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7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 16
Reciept No 133
Utilisation of Fly Ash in Cement Concrete
Pramey M ZodeSE (Civil)
Sinhgad Academy of Engineering
Kondhwa(Bk) Pune-48 (India)E-mail pramey17gmailcom
Abstract - To meet the ever increasing demand of electricity
Thermal Power Plants (TPPs) are being set up all over the
world thereby resulting into more consumption of the coal
in these plants The disposal of ash derived from combustion
has become a major issue now-a-days The study of Fly Ash
as it is called has found that it can be used in various civil
engineering applications such as bricks and concrete
making This paper reviews the utilisation of Fly Ash as the
admixture in partial replacement of ordinary Portland
cement to upto 35 and even more upto 50 in High-Volume Fly Ash (HVFA) concrete which reduces the water
demand improves the workability minimizes cracking due
to thermal and drying shrinkage and enhances durability to
reinforcement corrosion sulphate attack and alkali-silica
expansion This admixing proves to be a best filler material
which also reduce overall cost of construction and act as an
eco-friendly material
IINTRODUCTION
Ash is a residue resulting from combustion of pulverised
coal or lignite in Thermal Power Plants (TPPs) About 80 oftotal ash is in finely divided form which is carried away with
flue gases and is collected by electrostatic precipitator or other
suitable technology This ash is called Fly Ash or chimney
Ash or Hopper Ash In an industrial context fly ash usually
refers to ash produced as an industrial by-product during
combustion of coal in TPPs
Fly ash is a fine (85 of its mass passing through a 45983221m
screen) pozzolaneous or a siliceous andor aluminous glassy
powdered material having micron-sized earth elements which
in the presence of water and lime will react to form a
cementitous material It consists of inorganic materials mainly
silica and alumina with some quantum of organic material in
the form of unburnt carbon Fly ash also contains
environmental toxins in significant amounts including arsenic
(434 ppm) barium (806 ppm) beryllium (5 ppm) boron (311
ppm) cadmium (34 ppm) chromium (136 ppm) chromium
VI (90 ppm) cobalt (359 ppm) copper (112 ppm) fluorine
(29 ppm) lead (56 ppm) manganese (250 ppm) nickel
(776ppm) selenium (77 ppm) strontium (775 ppm)
thallium (9 ppm) vanadium (252 ppm) and zinc (178 ppm)
IISOURCES OF FLY ASH IN INDIA
According to National Thermal Power Corporation
(NTPC) coal is used for approximately 623 of electric
power generation in India According to Central Electricity
Authority of India there are around 83 major coal fired
thermal power plants in India As per the Ministry of Power
Statistics the total installed generating capacity (TPPs) is
about 79838 MW In addition to this there are more than
1800 selected industrial units which have TPPs of gt1MW
capacity These are the chief sources of fly ash in India
IIIASH CONTENT IN INDIAN COAL
The quality of coal depends upon its rank and grade The
coal rank arranged in an ascending order of carbon contents is
Lignite --gt sub-bituminous coal --gt bituminous coal --gt
anthracite
Indian coal is of mostly sub-bituminous rank followed by
bituminous and lignite (brown coal) Thus the ash content in
Indian coal ranges from 35 to 50
IVCURRENT FLY ASH GENERATION IN INDIA
The current electricity generation in India is about 112058
MW 65-70 of which is thermal (mostly coal based)
According to an estimate 100000 MW capacity or more
would be required in the next 10 years due to continually
increasing demand for electricity Thus the present fly ash
generation in India is around 110 million tonnes year and is
set to continue at a high rate into the foreseeable future
VCURRENT FLY ASH UTILISATION
According to the MOEF Gazette Notification dated Sept
14 1999 the then existing power stations were to achieve
20 ash utilization within three years and 100 utilization in
15 years from the date of notification New Stations were to
achieve 30 ash utilization within 9 years at the rate of 10
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 26
ash utilization within 3 years Presently out of 110 million
tonnes of total ash generated only about 30 is being
utilized Therefore thermal power stations are under great
pressure to find useful applications of fly ash The technology
utilizing fly ash in high volume fly ash concrete can provide
an avenue for utilization of fly ash on a bulk scale
VI PROBLEMS DUE TO FLY ASH
Fly ash is a very fine powder and tends to travel far in the
air When not properly disposed it is known to pollute air andwater and causes respiratory problems when inhaled When it
settles on leaves and crops in fields around the power plant it
lowers the yield The conventional method used for disposal
of both fly ash and bottom ash is to convert them into slurry
for impounding in ash ponds around the thermal plants Thismethod entails long-term problems The severe problems that
arise from such dumping are
1) The construction of ash ponds requires vast tracts of land
This depletes land available for agriculture over a period of
time
2) When one ash pond fills up another has to be built at great
cost and further loss of agricultural land
3) Huge quantities of water are required to convert ash into
slurry During rains numerous salts and metallic content inthe slurry can leach down to the groundwater and contaminate
it
Taking into account these facts fly ash is being used in
various construction activities as a raw material In this paper
detailed study of use of fly ash in raw materials like Portland
cement is considered Further this paper reviews the use of
high volume fly ash in cement making for better yield
FLY ASH BASED POZZOLANA PORTLAND
CEMENT
IPOZZOLANS
Pozzolans are defined as silicious and aluminous materials
which in themselves possess little or no cementitious value
but in finely divided form and in the presence of moisture it
chemically react with calcium hydroxide at ordinary
temperature to form compounds possessing cementitious
properties
IICLASS F FLY ASH
The burning of harder older anthracite and bituminous
coal typically produces Class F fly ash This fly ash is
pozzolanic in nature and contains less than 20 lime (CaO)
Possessing pozzolanic properties the glassy silica and
alumina of Class F fly ash requires a cementing agent such
Portland cement quicklime or hydrated lime with the
presence of water in order to react and produce cementitious
compounds
Most of the state and federal specifications allow and even
encourage the use of Fly Ash especially when specificdurability requirements are needed Fly Ash has a long history
of use in concrete Fly Ash is used in about 50 of ready
mixed concrete Class C Fly Ash is used at dosages of 15 to40 by mass of the cementitious materials in the concrete
Class F is generally used at dosages of 15 to 30
IIIFLY ASH IN PORTLAND CEMENT
Owing to its pozzolanic properties fly ash is used as a
replacement for some of the Portland cement content of
concrete The use of fly ash as a pozzolanic ingredient was
recognized as early as 1914 although the earliest noteworthystudy of its use was in 1937Before its use was lost to the Dark
Ages Roman structures such as aqueducts or the Pantheon in
Rome used volcanic ash (which possesses similar properties to
fly ash) as pozzolan in their concrete As pozzolan greatly
improves the strength and durability of concrete the use of
ash is a key factor in their preservation
Use of fly ash as a partial replacement for Portland cement
is generally limited to Class F fly ashes It can replace up to
30 by mass of Portland cement and can add to the final
strength of concrete and increase its chemical resistance and
durability Recently concrete mix design for partial cement
replacement with High Volume Fly Ash (50 cement
replacement) has been developed For Roller Compacted
Concrete (RCC) [used in dam construction] replacement
values of 70 have been achieved with processed fly ash at
the Ghatghar Dam project in Maharashtra India Due to the
spherical shape of fly ash particles it can also increase
workability of cement while reducing water demand The
replacement of Portland cement with fly ash is considered by
its promoters to reduce the greenhouse gas footprint of
concrete as the production of one ton of Portland cement
produces approximately one ton of CO2 as compared to zeroCO2 being produced using existing fly ash New fly ash
production ie the burning of coal produces approximately
twenty to thirty tons of CO2 per ton of fly ash Since the
worldwide production of Portland cement is expected to reach
nearly 2 billion tons by 2012 replacement of any large portion
of this cement by fly ash can significantly reduce carbon
emissions associated with construction
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 36
Inclusion of Fly Ash in Portland cement based plastic
concrete mixes improves concrete workability by reducing the
water content for a given consistency The spherical particles
create a lsquoball bearingrsquo effect in the mix ndash thus improving
workability Fly Ash particles also fill voids in the mix which
reduces the water requirement for a given plastic consistency
Workable Fly Ash concrete places easier finishes better and
produces better lsquooff-formrsquo surfaces than plain Portland cement
concrete For use in concrete Fly Ash is referred to as a
lsquosupplementary cementitious materialrsquo
IVCHEMICAL COMPARISION OF FLY ASH AND
PORTLAND CEMENT
The chemical composition of fly ash is very similar to that
of portland cement
TABLE I
TYPICAL CHEMICAL COMPOUNDS
IN POZZOLANIC CLASS F FLY ASH AND PORTLAND CEMENT
Chemical
compound
Class F fly ash Cement
SiO 5490 260
Al2O3 2580 430
Fe2O3 690 240
CaO 870 6440
MgO 180 210
SO2 060 230
Na2O amp K 2O 060 060
The table above shows typical compound analysis for
Class F fly ash and ordinary portland cement A glance at the
table reveals
1 The same compounds exist in fly ash and portland cement
Those of fly ash are amorphous (glassy) due to rapid cooling
those of cement are crystalline formed by slower cooling
2 The major difference between fly ash and portland cement
is the relative quantity of each of the several compounds in
them Portland cement is rich in lime (CaO) while fly ash is
low Fly ash is rich in reactive silicates while Portland cement
has smaller amounts
Portland Cement + Water Calcium Silicate Hydrate
Free Lime (CaOH)
Portland Cement + Water
+ Fly Ash Calcium Silicate Hydrate
Portland cement is manufactured with CaO some of which
is released in a free state during hydration As much as 20
pounds of free lime is released during hydration of 100
pounds of cement This liberated lime forms the necessary
