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| Autoclaved aerated concrete (AAC) |
Introduction - Autoclaved aerated concrete (AAC)
The full-form of AAC blocks is “Autoclaved aerated concrete”. They where invented in Sweden in the year 1924. The main purpose for the invention of these blocks where, the people in Sweden where looking for a material having properties similar to wood. These properties include the ease of doing work with the material, the thermal insulation properties wood shows irrespective of the fact showing a better withstand with decay and termites attack. They even tends to show good acoustics-friendly properties.
Autoclaved aerated concrete blocks is very popular in European countries and is widely been used. It is even growing rapidly to other countries, because of its handy performance providing ease of work resulting in reducing time, labour, economically etc.
Autoclaved aerated concrete (AAC) blocks are certified eco-friendly green building material as they are made up of high percentage of recycled industrial waste and does-not have any kind of bad effect to the environment because of its non-toxic characteristics.
IS 2185 Part-3 is the code referred for AAC blocks.
What is a AAC block?
AAC blocks are the mix of fly ash, cement, lime and water with a aerating agent. Because of the foam present while manufacturing, they contain numbers of tightly packed pores or small pockets inside them which results in making the aac block light weight.
The AAC block is produced by autoclaving a set mix of fine siliceous materials such as ground sand/fly ash with a binder.
At the time of production, they are added with a foaming agent to concrete in a mould, then the blocks or panels from the resulting ‘cake’ and ‘cooking’them with steam (autoclaving) are cut with a wire-cutting.
What is the Foam in AAC blocks
It is the reaction between aluminium paste and alkaline present in cement resulting in formation of hydrogen.
Aluminium paste + Alkaline = Hydrogen Gas (foam)
Raw materials - Manufacturing of AAC blocks
The raw materials used in manufacturing of aac blocks and there properties can be defined as
Manufacturing Process - AAC Block
In the manufacturing of aac blocks, the percentage of raw materials are taken as followed in the table provided below.
The manufacturing autoclaved aerated concrete (AAC) process is carried out in four stages such as
Stage 1 | Dosing & Mixing | l The ratio taken is, FLY ASH/SAND : CEMENT : LIME = 75:15:9, Alumina = 0.08% l The mix cycle is normally be of 5.5 minutes. l The mixture is ready for pouring once it is mixed homogeneously. l The process of dosing & Mixing is achieved with the help of automatic machines. With minimum man power.
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Stage 2 | Casting, Rising & Curing.
l Effect due to Hydrogen gas
l What is rising process in AAC.
l Time required for this stage. | l The moulds in which casting is to be done is greased. l After greasing slurry is poured inside it. l Hydrogen gas is formed inside the mould by the reaction of Alumina present in the mix with the alkaline Ca(OH)2 present in cement in the presence of water. l Leads to formation of tight air pockets (2mm-5mm) inside slurry mix. l Air pockets results in expansion of the slurry mix as much as three times. l In rising, the slurry is allowed to expand as much possible it can. l After rising process is completed, the mix which is known as green cake is made to settle and pre-cure. l The stage 2, usually takes 60-240 minutes. |
Stage 3 | De-moulding and cutting | l In this process, the green cake is de-moulded and cut. l Cutting can be done in two different process, (i) In first process, the green cake is allowed to move and the cutter is fixed at a position. The cake is moved towards the cutter and gets cut itself. (ii) In second process, the green cake is made to be fixed at the place and cutter I allowed to move to cut it. |
Stage 4 | Curing
Autoclave (purpose/Dimension)
Curing Period | l In this stage, after cutting the green cake, the AAC blocks are cured. l The machine have high pressure steam, used for curing. l Autoclave Length = 45m Diameter = 3m l 8-10 Hours, it takes more time for higher density/ strength of AAC block. l Once they are cooled, they are ready for the use in construction. |
Advantages of AAC blocks
l The construction process can be about 20% faster.
l They have different variety of panels such as blocks, floor panels,wall panels, roof panels and lintels
l Due to its lower density, high rise buildings construction use AAC since it is structurally lighter in weight.
l The products are lighter in weight compared to ordinary concrete blocks, the characteristic structure comprises of millions of tiny pores.
l They are approved eco-friendly building materials because the ingredients used in manufacturing of aac comes from industrial waste and are made from non-toxic ingredients.
Thank you sir/Madam for the best content in your blog. keep sharing more in future.
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ReplyDeleteDear Sir/Madam Thanks for the information about Autoclaved aerated concrete (AAC) Blocks - Raw material, Manufacturing, Advantage Hope to see more in future