Paul Degges
Paul Degges

Interstate 440, a seven-mile stretch of highway in Nashville that opened in 1987, underwent a $9-million rehabilitation in 2009. Expected to last 10 to 15 years, the repair job—slab replacement and surface diamond grinding, to provide texture and reduce hydroplaning—already is showing potholes. The Tennessee Dept. of Transportation is studying whether the segment can be rehabbed a second time or if replacement is the best next move.

More than 100,000 vehicles—about 8% of them heavy trucks—travel the highway daily, more than double the volume projected in 1982. “We have identified I-440 as a short-term need” for repair or replacement, says Paul Degges, TDOT’s chief engineer. “The pavement is bumpy, but it’s not slick. It’s safe.”

The estimated cost, however, “is $50 million, and that money doesn’t grow on trees,” he says.

There is no deadline for the study completion, and any work would have to be scheduled around other planned major highway projects in the area, Degges said. He hopes to  go to contract in 2018.

The big question is whether the pavement will continue as concrete or be changed to asphalt. “I don’t have a preference,” Degges said. “Both are good products. … I’m trying to make the best decision based on value to the taxpayer.”

Concrete is often chosen in urban areas because repairs are less frequent, but most highways in Tennessee are asphalt, which is typically cheaper and can be milled and replaced a lane at a time.

TDOT in 2005 decided to do interstate repair and construction work at night to alleviate traffic slowdowns, but I-440 runs through neighborhoods that had opposed its construction and filed a lawsuit that delayed its start.

Milling off and replacing the top layer of a multilayer asphalt highway offers “minimal disruption” to traffic, says Audrey Copeland, vice president for engineering, research and technology for the National Asphalt Pavement Association.

“This sort of easy resurfacing also keeps the pavement structure strong decade after decade, hopefully eliminating the sort of expensive and extremely disruptive removal and replacement” needed with concrete, she says. Polymer-modified binders prevent ruts and cracks, she adds.

The concrete industry claims its own additives improve performance of the mix, says Wayne Adaska, director of pavements for the Portland Cement Association. Adding fly ash reduces freeze-thaw problems, and slag provides strength and durability, he says.

Design changes over the years also improved concrete-pavement performance, he said. Reducing the space between joints to 15 ft or 18 ft from 20 ft, depending on the pavement thickness, transfers the weight of heavy trucks to more than one slab, he says.

Placing steel or high-strength plastic dowels at joints also transfers traffic loads. The dowels can be placed during the pour on new construction or drilled and added during a rehab, he adds.

TDOT is still compiling information before moving to the design phase next year. “At this time we do not know if we will utilize in-house, consultant, design-build or other procurement methods in the final design of the product,” Degges says.