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What’s a concrete mixer truck?

A concrete mixer truck (often called a cement truck, agitator truck, concrete truck, cement mixer or concrete mixer) is a rigid truck that has a rotating drum or ‘bowl’ on the back that keeps pre-mixed concrete moving so that it doesn’t set. They are built on a regular lorry chassis, then fabricated by adding the concrete mixing equipment. This way, they can be specified according to the weight of concrete carried (e.g. 10×4, 8×4 or 6×4), and the type of truck that the driver or company prefers.

An 8×4 concrete truck

The rotating drum contains blades that stir the material. When in transit, the drum rotates one way which pushes the concrete down the bottom of the drum and forces it to be mixed; this is called charging. When it’s being unloaded, the drum rotates the other way which brings the concrete up to the top of the drum into the chute.

The inside of the drum showing the vanes that stir the concrete.

The drum doesn’t rotate very fast in transit – usually just 1-3 revs per minute. The drum is usually powered by PTO which takes its power from the engine, but can be powered by an auxiliary engine.

Controller showing the speed dial for the drum or bowl

The trucks range in capacity from around 2 cubic meters to 9 cubic meters of concrete. Smaller trucks are used both for smaller jobs and also where access is difficult.

The driver operates the drum from a controller on the back.

Drum controls

The chute diverts the concrete down to the ground. It can be rotated 180 degrees around the back of the vehicle. Up to around 0.7m3 of concrete can be ejected per minute, depending on the mixer’s specifications.

Concrete is ejected from the chute onto the surface. The truck can move forward as required

The chute can be extended with mixer extension chutes, often carried on the truck.

Because concrete sets hard, the drum must be cleaned as soon as possible, otherwise it is difficult to get it clean.

Driver washing the drum and chute
Hose attached at the back of the truck near the chute

Concrete mixer truck drivers must be careful when cornering as the centre of gravity can shift dramatically if the vanes in the drum pick up the concrete (this can happen if the concrete starts to thicken).

Volumetric mixers

Volumetric mixers don’t carry pre-mixed concrete, they carry the separate components that are then mixed on-site, as and when they are needed, which can reduce waste. It also makes the truck less likely to be affected by a change in the centre of gravity of a rotating drum.

Darren has owned several companies in the automotive, advertising and education industries. He has run driving theory educational websites since 2010.

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