why we use fly ash in concrete , production of fly ash, how it improve the fresh and harden properties of concrete how it react when mix with concrete.

1. ______by__ Diksha
Chadha.
_Vishnu Dev.
Fly Ash Concrete

2. Defination of POZZOLAN
 A pozzolan is defined as a siliceous or aluminous material which in
itself possesses little or no cementing property, but will in a finaly
divided form and in the presence of moisture chemically react with
calcium hydroxide at ordinary temperature to form compounds
possessing cementitious properties.
TYPES OR CATEGORIES OF POZZOLAN
•Natural pozzolans
- Volcanic glasses
- Volcanic tuffs
- diatomaceous earth
- calcined clays or shales
•Industrial by-products (artificial)
- Fly ash
- Silica fume
- Slag
- Other such s rice husk, metakaolin, etc.
IS 3812 (part 1)
- Pulverized Fuel Ash- for use as
pozzolan in cement, cement mortar
and concrete
IS 3812 (part 2)
-pulverized Fuel ash- For use as
admuxture in cement mortar and
concrete.

3.  In India , The Generation Of Electricity Is Mostly Dependent On Combustion
Of High-ash Coal.
 The Thermal Power- Plant In India Are Primarily Depend On The Combustion
Of High-ash Bituminous Coal In Pulverized Fuel Fired System.
1. (pulverised lignite fired boiler)
2. (Pressurized fluidized-bed combustion system)
are in operation in limited extent.

4. PRODUCTIONOFFLYASH

5. Standerd Classification Of Fly
Ash
 IS and ASTM classification
- Siliceous or class F fly ash (if S+A+F >70%)
- Calcareous or Class C fly ash (if S+A+F >50%)
 Basis of fly ash is classified according to their
concentration.
- Low-lime fly ash
- high-lime flyash
- low-calcium flyash
- high calcium flyash

6.  Low lime flyash
- higher concentration of Sio2 and Al2o3 (Si02)
Silica
- lower content of Fe2o3.
(Al2o3)Alumina
 High lime flyash
- lower conentration of Sio2 and Al2o3
- higher concentration of Fe2o3
 Low calcium flyash
- Sio2 is double of Al2o3
 High calcium flyash
- concentration of Sio2 and Al2o3 is close to each other.
CLASSIFY ACCORDING TO OXIDE COMPOSITION OF
FLYASH
-the 3 main group of flyash have been identified
GROUP INDEX SiO2 % CaO%
1 53.0 – 63.1 0.6 – 3.0
2 39.0 – 50.0 3.0 - 16.0
3 30.0 – 38.0 16.0 – 29.0

7. -PHYSICAL PROPERTIES
-CHEMICAL PROPERTIES
Properties Of Fly Ash

8. CHARACTERSTICS
MORPHOLOGY
PARTICAL SHAPE
PARTICAL SIZE AND FINENESS
SPECIFIC GRAVITY
COLOR

9. MORPHOLOGY OF FLYASH (SHAPE)
MORPHOLOGY OF FLYASH
FLYASH IN
CONCRET
E

10. Shape Of Fly Ash Particle
 Shape depends upon the condition in which
combustion and subsequent condensation takes
place. Fly ash consists of
- Cenospheres (less amount)
- Pherospheres (more amount)
1. Cenospheres
(ash partical that are hollow inside)
2. Pherospheres
(hollow particles that have
smaller partical inside)

11. Effects On Concrete Property
 The shape and surface characteristics of PFA
affect the water requirement of concrete at the
desired slump.
 The spherical partical reduce inter-partical friction
(ball bearing effect) in the concrete mix, improve
its flow properties and reduce water requirement.

12. Particle Size And Fineness
 Particle size refers to the size of a single or an average of many
particles lying in the narrow range.
 Particle size of fly ash is _1 to 100 micron
 Fly ashes vary singnificantly in their particle size and fineness
Effect
 Fly ash partical <10 micron contribues to early strength of
concrete while particles _10 to 45 micron contributes to its later
strength.
Three ways of measuring size and fineness of fly ash particles
are as follows:
- Blaine apparatus
- Wet-sieve analysis
- Laser particle size analysis

13. Specific gravity
 Specific gravity of fly ash mostly depends upon its iron
content
- generally it is _2.0 to 2.8
 The variation in SG is due to change in the chemical
composition
 Fly ash rich in iron and calcium have higher density because
of higher atomic mass
 SG is important during concrete mix design

14. Bulk Density
 Bulk density of fly ash in loose condition is_ 1.12 to 1.49
g/cc (or) 1120 to 1490 kg/m3
 BD is affected by the amount of
-Cenosphere and Pleurosphere.
 BD, grain importance during packing,
handling, transporting and storing.

