Aerated concrete and foam concrete - familiarity with

What are cellular concretes? What are they like? Is it difficult to make foam concrete or aerated concrete with your own hands? Are there any features of the construction using the material of interest to us? Do walls of cellular concrete need exterior finish? Let's figure it out.

What it is

Cellular concrete is an artificial building stone with pores evenly distributed in it. Pore ​​size and quantity are determined by the brand of material; pores are not interconnected.

Cellular concretes are divided into two main categories, differing in manufacturing method:

• In the production of aerated concrete, the swelling of the concrete mixture is achieved by gas formation during a chemical reaction. (usually between fine aluminum powder and portland cement with evolution of hydrogen).
• Foam concrete is obtained by mechanical: foams the concrete mixture using a foam generator or a high-speed mixer, the cavitation of the blades of which saturates the material with bubbles.

Nuance: do not confuse cellular and lightweight concrete. The latter are distinguished by the fact that they are not harboring artificially; low density is achieved using light porous aggregates (perlite, expanded clay, vermiculite, polystyrene balls, pumice, etc.).

What is aerated concrete and foam concrete? Actually, in most cases, the composition is quite common for concrete mixes - cement and sand. More rarely, lime or its mixture with cement or gypsum is used as a binder, and industrial waste (slag, ash, etc.) is used as a filler.

For the formation of a cellular structure in foam concrete, aqueous solutions of surfactants (surfactants) are often used, which are foamed with a foam generator.

In aerated concrete, as already mentioned, aluminum powder is responsible for gas formation; however, it is very dusty and therefore quite uncomfortable to use. Used in industrial conditions, aluminum paste for aerated concrete is a dispersion of aluminum in water or other inert substance.

Classification

What brands of aerated concrete can be found on sale? In general, by what signs is it classified?

The main characteristic of the material - the brand density. It predictably corresponds to the mass of a cubic meter in kilograms: D500 brand blocks have a density of 500 kg / m3, D600 - 600 kg / m3, and so on.

Strength class - характеристика, практически линейно связанная с плотностью: так называется максимальная нагрузка в мегапаскалях, которую блок может выдержать без разрушения. Нередко вместо класса указывается марка прочности. Это та же максимально допустимая нагрузка на сжатие, но выраженная в килограммах на квадратный сантиметр поверхности (кгс/см2).

Frost resistance characterizes the number of freezing and thawing cycles that a material can withstand without a drop in strength of more than 5%.

To destination distinguish:

• Constructional (D1000 and higher);
• Structurally heat-insulating (D500 - D900);
• Thermal insulation concretes (below D500).

According to the method of manufacture (more precisely, according to the conditions of hardening) autoclave and non-autoclave concretes are separated. In the first case, the rapid curing of concrete products is achieved by exposure to superheated steam under pressure; in the second, the concrete is aged in a drying chamber or is gaining strength in atmospheric conditions.

Curiously, autoclave treatment not only shortens the production cycle, but also makes it possible to obtain a material of higher quality (greater strength and with less shrinkage relative to given sizes).

And what about foam concrete? Density grades and strength classes are used in this case; however, foam concrete with the same density has a slightly lower compressive strength.

Foam concrete can also be used as a material for load-bearing walls, and as a heat insulating filling for monolithic or prefabricated frames. Of course, the concept of frost resistance is relevant for him (as well as for any other building materials).

Comparison

What is the difference between gas and foam concrete in terms of consumer characteristics?

• Aerated concrete with the same density is somewhat stronger mechanically. In addition, aerated concrete walls are more permeable to steam and air.
• Foam concrete, on the other hand, is less hygroscopic. If this is the case, structures made of this material need less protection from precipitation and are more frost resistant.

Production

How to make cellular concretes? Of course, we are not interested in the production cycle of a large enterprise, but in the cottage industry: the relatively high price of finished building materials gives rise to an understandable desire to save.

Foam concrete

For the manufacture of blocks used form of non-absorbent material with limited adhesive properties (steel, laminated or oiled plywood, etc.).

Source of foam - factory or homemade foam generator; as a surfactant for its preparation can be used the finished product or homemade foaming agent. How to make it?

Frother

For 100 cubic meters of foam concrete we need:

• 6 kilograms of gum rosin.
• 1.6 kilograms of caustic soda (caustic soda).

• 6.3 kilograms of bone glue.

Cooking instructions are not too complicated:

1. 1.7 kg of caustic soda is dissolved in a liter of boiling water, after which crushed rosin is added. The mixture is boiled until the rosin is completely dissolved.
2. The crushed glue is mixed with water in a ratio of 1:10 and left to swell for a day, after which the mixture is heated to 60 ° C and stirred until the glue is completely dissolved.
3. At a temperature of the same 60 ° C, both solutions are mixed until a homogeneous liquid is obtained.

