Autoclaved aerated concrete, also known as autoclaved cellular concrete,
autoclaved lightweight concrete, autoclaved concrete, cellular concrete,
porous concrete, Aircrete, Hebel Block, and Ytong is a lightweight, precast,
Foam concrete building material invented in the mid-1920s that simultaneously
provides structure, insulation, and fire- and mold-resistance. AAC products
include blocks, wall panels, floor and roof panels, cladding panels and
lintels. History
AAC was perfected in the mid-1920s by the Swedish architect and inventor Dr.
Johan Axel Eriksson, working with Professor Henrik Kreüger at the Royal
Institute of Technology. It went into production in Sweden in 1929 in a
factory in Hällabrottet and quickly became very popular. Siporex was
established in Sweden in 1939 and presently licenses and owns plants in 35
locations around the world. In the 1940s, the trademark Ytong was
introduced, and was often referred to as "blue concrete" in Sweden due to its
blueish tinge. This version of Ytong was produced from alum shale, whose
combustible carbon content made it beneficial to use in the production
process. The competing concrete brand Siporex produced in Tuzla, Bosnia, used
other raw materials. "Ytong" acquired Siporex and today produces "Siporex"
under "Ytong" brand in Tuzla, Bosnia factory. Unfortunately, the slate
deposits used for Ytong also contain uranium, which makes the material give
off radioactive radon gas to the building. In 1972, the Swedish Radiation
Safety Authority pointed out the unsuitability of a radon-emitting
construction material, and the use of alum slate in the production of Ytong
ceased in 1975. Ytong produced after 1975 has used raw materials without the
uranium content. AAC production in Europe has slowed down
considerably, but the industry is growing rapidly in Asia due to strong
demand in housing and commercial space. China, Central Asia, India, and the
Middle-East are the biggest in terms of AAC manufacturing and consumption. AAC
production the Persian gulf started in 1978 with LCC SIPOREX, lightweight
Construction Company website www.lccsiporex.com supplying the Arabian
peninsula with AAC products Uses
AAC is a highly thermally insulating concrete-based material used for both
internal and external construction. Besides AAC's insulating capability, one
of its advantages in construction is its quick and easy installation, because the
material can be routed, sanded, or cut to size on site using standard carbon
steel power tools. AAC is well suited for urban areas with
high rise buildings and those with high temperature variations. Due to lower
density, high rise buildings constructed using AAC require less steel and
concrete for structural members. Requirement of mortar for laying AAC
blocks is reduced due to less number of joints. Similarly material required for
rendering is also lower due to dimensional accuracy of AAC. Better
thermal efficiency of AAC makes it suitable for use in areas with extreme
temperature as it eliminates need for separate materials for construction and
insulation leading to faster construction and savings.
Even though regular cement mortar can be used, most of the buildings erected with
AAC materials use thin bed mortar in thicknesses around ⅛ inch, depending on
the national building codes. AAC materials can be coated with a stucco or
plaster compound to guard against the elements, or covered with siding
materials such as brick or vinyl. Manufacturing
Unlike most other concrete applications, AAC is produced using no aggregate
larger than sand. Quartz sand, calcined gypsum, lime and/or cement and water are
used as a binding agent. Aluminum powder is used at a rate of 0.05%–0.08% by
volume. In some countries, like India and China, fly ash generated from
thermal power plants and having 50-65% silica content is used as an aggregate.
When AAC is mixed and cast in forms, several chemical reactions take place
that give AAC its light weight and thermal properties. Aluminum powder
reacts with calcium hydroxide and water to form hydrogen. The hydrogen gas foams
and doubles the volume of the raw mix creating gas bubbles up to 3mm in
diameter. At the end of the foaming process, the hydrogen escapes into the
atmosphere and is replaced by air. When the forms are removed from the
material, it is solid but still soft. It is then cut into either blocks or
panels, and placed in an autoclave chamber for 12 hours. During this steam
pressure hardening process, when the temperature reaches 190° Celsius and the
pressure reaches 8 to 12 bars, quartz sand reacts with calcium hydroxide to
form calcium silicate hydrate, which gives AAC its high strength and other
unique properties. Because of the relatively low temperature used AAC
blocks are not considered fired brick but a lightweight concrete masonry unit.
After the autoclaving process, the material is ready for immediate use on
the construction site. Depending on its density, up to 80% of the volume of an
AAC block is air. AAC's low density also accounts for its low structural
compression strength. It can carry loads of up to 8 MPa, approximately 50% of the
compressive strength of regular concrete.
Since 1980, there has been a worldwide increase in the use of AAC materials.
New production plants are being built in Australia, Bahrain, China, Eastern
Europe, India, Israel, and the USA. AAC is increasingly used by developers,
architects, and home builders worldwide. Advantages
AAC has been produced for more than 70 years, and it offers several significant
advantages over other cement construction materials, one of the most
important being its lower environmental impact.
Improved thermal efficiency reduces the heating and cooling load in buildings.
Porous structure allows for superior fire resistance.
Workability allows accurate cutting, which minimizes the generation of solid
waste during use. Resource efficiency gives it lower
environmental impact in all phases of its life cycle, from processing of raw
materials to the disposal of waste. Light weight saves cost & energy in
transportation, labor expenses, and increases chances of survival during
seismic activity. Larger size blocks leads to faster
masonry work. Reduces the cost of the project.
Environmentally Friendly: When used, it helps to reduce at least 30% of
environmental waste as opposed to going with traditional concrete. There is a
decrease of 50% of greenhouse gas emissions. When possible, using
autoclaved aerated concrete is a better choice for the environment.
Energy Saver: It is an excellent property that makes it an excellent
insulator and that means the interior environment is easier to maintain. When
it is used, there is usually not a need for any supplementary insulation.
Great Acoustics: When you think of concrete, you do not consider it to be
excellent for acoustics, however autoclaved aerated concrete has
excellent acoustic performance. It is able to be used as a very effective
sound barrier. Fire Resistant: Just like with regular
concrete, ACC is fire resistant. This material is completely inorganic and not
combustible. Great Ventilation: This material is very
airy and allows for the diffusion of water. This will reduce the humidity
within the building. ACC will absorb moisture and release humidity; this
helps to prevent condensation and other problems that are related to mildew.
Non-Toxic: There are no toxic gases or other toxic substances in autoclaved
aerated concrete. It does not attract rodents or other pests nor can it be
damaged by such. Lightweight: Concrete blocks that are
made out of ACC weigh about one-fifth of typical concrete. They are also produced
in sizes that are easy to handle for quick construction.
Accuracy: The panels and blocks made of autoclaved aerated concrete are produced
to the exact sizes needed before they even leave the factory. There is less
need for on-site trimming. Since the blocks and panels fit so well together,
there is a reduced use of finishing materials such as mortar.
Long Lasting: The life of this material is extended because if is not affected
by harsh climates or extreme changes in weather conditions. It will not degrade
under normal climate changes either. Quick Assembly: Since it is a
lightweight material and easy to work with, the assembly is much quicker and
smoother. References
External links Portland Cement Association's
information on construction with AEC/ACC Aircrete Products Association
Masonry Magazine, June 2008 Toolbase.org