31/10/2022
Introduction of foam concrete
Foam concrete, also called cellular light weight concrete is produced by the mixing of cement, sand, water and preformed stable foam. The foam is produced with the help of a foam generator by using foaming agent. The air content is typically between 40 to 80 percent of the total volume. The bubbles vary in size from around 0.1 to 1.5 mm in diameter. Foamed concrete differentiates from (a) gas or aerated concrete, where the bubbles are chemically formed through the reaction of aluminium powder with calcium hydro oxide and other alkalies released by cement hydration and (b) air entrained concrete, which has a much lower volume of entrained air is used in concrete for durability. Curing of foamed concrete unit may be done as per IS: 456-2000. Curing can be speeded up by steam.
Foamed concrete may be produce by mixing the above mentioned ingredients in ready mix plant or ordinary concrete mixer. Foamed concrete is self compacting concrete requires no compaction, and will flow readily from a pump outlet to fill mould, form, restricted and irregular cavities. It can be pumped successfully over significant height and distances. The 28 days strength and dry density of the material vary according to its composition, largely its air voids content, but usually they range from 0.3 to 25.00 N/mm2 and 400 to 1800 kg/m3. The plastic density of the material is about 150 to 200 kg/m3 higher than its dry density.
USES:
1. Foamed light weight concrete in the form of bricks, blocks or poured in-situ is used for thermal insulation over flat roofs or for cold storage walls or as non-load bearing walls in RCC/Steel framed buildings or for load bearing walls for low-rise buildings.
2. Fire rating of foamed concrete is far superior to that of brick work or dense concrete.
3. Bulk filling, using relatively low strength material, for redundant sewerage pipes, wells, disused cellars and basements, storage tanks, tunnels and subways etc.
4. Infill to the spandrel walls of arch bridges.
5. Backfill to retaining walls and bridge abutment.
6. Stabilizing soil, for example in the construction of embankment slopes.
7. Grouting for tunnel work.
BATCHING AND MIXING:
The dry ingredients like cement & sand shall be fed into the mixer first and thoroughly mixed to ensure even distribution of cement. The appropriate amount of water shall be added thereafter continuing the mixing. The preformed foam, which is made by blending the foam concentrate, water and compressed air in predetermine proportion in a foam generator, calibrated for a specific discharge rate, shall be added in measured amount to the slurry of cement, sand and water in the batch mixer. After an additional mixing to get uniform consistency, the slurry form of foamed cellular concrete of desired wet unit weight shall be ready to be poured out into forms/moulds etc. When truck mixing equipment is used for foamed concrete, the preformed foam shall be added at the job site just prior to pumping or otherwise conveying the concrete into forms.
The building blocks may be de-moulded after 24 hours from pouring of foamed concrete. Curing shall be done s per IS: 456-2000. To speed up the production, the blocks shall be cured by saturated steam at an average temperature of 460C ± 150C for a period of 24 hours or more to attained the required strength. After curing, the blocks shall be allowed to dry under shade for a period 2 to 3 weeks, so as to complete their initial shrinkage before being used in the work.
RECOMMENDED USAGE OF FOAM CONCRETE DENSITY
Density 400-600 kg/m³:
This density is primarily applied for thermal insulation or fire protection. It uses cement, fine sand, water and foam and can easily be pumped. Foam generators allow the production of stiff foam for slopes to be applied on roof-tops.
Density 600-800 kg/m³:
Is also used for void-filling, such as an landscaping (above underground construction), to fill voids behind archways and refurbishing of damaged sewerage systems. It is also been used to produce building blocks.
Density 800-1000 kg/m³:
Serves to fore mostly produce blocks and other non-load bearing building elements such as balcony railings, partitions, parapets and fence walls etc.
Density 1200-1400 kg/m³:
Are the most commonly densities for prefab and cast in situ walls, load-bearing and non-load-bearing. It is also successfully used for floor screeds (sound and insulation plus weight reduction).
Density 1600-1800 kg/m³:
Would be recommended for slabs and other load-bearing building elements where higher strength is obligatory.
