Aerated concrete technology: production and key features of

How is aerated concrete produced? How do the technical characteristics of aerated concrete blocks relate to the practical qualities of this building material? What features of the material to consider when building? Let's figure it out.

History

It begins with the Czech industrialist Hoffman obtaining a patent on the technology of foaming cement and gypsum solutions. The patent was granted in 1889; the invention was reduced to the addition of acid and reacting salts with it to the solution.

The goal - to obtain a material with a density inferior to concrete and improved thermal insulation characteristics - was achieved; however, the method was expensive and extremely inconvenient to use.

The idea was developed a quarter of a century later: the Americans Dyer and Ausworth used as a gas-forming additive powders of metals - zinc and aluminum. Actually, modern technology for the production of aerated concrete is not too different from that developed then. 1914 is considered the year of birth of the material.

However: the first autoclaved aerated concrete began mass-produced in Sweden another 15 years later. In 1929, Ytong set up an industrial production of blocks of a mixture of lime and silica, which underwent steaming at elevated temperatures. Ytong is still considered one of the leading manufacturers of material.

In 1934, the production of blocks was set up in Sweden using a slightly different technology: cement, not lime, was used as a binder.

In the USSR, the production of autoclaved cellular concrete became widespread by the mid-20th century. By our time, the volume of block production reached approximately 3.5 million cubic meters per year.

Description

What is the reason for the popularity of the material? What technical characteristics of aerated concrete made it so in demand?

Virtues

• Thermal insulation qualities of aerated concrete walls approximately correspond to the corresponding characteristics of dry wood, at times surpassing heavy concrete, silicate and ceramic bricks. Similar material - foam concrete - also lags behind in this parameter.

• Mechanical strength surpasses foam concrete, although it is noticeably inferior to more dense materials.

To clarify: depending on the brand, there are structural, structural and thermal insulating and strictly thermal insulating blocks. The strength of the first products allows them to be used for the construction of load-bearing walls and floors; the latter are used in frame-monolithic construction as a wall filling.

• Thanks to the same porous structure, production turns out to be quite economical: less material is spent on a fixed volume of building material.
• The open cell structure promotes natural ventilation of the walls. This feature is reminiscent of wooden houses: part of the air exchange with the street and up to a third of the steam exchange is carried out directly through the building envelope.
• Ease of processing also reminds of wood: aerated concrete can be easily sawn with a hand saw, it can be drilled and nails can be driven into its thickness.

Specifications

It is necessary to make a small digression and talk about the methods of classification of aerated concrete.

The main characteristics describing the material look like this:

And now let's see what values ​​these and some other parameters important for the builder take for the most demanded types of aerated concrete blocks.

Please note: mark on the density of D500 correspond to two classes of strength. The difference between them lies in the ratio of the amount of binder and filler in the production of blocks.

What does this set of characteristics mean in practical terms?

• Aerated concrete provides about three times - five times more effective insulation compared with ceramic brick. So, in order to provide heat transfer resistance of 2.5 m2 * C / W, aerated concrete masonry 375 mm thick or brick 1100 mm thick is required.

• At the above-mentioned ratio of the thickness of the load on the foundation, the corresponding square meter of masonry, in the first case is equal to 205 kilograms, and in the second - 2000 kg.
• The minimum width of the strip foundation in the first case is 400 mm, in the second - 1200.

Production

What makes aerated concrete?

Raw material

The composition of the material includes two main components - filler and binder. What can be used in this capacity?

Filler

• Fine ground quartz sand.

• Crushed waste mining industry (rock and sedimentary rocks).
• Ash generated by burning coal.
• Secondary products of ore dressing.
• Metallurgical slag.

Binder

• Lime.
• Portland cements.
• Mixed binder (cement + lime, lime + gypsum, etc.).

Technology

Technology изготовления газобетона в промышленных масштабах включает следующие основные операции:

1. Filler смешивается со связующим, после чего в полученную массу добавляется суспензия газообразователя - алюминиевого порошка. In its pure form, the powder is not used: it is too easily carried by any draft.
2. The mixture is poured into molds.where hydrogen released by the reaction of aluminum with an alkaline medium expands it.
3. After setting, the porous mass is cut into blocks. For cutting use durable strings up to a millimeter thick; pockets for gripping and carrying blocks are cut out by a mill.
4. The last stage - drying in heated chambers or steaming in an autoclave. The second scenario requires more expensive equipment, but contributes to the speedy set of aerated concrete strength. The average exposure time of the blocks in the autoclave is 12 hours; working pressure is about 12 bar at a temperature of 190 C.

