2. Introduction
History
Cellular Structure and Composition
Production and Manufacturing process
Characteristics and Properties
Laying of AAC
Comparative Analysis
Advantages and Limitations
Plant Locations across India
References
CONTENTS
3. INTRODUCTION
Autoclave - an apparatus in which special conditions (such as high or low pressure or
temperature) can be established for a variety of applications especially: an apparatus using
steam under high pressure. (Ref. Mariam–Webster Dictionary)
AAC blocks have a porous and lightweight texture
AAC blocks are created and fed to an autoclave to harden
MANUFACTURING PROCESS OF AAC BLOCK https://www.researchgate.net/publication/349366832
5. 1. Autoclaved Aerated Concrete (AAC) has a porous structure created by small air bubbles by foaming
agents or aluminum powder in cement, fly ash, and sand slurry and cured in high-pressure steam
(autoclaved).
2. AAC blocks are 2-3 times lighter than traditional bricks. Incorporation of pozzolanic materials like fly ash
into cement or concrete provides advantages such as reduction in heat, low permeability, and
resistance to sulfate attack.
3. Fly ash is also used to replace part of Portland cement and part of fine aggregates for the production of
AAC blocks.
4. These Blocks have low density and low thermal conductivity compared to clay bricks or concrete blocks.
5. There are many advantages of Aerated Concrete blocks such as reduction of dead load, faster building
rate, and lower transport cost.
6. Other advantages include a relatively high strength-to-weight ratio, availability, fire resistance, good
thermal resistance, and high sound insulation value.
7. Aerated concrete blocks are masonry units used in the construction of partition/non-load-bearing walls
in RC framed buildings using cement mortars.
8. Autoclaved Aerated Concrete (AAC) Blocks are manufactured in specialized manufacturing facilities in
various sizes.
INTRODUCTION
.
6. HISTORY
He was working on aerated concrete samples, and
that’s when the accidental discovery occurred.
Running short of time, he decided to speed up the
curing process. He placed one of his samples of burnt
shale limestone, water, and aluminum powder in the
laboratory autoclave. The porous mass survived the
overnight autoclaving, and the resulting cured concrete
possessed greatly increased strength and a new,
stronger crystalline composition. In the heat and
pressure of the steam curing, the silica and lime
components fused to form a calcium silicate hydrate
crystal, similar to the volcanic rock, Tobermorite.
(For more info refer to notes of the slide)
https://greenjams.org/aac-blocks-an-accidental-invention/
An Accidental Discovery
Autoclave aerated concrete blocks are also known as autoclaved lightweight concrete(ALC)
Autoclaved Aerated Concrete (AAC) is one of the eco–friendly and certified green building
materials. AAC was perfected in the mid of 1920s by the Swedish architect, Dr. Johan Axel
Ericksson. The process was patented in 1924.
7. HOW IS CELLULAR STRUCTURE FORMED
Generation of the cellular structure is normally done through the addition of
aluminum powder as the mixing procedure is ending.
The aluminum powder in the alkaline medium (due to the cement or lime)
produces hydrogen gas which, in turn, generates the cells.
The addition of the aluminum powder is controlled so that gassing does not
begin during mixing but during the molding stage.
https://www.understanding-cement.com/autoclaved-aerated-concrete.html
8. COMPOSITION OF AAC
1. Cement
2. Fly-Ash
3. Quartz Sand (Sio2 with Impurities)
4. Calcined Calcium Sulfate (Gypsum/Plaster Of Paris)
5. Aluminum Powder/Hydrogen Peroxide
6. Lime (Cao)
7. Water
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1
2
3
4
6 5
9. CHEMICAL COMPOSITION AND PROPORTION OF RAW MATERIALS
Compound Chemical Composition (In%)
CaO 57.84
SiO2 20.33
Fe2O3 4.68
Al2O3 3.40
MgO 1.51
MnO 0.10
TiO2 0.09
K2O 0.72
Na2O 0.51
SO3 7.26
Loss of ignition 3.42
Insoluble residue 1.23
MANUFACTURING PROCESS OF AAC BLOCK https://www.researchgate.net/publication/349366832
Code Provision – IS 269:1989 and IS 383:1970
10. Production
Production is a continuous
process that may be
envisioned as having four
stages.