ingredient for reaction with fly ash silicates to form strong and
durable cementing compounds no different from those formed
during hydration of ordinary Portland cement A review of the
chemistry of both materials makes it apparent that a blend of
the two will enhance the concrete product and efficiently
utilize the properties of both
VADVANTAGES OF FLY ASH BASED PORTLAND
CEMENT
AFly Ash improves concrete workability and lowers waterdemand
Fly Ash particles are mostly spherical tiny glass beads
Ground materials such as Portland Cement are solid angular particles 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 waterrequirement for the same concrete consistency Pump ability
is greatly enhanced
BFly Ash generally exhibit less bleeding and segregation than plain concretes
This makes the use of Fly Ash particularity valuable in
concrete mixtures made with aggregates deficient in fines
CSulphate and Alkali Aggregate Resistance
Class F and a few Class C Fly Ashes impart significant
sulphate resistance and alkali aggregate reaction resistance tothe concrete mixture
DFly 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
FFly Ash generally reduces the permeability and adsorption
of concrete
By reducing the permeability of chloride ion corrosion of
embedded steel is greatly decreased Also chemical resistanceis improved by the reduction of permeability and adsorption
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 46
GFly Ash is economical
The cost of Fly Ash is generally less than Portland Cement
depending on transportation Significant quantities may be
substituted for Portland Cement in concrete mixtures and thusincrease the long term strength and durability Thus the use of
Fly Ash may impart considerable benefits to the concrete
mixture over a plain concrete for less cost
HIGH-VOLUME FLY ASH (HVFA) CONCRETE
Fly Ash has a vast potential for use in High Volume Fly
Ash (HVFA) concrete especially due to its physic-chemical
properties Considerable amount of research has already been
done in India and abroad on its strength and other requisite
parameters In commercial practice the dosage of fly ash is
limited to 15-20 by mass of the total cementitious
material Usually this amount has a beneficial effect on the
workability and cost economy of concrete but it may not be
enough to sufficiently improve the durability to sulphate
attack alkali-silica expansion and thermal cracking Thus
from theoretical considerations and practical experience it is
established that with 50 or more cement replacement by fly
ash it is possible to produce sustainable high performance
concrete mixtures that show high workability high ultimate
strength and high durability
ICHARACTERISTICS DEFINING HVFA CONCRETE
MIXTURE
The characteristics defining a HVFA concrete mixture are
as follows
1) Minimum of 50 of fly ash by mass of the cementitious
materials must be maintained
2) Low water content generally less than 130 kgm3 is
mandatory
3) Cement content generally no more than 200kgm3 is
desirable
4) For concrete mixtures with specified 28-day compressive
strength of 30 MPa or higher slumps greater than 150 mm
and water-to-cementitious materials ratio of the order of 030
the use of high range water-reducing admixtures
(superplasticizers) is mandatory
5) For concrete exposed to freezing and thawing
environments the use of an air-entraining admixture resulting
in adequate air-void spacing factor is mandatory
6) For concrete mixtures with slumps less than 150 mm and
28-day compressive strength of less than 30 MPa HVFA
concrete mixtures with a water-to-cementitious materials ratio
of the order of 040 may be used without superplasticizers
IIMECHANISMS BY WHICH FLY ASH IMPROVES THE
PROPERTY OF CONCRETE
A good understanding of the mechanisms by which fly ash
improves the rheological properties of fresh concrete and
ultimate strength as well as durability of hardened concrete is
helpful to insure that potential benefits expected from HVFA
concrete mixtures are fully realized These mechanisms are
discussed next
AFly ash as a water reducer
There are two reasons why typical concrete mixtures
contain too much mixing-water Typical concrete mixtures do
not have an optimum particle size distribution and this
accounts for the undesirably high water requirement to
achieve certain workability Secondly to plasticize a cement
paste for achieving a satisfactory consistency much larger
amounts of water than necessary for the hydration of cement
have to be used because portland cement particles due to the
presence of electric charge on the surface tend to form flocs
that trap volumes of the mixing water It is generally observed
that a partial substitution of portland cement by fly ash in a
mortar or concrete mixture reduces that water requirement for
obtaining a given consistency Experimental studies have
shown that with HVFA concrete mixtures depending on thequality of fly ash and the amount of cement replaced up to
20 reduction in water requirements can be achieved This
means that good fly ash can act as a superplasticizing
admixture when used in high-volume The phenomenon is
attributable to three mechanisms First fine particles of fly ash
get absorbed on the oppositely charged surfaces of cement
particles and prevent them from flocculation The cement
particles are thus effectively dispersed and will trap large
amounts of water that means that the system will have a
reduced water requirement to achieve a given consistency
Secondly the spherical shape and the smooth surface of flyash particles help to reduce the interparticle friction and thus
facilitates mobility Thirdly the ldquoparticle packing effectrdquo is
also responsible for the reduced water demand in plasticizing
the system It may be noted that both portland cement and fly
ash contribute particles that are mostly in the 1 to 45 983221m size
range and therefore serve as excellent fillers for the void
space within the aggregate mixture In fact due to its lower
density and higher volume per unit mass fly ash is a more
efficient void-filler than portland cement
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 56
BDrying shrinkage
Perhaps the greatest disadvantage associated with the use
of neat portland-cement concrete is cracking due to drying
shrinkage The drying shrinkage of concrete is directly
influenced by the amount and the quality of the cement paste
present It increases with an increase in the cement paste-to-
aggregate ratio in the concrete mixture and also increases
with the water content of the paste Clearly the water-
reducing property of fly ash can be advantageously used for
achieving a considerable reduction in the drying shrinkage of
concrete mixtures Table 2 shows mixture proportions of a
conventional 25 MPa concrete compared to a superplasticized
HVFA concrete with similar strength but higher slump Due to
a significant reduction in the water requirement the total
volume of the cement paste in the HVFA concrete is only
25 as compared to 296 for the conventional portland-
cement concrete which represents a 30 reduction in the
cement paste-to-aggregate volume ratio
TABLE 2
COMPARISION OF CEMENT PASTE VOLUMES
Conventional
concrete
HVFA
concrete
kgm3 m
3 kgm
3 m
3
Cement 307 0098 154 0149
Fly ash - - 154 0065
Water 178 0178 120 0120
Entrapped air
(2)
- 0020 - 0020
Course aggregate 1040 0385 1210 0448
Fine aggregate 825 0305 775 0287
Total 2350 0986 2413 0989
wcm 058 - 039 -
Paste volume - 0296 - 0254
Paste percent - 300 - 257
CThermal cracking
Thermal cracking is of serious concern in massive concrete
and reinforced concrete structures For unreinforced mass-
concrete construction several methods are employed to
prevent thermal cracking and some of these techniques can be
successfully used for mitigation of thermal cracks in massive
reinforced-concrete structures For instance a 40-MPa
concrete mixture containing 350 kgm3 portland cement can
raise the temperature of concrete by approximately 55-60oC
within a week if there is no heat loss to the environment
However with a HVFA concrete mixture containing 50
cement replacement with a Class F fly ash the adiabatic
temperature rise is expected to be 30-35oC
DWater-tightness and durability
In general the resistance of a reinforced-concrete structure
to corrosion alkali aggregate expansion sulphate and other
forms of chemical attack depends on the water-tightness of theconcrete The water-tightness is greatly influenced by the
amount of mixing-water type and amount of supplementary
cementing materials curing and cracking resistance of
concrete High-volume fly ash concrete mixtures when
properly cured are able to provide excellent water-tightness
and durability The mechanisms responsible for this
phenomenon are discussed briefly below
When a concrete mixture is consolidated after placement
along with entrapped air a part of the mixing-water is also
released As water has low density it tends to travel to the
surface of concrete However not all of this ldquobleed waterrdquo is
able to find its way to the surface Due to the wall effect of
coarse aggregate particles some of it accumulates in the
vicinity of aggregate surfaces causing a heterogeneous
distribution of water in the system Obviously the interfacial
transition zone between the aggregate and cement paste is the
area with high watercement and therefore with more available
space that permits the formation of a highly porous hydration
product containing large crystals of calcium hydroxide and
ettringite Microcracks due to stress are readily formed
through this product because it is much weaker than the bulk
cement paste with a lower watercement It has been suggested
that microcracks in the interfacial transition zone play an
important part in determining not only the mechanical
properties but also the permeability and durability of concrete
exposed to severe environmental conditions This is because
the rate of fluid transport in concrete is much larger by
percolation through an interconnected network of microcracks
than by diffusion or capillary suction The heterogeneities in
the microstructure of the hydrated portland-cement paste
especially the existence of large pores and large crystalline
products in the transition zone are greatly reduced by the
introduction of fine particles of fly ash With the progress ofthe pozzolanic reaction a gradual decrease occurs in both the
size of the capillary pores and the crystalline hydration
products in the transition zone thereby reducing its thickness
and eliminating the weak link in the concrete microstructure
In conclusion a combination of particle packing effect low
water content and pozzolanic reaction accounts for the
eventual disappearance of the interfacial transition zone in
HVFA concrete and thus enables the development of a highly
crack-resistant and durable product
