Asphalt paving machines with operating weights of 19,000 pounds or more are conventionally categorized as “highway class.” Most paver manufacturers, however, say that the large spread in operating weights for highway-class machines (from 19,000 to more than 60,000 pounds) really calls for several categories, perhaps loosely identified as commercial, heavy commercial/light highway, and heavy highway. Practically, though, the capabilities of a specific machine depend on its design and construction.
“For the last three years or so, larger commercial contractors seem to be looking for machines that can go from driveways to highways, because of the scope of the work they’re securing,” says Brian Hall, LeeBoy’s territory manager, mid-South region. “The 20,000-pound machine allows crews to pave a medium-size parking lot today, and move directly to a city/county road project tomorrow.”
Asphalt Paver Costs
Weight (lb.) List Price Hourly Rate Wheel Type 19,000-28,999 $369,085 $196.72 29,000-34,999 $398,361 $208.96 35,000 & up $433,786 $251.85 Track Type 19,000-24,999 $371,285 $183.03 25,000-28,999 $388,409 $208.71 29,000-34,999 $463,134 $264.13 35,000 & up $519,321 $288.46
Current Unit Prices: Diesel: $3.98; Mechanic’s Wage: $49.80; Cost of Money: 2.125 %; Hourly Rate = Monthly Ownership Costs / 176 + Operating Cost
Source: Based on data from EquipmentWatch.com
Bill Rieken, road-building specialist for Bomag, commenting about the asphalt-paving market and contractor buying practices earlier this year, when debate about a new highway bill was just getting started, said that many state budgets are tight and public entities are forced to seek ways to cut costs. The uncertainty of funding, he said, can result in buyers giving more consideration to machine price rather than to lifetime operating costs and features that help improve mat quality.
John Mooney, Volvo Construction Equipment’s product manager for paving and milling products, North America, also notes the “stressed environment” of state and federal funding, saying that road work, in some instances, has taken second place to bridge work.
“Bridges in poor condition tend to get more public attention than roads in poor condition,” says Mooney, “and road work can suffer as a result.”
As a consequence, says Mooney, many paving contractors have extended paving-equipment replacement cycles, and at the same time, consolidation among paving firms has reduced the number of contractors willing to invest in a highway-class paver—and the related equipment used to support it. But during the past two years, he says, contractors who no longer can defer replacement of old machines are buying, and the industry is seeing a modest sales recovery.
Along the way, of course, the asphalt-paving industry has continued to develop innovative approaches for economically restoring road quality. For example, the National Asphalt Pavement Association, working with state asphalt pavement associations and the National Center for Asphalt Technology, is currently testing the “Thinlay” process—placing extremely thin overlays, some no more than 5/8-inch thick, containing a high level of recycled material and produced as warm mixes.
Also, the Strategic Highway Research Program (SHRP2) recently published a report, “Using Infrared and High-Speed Ground Penetrating Radar for Uniformity Measurements on New Asphalt Concrete Layers,” which states as a deployment goal to have 15 percent of transportation agencies using infrared technology to measure variations in mat temperatures by 2016.
Continuing product development
As the industry develops new techniques for restoring aging pavements at modest costs, equipment manufacturers continue to develop innovative technology that enables machines to efficiently apply these techniques.
Steve Hourscht, regional sales consultant for Cat Paving Products, cites several technical developments in asphalt pavers that he considers significant: machine self-diagnostics that help detect potential problems before they cause job-site delays or major repairs; machine automation that assists operators in precisely replicating repetitive tasks, thus contributing to consistent, high-quality paving; and advanced engine technology, which, he says, has lowered emissions, lessened noise in the working environment, and significantly improved fuel efficiency.
Volvo Construction Equipment’s Mooney says that fuel efficiency is becoming more important in machine design, noting that in the past, the contractor’s primary concern about fuel was having enough onboard to complete a long day of paving without having to stop for refueling. Adequate supply is still a concern, says Mooney, but fuel economy is becoming a greater issue as contractors work to control overall costs.