Curiously: the exit to the operating mode and the preparation for unloading the autoclave are gradual and take 1.5 - 2 hours.

1. The last stage - packaging products in waterproof packaging and palletizing.

When is block drying used instead of steaming? First of all, in the manufacture of aerated concrete with their own hands, at home or in the semi-handicraft production of small lots for sale.

As already mentioned, the price of the necessary equipment in this case is much lower; However, product quality will deteriorate somewhat:

• Shrinkage during the drying process will reach 3-5 mm / meter.
• The compressive strength of concrete products will not exceed 10 - 12 kgf / cm2. However, a gradual increase in strength when the binder absorbs atmospheric moisture will last for several years.

Features of construction

What restrictions does the use of aerated concrete blocks impose on the construction?

Foundation

The main requirement for it is the maximum rigidity, which excludes any deformation of the bearing walls. Despite the relatively high strength, aerated concrete is completely devoid of elasticity and cracks under bending loads.

What types of foundations are used in aerated construction?

• On rocky and dry sandy soils shallow-drenched strip bases are used.
• On heaving soils (clay, loam) the optimal solution is a pile foundation on bored piles with a monolithic reinforced concrete grillage.
• Concrete slab foundation is poured on marshy soils and other unstable soils. It evenly distributes the load over a large area and eliminates any uneven subsidence of the walls.

Walls

The key requirement for the walls is high heat transfer resistance. It is normalized by the current SNiP and for the center of the country is equal to 3 - 3.2 m2 * C / W.

According to the manufacturers, the following thermal characteristics can be provided:

• D500 density block blocks with a wall thickness of 500 mm.
• D600 blocks - with a wall thickness of 600 mm.

For load-bearing walls of aerated concrete, there are restrictions on the height of the building.

In addition: in earthquake-prone areas, reinforced reinforced concrete frame is designed to improve the seismic resistance of the building structure.

What rules apply to internal load-bearing walls and unloaded partitions?

• Если на стену опирается одна плита перекрытия, она возводится из блоков прочностью AT 2,5 с толщиной 240 мм или из блоков прочностью 3.5 толщиной 200 мм.
• The wall on which the two plates rest should be thicker — 300 and 400 mm, respectively.
• Unloaded interroom partitions are made of blocks of normalized strength with a thickness of at least 240 mm. The instruction is connected with the need to provide high-quality sound insulation.
• Interior partitions have a thickness of 100 - 150 mm. Strength, of course, is not standardized in this case.

Jumpers

They can be made of monolithic reinforced concrete (in this case, the lintel is filled in place; masonry walls are used as part of the formwork) or from special U-shaped blocks. In the latter case, the jumper can be a team.

How is a sufficient bearing capacity of the structure ensured?

1. U-shaped blocks are exposed on a temporary support cavity upwards. They should go beyond the edges of the opening at least 10 cm on each side.
2. The reinforcement cage is laid in the block cavity.
3. The cavity is concreted. The prop is removed after the concrete has firmly set.

Masonry mortar

On the usual cement-sand mortar prepared in a ratio of 1: 3, only the first row of blocks is laid out. The following rows are placed only and exclusively on a special glue for cellular concrete, providing a joint thickness of not more than 3 mm.

Why ordinary solution should not be used for laying?

• Thick seam is a cold bridge leading to a room with high-quality thermal insulation. How heat losses will grow - I think, you can not explain.
• In addition, the blocks have exact dimensions and perfect geometry. Thin seams allow you to use this advantage, making the appearance of the masonry flawless.

Exterior and interior finish

The main requirement for it is quite standard: the vapor permeability of the walls should increase from the inside to the outside. Violation of this simple rule leads to dampness of the walls, and in the future - and to their accelerated destruction.

Since the vapor permeability of aerated concrete is exceptionally high, special plaster mixtures with increased vapor and air permeability are usually used for walls made of it. Another popular solution is ventfacades, which provide additional warming and do not interfere with natural ventilation of walls.

Conclusion

We hope that the proposed information will be useful both for novice builders and potential manufacturers of an inexpensive and practical building material. As always, the video in this article contains additional material. Successes!