The technique involves reclaiming the worn asphalt pavement, mixing it with a portion of the base and placing the mixed material in-situ. The technique adds strength to the base and allows the reuse of the old pavement. Later the new base material is either capped with a double chip seal or overlaid with hot-mix asphalt.
The process can be a cost saver because it allows the reuse of the old asphalt material without having to cart the material to a landfill or move the material off site to be stockpiled and reused at a later time.
The 12,000-sq-yd project included the pulverization of 6-8 in. of asphalt pavement and base material on a quarter-mile stretch of Henrys Mill Road, a two-lane road, which runs through the heart of Moriah, as well as a third-of-a-mile section of an intersecting two-lane roadway. A new Wirtgen WR-2500 reclaimer-stabilizer was used on the project by the contractor, Gorman Bros. Inc., Albany, N.Y., an 80-year-old emulsion manufacturer and paving contractor.
"We're going just deep enough to get underneath the pavement," said Dave Skellie, the reclaimer-stabilizer operator for Gorman. However, "going just deep enough" was a great deal more difficult than Skellie made it sound. The machine demonstrated its flexibility by being able to adjust to the fluctuation in pavement depth. "We didn't know how deep it was at times," said Skellie. "I've had to keep raising and lowering the depth of cut."
Gorman Bros.' Mark Gorman stressed that the project involved more than planning; that the key to the project was the mixing of the reclaimed asphalt with the underlying base material. "You want to bring up some of the base material," said Gorman. "It gives you a thicker base course, and in this case, the town felt the reclaimed asphalt would improve the base." He added that in an ideal situation the company would try to pulverize to a depth twice the thickness of the pavement.
In addition to pulverizing varying depths of asphalt, the project presented another challenge in what lay just beneath the aged pavement. "There's a lot of rock ledge under the pavement," said Richard Perry, of the Town of Moriah Highway Department. According to Skellie, the large stone rock was difficult to cut through when encountered, and occasionally a chunk could be seen in the path of the machine, but on the whole the machine was "taking out the stone."
With the project not yet completed, Skellie said that he had replaced two tooth holders and approximately 200 teeth. The Wirtgen Type II bolt-on replaceable tooth holders used on the WR-2500 rotar also are used on the rotar of Gorman's CMI RS model reclaimer-stabilizer.
"[The machine] works like an animal," said Skellie, referring to the machine's pace on the job. At points during the project, the machine's production rate was measured at 94 fpm by Ron Graham, Wirtgen regional manager. "The machine's production rate can run anywhere from 30 fpm to 90 fpm," said Mark Gorman. "The machine worked out well for us."
According to Skellie, other benefits of the machine are that it provides good visibility for the operator, it features a comfortable, covered cab and a sharp turning radius.
Although the up-front cost of the new Wirtgen machine can range from $432,000 to $451,000 with options, Wirtgen's Graham says the machine is cost effective if you consider life-cycle cost and its production capacity. "Contractors like Gorman make their living on what they can produce," Graham said, speaking with a forthright Scottish accent. "They don't make their living on what they spend up front."
After the reclaimer-stabilizer completed its first pass, a Deere 670A motor grader followed to fine grade the reclaimed base material. A 15-ton Caterpillar CS-5636C single-drum vibratory roller, operated in a static mode, then compacted the base material. Mark Gorman said a sheep's foot roller can be substituted for the vibratory roller.
According to Albie Lewis, Gorman's area sales representative, following its initial pass, the reclaimer-stabilizer remixed the pulverized material at a depth of 6 in. Prior to this a spray unit applied 75/100th of a gal per sq yd of corrosion-inhibited calcium chloride supplied by General Chemical to the base material.
After completion of this second pass by the reclaimer-stabilizer, the roadway was again graded and compacted. The project was then capped off by spraying 25/100th of a gal per sq yd of calcium chloride on top of the base material. In total, 1 gal per sq yd of calcium chloride was used on the project to enhance the performance of the base material.
"The calcium chloride helps prevent frost heave, harden the base and repel moisture," Lewis told ROADS & BRIDGES. "Here in Moriah, with the frost heave in this area, the calcium chloride really works well." Lewis noted that Gorman is specifying that its calcium chloride be at least 80% corrosion-inhibited.
Following the reclamation-stabilization procedure, the project was paved with a layer of hot-mix asphalt.