Aerated concrete may be defined as concrete made very light and cellular by the addition of prepared foam or by generation of gas within the unhardened mixture. It is also termed as cellular concrete and foamed concrete.
By Generation of Gas
The addition of powered aluminium or zinc to the cement causes evolution of hydrogen gas on addition of water. The powered metal is added to the cement in dry state in the ratio of 1:1000. After thorough mixing in the dry state, water is mixed. This cause the evolution of gases and the process goes on for an hour or so. This cement paste is filled in the moulds up to about 1/3rd depth and soon afterwards, the paste fills the mould up to top and overflows. The excess paste is then struck off and the paste allowed to set. The paste hardens to a mass having the innumerable small bubbles surrounded by cement. This concrete is quite impervious to water but has a high drying shrinkage. So each block or unit should be fully cured and dried, before being used to eliminate any subsequent shrinkage. The density of this concrete is about 650 to 950 kg/m3 and its strength is about 15 to 30 kg/cm2.
By Use of Foaming Agents
Sometimes ordinary concrete can be made light by adding foaming agents like resin soaps. These agents develop bubbles inside the concrete and its density is reduced. The ordinary heavy aggregates are also sometimes replaced by wooden fibres, chips and saw dust etc. this also helps to reduce the weight of concrete.
Where to Use Aerated Concrete?
Aerated concrete is used for the following purpose
- Partitions for heat insulation because of its low thermal conductivity and weight
- In fir proofing because of its better fire resistivity
- Floor construction and light insulation