Study on properties of concrete with different levels of replacement of cement by fly ash

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 04 Issue: 08 | August-2015, Available @ http://www.ijret.org 158
STUDY ON PROPERTIES OF CONCRETE WITH DIFFERENT LEVELS
OF REPLACEMENT OF CEMENT BY FLY ASH
Nagabhushana1
1
Associate Professor of Civil Engineering, JSS Academy of Technical Education, Bangalore-560060
Abstract
Concrete is a widely used construction material which contains four major ingredients such as coarse aggregate, fine aggregate,
cement and water. The consumption of concrete is increasing every year with the number of developmental activities in
infrastructure sector. The production of cement involves high energy consumption. Hence, there is a need to reduce the
consumption of cement in concrete by using other alternate materials which posses cementitious properties. Fly ash is one such
material which can be used as a replacement to cement in concrete. The present study aims in observing the variation of strength
of different grades of concrete with different levels of fly ash replacement. The objective of the study is to re-establish the findings
of earlier research done in the area of fly ash concrete. The grades of concrete selected for the study are M20, M35 and M50.
The fly ash replacements considered for the study are 0%, 20%, 35% and 50% of cement by weight. The results of this study
indicates that for M20 and M35 grades of concrete, there is increase in strength with 35% cement replacement by fly ash. For
M50 grade of concrete, there is decrease in strength for all replacement levels selected for the study.
Keywords: Concrete, Cementitious material, Fly ash.
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1. INTRODUCTION
Cement is a costly component of concrete. Even though, it is
available without any scarcity, it involves high energy
consumption for it‟s production. Hence, it is advisable to
minimize the use of cement. However, concrete is a highly
versatile construction material because of it‟s strength,
durability and mouldability. Therefore, it is highly worthful
to search for an alternate material which can replace cement
without compromising the quality of concrete. Fly ash is one
such material which is considerably cementitious in nature
[1]. There are many research findings to support the use of
fly ash in producing concrete. In one of the earlier research,
it is observed that even though there is small reduction in
strength at 28 days, there is considerable increase in strength
at 90 days of curing [2]. There is improvement in
workability of concrete due to increased cohesiveness when
fly ash is used as a replacement of cement up to 30% [3].
When concrete contains 20% of fly ash as replacement to
cement, there is improved strength at the age of 56 days [4].
The fly ash particles are nearly spherical in shape and hence
it results in more cohesive mix with no sign of segregation
and bleeding [5]. When a part of cement is replaced by fly
ash, the durability of concrete gets enhanced [6]. When fly
ash is used in nano size, there is formation of C-S-H
(Calcium Silicate Hydrate) which improves the strength of
concrete [7]. In the present study, it is examined to use fly
ash as a replacement to cement. For the purpose of study,
three grades of concrete are selected (M20, M35 and M50).
Also, four levels of replacement of cement by fly ash are
considered (0%, 20%, 35% and 50%). For each grade of
concrete and for each replacement level, various strength
properties such as compressive strength, split tensile
strength and flexural strength are observed at 28 days of
curing period.
1.1 Materials Used
(a) Cement: Ordinary Portland Cement(OPC) of 53 grade
conforming to IS 12269-1987 has been used
(b) Sand: The normal sand used for the study is tested as
per IS 383-1970. The value of specific gravity is 2.4,
bulk density is 1660 kg/m3
and fineness modulus is
2.56.
(c) Water: Clean, potable water was used.
(d) Coarse aggregate: The Coarse aggregate of maximum
size of 20mm has been used. The value of specific
gravity is 2.7. The material is retained on IS480.
(e) Fly ash Class F fly ash is used in this study. Fly ash is
a waste product generated in thermal power plants [8].
During the combustion of pulverized Coal in thermal
power plants, the volatile matter is vaporized and the
majority of Carbon is burnt off. The mineral matter
associated with coal such as Clay, quartz and felsbar
will disintegrate to varying degree. This unburnt
Carbon is collected as ash. The coarser particles fall in
the bottom of the furnace. The finer particles are
collected using cyclone separators. It is termed as „fly
ash‟.
For the present study, fly ash obtained from Raichur
Thermal Power Corporation (RTPC) is used. It falls under
Class F category, as per ASTM (American Society for
Testing of Materials) classification. It constrains Cao less
than 10%.
2. EXPERIMENTAL INVESTIGATIONS
The object is to study the strength properties of M20, M35
and M50 grades of concrete with various levels of
replacement of cement by fly ash and to arrive at optimum

