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A

SEMINAR REPORT

ON

“FLY ASH CONCRETE”

SUBMITTED TO: SUBMITTED TO:

LOKESH KUMAR Frof.S.K.PATIDAR

1130260 (CIVIL ENGINEERING DEPT.)

C-3

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ACKNOWLEDGEMENT

I would like to thank respected Prof. S.K.PATIDAR for

giving me such a wonderful opportunity to expand my

knowledge for my own branch and giving me guidelines

to present a seminar report. It helped me a lot to realize

of what we study for.

I would like to thank my friends who helped me to make

my work more organized and well-stacked till the end.

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CONTENTS

INTRODUCTION

DEFINATION

HISTORY

CHEMICAL COMPOSITION

EFFECT OF FLY ASH ON FRESH CONCRETE

EFFECT OF FLY ASH ON HARDENED

CONCRETE AND DURABILITY

ADVANTAGES

USES OF FLY ASH CONCRETE

LIMITATIONS

CONCLUSION

REFERENCES

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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 pozzolona siliceous or aluminosiliceous in nature

in a finely divided form .They are spherical shaped “balls’’

finer than cement particles.

Fly ash is a fine, glass like powder recovered from the gases of

coal fired electricity production Inexpensive replacement of

Portland Cement Improves strength, segregation and ease of

pumping the concrete

DEFINATION:

“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.”

Fly ash is a by-product of coal-fired electric generating

plants.

HISTORY:

The Fly Ash story begins 2000 years ago...

When the Romans built the Colosseum in the year 100 A.D.

- that still stands the test of time!!

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The Roman Colosseum

The ash generated from Volcanoes was used extensively in

the construction of Roman structures. Colosseum is a classic

example of durability achieved by using volcanic ash.

This is a building constructed 2000 years ago and still

standing today.

The Roman Empire

The Romans knew that certain volcanic materials (now called

pozzolans) when finely ground and mixed with lime and sand,

yielded a mortar that was not only cementitious, but water

resistant and very strong.Both the Pantheon temple and the

Roman Coliseum were built with high volumes of volcanic

ash in the cement mixture.The Pantheon, built in Rome in 128

A.D., is a circular concrete temple with walls 6.1 meters thick

and a dome measuring 43.3 meters in diameter. The building

still stands in its original form due to the excellent quality of

the mortar mixture and careful selection of aggregate material.

In the event of an earthquake, the building distorts rather than

collapsing and moves with the shifts of the earth instead of

cracking.

Ancient concrete mixtures were characterized by low

cementitious material content, low water content, a very slow

rate of development and little shrinking or cracking from

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drying. Today’s ashes from coal-fired power plants have

similar properties to the volcanic ash used by the Romans.

Fly ash concrete was first used in the United States in 1929

for construction of the Hoover Dam.

In India, first used in RIHAD dam.

CHEMICAL COMPOSITION:

1. Fly ash are amorphous (glassy) due to rapid cooling; those

of cement are crystalline, formed by slower cooling.

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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

EFFECT OF FLY ASH ON FRESH CONCRETE:

Workability

Fly ash improves the workability of the concrete. Workability

refers to the ease of handling, placing and finishing of fresh or

“plastic” concrete. The fly ash concrete is more workable than

a plain cement concrete at equivalent slump. Less water is

needed for the same slump, the concrete gets more cohesive

and the occurrence of costly segregation decreases. The amount

of fines will increase and make the concrete more workable and

a more complete compaction.

According to ACI Bulletin the fly ash particles fill the voids

between aggregates, and the spherical particle shape acts as a

lubricant in the pump line. Another explanation of the better

workability is the greater paste volume when the cement is

replaced 1-to-1. The fly ash occupies 30 % greater volume than

the cement.

Concrete pumping is made easier. Form filling becomes easier.

Fly ash concrete is more responsive to vibration. Segregation,

voids, rock pockets are reduced because of increased

cohesiveness and workability.

Water content

The water demand and workability are controlled by particle

size distribution, particle packing effect, and smoothness of

surface texture.

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As mentioned above the fly ash replacing some of the cement

will increase the paste volume. The fly ash concrete is more

workable and less water is needed for the same slump.

Although increased fineness usually increases the water

demand, the spherical particle shape of the fly ash lowers

particle friction and offsets such effects.

The use of fly ash as a partial replacement for Portland cement

will usually reduce water demand.

Setting time

NS-EN 450-1 demands the initial setting time not to be more

than 120 minutes longer when the fly ash is tested. When the

fly ash is ground together with the clinker the setting time of

the composite cement is improved and regulated with the

fineness and the gypsum content.