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 66
IIIPROPERTIES OF HVFA CONCRETE
Based on field experience and laboratory tests the
properties of HVFA concrete when compared to conventional
portland cement concrete can be summarized as follows
1) Easier flowability pumpability and compactability
2) Better surface finish and quicker finishing time when
power finish is not required
3) Slower setting time which will have a corresponding effect
on the joint cutting and lower power-finishing times for slabs
4) Early-strength up to 7 days which can be accelerated with
suitable changes in the mix design when earlier removal of
formwork or early structural loading is desired
5) Much later strength gain between 28 days and 90 days or
more (With HVFA concrete mixtures the strengthenhancement between 7 and 90-day often exceeds 100
therefore it is unnecessary to over design them with respect to
a given specified strength)
6) Superior dimensional stability and resistance to cracking
from thermal shrinkage autogenous shrinkage and drying
shrinkage
7) After three to six months of curing much higher electrical
resistivity and resistance to chloride ion penetration
according to ASTM Method C1202
8) Very high durability to the reinforcement corrosion alkali-
silica expansion and sulphate attack
9) Better cost economy due to lower material cost and highly
favorable lifecycle cost
10) Superior environmental friendliness due to ecological
disposal of large quantities of fly ash reduced carbon-dioxide
emissions and enhancement of resource productivity of the
concrete construction industry
CONCLUSION
The study of Fly Ash has shown that owing to its numerous
advantageous physical and chemical properties the material is
found to be one of the best admixtures in Portland cement
concrete and High Volume Fly Ash (HVFA) concrete making
which improves not only the quality but also its workability
subjected to various parameters Moreover the fly ash
concrete offers a holistic solution to the problem of fly ash
disposal which is one of the major issues now-a-days that too
in a sustainable manner at a reduced or no additional cost and
at the same time reducing the environmental impact of two
industries that are vital to economic development namely the
cement industry and the coal-fired power industry Thus it
also favours the Green Technology and waste management
which in turn helps in sustainable development
ACKNOWLEDGMENT
I wish to acknowledge the instructive guidance of Prof
RB Bajare Asst Professor and Prof Dr S R Parekar
HOD Dept of Civil Engineering Sinhgad Academy of
Engineering
REFERENCES
[1] Parisara ENVIS Newsletter (Vol2 No 6 January 2007) by State
Environment Related Issues Department of Forests Ecology and
Environment Government of Karnataka
[2 ] High Volume Fly-Ash Concrete Technology Fly Ash Summary Report in
India by Canadian International Development Agency (CIDA)
[3] P Kumar Mehta HIGH-PERFORMANCE HIGH-VOLUME FLY ASH
CONCRETE FOR SUSTAINABLE DEVELOPMENT International
Workshop on Sustainable Development and Concrete Technology University
of California Berkeley USA
[4] httpwwwashgroveresourcescom
[5] Fly ash From Wikipedia the free encyclopedia
[6] C N Jha amp J K Prasad ldquoFLY ASH A RESOURCE MATERIAL FOR
INNOVATIVE BUILDING MATERIAL - INDIAN PERSPECTIVErdquo
[7] Headwaters Resources Chemical Comparison of Fly Ash and Portland
Cement Bulletin No 2
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 26
ash utilization within 3 years Presently out of 110 million
tonnes of total ash generated only about 30 is being
utilized Therefore thermal power stations are under great
pressure to find useful applications of fly ash The technology
utilizing fly ash in high volume fly ash concrete can provide
an avenue for utilization of fly ash on a bulk scale
VI PROBLEMS DUE TO FLY ASH
Fly ash is a very fine powder and tends to travel far in the
air When not properly disposed it is known to pollute air andwater and causes respiratory problems when inhaled When it
settles on leaves and crops in fields around the power plant it
lowers the yield The conventional method used for disposal
of both fly ash and bottom ash is to convert them into slurry
for impounding in ash ponds around the thermal plants Thismethod entails long-term problems The severe problems that
arise from such dumping are
1) The construction of ash ponds requires vast tracts of land
This depletes land available for agriculture over a period of
time
2) When one ash pond fills up another has to be built at great
cost and further loss of agricultural land
3) Huge quantities of water are required to convert ash into
slurry During rains numerous salts and metallic content inthe slurry can leach down to the groundwater and contaminate
it
Taking into account these facts fly ash is being used in
various construction activities as a raw material In this paper
detailed study of use of fly ash in raw materials like Portland
cement is considered Further this paper reviews the use of
high volume fly ash in cement making for better yield
FLY ASH BASED POZZOLANA PORTLAND
CEMENT
IPOZZOLANS
Pozzolans are defined as silicious and aluminous materials
which in themselves possess little or no cementitious value
but in finely divided form and in the presence of moisture it
chemically react with calcium hydroxide at ordinary
temperature to form compounds possessing cementitious
properties
IICLASS F FLY ASH
The burning of harder older anthracite and bituminous
coal typically produces Class F fly ash This fly ash is
pozzolanic in nature and contains less than 20 lime (CaO)
Possessing pozzolanic properties the glassy silica and
alumina of Class F fly ash requires a cementing agent such
Portland cement quicklime or hydrated lime with the
presence of water in order to react and produce cementitious
compounds
Most of the state and federal specifications allow and even
encourage the use of Fly Ash especially when specificdurability requirements are needed Fly Ash has a long history
of use in concrete Fly Ash is used in about 50 of ready
mixed concrete Class C Fly Ash is used at dosages of 15 to40 by mass of the cementitious materials in the concrete
Class F is generally used at dosages of 15 to 30
IIIFLY ASH IN PORTLAND CEMENT
Owing to its pozzolanic properties fly ash is used as a
replacement for some of the Portland cement content of
concrete The use of fly ash as a pozzolanic ingredient was
recognized as early as 1914 although the earliest noteworthystudy of its use was in 1937Before its use was lost to the Dark
Ages Roman structures such as aqueducts or the Pantheon in
Rome used volcanic ash (which possesses similar properties to
fly ash) as pozzolan in their concrete As pozzolan greatly
improves the strength and durability of concrete the use of
ash is a key factor in their preservation
Use of fly ash as a partial replacement for Portland cement
is generally limited to Class F fly ashes It can replace up to
30 by mass of Portland cement and can add to the final
strength of concrete and increase its chemical resistance and
durability Recently concrete mix design for partial cement
replacement with High Volume Fly Ash (50 cement
replacement) has been developed For Roller Compacted
Concrete (RCC) [used in dam construction] replacement
values of 70 have been achieved with processed fly ash at
the Ghatghar Dam project in Maharashtra India Due to the
spherical shape of fly ash particles it can also increase
workability of cement while reducing water demand The
replacement of Portland cement with fly ash is considered by
its promoters to reduce the greenhouse gas footprint of
concrete as the production of one ton of Portland cement
produces approximately one ton of CO2 as compared to zeroCO2 being produced using existing fly ash New fly ash
production ie the burning of coal produces approximately
twenty to thirty tons of CO2 per ton of fly ash Since the
worldwide production of Portland cement is expected to reach
nearly 2 billion tons by 2012 replacement of any large portion
of this cement by fly ash can significantly reduce carbon
emissions associated with construction
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 36
Inclusion of Fly Ash in Portland cement based plastic
concrete mixes improves concrete workability by reducing the
water content for a given consistency The spherical particles
create a lsquoball bearingrsquo effect in the mix ndash thus improving
workability Fly Ash particles also fill voids in the mix which
reduces the water requirement for a given plastic consistency
Workable Fly Ash concrete places easier finishes better and
produces better lsquooff-formrsquo surfaces than plain Portland cement
concrete For use in concrete Fly Ash is referred to as a
lsquosupplementary cementitious materialrsquo
IVCHEMICAL COMPARISION OF FLY ASH AND
PORTLAND CEMENT
The chemical composition of fly ash is very similar to that
of portland cement
TABLE I
TYPICAL CHEMICAL COMPOUNDS
IN POZZOLANIC CLASS F FLY ASH AND PORTLAND CEMENT
Chemical
compound
Class F fly ash Cement
SiO 5490 260
Al2O3 2580 430
Fe2O3 690 240
CaO 870 6440
MgO 180 210
SO2 060 230
Na2O amp K 2O 060 060
The table above shows typical compound analysis for
Class F fly ash and ordinary portland cement A glance at the
table reveals
1 The same compounds exist in fly ash and portland cement
Those of fly ash are amorphous (glassy) due to rapid cooling
those of cement are crystalline formed by slower cooling
2 The major difference between fly ash and portland cement
is the relative quantity of each of the several compounds in
them Portland cement is rich in lime (CaO) while fly ash is
low Fly ash is rich in reactive silicates while Portland cement
has smaller amounts
Portland Cement + Water Calcium Silicate Hydrate
Free Lime (CaOH)
Portland Cement + Water
+ Fly Ash Calcium Silicate Hydrate
Portland cement is manufactured with CaO some of which
is released in a free state during hydration As much as 20
pounds of free lime is released during hydration of 100
pounds of cement This liberated lime forms the necessary
ingredient for reaction with fly ash silicates to form strong and
durable cementing compounds no different from those formed
during hydration of ordinary Portland cement A review of the
chemistry of both materials makes it apparent that a blend of
the two will enhance the concrete product and efficiently
utilize the properties of both
VADVANTAGES OF FLY ASH BASED PORTLAND
CEMENT
AFly Ash improves concrete workability and lowers waterdemand
Fly Ash particles are mostly spherical tiny glass beads
Ground materials such as Portland Cement are solid angular particles 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 waterrequirement for the same concrete consistency Pump ability
is greatly enhanced
BFly Ash generally exhibit less bleeding and segregation than plain concretes
