Producers can provide a value-added service with concrete conveyors when the job calls for relatively low volume and low-slump concrete. Conveyors require little driver training to operate, help producers maximize mixer-truck utilization and can reduce mixer fleet maintenance costs by limiting the need for off-road driving.
Configurations include mixer-mounted units and conveyors mounted on separate trucks. Producers who place less than 100 cubic yards for most jobs will find mixer-mounted conveyors more cost-effective, while conveyor trucks are more appropriate for 100- to 200-yard pours.
Conveyors are ideal for short- or medium-reach jobs requiring placement of zero- to 2-inch-slump concrete about 25 to 130 feet from the chute. Bridges and foundations are examples. This equipment also provides precise placement into above-grade wall forms, including insulating concrete forms. When used to place concrete for at- or below-grade slab pours through small window openings, conveyors eliminate the need for buggies. Finally, conveyors enable producers to offer customers backfill or structural-fill gravel placement, thus keeping the equipment from sitting idle when it is not delivering concrete.
Producers can expect to spend $30,000 to $40,000 on a new mixer-mounted conveyor and up to half a million dollars for a conveyor truck. Producers report charging premiums of $5 to $8 per cubic yard of conveyed concrete, which go toward payback.
Mixer-mounted conveyors typically have horizontal reaches up to 40 feet and can reportedly reach pour heights and below-grade pour depths of 25 feet. Reach from the chute ranges from about 50 to 140 feet, and producers report pour rates up to 200 yards. Conveyor trucks can reportedly place concrete or stone at heights and below-grade depths of 60 feet. The conveyors either swivel or telescope into a reclined position for hauling.
Safety considerations include keeping conveyors at least 17 feet away from power lines, shifting the rear pivot to the side opposite the conveyor to prevent tip-overs, extending all four outrigger pads, keeping hands away from the belt and never standing under a conveyor.
To avoid segregation when conveying concrete, producers should use the standard tremie attachment, which prevents coarse aggregate particles from flying away from the head pulley and separating from mortar within 2 feet of the head pulley. Contractors should vibrate concrete with more than one vibrator immediately after placement. It's also important to avoid inserting vibrators within 2 feet of any unconfined edge of fresh concrete.
KEYWORDS: concrete conveyors