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percentage of fly ash content which gives higher strength.
The experimental investigation includes determination of
compressive strength, split tensile strength and flexural
strength of all the selected grades of concrete with various
levels of replacement of cement by fly ash. The replacement
levels selected for the study are 0%, 15%, 35%, and 50% of
cement by weight.
The Mix proposition is done as per IS 10262-2009[9]. The
proportions of various ingredients of concrete are shown in
Table 1.
Table 1 Proportions of materials for M20, M35 and M50
grades of normal concrete
Sl
n
o
Grade
of
concret
e
Cemen
t
Fine
aggregat
e
Coarse
aggreg
ate
Wate
r-
ceme
nt
ratio
1 M20 1 1.41 3.21 0.5
2 M35 1 0.95 2.36 0.38
3 M50 1 1.50 2.50 0.39
For M20 grade, workability is achieved without super
plasticizer. However, for M35 and M50 grades, required
quantity of super plasticizer was added to get workable
concrete. The compressive strength specimen is of size
150mm x 150mm x 150mm. The split tensile strength
specimens are of diameter 150mm and height 300mm. The
flexural strength specimen are beams of dimension 100mm
x 100mm x 500mm. Beam specimens were tested with two-
point loading with an effective span of 400mm.
The specimens were tested at the age of 28 days of curing.
The procedure as described in IS 516-1959 (Indian Standard
Methods of test for Strength of Concrete) [10] is followed
for all the tests.
3. RESULTS AND DISCUSSIONS
The results of the present investigation are presented in this
section. Table 2 gives compressive strength of M20, M35
and M50 grades of concrete with various levels of
replacement of cement by fly ash. Table 3 gives split tensile
strength of these grades of concrete. Table 4 gives flexural
strength of these grades of concrete.
Fig 1 shows variation of 28 day compressive strength of the
concrete with different percentage of replacement of cement
by fly ash. Fig2 shows the corresponding variation of split
tensile strength Fig 3 shows the variation of flexural strength
of concrete.
From the result of this investigation, the following
observations are made.
For M20 grade of concrete, the 28 days compressive
strength is increased by 8% when compared to normal
concrete with 35% replacement of cement. At 50%
replacement of cement by fly ash, there is decrease in
strength. The increase in split tensile strength at 35%
replacement is 14%. The increase in flexural strength at
35% replacement is 8% when compared to normal concrete.
For M35 grade of concrete the 28 days compressive strength
is increased by 7% when compared to normal concrete at
35% replacement of cement. The increase in split tensile
strength is 12%. The increase in flexural strength is 28%
with respect to normal concrete.
Table 2: Compressive strength of M20, M35 and M50
grades of concrete with various levels of replacement of
cement by fly ash.
Sl
no
Specimen
designation
Fly ash
Replacement
in %
28days
strength in
N/mm2
M20 concrete
1 M20-NC 00 36.37
2 M20-FARC-20 20 38.87
3 M20-FARC-35 35 39.38
4 M20-FARC-50 50 24.30
M35 concrete
5 M35-NC 00 45.19
6 M35-FARC-20 20 47.45
7 M35-FARC-35 35 48.35
8 M35-FARC-50 50 35.25
M50 concrete
9 M50-NC 00 56.68
10 M50-FARC-20 20 45.34
11 M50-FARC-35 35 42.51
12 M50-FARC-50 50 30.96
Table 3: Split tensile strength of M20, M35 and M50 grades
of concrete with various levels of replacement of cement by
fly ash
Sl no
Specimen
designation
Fly ash
Replacement
in %
28days
strength in
N/mm2
M20 concrete
1 M20-NC 00 2.66
2 M20-FARC-20 20 2.57
3 M20-FARC-35 35 3.04