15. COLOR
 Color of fly ash depends upon the type of coal used during the
production process
- bituminous coal – darker in colour (grey)
- lignite sub-bituminous coal – lighter in color (yellowish brown)
 Color of fly ash could be dark grey, grey and pale yellow.
 Carbon and iron tends to impart grey color to fly ash
 Color of fly ash particles change to brown when the ash is
heated in the presure of air.

17. •MINERALOGY OR MINERALS
•OXIDE COMPOSITION
•REACTIVE PHASES OR COMPONENT
Chemical Properties

18. Minerals In Fly Ash
 Quartz (SiO2)
 Mullite (3Al2O3.2SiO2)
 Free CaO
 Periclase (MgO)
 Anhydrite (CaSO4)
 Alkali-sulfates
 Other minor compounds
Substantial
amount

19. Oxide Components (Based Upon
Sources)

20. REACTIVE COMPONENT OR
PHASES
Material Reactive component
Fly ash Aluminosilicate or calcium aluminosilicate glass

21. Reaction Mechanism

22.  Ordinary Portland Cement (OPC) is a product of four principal
mineralogical phases. These phases areTricalcium Silicate -
CS(3CaO.SiO ), Dicalcium Silicate C S (2CaO.SiO ), Tricalcium
Aluminate- C A (3CaO.Al O ) and Tetracalcium alumino -ferrite - C
AF(4CaO. AlOFeO ). The setting and hardening of the OPC takes place
as a result of reaction between these principal compounds and water.
The reaction between these compounds and water are shown as under:
- 2C3S + 6H C3S2H3 +
3CH
tricalcium silicate water C-S-H gel
Calcium hydroxide
- 2C2S + 4H C3S2H3 + CH
dicalcium silicate water C-S-H gel
Calcium hydroxide
The hydration products from C3S and C2S are similar but quantity of calcium
hydroxide(lime) released is higher in C3S as compared to C2S.
The reaction of C3A with water takes place in presence of sulphate ions
supplied by dissolution of gypsum present in OPC. This reaction is very fast
and is shown as under:
- C3A + 3(CSH2) + 26H C A(CS) H32 33
tricalcium alluminate + gypsum + water ettringite
- C3A + CSH2 + 10H C3ACSH12

23. Tetracalcium alumino-ferrite forms hydration product similer to those of C3A, with
iron substituting partilly for alumina in the crystal structures of ettringite and
monosulpho-aluminate hydrate.
Above reaction indicates that during he hydation process of cement, lime is
released out and remains as surplus in the hidrated cement. This leached out
surplus lime renders deleterious effect to concrete suct as make the conrete
porous, give chance to the development of micro-cracks, weekening the bond
with aggergates and thus effect the durability of concrete .
If fly ash is avalable in the mix, this sulpher lime becomes the source of
pozzolanic reaction with flyash and forms additional C-S-H gel having similer
binding propreties in the concrete as those produced by hydration of cement
paste. The reaction of flyash with sulphur lime continous as long as lime is
present in the pores of liquid cement paste.
The process can also be understood as follow:
Ordinary portland cement + Water
Surplus lime
Fly ash
Additional cementitious
materialCementitious material

24. Proportioning of flyash concrete
There are three basic approches for selecting the quantiy
of fly ash in cement concrete:
- Simple replacement method
- The additional method
- A Modified replacement method

25. Simple replacement method
 In this method a part of the OPC is replaced by flyash on a one tone basis by mass
of cement. In this process, the early strength of concrete is lower and higher
strength is developed after 56-90 days. At early ages fly ash exhibits very little
cementing value. At later ages when liberated lime resulting from hydration of
cement, reacts with fly ash and contributes considerable strength to the concrete.
This method of flyash use is adopted for mass concrete works where initial strength
of concrete has less importance compared to the reduction of temperature rise.
The additional method
 In this method, fly ash is added to the concrete without corresponding reduction in
the quantity of OPC. This increases the effective cementitious content of the
concrete and exhibits increased strength at all ages of the concrete mass. This
method is useful when there is a minimum cement content criteria due to some
design consideration.
Modified replacement method
 This method is useful to make strength of fly ash concrete equivalent to the strength
of control mix (without fly ash concrete) at early ages i.e. between 3 and 28 days. In
this method fly ash is used by replacing part of OPC by mass along with adjustment
in quantity of fine aggregates and water. The concrete mixes designed by this
method will have a total weight of OPC and fly ash higher than the weight of the
cement used in comparable to control mix i.e. without fly ash mix. In this method the
quantity of cementitious material (OPC + Fly ash) is kept higher than quantity of
cement in control mix (without fly ash) to offset the reduction in early strength.