This makes the use of Fly Ash particularity valuable in
concrete mixtures made with aggregates deficient in fines
CSulphate and Alkali Aggregate Resistance
Class F and a few Class C Fly Ashes impart significant
sulphate resistance and alkali aggregate reaction resistance tothe concrete mixture
DFly 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
FFly Ash generally reduces the permeability and adsorption
of concrete
By reducing the permeability of chloride ion corrosion of
embedded steel is greatly decreased Also chemical resistanceis improved by the reduction of permeability and adsorption
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 46
GFly Ash is economical
The cost of Fly Ash is generally less than Portland Cement
depending on transportation Significant quantities may be
substituted for Portland Cement in concrete mixtures and thusincrease the long term strength and durability Thus the use of
Fly Ash may impart considerable benefits to the concrete
mixture over a plain concrete for less cost
HIGH-VOLUME FLY ASH (HVFA) CONCRETE
Fly Ash has a vast potential for use in High Volume Fly
Ash (HVFA) concrete especially due to its physic-chemical
properties Considerable amount of research has already been
done in India and abroad on its strength and other requisite
parameters In commercial practice the dosage of fly ash is
limited to 15-20 by mass of the total cementitious
material Usually this amount has a beneficial effect on the
workability and cost economy of concrete but it may not be
enough to sufficiently improve the durability to sulphate
attack alkali-silica expansion and thermal cracking Thus
from theoretical considerations and practical experience it is
established that with 50 or more cement replacement by fly
ash it is possible to produce sustainable high performance
concrete mixtures that show high workability high ultimate
strength and high durability
ICHARACTERISTICS DEFINING HVFA CONCRETE
MIXTURE
The characteristics defining a HVFA concrete mixture are
as follows
1) Minimum of 50 of fly ash by mass of the cementitious
materials must be maintained
2) Low water content generally less than 130 kgm3 is
mandatory
3) Cement content generally no more than 200kgm3 is
desirable
4) For concrete mixtures with specified 28-day compressive
strength of 30 MPa or higher slumps greater than 150 mm
and water-to-cementitious materials ratio of the order of 030
the use of high range water-reducing admixtures
(superplasticizers) is mandatory
5) For concrete exposed to freezing and thawing
environments the use of an air-entraining admixture resulting
in adequate air-void spacing factor is mandatory
6) For concrete mixtures with slumps less than 150 mm and
28-day compressive strength of less than 30 MPa HVFA
concrete mixtures with a water-to-cementitious materials ratio
of the order of 040 may be used without superplasticizers
IIMECHANISMS BY WHICH FLY ASH IMPROVES THE
PROPERTY OF CONCRETE
A good understanding of the mechanisms by which fly ash
improves the rheological properties of fresh concrete and
ultimate strength as well as durability of hardened concrete is
helpful to insure that potential benefits expected from HVFA
concrete mixtures are fully realized These mechanisms are
discussed next
AFly ash as a water reducer
There are two reasons why typical concrete mixtures
contain too much mixing-water Typical concrete mixtures do
not have an optimum particle size distribution and this
accounts for the undesirably high water requirement to
achieve certain workability Secondly to plasticize a cement
paste for achieving a satisfactory consistency much larger
amounts of water than necessary for the hydration of cement
have to be used because portland cement particles due to the
presence of electric charge on the surface tend to form flocs
that trap volumes of the mixing water It is generally observed
that a partial substitution of portland cement by fly ash in a
mortar or concrete mixture reduces that water requirement for
obtaining a given consistency Experimental studies have
shown that with HVFA concrete mixtures depending on thequality of fly ash and the amount of cement replaced up to
20 reduction in water requirements can be achieved This
means that good fly ash can act as a superplasticizing
admixture when used in high-volume The phenomenon is
attributable to three mechanisms First fine particles of fly ash
get absorbed on the oppositely charged surfaces of cement
particles and prevent them from flocculation The cement
particles are thus effectively dispersed and will trap large
amounts of water that means that the system will have a
reduced water requirement to achieve a given consistency
Secondly the spherical shape and the smooth surface of flyash particles help to reduce the interparticle friction and thus
facilitates mobility Thirdly the ldquoparticle packing effectrdquo is
also responsible for the reduced water demand in plasticizing
the system It may be noted that both portland cement and fly
ash contribute particles that are mostly in the 1 to 45 983221m size
range and therefore serve as excellent fillers for the void
space within the aggregate mixture In fact due to its lower
density and higher volume per unit mass fly ash is a more
efficient void-filler than portland cement
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 56
BDrying shrinkage
Perhaps the greatest disadvantage associated with the use
of neat portland-cement concrete is cracking due to drying
shrinkage The drying shrinkage of concrete is directly
influenced by the amount and the quality of the cement paste
present It increases with an increase in the cement paste-to-
aggregate ratio in the concrete mixture and also increases
with the water content of the paste Clearly the water-
reducing property of fly ash can be advantageously used for
achieving a considerable reduction in the drying shrinkage of
concrete mixtures Table 2 shows mixture proportions of a
conventional 25 MPa concrete compared to a superplasticized
HVFA concrete with similar strength but higher slump Due to
a significant reduction in the water requirement the total
volume of the cement paste in the HVFA concrete is only
25 as compared to 296 for the conventional portland-
cement concrete which represents a 30 reduction in the
cement paste-to-aggregate volume ratio
TABLE 2
COMPARISION OF CEMENT PASTE VOLUMES
Conventional
concrete
HVFA
concrete
kgm3 m
3 kgm
3 m
3
Cement 307 0098 154 0149
Fly ash - - 154 0065
Water 178 0178 120 0120
Entrapped air
(2)
- 0020 - 0020
Course aggregate 1040 0385 1210 0448
Fine aggregate 825 0305 775 0287
Total 2350 0986 2413 0989
wcm 058 - 039 -
Paste volume - 0296 - 0254
Paste percent - 300 - 257
CThermal cracking
Thermal cracking is of serious concern in massive concrete
and reinforced concrete structures For unreinforced mass-
concrete construction several methods are employed to
prevent thermal cracking and some of these techniques can be
successfully used for mitigation of thermal cracks in massive
reinforced-concrete structures For instance a 40-MPa
concrete mixture containing 350 kgm3 portland cement can
raise the temperature of concrete by approximately 55-60oC
within a week if there is no heat loss to the environment
However with a HVFA concrete mixture containing 50
cement replacement with a Class F fly ash the adiabatic
temperature rise is expected to be 30-35oC
DWater-tightness and durability
In general the resistance of a reinforced-concrete structure
to corrosion alkali aggregate expansion sulphate and other
forms of chemical attack depends on the water-tightness of theconcrete The water-tightness is greatly influenced by the
amount of mixing-water type and amount of supplementary
cementing materials curing and cracking resistance of
concrete High-volume fly ash concrete mixtures when
properly cured are able to provide excellent water-tightness
and durability The mechanisms responsible for this
phenomenon are discussed briefly below
When a concrete mixture is consolidated after placement
along with entrapped air a part of the mixing-water is also
released As water has low density it tends to travel to the
surface of concrete However not all of this ldquobleed waterrdquo is
able to find its way to the surface Due to the wall effect of
coarse aggregate particles some of it accumulates in the
vicinity of aggregate surfaces causing a heterogeneous
distribution of water in the system Obviously the interfacial
transition zone between the aggregate and cement paste is the
area with high watercement and therefore with more available
space that permits the formation of a highly porous hydration
product containing large crystals of calcium hydroxide and
ettringite Microcracks due to stress are readily formed
through this product because it is much weaker than the bulk
cement paste with a lower watercement It has been suggested
that microcracks in the interfacial transition zone play an
important part in determining not only the mechanical
properties but also the permeability and durability of concrete
exposed to severe environmental conditions This is because
the rate of fluid transport in concrete is much larger by
percolation through an interconnected network of microcracks
than by diffusion or capillary suction The heterogeneities in
the microstructure of the hydrated portland-cement paste
especially the existence of large pores and large crystalline
products in the transition zone are greatly reduced by the
introduction of fine particles of fly ash With the progress ofthe pozzolanic reaction a gradual decrease occurs in both the
size of the capillary pores and the crystalline hydration
products in the transition zone thereby reducing its thickness
and eliminating the weak link in the concrete microstructure
In conclusion a combination of particle packing effect low
water content and pozzolanic reaction accounts for the
eventual disappearance of the interfacial transition zone in
HVFA concrete and thus enables the development of a highly
crack-resistant and durable product
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 66
IIIPROPERTIES OF HVFA CONCRETE
Based on field experience and laboratory tests the
properties of HVFA concrete when compared to conventional
portland cement concrete can be summarized as follows
1) Easier flowability pumpability and compactability
2) Better surface finish and quicker finishing time when
power finish is not required
3) Slower setting time which will have a corresponding effect
on the joint cutting and lower power-finishing times for slabs
4) Early-strength up to 7 days which can be accelerated with
suitable changes in the mix design when earlier removal of
formwork or early structural loading is desired
5) Much later strength gain between 28 days and 90 days or
