Palmer Paving Corp., which was founded in 1955 by Charles M. Callahan Jr., milled and paved 96 lane miles of I-90, the Massachusetts Turnpike, just west of Springfield, MA, and the technology solution employed to deliver the job paid off.
The paving contractor executed a 2-inch-deep cold milling of the existing asphalt surface, then followed with a "shim" or leveling course prior to placement of a 2-inch surface wearing course overlay.
"The existing asphalt was cracked and broken. Normal wear and tear had taken its toll. The pavement was not oxidized or raveling, but was delaminating with quite a few cracks. It was due for replacement," says Rob Mucha, project supervisor, Palmer Paving Corp., Palmer, MA. "We paved a total of 24 miles, two lanes each way, plus the breakdown [shoulder] lane."
The project was enhanced by the use of oscillation compaction via a new HD+120 VO roller, which boosted the speed of placement, and two HD 110 VHV high-frequency rollers, all from Hamm Compaction Division of Wirtgen America Inc.
A 10-foot Vision 5203-2 wheeled paver from Vögele America Inc. was used to place hot mix asphalt. They're among three Hamm rollers and two Vision pavers - the other being an 8-foot 5100-2 tracked paver - used by Palmer in 2009.
Removal of existing pavement
To remove the old asphalt to a depth of 2 inches, Palmer used two W 2000 cold mills from Wirtgen America Inc., one with a standard 6-foot 6-inch drum, and the other with a 7-foot 3-inch offset drum.
State specs recommended that the milled surface be overlaid within seven days. "They do not want the milled surface to become raveled, in case the 2 inches removal did not get down to good, solid material." Mucha says. "We hold to that standard for our own purposes, because raveling will open up a can of worms."
Standard bit spacing was used. "Micro-milling has been done in this state to correct an error in paving," Mucha says. "But micro-milling as a standard practice we have not yet seen in Massachusetts.
"The offset drum is useful for city work, giving us the ability to offset away from the curb," Mucha says. "When running it down the curb in the city, we are kept away from the trees, fire hydrants and street signs. It pushes the machine farther into the roadway. In the city we will get trees right on the belt, and the operator can wind up in the branches. It also can mean one less pass for a machine just to catch two or three feet. That means a lot in time."
Placement of asphalt lifts
On the MassTurnpike, following milling, a 14,000-ton shim course was placed 3/4-inches above the substrate and compacted to about 1/2 inches in depth.
"The shim course is placed to take out any irregularities or ‘scabbing' between layers that may result from the milling," Mucha says. "It results in a smoother surface on which to place the top course. The shim mix is a denser mix than the surface course. Because we only place it 3/4-inches thick, we don't use larger aggregate." Top-size aggregate in this leveling course was 3/8-inch NMAS. A compaction factor was not required for this thin lifoot
The paver used on the I-90 project was rubber-tired Vision 5203-2, but Palmer also owns a tracked Vision paver.
"When you need to move a paver during or at the end of a day a sizeable distance down the road, or park it or move it off the road, you don't want to be running tracked pavers any farther than you have to," Mucha says. "You want to get down the road as quick as you can, and get off the road as well. A rubber-tired paver in that respect will work a little better than the tracked."
Palmer's Vision 5203-2 has a Carlson screed and built-in Niveltronic high-performance leveling system with averaging skis from Vögele AG.
"We are working for a smoothness bonus," Mucha says. Ride quality was the only mix property with a bonus clause; and preliminary data indicates nearly the full potential of 110% of pay was achieved on this project.
"The machine is working well. Both the manufacturer, and our distributor, W.I. Clark Co., have been super. Clark is there on a moment's notice, taking care of any problems that arise," Mucha says. "W.I. Clark and Palmer have had an over-four-decade relationship. They have always been an important partner in our business and we know that they're there for us 100%."
This leveling course was compacted in all-static mode, with no vibration or oscillation. "We put the big HD+ 120 VO in the middle, and the two HD 110s front and rear," Mucha says. "Because we were not running vibratory on the shim course, the order of the rollers doesn't mean a lot. But on the top course, for compaction purposes, that order helped us best get density."
The 66,000 tons of the top surface wearing course, a ½-inch NMAS Marshall mixture, was placed at 2.5 inches deep and compacted to a final 2-inch-thick mat with a minimum 92% density.
The mix was produced by Palmer Paving's HMA facility in Springfield, MA. The high-production plant is one of three facilities with dual plant configurations owned by the company. "We make our own mix," Mucha says. "Depending on where we were on the job, the haul was no more than six miles."
A 28,800-pound HD 110 VHV was used as the breakdown roller, with the HD+ 120 VO the intermediate roller. Finish rolling was accomplished with the second HD 110 VHV.
"The mix designed for the project contained a lot of coarse aggregate so we revved up the vibrations in the breakdown position to get compaction," Mucha says. "We were using the intermediate HD+ in oscillation mode, which sped our compaction rate and helped the roller train keep up with the speed of paving. If we can't keep up with the paver, our production rate has to slow down to achieve compaction. If the rollers can't keep up, everything slows down."
The finish roller was used in static mode, but vibration was turned on in the few spots where density had not been achieved. "There we used vibration only as needed," Mucha says. "Most of the time it was static, but if we came to a spot where the density wasn't what we were looking for, we'd hit it once and were done."
Palmer has used the Hamm platform for several years. "The operators like them," Mucha says. "They provide good visibility and dependability. We have been retiring the older machines that are becoming outdated for what we are doing now. But with the HD+, they have it down right, for example, with the computer-controlled water system. That's a key bonus for us, limiting how much water we use in a night. It becomes very involved to have somebody running water in a truck all night to keep the rollers full of water."
The Hamm rollers also reduced fuel consumption. "For us, we are always looking for ways to optimize our operation. When you don't have to worry about looking in the fuel tank to see if you have enough fuel to make the evening, that's a bonus," Mucha says. "We know we can go all night without having to refuel them."
And it's that type of technology that allows a leading paving contractor like Palmer to complete a project according to spec requirements in the most cost-effective manner possible.