Fly ash based building products are manufactured by using Major percentage of fly ash generated from Thermal Power stations and plants like (i) HEG Pvt. Ltd. Mandideep (ii) Vardhman Yarn, Mandideep, (iii) Vardhman Fabric, Budhni. (iv) Satpura Thermal Power Plant, Sarni etc. and many Paper Mills , Aluminium Industries, who uses Boiler & captive power plant produces bulk quantity of Fly Ash in the State of Madhya Pradesh. Other raw materials used along with Fly Ash are Quick lime and calcined gypsum. FLY ASH Bricks are popular out of all building products can be manufactured with low investment in comparison to Fly ash lime bricks and Clay fly ash bricks.
Other building products are Fly Ash concrete blocks, solid & hollow types, Fly Ash low cement concrete, Fly Ash castable & many other low moisture Fly Ash ready-mix. At present FLY ASH building bricks technology is much popular in Madhya Pradesh who have accepted this eco-friendly technology being inspired and encourages by the Govt. authority and promotional agencies like Fly Ash Bricks Manufacturing Association (FABMA), and different Environmental Programme of State Govt. FLY ASH bricks do not lose strength unduly even upon socked in water continuously. Hence plastering is optional rather than necessity. Well cured Fly Ash bricks absorb 4-12% water only.
On account of less water absorption, rationalisation of plastering and mortar, a finished Fly Ash brick wall is lighter and cheaper in comparison to finished clay brick wall. Fly Ash bricks can be made to order with engineering properties comparable to cement concrete befitting for specialized applications such as canal liming, dam construction, water tanks etc. The Fly Ash mix is nothing but a slow setting pozzolana cement mix. The process is same as making cement in cement factories where clay and lime stones are burnt with coal and gypsum is mixed and ground to make cement. When fly ash, hydrated lime powder and gypsum are mixed and ground in a pan mixer the resulting mixture acts as slow setting pozzolana cement and thus a cement bonding property is attained in the said mixture.
Sand or crushed stone dust may be added to bring down the cost of mix. The above mix is pressed with lower moisture cement in a brick press, specially and indigenously designed to give high pressure load at slow rate, in the order of 350 kg./sq. inch. Thus Fly Ash bricks are the substitute to common burnt clay bricks which every class of people can easily accept for constructional activities.
Process of manufacture of Fly Ash bricks involve the following stages ofoperations.
i) Proportioning and mixing of batch materials such as fly ash, Quick lime, calcined gypsum, Dust and water.
ii) Shaping of bricks in the press.
iii) Drying of green bricks over wooden pallets.
iv) Curing of the bricks by spraying/sprinkling water for 10 to 15 days.
v) Sorting, inspection and quality control tests prior to sale.
Fly ash, Quick lime, calcined gypsum, Stone Dust are the raw materials Required for making fly ash bricks and blocks. The raw materials of brick mix in desired proportion (Fly Ash 40-45%,Quick Lime 12-15%, Crushed Stone Dust50-55% and calcined gypsum 2% by weight) are blended intimately in dry or wet form in a suitable blender/mixer.
The wet brick mix is fed into the machine mould. The vibration is given for a while the mould is again fed. The stripper head is pressed and vibration is given simultaneously for about 10 seconds.
The mould is lifted and Seven bricks produced pallet is removed and kept on the platform for air drying. The next day the bricks produced on the previous day are put in the stack. The stack is formed with much care to see that curing water and air for drying reaches to every brick. After 3 days warm water on small quantity is poured in the stacked bricks without any pressure. After 5 days hot water is sprinkled on the brick stack for 2 times a day. The bricks stack after each watering are immediately covered with black PVC sheets. The bricks are then left in the stack for drying for 7 days. The bricks are ready for dispatch after 22 days from the date of manufacture. The compressive strength of the bricks produced from the brick mix and manufacturing process suggested herein would be 80 Kg./cm2 to 110 kg./cm.2
Bureau of Indian Standards formulated specifications for clay fly ash bricks, lime fly ash bricks, common burnt clay bricks and calcium silicate bricks which can be referred to as regards to the quality of Fly Ash bricks.
IS: 12894:1990 - Specification for Fly Ash Lime bricks.
IS: 13757:1976 - Specification for Burnt clay fly ash building Bricks.
IS: 4137:1989 - Specification for calcium silicate bricks.
IS: 3102:1976 - Classification of burnt clay solid bricks.
The other relevant BIS specifications are :
IS: 3812:1981 - Specification for Fly Ash for use as Pozzolana and admixture.
IS: 712:1984 - Specification for Building limes.
IS: 3495(Pt.I)1976 - Methods of tests of burnt clay building bricks.
For production of good quality fly ash bricks the quality of Fly Ash should be as follows:
i) Moisture content of fly ash should not exceed 5%.
ii) Visual appearance of fly ash should be of light steel grey or smoky grey Colour.
iii) Unburnt carbon content in the fly ash be around 5%.