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Foamed concrete admixtures

Foamed concrete admixtures are surfactants that are diluted with water before passing through a foam generator to produce a stable foam, similar to shaving cream. This is then blended into a cementitious mortar in a quantity that produces the required density for the foamed mortar (more usually called foamed concrete).

Low-density fill material admixtures are also surfactants but are added directly into a sand-rich low-cement-content concrete to give 15 to 25% air. This low-density fill – also called controlled low-strength material (CLSM) – has good flow properties and finds use for trench filling and other similar low-strength void-filling jobs.

For foamed concrete, a foam is first produced in a generator. As the raw foam has no significant density, blending 50% by volume with a mortar of density 2200 kg/m3 produces a 1100 kg/m3 foamed concrete. Any density can be obtained from about 600 to 2200 kg/m3 by adjusting the foam/mortar ratio. The blending can be done in the back of a ready-mixed concrete truck or can form part of a continuous process in dedicated equipment.

Low-density fill is produced in a similar way, or by entraining the air within the batching process.

Note: Not all admixture types are covered by EN 934. BS 8443:2005 Specification for establishing the suitability of special purpose concrete admixtures, covers the following; underwater concrete admixtures, shrinkage reducing admixtures, corrosion inhibiting admixtures, pumping aids, segregation reducing admixtures, foaming admixtures, semi-dry concrete admixtures.

Acknowledgement: The Concrete Society

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TR18 A guide to the selection of admixtures for concrete