effect of flyash on properties of fresh and hardened concrete

1. FLY ASH CONCRETE
by
SK ABDULLA
UNDER THE GUIDANCE OF PROFESSOR MITHU DEY
DEPARTMENT OF CIVIL ENGINEERING
NATIONAL INSTITUTE OF TECHNICAL TEACHERS’ TRAINING AND RESEARCH, KOLKATA

2. OUTLINE OF TODAY’S PRESENTATION
INTRODUCTION
WHAT IS CONCRETE?
INGREDIENT OF CONCRETE
GRADE OF CONCRETE
PROPERTIES OF CONCRETE
INTRODUCTION TO FLY ASH
PROPERTIES OF FLY ASH
CLASSIFICATION OF FLY ASH
QUALITY OF FLY ASH AS PER BIS,ASTM
EFFECT OF FLY ASH ON PROPERTIES OF CONCRETE
WHT TO USE FLY ASH

3. INTRODUCTION
• Concrete most widely used construction material in the world over,
commonly consists of cement, aggregates (fine and coarse) and water.
• It is the material, which is used more than any other man made
material on the earth for construction works.

4. WHAT IS CONCRETE?
• Concrete is a composite material, which is made from a mixture of
cement, aggregate (coarse and fine), water and sometimes
admixtures in required proportions.

5. INGREDIENTS OF CONCRETE
• According to the present state-of-the-art, concrete has bypassed the
stage of mere four component system, that is, cement, water, coarse
aggregate and fine aggregate.
• It can be a combination of far more number of ingredients for
example, a judicious combination of ingredients from as many as ten
materials. In the recent past, apart from the four ingredients
mentioned above, fly ash, ground granulated blast furnace slag, silica
fume, rice husk ash, metakaoline and superplasticizer are six more
ingredients which are generally used in concrete produced in practice
as the situation demands.

6. GRADE OF CONCRETE
• The concrete shall be in grades designated as per table 2(IS 456:2000)
• In the designation of concrete mix M refers to the mix and the number to the specified
compressive strength of 150 mm size cube at 28 days, expressed in N/mm2 .

7. PROPERTIES OF CONCRETE
1. Workability
we should note that the strength of concrete of given mix proportions
is very seriously affected by the degree of its compaction. It is
vital,therefore, that the consistency of the mix be such that the
concrete can be transported,placed,compacted, and finished
sufficiently easily and without segregation.
Definition of workability
A concrete which can be readily compacted is said to be workable, but
to say merely that workability determines the ease of placement and
the resistance to segregation.

8. PROPERTIES OF CONCRETE
2. Strength of concrete
• Strength of concrete is commonly considered its most valuable
property, although, in many practical cases, other characteristics,
such as durability and permeability, may in fact be more important.
• Nevertheless, strength usually gives an overall picture of the quality
of concrete because strength is directly related to the structure of the
hydrated cement paste.

9. PROPERTIES OF CONCRETE
3. Durability of concrete
• It is essential that every concrete structure should continue to
perform its intended functions, that is maintain its required strength
and serviceability,during the specified or traditionally expected
service life.
• It follows that concrete must be able to withstand the processes of
deterioration to which it can be expected to be exposed. Such
concrete is said to be durable.

10. INTRODUCTION TO FLY ASH
• Fly ash is a finely divided by-product resulting from the combustion of
coal in power plants.
• It contains large amount of silica, alumina and small amount of
unburned carbon, which pollutes environment.
• It is grey in colour and alkaline in nature.
• The particle size ranges between 1-100 microns.

11. PROPERTIES OF FLY ASH
• Chemical Composition
The major constituents of most of the fly ashes are
1) Silica (Sio2)
2) Alumina (Al2O3)
3) Ferric Oxide (Fe2O3)
4) Calcium Oxide (CaO)
The other minor constituent of the fly ash are MgO, Na2O, K2O, SO3, MnO,
TiO2 and unburnt carbon.
There is wide range of variation in the principal constituents - Silica (25-
60%),Alumina (10-30%) and Ferric Oxide (5-25%).

12. PROPERTIES OF FLY ASH
• Physical Properties
1) The fly ash particles are generally glassy, solid or hollow and
spherical in shape. The hollow spherical particles are called as
cenospheres.
2) The fineness of individual fly ash particle rage from 1 micron to 1
mm size. The fineness of fly ash particles has a significant influence
on its performance in cement concrete.
3) The specific gravity of fly ash varies over a wide range of 1.9 to
2.55.

13. PROPERTIES OF FLY ASH
• Pozzolanic Properties
1) Fly Ash is a pozzolanic material which is defined as siliceous or
siliceous and aluminous material which in itself possesses little or
no cementitious value, chemically react with Calcium Hydroxide
(lime) in presence of water at ordinary temperature and form
soluble compound comprises cementitious property similar to
cement.

14. Classification of Fly Ash

15. Quality of Fly Ash as per BIS,ASTM
A. Bureau of Indian Standard
To utilize fly ash as a Pozzolana in Cement concrete and Cement Mortar,
Bureau of Indian Standard (BIS) has formulated IS: 3812 Part - 1 2003.
In this code quality requirement for siliceous fly ash (class F fly ash) and
calcareous fly ash (class C fly ash) with respect its chemical and physical
composition have been specified. These requirements are given in
table1 & table2:

18. B) ASTM International for Fly ash
• ASTM International C-618-03 specifies the chemical composition and
physical requirements for fly ash to be used as a mineral admixture in
concrete.The standard requirements are given in table3 and table4:

20. EFFECT OF FLY ASH ON PROPERTIES OF
CONCRETE
Effect of fly ash on properties of fresh concrete
1) Workability
2)Setting time
3)Heat of hydration
Effect of fly ash on properties of hardened concrete
1) Compressive Strength Development.

