Beat the Heat
Polymer-modified mix in Miss. holds up under higher temperatures

The Mississippi Department of Transportation chose to add polymer at a Mississippi asphalt plant to boost the mix’s temperature range and improve its durability under the roadway’s heavy truck traffic.

A decision to use costlier polymer-modified asphalt during an $8.2 million overlay of Interstate 59 north of Hattiesburg has added 10 years to the road’s life.

The 5-mi project on Interstate 59 north of Hattiesburg, Miss., will have required about 80,000 tons of the polymer asphalt upon completion.

The Mississippi Department of Transportation chose to add polymer at the Dunn Roadbuilders LLC plant to boost the asphalt’s temperature range and improve its durability under the roadway’s heavy truck traffic.

“On the interstate you want the best asphalt Superpave that you can get, and the polymer modified mix is designed so that it holds up under a higher temperature than other mixes,” says Robert Hinton, MDOT project engineer for the Mosell to Rocky Creek project. The heat comes from the sticky Mississippi summers and the relentless friction generated by the heavy tractor-trailer rigs that use the highway.

“The polymer additive also makes the asphalt less likely to rut,” he adds. “It’s absolutely worth the additional cost. We had the option of coming back with concrete or using this polymer modified asphalt. We usually try to use asphalt as much as we can because of the reduced cost.”

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Dan Ashley, a project manager with Dunn Roadbuilders of Laurel, Miss., says the polymer mix works well on an interstate project, although it’s “a little stiffer mix so it would be more difficult to spread it manually like you might on a smaller job.” Jason Wooten is the project’s manager.

“Fortunately, on an interstate job the asphalt comes right out of the paver and the rollers hit it, so there’s not a lot of manual work,” he adds.

Ashley says work at the site began in March and he expects the project to finish ahead of schedule in late August because of good weather and an uninterrupted paving process.

“With the exception of some drainage work, it’s strictly an asphalt overlay,” Ashley says, so the crew is not waiting on the completion of other phases of work before paving.

A crew with Dunn Roadbuilders LLC of Laurel, Miss., is using a material transfer vehicle and Caterpillar paver to place three lifts of asphalt in 12-ft widths on Interstate 59.

The 5-mi project will have required about 80,000 tons of the polymer asphalt upon completion.

“To prepare for the overlay, we did some spot milling down to the concrete base,” Ashley says. American Field Services of Madison, Miss., then performed base repairs where the concrete had failed.

To pave the highway, the Dunn crew is using a material transfer vehicle and Caterpillar paver to place three lifts of asphalt in 12-ft widths. Intermediate lifts measure 2 to 2.5 in thick, topped with a 1.5-in surface lift. Eight to 10 trucks are delivering asphalt to the site.

A subcontractor is building four single barrel box culverts in the median of Interstate 59, necessary to connect existing drainage culverts beneath the driving lanes.

“There are two different mixes using the polymer, a 12.5-mm limestone mix for the intermediate lift and a 9.5-mm mix for the surface,” he says.

MDOT has placed restrictions on lane closures to ensure minimal impact to travelers. The contractor cannot have two consecutive lane closures and the closures must be from 1 to 3 mi apart.

“Some of the traffic requirements were a little unique on this job,” Ashley adds. “They put up some extra message boards about 2 mi from the job. Usually they’re a little closer, but because that section of I-59 is such a high traffic area they felt it was necessary.

The 5-mi overlay of MS Hwy. 11 has the two-fold purpose of widening and overlaying the existing two-lane roadway.

“We started paving the final, surface lift in mid June in the southbound lanes,” Ashley says. The 15-man paving crew is working 10- to 12-hour shifts.

Other work requires the construction of some single barrel box culverts in the interstate median, necessary to connect existing drainage culverts beneath the driving lanes.

“The median ditches were pretty deep and to fill that in they had to put in about four to five boxes, followed by backfill,” he says. G & M Inc. of Toomsuba, Miss., is performing the work.

Dunn is performing another 5-mi overlay on nearby MS Hwy. 11, with the two-fold purpose of widening and overlaying the existing two-lane roadway.

“It’s called trench widening,” Ahsley says. “They’re trying to increase the width from 22 to 24 ft. in order to create a small 2-ft shoulder with a 1-ft rumble strip. So there will still be some pavement outside the rumble strip.

The short-duration MS Hwy. 11 project, which required about 13,800 tons of asphalt, began in the spring and ended in late June.

”The crew doesn’t have to build up the embankment for the widened sections, since “a pretty decent base already exists, although in some pipe crossings we have to narrow the road a little.”

The two-lift paving process required a leveling lift that runs as deep as 3 in for the newly widened sections, followed by a 1.5-in surface lift. The entire length of the project will have a 2 percent slope.

The short-duration project, which required about 13,800 tons of asphalt, began in the spring and ended in late June.“The project actually runs right by the asphalt plant, so that significantly reduced the number of trucks required for the job, not to mention the shortened delivery time,” Ashley says.