the aggregate required for the SMA section is more coarsely graded and has less fines than other mixes.

"We had a little difficulty in obtaining the SMA rock," said Kyle Spivey, operations manager for Douglas Asphalt. "The materials supplier had trouble getting the rock approved, and that delayed the completion some."

The contractor will eventually be placing the same aggregate as part of the Lowndes County project, too.

Douglas Asphalt used Blaw-Knox pavers and placed mats ranging from 12- to 18-ft. wide, with most of the wider pavement being laid for the new lane. The paving contractor also used Blaw-Knox and Roadtec material-transfer devices to feed the hot mix into the paver.

The project included the jacking of roughly six overhead bridges and superstructure replacement on one mainline bridge. Bellamy Brothers performed the bridge jacking.

"We had to raise the overhead bridges in order to maintain a minimum vertical clearance," Chambers said. "The bridge sub came in and built some jacking piers and basically put out a bunch of hydraulic jacks and raised the existing bridge up."

Chambers added that most of these bridges were raised an average of about 6 -7 in. "We jacked them, usually about an inch at a time, and we'd pave up 1 in. to the new elevation of the bridge. So we put additional asphalt on either end of the bridge."

Spivey added that Douglas Asphalt "worked 24 hours a day, most of the time, during the grading and dumping of the base stone."

Even so, Chambers said the project was somewhat behind schedule and was headed for a late June completion.

Lowndes County: Concrete Rehab

The Lowndes County project was considerably different. About two-thirds of the 15-mi. project featured existing concrete pavement, with significant amounts of it requiring rehabilitation before a new asphalt pavement was placed.

"We basically went in and tore out a bunch of the old concrete slabs that had busted and cracked and spalled, and we poured new slabs in and doweled into the existing pavement," Chambers said. Michigan-based Causey handled this work.

Spivey added that once the contractor started working the project, the team found that the amount of rehabilitation required exceeded GDOT's initial estimate.

The existing concrete averaged roughly 7-8 in. deep. Once the old concrete was torn out and the new slabs placed, Douglas Asphalt overlaid it with approximately 9.25 in. of asphalt. For the one-third of the project that was already asphalt, the contractor milled off the existing friction course and placed 7.5 to 8 in. of new asphalt.

Paving over the rehabbed areas was difficult, Spivey said.

"We had a little trouble getting the compactions there," he added. "We worked with the state trying to get the compaction right. We finally had to (increase) the AC content."

Like the Crisp/Turner project, the new lane is built of approximately 12.25 in. of asphalt atop a 12-in. graded aggregate base.

Design-Build

The two Douglas Asphalt contracts were unusual for GDOT in that they were let as design-build. On both, the paving contractor teamed up with designer Wilbur Smith Associates of Columbia, S.C.

Some of the differences between these and other contracts was that the state did not always provide project specifics, such as quantities, which is usually the case. At the same time, GDOT provided a strict specification for the mix design.

"We gave them a typical section and told them this is what we wanted," Chambers said.

The biggest difference was in the culture of design-build. The two jobs were Douglas Asphalt's first design-build contracts with GDOT, and the department's experience with the process is also limited. Even so, Spivey said the effort was mostly smooth.

"Sometimes there might be some delays in the approval process, but it (design-build) gave more of an atmosphere of partnering with the DOT," he added. "There was good cooperation. The DOT had good qualified people, and it went well. The good parts of it outweighed the bad."

As for Douglas Asphalt's performance, Chambers said, "The workmanship has been pretty much on par with the work they've done for us in the past."

Project Team:

Owner: Georgia Department of Transportation
General Contractor: Douglas Asphalt Co., Douglas, Ga.
Designer: Wilbur Smith Associates, Columbia, S.C.