Perhaps the starting point in any discussion about “highway-class” asphalt pavers is to define the term. We’ve chosen the conventional definition, that is, machines with operating weights of more than 19,000 pounds, but some manufacturers believe that minimum operating weights of more than 25,000 or 30,000 pounds are required for machines to perform successfully in this market. No matter how they’re defined, however, “highway class” machines need the strength and capacity to achieve demanding density and smoothness specs on big jobs.
The demanding smoothness—or “rideability”—specifications in today’s contracts require that the paving process be as continuous as possible to eliminate the stops and starts that can so easily jeopardize a level mat surface. In fact, that requirement might be influencing the practical definition of a “highway class” paver.
“The definition has changed with the way we’re paving now,” says Bill Rieken, field service paving specialist for Terex Roadbuilding. “You not only need a full-size paver, but the machine also needs the structural integrity to take the extra loads placed on it by hopper inserts, which often are a key component for continuous paving to be successful. A well-designed insert not only allows the machine to take on more mix, but greatly aids in thermal uniformity of the mix, which is a huge plus for attaining a good ride and uniform density.”
Given the considerable bonuses or penalties at stake for attaining or missing smoothness specifications, says John Sunkenberg, product competency manager, road industry, for Volvo Construction Equipment, the more stable the platform towing the screed, the more consistent will be mat quality. Stability, he says, is a function of overall machine design, including such elements as undercarriage type, machine length and machine weight.
“A longer machine will better carry an uneven sub-base,” says Sunkenberg, “but critical, too, is a consistent head of material in front of the screed. If the material is segregated and inconsistent, you’ll struggle to get density.”
State of the asphalt paving market
According to the best sales numbers available for models in the more-than-19,000-pound category, the market for these machines over the past 10 years has fluctuated annually between 450 and 800 units, for an average of some 600 per year. Sales estimates for last year are around 500 units, below average, but perhaps not too bad in light of an uncertain economy and uncertain funding for large highway projects. Nonetheless, some see continuing economic uncertainty as prompting changes in the industry.
“Without the ongoing highway funding to acquire these machines, we’re seeing more of a trend toward renting pavers,” says Terry Healy, value stream manager, pavers & UCOMs, for Caterpillar Global Paving. “It’s probably partially due to a lack of confidence and partially due to a concern about return on assets.”
According to Terex Roadbuilding’s Rieken, the work outlook varies from state to state, but overall, he says, lack of a highway bill will likely result in many paving contractors opting to repair present machines in the coming year, rather buying new.
Volvo’s Sunkenberg agrees: “Lack of a highway bill is having a negative effect. If these guys are concerned about the amount of work they have on the books, they’re going to patch their paver instead of buying new.”
Sunkenberg also says that consolidation among firms using large pavers is changing the overall market.
“Instead of five contractors, each placing maybe 60,000 or 80,000 tons annually,” he says, “now you have one company running many more tons through each of its pavers.”
Sunkenberg also sees a trend for dirt-moving contractors, more often than in the past, to hire out the paving portion of road jobs:
“General contractors are getting out of the paving business and calling in specialists,” he says. “They’re finding it’s easier and less expensive in the long run to hire the work done by a competent specialist, rather than owning a machine that sits alongside the road until the dirt work is finished.”
But in governmental markets—county and state agencies, in particular— Brian Hall, territory manager, mid-South region, for VT LeeBoy, sees a trend toward pulling paving work in-house.
“I see more governmental agencies doing their own paving, instead of farming it out,” says Hall. “Their primary reason seems to be that they can exercise greater control over product quality, and they seem willing to make the investment in properly training their crews.”
Regarding training for paving crews, Caterpillar’s Healy says that this issue remains an ongoing concern:
“Lack of experienced crews and the need for training in basic operation of the machine and new control systems have been evolving concerns for the past decade,” says Healy.
Terex Roadbuilding’s Rieken agrees: “Contractors need to have better training programs in place. Don’t get me wrong, we have a lot of outstanding crews out there, but there are areas where we just don’t have enough training—people knowing how to use this equipment properly.”
Asphalt paver refinement
Despite market uncertainties, manufacturers seem undeterred in refining their products. Part of that refinement is mandated, of course, as manufacturers continue to implement Tier 4-Interim emissions standards. But some are choosing to take modifications beyond an engine swap.
“You can look at this as a problem or as an opportunity,” says Caterpillar’s Healy. “We knew that heat rejection would increase with Tier 4-Interim, and that hotter air exhausting from the side of the machine would adversely effect the ground crew and potentially interfere with sensors for the feeder system. So we redesigned airflow, using a top-mounted cooling system with two large fans to push both engine heat and asphalt fumes up and forward—away from the operator and crew. The fans are larger than previously used, but run slower, so they’re quieter.”
But with these emissions-compliant engines come attendant problems (or opportunities): Emissions hardware must be compactly packaged so as not to substantially change machine dimensions (thus impairing visibility) and must be capable of functioning transparently (so as not to demand more of the operator).
The paving crew’s job, in some respects, has become less burdensome with the evolving refinement of these machines.
“The use of microprocessors has changed the interface between the operator and the machine,” says Volvo’s Sunkenberg. “The travel pumps in the propel system, for example, are now managed via an electronic displacement control, which is like an electric motor on the pump, compared with using a system of mechanical cables for control. This allows the operator to set speed more accurately with a dial or switch, combined with a digital readout on the dash.”
In some instances, electronic systems also are helping keep a more consistent head of the material in front of the screed, allowing more precise control of independently adjustable conveyor and auger speeds in the material feed system, based on signals from sonic sensors, which replace mechanical wands.
“Electronic systems allow more adjustment from the control panel, versus actually making manual adjustments on the tractor,” says Sunkenberg. “The operator has more control at his fingertips, and there’s also safety and reliability aspects with these electronic systems.”
VT LeeBoy’s Hall notes, for example, that CAN (Controller Area Network), or CAN-bus, systems significantly reduce the amount of wiring and number of connectors in the paver, thus eliminating many potential sources of difficult-to-diagnose problems. (CAN-bus systems allow electric components to communicate via a single or dual-wire network, compared with individually wiring each component with conventional multi-wire looms.)
“CAN-bus not only reduces the number of wires and boosts reliability,” says Hall, “but also provides an excellent on-board diagnostic system and provides real-time information about the paving process—for instance, how fast conveyors and augers are moving and depth of material in front of extensions. With the bonus money at stake today, downtime is a critical issue.”
Yet another area of refinement for today’s pavers is screed heating. Although electrically heated screeds are nearly universally used on today’s large pavers, heating technology is “being taken to the next level to ensure fast, uniform heating, versus simply having electric heat,” says Caterpillar’s Healy.
“Software has been added to electrically heated screed-control systems,” he says, “allowing heating elements to cycle on and off to achieve more uniform heat, while using less energy.”
Continuing development in asphalt pavers
A major focus of coming development, according to many manufacturers, will be that of crew wellbeing when working around the machine—more effectively managing air quality, noise and vibration, while affording adequate protection from the elements.
Also near the top of the list is timely assessment of mat quality:
“Paving contractors need information to make real-time decisions on the job,” says Caterpillar’s Healy. “Being able to immediately evaluate what’s just come out of the screed and to take appropriate action will become key values for customers in the future.”
At the other end of the process, so to speak, is the prospect of increased use of 3D paving systems, based on total-station technology and offering automatic screed control referenced from a digital model of the job. Proponents say that 3D paving systems enhance rideability, conserve material, and allow precise placement of complex designs—super elevations, intricate transitions, and frequently changing cross-slopes.