1. Fly ash
Fly ash is finely divided residue resulting from the combustion of powdered coal and transported by the flue gases and collected by;
Electrostatic
Precipitator
Fly ash is the most widely used
pozzolanic material all over the world.
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2. Types of fly ash Class F Class C
Fly ash normally produced by burning anthracite or bituminous coal, usually has less than 5% CaO. Class F fly ash has pozzolanic properties only.
Fly ash normally produced by burning lignite or sub-bituminous coal. Some class C fly ash may have CaO content in excess of 10%. In addition to pozzolanic properties, class C fly ash also possesses cementitious properties.
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3. Fly ash Amount used Results - effects
Up to 35% by mass of cement (According to IS: 456 – 2000) & minimum shall not be less than 15%.
Results - effects
Reduction of water demand for desired slump. With the reduction of unit water content, bleeding and drying shrinkage will also be reduced.
fly ash is not highly reactive, the heat of hydration can be reduced through replacement of part of the cement with fly ash.
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4. High Volume Fly Ash Concrete.
Use of fly ash is because of many factors such as:
Abundance of fly ash
Fly ashes from major TPP(Trans-Pacific Partnership) are of very high quality i.e. quality of fly ash.
Economic factor i.e. Cost of fly ash with in 200 km from a TPP is as low as 10% to 20% of the cost of cement.
Environmental factors i.e. reduction in CO2 emission.
HVFAC is a concrete where excess of 35%of fly-ash is used as replacement
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5. Effects of Fly Ash on Hardened Concrete
contributes to the strength of concrete due to its pozzolanic reactivity.
continued pozzolanic reactivity concrete develops greater strength at later age not at initial stage.
contributes to making the texture of concrete dense, resulting in decrease of water permeability and gas permeability.
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6. Fly ash Used at Many high-rise buildings Industrial structures
Water front structures
Concrete roads
Roller compacted concrete dams.
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7. THE END……
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