Foam concrete consists mainly of cement, air pores with fillers such as fly ash or sand. Coarse aggregates are not used in foamed concrete. Air pores in foam concrete are formed by agitating air with a foaming agent. The size of air bubbles ranges from 0.3 to 0.4 mm. The volume of air is at least 20% of concrete volume. The foam concrete possesses high flowability, low self-weight, controlled low strength, and excellent thermal insulation. The density of foam concrete ranges from 400 kg/m3 to 1600 kg/m3 with compressive strength ranging from 1 to 15 Mpa. The high flowability of foam concrete eliminates the need for using mechanical vibration to consolidate concrete during placing.
Also read: Fiber-reinforced concrete
Foam concrete can be produced either by the pre-foaming method or the mixed foaming method. In the pre-foaming method, the base mix (cement, filler, water) and the stable preformed aqueous foam are produced separately. Then blending the foam and the base mix together. In the mixed foaming method, the active surface agent is mixed with the ingredients of the base mix, and during the mixing, the foams will be formed.
Properties of Foam Concrete
- Drying shrinkage: foam concrete has a high drying shrinkage. It is estimated to be 10 times greater than the normal concrete. The high drying shrinkage is attributed to the absence of aggregates in foamed concrete. The drying shrinkage of foam concrete is reduced with density, and this attributed to lower paste content affecting the shrinkage in low-density mixes.
- Self-compacting: high flowability of foam concrete allow easier placement of concrete. Foam concrete can fill the smallest voids without the need for mechanical vibration. Foam concrete will not exert high stresses on formwork due to low self-weight of foam concrete.
- Resistance to the aggressive environment: foam concrete with low density provides excellent resistance to thaw-freezing cycles of water. Also, foam concrete offers good resistance to aggressive chemical attacks such as sulfate. A study on accelerated carbonation of foam concrete by Jones and McCarthy indicates that lower density concrete appears to carbonate at a relatively higher rate.
- Fire resistance: foam concrete possesses a high resistance to fire. The tests have shown that the foam concrete under fires doesn’t spall like normal density concrete.
- Thermal insulation: foam concrete has high thermal insulation. The high thermal insulation is attributed to the cellular microstructure of foam concrete.
Application of Foam Concrete
- Building blocks: foam concrete can be used to produce building blocks for patriation and load-bearing walls with any dimension.
- Floor screed: foamed concrete can be used to create a flat surface on uneven ground, and it can be used to raise the floor levels.
- Roof insulation: foam concrete possesses excellent thermal and sound insulation properties. The foam concrete can be used for roof insulation. The low self-weight of concrete will not impose a large loading in the building.
- Road sub-base: Foamed Concrete is being used road sub-base on a bridge. Foamed concrete is lightweight so that the loading imposed on the bridge is minimized.