Flyash is defined in Cement and Concrete Terminology (ACI Committee 116) as "the finely divided residue resulting from the combustion of ground or powdered coal, which is transported from the firebox through the boiler by flue gases." Flyash is a by-product of coal-fired electric generating plants.
Classification: The Classification of Flyash is done on the basis of the coal used. One reason for this could be that Flyash is one of three general types of coal combustion byproducts. So, The two basic categories of classification are Class C Flyash & Class F Flyash.
Burning lignite or sub bituminous coal produces Class C Flyash. Class C Flyash is preferable for the applications presented in the Green Building Guide and is the main type offered for residential applications from ready-mix suppliers.
Where as Anthracite and bituminous coal produces Flyash classified as Class F.
Benefits: Flyash has a number of benefits to bestow under its belt. A few of them are as follows:
- Being one of the by-products of coal combustion. It offers environmental advantages by diverting the material from the waste stream, reducing the energy investment in processing virgin materials, conserving virgin materials, and allaying pollution
- Along with being eco-friendly, Flyash also improves the performance and quality of concrete.
- Flyash affects the plastic properties of concrete by improving workability, reducing water demand, reducing segregation and bleeding, and lowering heat of hydration.
- Facilitates in increase of strength and sulphate resistance.
- Reduces alkali-aggregate reaction.
- It reduces permeability and corrosion of reinforcing steel.
Usage in the construction arc:
- No person shall within a radius of fifty kilometers from coal or lignite based thermal power plants, manufacture clay bricks or tiles or blocks for use in construction activities without mixing at least 25 per cent of ash (fly ash, bottom ash or pond ash) with soil on weight to weight basis.
- The authority for ensuring the use of specified quantity of ash as per Para (1) above shall be the concerned Regional Officer of the State Pollution Control Board or the Pollution Control Committee as the case may be. In case of non-compliance, the said authority, in addition to cancellation of consent order issued to establish the brick kiln, shall move the district administration for cancellation of mining lease. The cancellation of mining lease shall be decided after due hearing. To enable the said authority to verify the actual use of ash, the thermal power plant shall maintain month-wise records of ash made available to each brick kiln.
- In case of non-availability of ash from thermal power plant in sufficient quantities as certified by the said power plant, the stipulation under Para (1) shall be suitably modified (waived/ relaxed) by the concerned State/Union Territory Government.
- Each coal or lignite based thermal power plant shall constitute a dispute settlement committee which shall include the General Manager of the thermal power plant and a representative of All India Brick and Tile Manufactures Federation (AIBTMF). Such a committee shall ensure unhindered loading and transport of ash without any undue loss of time. A State/Union Territory level committee to be set up by State/Union Territory Government comprising Member Secretary of the State Pollution Control Board/Pollution Control Committee, representatives of Ministry of Power in the State/Union Territory Government and a representative of AIBTMF shall deal with any unresolved dispute.