Aerated concrete - close-up
|raw materials||quartz-containing sand flour, lime, cement|
|Thermal conductivity λ||0.06 W / (m K) to 0.21 W / (m K)|
|Specific heat capacity c||approx. 1 kJ / (kg K)|
|Bulk density ρ||200 to 800 kg / m³|
|Vapor diffusion resistance μ||5-10|
|Areas of application||load-bearing homogeneous walls or ceilings|
AAC (including aerated concrete ) is a highly porous , mineral building material with low density on the basis of lime -, lime cement or cement mortar , which made porous by blowing and in principle a steam curing is subjected. The best-known brands are Ytong , Hebel and Greisel.
It is not a concrete according to the usual definition, because aerated concrete does not contain any aggregates such as sand or gravel . The main component is usually finely ground quartz-containing sand in the form of rock flour . However, this takes a large part in the chemical reactions.
After the steam hardening process, the finished product consists of a crystalline phase, which corresponds to the naturally occurring mineral tobermorite , a remainder of quartz sand that was not converted during the reactions during production, as well as some anhydrite and other phases (mainly CSH (I. )). There is nothing left in the product of the raw materials cement and lime , as these are completely converted into CSH phases.
Aerated concrete, like sand-lime brick, is one of the so-called steam - hardened building materials . However, sand-lime brick is not expanded or porous. Comparable properties such as aerated concrete has foam concrete (also expanded concrete ), a porosierter by foaming or blowing lightweight concrete , which no one is subjected to steam curing and therefore also as in-situ concrete can be produced.
Aerated concrete is a steam-hardened, solid building material with a bulk density of 300 to 800 kg / m³ and is generally made from the raw materials quicklime , water and quartz sand . The sand has to be ground fine and can also be completely replaced by fly ash from coal-fired power plants. After the raw materials have been mixed, a small amount of aluminum powder or paste is usually added to the suspension . The mortar mixture is poured into tubs. The reaction of the aluminum powder with the alkaline mortar suspension results in finely divided hydrogen bubbles, which foam the gradually hardening mixture. The final volume is reached after 15 to 50 minutes. There are now blocks three to eight meters long, one to one and a half meters wide and 50 to 80 cm high. The blocks, which are only cake-proof, are cut into the required stone or component sizes using wires. Hardening in special steam pressure vessels , the autoclave, at temperatures of 180 to 200 ° C in steam under saturated steam pressure of 10 to 12 bar gives the material its final properties after six to twelve hours. In chemical terms , the aerated concrete largely corresponds to the natural mineral tobermorite , but in a synthetic form.
Due to the hardening in water vapor, aerated concrete requires less energy in production compared to clay bricks. The manufacturing process also allows the production of reinforced and unreinforced components. The reinforcement , usually in the form of reinforcement cages, is coated with paint to protect it from corrosion.
Unreinforced aerated concrete
The even distribution of the pores and its typically high proportion of pores make this building material, due to its low weight, even in larger formats, universally applicable and versatile in static border areas. These are known as plan stones or blocks. In addition, the good thermal insulation properties and the high load-bearing capacity of aerated concrete flat stone masonry (with regard to its low bulk density ) are important features. These properties and its better compressive strength are also taken into account in DIN 1053 as a basic standard for the calculation and execution of masonry .
The stone compressive strength classes are also color-coded for better representation (mostly on some stones on a pallet). The following applies here:
- Strength class 2: green
- Strength class 4: blue
- Strength class 6: red
- Strength class 8: black
The full designation consists of the following information (example):
|DIN V 4165 - PPW 2 - 0.40 - 624 × 300 × 249|
|DIN V 4165||The aerated concrete DIN (from April 2006: EN 771-4)|
|PPW 2||P orenbeton - P Lanstein - W ärmedämmend - strength class 2|
|0.40||Bulk density class|
|624 × 300 × 249||Dimensions length × width × height|
This building material was increasingly used with the introduction of the 1995 Thermal Insulation Ordinance (WSV 95) and the Energy Saving Ordinance (EnEV), which has been in force since 2002 and which tightened the guidelines . The decisive factor here are the very low calculated values of the thermal conductivity λ (in W / (m · K)) of 0.11 for PPW 2 to 0.18 for PPW 6. The attempts to improve these low values even further (e.g. PPW 2 with 0.09 W / (m · K)) have meanwhile led to material with 0.06 W / (m · K), although other properties, such as e.g. B. the compressive strength, are negatively influenced.
