Better Roads Staff
A Superior Asphalt Haul
Live-bottom trucks and trailers earning high marks
By Mike Anderson
“At some point,” says Volvo Construction Equipment’s John Sunkenberg, “you just have to put a load of asphalt on rubber. It’s the only way to get it from the plant to the paver.”
Fellow industry veteran Bill Rieken, paver applications specialist with Terex Roadbuilding, readily admits he’d just as soon never again see a conventional square- or rectangular-bodied dump truck back up to a paver or material transfer vehicle. “Conventional dump trucks are part of the problem of temperature differential and material segregation. They only contribute to the problem; they are not part of the solution,” he says.
A long hauling distance combined with a low ambient temperature can result in material coming out of the truck in cold clumps in need of extensive re-mixing or re-blending – a scenario only exasperated by an end dump. “When you raise that truck bed, you generally have material breaking and running in the hopper,” says Sunkenberg, Volvo road industry competency manager, “and you can deal with segregation on the sides and the corners.”
Live-Bottoms: “You’re moving the material more as a mass horizontally, rather than vertically, and that’s a good thing.”
-John Sunkenberg, Volvo Construction Equipment
“If we’re forced to use dump trucks,” says Rieken, “what some contractors will do is make you put in deflector plates in the back so the discharge area is the same width as the slats or the augers you are feeding, so you get some re-blending of the mix as you dump it out of that truck. This way, you’re not held to the paver too long. Otherwise, the mix that sits in the hopper wings prevents the truck from getting empty quickly, and you end up holding the truck.”
Even before considering the material unloading issues, including the safety hazards of lifting an end dump bed on uneven terrain or near overhead wires, the basic geometry of the hauling space itself is an issue with conventional dump bodies, says Rieken. “You’ve simply got more surface area on which to lose temperature.”
Three-point loading – asphalt placed at each end of the truck body or trailer topped off by a third load in the middle – is now an established practice at plants, says Sunkenberg. When the material is dropped from the surge bin in one large pile, aggregate will separate, roll off and collect at the base; dropping smaller amounts of mix at different points in the truck will minimize the risk of segregation. “I don’t think there is anyone not loading a truck that way these days,” says Sunkenberg, “because it’s just such an easy thing to do.”
End of ‘The End’?
With their reduced surface area, and less drop segregation, live-bottom truck bodies or trailers should be used for hauling asphalt, “whenever possible,” says Rieken.
“The really good contractors are using them,” he says. “It allows them to fill the hopper up more effectively, and allows them to empty the truck much quicker and get away from the paver, transfer vehicle or whatever they’re filling. It just allows for a better truck exchange on the site.” Keeping the hopper full, says Rieken, minimizes cyclical segregation by allowing hot uniform material from the next truck to blend with mix from the previous dump.
“You’re moving the material more as a mass horizontally rather than vertically, and that’s a good thing. Anytime you can eliminate dribbling and dropping of that material versus moving it as one piece, certainly you’re going to get better material in the end,” concurs Sunkenberg. “And you can tend to keep the hopper a little bit more full during that process. You don’t have stones falling, what, 15 feet from above.”