Cold weather can have detrimental effects on concrete

construction unless adjustments are made and precautions are

taken to ensure acceptable performance. The ACI defines cold

weather as any time three consecutive days exhibit average

daily temperature less than 40°F (4.4 °C). Both conventional

and fly ash concrete that performs well at normal temperatures

may perform unacceptably in cold condition because of the

decreased rate of hydration. If the concrete mix is adjusted, it

is possible to reach the setting and strength gain required.

The setting time for the high volume fly ash concrete at Liu

Centre was in general somewhat longer than for a conventional

concrete.

High volume fly ash concrete hydrates more slowly than an

ordinary concrete. This factor, which increases with increasing

fly ash replacement dosage, presents a problem in concrete

construction where rapid stripping and turnaround are essential.

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Bleeding and segregation

The bleeding of high volume fly ash concrete ranges from

negligible to very low because of its low water content. It is

important to cure the concrete as soon as possible after

placement. In flat work, the use of foggers at the job site is

strongly recommended in order to prevent plastic shrinkage

cracking.

Less water is needed for the same slump, the concrete gets more

cohesive and the occurrence of costly segregation reduces.

Using fly ash in concrete mixtures usually reduces bleeding.

The use of fly ash compensate for a deficiency of fines in the

mixture, at the same time, it acts as a water-reducer to promote

workability at lower water content. This results in adequate

cohesion and plasticity with less water available for bleeding.

Using fly ash concrete mixtures usually reduces bleeding by

providing greater fines volume and lower water content for a

given workability. Increased fineness usually increases the

water demand, the spherical particle shape of fly ash lowers

particle friction and offsets such effects. Concrete with

relatively high fly ash content will require less water than non-

fly ash concrete of equal slump.

In 1985, CANMET developed a concrete with large volumes

of fly ash8. When building the Liu Centre for the Study of

Global Issues it was used high-volume fly ash concrete in part

of the building to demonstrate the potential of this type of

concrete with 50-55 % fly ash. The bleeding of this type of

concrete ranges from being very low to negligible due to the

very low water content (w/cm<0,35).

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Heat of hydration

In large concrete block, 3.05 x 3.05 x 3.05 m, the maximum

temperature reached in the middle of the block was 54°C (a rise

of 35°C when the start temperature was 19°C)3. The control

concrete incorporating ASTM type I Portland cement has a

temperature rise of 65°C.

A slower reaction rate of fly ash, when compared to hydraulic

cement, limits the amount of early heat generation and the

detrimental early temperature rise in massive structures1.

The high-volume fly ash concrete used in the Liu Centre show

a rather low autogenous temperature rise8. Several

investigations have shown that the autogenous temperature rise

of high-volume fly ash concrete was about 15-25°C less than

that of a reference concrete without fly ash. This is an

advantage where thermal gradient and stress are an issue.

Concretes have been made using high-volume fly ash blended

cements (55 % Class F fly ash), one coarse and one finer fly

ash and concrete in which the same fly ash had been added as

a separate material at the mixer9. Blaine of the fly ashes were

respectively 196 and 306 m2/ kg. Reference concretes (ASTM

type III cement and laboratory made normal Portland cement)

without fly ash were also made. The autogenous temperature

rise was significantly lower and slower for the concrete

incorporating fly ash (both fly ash blended cement and fly ash

to the concrete mixer) than for the control concretes without fly

ash.

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EFFECT OF FLY ASH ON HARDENED

CONCRETE AND DURABILITY:

Strength development

Usually strength development is very slow due to pozzolanic

reaction of fly ash.

Later age strength is higher.

Exceeds the strength of concrete without fly ash.

Enough curing should be available for long time.

Fly ash under water will be more beneficial.

In conventional concrete the flexural strength reaches a

maximum value between 14 and 28 days3. In high volume fly

ash concrete the strength keeps on increasing with age because

of the pozzolanic reaction of fly ash, and strengthening of the

interfacial bond between cement paste and aggregate.

Due to slow pozzolanic reaction, the compressive strength at

later ages of high volume fly ash concrete will be general

good8. The properties are strongly dependent on the

characteristics of the cement and fly ash used. The ratios of the

flexural and splitting-tensile strengths to compressive strength

are comparable to the conventional concrete.

Concrete cores taken from a large experimental blocks made

from ready-mixed high volume fly ash concrete have shown a

compressive strength of 110 MPa after 10 years in outdoors

exposure10. This demonstrates a potential for long-term

strength gain in this type of concrete.

Concretes have been made using high-volume fly ash blended

cements (55 % Class F fly ash), one coarse and one finer fly

ash and concrete in which the same fly ash had been added as

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a separate material at the mixer9. The blain of the fly ash was

respectively 196 and 306 m2/ kg. The strength development of

the concrete made with blended cements was faster up to 28

days than that of the concrete in which unground fly ash was

added at the concrete mixer. The improvement when grinding

the fly ash with the cement is more significant for the fly ash

which has the lowest blain.

