EFFECT OF FLY ASH WITH LIME ADDITION ON DURABILITY OF

CONCRETE

ADITYA DIVYADARSHI 1311022 CV-05

BY

FLY ASH-INTRODUCTION

• Fly ash is a fine powder produced as a product from industrial plants using pulverized coal or lignite as fuel.

• It is the most widely used pozzolan siliceous or aluminosiliceous in nature in a finely divided form.

• They are spherical shaped “balls’’ finer than cement particles.

FLY ASH AS A SUPPLEMENTARY:

Apart from technical advantages it attributes to the concrete properties, fly ash has its own benefits

• Problem of disposal: In India alone, we produce 75 million tons of fly

ash every year, the disposal of which has become a serious environmental problem. The effective use of fly ash in concrete making is therefore attracting serious considerations of concrete technologists and government departments.

Global CO2 emissions:

Global cement production is about 1.3 billion tons in 1996 and production of every 1 ton of cement emits 0.87 ton of carbon dioxide.

In broader terms, 7% of global CO2 emissions can be attributed to Portland cement industry.

FLY ASH IN CONCRETE:

Fly ash could be an expensive replacement for Portland cement in concrete and using it, improves strength, segregation and ease of pumping 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.

The rate of substitution typically specified is a minimum of 1 to 1 ½ pounds of fly ash to 1 pound of cement

• Class F is fly ash produced from burning anthracite or bituminous coal, and Class C is produced from the burning of sub-bituminous coal and lignite.

• Class F is low in lime, under 15 percent, and contains a greater combination of silica, alumina and iron (greater than 70 percent) than Class C fly ash.

• Class C fly ash comes from coals which may produce an ash with higher lime content — generally more than 15 percent often as high as 30 percent. Elevated CaO may give Class C unique self-hardening characteristics.

PHYSICAL PROPERTY OF FLY ASH

PROPERTIES OF FLY ASH

CHEMICAL PROPERTY OF FLY ASH

The fly ash from boilers where mechanical collectorsare used is coarser than fly ash from electrostatic precipitators.

The color varies from light to dark grey depending upon its carbon contents.

The quality of fly ash varies from source to source.

fly ash particles are small, they effectively fill voids

 

PHYSICAL ASPECTS:

Though fly ash offers environmental advantages it also improves the:

Performance and quality of concrete. Fly ash affects the plastic properties of

concrete by improving workability Reduces water demand Reduces segregation and bleeding.Lowers heat of hydration. Fly ash increases strengthReduces permeability

MECHANICAL ATTRIBUTES:

The main benefit of fly ash in concrete is that it not only reduces the amount of non durable calcium hydroxide (lime), but in the process converts it into calcium silicate hydrate (CSH), which is the strongest and most durable portion of the paste in concrete. 

REACTION WITH MOISTURE:

HEAT OF HYDRATION:

•Fly Ash has a lower heat of hydration.

•Portland Cement produces considerable heat upon 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.

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.

• http://www.concretebasics.org/articlesinfo/fa8.php#sthash.r8p7Ivtk.dpuf

• magazine of concrete research- volume 64

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