How is foam concrete fundamentally different from aerated concrete?

I am building my house from autoclaved aerated concrete and I describe this process here in articles. Perhaps someone will be interested in my experience. But in the comments, many readers constantly refer to autoclaved aerated concrete as foam blocks (foam concrete).

Although foam concrete and aerated concrete are practically indistinguishable in appearance and have similar characteristics, they are different in principle and conditions production materials and they have critical differences in characteristics that uniquely determine the choice towards one of these materials.

Foam concrete is more gray in color. Although, some manufacturers of autoclaved aerated concrete also have gray blocks (due to the addition of slag, as in cement).

1. The principle of production of foam concrete and aerated concrete

Those who have studied even superficially these wall materials know that autoclaved aerated concrete is produced in large automated factories. Blocks are produced in various standard sizes and densities. In addition, the blocks gain increased strength in autoclaves (at high temperatures and pressures). This leads to an increase in the strength of the material and some increase in cost.

Foam concrete, however, is often produced in small manual production facilities. Sometimes even in a garage:

The foam concrete mixture is poured into molds, or containers are poured and after gaining initial strength and removing the formwork, the masses are cut with a string into blocks. Aerated concrete is also cut with a string. But they do it on fully automated lines.

Foam concrete and aerated concrete are porous materials. But the formation of pores occurs in a different chemical way. In aerated concrete - due to the interaction of aluminum with the alkaline medium of concrete (hydrogen evolution). And in foam concrete - due to organic foaming.

2. Characteristics of foam concrete and aerated concrete

More or less objective figures are shown in this table:

Just don't look at the price - this is outdated information.

Many characteristics are close in value. But the shrinkage of foam concrete in fresh masonry has critical values ​​that lead to tereschin formation. I am familiar with the reviews of those who used foam concrete as partition blocks and plastered them immediately after laying - the entire surface was covered with cracks. On YouTube, you can also find reviews after the construction of houses from foam concrete. Similar reviews.

Despite the fact that foam concrete absorbs moisture worse, its frost resistance class is lower. And with the same densities as aerated concrete, the strength of foam concrete is lower. All due to the fact that the foam concrete has not been in the autoclave. The concrete in its structure was gaining strength under natural conditions. And foam concrete delivered to the site, but produced in the heat, will differ in strength from another batch produced recently or in the fall (when the temperatures were slightly above zero).

It is not advisable to leave foam concrete wet for the winter. During the spring month (for daily thaws and frosts), it can crumble into crumbs:

Foam concrete wins from aerated concrete only in one thing - in price. It's about 20% cheaper.

I hope that for many, this information will be useful in choosing a wall material.

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Photo taken from open sources, from Yandex. Pictures

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