The four stages are depicted
as:
1. Raw materials
2. Molding and cutting,
3. Autoclaving, and
4. Stocking and shipping.
11. MANUFACTURING PROCESS (1-11, then A-E)
http://www.builtconstructions.in/OnlineMagazine/Bangalore/Pages/High-Performance-Cellular-Concrete-836.aspx
13. MANUFACTURING PROCESS OF AAC BLOCK https://www.researchgate.net/publication/349366832
MANUFACTURING PROCESS – FLOW CHART
14. STEP-WISE PRODUCTION PROCESS
https://www.greenblock.co.in/green-aac-block-brochure.pdf
1. Dosing and mixing of fly ash with lime, Ordinary Portland Cement (OPC), stabilizers, and
gypsum at a high dosing speed at very high accuracy.
2. Casting and rising/pre-curing of the mixture to enable the fresh mix to rise and harden to a
firm green cake with the volume of the mold.
3. Tilting mold cakes with the tilt manipulator onto a cutter machine and oiling them to prevent
the sticking of the green cakes for reuse.
4. Horizontal and cross-cutting of the cakes by a cutter which is equipped with the broken-wire-
detection system.
5. Milling and back tilting onto a cooking frame.
6. Green separation of cut cakes by passing through the green separator to avoid sticking of cut
layers during autoclaving and eliminating further mechanical separation in white state.
7. Curing with steam at a pressure of approximately 12 Bar in an autoclave system for 12 hours.
8. 8. Buffering and de-stacking of hardened cakes from the cooking frames to the packaging line
for final packaging.
15. 1. RAW MATERIALS
The major raw materials are, in many processes, sand and Portland cement. In place of sand,
other siliceous materials such as sandstone, shale ash, fly ash, and mixtures are often used.
The raw materials are used as fine powders which are normally obtained through grinding.
Grinding may be done either through a wet or dry procedure.
Accurately proportioned quantities of the raw materials form the mix. In many cases, a slurry of
the siliceous component is made in heated water whose temperature is controlled.
The slurry is placed in a mixer into which the cement and/or lime are added.
Admixtures such as surfactants and compounds for controlling the rate of cure may also be
added.
16. 2. Molding and Cutting
The mixture formed after adding all the materials is put into steel molds where the production of
hydrogen begins and the mass expands, creating the aerated cellular structure.
The expanded mass is allowed to be set to a soft cake under controlled temperature and humidity
conditions.
The reaction time for expansion and setting is 30 minutes to a few hours (about 1 to 4) depending upon
the raw materials. After setting, the cake is cut into the dimensions of the final product using highly strung
wires (piano wires) or multiple circular saws.
If the final product is to be used for structural applications, steel reinforcement is placed in the mold
before casting the autoclaved aerated concrete.
The factory procedure allows accurate placement of the reinforcement in the molds so that the set cake
may be cut into the intended dimensions without damage.
The steel reinforcement is protected from corrosion, normally by coating.
17. 3. Autoclaving
The third stage of the process is autoclaving whereby the aerated concrete cures to its final
strength and dimensions.
Autoclaving changes the physical-chemical nature of the hydrated cement materials and
produces a material with lower drying shrinkage.
The conditions for autoclaving vary somewhat for different proprietary products.
In general, the temperature is about 356°F (180°C) at a pressure of about 1.0 - 1.2 MPa.
The time varies depending on the size and density of the products and may range from about
10 to 20 hours.
Storage of the uncured cake, even though moisture and warmth, for more than 2 or 3 days
before autoclaving may be detrimental.
18. 4. Stocking and Shipping
After the cured units are removed from the autoclave, quality assurance tests are normally
conducted.
Also, if desired, additional shaping through milling or related means may be carried out and a
surface finish may also be applied.
After autoclaving and cooling the units are ready for use without storage.
If not needed immediately after production, the units are stored at the factory site and then
delivered to the job site for installation.
19. CHARACTERISTICS OF AAC BLOCKS
https://aacblockmachine.com/blog.php
• Light in Weight
• Eco Friendly
• High Thermal Insulation
• Lower Water Absorption
• High Sound Insulation
• Termite Free
• High Fire Protection
• High Structural savings in steel and concrete
20. Capillarity
Coefficient of Thermal Expansion o Cracking
Creep
Density
Deterioration Resistance
Fire Resistance
Frost Resistance
Moisture Expansion and Shrinkage
• The physical and mechanical properties vary over a considerable range, depending on the
quantities of the raw materials used, the mix design, and curing conditions.
• The properties of cellular concrete can be given as functions of bulk density and thickness.
• The properties summarized are as follows:
PROPERTIES OF AUTOCLAVED AERATED CONCRETE
21. Capillarity
for wetting and drying out the materials.
capillary suction is slow - compared with some other porous materials such as clay bricks
Capillary suction takes place exclusively through the micropores in the cell walls
Coefficient of Thermal Expansion
coefficient of linear thermal expansion for autoclaved aerated concrete is 8 x 10^6 per °C --
compared to 12 x 10”^ per °C for dense concrete.
