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SUBMITTED TO: - SUBMITTED BY: -MR.PANKAJ DHEEMLA BRAJESH KR.
MEENAHOD,CIVIL DEPT. P IET/CIV/12 /030
CONCRETE DESIGN WITH FLY ASH
INTRODUCTION Fly ash is generated in combustion of coal in fine
grey powder .Its size is spherical .Fly ash has pozzolonic properties, as a product from industrial plants using pulverized coal or lignite as fuel.That it react with lime from cementitious compound. It is known as supplementry cementition material.
It is used pozzolan siliceous or aluminosiliceous in nature in divided form. It is one of the residues generated in combustion of coal. Comprises of fine particles which rise with the flue gases
Classification
It is divided in two classes :
1.Class F
2.Class C
Class F
Class F is fly ash produced from burning anthracite or bituminous coal.
lime contain is less than 20%.contains a greater combination of silica, alumina and
iron (greater than 70 percent) than Class C fly ash.
Class C
Class C is produced from the burning of sub-bituminous coal and lignite.
Class C fly ash comes from coals which may produce an ash with higher lime content more than 20%. Elevated CaO may give Class C unique self-hardening characteristics
FLY ASH IN CONCRETE:
Fly ash could be an expensive replacement for Portland cement in concrete
Fly Ash particles provide a greater workability of the powder portion of the concrete mixture which results in greater workability of the concrete and a lowering of water requirement for the same concrete consistency.
Properties of Fly Ash
Chemical
Physical
CHEMICAL
MATERIALS PORTLAND CEMENT%
FLY ASH%
SiO2 21.82 53.39
Al2O3 6.49 16.07
Fe2O3 1.93 13.05
CaO 60.74 6.33
MgO 1.08 5.48
SO3 2.62 1.06
Na2O 0.14 1.59
Free Cao 0.84 0.11
1.fly ash are glassy due to rapid cooling; cement are crystalline & formed by slower cooling.
2. Portland cement is rich in lime (CaO) while fly ash is low. Fly ash is high in reactive silicates while Portland cement has smaller amounts
The color varies from light to dark grey depending upon its carbon contents.
fly ash particles are small, they effectively fill voids
PHYSICAL
COMPARISON BETWEEN CLASSES OF FLY ASH
HEAT OF HYDRATION:
•Fly Ash has a lower heat of hydration.
•Portland Cement produces considerable heat on hydration.
•In mass concrete placements the excess internal heat may contribute to cracking.
•The use of Fly Ash may greatly reduce this heat build up and reduce external cracking.
COMPRESSIVE STRENGTH: Typically, concrete made with fly ash will be slightly lower in
strength than straight cement concrete up to 28 days, equal strength at 28 days, and substantially higher strength within a year’s time.
Thus, fly ash concrete achieves significantly higher ultimate strength than can be achieved with conventional concrete.
HOW FACTORIES WORK
Use of fly ash stabilization
It is the process by which we can change the properties or design purpose
Stabilization is done by many method 1. cement stabilization 2. fly ash stabilization 3. lime stabilization..
Benefit of fly ash
Reduced Water Content Improved Workability Reduced Segregation Improved Pumpability Improved Finishing Low Heat of Hydration Lower Drying Shrinkage Improved Long Term Strength Decreased Permeability Increased Durability Improved resistance to Alkali Silica Reactivity Improved resistance to Sulfate Attack Low Chloride Ingress Good Carbonation Protection Reduced Efflorescence
CONCLUSION:
Fly ash thus holds a vast potential for improving the modern day concrete when it comes to quality in the long term. In spite of being an industrial waste, it can improve durability and reduce heat of hydration.
The prospects of fly ash are still being underused even today. Thus keeping in mind about environmental concerns and its indispensability as a mineral admixture, the values of fly ash should be effectively garnered .
REFERENCES:
Concrete technology(theory and practice) –M.S shetty
Activation of fly ash through Nanomodification- ACI spring convention Shiho
Kawashima, Columbia University
Enhancing performance of high volume fly ash concrete –ACI spring convention.
magazine of concrete research- volume 64
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