Volumetric Concrete Mixer Truck

Overview

A volumetric concrete mixer truck carries the dry ingredients of concrete separately and mixes them only at the moment of pour. A standard drum mixer leaves the plant with a fixed batch already wetted, and that batch begins to cure on the road, so it must be placed within about ninety minutes. The volumetric truck instead carries sand, stone, cement powder and water in separate compartments and combines them through a Mixing Auger at the back of the truck. Nothing is wet until the operator starts the pour, so the same load can sit all day, mix one batch at a curb and another an hour later across town, and adjust the recipe between pours without waste.

The whole rig sits on a Carrier Truck Chassis, a heavy 6x4 or 8x4 truck. The mixer body bolts to the frame rails and draws its power from a Power Take-Off (PTO) geared off the transmission. The five process streams are the Aggregate Bin, the Cement Powder Bin, the Water System, the Admixture System, and the conveyor and augers that carry and blend them. A Batch Control System ties the streams together so the proportions stay correct at any output rate.

Aggregate, cement and water storage

The Aggregate Bin is a steel hopper split by a Bin Divider Wall into a sand compartment and a coarse stone compartment, holding three to five cubic metres together. Each compartment feeds the belt through a Strike-Off Gate, an adjustable strike-off plate that sets how deep a layer of material the belt draws out. Bin vibrators shake the walls so material does not bridge over the gate. Above the belt sits the Cement Powder Bin, a sealed Cement Silo Tank holding two and a half to four tonnes of dry powder, vented through a dust filter and fluidised by a Cement Aerator Pad so the powder flows to the metering auger instead of packing. The Water System holds about 750 litres in a polyethylene tank, pumped through a Water Flow Meter accurate to one percent.

How metering works

Volume, not weight, is the basis of every dose, which is where the machine gets its name. Aggregate is metered by the Aggregate Conveyor: the gate sets the cross-section of the material layer and the belt speed sets how fast that layer moves, so the product of layer height and belt travel gives a known volume per minute. A Belt Encoder on the tail pulley counts belt travel so the computer knows exactly how much aggregate has passed. Cement is metered by the Cement Metering Auger, a variable-speed screw auger calibrated so each revolution delivers a fixed volume of powder; its Auger Encoder reports revolutions back to the computer. Water is metered by the turbine Water Flow Meter, and admixtures by small Admixture Dosing Pump units that inject plasticiser or accelerator in proportion to the cement. To change the strength of the mix, the operator changes one ratio on the panel: the computer trims belt speed, auger speed and water rate together so the proportions hold from the first cubic metre to the last.

How mixing works

The metered streams meet at the Mixing Auger, an inclined trough running up to the discharge. Aggregate arrives on the belt, cement drops onto it from the metering auger, and water sprays in as the combined stream tumbles into the trough. A hardfaced Mixing Auger Screw fitted with bolt-on Mixing Paddle blades folds the dry material through the water as it climbs the incline, so concrete leaves the Discharge Chute fully blended after only a few seconds in the auger. Because mixing is continuous, output is set by how fast the streams run: a typical truck discharges 40 to 60 cubic metres per hour and carries enough dry material for six to ten cubic metres of finished concrete before it needs reloading.

Power and materials

Every moving part runs on oil. The Power Take-Off (PTO) turns a load-sensing Hydraulic Pump, and a Hydraulic Valve Block of proportional valves feeds the belt motor, the two auger motors and the gate cylinders, each trimmed by the control computer. Contact surfaces are built for abrasion: the Mixing Trough and the auger flighting use wear-resistant hardfaced steel, the bins are welded steel plate, and the water and admixture tanks are polyethylene to resist the alkaline mix water. Rotating joints throughout use a Ball Bearing running against an Oil Seal to keep cement dust and grit out of the bearings.

Use

Volumetric trucks suit jobs where the quantity is uncertain or the site is far from a batch plant: footings, small foundations, repair work, remote rural pours, and any job billed for exactly the concrete placed rather than a full drum. The Batch Control Computer logs every dose and a Ticket Printer issues a delivery ticket showing the volume and mix produced, which is what the customer is billed against. Calibration is the one discipline the machine demands: the belt, the cement auger and the water meter must each be checked against a known volume on a schedule, because the finished concrete is only as accurate as those three meters.