Concrete mix

It includes:

How to get ready blocks from these components?

1. Sand-cement mixture with the addition of a small amount of water is kneaded in a concrete mixer.
2. With continuous stirring, foam is introduced into it. The solution is stirred until a homogeneous porous mass.
3. Then it is poured into forms, from which grabbed blocks can be removed after 12 hours. A set of full strength takes up to a month.

Aerated

How and from what makes homemade aerated concrete?

As a rule, the composition of aerated concrete includes:

By varying the ratio of cement and sand, you can get either cheaper and heavier, or more quick-setting and durable material. Increasing the amount of aluminum powder, we get blocks with a higher degree of porosity.

What order of operations should be followed?

1. The sand-cement mixture is thoroughly mixed in a concrete mixer. Separately kneaded lime dough with a small amount of water and aluminum powder.
2. All components are mixed; then the concrete mix is ​​diluted with water to a working consistency.
3. The mixture is poured into molds.

Do not forget: in the process of gas formation blocks will increase in size. Forms are filled in about half.

1. After six hours, the material protruding over the edges of the form is removed from it. It is better to use for this purpose a thin steel string: it will cut off the excess, rather than push them into the form.
2. After another 12 hours, the blocks can be removed from the forms for storage in a single horizontal row. The strength needed for stacked warehouses will be gained by them in a couple of days; working strength is gained up to a month.

Standard

Несмотря на разницу в способе изготовления и физических характеристиках материалов, их производство регламентируется общим нормативным документом - ГОСТ 25485-89 «Бетоны ячеистые».

Let's pay attention to the main points of the standard.

• For all cellular concrete, strength classes from B0.5 to B15 are established.
• Brand density can vary from D300 to D
• Frost resistance can take values ​​from F15 to F

The coefficient of thermal conductivity is regulated for all brands with reference to the type of filler and ranges from 0.08 to 0.38 W / m * s.

Specify: the maximum value is set for structural aerated concrete brand D1200. In private construction are used, as a rule, brand D 400 - D600.

As a binder can be used:

1. Portlandcement of GOST 10178;
2. Quicklime GOST 9179;
3. Highly basic ash with a CaO content of at least 40%.

In the role of a binder are:

1. Construction sand GOST 8736.
2. Fly ash (a product of combustion of fuel at thermal power stations).
3. Ore beneficiation products with a SiO2 silica content not lower than 60%.

GOST regulates the composition and characteristics of additives (including gas and frother), labeling, quality control methods and packaging materials.

Application: useful tips

Allow yourself to give the reader a number of tips on the use of gas and foam concrete blocks in private construction.

Floors строения с несущими стенами из ячеистого бетона ограничена его прочностью на сжатие. Для газобетона строители придерживаются следующих норм:

For foam blocks and non-autoclaved aerated concrete, the maximum height of a building with bearing walls is limited to 3 floors or 10 meters.

The norms of thermal resistance of walls for the center of the country laid down in the current SNiP are carried out at a thickness of 500 mm for the density mark D500 and 600 mm for the density D600.

The first row of blocks in the wall is laid on the foundation above the waterproofing on the cement mortar. The subsequent ones are for special glue only; the thickness of the seam should not exceed 3 millimeters.

Aerated concrete groove - the comb needs to apply glue to the side faces; however, glue should be applied with two strips of 50 mm along the edges. Where the ridges interfere with styling (in the openings, at the beginning or end of a row), they are simply removed. The tool is a plane on aerated concrete or a grater with coarse sandpaper.

Mauerlat on aerated concrete is fastened not to the blocks themselves, but only exclusively to reinforced concrete armor. Conventional anchors do not hold in porous material; laying and concreting studs in drilled holes is also not an option: with moisture fluctuations, a massive timber can lead with obvious consequences for the walls.

Do I need to plaster the outer walls and the bay window of aerated concrete? Many houses are without exterior decoration for decades; however, with repeated wetting and drying, the appearance of the walls suffers. Plastering solves this problem. In this case, you can use only special vapor-permeable mixtures for cellular concrete.

Rule: vapor permeability of external walls should increase from the inside to the outside. Failure to comply with this rule will inevitably lead to dampening of the walls and the fall of their insulating qualities. The fungus is also not long in coming.

Conclusion

In a small article, we were able to acquaint the reader only with the most general information concerning cellular concrete. Additional materials telling which aerated concrete is better to choose and how to use it in the construction process contains a video in this article. Successes!