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Aerated Concrete is made by introducing air or gas into a slurry composed of Portland cement or lime and finely crushed siliceous filler so that when the mix hardens, a uniformly cellular structure is formed. Though it is called aerated concrete it is really not concrete in the correct sense of the word.
As described above, it is a mixture of water, cement, and finely crushed sand. Aerated concrete is also referred t gas concrete, foam concrete, or cellular concrete.
In India, there are few factories manufacturing aerated concrete at present. A typical outcome of aerated concrete in India is Siporex.
1. Manufacture of Aerated Concrete
There are many ways in which aerated concrete can be prepared which are as follow:
a. By the formation of gas by a chemical reaction within the mass during liquid or plastic state.
b. By mixing the preformed stable foam with the slurry.
c. By using finely powdered metal (usually aluminum powder) with the slurry and made to react with the calcium hydroxide liberated during the hydration process, to out large quantity of hydrogen gas. This hydrogen gas when contained In the mix, gives the cellular structure.
Powdered zinc may also be added in place of aluminum powder. Hydrogen pe7: and bleaching powder have also been used instead of metal powder. But this manufacturing is not majorly used nowadays.
In the second method performed, stable foam is mixed with cement fly ash or crushed sand slurry thus causing the cellular structure when this gets set and hardened. As a minor modification, some foam giving agents are also mixed and thoroughly churned or beaten (in the same manner as that of preparing foam with the white egg) to obtain the foam effect in the concert. In a similar way, air-entrained agents in large quantities can also be used and mixed thoroughly to introduce cellular aerated structure in the concrete.
However, this method can not be employed for decreasing the density of the concrete beyond a certain point and as such, the use of air entrainment is not often practiced for making aerated concrete.
The gasification method is of the most widely adopted methods using aluminum powder or other similar materials.
This method is taken in the large-scale production of aerated concrete in the factory wherein the entire process is mechanized and the outcome is put through to high-pressure steam curing.
in other words, the products are autoclaved. Such products will suffer neither retrogression of strength nor dimensional instability. The practice of using preformed foam with slurry is limited to small-scale production and in situ work where a small change in the dimensional stability can be tolerated. But the advantage is that any density desired at the site can be made in this method.
2. Properties of Aerated Concrete
The use of foam concrete has gained popularity not only because of the low density but also because of other properties mainly the thermal insulation property. Aerated concrete is prepared in the density of 300 kg/m3 to about 800 kg/m3.
Lower density grades are utilized for insulation use, while medium-density grades are utilized for the manufacture of building blocks or load-bearing walls and comparatively higher density grades are utilized in the manufacture of prefabricated structural members in conjunction with steel reinforcement.
3. Uses of Aerated Concrete
The aerated concrete is used in:
1. It is utilized for heat insulation because of its low thermal conductivity and weight.
2. It is utilized for fireproofing because it provides more fire resistance than normal concrete.
3. Structurally aerated concrete is utilized mainly in the form of precast members or autoclaved blocks. It can also be utilized for floor construction in place of hollow tile floors.
4. It can also be used for light insulation.
|Read Also: No-Fines Concrete|