Foamed Concrete Application and specification

Which this paper aims to summarise.Although foamed concrete
was used some 2000 years ago it wasn’t until recently that modern foamed concrete began to be developed. In
1987 a full scale trial on the use of foamed concrete for trench reinstatement was conducted in the UK, which
led to a further increase in use in this country. Foamed concrete has the following properties: it is lightweight,
free flowing and easy to level, it does not require compaction, has good thermal insulation and frost resistance
properties, and it is easy to pump, both vertically and horizontally. Its uses include: Trench Reinstatement,
Blinding, Filling (basements, pipes, tunnels, subways, mine workings), Building use (under floors and roofing),
Soil stabilisation, Reductions in lateral loading, Sports fields and athletics tracks and Sandwich fill for precast
units. As well as the composition and production methods, this paper covers some of the practicalities and
properties of the material.



The term ‘Foamed Concrete’ may be somewhat misleading

in that most do not contain large aggregates

(indeed it may be considered to be foamed mortar

or foamed grout). It is a lightweight concrete manufactured

from cement, sand or fly ash, water and

a preformed foam. Its dry density ranges from 300

to 1600 kg/m3 with 28 day strength normally ranging

from 0.2 to 10 N/mm2 or more.

A widely cited definition of foamed concrete is:

“A cementitious material having a minimum of

20 per cent by volume of mechanically entrained foam

in the plastic mortar or grout”.

This differentiates it from air entrained concrete

which has a far lower volume of entrained air (typically

3–8%), retarded mortar systems (typically 15–22%)

and aerated concrete where the bubbles are chemically


In the production of foamed concrete, a surfactant

is diluted with water and passed through a foam generator

which produces a stable foam. This foam is then

blended into a cementitious mortar or grout in a quantity

that produces the required density in the foamed


Surfactants are also used in the manufacture of Low

Density Fills (also called Controlled Low Strength

Material (CLSM)). In this case, however, they are

added directly into a sand rich, low cement content

concrete to give 15 to 25% air. Somewhat confusingly,

some suppliers of Low Density Fills refer to

these materials as foamed concrete, but as the foam is

not formed separately to the concrete they are not true

foamed concretes.



The value of foamed concrete lies in its good void

filling ability with a rigid hardened structure which

will not deflect under low loading and also the low

density where loading on other parts of the structure

are critical.Although it will give enhanced thermal and

fire rating properties, it is not usually the most cost

effective solution for these applications unless access

is difficult.

Some examples of the wide variety of applications

where foamed concrete has been used include:

2.1 Trench reinstatement

One of the main causes of damage to road pavements

are excavations carried out by utilities companies.

Settlement of backfill means that the surfacing is damaged

and constant patching will be required. Foamed

concrete meets the criteria for the ideal backfilling

technique in that: it normally requires no compactive

effort and does not settle after placing; it does not

transmit axle loads directly to the services in the

trench; final resurfacing is possible the next day;

it is economic; it is readily available; it permits

easy re-excavation; it does not require unreasonably

complicated equipment or skilled labour



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