Autoclaved Aerated Concrete
The Manufacture and Application
of Autoclaved Aerated Concrete
For many years, aerated concrete was known in Germany as "Gas-
beton" (gas concrete). Simply on the basis of the construction material
it quickly becomes clear that "gas concrete" is not only an erroneous
description but also a misleading name, which has led to confusion
in the past. The German expression "Porenbeton" conforms to the
English "Autoclaved Aerated Concrete" and all of the usual linguistic
descriptions from other countries such as "Cellenbeton" in Dutch and
"Béton Celulaire" in French.
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The Development
of Autoclaved Concrete
1800
� The first attempts go back to Zernikov, who "boiled" calcium sand-
based cement in high-tension steam but achieved little stability
and firmness. W. Michaelis followed a similar line but used
reduced water content. The result was a hard and waterproof
calcium hydro silicate for which he was granted a patent in
1880. This is the basis of all steam-cured building materials.
1924
� The Swedish architect A. Eriksson combined the process of pore-
formation with steam-curing and thus became the first to create
the modern aerated concrete. In 1924 Eriksson was granted a
patent for this invention.
1929
� The industrial production of aerated concrete items began in
Sweden. In the early 30s, further plants had to be built in order to
cover the demand for the aerated concrete products.
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The Manufacture
of Autoclaved Aerated Concrete
and its Main Constituents
ground
sand =
< 0,05 mm
water
aluminium
as paste
or powder
cement
lime/
quicklime
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Autoclaved Aerated Concrete
Autoclaved aerated concrete is manufactured with the
raw materials of quicklime, cement and siliceous sand. The sand
must be finely ground. A proportion of the sand may be replaced
with quick ash. First the ingredients are mixed using a ratio of, (for
example), 1:1:4, then water is added and a mortar mix is created. A
small amount of aluminium powder is then mixed into the resulting
suspension. The mortar is poured into a tub, where the metallic, fine
particled aluminium develops hydrogen gas in the alkaline mortar
mixture. Many small gas bubbles are created, which expand the
gradually stiffening mixture. After 15 - 50 minutes, the final volume is
achieved and blocks of between 3 and 8 metres long, up to 1,5
metres wide and 50 - 80 cm high are created. These doughy blocks
are cut into the required building element sizes with wire. After 8 -
12 hours the aerated concrete attains its final properties via curing
in special autoclaves (high-pressure steam boilers) at
temperatures of 180° - 200° C in steam under saturated vapour
pressure of 10 - 12 Bar. The autoclaved aerated concrete
corresponds chemically to the mineral tobermorite, which can be
found in natural environments. The production takes place in a
sealed cycle and thus no pollutants to water, air or ground are
released. Via the curing with steam, the autoclaved aerated
concrete avoids a great deal of potential energy waste.
4
Production
of Autoclaved Aerated Concrete
and its Technology
� From the main
constituents
� Movable curing
vehicles and static
moulds
� Via the creation of hydrogen
(lime and aluminium), the
compound is forced from a
height of 20 to around 80 cm
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Mixing
Process
Pouring
process into
pre-lubricated
moulds
Fermentation
process
Production
of Autoclaved Aerated Concrete
and its Technology
� The raw "cakes”
are cut with steel
wire before the
steam-curing
� The cut cakes are
cured at a temperature
of around 200°C and a
pressure of 13 Bar for
ca. 8 hours
� After curing the stones
are packaged and stored
in the warehouse
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Cutting
Curing
by steam in
autoclaves
Packaging
The Properties
of Autoclaved Aerated Concrete
� Autoclaved aerated concrete, being a natural, non-combustible, solid building material, possesses the best possible fire-protection properties
� Solid building materials are proven to provide very good sound insulation values
� For example, the lightweight autoclaved aerated concrete compares favourably in terms of sound insulation with other equally heavy walls made from other types of stone. This is because the pore structure aids internal sound muffling
� Autoclaved aerated concrete is produced with a compressive strength of between 2 and 6 N/mm2
� The bulk density of the autoclaved aerated concrete is crucial to good thermal conductivity
� The upshot is, the lighter the material, the higher the thermal conductivity
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Fire
protection
Sound
isolation
Fermentation
process
The Benefits
of Autoclaved Aerated Concrete
� The simple technique for using the material ensures that an
absolutely straight and smooth wall is achieved with the shaped
brick. This wall can be finished with a thin coating of plaster
prior to being wallpapered or painted.
� Thanks to the balance between thermal insulation and thermal
storage, the autoclaved aerated concrete provides for a pleasant
room climate.
� On the other hand, tiles can be applied directly to the smooth
surface of the autoclaved aerated concrete wall. Adhesion slits
are manually scratched into the stone, using a special groove-
cutter, and plug and switch sockets can be created where
required using a dry-wall socket drill.
� Ceramic tiles or flagstones can be simply and economically
applied to all autoclaved aerated concrete walls as an interior
room cladding. In most cases the surfaces are already suitable
even for application using the thin-bed method.
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The Benefits
of Autoclaved Aerated Concrete
� Among the outstanding properties of autoclaved aerated
concrete are a high level of stability and a relatively low
bulk density. As a result of the low bulk density, autoclaved
aerated concrete is a solid building material with excellent
thermal insulation properties. Furthermore, the sound
insulation and fire protection are of the highest level. In the
end, autoclaved aerated concrete can really only be
characterised by the sum of its properties.
� Many coordinated building elements
� Ease of use and application
� Good ecological structure and biological building properties
� A high level of heat protection in summer thanks to the exellent
heat-storage properties together with the cooling characteristics.
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The Application
of Autoclaved Aerated Concrete
� Because of the way autoclaved aerated concrete is applied in the
thin bed mortar system, a valuable but inexpensive masonry is
created.
