Concrete mixer: types, use, research samples

How does a concrete mixer interfere with concrete? What types of these devices does the modern market of construction and industrial equipment offer? How to use them to prepare concrete of various types? Let's try to find the answers.

History

Dear reader, how old do you think concrete is?

A table?

Two hundred?

We will not torment you with uncertainty: the history of the material has more than 6000 years. For the first time, concrete was used in construction in a place known to us as Ancient Mesopotamia (the territory of modern India); later it was widely used in the Roman Empire.

Nuance: the so-called Roman concrete composition is quite different from the usual cement-sand-crushed stone mixtures. Although it was called opus caementicium, lime was used as a binder; sea ​​sand, boulders and fragments of pottery served as placeholders.

As a century ago, and now the main problem was to ensure the most uniform mixing of the components. The glut of any part of the monolith with aggregate or binder will be equally detrimental to the strength of the structure.

Traditionally, concrete mixes were mixed in a large wooden, and later - a metal trough. You will not refuse our ancestors in hard work; however, the result of the work was, frankly, not always stable.

The first attempts to mechanize hard work were undertaken shortly after obtaining a patent for the cement concrete that was familiar to us in 1844: the ancestors of modern concrete mixers were driven by horse thrust and were very cumbersome.

The prototype of the modern device was invented relatively recently - in 1916. Structurally, it was closest to modern automixers: the rotation of the wheels of a vehicle set in motion a drum with blades statically fixed in it; the collapse of the mixture at each turn of the mixer provided a fairly uniform mixing.

A modern household concrete mixer differs from a century-old prototype only by a source of mechanical energy that provides drum rotation: in most cases it is driven by an electric motor using a gear or belt drive.

Classification

According to what signs are modern concrete mixers classified?

Principle of operation

• Gravitational devices, in general, are described in detail in the paragraph above. The rotating inclined drum is equipped with rigidly fixed vanes that prevent slipping of the stirred mass. At a certain position of the drum, the mixture inside loses its static equilibrium and collapses downwards, mixing with the mass lying at the bottom - and so on and on.

Devices of this type are most versatile: they are able to work with concrete of any gravity and aggregate fractions size, with masonry, plaster solutions and ready-made mixtures of any type.

The only drawback (and this, in general, is quite conditional) is limited productivity: the gravitational concrete mixer mixes the components relatively slowly, which limits its use in industrial volumes.

• Forced concrete mixers represent a fixed drum and a rotor rotating in it. Productivity increases markedly, somewhat improves the homogeneity of the concrete mix at the exit. The downsides are the high price of such devices, their considerable mass and the need to use different devices for concrete with coarse aggregates (30–70 mm) and mortars.

Mobility

• Mobile devices again are all household mixers and, quite predictably, automixers.
• Stationary concrete mixers are used in industrial conditions, mounted on a rigid foundation and can be moved only during the reconstruction of the enterprise.

Rotation gear

If the choice of a household concrete mixer according to the principle of operation and the degree of mobility is quite predictable - all inexpensive concrete mixers of moderate productivity are mobile gravity devices - then the method of transmitting rotation from the electric motor to the drum needs a separate comment.

In the wide sale can be found units with the transfer of rotation gear or belt.

The main problems of the first class of devices associated with the destruction of the gear. In the second case, sooner or later the belt breaks.

In the humble opinion of the author, the second scheme is more viable.

The reasons?

• The belt costs less than making a new gear, much less replacing a gearbox.
• Replacing the belt is much easier to do with your own hands.
• Belt drive is less dependent on a factor that is difficult to assess visually - the quality of the metal from which the main components are made.
• A wedged drum will only lead to the belt slipping on the pulleys, and not to the destruction of the mechanism.

Curiously: a separate song - cheap concrete mixers from you-know-what Asian country. In addition to cast-iron corolla and steel gears of low quality, among these products can be found units with a plastic crown. The result of the purchase is quite predictable: a distressed buyer in a couple of months comes for a new concrete mixer.

Using

How to mix concrete in a concrete mixer?

Heavy concrete

When it comes to heavy concretes, the instructions are extremely simple:

1. Device устанавливается на ровную горизонтальную поверхность и включается.
2. A small amount of water is poured into the rotating drum, to which crushed stone, cement and sand are sequentially added.. The order of addition of the components may, in general, be different, but it seems convenient to the author to do just that: the cement that fell into the drum is immediately and uniformly mixed with water in a gravel mill; then the cement milk soaks up the sand added last.
3. Then water is added to the semi-dry mixture in small portions. - up to working concentration.

