Superpave is renowned for holding up to heavy traffic loads, and that's why the Kentucky Transportation Cabinet (DOT) specified its use on a rural two-lane highway, U.S. 127 near Albany, KY.
Though traversing a rural, mountainous area just north of the Tennessee border, heavy truck and local traffic indicated use of a durable Superpave mix. The jobsite is located only 16 miles north of the Alvin C. York State Historic Area, home of the Tennessee World War I hero immortalized in the 1941 Gary Cooper classic film, Sergeant York.
"It's not unusual to put Superpave on a rural road like this," says Doug Beard, who with his brother Roy, is co-owner of asphalt producer and contractor Gaddie-Shamrock LLX, Columbia, KY."It's a very heavily traveled highway, which runs way to the north and south of here. Superpave is used for high-volume type roads and is needed for the two-lane roads as well as the four-lanes."
PG 76-22 Superpave mix used
Under construction in May 2005, U.S. 127 in Clinton County was a four-mile, two-lane project, using a PG 76-22 Kentucky Class III Superpave mix. The leveling or"scratch"course also was a PG 76-22 mix."This is a little bit coarser mix than we normally run, for strength,"Beard says."The commonwealth has gone to certain projects with the 0.50-size mix to help maintain stability. It has a fair amount of fines in addition to the coarse aggregate."Straight virgin mix was used, with no RAP included.
"We put a half-inch 'scratch' level or leveling course down, and are laying asphalt approximately 1 3/4 inches loose, compacted to 1 1/2 inches of surface overlay,"Beard says. The road was not milled prior to the overlay, but the scratch course served to smooth the underlayer ahead of the friction course.
"The scratch course varies in depth," Beard says. "If there are lower spots we will thicken up the course to make it level." The surface course is being compacted from 94 to 96 percent compaction, which is being checked with a Troxler nuclear density gauge."We're trying to compact the mix at about 315 to 320 degrees F, and are using twin articulated rollers right up to the screed. The whole idea is to hit it as soon as it comes out from under the screed. We see a tender zone every now and then, but our experience generally -and on this project -is that we just don't see the problem that much."
Final compaction was achieved with a 10-ton static roller."Once the mat gets under 150 degrees you're not going to compact it any more,"Beard says."That back roller will put the finishing touches on, eliminating marks from the breakdown rollers, and smoothing the surface nicely."
About 5,400 tons of HMA were being placed on this project, including leveling course and friction course. "We're also adding a pavement wedge, a foot-wide shoulder with formed rumble strips,"Beard says. As the main line was 21 feet wide, the total project width was generally 23 feet.
Uses rubber-tired exclusively
Gaddie-Shamrock uses rubber-tired pavers exclusively."Most of the big tracked pavers are for larger applications,"Beard says."The rubber-tired pavers are especially useful in commercial work, because they permit us to move the paver without trailering it. We can ‘walk' it to the next job if it's reasonably close. It's a lot quicker than loading and unloading the equipment, it happens quite often."
The contractor was using a new paver - the new 2116W with HF400E screed from Vögele America Inc. Introduced at ConExpo/ConAgg 2005 in Las Vegas, the 2116W has an overall width of 8 feet, 6 inches with maximum paving width of 21 feet, 6 inches, and replaces the former model 880 WB. The machine used by Gaddie-Shamrock has a maximum width of 15 feet, 5 inches. The HF400E screed, also new in 2005, is an electric-heat, 8-foot main screed with hydraulic-extendable front-mount extensions.