What is aerated autoclaved concrete?

Aerated autoclaved concrete is a popular construction material, which in most cases has the form of individual blocks, or seldom beams, ceiling slab hollow bricks or floor slabs and roof slabs. It is basically used for the construction of walls, but may also be used for example for the construction of lintels, floor slabs or columns in knee walls.
The basic difference between a traditional composite and aerated autoclaved concrete is the presence of gas, thanks to which this type of concrete is considered to be a light composite. Gas may be introduced into a concrete mix by its foaming, caused by the application of aluminium powder or foam making additives. In both cases admixtures react with the remaining components of the mix, which also include lime. Chemical reactions taking place inside the mix cause the release of gas bubbles, thanks to which it acquires the desired properties.
As it turns out, aerated autoclaved concrete is lighter and cheaper than the traditional one. Due to its structure it is also easier to process. Thanks to the presence of gas aerated autoclaved concrete offers a perfect thermal insulation material, and large precast blocks allow a very quick progress of construction works. What is more, it is suitable to use as building material not only for the majority of wall types (internal and external, load bearing walls and partition walls etc.), but also shelves or fireplace casing. There are several brands of aerated autoclaved concrete, which differ from each other among others by density. The density classes of the most popular brands acquire values within the range from 300 to 700 kg/m3. What is equally important is that this material is fire resistant.
Unfortunately, aerated autoclaved concrete also has a few shortcomings. Due to its porous structure it is quite absorbable, as a consequence of which it does not tolerate the presence of humidity too well, and if made of low quality materials, does not react well to frost either. It is also much softer and has a lower compressive strength than traditional composite. For this reason it should better not be used for the construction of foundation walls or as elevation material. What is more, aerated autoclaved concrete also is not the best choice for sound proofing, and the presence of gas bubbles hastens the corrosion of unprotected reinforcing, which may be found in it.
Yet those unfavourable features may quite easily be overcome, among others by way of assuring an appropriate dampproofing, well executed bricklaying works or high quality elevation coatings. This makes aerated autoclaved concrete an increasingly popular construction material, the relatively low price of which is certainly an additional advantage.

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