Autoclaved aerated concrete (AAC) block is a building material made of Portland cement, fine aggregates (fly ash or sand), water and an expansion agent in an autoclaving process heated under pressure which results in the production of air voids in the material, making it less dense, easy to cut/mould and better insulating
2. History
• Developed in Sweden in the 1920s in response to
increasing demands on timber supplies.
• Industries like Durox, Siporex etc. were established in
the early 1940s.
• Soon started spreading to other parts of the world
though its main hub remained at Western Europe
• Huge acceptance in Asia especially in the middle-east
countries because of the strong demand in housing
and commercial space.
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3. Introduction
• AAC block is made of Portland cement, fine
aggregates (fly ash or sand), water and an expansion
agent.
• The autoclaving process results in the production of
air voids in the material, making it less dense, easy to
cut/ mould and better insulating.
• Autoclave is a strong, pressurized, steam-heated
vessel
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5. Reduced Dead Loads
Using AAC Blocks reduces the load on the foundation
and other structural components in a structure due to
its lower self-weight.
About 55% reduction in weight of walls can be
obtained when compared to that of walls made with
clay bricks.
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6. AAC blocks uses fly ash (70% of its weight),
thus provides the most constructive solution to
the nation’s fly-ash utilization problem.
Fly ash is an industrial waste product and use
of fly ash in the AAC block production process
takes care of the issues concerned with its
disposal.
Environmental impact
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7. Autoclaved Aerated Concrete has excellent
acoustic performance and can be used as an
effective sound barrier, e.g. (AAC wall panel).
The small air pockets that are generated during
AAC production prevents the sound from
travelling from one side of a wall to the other
Excellent acoustics
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8. An important reason for the AAC good fire
resistance is it's is relatively homogeneous
structure.
Unlike the normal concrete where the
presence of coarse aggregate leads to
deferential rates of expansion, cracking and
disintegration.
Fire resistance
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10. Autoclaved Aerated Concrete is very airy thus
allowing more diffusion of water, reducing
humidity of the building.
Ventilation
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11. The remarkably good insulation properties
of Autoclaved Aerated Concrete mean a
pleasant interior environment is achieved.
In most cases the need for supplementary
insulation can be avoided.
It has very low specific conductivity. This
makes heating or cooling (Air Conditioning)
very efficient.
Energy saving
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13. The accurate manufacturing process ensures
that Autoclaved Aerated Concrete panels and
blocks are always produced to size as they
leave the factory.
This results in less on-site trimming and
reduced quantities of mortar and finishing
materials used.
Accuracy
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14. The low weight of AAC blocks helps in the easy
loading and unloading of these items when
transportation to work sites are required.
Besides it also helps the mason as he can easily
lift and place the blocks.
Rapid on - site assembly
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15. AAC does not deteriorate over time and they
retain good finishes even after many years.
They have better resistance against alternate
cycles of heating and cooling.
Long life
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21. Physical properties
Density
• Ranges between 300- 1800 kg/m3 according to a
source (RILEM)
• AAC is thus a unique industrial product that covers
such a range in apparent density.
• AAC products with density up to 350 kg/m3 can be
used as load bearing construction material
• AAC with lower density are generally used for thermal
insulation purposes
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22. Porosity
• Classified as capillary pores, gel pores, macro-pores
due to deliberately entrained air, and micro-pores due
to inadequate compaction.
• Fly ash is used as for more uniform distribution of air-
voids by providing uniform coating on each bubble
and thereby prevents merging of bubbles.
• It is observed that the strength, permeability,
diffusivity, shrinkage and creep properties of AAC
blocks are considerably related to its porosity and
pore size distribution.
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23. Permeability
• Permeability of aerated concrete is greatly influenced
by the type, size and distribution of the pores, and
not the pore volume.
• Pores are generally classified into two types - open
pores and closed pores.
• Permeability of aerated concrete is contributed by
the open pores and not the closed pores.
