What is Cellular Concrete
Cellular concrete is a lightweight product consisting of portland cement, cement-pozzolan, cement sand, lime-pozzolan or lime-sand pastes or pastes containing blends of these ingredients and having a homogeneous void or cell structure, attained with gas forming chemicals or foaming agents. For cellular concretes, containing binder ingredients other than or in addition to portland cement, autoclave curing is usually employed.
There are two basic methods of producing aeration and appropriate name is being given to each end product:
- Gas concrete
- Foamed concrete.
Gas concrete is obtained by a chemical reaction generating a gas in fresh mortar, so that when it sets it contains a large number of gas bubbles. Finely divided aluminum power is most commonly used, its proportion being the order of 0.2 percent of the weight of the cement.
The reaction of the active power with a hydroxide of calcium or alkali liberates hydrogen, which forms the bubbles Powdered zinc can also be used. Sometimes hydrogen peroxide is used. This generates oxygen.
Foamed concrete is produced by adding to the mix a foaming agent (soap and synthetic detergents) which introduces and stabilizes air bubbles during mixing at high speed.
Cellular concrete may or may not contain aggregate, the latter generally being the case with non-structural concrete required for heat insulation when a density of 12 to 20 lb/ft3 can be obtained. More usual mixes have densities between 30 and 70 lb/ft3 when mixture of cement and very find sand is used. Cellular concrete has a high shrinkage and moisture movement and these may be reduced by high pressure steam curing.
Use of Cellular Concrete
Cellular concretes are mostly used for partitions for heat insulation purposes because of its low thermal conductivity and for fire proofing.