Concrete Slipform Spreader

Overview

A concrete slipform spreader, often called a placer-spreader, is the machine that runs just ahead of a slipform paver on a concrete paving train. Its job is to take the concrete delivered by trucks and lay it down across the full lane width at an even depth, slightly higher than the finished slab so the paver behind it has a uniform surcharge to consolidate and shape. An even, correctly placed mat is what lets the paver run steadily and produce a flat, dense slab; lumps and gaps would force the paver to fight the material and leave a poor surface. The spreader does the rough placing so the paver can do the precise finishing.

The machine rides on a Main Frame and Tracks with four crawler tracks. Concrete enters the Receiving Hopper hopper, the Distribution System system moves it across the lane, the Strike-off Spreader spreader levels it, the Grade Control system keeps it on line and elevation, and the Engine and Hydraulics unit drives it all while the operator works from the Operator Station.

Frame and tracks

The Main Frame and Tracks spans the lane on four Crawler Track crawlers. A telescoping Main Beam lets the same machine set up for different lane widths, and each track hangs on a Track Leg that extends to set the width and a Leg Cylinder that raises it to set ride height and crossfall. Each crawler has its own Track Motor and runs a Track Chain with Track Pad pads over an Idler Wheel and a Drive Sprocket, so the machine creeps along the prepared base smoothly and grips without tearing it up. Independent leg height is what lets the spreader follow grade precisely.

Receiving the concrete

The Receiving Hopper hopper catches concrete dumped by ready- mix trucks or delivered by a belt. The Receiving Hopper is a wide bin protected by a Grizzly Screen grate that stops oversize lumps and a replaceable Abrasion Liner where the concrete scours the steel. Hopper Gate gates control how fast it discharges, and Hopper Vibrator units keep stiff low-slump paving concrete moving instead of bridging. Holding a buffer of concrete here lets trucks dump and leave quickly while the spreader meters out a steady flow.

Distribution across the lane

Trucks dump concrete in a pile, but the slab needs it spread evenly edge to edge, which is the Distribution System system's task. Most machines use a Cross Conveyor carrying a wide Conveyor Belt, driven by a Belt Motor and kept clean by Belt Scraper blades, to carry concrete sideways and drop it where the lane is low. Some machines instead use a reversible Plow Blade that drags the pile across the width. Either way the goal is the same: turn a few dumped piles into a continuous ribbon of concrete across the whole paving width before the strike-off acts on it.

Strike-off and spreading

The Strike-off Spreader spreader sets the final depth ahead of the paver. Reversible Spreading Auger augers, each turned by a Auger Motor, push concrete out toward the lane edges to fill them and even out the mat, then an adjustable Strike-off Plate held by Strike-off Cylinder rams trims the concrete to a set surcharge height. Surcharge is the small excess depth the paver behind needs to consolidate the slab to finished thickness, so getting it uniform is the whole point of the spreader.

Grade control and power

The Grade Control system keeps the machine on line and at the right elevation. Traditional setups use Grade Sensor wands riding a tensioned stringline and Steer Sensor units to follow it, feeding the Grade Controller that drives the Grade Valve and the leg cylinders. Modern machines add a 3D Receiver for stringless control off a digital model, removing the stringline. All of this is powered by the Engine and Hydraulics unit: a turbocharged Diesel Engine drives the Main Pump, which feeds the Valve Bank for the tracks, conveyors, and augers, with oil held in the Hydraulic Reservoir and cooled by the Cooling Package package. The operator runs spreading and grade from the Operator Station using the Control Console and a Operator Display.

Use in the paving train

The spreader is the second machine in a concrete paving train, behind the trucks and ahead of the slipform paver, with curing and texturing machines following. It matters most on thick, low-slump highway and airfield slabs, where dumping concrete straight in front of the paver would overload it and ruin the surface. By placing an even surcharge across the full width, the spreader lets the paver run at a steady speed and produce a flat, dense, well-consolidated slab. On lighter work a paver may be fed directly without a separate spreader, but for high-volume mainline paving the placer-spreader sets the pace and the quality of everything the paver does behind it.