more (With HVFA concrete mixtures the strengthenhancement between 7 and 90-day often exceeds 100
therefore it is unnecessary to over design them with respect to
a given specified strength)
6) Superior dimensional stability and resistance to cracking
from thermal shrinkage autogenous shrinkage and drying
shrinkage
7) After three to six months of curing much higher electrical
resistivity and resistance to chloride ion penetration
according to ASTM Method C1202
8) Very high durability to the reinforcement corrosion alkali-
silica expansion and sulphate attack
9) Better cost economy due to lower material cost and highly
favorable lifecycle cost
10) Superior environmental friendliness due to ecological
disposal of large quantities of fly ash reduced carbon-dioxide
emissions and enhancement of resource productivity of the
concrete construction industry
CONCLUSION
The study of Fly Ash has shown that owing to its numerous
advantageous physical and chemical properties the material is
found to be one of the best admixtures in Portland cement
concrete and High Volume Fly Ash (HVFA) concrete making
which improves not only the quality but also its workability
subjected to various parameters Moreover the fly ash
concrete offers a holistic solution to the problem of fly ash
disposal which is one of the major issues now-a-days that too
in a sustainable manner at a reduced or no additional cost and
at the same time reducing the environmental impact of two
industries that are vital to economic development namely the
cement industry and the coal-fired power industry Thus it
also favours the Green Technology and waste management
which in turn helps in sustainable development
ACKNOWLEDGMENT
I wish to acknowledge the instructive guidance of Prof
RB Bajare Asst Professor and Prof Dr S R Parekar
HOD Dept of Civil Engineering Sinhgad Academy of
Engineering
REFERENCES
[1] Parisara ENVIS Newsletter (Vol2 No 6 January 2007) by State
Environment Related Issues Department of Forests Ecology and
Environment Government of Karnataka
[2 ] High Volume Fly-Ash Concrete Technology Fly Ash Summary Report in
India by Canadian International Development Agency (CIDA)
[3] P Kumar Mehta HIGH-PERFORMANCE HIGH-VOLUME FLY ASH
CONCRETE FOR SUSTAINABLE DEVELOPMENT International
Workshop on Sustainable Development and Concrete Technology University
of California Berkeley USA
[4] httpwwwashgroveresourcescom
[5] Fly ash From Wikipedia the free encyclopedia
[6] C N Jha amp J K Prasad ldquoFLY ASH A RESOURCE MATERIAL FOR
INNOVATIVE BUILDING MATERIAL - INDIAN PERSPECTIVErdquo
[7] Headwaters Resources Chemical Comparison of Fly Ash and Portland
Cement Bulletin No 2
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 36
Inclusion of Fly Ash in Portland cement based plastic
concrete mixes improves concrete workability by reducing the
water content for a given consistency The spherical particles
create a lsquoball bearingrsquo effect in the mix ndash thus improving
workability Fly Ash particles also fill voids in the mix which
reduces the water requirement for a given plastic consistency
Workable Fly Ash concrete places easier finishes better and
produces better lsquooff-formrsquo surfaces than plain Portland cement
concrete For use in concrete Fly Ash is referred to as a
lsquosupplementary cementitious materialrsquo
IVCHEMICAL COMPARISION OF FLY ASH AND
PORTLAND CEMENT
The chemical composition of fly ash is very similar to that
of portland cement
TABLE I
TYPICAL CHEMICAL COMPOUNDS
IN POZZOLANIC CLASS F FLY ASH AND PORTLAND CEMENT
Chemical
compound
Class F fly ash Cement
SiO 5490 260
Al2O3 2580 430
Fe2O3 690 240
CaO 870 6440
MgO 180 210
SO2 060 230
Na2O amp K 2O 060 060
The table above shows typical compound analysis for
Class F fly ash and ordinary portland cement A glance at the
table reveals
1 The same compounds exist in fly ash and portland cement
Those of fly ash are amorphous (glassy) due to rapid cooling
those of cement are crystalline formed by slower cooling
2 The major difference between fly ash and portland cement
is the relative quantity of each of the several compounds in
them Portland cement is rich in lime (CaO) while fly ash is
low Fly ash is rich in reactive silicates while Portland cement
has smaller amounts
Portland Cement + Water Calcium Silicate Hydrate
Free Lime (CaOH)
Portland Cement + Water
+ Fly Ash Calcium Silicate Hydrate
Portland cement is manufactured with CaO some of which
is released in a free state during hydration As much as 20
pounds of free lime is released during hydration of 100
pounds of cement This liberated lime forms the necessary
ingredient for reaction with fly ash silicates to form strong and
durable cementing compounds no different from those formed
during hydration of ordinary Portland cement A review of the
chemistry of both materials makes it apparent that a blend of
the two will enhance the concrete product and efficiently
utilize the properties of both
VADVANTAGES OF FLY ASH BASED PORTLAND
CEMENT
AFly Ash improves concrete workability and lowers waterdemand
Fly Ash particles are mostly spherical tiny glass beads
Ground materials such as Portland Cement are solid angular particles 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 waterrequirement for the same concrete consistency Pump ability
is greatly enhanced
BFly Ash generally exhibit less bleeding and segregation than plain concretes
This makes the use of Fly Ash particularity valuable in
concrete mixtures made with aggregates deficient in fines
CSulphate and Alkali Aggregate Resistance
Class F and a few Class C Fly Ashes impart significant
sulphate resistance and alkali aggregate reaction resistance tothe concrete mixture
DFly 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
FFly Ash generally reduces the permeability and adsorption
of concrete
By reducing the permeability of chloride ion corrosion of
embedded steel is greatly decreased Also chemical resistanceis improved by the reduction of permeability and adsorption
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 46
GFly Ash is economical
The cost of Fly Ash is generally less than Portland Cement
depending on transportation Significant quantities may be
substituted for Portland Cement in concrete mixtures and thusincrease the long term strength and durability Thus the use of
Fly Ash may impart considerable benefits to the concrete
mixture over a plain concrete for less cost
HIGH-VOLUME FLY ASH (HVFA) CONCRETE
Fly Ash has a vast potential for use in High Volume Fly
Ash (HVFA) concrete especially due to its physic-chemical
properties Considerable amount of research has already been
done in India and abroad on its strength and other requisite
parameters In commercial practice the dosage of fly ash is
limited to 15-20 by mass of the total cementitious
material Usually this amount has a beneficial effect on the
workability and cost economy of concrete but it may not be
enough to sufficiently improve the durability to sulphate
attack alkali-silica expansion and thermal cracking Thus
from theoretical considerations and practical experience it is
established that with 50 or more cement replacement by fly
ash it is possible to produce sustainable high performance
concrete mixtures that show high workability high ultimate
strength and high durability
ICHARACTERISTICS DEFINING HVFA CONCRETE
MIXTURE
The characteristics defining a HVFA concrete mixture are
as follows
1) Minimum of 50 of fly ash by mass of the cementitious
materials must be maintained
2) Low water content generally less than 130 kgm3 is
mandatory
3) Cement content generally no more than 200kgm3 is
desirable
4) For concrete mixtures with specified 28-day compressive
strength of 30 MPa or higher slumps greater than 150 mm
and water-to-cementitious materials ratio of the order of 030
the use of high range water-reducing admixtures
(superplasticizers) is mandatory
5) For concrete exposed to freezing and thawing
environments the use of an air-entraining admixture resulting
in adequate air-void spacing factor is mandatory
6) For concrete mixtures with slumps less than 150 mm and
28-day compressive strength of less than 30 MPa HVFA
concrete mixtures with a water-to-cementitious materials ratio
of the order of 040 may be used without superplasticizers
IIMECHANISMS BY WHICH FLY ASH IMPROVES THE
PROPERTY OF CONCRETE
A good understanding of the mechanisms by which fly ash
improves the rheological properties of fresh concrete and
ultimate strength as well as durability of hardened concrete is
helpful to insure that potential benefits expected from HVFA
concrete mixtures are fully realized These mechanisms are
discussed next
AFly ash as a water reducer
There are two reasons why typical concrete mixtures
contain too much mixing-water Typical concrete mixtures do
not have an optimum particle size distribution and this
accounts for the undesirably high water requirement to
achieve certain workability Secondly to plasticize a cement
paste for achieving a satisfactory consistency much larger
amounts of water than necessary for the hydration of cement
have to be used because portland cement particles due to the
presence of electric charge on the surface tend to form flocs
that trap volumes of the mixing water It is generally observed
that a partial substitution of portland cement by fly ash in a
mortar or concrete mixture reduces that water requirement for
obtaining a given consistency Experimental studies have
shown that with HVFA concrete mixtures depending on thequality of fly ash and the amount of cement replaced up to
20 reduction in water requirements can be achieved This
means that good fly ash can act as a superplasticizing
admixture when used in high-volume The phenomenon is
attributable to three mechanisms First fine particles of fly ash
get absorbed on the oppositely charged surfaces of cement
particles and prevent them from flocculation The cement
particles are thus effectively dispersed and will trap large
amounts of water that means that the system will have a
reduced water requirement to achieve a given consistency
Secondly the spherical shape and the smooth surface of flyash particles help to reduce the interparticle friction and thus
facilitates mobility Thirdly the ldquoparticle packing effectrdquo is
also responsible for the reduced water demand in plasticizing
the system It may be noted that both portland cement and fly
ash contribute particles that are mostly in the 1 to 45 983221m size
range and therefore serve as excellent fillers for the void
space within the aggregate mixture In fact due to its lower
density and higher volume per unit mass fly ash is a more
efficient void-filler than portland cement
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 56
BDrying shrinkage
Perhaps the greatest disadvantage associated with the use
of neat portland-cement concrete is cracking due to drying
