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Foam concrete is mainly composed of cement, water and air pores with filler (such as PFA, sand etc.) without any course aggregates. The air pores are formed by agitating air with a foaming agent. The typical size of air bubbles is around 0.3-0.4mm in diameter. For cement grout, it mainly consists of cement and water.
Foam concrete is characterized by have low density and low cost when compared with normal concrete. The density of foam concrete is around 400 – 1600 kg/m3. Therefore, the low density enhances low dead load and has extensive applications when low loadings are required. Foam concrete does not require compacting and hence imposes no lateral forces on adjacent structures. Moreover, it also displays good resistance to water and produces high level of sound and thermal insulation. However, it suffers from the demerit that it have low compressive strength only (e.g. less than 15 MPa) which is drastically different from cement grout which possesses high compressive strength. There is recent development of foam concrete as road sub-base.