What should be the percentage of components for the production of heavy concrete of a particular brand?

Which brand of concrete should be preferred in one way or another?

• M100 is used for concrete cushions for foundations (belt and slab), for concreting fences and pillars.
• M150 может применяться при заливке бетонных стяжек в помещениях с умеренной нагрузкой на пол (погреба, технические подвалы и т.д.).
• M200 is suitable for screeds in residential premises, garages and workshops, for pouring monolithic foundations with a small number of floors.
• M300 годится для монолитных и каркасно-монолитных зданий небольшой этажности в качестве материала, воспринимающего основную нагрузку на сжатие.
• M400 is used in the manufacture of loaded ceilings, beams, beams, columns and other critical structures.

Solutions

How to mix concrete in a concrete mixer, if rubble is not included in the number of its components?

Strictly speaking, the described building material is not a concrete, but a mortar. Depending on the destination - masonry, plastering, spackling, etc.

The difference with concrete is in the order of loading. In a dry tank, it is better to first pour sand and cement, mix them, then gradually add water.

However, if this batch is not the first, a part of the cement forms hard-breakable lumps on the wet surface.

The problem is solved by changing the boot order:

1. Fill a small amount of water (about 1/5 of the total).
2. Gradually pour sand and cement into the tank.
3. After mixing, gradually add water.

Foam concrete

A specialized concrete mixer for foam concrete is, strictly speaking, not a mixer, but a small production complex of several units:

However, if you have a separate foam generator, you can use an ordinary household concrete mixer to produce a small amount of foam blocks.

How to mix concrete in a concrete mixer in this case?

1. Initially, the cement-sand mortar is mixed with a reduced amount of water.
2. Then foam is introduced into the tank with continuous stirring, after which the foam mass is poured into forms.

Nuance: thermal insulating foam blocks (grade in density below D500) are kneaded without sand, on one cement.

Lightweight concrete

How to knead concrete in a concrete mixer, if it is prepared on porous aggregates (expanded clay, perlite, polystyrene foam, etc.)?

The optimal loading scheme is similar to that for heavy concrete:

1. Some water is poured into the drum.
2. Large aggregate filler is loaded (expanded clay, etc.).
3. Cement and small fraction aggregate (expanded clay or perlite sand) are consistently filled up.
4. Gradually add water.

Polystyrene concrete is an exception: polystyrene balls have too low density to grind clumps of cement. In this case, it is better to prepare a dry cement-sand mixture, then add water to it and only then load polystyrene foam.

Tip: a typical mistake when mixing concrete - the addition of a large amount of water to increase the mobility of the mixture. Excess water leads to a catastrophic drop in the strength of the monolith. The correct solution is an increase in mobility due to the addition of plasticizers (specialized modifiers or ordinary liquid soap at the rate of 1 tablespoon per bucket of cement).

Research samples

Let's take a look at several models of domestic concrete mixers offered through online stores.

B-165

Before us is a gravitational concrete mixer with a 750-watt electric motor and the transfer of rotation to the whisk using a gearbox. How many cubes of concrete in a concrete mixer - it is not difficult to guess from its name: the volume of loading is 165 liters, or 0.165 m3. The mass of the device is 54 kg, the retail price is 17,820 rubles.

SB-80-08

A stationary unit with a rotary mixer is capable of producing up to 375 liters of ready-mixed concrete per cycle with a drum volume of 500 liters. Components are loaded manually, unloading - through the sector valve at the bottom of the tank. Other characteristics are as follows:

SB-80-10

To supply the components to the drum, there is a skip lift - a movable bowl actuated by a pneumatic cylinder. Unloading - through the sector shutter at the bottom of the tank. Technical details:

Conclusion

In parting, let us give the reader some more tips.

• The normal duration of mixing the solution in a gravity mixer is 2 minutes from the moment all components are added. Longer mixing will only lead to a drop in the mobility of the concrete due to evaporation of water.
• The concrete mixer is washed after unloading each batch of solution. Water poured into it (usually half a bucket is enough) can be used during the next batch.

• Hands and tools are best kept outside of the rotating drum. The force on the shoulder blades can reach hundreds of kilograms.

As always, the video in this article will offer additional information. Successes!