The rapid increase in the capacity of thermal power generation in India has resulted in the production of a huge quantity of fly ash, which is approximately 50 million tons per year. The prevailing disposal methods are not free from environmental pollution and ecological imbalance. Large stretches of scarce land, which can be used for shelter, agriculture or some other productive purposes, are being wasted for disposal of fly ash. Fly ash, lime and gypsum (FALG) can be used to make bricks and hollow blocks of adequate strength, an economical alternative to conventional burnt clay bricks will be available. Lime and gypsum are either available from mineral sources or can be procured from industrial wastes.
Fly ash bricks are made of fly ash, lime, gypsum and sand. Fly ash, lime sand and gypsum are manually fed into a pan mixer where water is added in the required proportion for intimate mixing. The proportion of the raw material is generally in the ratio of 60–80 per cent of fly ash, 10–20 per cent lime, 10 per cent Gypsum and 10 per cent sand, depending upon the quality of raw materials. The mixture is slow-setting pozzalona cement mix. After mixing, the mixture is shifted to the hydraulic/mechanical presses. A specially designed machine which gives a very high pressure load at slow rate (in the order of 280–350 kg/inch) is used to mould the bricks. Holding the pressure at specific times gives more strength to the finished product. The moulded bricks are then transferred to hydraulic-operated wooden pellets manually and stored in covered space for 3 days (minimum) for setting.
Then the bricks are taken to the yard for water curing for 15–20 days. Then it is sorted and tested before despatch. These can be extensively used in all building constructional activities similar to that of common burnt clay bricks. The fly ash bricks are comparatively lighter in weight and stronger than common clay bricks. Fly ash bricks are used in multi-storeyed apartment houses for non-load bearing purposes and in making curtain and partition walls of these houses. Use of fly ash bricks in this type of construction is meant mainly to achieve economy and make profits. The domestic buildings of low- or middle-income groups mostly have single or two-storied dwelling units. Therefore the cost effectiveness along with the strength and durability of fly ash bricks are very important for them.