The American Concrete Pavement Association (ACPA) produces a quarterly publication called the Concrete Paving Progress to share industry news, project snapshots, best practices and networking events with its members. A project McCarthy Improvement was heavily involved in – NC I-85 Unbonded Overlay – was recently featured in the magazine, and ACPA graciously permitted us to share the following story on our website.
Accelerated Overlay Project Meets Demands From Increased Traffic
A $137 million rehabilitation of I-85 between Henderson, N.C., and the Virginia state line has greatly improved the ride for this heavily trafficked, 21.6-mile highway section.
The recently placed unbonded concrete pavement overlay has an expected design life of 30-plus years and is designed to meet the needs associated with higher traffic counts, including an increasingly high volume of truck traffic.
Originally paved in 1960, the 55-year-old roadway underwent a rehabilitation project in 2007 that focused on spall repair, slab replacement with asphalt, polymer patching of cracks and an overlay that kept traffic moving, albeit on a less than ideal pavement.
“The original pavement exceeded its expected life, but we were seeing slab failures, and we also needed to bring the entire corridor up to current design standards and create a pavement that can handle increasing truck traffic,” says E. Boyd Tharrington, P.E., Division Construction Engineer for Division 5 of the North Carolina Department of Transportation.
Over the last decade, truck traffic has increased steadily. This section of I-85 currently carries nearly 40,000 vehicles per day (VPD), with 23% of all traffic consisting of trucks. According to FHWA’s office of Freight Management and Operations, freight truck traffic is expected to increase by another 40% in the next 30 years, which will mean that I-85’s average truck traffic will be over 12,800 trucks per day.
The 10-in. unbonded concrete overlay is placed on top of an asphalt interlayer, says Adam Bruner, Carolinas Regional Manager for McCarthy Improvement, an ACPA member. “We paved over 80 lane miles—just over 21 miles of two northbound lanes and two southbound lanes,” he explains. Almost 662,200 SY of concrete was used, making it one of the largest unbonded concrete overlay projects in the southeast.
When this section of I-85 was first paved, standard design specifications called for 30-ft joint spacings with no dowel bars to transfer loads between slabs. “Now, the joint spacing is at 15-ft and dowel baskets were placed,” explains Bruner. The current design produces a pavement that can handle the expected volume and type of traffic expected in the future, he adds.
Although the concrete contractor was able to work on two-lane sections throughout the project, with traffic diverted to one lane each way on the other side of I-85, space in the work zone was tight. “Stringless paving was a lifesaver for us on this project,” says Bruner. “There were a number of operations in the work zone at one time, so there was no room for a stringline.”
“This was the first time stringless paving has been used in a project I’ve handled,” says Tharrington. “It provided a great advantage in access through work areas, getting material to the paver, and improving overall safety on the site.”
Although a constricted work zone is a challenge, the greatest challenge faced was the acceleration of the project schedule two years into construction. “One of our department initiatives is to identify major projects that can be accelerated when we have the funding to do so,” explains Tharrington. Because traffic could be diverted onto the opposite side of the interstate to keep it moving, the project lent itself to an accelerated schedule, he explains. “The original plan called for five-mile closures at a time, but the accelerated schedule allowed the entire 21-mile section of the southbound lanes to be closed—moving all traffic to a two-lane, two-way pattern in the northbound lane.”
Along with the extended work zone, the accelerated schedule also meant off-season paving, which required some adjustments for the cold weather, says Bruner. “In addition to using hot water for the mix, we also covered the pavement at the end of each day,” he explains. “This required an additional crew to blanket the concrete and we worked seven days a week.” During summer months, work continued at night, but during winter months, the temperature determined how late in the day crews could work, he adds.
Extending the work zone closure allowed for a more efficient paving operation and working throughout most of the winter months meant opening all lanes to traffic one year earlier than originally planned.
NCDOT specifications call for diamond grinding of concrete pavements to produce a better ride quality and reduce noise, but Tharrington points out that the combination of stringless technology and the ability to extend the length of work zones to allow continuous paving contributed to a high-quality product. He says, “The ride quality of this pavement is outstanding.”
The original article can be found here.