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First used in mainland Europe during the 1920s, foam concrete has properties and applications that are different from conventional concrete, where low compressive strengths are acceptable. This article outlines the basic properties of the material and its manufacturing technique. The material is suitable for a number of applications, including backfill and trench reinstatement. One of the most cost-effective uses has been found in sub-bases for roads, and four examples are included from the USA, The Netherlands and UK.
The term 'foam concrete' is possibly more accurate than the more frequently used `foamed concrete', as the product is not created by foaming ordinary concrete but is a totally different material. In its most fundamental form, foam concrete is composed of cement, water and air pores. The air pores are introduced by agitating air with a foaming agent diluted with water, creating a mechanically manufactured foam. This foam is then carefully blended with the cement slurry or base mix.
With ordinary concrete, there is a compact aggregate/sand skeleton, and cohesion is achieved by the cement matrix: compression loads are predominantly transferred via this well-- stacked aggregate/sand skeleton. Foam concrete is composed without coarse aggregates, but with a substantial volume of foam bubbles. The bubbles are typically 0.3-0.4mm in diameter, surrounded by cement, the highest concentration being near the plateau border where there is the conjunction of three foam bubbles. In foam concrete mortar, these bubbles provide the stability of the foam concrete. Once the material hydrates, load transfer takes place via the cement matrix around the bubbles.
Mix designs and properties
In addition to cement, water and foam, various fillers are used for foam concrete. Popular fillers are pfa, sand, (lime) stone dust or chalk, and polystyrene beads.
All materials that are compatible with cement and have fineness between that of cement...