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4 M20-FARC-50 50 2.15
M35 concrete
5 M35-NC 00 3.25
6 M35-FARC-20 20 3.19
7 M35-FARC-35 35 3.63
8 M35-FARC-50 50 2.48
M50 concrete
9 M50-NC 00 4.89
10 M50-FARC-20 20 3.83
11 M50-FARC-35 35 3.57
12 M50-FARC-50 50 2.61
Table 4 Flexural strength of M20, M35 and M50 grades of
concrete with various levels of replacement of cement by fly
ash
Sl
no
Specimen
designation
Fly ash
Replacement
in %
28days
strength in
N/mm2
M20 concrete
1 M20-NC 00 5.20
2 M20-FARC-20 20 5.47
3 M20-FARC-35 35 5.60
4 M20-FARC-50 50 4.07
M35 concrete
5 M35-NC 00 6.13
6 M35-FARC-20 20 7.47
7 M35-FARC-35 35 7.87
8 M35-FARC-50 50 5.60
M50 concrete
9 M50-NC 00 8.83
10 M50-FARC-20 20 6.89
11 M50-FARC-35 35 6.24
12 M50-FARC-50 50 4.47
Fig 1 Variation of 28 day compressive strength of M20,
M35 and M50 concretes with different percentage of
replacement of fly ash
Fig 2 Variation of 28 day split tensile strength of M20, M35
and M50 concretes with different percentage of replacement
of fly ash

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Fig 3 Variation of 28 day flexural strength of M20, M35 and
M50 concretes with different percentage of replacement of
fly ash.
For M50 grade of concrete the 28 days compressive strength
is found to be decreasing when compared to normal
concrete. It is 80%, 75% and 55% of strength of normal
concrete with cement replacement of 20%, 35% and 50%.
The corresponding values of split tensile strength are 78%,
73% and 53% of normal concrete. The corresponding values
of flexural strength are 78%, 71% and 51% with the cement
replacement of 20%, 35% and 50% respectively.
4. CONCLUSION
From the result of this study, it can be concluded that
cement replacement by fly ash is useful in lower grades of
concrete such as M20 and M35. It can be stated that at 35%
of replacement of cement by fly ash, there is considerable
increase in strength properties. Hence, 35% replacement can
be considered as optimum replacement level to get enhanced
strength. Also, it can be concluded that replacement of
cement by fly ash is not suitable for higher grades of
concrete such as M50. It results in decreased value of
strength properties for the selected replacement levels of
cement by fly ash.
REFERENCES
[1] Ganesh Babu K and Siva Nageswara
Rao(1995)”Efficiency of fly ash in concrete”,
Cement and Concrete research, Vol.26,No.3,Dec
1995.
[2] S.L Patil, J N Kale, S Suman(2012) “Fly ash
concrete- A technical analysis for compressive
strength” , International journal of advanced
engineering research and studies, Vol 2, No1,
December-2012.
[3] Heba A Mohamed (2011) “ Effect of fly ash and
silica on compressive strength of self compacting
concrete” Vol. 2 No. 2, Ain Shams engineering
journal, june 2011.
[4] Alvin Harison, Vikas Srivastava and Arpan Herbert
(2014) “Effect of fly ash on compressive strength of
Portland pozzolona cement concrete”, journal of
academia and industrial research(JAIR), Vol.2, No.8,
January-2014.
[5] N Nagabhushana and H Sharada Bai (2011) Use of
Crushed rock powder as replacement of fine
aggregate in mortar and concrete, Indian J. Science
and Technology, Vol4, No. 8 , 917-922.
[6] A.K Mullick (2005) “Use of fly ash in structural
concrete”, Indian concrete journal, Vol.19, No.6
June-2005.
[7] S. Yuvaraj, Suji mohan kumar, N Dinesh, C Karthic
(2012) “Experimental research on improvement of
concrete strength and enhancing the resisting
property of corrosion and permeability by the use of
nano silica fly ashed concrete”, International journal
of emerging technology and advanced engineering,
Vol.2, No.6, June-2012.
[8] Freeda christy and Tensing.D(2010)”Effect of class-
F fly ash as partial replacement with cement and fine
aggregate in mortar”, Indian journal of Engineering
and material science,Vol.17,No.4,April 2010.
[9] IS 10262-2009, Indian Standard recommended
guidelines for concrete mix design, Bureau of Indian
standards, New Delhi.
[10] IS 516-1959, Indian standard methods of test for
strength of concrete, Bureau of Indian standards,
New Delhi.
BIOGRAPHY
Dr. Nagabhushana has completed B.E
and M.Tech degree from Mysore
University and PhD from Bangalore
University. He has more than 20 years
of experience in teaching. He has
published research papers in
international journals. Presently, he is
working as associate Professor of Civil engineering at J.S.S
Academy of Technical Education, Bangalore.

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