Foam concrete-Materials, Properties, Advantages and Production Methods

Foam concrete is a type of lightweight concrete that is manufactured from cement, sand or fly ash, water, and the foam. Foam concrete is in the form of foamed grout or foamed mortar.

Foam concrete can be defined as a cementitious material that consists of minimum 20 percent of foam, that is mechanically entrained into the plastic mortar. The dry density of foamed concrete may vary from 300 to 1600 kg/m3. The compressive strength of foam concrete determined at 28 days, ranges from 0.2 to 10N/mm2 or can go higher.

Foam concrete is differentiated from air entrained concrete in terms of the volume of air that is entrained. The air entrained concrete takes in the air of 3 to 8 percent. It also differs from the retarded mortar and aerated concrete for the same reason of percentage of air entrained.

In the case of retarded mortar systems, it is 15 to 22 percent. The bubbles are chemically formed in the case of an aerated concrete.

The production of foam concrete involves the dilution of surfactant in water, which is passed through a foam generator that will produce foam of stable form. The foam produced in mixed with the cementitious mortar or the grout, so that foamed quantity of required density is produced.

These surfactants are also used in the manufacture of low density fills. These are also called as controlled low strength Material (CLSM). Here, to obtain an air content of 15 to 25 percent, the foam is added directly to a mix of low cement content and rich sand.

It must be kept in mind that low density fillers are supplied as foamed concrete by some manufacturers, so misleading must be taken care.

Materials for Foamed Concrete

Cement for Foam Concrete

Ordinary Portland cement is commonly used, but rapid hardening cement can also be used if necessary. Foam concrete can incorporate a wide range of cement and other combination, for example, 30 percent of cement, 60 percent of fly ash and limestone in 10 percent. The content of cement range from 300 to 400 kg/m3.

Sand for Foam Concrete

The maximum size of sand used can be 5mm. Use of finer sands up to 2mm with amount passing through 600 micron sieve range from 60 to 95%.

Pozzolanas

The supplementary cementitious materials like fly ash and ground granulated blast furnace slag have been used widely in the manufacture of foam concrete. The amount of fly ash used ranges from 30 to 70 percent. White GGBFS range from 10 to 50%. This reduces the amount of cement used and economical.

Silica fume can be added to increase the strength; at an amount of 10 percentage by mass.

Foam

The hydrolyzed proteins or the synthetic surfactants are the most common forms based on which foams are made. The synthetic based foam agents are easier to handle and are cheap. They can be stored for a longer period.

Lesser energy is required to produce these foams. The protein based foam are costly but have high strength and performance. The foam can be of two types: wet foam and dry foam.

Wet foams with densities lesser than 100 kg/m3 are not recommended for the manufacture of foam concrete. They have a very loosely place large bubble structure. To a fine mesh, the agent and the water are being sprayed. This process produces foam that has bubbles with size ranging from 2 to 5mm.

Dry foam is highly stable in nature. A solution of water and the foaming agent is forced by restrictions into a mixing chamber by compressor air. The produced foam have bubble size which is smaller than the wet foam. That is less than 1mm. These give a structure of bubbles, which are evenly arranged.