How a self-loading concrete mixer works, step by step

A self-loading mixer replaces a supply chain, not a headcount. On a conventional pour, concrete is batched at a plant, carried to site by a truck mixer and placed by a third arrangement — a pump, a crane skip or barrows. A self-loading machine does the first two itself: it drives into the aggregate stockpile, fills its own drum through a hydraulic bucket, carries water on board, mixes while it travels and discharges at the pour. It is bought where that chain breaks down — no batching plant within reach, an old street a truck mixer cannot turn into, a paving front that moves all day. Ten of the sixteen self-loading mixers in our specification table have a measured overall width, and those ten run from 1.60 m to 2.30 m. Whether that clears a particular gateway is measured on site, not claimed from here.

Loading starts with the machine driving at the pile, not with a wheel loader filling it. One standard-equipment list names it in full: a hydraulically controlled bucket that loads at the front and discharges to the rear. The rest of the evidence is in what the chassis carries. Four-wheel drive is recorded on all five mixers whose full factory specification sheet we hold. A reinforced heavy-duty frame appears on eight of the sixteen lists and an eight-wheel-drive chassis on three. Tyres are recorded on fifteen of the sixteen and differ by machine: a 10.5/46-16 mountain-terrain tyre on one of the smaller machines, a heavy-duty 23.5/70-16 on three mid-range ones, steel-cord high-pressure tubeless tyres on three of the larger. Travel speed comes off those same five sheets — 0 to 23 km/h on one, 0 to 36 km/h on the other four — and four of them describe service and emergency brakes on all four wheels plus a separate double parking brake.

Weighing is where the lists stop agreeing, and it is the first thing to settle in writing. All sixteen mixers carry a standard-equipment list; exactly one of them names an electronic hydraulic weighing system, and that machine is among the six models published here. Of the other five published models, four list the same system as optional equipment and one lists no optional equipment at all. Eleven of the sixteen mixers, the ten not published here and that one published model, carry no weighing entry of any kind, as standard or as an option. Eight of the sixteen lists name a high-definition LCD driving display in that position, which is a screen and not evidence of a load cell behind it. So whether a given machine weighs its batch is settled by the equipment list issued for that unit, and by nothing else.

The machine carries and draws its own water, and the two product lines in our data describe it differently. Seven of the sixteen lists — every machine of one line — pair an automatic water-fill controller with an external suction pump. Eight lists on the other line name a high-capacity water tank with a water-fill system and name no separate pump. Whether that second arrangement also draws from an outside source is not settled by the list; it is a question for the equipment list of the unit being quoted, not for a range sheet. What neither side gives is a capacity. No water-tank volume is recorded for any of the sixteen mixers: the entry exists on every published model and holds a value on none, and the five factory specification sheets we hold state fuel-tank, hydraulic-system and engine-oil volumes with no water figure at all. Anyone quoting litres of on-board water is quoting something no sheet we hold contains.

The drum turns while the machine drives, which is the whole of the category's claim. Five of the sixteen mixers have a full factory specification sheet behind them, and all five give the same drum speed: 16 revolutions per minute. Seven lists state that the drum lifts and rotates through 270°, so the drum is not fixed to the chassis — it can be raised and turned while the machine stands still. One further mixer in our data is a distinct synchronised-rotation build whose list records that the drum holds its mixing direction while the machine travels; that is one entry of sixteen, and it is not among the models published here. What none of this gives is a mixing time. No figure in our records states how long a batch must turn before it is ready, and that is a question the mix design and the specifier answer, not the machine's data sheet.

Discharge is aimed by moving the drum, not by repositioning the machine, and that is what the 270° figure buys. On the seven lists that carry it the drum both lifts and rotates, so the discharge point is chosen by turning the drum rather than by driving the machine round to a new angle — the difference between pouring a strip footing from one position and shuffling a delivery truck along it. One list describes the bucket itself as front-load, rear-discharge. A discharged-volume figure exists for fourteen of the sixteen mixers and runs from 1.0 to 4.5 m³. That is the volume of mixed concrete produced. The drum's geometric volume is recorded on four mixers only, from 2,900 to 6,500 L, and is a different number again. The capacity guide on this site sets out which is which, and which of them a buyer should be quoting.

Height is where this page is thinnest. Exactly one of the sixteen mixers has both heights taken off a dimensioned drawing: the SLM-18, at 2.58 m standing and 3.45 m with the bucket raised. For the other nine measured machines we hold a single overall height and no statement of the posture it was taken in, so none of those nine is presented here as a travelling height. Width is barely affected by how the drum sits and stays usable; height is affected, and a height read as travelling when it was in fact measured working is wrong in the direction that costs money at a gateway. We leave it recorded as an open question rather than resolve it. For anyone discharging over formwork or into a raised hopper, the figure worth having in writing is the one for the unit being bought.

One operator runs the whole cycle from the cab, and the equipment lists imply its order rather than state it: drive to the stockpile, fill the bucket, tip it into the drum, add cement and water, mix on the way to the pour, raise and turn the drum, discharge. What the lists evidence is that the steps are cab controls, not jobs on the ground — an automatic water-fill controller on seven of the sixteen, so filling is a cab control; a reversing and drum-monitoring camera on seven, so the operator can watch a mix he is not beside; an automatic lubrication system, standard on one machine and optional on four published models. A cement hopper appears on five published models' optional lists and no standard one, so how cement reaches the drum is asked model by model. We publish no output figure — that entry exists on every published model and holds a value on none — and no cycle time, for which our records hold no entry at all.

Three documents would change this page, and all three are ordinary things a plant sends on request. The first is the equipment list for the exact machine quoted, issued for that unit, not lifted from a range sheet, because the weighing question above has three answers across our sixteen mixers. The second is a stated posture for the overall dimensions: nine of the ten measured mixers come with one set of dimensions and no note of what the drum was doing, and only one comes from a drawing that separates standing height from bucket-raised height. The third is engine data on the machines that have none — a rated power is recorded for seven of the sixteen and an engine make for seven — because a machine whose power we cannot state is one we cannot compare. Until those arrive, this page describes a cycle and declines to describe a specific machine beyond what is written down.