Non-autoclaved aerated concrete: production technology and

Aerated concrete has recently become a very popular building material, due to a number of its advantages. Often, developers prefer a cheaper version of it - non-autoclaved aerated concrete. But what is this material, how does autoclave and non-autoclaved aerated concrete differ and is it worth saving on it?

Next, we will try to answer all these questions and provide comprehensive information on this type of cellular concrete.

General information

Many people believe that aerated concrete is a modern material. However, in fact, it was patented for the first time back in 1889 in Prague by a certain inventor Hoffmann. He came up with the idea of ​​producing a material based on gas produced as a result of a chemical reaction between sodium bicarbonate and hydrochloric acid.

In Holland at the beginning of the last century, the technology of making aerated concrete using yeast was patented. A little later in Germany they suggested using metal powder as a gas-forming substance.

Practically, the modern manufacturing technology of porous concrete was developed in Switzerland by inventor Erickson in 1923. Already in 1925, industrial production of non-autoclaved aerated concrete as a building material was launched. Very soon its production appeared in many other countries.

At that time, the material was prepared on the basis of Portland cement, and a little later they began to use binders based on evils and slags. Initially, the material was invented as insulating, but in the 30s it was possible to obtain structural aerated concrete. It was used for enclosing structures in low-rise buildings.

Thus, the material can hardly be called completely new, since it has already passed a sufficient and quite successful test of time. Of course, today they use modern technological equipment for the production of non-autoclaved aerated concrete, with new types of heat and moisture treatment. In addition, the most optimal compositions were selected, which significantly improved the quality of the product.

Production technology

Composition

In the composition of this type of cellular concrete use the following main components:

• Portland cement is a binder;
• Fillers - pure sand or with the addition of fly ash CHP, chalk, gypsum, etc.
• Aluminum powder - used in the formation of the material as a vapor-forming substance.

In addition, to improve the performance, various modified additives are added to the composition of non-autoclaved aerated concrete, for example, semi-silica fume or gypsum. To speed up the hardening process using calcium chloride.

To date, work is underway to increase the strength characteristics of the product made by the non-autoclave method. The most promising is the use of various reinforcing additives, which are fibers of different origin.

It can be:

• Fiberglass;
• Polymer fibers;
• Basalt;
• Asbestos, etc.

In addition, a positive result gives an increase by 5-10 percent of the content of the filler in the composition, for example, fly ash or silica fume. Moreover, this allows not only to increase the strength of cellular concrete, but also to reduce its cost.

Manufacturing

Production technology неавтоклавного газобетона основана на том, что в результате химической реакции алюминиевой пудры и щелочи в составе смеси, внутри нее образуются поры, которые заполняются воздухом. Получившуюся пористую смесь оставляют застывать в естественных условиях, т.е. без применения автоклавов (специальных печей).

Sometimes equipment for non-autoclaved aerated concrete contains steam ovens. Due to the high-quality steamed mode, the strength characteristics of the product are also improved.

I must say that non-autoclaved cellular concrete is characterized by through pores, as a result of which it has poor waterproofing properties. However, thanks to the introduction of modern technology, this parameter has begun to approach the autoclave aerated concrete.

Material Features

Virtues

The characteristics of non-autoclaved aerated concrete are in many ways similar to autoclaved material.

In particular, the following points can be highlighted:

• Low density with high strength. Due to the porosity of the material, its price is reduced by reducing the consumption of components.
• Low weight, resulting in easy material handling. In addition, the load on the building foundation is reduced. This provides not only the durability of the building, but also savings in its construction, as you can use a less powerful base.
• Excellent thermal insulation properties due to porosity. This property provides energy savings in space heating.
• Easy to handleIf it is common to cut reinforced concrete with diamond circles, then a regular hacksaw can be used for aerated concrete.

Accordingly, in order to bring communications into the room, diamond drilling of holes in concrete is not required, as it is possible to use ordinary drills.

• Fire resistance. The material is absolutely non-flammable. Therefore, it can be used for wall cladding when it is necessary to ensure reliable passive fire safety. (See also the article Aerated concrete facing: how to do.)
• Environmental friendliness. The material is not only made from environmentally friendly components, but also has excellent vapor permeability, which provides a favorable microclimate inside buildings constructed of aerated concrete.
• Instructions for laying, the same as when working with a more traditional material, for example, brick.

Tip! Aerated concrete is an excellent material for interior partitions, as it has good noise insulation properties.

Differences between materials made by different technologies

Now consider the difference between autoclaved aerated concrete and non-autoclaved.

And they are just a few points:

• Non-autoclave material has greater shrinkage, which is about 2-3 mm / m, while autoclave material has a shrinkage of no more than 0.3 mm / m. If, when casting monolithic products, this deficiency is almost imperceptible, then during the erection of prefabricated structures it appears much more. (See also the article Putty for concrete: features.)
• Hardening time - as it is not difficult to guess, the material produced by the non-autoclave method has a significantly longer hardening time. However, this disadvantage is only relevant in the manufacture of the product.
• The aerated concrete, made by the autoclave method, is more durable, as it contains mineraltodermorite. In the manufacture of non-autoclaved cellular concrete, the formation of tobermorite is impossible. Therefore, the product is used in cases where it is not assumed to be heavy loads.
• The thermal insulation properties of non-autoclaved aerated concrete are slightly better, which is due to its greater porosity.

The rest of the characteristics of the products are very similar.

Note! On sale you can often find low-quality aerated concrete, made by "artisanal" method. It is not difficult to determine it, as it crumbles heavily.

Conclusion

Despite the fact that the gas concrete obtained by the non-autoclave method appeared quite a long time ago, thanks to the constant improvement of its manufacturing technology, it can be considered quite modern material. In some cases, its use is more appropriate than the use of autoclaved aerated concrete. However, if high material strength is important, then autoclave is more preferable.

From the video in this article you can get more information on this topic.