Cracking
caused by shrinkage, creep, temperature, moisture effects, or by deformation and settlement
of foundations.
prestress of autoclaved aerated concrete slabs, due to differential drying and cooling after
autoclaving, may in some cases increase crack resistance to some extent.
22. Creep
Low about the elastic deformation
Factors affecting the creep of autoclaved aerated concrete are stress
level, moisture content, ambient temperature, and relative humidity.
Density
the practical density is higher because of the moisture content and the
presence of any reinforcement
range of (300 - 1000 kg/m3 ), with (500 kg/m3 ) or more as the most
common density for load-bearing products and reinforced flexural
members.
Deterioration Resistance
because of its porosity and relatively low alkalinity (pH = 9 - 10.5), does
not provide the same corrosion protection of reinforcement as that
provided by dense concrete
23. Termite Resistance
AAC is also resistant to insects, termites, and fungi.
Fire Resistance
non-combustible, Because of its low thermal conductivity, heat migration takes
place at a lower rate than in dense concrete.
gives fire resistance of 2 hours, thus increasing the fire resistance by 30 to 40
percent compared to other building materials
Frost Resistance
It is resistant to frost. Nevertheless, a risk of frost damage exists if the moisture
content in any part of the construction unit exceeds the critical moisture content
24. Permeability
varies with the moisture content of the material. It decreases with an increase in moisture
content in the pores
penetration can take place through improperly formed joints and other connections in the
building
The water vapor permeability by diffusion also decreases with an increase in the moisture
content
Shaping and Working
can be easily cut, nailed, drilled, milled, or shaped to accommodate building needs such as
utilities, or other construction requirements
Sound Absorption
provide good sound insulation, having sound absorption properties somewhat better than that
of smooth dense concrete
If the aerated concrete is painted or coated, its sound insulation effectiveness is reduced.
25. STRENGTH
Strength tends to increase with an increase in density,
while thermal resistance tends to increase with a
decrease in density
Compressive Strength
increases with an increase in density
decreases with an increase in the moisture content of
the material.
Tensile Strength
The tensile strength of autoclaved aerated concrete is
normally 1/4 to 1/6 of the compressive strength. (about
20 percent)
26. STRUCTURE
The structure of autoclaved aerated concrete is characterized by pores or cells which are
formed by the hydrogen gas, air, and water during the molding and expanding phases of
productioa n
If the cells are irregularly shaped rather than spherical, excessive reduction in strength occurs
31. https://www.magicbricks.com/blog/aac-blocks/129206.html
AAC Blocks
◦ AAC blocks are lightweight and easy to handle
◦ Each of the AAC blocks can weigh anywhere from 3 kg to 15 kg,
depending on the size of the individual blocks
◦ AAC blocks are very large in size
◦ AAC blocks are usually uniform in size and don’t come with
rugged or rough edges that need to be trimmed
◦ AAC blocks are mostly used for non-load bearing purposes and
used to create partition walls
◦ The construction process is relatively quicker
◦ AAC block prices are high for small quantities of production
◦ AAC blocks may need a weather-coating finish if they are
exposed externally
Red Bricks
◦ Red bricks come in different weights depending on the seller
◦ The average weight can range between 2-3.5 kg for one block
◦ Red bricks are smaller in size
◦ The size and shape of red bricks can be slightly different as they
are mostly handmade. They also have rough edges that need
trimming before use
◦ Red bricks can be used for constructing internal and external
walls, structural units, and even arches and aesthetic setups
◦ The construction process is tedious and time-consuming
◦ The production cost may be cheaper for smaller production
quantities
◦ The size and shape of red bricks can be slightly different as they
are mostly handmade. They also have rough edges that need
trimming before use
COMPARISON WITH RED BRICKS
32. S.NO. DESCRIPTION AAC BLOCK CLAY BLOCK
1 Structural Cost Steel Saving Up to 15% No Saving
2 Breakage /Wastage Less than 5% Average 10 to 12 %
3 Construction speed Speedy construction Comparatively slow
4 Availability Anytime Shortage in monsoon
5 Energy Saving 30% reduction No such saving
6 Accuracy in dimension 99% 90%
7 Cost 30% cheaper than Red bricks -
MANUFACTURING PROCESS OF AAC BLOCK https://www.researchgate.net/publication/349366832
COMPARISON WITH CLAY BLOCKS
33. Sr.No. Autoclaved Aerated Concrete Normal Aggregate Concrete
1 Autoclaved aerated concrete is a versatile
lightweight construction material and usually used
as blocks.
