Chip Spreader

Overview

A chip spreader is a truck carrying loose aggregate chips (8–14 mm stone) and designed to distribute them uniformly across a road surface that has just been coated with hot tack bitumen. The aggregate embeds into the tacky asphalt, and after traffic compaction and binder hardening, forms a chip seal, a low-cost surface suitable for secondary and rural roads.

The spreader consists of a receiving Receiving Hopper filled by a loader, a Spreader Hopper & Chute with adjustable Left Spread Gate and Right Spread Gate to control flow rate, and a Carry-Back Conveyor that allows the operator to return excess chips to the hopper if the job is over-supplied.

How it works

The truck is filled from a nearby aggregate stockpile using a front-end loader bucket, which dumps chips into the Receiving Hopper. The hopper has a sloped Hopper Bottom Slope (30–35°) that directs chips toward the Spreader Hopper & Chute, a compartment directly above and behind the truck cab.

The operator sits in the Operator Cab, watching the road ahead and controlling the spread pattern. The main controls are the truck accelerator (speed), and two hydraulic Gate Control Cylinder cylinders operating the left and right Left Spread Gate and Right Spread Gate. By adjusting the gates, the operator controls the flow rate in gallons per metre of road (or tonnes per kilometre). Both gates should be opened equally to maintain a symmetric spread pattern across the truck width.

As the truck moves forward at 2–8 km/h, chips fall through the adjustable openings in the spread gates and cascade out the Discharge Chute onto the tack-coated road. The chute is angled to center the chips on the pavement, typically discharging directly behind the truck's rear axle. A skilled operator achieves near-uniform coverage; over-spreading creates a slippery surface, under-spreading leaves bare spots.

The spread gates are operated by the Proportional Control Valve, fed by a Hydraulic Pump powered by the truck's PTO. The proportional valve responds to the operator's control lever, allowing smooth modulation of gate opening. The Hydraulic Tank and Pressure Relief Valve protect the system from overload.

On some jobs, the truck arrives with slightly too much material, or the operator reduces the application rate toward the end of the run. The Carry-Back Conveyor, a return belt, can carry excess chips backward into the Receiving Hopper, allowing the operator to recycle material and avoid dumping. The conveyor is driven by an electric motor or a second hydraulic motor, running at 50–100 tonnes per hour, and can empty the truck in minutes if needed.

Once a section is spread, the chips stay loose on the road surface. Traffic (typically controlled to light speeds) compresses and embeds the chips into the tacky binder. Within 3–7 days, depending on temperature and traffic, the binder hardens, locking the chips in place and forming a durable chip-seal surface. Excess loose chips are swept up by a separate chip sweeper truck before full traffic is restored.

The Widening Gates (Optional), optional hydraulic-powered side chutes, extend the spread pattern beyond the truck width, allowing a single pass to cover full lane widths on narrow roads. Without widening gates, a standard spreader typically covers 2.0–3.5 m; with widening gates, up to 5.0 m.

Typical daily production is 500–2,000 m² per truck depending on truck speed, application rate, and site layout. A chip-seal project on a rural road often uses two spreaders in tandem: one delivering tack coat ahead, the second following with chips. Lane discipline and load planning are essential, material must be staged to feed the spreader without idle time, and the tack coat crew must work at the same pace to avoid chips landing on dry pavement or tack sitting uncoated.