shrinkage The drying shrinkage of concrete is directly
influenced by the amount and the quality of the cement paste
present It increases with an increase in the cement paste-to-
aggregate ratio in the concrete mixture and also increases
with the water content of the paste Clearly the water-
reducing property of fly ash can be advantageously used for
achieving a considerable reduction in the drying shrinkage of
concrete mixtures Table 2 shows mixture proportions of a
conventional 25 MPa concrete compared to a superplasticized
HVFA concrete with similar strength but higher slump Due to
a significant reduction in the water requirement the total
volume of the cement paste in the HVFA concrete is only
25 as compared to 296 for the conventional portland-
cement concrete which represents a 30 reduction in the
cement paste-to-aggregate volume ratio
TABLE 2
COMPARISION OF CEMENT PASTE VOLUMES
Conventional
concrete
HVFA
concrete
kgm3 m
3 kgm
3 m
3
Cement 307 0098 154 0149
Fly ash - - 154 0065
Water 178 0178 120 0120
Entrapped air
(2)
- 0020 - 0020
Course aggregate 1040 0385 1210 0448
Fine aggregate 825 0305 775 0287
Total 2350 0986 2413 0989
wcm 058 - 039 -
Paste volume - 0296 - 0254
Paste percent - 300 - 257
CThermal cracking
Thermal cracking is of serious concern in massive concrete
and reinforced concrete structures For unreinforced mass-
concrete construction several methods are employed to
prevent thermal cracking and some of these techniques can be
successfully used for mitigation of thermal cracks in massive
reinforced-concrete structures For instance a 40-MPa
concrete mixture containing 350 kgm3 portland cement can
raise the temperature of concrete by approximately 55-60oC
within a week if there is no heat loss to the environment
However with a HVFA concrete mixture containing 50
cement replacement with a Class F fly ash the adiabatic
temperature rise is expected to be 30-35oC
DWater-tightness and durability
In general the resistance of a reinforced-concrete structure
to corrosion alkali aggregate expansion sulphate and other
forms of chemical attack depends on the water-tightness of theconcrete The water-tightness is greatly influenced by the
amount of mixing-water type and amount of supplementary
cementing materials curing and cracking resistance of
concrete High-volume fly ash concrete mixtures when
properly cured are able to provide excellent water-tightness
and durability The mechanisms responsible for this
phenomenon are discussed briefly below
When a concrete mixture is consolidated after placement
along with entrapped air a part of the mixing-water is also
released As water has low density it tends to travel to the
surface of concrete However not all of this ldquobleed waterrdquo is
able to find its way to the surface Due to the wall effect of
coarse aggregate particles some of it accumulates in the
vicinity of aggregate surfaces causing a heterogeneous
distribution of water in the system Obviously the interfacial
transition zone between the aggregate and cement paste is the
area with high watercement and therefore with more available
space that permits the formation of a highly porous hydration
product containing large crystals of calcium hydroxide and
ettringite Microcracks due to stress are readily formed
through this product because it is much weaker than the bulk
cement paste with a lower watercement It has been suggested
that microcracks in the interfacial transition zone play an
important part in determining not only the mechanical
properties but also the permeability and durability of concrete
exposed to severe environmental conditions This is because
the rate of fluid transport in concrete is much larger by
percolation through an interconnected network of microcracks
than by diffusion or capillary suction The heterogeneities in
the microstructure of the hydrated portland-cement paste
especially the existence of large pores and large crystalline
products in the transition zone are greatly reduced by the
introduction of fine particles of fly ash With the progress ofthe pozzolanic reaction a gradual decrease occurs in both the
size of the capillary pores and the crystalline hydration
products in the transition zone thereby reducing its thickness
and eliminating the weak link in the concrete microstructure
In conclusion a combination of particle packing effect low
water content and pozzolanic reaction accounts for the
eventual disappearance of the interfacial transition zone in
HVFA concrete and thus enables the development of a highly
crack-resistant and durable product
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 66
IIIPROPERTIES OF HVFA CONCRETE
Based on field experience and laboratory tests the
properties of HVFA concrete when compared to conventional
portland cement concrete can be summarized as follows
1) Easier flowability pumpability and compactability
2) Better surface finish and quicker finishing time when
power finish is not required
3) Slower setting time which will have a corresponding effect
on the joint cutting and lower power-finishing times for slabs
4) Early-strength up to 7 days which can be accelerated with
suitable changes in the mix design when earlier removal of
formwork or early structural loading is desired
5) Much later strength gain between 28 days and 90 days or
more (With HVFA concrete mixtures the strengthenhancement between 7 and 90-day often exceeds 100
therefore it is unnecessary to over design them with respect to
a given specified strength)
6) Superior dimensional stability and resistance to cracking
from thermal shrinkage autogenous shrinkage and drying
shrinkage
7) After three to six months of curing much higher electrical
resistivity and resistance to chloride ion penetration
according to ASTM Method C1202
8) Very high durability to the reinforcement corrosion alkali-
silica expansion and sulphate attack
9) Better cost economy due to lower material cost and highly
favorable lifecycle cost
10) Superior environmental friendliness due to ecological
disposal of large quantities of fly ash reduced carbon-dioxide
emissions and enhancement of resource productivity of the
concrete construction industry
CONCLUSION
The study of Fly Ash has shown that owing to its numerous
advantageous physical and chemical properties the material is
found to be one of the best admixtures in Portland cement
concrete and High Volume Fly Ash (HVFA) concrete making
which improves not only the quality but also its workability
subjected to various parameters Moreover the fly ash
concrete offers a holistic solution to the problem of fly ash
disposal which is one of the major issues now-a-days that too
in a sustainable manner at a reduced or no additional cost and
at the same time reducing the environmental impact of two
industries that are vital to economic development namely the
cement industry and the coal-fired power industry Thus it
also favours the Green Technology and waste management
which in turn helps in sustainable development
ACKNOWLEDGMENT
I wish to acknowledge the instructive guidance of Prof
RB Bajare Asst Professor and Prof Dr S R Parekar
HOD Dept of Civil Engineering Sinhgad Academy of
Engineering
REFERENCES
[1] Parisara ENVIS Newsletter (Vol2 No 6 January 2007) by State
Environment Related Issues Department of Forests Ecology and
Environment Government of Karnataka
[2 ] High Volume Fly-Ash Concrete Technology Fly Ash Summary Report in
India by Canadian International Development Agency (CIDA)
[3] P Kumar Mehta HIGH-PERFORMANCE HIGH-VOLUME FLY ASH
CONCRETE FOR SUSTAINABLE DEVELOPMENT International
Workshop on Sustainable Development and Concrete Technology University
of California Berkeley USA
[4] httpwwwashgroveresourcescom
[5] Fly ash From Wikipedia the free encyclopedia
[6] C N Jha amp J K Prasad ldquoFLY ASH A RESOURCE MATERIAL FOR
INNOVATIVE BUILDING MATERIAL - INDIAN PERSPECTIVErdquo
[7] Headwaters Resources Chemical Comparison of Fly Ash and Portland
Cement Bulletin No 2
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 46
GFly Ash is economical
The cost of Fly Ash is generally less than Portland Cement
depending on transportation Significant quantities may be
substituted for Portland Cement in concrete mixtures and thusincrease the long term strength and durability Thus the use of
Fly Ash may impart considerable benefits to the concrete
mixture over a plain concrete for less cost
HIGH-VOLUME FLY ASH (HVFA) CONCRETE
Fly Ash has a vast potential for use in High Volume Fly
Ash (HVFA) concrete especially due to its physic-chemical
properties Considerable amount of research has already been
done in India and abroad on its strength and other requisite
parameters In commercial practice the dosage of fly ash is
limited to 15-20 by mass of the total cementitious
material Usually this amount has a beneficial effect on the
workability and cost economy of concrete but it may not be
enough to sufficiently improve the durability to sulphate
attack alkali-silica expansion and thermal cracking Thus
from theoretical considerations and practical experience it is
established that with 50 or more cement replacement by fly
ash it is possible to produce sustainable high performance
concrete mixtures that show high workability high ultimate
strength and high durability
ICHARACTERISTICS DEFINING HVFA CONCRETE
MIXTURE
The characteristics defining a HVFA concrete mixture are
as follows
1) Minimum of 50 of fly ash by mass of the cementitious
materials must be maintained
2) Low water content generally less than 130 kgm3 is
mandatory
3) Cement content generally no more than 200kgm3 is
desirable
4) For concrete mixtures with specified 28-day compressive
strength of 30 MPa or higher slumps greater than 150 mm
and water-to-cementitious materials ratio of the order of 030
the use of high range water-reducing admixtures
(superplasticizers) is mandatory
5) For concrete exposed to freezing and thawing
environments the use of an air-entraining admixture resulting
in adequate air-void spacing factor is mandatory
6) For concrete mixtures with slumps less than 150 mm and
28-day compressive strength of less than 30 MPa HVFA
concrete mixtures with a water-to-cementitious materials ratio
of the order of 040 may be used without superplasticizers
IIMECHANISMS BY WHICH FLY ASH IMPROVES THE
PROPERTY OF CONCRETE
A good understanding of the mechanisms by which fly ash
improves the rheological properties of fresh concrete and
ultimate strength as well as durability of hardened concrete is
helpful to insure that potential benefits expected from HVFA
concrete mixtures are fully realized These mechanisms are
discussed next
AFly ash as a water reducer
There are two reasons why typical concrete mixtures
contain too much mixing-water Typical concrete mixtures do
not have an optimum particle size distribution and this