26. Steps to be followed for proportioning of concrete utilizing fly
ash are given below.
 Selecting of slump for required consestency
 Selecting of maximum size of aggregate
 Estimating of mixing water and air content
 Selection of water cementitious materials [w /(c+p)] or
water cement ratio (w/c)
 Calculation of cementitious material content
 Estimation of coarse aggregate content
 Estimation of fine aggregate content
 Adjustments for aggregate moisture

27. •The use of fly ash in portland cement concrete (PCC) has many
benefits and improves concrete performance in both
-the fresh
-hardened state.
Fly ash use in concrete improves the workability of plastic
concrete, and the strength and durability of hardened concrete. Fly
ash use is also cost effective. When fly ash is added to concrete,
the amount of portland cement may be reduced.
Properties Of Concrete In Fresh
And Harden Stage

28. In Fresh Concrete
Generally, fly ash benefits fresh concrete by reducing the mixing water
requirement and improving the paste flow behavior. The resulting
benefits are as follows:
 Improved workability. The spherical shaped particles of fly ash act as
miniature ball bearings within the concrete mix, thus providing a
lubricant effect. This same effect also improves concrete pumpability
by reducing frictional losses during the pumping process and flat work
finishability.
 Decreased water demand. The replacement of cement by fly ash
reduces the water demand for a given slump. When fly ash is used at
about 20 percent of the total cementitious, water demand is reduced
by approximately 10 percent. Higher fly ash contents will yield higher
water reductions. The decreased water demand has little or no effect
on drying shrinkage/cracking. Some fly ash is known to reduce drying
shrinkage in certain situations.
 Reduced heat of hydration. Replacing cement with the same amount
of fly ash can reduce the heat of hydration of concrete. This reduction
in the heat of hydration does not sacrifice long-term strength gain or
durability. The reduced heat of hydration lessens heat rise problems in

29. In Harden Concrete
One of the primary benefits of fly ash is its reaction with available
lime and alkali in concrete, producing additional cementitious
compounds. The following equations illustrate the pozzolanic
reaction of fly ash with lime to produce additional calcium silicate
hydrate (C-S-H) binder:
(hydration)
Cement Reaction: C3S +H → C-S-H +
CaOH
Pozzolanic Reaction: CaOH +S → C-S-
H (silica from ash constituents )
 Increased ultimate strength. The additional binder produced by
the fly ash reaction with available lime allows fly ash concrete to
continue to gain strength over time. Mixtures designed to produce
equivalent strength at early ages (less than 90 days) will ultimately
exceed the strength of straight cement concrete mixes.
 Reduced permeability. The decrease in water content combined
with the production of additional cementitious compounds reduces
the pore interconnectivity of concrete, thus decreasing
permeability. The reduced permeability results in improved long-

30. Duriability Of Fly Ash Concrete

31. Improved durability.
 The decrease in free lime and the resulting increase in cementitious compounds,
combined with the reduction in permeability enhance concrete durability. This
affords several benefits:
 Improved resistance to ASR. Fly ash reacts with available alkali in the concrete,
which makes them less available to react with certain silica minerals contained in
the aggregates.
 Improved resistance to sulfate attack. Fly ash induces three phenomena that
improve sulfate resistance:
-Fly ash consumes the free lime making it unavailable to react with sulfate
-The reduced permeability prevents sulfate penetration into the concrete
-Replacement of cement reduces the amount of reactive aluminates available
 Improved resistance to corrosion. The reduction in permeability increases the
resistance to corrosion.
Some properties which are improved by addition of flyash in concrete
• Permeability of concrete
• Carbonation of concrete
• Durability of concrete subjected to repeated cycles of freezing and thawing
• Abrasion and erosion of fly ash concrete
• Sulfate resistance of concrete
• Alkali aggregate reactions in concrete
• The corrosion of steel reinforcement in concrete

32. Use Of Flyash in
construction