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24. Compositional Properties
• Scanning Electron Microscopy (SEM) showed that the
micro capillaries in AAC are plate shaped crystals of
11.3 Å tobermorite with a double-chain silicate
structure.
• The growth rate and the degree of orientation of this
structure cause differential pore distribution.
• Tobermorite is a calcium silicate hydrate mineral with
chemical formula:
Ca5Si6O16(OH)2·4H2O or Ca5Si6(O,OH)18·5H2O
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25. Mechanical Properties
Compressive Strength
• Can carry loads of up to 8 MPa approximately 50% of
the compressive strength of regular concrete.
• Influenced by factors such as density, age, curing
method, component and mix proportion.
• The rate of strength development is initially very high
and it gets decreased with age.
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27. Thermal conductivity
• Thermal conductivity increases as the moisture
content of AAC increases.
• Also increases with the increasing density.
• The amount of pores and their distribution are also
critical for thermal insulation.
• Finer the pores, better the insulation.
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29. Durability
• Carbonation is one of the main factors of the ageing
deterioration of AAC
• In cold countries frost deteriorations are observed in
outer walls made from AAC
• Surface scaling caused by freezing and thawing;
• the other is the wide cracks formed due to the inner
part AAC temperature being reduced to 0℃
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31. COMPARISON BETWEEN AAC BLOCKS AND
CLAY BRICKS
• Fly ash is an industrial waste product and its use in
AAC block production process takes care of the issues
concerned with its disposal whereas brick industry
consumes our natural top soil
• The AAC block is dimensionally more accurate as it is
produced with wire cut technology in a certified
factory.
• AAC blocks have air voids and hence have better fire
resisting property compared to red clay bricks.
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32. • Using AAC Blocks reduces the load on the foundation
and other structural components in a structure due to
its lower self-weight.
• AAC Blocks do not have any “micro-pores” or
continuous ‟capillaries‟ through which exterior
surface water can be absorbed to interiors. It means
longer life to the paints and interiors free from
growth of any kind of fungus, providing healthier and
long lasting interiors to the occupants
• AAC Blocks can be easily cut, drilled, nailed, milled
and grooved to fit individual requirements. Available
in custom sizes.
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33. AAC Blocks in India
• Currently there are around 35 largescale AAC blocks
manufacturing plants across India with a heavy
concentration near Surat, Gujarat.
• Besides there are a number of small scale
manufacturers concentrated near the coal industries.
• More and more AAC blocks plants are set up across
the India, as awareness about AAC blocks is growing.
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35. Disadvantages
Familiarisation of the Product
• Few contractors are currently familiar with the
product, and masons must adjust to using thin-set
mortar as opposed to traditional cement-based
mortar, which requires less precision in its application.
Scarcity of Manufacturing Plants.
• Projects far from manufacturing facilities will suffer
from higher initial costs
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36. Conclusion
• Autoclaved Aerated Concrete block is different from
conventional concrete in the mix materials and
properties.
• Though the compressive strength of Autoclaved
Aerated concrete is less than that of concrete, AAC
blocks possess many beneficial factors such as lower
density, enhanced thermal and sound insulation and
reduced dead loads.
• Hence it is an ideal alternative for traditional wall
brick or stone materials owing to its environmental
impact and eco- friendly features.
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Fly ash is a byproduct from burning pulverized coal in electric power generating plants.
Ideal material for wall construction in hotels, auditoriums, studios, hospitals.
The good fire resisting property of aerated concrete is due to the presence of high number of solid-air interfaces, which reduces the heat transfer. This coupled with their low thermal conductivity and diffusivity gives an indication that aerated concrete possesses better fire-resisting properties.
So in the picture you can see an aac wall unaffected by the industrial fire that destroyed an adjacent wing, a surviving roof serves as a platform for fireman fighting the blaze.
The aerated concrete demising wall protected the remaining portion of the building, enabling it to maintain its structural integrity.
AAC Blocks do not have any “micro-pores” or continuous ‟capillaries‟ through which exterior surface water can be absorbed to interiors. It means longer life to the paints and interiors free from growth of any kind of fungus, providing
healthier and long lasting interiors to the occupants.