Another advantage of the aerated concrete blocks is the high dimensional accuracy already achieved through production processes, which allows processing using the thin-bed method , whereby the joints reach a thickness of 1 to 3 mm, which minimizes a thermal bridge in the joint area and increases the compressive strength of the masonry . Flat stones have a dead weight of 7 to a maximum of 25 kg.
Aerated concrete is easy to process. So the masonry is already possible by skilled craftsmen. The stones can be removed with simple tools, e.g. B. a hand saw or a band saw can be cut.
Structural elements with reinforcement
Components of cellular concrete containing such components made of reinforced concrete , a reinforcement , the tensile forces can hold. Prefabricated components made of aerated concrete are used as wall panels, wall, ceiling and roof panels in industrial, residential and municipal construction, also here as the simplest solution for high thermal insulation. Floor-to-ceiling wall panels are produced for load-bearing walls and wall panels for non-load-bearing walls. Aerated concrete wall panels can be used variably in connection with supporting structures made of steel, reinforced concrete or wood. The different component sizes and the horizontal or vertical laying method open up many ways in facade design and give the opportunity to create every building envelope in assembly. The assembly is usually carried out by specialized assembly companies. The services range from the creation of laying plans and static calculations through assembly to grouting and surface treatment (coating, cladding).
Aerated concrete wall construction elements, also known as system wall elements, when combined, result in a complete and therefore efficient assembly system.
Aerated concrete roof panels can be used for flat and pitched roofs and are placed on the partial construction. With the appropriate connection or anchoring, the elements can also be counted as a roof panel for reinforcing the building.
Fire and complex partition walls made of aerated concrete are one of their main areas of application in commercial construction due to their high fire resistance of up to 360 minutes. A corresponding test showed that a fire with up to 1200 ° C on one side of a 150 mm thick wall only led to a wall temperature of around 70 ° C on the side facing away from the fire after six hours.
F90 fire walls made of aerated concrete assembly components with a minimum wall thickness of 175 mm are possible between, in front of or behind the supports of the building's supporting structure. In contrast, the minimum wall thickness of F180 complex partition walls made of aerated concrete assembly components is 250 mm.
Wall stones (block, flat stone, flat block elements) and prefabricated components (wall, roof and ceiling panels) are made from aerated concrete. The low density of the material has a thermal insulation effect that is equivalent to that of masonry bricks, but the sound insulation is less. Aerated concrete is used in masonry construction for exterior and interior walls. Its advantages (thermal insulation and homogeneous solid material) come into their own especially with monolithic exterior walls. Its disadvantages are unfavorable behavior when absorbing moisture and poor sound insulation. Due to the easy and versatile workability of the material, it is also popular for individual interior design and for objects of plastic art .
Aerated concrete is also used as a nest for the colony to keep ants, as chambers and passages can be incorporated very easily, the material is permeable to air and absorbs moisture.
The historical development of aerated concrete as a building material, which began in the 19th century, goes back to laboratory tests by the Swedish architect Axel Erikson in the years 1918 to 1923. The process was patented in 1924. Production started in Yxhult, Sweden, in 1929. “Yxhults Ånghärdade Gasbetong” later became the world's first registered building material brand: Ytong . The second internationally important aerated concrete brand, Hebel, goes back to company founder and construction technician Josef Hebel from Memmingen. In 1943 the first Hebel factory was opened in Germany.
Today, aerated concrete is produced by numerous companies, especially in Europe and Asia. Today, China is the largest aerated concrete market in the world with several hundred plants. There are a few factories in North and South America and only one in Egypt in Africa. The aerated concrete product is sold under different brand names, similar to other masonry building materials. Ytong and Hebel belong to the Xella company based in Duisburg , other internationally significant brand names are H + H Celcon and Solbet in Poland.
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- https://www.bv-porenbeton.de/index.php/vorteile/optimaler-brandschutz Bundesverband Aorenbeton: Optimal fire protection with aerated concrete , section aerated concrete fire wall, accessed on August 31, 2019