Stockpile segregation has long been a thorn in the sides of aggregate producers. Product quality, equipment maintenance costs, government specifications and the risk of alarmingly high penalties are encouraging aggregate producers to consider an alternative to blending coarse and fine materials with loaders, bulldozers and dump trucks. Radial telescopic conveyors, some with programmable controls, can provide cost savings versus managing stockpiles with stationary conveyors and bulldozers.

One of Michigan's largest asphalt contractors, Thompson & McCully Construction Co., added a portable radial telescoping stacking conveyor to its recycling division operation. Previously, the company stockpiled recycled asphalt pavement (RAP) with a 100-ft fold-out portable stacker.

"We would stockpile with the stacker and push the material with the dozer to blend it and desegregate it and then mix the fines with the coarse," said John Thompson, manager of the recycle division. "Our asphalt plant loaders could then come into the pile from any direction and the material would be consistent."

Costs associated with blending with a bulldozer, however, forced Thompson & McCully to explore different options last year.

"Recycle is awfully abrasive," Thompson said. "We were getting into $30,000 to $40,000 a year just to keep the dozer running, and that was before you pay for the fuel and an operator. So in 1997, we looked to the alternative of buying a piece of equipment to help eliminate the problem without having to buy a tractor."

The equipment had to be portable. Thompson & McCully's recycle division serves 17 asphalt plants, both company-owned and outside customers. Last year the company moved its recycle crushing plant 50 times and produced more than 1 million tons of material.

Thompson & McCully purchased a TS-150 portable radial telescoping stacking conveyor manufactured by Superior Equipment. The unit has a programmable logic controller that moves the stacker in any direction, extending and retracting it to build stockpiles in layers. Multiple piles are built in windrow fashion, blending fine and coarse material and reducing segregation. The stacker can retract from full extension and be ready to travel within 15 to 20 minutes, according to Thompson.

"Conveying material at a rapid rate with conventional conveyors, larger materials get thrown further from the head of the conveyor and the smaller particles fall closer to the conveyor," said Rick Kellenburger, engineer for Superior Equipment. "That's where you get segregation. The heavier (larger) material is on the far side of the pile and the lighter (smaller) material is on the near side. Rather than the conveyor sitting in one position and building a cone 30, 40 or 50 ft high, the conveyor is continuously moving and mixing the material as it falls."

Thompson said it has taken about two months, working with programmers from Superior, to make the minor adjustments necessary for his operation. "We knew when we bought it we would have [the manufacturer] out here, whether it was Superior or anyone else," Thompson said. "They would get the program to work the way we wanted it to work to eliminate segregation."

Thompson estimated that the telescopic stacker is solving 95% to 99% of RAP pile segregation problems.

The purchase price of a programmable telescopic conveyor is similar to that of a bulldozer. A dozer, however, requires an extra person to operate the machine and increases the risk of segregation, potentially creating unsaleable products.

"If we were to stockpile the material with a regular conveyor and then one of our asphalt plants goes into penalty on a mix design because the RAP was inconsistent, no matter who or what is at fault, some of those penalties can add up to hundreds of thousands of dollars," Thompson said.

Cost savings with the telescopic conveyor have been immediate. "A [dozer] operator is going to cost about $80,000 a year by the time you pay benefits," Thompson said. "A D-6 dozer is going to run right about $200,000 and is going to cost $150 a day just for fuel. Maintenance is going to average another $100 a day."

Conveyors are more reliable, according to Thompson. "There will be things that wear out-troughing rollers or turn rollers, bearings, lagging on the head pulleys," he said. "We own conveyors that have been in inventory for 15 to 20 years. As long as you maintain them, they're the cheapest way to move material."

Programmable telescopic conveying is the wave of the future in the industry, according to Thompson. It has attracted interest from many major players in the material-handling business.

"The buzz is flying," Thompson said. "We've had a lot of people up here to look at this thing. What we have is a continuous-movement stacker. If you drove up to Kalamazoo (Mich.) today, all you would see is a conveyor walking by itself."