21. 1. WORKABILITY
• Fly ash improves the workability of the concrete.
• The fly ash concrete is more workable than a plain cement concrete
at equivalent slump.
• The amount of fines will increase and make the concrete more
workable and a more complete compaction.
• Concrete pumping is made easier. Form filling becomes easier. Fly ash
concrete is more responsive to vibration. Segregation, voids, are
reduced because of increased cohesiveness and workability.

22. 1. WORKABILITY
• Generally higher substitution of Portland cement by fly ash reduces the
water requirement for obtaining a given workability.
reduction in water requirement is mainly due to three mechanisms:
1. Fly ash gets absorbed on the surface of oppositely charged cement
particles and prevent them from flocculation, releasing large amounts of
water, thereby reducing the water-demand for a given workability.
2. The spherical shape and the smooth surface of fly ash particles help to
reduce the interparticle friction and thus facilitate mobility.
3. Due to its lower density and higher volume per unit mass, fly ash is a
more efficient void-filler than Portland cement.

23. 1. WORKABILITY
Bleeding and Segregation
• The bleeding of high volume fly ash concrete ranges from negligible
to very low because of its low water content.
• Less water is needed for the same slump, the concrete gets more
cohesive and the occurrence of segregation reduces.
• Using fly ash in concrete mixtures usually reduces bleeding.
• The use of fly ash compensate for a deficiency of fines in the mixture,
at the same time, it acts as a water-reducer to promote workability at
lower water content. This results in adequate cohesion and plasticity
with less water available for bleeding.

24. 1. WORKABILITY
Contributions of enhanced workability:
• Light weight concrete is easier to pump as pumping requires less
energy.
• Improved finishing.
• Reduced segregation.
• Reduced Bleeding.
• Less sand is needed in the mix to produce required workability.

25. 2. SETTING TIME
• The impact of fly ash on the setting behavior of concrete is
dependent not only on the composition and quantity of fly ash used,
but also on the type and amount of cement, the water-to-
cementitious materials ratio (w/cm), the type and amount of
chemical admixtures, and the concrete temperature.
• It is fairly well-established that low-calcium fly ashes extend both the
initial and final set of concrete.
• Higher-calcium fly ashes generally retard setting to a lesser degree
than low-calcium fly ashes, probably because the hydraulic reactivity
of fly ash increases with increasing calcium content.

26. 2. SETTING TIME
• During hot weather the amount of retardation due to fly ash tends to
be small and is likely to be a benefit in many cases.
• During cold weather, the use of fly ash,especially at high levels of
replacement, can lead to very significant delays in both the initial and
final set.
• These delays may result in placement difficulties especially with
regards to the timing of finishing operations for floor slabs and
pavements or the provision of protection to prevent freezing of the
plastic concrete.
• Practical considerations may require that the fly ash content is limited
during cold-weather concreting.

27. 3. HEAT OF HYDRATION
• The reduction in the rate of the heat produced and hence the internal
temperature rise of the concrete has long been an incentive for using fly
ash in mass concrete construction.
• One of the first full-scale field trials was conducted by Ontario Hydro
(Mustard 1959) during the construction of the Otto Holden Dam in
Northern Ontario around 1950.
• Two elements of the dam, measuring 3.7 x 4.3 x 11.0 m were constructed
with embedded temperature monitors. One element was constructed
using a concrete with 305 kg/m3 of portland cement and the other with a
concrete with the same cementitious material content but with 30% of the
portland cement replaced with a Class F fly ash.

28. 3. HEAT OF HYDRATION
• Figure 10 shows the results from this study indicating that the use of
fly ash reduced the maximum temperature rise over ambient from
47°C to 32°C (85°F to 58°F).

29. 3. HEAT OF HYDRATION
• In massive concrete pours where the rate of heat loss is small,the
maximum temperature rise in fly ash concrete will primarily be a
function of the amount and composition of the Portland cement and
fly ash used,together with the temperature of the concrete at the
time of placing.

30. 3. HEAT OF HYDRATION
• For example,Langley and coworkers (Langley 1992) cast three 3.05 x
3.05 x 3.05 m blocks.

31. 1. Compressive Strength Development
• As the level of replacement increases the early-age strength
decreases.
• However, long-term strength development is improved when fly ash is
used and at some age the strength of the fly ash concrete will equal
that of the portland cement concrete so long as sufficient curing is
provided.

32. 1. Compressive Strength Development
Figure 12. Effect of fly ash on compressive strength development of concrete.

33. 1. Compressive Strength Development
• The age at which strength parity with the control (portland cement)
concrete is achieved is greater at higher levels of fly ash.
• Generally, the differences in the early-age strength of portland
cement and fly ash concrete are less for fly ash with higher levels of
calcium,but this is not always the case.
• The rate of early-age strength development is strongly influenced by
temperature, and this is especially the case for fly ash concrete as the
pozzolanic reaction is more sensitive to temperature than is the
hydration of portland cement.

34. 1. Compressive Strength Development

35. WHY TO USE FLY ASH?
• Being a pozzolanic, it can actually replace a part of Portland cement
• Result in more durable concrete
• High ultimate strength
• Improve workability
• Improves cost economy of concrete
• Reduction in heat of hydration
• Decreases density of concrete

36. REFERENCES
• A.M NEVILLE BOOKS
• MENON BOOKS
• OPTIMIZING THE USE OF FLY ASH IN CONCRETE
By Michael Thomas

37. THANK YOU