Laikram “Nars” Narsingh, product manager for Wirtgen America’s Vögele range of asphalt pavers, touches on several developments he considers important, including on-board diagnostics, compaction screeds, material-feed systems that provide added control, more precise propulsion control, screed-control systems with a “hold and freeze” function that prevents screed settling during stops, and integrated automatic grade and slope controls.
“Compaction screeds use a tamper bar located in front of the screed to provide initial compaction,” says Narsingh, “and this technology is making a comeback in North America, mainly because of globalization of the paving industry. The compaction screed increases in-place density, reduces roll-down, and results in a smoother pavement. These screeds usually have the rigidity for wide paving, with the concomitant ability to eliminate cold longitudinal joints.”
In addition, says Narsingh, material-feed systems that allow more precise independent control of augers and conveyors contribute to material consistency under the screed. And for track pavers, he says, systems that permit the operator to more easily maintain straight-line travel, such as the Vögele single-steering joystick, improve smoothness and joint quality. He notes, too, that new Vögele technology also allows the operator to automatically set the paver’s turning radius, among the most challenging aspects of paver operation, he says.
Bomag’s Rieken also cites a steering refinement—proportional steer assist, for rubber-tire machines—as a significant development that provides contractors greater flexibility and control in machine operation.
“Proportional steer assist keeps the differential lock engaged to help improve tractive effort,” says Rieken, “allowing the paver to better pull through marginal sub-base conditions. Additionally, it helps hold the line when paving with a pick-up machine during windrow paving.”
Rieken also notes that potentially eliminating centerline segregation is a benefit accruing from outboard auger-drive systems, which eliminate the center gearbox and the need for reversing augers to direct mix under the gearbox. Also concerning segregation, whether thermal or material, Rieken gives high marks to Bomag’s Remix system, which uses longitudinal augers in the paver’s hopper to mix material before it reaches the screed.
“Auger pavers thoroughly re-blend material inside the paver hopper to reduce segregation at the last stage of the paving process,” says Rieken. “Re-blending material also is critical when working with mixes that contain additives, because it helps deliver a more homogeneous mix for a better end result.”
To effectively deal with the problem of thermal segregation, says Rieken, an increasing number of states are moving toward requiring pavers to be equipped with an infrared measuring system to promote temperature uniformity across the mat.
“Thermal imaging devices give the paving crew immediate feedback if there’s longitudinal or truck-exchange thermal issues,” says Rieken. “These systems allow the crew to tweak techniques to improve the end result. Contractors can adjust the temperature band to meet the spec, then they can immediately react to issues that cause variation from the set temperature band.”
Caterpillar’s Hourscht adds that if an out-of-spec temperature differential is indicated, a core sample typically is taken to check the density of material behind the screed. “If a problem is identified, finding and remediating the root cause is critical,” says Hourscht. He suggests that contractors investigate production methods at the plant, truck loading techniques, and the process of transferring mix to the paver.
From LeeBoy’s Hall’s point of view, important technical refinement in asphalt pavers includes the use of CAN Bus (controller area network) systems, which allow micro-controllers and electronic devices to communicate with each other within the machine without a host computer. These systems, says Hall, place all the controls in one location and provide continuous updates from systems controlling the paving process. On the list of refinements, too, Hall includes electrically heated screeds and enhanced screed designs that provide smaller pavers added capability to produce smooth mats.
“In the past, only heavy/highway contractors had to worry about smoothness,” says Hall. “Commercial contractors had to make sure the water flowed in the right direction and that the end product was esthetically appealing, of course, but smoothness really wasn’t an issue. But the contractor’s customers have become more demanding, and rightfully so. Today’s screed designs must be engineered precisely—and operators trained in using them—to make sure the machine performs as it was designed.”
Volvo Construction Equipment’s Mooney sums up by saying that paving contractors today work in an increasingly competitive environment that demands careful control of costs. To that end, he says, more contractors are buying service contracts from their dealers, a practice that is furthered by the increasing difficulty of finding qualified maintenance people to work in contractor shops.
“When there’s a potential risk factor of $20,000 to $40,000 per hour if the paver fails,” says Mooney, “the cost of a service agreement seems a bargain.”