AAC Block’s water barrier properties are further enhanced by adding silicone based additives.
AAC blocks are resistant to thermal variations.
The low weight of AAC blocks helps in the easy loading and unloading of these items when transportation to work sites are required.
Besides it also helps the mason as he can easily lift and place the blocks.
The main raw material used in AAC production is fly ash (or pond ash), which is an inert material. Hence pests and termites do not survive on these kinds of blocks thus protecting the building from deterioration.
After the mixing process, expansion agent (i.e. Aluminum Powder) is added to the mix which causes an increase in volume. The expansion can be from 2 to 5 times more than original volume of the paste. Aluminum powder reacts with calcium hydroxide which is the product of reaction between cement and water.
The hydrogen that is formed in this process bubbles ( up to 3mm in size) up which comes out of the mixture and is replaced by air. This is because hydrogen, which is a lighter gas than air is replaced by air that gets into the mix as the hydrogen foams up out of the mixture.
The volume increase depends upon the quantity of Aluminum powder/paste that is added to react with the calcium hydroxide in the mixture. This reaction is shown below by the equation:
2Al + 3Ca(OH)2 + 6H2O → 3CaO.Al2O3.6H2O + 3 H2
Aluminum powder + Hydrated Lime → Tricalcium Hydrate + Hydrogen ↑
Lesser the expansion that is induced higher would be the strength of the material (more dense) versus the maximum amount of expansion that is induced, produces a lower strength material (less dense).
Reunion Internationale des Laboratoires et Experts des Materiaux, Systemes de Construction et Ouvrages(French: International Union of Laboratories and Experts in Construction Materials, Systems, and Structures)
, aerated concrete with a wide range of densities for specific applications can be manufactured by varying the composition, which in turn affects the pore structure, size and distribution. A stable and preferably spherical cell structure is necessary for optimum functional and structural properties. Also, there must be a uniform distribution of pores in the mass to obtain products of uniform density.
The gel pores do not influence the strength of concrete through its porosity, although these pores are directly related to creep and shrinkage.
Capillary pores and other large pores are responsible for reduction in strength and elasticity of AAC blocks.
open pores, which connect to the outside boundary of the material, and closed pores, which are isolated from the outside and may contain fluid.
Ca rich C-S-H → C-S-H → 11.3Å Tobermorite
where tobermorite-11Å and well-crystallized C-S-H, the main structural minerals of AAC, react with carbon dioxide under the existence of moisture and finally decomposed to silica gels and calcium carbonate.
Carbonation occurs in concrete because the calcium bearing phases present are attacked by carbon dioxide of the air and converted to calcium carbonate.
Ca rich C-S-H → C-S-H → 11.3Å Tobermorite *this raection in reverse
Flexural strength, also known as modulus of rupture, bend strength, or fracture strength, [dubious – discuss] is a material property, defined as the stress in a material just before it yields in a flexure test
thermal conductivity (often denoted k, λ, or κ) is the property of a material to conduct heat.
Thermal conductivity is actually a tensor, which means it is possible to have different values in different directions.
determined as the heat energy transferred per unit of time and per unit of surface area divided by thetemperature gradient
which is the temperature difference divided by the distance between the two surfaces (thethickness of the material), expressed in watts per kelvin per meter.
Can be cut into required sizes. It can be sawn, drilled, nailed, grooved etc. Can be used to create arches, curves etc. Can have Hand Grips, which gives ease in lifting & placement.
In Ahmedabad, 1 m3 of AAC blocks cost around Rs. 3200-3500 while 1 m3 of clay bricks would cost Rs. 2400-2700.
Considering the maintenance and mortar costs aac is preferred.
Standard size-Length- 625 mm - Height- 250 mm - Width- varies from 100 to 300 mm
normally equal to four to six times the standard clay brick size of 230mm x 115mm x 75mm.
Besides the scarcity of these traditional building materials