Recently, aerated concrete has gained great popularity in the building materials market. According to their technical characteristics, aerated concrete blocks are a unique wall building material that combines the strength of stone and the thermal conductivity of wood. All this became possible due to the high (up to 85%) porosity of the material. Aerated concrete is a kind of cellular concrete, on the surface of which there are holes-pores. The entire structure of aerated concrete throughout its volume is saturated with spherical pores (1-3 mm in diameter).
The composition of aerated concrete includes the following components: quartz sand, water, lime, Portland cement, aluminum powder.
The production technology is quite simple, but high-quality high-tech industrial equipment is required to achieve high quality and excellent physical and technological properties. According to the production technology, autoclave and non-autoclave manufacturing methods are distinguished. The autoclave method or the so-called synthesis hardening method is of higher quality.
When using it, aerated concrete blocks get a more durable structure, since the blocks are baked at high temperatures and pressure in a saturated steam environment. The non-autoclave method (hydration hardening method) provides for the hardening of blocks in natural conditions, with low electrical heating or in a saturated steam environment at normal atmospheric pressure.
Non-autoclaved aerated concrete has a large number of through pores and therefore has poor waterproofing characteristics.
We owe the appearance of aerated concrete to the Czech Hoffmann, who added acids, chloride and carbonic salts to gypsum and cement mortars. Salts, when interacting with solutions, released gas, which gave concrete porosity. For this invention in 1889, Hoffmann received a patent, but the production of aerated concrete never began. Using the works of Hoffmann in 1914, two Americans Dyer and Aulsworth were the first to use zinc and aluminum powders as a blowing agent. When these powders interact with slaked lime, hydrogen is released, which in turn contributes to the formation of a porous concrete structure. The Swedish scientist and architect A. Eriksson also contributed to the improvement of production technology. He invented the technology of “fluffing” concrete by adding aluminum powder to it. Since 1929, Ytong (Itong) for the first time begins the industrial production of aerated concrete. By production the autoclave method of thermal and moisture influence on lime-silica components is used. In this case, cement was not used at all. A slightly different approach to the production of aerated concrete in 1934 was found by the Swedish company Siporex. Their technology involved the use of a mixture of silica components and Portland cement. In this case, lime was not included in the composition of the solution. This method was invented and implemented by Finnish engineer Lennart Forsen and Swedish engineer Ivar Eklund. Their practical and scientific achievements subsequently became the basis for the industrial production of aerated concrete and gas silicates.
Consider the main characteristics, physical and mechanical properties, advantages and disadvantages of aerated concrete blocks.
- . Blocks made of aerated concrete are able to withstand heavy loads. It is worth noting that this is one of the materials that, with its sufficient lightness, has the highest possible strength. This is the best ratio of strength and lightness for wall materials.
- Fire resistance. The gas block is a non-combustible building material, it is resistant to open fire. In the process of testing finished products, aerated concrete blocks are required to undergo fire resistance tests.
- Low density. Aerated concrete blocks, due to their low density, are light in weight, which greatly facilitates the work during construction.*
- Frost resistance. High resistance to repeated freezing and thawing without visible defects in the structure characterizes aerated concrete as a material with high frost-resistant properties (at least F35).
- Soundproofing. The walls erected from aerated concrete blocks comply with GOST for sound insulation and do not require additional sound insulation work.
- Thermal insulation. Due to its porous structure, aerated concrete is an excellent heat-insulating building material. This is due to the presence of pores with air, which has a low thermal conductivity. Houses built of aerated concrete blocks are able to perfectly smooth out temperature fluctuations, they will maintain the optimum temperature in both cold and hot weather. It is also worth noting that aerated concrete is capable of accumulating heat, which in the winter season will help to avoid unnecessary spending on heating.
- Environmental friendliness. The production of aerated concrete blocks is harmless and virtually waste-free. During operation, it does not emit harmful substances; when interacting with the atmosphere, no rusting or rotting processes occur in it. It is not susceptible to the formation and development of fungi, bacteria and mold. In terms of environmental friendliness, aerated concrete blocks are second only to wood.
- Compressive strength. This parameter directly depends on the value of bulk density. The greater the bulk density, the stronger the aerated concrete blocks (for the D500 grade – 2.5 MPa, and for the D600 grade – 3.2 MPa). When choosing the brand of aerated concrete blocks used, it is worth noting the fact that the lower the bulk density, the “warmer” the block.
- Ease of processing. Aerated concrete blocks have earned special appeal due to their ease of surface treatment. They are easily cut, chiselled, sawn with almost any hand and mechanical tool.
- Vapor permeability. Due to the excellent vapor permeability of aerated concrete, there is no excessive humidity or dryness indoors. An optimal microclimate is maintained inside the house.
- Durability. Houses built of aerated concrete, with high-quality installation, have a service life of at least 100 years. This has been confirmed in real life conditions. So in the Scandinavian countries there are a large number of houses built from aerated concrete more than 75 years ago. They show no signs of destruction.
- Ease. A standard block with overall dimensions of 588x300x188 mm and an average density of 600 kg/m3 has a mass of 25 kg. During construction, it replaces 28 bricks in a brick wall, the weight of which will be about 120 kg. When using aerated concrete blocks, the amount of required masonry mortar is reduced by 5-7 times, and the masonry speed increases by 4 times.
In addition to a large number of advantages, aerated concrete blocks also have disadvantages. Here are some vulnerabilities of aerated concrete:
- Fragility. Aerated concrete blocks are very critical to shock loads. They may crack or split if dropped or hit. Blocks should not be turned over or thrown. Particular care must be taken during transport and handling. High hygroscopicity. Aerated concrete blocks should not be stored outdoors, and the walls laid out from it must be plastered or lined.
- Aerated concrete blocks are not used in the arrangement of foundations or sewer wells. Also, a high level of hygroscopicity creates additional inconvenience during plastering, as it quickly takes away moisture and worsens the elasticity of the mortar used for finishing. In general, the use of aerated concrete blocks in construction as a wall material will provide the house with sufficient strength, durability, environmental friendliness, excellent sound and heat insulation, and fire safety.