On California Highway 50 between Placerville and South Lake Tahoe, an ultra-thin bonded wearing course lasted seven years, says Brian D. Toepfer, maintenance engineer, Caltrans. “I think it [performs] better than a mill-and-fill, and it is a lot less expensive.”

On the Silverado Trail, the Construction Division of Telfer Oil, Martinez, Calif., used the specially-equipped paver to spray down a heavily polymer-modified emulsion at a rate of 0.17 to 0.20 gallons per square yard. “The emulsion is similar to a PMCRS-2H emulsion, which is a standard chip sealing emulsion,” says Karl Meyers, general manager of Telfer’s Construction Division.

The paver immediately followed the emulsion with a 7/8-inch-thick layer of open-graded hot mix made with PG 64-16 liquid asphalt that was modified with crumb rubber. The target value for binder content was 8.5 percent, and the top-size aggregate in the mix was 3/8 inch. It also contained a small amount of sand.

Static compaction with two double-drum rollers followed the paver. “You have to run two rollers because you need to hit the temperature range on compaction, which is 180 to 280 degrees,” Meyers says. “That thin lift behind the screed is cooling fast, and you want to release the road to traffic quickly. Plus, the paver is moving at 70 to 100 feet per minute, so you need to run two rollers behind.”

The process has a number of advantages, Meyers says. “You are not getting any tack coat dragged around the city, you get an outstanding bond with the hot mix, you are forming a waterproof membrane, there is no water splash, and you can release the road quickly to traffic,” he says.

Polymer-Modified UTACS

In the meantime, a specialized paver has given a Las Vegas asphalt contractor entry into the growing market of ultra-thin asphalt concrete surfacings in Nevada and throughout the Southwest.

However, to correctly place UTACS or other bonded wearing courses, the right kind of paver is needed: One that has the ability to spray asphalt emulsion onto a pavement, and then immediately place a thin overlay on top. Las Vegas Paving found the Super 1800-2 with optional SprayJet module from Vögele fit the bill.

With its new Super 1800-2 SprayJet paver, Las Vegas Paving now is able to undertake pavement preservation contracts as agencies like Clark County, Nev., use available funds to prolong the life of pavement structures in its desert locale.

Las Vegas Paving acquired its Super 1800-2 SprayJet in early 2010, and has been using it for UTACS ever since. “We were the new kids on the block with this process,” says Clark Webster, general superintendent. “2010 was our first year paving UTACS, and we were concerned that interest would not last, but agencies are still interested.”

Late in 2010, Las Vegas Paving was applying a UTACS to busy Jones Avenue between Tropicana Avenue and Russell Road for the Clark County Department of Public Works. This 2,700-ton job involved three lanes each way, including shoulders and turn pockets. “Jones Avenue is a piece of a larger contract we have with the county, with each piece being anywhere from 15,000 to 20,000 square yards of UTACS,” Webster says. “Jones was a 1-inch deep UTACS, with almost 100-percent passing 1/2-inch with some fines.”

On Jones, warm polymer-modified emulsion was being sprayed directly ahead of the screed via spray bars on each side of the Super 1800-2 SprayJet at a rate of 13/100-gallon per square yard. “It’s not unlike a prime or tack coat, but it provides much more coverage,” Webster says. “And no one can run on it. The Super 1800-2 places the coat behind the wheels but ahead of the material, so cars or our haul vehicles can’t drive over it and pick up the sticky, polymer-modified emulsion. It gives us the best of both worlds – we are able to use a polymer-modified emulsion without having the mess of tires tracking it everywhere.”