accounts for the undesirably high water requirement to
achieve certain workability Secondly to plasticize a cement
paste for achieving a satisfactory consistency much larger
amounts of water than necessary for the hydration of cement
have to be used because portland cement particles due to the
presence of electric charge on the surface tend to form flocs
that trap volumes of the mixing water It is generally observed
that a partial substitution of portland cement by fly ash in a
mortar or concrete mixture reduces that water requirement for
obtaining a given consistency Experimental studies have
shown that with HVFA concrete mixtures depending on thequality of fly ash and the amount of cement replaced up to
20 reduction in water requirements can be achieved This
means that good fly ash can act as a superplasticizing
admixture when used in high-volume The phenomenon is
attributable to three mechanisms First fine particles of fly ash
get absorbed on the oppositely charged surfaces of cement
particles and prevent them from flocculation The cement
particles are thus effectively dispersed and will trap large
amounts of water that means that the system will have a
reduced water requirement to achieve a given consistency
Secondly the spherical shape and the smooth surface of flyash particles help to reduce the interparticle friction and thus
facilitates mobility Thirdly the ldquoparticle packing effectrdquo is
also responsible for the reduced water demand in plasticizing
the system It may be noted that both portland cement and fly
ash contribute particles that are mostly in the 1 to 45 983221m size
range and therefore serve as excellent fillers for the void
space within the aggregate mixture In fact due to its lower
density and higher volume per unit mass fly ash is a more
efficient void-filler than portland cement
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 56
BDrying shrinkage
Perhaps the greatest disadvantage associated with the use
of neat portland-cement concrete is cracking due to drying
shrinkage The drying shrinkage of concrete is directly
influenced by the amount and the quality of the cement paste
present It increases with an increase in the cement paste-to-
aggregate ratio in the concrete mixture and also increases
with the water content of the paste Clearly the water-
reducing property of fly ash can be advantageously used for
achieving a considerable reduction in the drying shrinkage of
concrete mixtures Table 2 shows mixture proportions of a
conventional 25 MPa concrete compared to a superplasticized
HVFA concrete with similar strength but higher slump Due to
a significant reduction in the water requirement the total
volume of the cement paste in the HVFA concrete is only
25 as compared to 296 for the conventional portland-
cement concrete which represents a 30 reduction in the
cement paste-to-aggregate volume ratio
TABLE 2
COMPARISION OF CEMENT PASTE VOLUMES
Conventional
concrete
HVFA
concrete
kgm3 m
3 kgm
3 m
3
Cement 307 0098 154 0149
Fly ash - - 154 0065
Water 178 0178 120 0120
Entrapped air
(2)
- 0020 - 0020
Course aggregate 1040 0385 1210 0448
Fine aggregate 825 0305 775 0287
Total 2350 0986 2413 0989
wcm 058 - 039 -
Paste volume - 0296 - 0254
Paste percent - 300 - 257
CThermal cracking
Thermal cracking is of serious concern in massive concrete
and reinforced concrete structures For unreinforced mass-
concrete construction several methods are employed to
prevent thermal cracking and some of these techniques can be
successfully used for mitigation of thermal cracks in massive
reinforced-concrete structures For instance a 40-MPa
concrete mixture containing 350 kgm3 portland cement can
raise the temperature of concrete by approximately 55-60oC
within a week if there is no heat loss to the environment
However with a HVFA concrete mixture containing 50
cement replacement with a Class F fly ash the adiabatic
temperature rise is expected to be 30-35oC
DWater-tightness and durability
In general the resistance of a reinforced-concrete structure
to corrosion alkali aggregate expansion sulphate and other
forms of chemical attack depends on the water-tightness of theconcrete The water-tightness is greatly influenced by the
amount of mixing-water type and amount of supplementary
cementing materials curing and cracking resistance of
concrete High-volume fly ash concrete mixtures when
properly cured are able to provide excellent water-tightness
and durability The mechanisms responsible for this
phenomenon are discussed briefly below
When a concrete mixture is consolidated after placement
along with entrapped air a part of the mixing-water is also
released As water has low density it tends to travel to the
surface of concrete However not all of this ldquobleed waterrdquo is
able to find its way to the surface Due to the wall effect of
coarse aggregate particles some of it accumulates in the
vicinity of aggregate surfaces causing a heterogeneous
distribution of water in the system Obviously the interfacial
transition zone between the aggregate and cement paste is the
area with high watercement and therefore with more available
space that permits the formation of a highly porous hydration
product containing large crystals of calcium hydroxide and
ettringite Microcracks due to stress are readily formed
through this product because it is much weaker than the bulk
cement paste with a lower watercement It has been suggested
that microcracks in the interfacial transition zone play an
important part in determining not only the mechanical
properties but also the permeability and durability of concrete
exposed to severe environmental conditions This is because
the rate of fluid transport in concrete is much larger by
percolation through an interconnected network of microcracks
than by diffusion or capillary suction The heterogeneities in
the microstructure of the hydrated portland-cement paste
especially the existence of large pores and large crystalline
products in the transition zone are greatly reduced by the
introduction of fine particles of fly ash With the progress ofthe pozzolanic reaction a gradual decrease occurs in both the
size of the capillary pores and the crystalline hydration
products in the transition zone thereby reducing its thickness
and eliminating the weak link in the concrete microstructure
In conclusion a combination of particle packing effect low
water content and pozzolanic reaction accounts for the
eventual disappearance of the interfacial transition zone in
HVFA concrete and thus enables the development of a highly
crack-resistant and durable product
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 66
IIIPROPERTIES OF HVFA CONCRETE
Based on field experience and laboratory tests the
properties of HVFA concrete when compared to conventional
portland cement concrete can be summarized as follows
1) Easier flowability pumpability and compactability
2) Better surface finish and quicker finishing time when
power finish is not required
3) Slower setting time which will have a corresponding effect
on the joint cutting and lower power-finishing times for slabs
4) Early-strength up to 7 days which can be accelerated with
suitable changes in the mix design when earlier removal of
formwork or early structural loading is desired
5) Much later strength gain between 28 days and 90 days or
more (With HVFA concrete mixtures the strengthenhancement between 7 and 90-day often exceeds 100
therefore it is unnecessary to over design them with respect to
a given specified strength)
6) Superior dimensional stability and resistance to cracking
from thermal shrinkage autogenous shrinkage and drying
shrinkage
7) After three to six months of curing much higher electrical
resistivity and resistance to chloride ion penetration
according to ASTM Method C1202
8) Very high durability to the reinforcement corrosion alkali-
silica expansion and sulphate attack
9) Better cost economy due to lower material cost and highly
favorable lifecycle cost
10) Superior environmental friendliness due to ecological
disposal of large quantities of fly ash reduced carbon-dioxide
emissions and enhancement of resource productivity of the
concrete construction industry
CONCLUSION
The study of Fly Ash has shown that owing to its numerous
advantageous physical and chemical properties the material is
found to be one of the best admixtures in Portland cement
concrete and High Volume Fly Ash (HVFA) concrete making
which improves not only the quality but also its workability
subjected to various parameters Moreover the fly ash
concrete offers a holistic solution to the problem of fly ash
disposal which is one of the major issues now-a-days that too
in a sustainable manner at a reduced or no additional cost and
at the same time reducing the environmental impact of two
industries that are vital to economic development namely the
cement industry and the coal-fired power industry Thus it
also favours the Green Technology and waste management
which in turn helps in sustainable development
ACKNOWLEDGMENT
I wish to acknowledge the instructive guidance of Prof
RB Bajare Asst Professor and Prof Dr S R Parekar
HOD Dept of Civil Engineering Sinhgad Academy of
Engineering
REFERENCES
[1] Parisara ENVIS Newsletter (Vol2 No 6 January 2007) by State
Environment Related Issues Department of Forests Ecology and
Environment Government of Karnataka
[2 ] High Volume Fly-Ash Concrete Technology Fly Ash Summary Report in
India by Canadian International Development Agency (CIDA)
[3] P Kumar Mehta HIGH-PERFORMANCE HIGH-VOLUME FLY ASH
CONCRETE FOR SUSTAINABLE DEVELOPMENT International
Workshop on Sustainable Development and Concrete Technology University
of California Berkeley USA
[4] httpwwwashgroveresourcescom
[5] Fly ash From Wikipedia the free encyclopedia
[6] C N Jha amp J K Prasad ldquoFLY ASH A RESOURCE MATERIAL FOR
INNOVATIVE BUILDING MATERIAL - INDIAN PERSPECTIVErdquo
[7] Headwaters Resources Chemical Comparison of Fly Ash and Portland
Cement Bulletin No 2
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 56
BDrying shrinkage
Perhaps the greatest disadvantage associated with the use
of neat portland-cement concrete is cracking due to drying
shrinkage The drying shrinkage of concrete is directly
influenced by the amount and the quality of the cement paste
present It increases with an increase in the cement paste-to-
aggregate ratio in the concrete mixture and also increases
with the water content of the paste Clearly the water-
reducing property of fly ash can be advantageously used for
achieving a considerable reduction in the drying shrinkage of
concrete mixtures Table 2 shows mixture proportions of a
conventional 25 MPa concrete compared to a superplasticized
HVFA concrete with similar strength but higher slump Due to
a significant reduction in the water requirement the total
