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