� Fundamental features are a constant thermal insulation without
the need for thermal bridges, a high compressive strength and
especially flat, even wall surfaces. This facilitates all follow up
tasks such as plastering, tiling and wallpapering.
� Among the very important advantages of the thin bed system are
the fast application and the low amount of water used. Thus
only very little damp can penetrate the brickwork. The grouting
cement volume for the thin bed system is - depending on the
stone format - between 6 and 10 litres per cubic metre.
� If the bricks have tongue and groove joints, where grouting
cement is only applied to the horizontal joints, the mortar
consumption is reduced to 5 litres per cubic metre.
� The reduced grouting of the butting joints leads to a substantial
saving on time as well as cost, when compared to bricks which are
laid in "normally" grouted brickwork.
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Autoclaved Aerated Concrete Bricks
� The advantages of autoclaved aerated concrete - namely the
extremely small tolerances, precise surfaces and low thermal
conductivity - can be especially exploited by its use in brick form.
� Length = 332, 339, 499, 599 and 624 mm
� Height = 199 and 249 mm
� Thickness/Width = 115, 150, 175, 200, 240, 300 and 365 mm
� Characteristic strength = 0,2 mm/m of material shrinkage
stability class bulk density thermal conductivity
• 2,0 N/mm2 = 0,4 kg/dm
2 = 0,09 W/(m*K)
• 4,0 N/mm2 = 0,6 kg/dm
2 = 0,13 W/(m*K)
• 6,0 N/mm2 = 0,7 kg/dm
2 = 0,15 W/(m*K)
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The Application
of Autoclaved Aerated Concrete
� Owing to the use of the thin-bed system, grouts with a maximum
thickness of 1 mm are created. The adhesive is applied with a
mortar trowel.
� The cost-sinking use of the thin-bed system reduces the building
dampness significantly. The brickwork achieves the outstanding
thermal insulation properties of autoclaved aerated concrete
rapidly, avoiding the need for a lengthy drying out process.
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The Application
of Autoclaved Aerated Concrete
� Cuts can be quickly and precisely made using a band-saw.
� Using a band-saw, even round cuts can be effected.
� Band-saws are provided by many autoclaved aerated concrete
suppliers as a complementary service.
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The Uses
of Autoclaved Aerated Concrete
� U-forms are supplied by the autoclaved aerated concrete
manufacturers
� U-forms are used for the construction of ring bracing
� U-forms can also be utilised in Lintels for windows and doors
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The Process of Working
with Autoclaved Aerated Concrete
� The material allows an easy application.
� Cutting of autoclaved aerated concrete with band-saw.
� Channeling for electric cables with scraping tool.
� Drilling of switches and sockets with dry wall countersinking
accessories.
The entire mechanical process of working with autoclaved
aerated concrete can best be compared to working with
wood.
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Autoclaved Aerated Concrete
in External Walls
� Autoclaved aerated concrete is used in the construction of
dwellings and businesses.
� Autoclaved aerated concrete is used preferentially in external
walls because of its outstanding insulation properties.
� Autoclaved aerated concrete is used in multi-storey construction
up to a level of around 5 stories.
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Autoclaved Aerated Concrete
in Many Residential Areas
� Entire residential areas are built using autoclaved aerated
concrete.
� A very big reason for this is the ease of application, even for the
non-professional, thus enabling a high level of personal
contribution and resulting in a reduction of building costs.
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Autoclaved Aerated Concrete
in Internal Walls
� Autoclaved aerated concrete can also be used for internal walls.
� Because the walls are so level, they can be finished with a very
thin coat of plaster (3 - 5 mm).
� Use of adhesive considerably reduces dampness in the brickwork.
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Autoclaved Aerated Concrete
as Shelving !
Autoclaved aerated concrete has the advantage that it can be shaped
with saws, files and rasps. It is nevertheless very stable and thus
suitable for load-bearing and non-load-bearing elements alike.
Autoclaved aerated concrete is supplied in a variety of formats and
compressive strength grades. Constructions should be planned as
much as possible around the standard formats, in order to avoid too
much cutting and shaping. Slabs come with a length of 50 cm, a
height of 25 cm and thicknesses of 7,5; 10; 12,5; 15; 17,5; 20; 25;
30 and 37,5 cm. Additionally there are special formats which can be
used for the construction of shelving elements and compartments.
These have a length of 62,5 m, a height of 25 cm and thicknesses
of 5; 7,5; 10; 12,5; 15; 17,5 and 20 cm. In 75 cm lengths with a height of
50 cm, autoclaved aerated concrete bricks are available in the
thicknesses of 7,5; 10 and 12,5 cm, which are especially suitable
for worktops and shelving.
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Autoclaved Aerated Concrete
for Fireplaces
Because of its low weight, autoclaved aerated concrete enables the
construction of a fireplace as an add-on after the initial loads have
been calculated without leading to significant extra stress on
ceilings with standard load-bearing properties. For the combustion
chamber itself, only fireproof materials can be used. The cladding
and plinth must also be made of non-combustible and heat-resistant
materials. Autoclaved aerated concrete fulfils these demands as a
non-combustible, solid, A1-classified building material. Because of
its low thermal conductivity, the temperature increase on the outer
surface is very low.
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Autoclaved Aerated Concrete
for the Kitchen
� The advantage for the tenant is that such a kitchen can easily be
removed without damage to the surroundings. We have used
thicker stones for the tile border and stuck them to the existing
PVC floor covering. Cross-grouting is thus avoided ! We have
located the architrave under the duct, so that a gapped butt joint to
the wall is established which can be used for cables and pipes.
Additionally, hardly any bricks have to be cut.
� A typical, cheap handsaw is quickly blunted by a great deal of
cutting, although a more expensive specialised autoclaved
aerated concrete saw is longer-lasting.
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