On the level

Asphalt Pavers Article May 14, 2008
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Lindy Paving found challenges around every corner with the repair of I-79 in western Pennsylvania, which included performing accelerated concrete patching, joint repair and Superpave overlay work on the interstate’s mainline and shoulder areas. The contractor was recognized for its efforts by being named a 2008 Hayes Finalist by the National Asphalt Pavement Association.

“The coordination required to perform all the work was the biggest challenge,” said Dan Ganoe, operations manager for Lindy. “We only had a small window—7 p.m. to 6 a.m.—to set traffic, get the equipment on the road, pave, get the equipment back off and open to traffic for the morning commute.”

“A few of those hours were involved with setting up traffic and doing preparatory work, so we actually only had seven or eight hours of paving time a night,” Joe Conti, quality control manager for Lindy, told ROADS & BRIDGES.

Time is of the essence

Prior to the paving operation every night, Lindy Paving placed a heavy-duty membrane seal over the existing concrete roadway longitudinal joint the entire distance from one end to the other to help prevent reflective cracking of that joint coming up through the asphalt pavement.

“In order to get the best ride and enhance our productivity, we paved one lane every night by using a notch wedge, or Michigan joint, instead of a more traditional butt joint, which could be used on the 2-in. binder lift or the 1 1/2-in. wearing lift,” Conti said. “That notch joint allowed us to pave end-to-end and open that lane at the end of the paving shift.”

Everything was open in the morning, Conti said. The team would come back and pave, meet that joint, leave a notch wedge joint in the center lane and restart the process.

“That was kind of an innovative technique,” Conti said. “It arose out of the necessity to be off the road in the short period of time we had to work.”

There were 3 ft of lanes—travel, center and passing—so Lindy Paving would work its way across the mat. Each night they would take a different lane and pull it—nonstop except for a couple of bridges. The team ran depth on one side of the paver and slope on the other side, so they established their cross-slope going across the road with the binder, which they referred to as “binder leveling.”

On top of that, they placed 90 lb of scratch, which is another thin lift variable-depth placement, and placed the 1½ in. of wearing over that. Once the scratch course was reached, automatics for smoothness were run.

Good sense

The team ran two 44-ft skis in conjunction with a Topcon automated sensing system, which along with the coordination of trucking and nonstop paving is what provided Lindy Paving with their ride on the job. The over-the-screed skis were mounted on the paver, a Cat 1055, for the binder and scratch courses. For the surface course, Lindy Paving continued to use the skis on the free edge side of the paver and a joint matching shoe on the joint edge side of the paver to assure both ride quality and tight joint construction on the surface, said Conti.

There was no milling involved with the project. Instead it was basically an overlay of a concrete pavement. The existing pavement was continuously reinforced concrete pavement that was experiencing various forms of failure, including cracking, slab failures and joint failures. The remediation included concrete pavement patching with an accelerated concrete mix prior to placing the asphalt pavement structure.

First, a 19-mm Superpave binder mix was placed at a 2-in. minimum variable-depth lift. This was followed by the 9½-mm Superpave wearing scratch course placed at 90 lb per sq yd. Finally, a 9½-mm Superpave wearing surface course with 76-22 binder, designed to handle more than 30 million ESALs, was placed at 1.5 in.

The maximum stone size was No. 8 limestone with a skid-resistance level of E—in Pennsylvania, the highest-rated skid resistance, according to Conti.

Lindy Paving used their Neville Island plant, which is a CMI plant. The asphalt plant temperature was 310-315º and was cranking out asphalt at 200 tons per hour. Plant testing was performed as per Lindy Paving’s plan, which required testing for asphalt content and gradation and also performing volumetrics testing.

The temperature in compaction was around 280º-290º behind the paver, and generally 200º after compaction was completed, said Conti. The test compaction was monitored with a nuclear gauge in the field, where the Cat 1055 paver was used, equipped with a receiving hopper to work in conjunction with a Roadtec SB2500 material transfer unit.

Generally, three Sakai rollers would operate at one time, said Conti. The nuclear gauge operator would monitor compaction between the first and second roller, which operated in vibratory mode. The third roller was just a finish roller operating in static. Restricted performance specifications (RPS) was performed for surface testing. The primary field requirement was to get within 92%-97% density.

Between the primary and intermediate roller, Lindy Paving had a total of about 12 vibratory passes, which averaged 94.3% compaction on the cores. Because of that percentage, the air void was an average of about 5.7%. The mix design itself was 4% voids.

Smoothing it over

Lindy Paving employed a K.J. Law lightweight profilometer to perform the smoothness testing. They operated the profilometer as closely behind the finish roller as possible during the paving process, so feedback was immediate and adjustments to the paver, sensors or skis if necessary could be made as quickly as possible. There were 161 lots on the project to be profiled.

The project was subject to PennDOT’s ride-quality specifications, so Lindy Paving profiled every lift of material they placed, said Conti. The existing concrete pavement had an IRI of over 150 in. per mile. When the project was finished, the ride on the project had been improved to 32.8 ipm IRI.

“In order to achieve that number and to be able to pave that job continuously the way we did end-to-end—and pass all the plant and field testing with zero failures—you have to have complete cooperation with your operations and construction units, your plants and your equipment team and your trucking, as well as quality control. So it was a real team effort to pull it off.”

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