Normal concrete has heavy weights compared to the
AAC. 1 AAC Block size = 6 * brick size 1 AAC Block weight
= 1/2 of aggregate block weight
2 A low density and excellent insulation properties
due to high porosity.
High density and lower insulation property
3 The low density is achieved by the formation of air
voids to produce a cellular structure
The concrete so formed has a high density and compact
4 Densities range from about 460 to 750 kg/ m3 Medium density concrete blocks have a typical density
range of 1350-1500 kg/m3 and dense concrete blocks a
range of 2300- 2500 kg/ m3
5 The finished product is up to five times the volume
of the raw materials used, with an air content of
70% to 80% (depending on the required strength
and density.)
The finished product is compact and nonporous.
6 Easily workable – can be sawed, nailed and drilled
easily even than wood.
Cannot be sawed, nailed or drilled as easy as AAC blocks.
7 No curing required – labour cost is saved of curing. Curing is must.
COMPARISON WITH NORMAL AGGREGATE CONCRETE
35. ADVANTAGES OF AAC BLOCKS
https://www.magicbricks.com/blog/aac-blocks/129206.html
Thermal efficiency is one of the biggest advantages of these AAC blocks. They
keep the house pleasant during both summers and winters and reduce heating
and cooling loads.
The blocks handle fire better than traditional blocks.
Individual blocks are much larger in size than clay bricks. As a result, the
structure completion happens faster.
For large constructions, the AAC block prices are better when compared to
using burnt clay bricks.
AAC blocks are environmentally friendly as no toxic materials are used to
create these bricks. The production process also involves 50% lesser emission
of greenhouse gases and 30% lesser creation of solid wastes.
36. ADVANTAGES OF AAC BLOCKS
https://www.magicbricks.com/blog/aac-blocks/129206.html
The porous material of AAC blocks helps absorb moisture naturally, resulting in
lesser mildew, moisture, and humidity inside the house.
These blocks are up to 3 times lighter in weight than traditional clay
or cement blocks.
The need to trim and cut AAC blocks might be more compared to traditional
blocks. AAC blocks are, however, more precise. These come in perfect
dimensions with no need for trimming.
Since these blocks are lightweight, you will spend less on the AAC block prices
when you consider transportation costs and labor charges for loading and
unloading blocks.
These porous and airy materials last very long and are not affected by climatic
changes.
37. LIMITATIONS OF AAC BLOCKS
https://www.magicbricks.com/blog/aac-blocks/129206.html
Improper installation can cause cracks in the structure of the blocks, and this will affect the
final finish of the building.
AAC blocks porous material means they have to be handled carefully during loading and
unloading. Also, the fact that these are lightweight may make the laborers handle them causally,
causing unwanted breakage.
AAC block prices vary with the quantity you order. If you are constructing a low-rise, small
building, then the overall brick prices may be high when compared to traditional bricks. These
are best used in high-rise buildings.
Not any mason can lay AAC blocks. These need to be done only by experts.
AAC blocks cannot handle heavy loads and are called non-load-bearing materials. Therefore,
these should be mostly used for partition walls.
38. PLANT LOCATION ACROSS INDIA
MANUFACTURING PROCESS OF AAC BLOCK https://www.researchgate.net/publication/349366832
39. REFERENCES
• The manufacturing process of AAC block https://www.researchgate.net/publication/349366832
• Research paper - AERATED AUTOCLAVED CONCRETE (AAC) BLOCKS: A REVOLUTION BUILDING MATERIAL IN THE CONSTRUCTION INDUSTRY – IJSTM
• A Review of Autoclaved Aerated Concrete Products by NBSIR – US Department of Energy
• Code Provision – IS 269:1989 and IS 383:1970
• Videos
• http://youtube.com/watch?v=FS3BTDBMt7I
• https://www.youtube.com/watch?v=6iiPL-U8uJs
• https://www.youtube.com/watch?v=4Hy9xuCiwIs
• https://www.understanding-cement.com/autoclaved-aerated-concrete.html
• https://greenjams.org/aac-blocks-an-accidental-invention/
• https://www.understanding-cement.com/autoclaved-aerated-concrete.html
• http://www.builtconstructions.in/OnlineMagazine/Bangalore/Pages/High-Performance-Cellular-Concrete-836.aspx
• https://www.magicbricks.com/blog/aac-blocks/129206.html
• https://www.greenblock.co.in/green-aac-block-brochure.pdf
• https://civilsir.com/concrete/
• https://aacblockmachine.com/blog.php
• https://dir.indiamart.com/
• https://buildecoaac.com/wp-content/uploads/2020/10/Build-Eco-Brochure-Final-for-print.pdf
