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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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