volume of the cement paste in the HVFA concrete is only
25 as compared to 296 for the conventional portland-
cement concrete which represents a 30 reduction in the
cement paste-to-aggregate volume ratio
TABLE 2
COMPARISION OF CEMENT PASTE VOLUMES
Conventional
concrete
HVFA
concrete
kgm3 m
3 kgm
3 m
3
Cement 307 0098 154 0149
Fly ash - - 154 0065
Water 178 0178 120 0120
Entrapped air
(2)
- 0020 - 0020
Course aggregate 1040 0385 1210 0448
Fine aggregate 825 0305 775 0287
Total 2350 0986 2413 0989
wcm 058 - 039 -
Paste volume - 0296 - 0254
Paste percent - 300 - 257
CThermal cracking
Thermal cracking is of serious concern in massive concrete
and reinforced concrete structures For unreinforced mass-
concrete construction several methods are employed to
prevent thermal cracking and some of these techniques can be
successfully used for mitigation of thermal cracks in massive
reinforced-concrete structures For instance a 40-MPa
concrete mixture containing 350 kgm3 portland cement can
raise the temperature of concrete by approximately 55-60oC
within a week if there is no heat loss to the environment
However with a HVFA concrete mixture containing 50
cement replacement with a Class F fly ash the adiabatic
temperature rise is expected to be 30-35oC
DWater-tightness and durability
In general the resistance of a reinforced-concrete structure
to corrosion alkali aggregate expansion sulphate and other
forms of chemical attack depends on the water-tightness of theconcrete The water-tightness is greatly influenced by the
amount of mixing-water type and amount of supplementary
cementing materials curing and cracking resistance of
concrete High-volume fly ash concrete mixtures when
properly cured are able to provide excellent water-tightness
and durability The mechanisms responsible for this
phenomenon are discussed briefly below
When a concrete mixture is consolidated after placement
along with entrapped air a part of the mixing-water is also
released As water has low density it tends to travel to the
surface of concrete However not all of this ldquobleed waterrdquo is
able to find its way to the surface Due to the wall effect of
coarse aggregate particles some of it accumulates in the
vicinity of aggregate surfaces causing a heterogeneous
distribution of water in the system Obviously the interfacial
transition zone between the aggregate and cement paste is the
area with high watercement and therefore with more available
space that permits the formation of a highly porous hydration
product containing large crystals of calcium hydroxide and
ettringite Microcracks due to stress are readily formed
through this product because it is much weaker than the bulk
cement paste with a lower watercement It has been suggested
that microcracks in the interfacial transition zone play an
important part in determining not only the mechanical
properties but also the permeability and durability of concrete
exposed to severe environmental conditions This is because
the rate of fluid transport in concrete is much larger by
percolation through an interconnected network of microcracks
than by diffusion or capillary suction The heterogeneities in
the microstructure of the hydrated portland-cement paste
especially the existence of large pores and large crystalline
products in the transition zone are greatly reduced by the
introduction of fine particles of fly ash With the progress ofthe pozzolanic reaction a gradual decrease occurs in both the
size of the capillary pores and the crystalline hydration
products in the transition zone thereby reducing its thickness
and eliminating the weak link in the concrete microstructure
In conclusion a combination of particle packing effect low
water content and pozzolanic reaction accounts for the
eventual disappearance of the interfacial transition zone in
HVFA concrete and thus enables the development of a highly
crack-resistant and durable product
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 66
IIIPROPERTIES OF HVFA CONCRETE
Based on field experience and laboratory tests the
properties of HVFA concrete when compared to conventional
portland cement concrete can be summarized as follows
1) Easier flowability pumpability and compactability
2) Better surface finish and quicker finishing time when
power finish is not required
3) Slower setting time which will have a corresponding effect
on the joint cutting and lower power-finishing times for slabs
4) Early-strength up to 7 days which can be accelerated with
suitable changes in the mix design when earlier removal of
formwork or early structural loading is desired
5) Much later strength gain between 28 days and 90 days or
more (With HVFA concrete mixtures the strengthenhancement between 7 and 90-day often exceeds 100
therefore it is unnecessary to over design them with respect to
a given specified strength)
6) Superior dimensional stability and resistance to cracking
from thermal shrinkage autogenous shrinkage and drying
shrinkage
7) After three to six months of curing much higher electrical
resistivity and resistance to chloride ion penetration
according to ASTM Method C1202
8) Very high durability to the reinforcement corrosion alkali-
silica expansion and sulphate attack
9) Better cost economy due to lower material cost and highly
favorable lifecycle cost
10) Superior environmental friendliness due to ecological
disposal of large quantities of fly ash reduced carbon-dioxide
emissions and enhancement of resource productivity of the
concrete construction industry
CONCLUSION
The study of Fly Ash has shown that owing to its numerous
advantageous physical and chemical properties the material is
found to be one of the best admixtures in Portland cement
concrete and High Volume Fly Ash (HVFA) concrete making
which improves not only the quality but also its workability
subjected to various parameters Moreover the fly ash
concrete offers a holistic solution to the problem of fly ash
disposal which is one of the major issues now-a-days that too
in a sustainable manner at a reduced or no additional cost and
at the same time reducing the environmental impact of two
industries that are vital to economic development namely the
cement industry and the coal-fired power industry Thus it
also favours the Green Technology and waste management
which in turn helps in sustainable development
ACKNOWLEDGMENT
I wish to acknowledge the instructive guidance of Prof
RB Bajare Asst Professor and Prof Dr S R Parekar
HOD Dept of Civil Engineering Sinhgad Academy of
Engineering
REFERENCES
[1] Parisara ENVIS Newsletter (Vol2 No 6 January 2007) by State
Environment Related Issues Department of Forests Ecology and
Environment Government of Karnataka
[2 ] High Volume Fly-Ash Concrete Technology Fly Ash Summary Report in
India by Canadian International Development Agency (CIDA)
[3] P Kumar Mehta HIGH-PERFORMANCE HIGH-VOLUME FLY ASH
CONCRETE FOR SUSTAINABLE DEVELOPMENT International
Workshop on Sustainable Development and Concrete Technology University
of California Berkeley USA
[4] httpwwwashgroveresourcescom
[5] Fly ash From Wikipedia the free encyclopedia
[6] C N Jha amp J K Prasad ldquoFLY ASH A RESOURCE MATERIAL FOR
INNOVATIVE BUILDING MATERIAL - INDIAN PERSPECTIVErdquo
[7] Headwaters Resources Chemical Comparison of Fly Ash and Portland
Cement Bulletin No 2
7172019 Utilisation of Fly Ash in Cement Concrete
httpslidepdfcomreaderfullutilisation-of-fly-ash-in-cement-concrete-568da7817c004 66
IIIPROPERTIES OF HVFA CONCRETE
Based on field experience and laboratory tests the
properties of HVFA concrete when compared to conventional
portland cement concrete can be summarized as follows
1) Easier flowability pumpability and compactability
2) Better surface finish and quicker finishing time when
power finish is not required
3) Slower setting time which will have a corresponding effect
on the joint cutting and lower power-finishing times for slabs
4) Early-strength up to 7 days which can be accelerated with
suitable changes in the mix design when earlier removal of
formwork or early structural loading is desired
5) Much later strength gain between 28 days and 90 days or
more (With HVFA concrete mixtures the strengthenhancement between 7 and 90-day often exceeds 100
therefore it is unnecessary to over design them with respect to
a given specified strength)
6) Superior dimensional stability and resistance to cracking
from thermal shrinkage autogenous shrinkage and drying
shrinkage
7) After three to six months of curing much higher electrical
resistivity and resistance to chloride ion penetration
according to ASTM Method C1202
8) Very high durability to the reinforcement corrosion alkali-
silica expansion and sulphate attack
9) Better cost economy due to lower material cost and highly
favorable lifecycle cost
10) Superior environmental friendliness due to ecological
disposal of large quantities of fly ash reduced carbon-dioxide
emissions and enhancement of resource productivity of the
concrete construction industry
CONCLUSION
The study of Fly Ash has shown that owing to its numerous
advantageous physical and chemical properties the material is
found to be one of the best admixtures in Portland cement
concrete and High Volume Fly Ash (HVFA) concrete making
which improves not only the quality but also its workability
subjected to various parameters Moreover the fly ash
concrete offers a holistic solution to the problem of fly ash
disposal which is one of the major issues now-a-days that too
in a sustainable manner at a reduced or no additional cost and
at the same time reducing the environmental impact of two
industries that are vital to economic development namely the
cement industry and the coal-fired power industry Thus it
also favours the Green Technology and waste management
which in turn helps in sustainable development
ACKNOWLEDGMENT
I wish to acknowledge the instructive guidance of Prof
RB Bajare Asst Professor and Prof Dr S R Parekar
HOD Dept of Civil Engineering Sinhgad Academy of
Engineering
REFERENCES
[1] Parisara ENVIS Newsletter (Vol2 No 6 January 2007) by State
Environment Related Issues Department of Forests Ecology and
Environment Government of Karnataka
[2 ] High Volume Fly-Ash Concrete Technology Fly Ash Summary Report in
India by Canadian International Development Agency (CIDA)
[3] P Kumar Mehta HIGH-PERFORMANCE HIGH-VOLUME FLY ASH
CONCRETE FOR SUSTAINABLE DEVELOPMENT International
Workshop on Sustainable Development and Concrete Technology University
of California Berkeley USA
[4] httpwwwashgroveresourcescom
[5] Fly ash From Wikipedia the free encyclopedia
[6] C N Jha amp J K Prasad ldquoFLY ASH A RESOURCE MATERIAL FOR
INNOVATIVE BUILDING MATERIAL - INDIAN PERSPECTIVErdquo
[7] Headwaters Resources Chemical Comparison of Fly Ash and Portland
Cement Bulletin No 2
Recommended