Coefficient of thermal expansion

For 40% replacement of fly ash the coefficient of thermal

expansion reduces by 4%.

Permeability

Reduced. fly ash blocks bleed channels reacting with lime and

alkalis filling pore spaces.

Increased fines and reduced water content.

Resistance to freeze thaw

Since more strength is attained it can with stand more freeze

thaw. Because intrusion of air voids is not there, freeze thaw

effect is less.

Durability of fly ash concrete

Sufficiently cured fly ash concrete has a dense structure and

hence more resistance to deleterious substances.

This reduces the corrosion of reinforcement.

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Class f fly ash reduces alkali -silica reactivity because of the

dense structure and hence expansion is reduced which increases

durability.

Because of the reduced permeability the chloride ingress is

reduced.

ADVANTAGES:

Increased workability

Concrete is easier to place with less effort, responding better

to vibration to fill forms more completely.

Increased ease of pumping

Pumping requires less energy; longer pumping distances are

possible.

Improved finishing

Sharp, clear architectural definition is easier to achieve.

Reduced bleeding

Fewer bleed channels decreases porosity and chemical attack.

Improved paste to aggregate contact results in enhanced bond

strengths.

Reduced segregation

Improved cohesiveness of fly ash concrete reduces segregation

that can lead to rock pockets.

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Greater strength

Fly ash increases in strength over time, continuing to combine

with free lime.

Decreased permeability

Increased density and long-term pozzolanic action of fly ash,

which ties up free lime, results in fewer bleed channels and

decreases permeability.

Increased durability

The lower permeability of concrete with fly ash also helps keep

aggressive compounds on the surface, where destructive action

is lessened. Fly ash concrete is also more resistant to attack by

sulfate, mild acid, and soft water.

Reduced heat of hydration

The pozzolanic reaction between fly ash and lime generates less

heat, resulting in reduced thermal cracking when fly ash is used

to replace a percentage of Portland cement.

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USES OF FLY ASH CONCRETE:

Used in buildings.

Used in roads.

Used in dam constructions.

Used in Water retaining structure.

Used in Self compacting concrete.

Used in Fly Ash Bricks:

Reduces excavation of clay.

Low cost of brick as compared to clay brick of same quality.

Number of bricks required per unit volume of construction is

less as dimensional accuracy is maintained.

Lesser consumption of mortar.

Better resistance to water damage.

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LIMITATIONS:

Bonding is lower due to smooth finish.

Longer Setting Times.

Life cycle is less than Portland cement concrete.

Groundwater contamination due to runoffs carrying ill-treated

flyash.

Cannot be used for structures requiring shorter setting time, a

demand which is expected by most of the engineers and

builders.

Air content control plays a vital role and can prove crucial for

the quality of flyash concrete. Too much reduction in air

content can be disastrous.

It is very difficult to use in winter season due to further

increase in already longer setting time.

Difficult to control colour of cement containing flyash. Hence,

a bit problematic to use where cosmetic quality plays a

significant role.

Groundwater contamination due to runoffs carrying ill-treated

flyash.

Cannot be used for structures requiring shorter setting time, a

demand which is expected by most of the engineers and

builders.

Air content control plays a vital role and can prove crucial for

the quality of flyash concrete. Too much reduction in air

content can be disastrous.

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It is very difficult to use in winter season due to further increase

in already longer setting time.

Difficult to control colour of cement containing flyash. Hence,

a bit problematic to use where cosmetic quality plays a

significant role.

CONCLUSION:

Fly ash can be declared as one of the most advantageous waste

material. Using it as a construction material will not only help

in its disposal but will also add strength and durability of

structures. Since, the current usage of fly ash in India is still

around 25% and below 45% even in the developed countries

like United States, there is a huge scope for fly ash in upcoming

years. So let us harness a billion dollar resource that has been

wasted so far.

REFERENCES:

http://civilengineersforum.com/fly-ash-in-concrete-

advantages-disadvantages/

https://en.wikipedia.org/wiki/Fly_ash

http://flyash.com/data/upfiles/resource/Fly%20Ash%20for%2

0Concrete%202014.pdf

https://www.fhwa.dot.gov/pavement/images/fafig33.gif

http://www.slideshare.net/mkmanish454/fly-ash-concrete-ppt

https://books.google.co.in/books?id=8ITxm7zHul4C&printse

c=frontcover&dq=fly+ash+concrete&hl=en&sa=X&ved=0ah

UKEwjH_IujgrnKAhXBVo4KHfXUAUoQ6AEIHDAA#v=o

nepage&q=fly%20ash%20concrete&f=false

www.sintef.no/publikasjon/download/?pubid=sintef+a20092

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