A study on influence of fly ash and nano silica on strength properties of concrete

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 5, Issue 7, July (2014), pp. 94-102 © IAEME
94
A STUDY ON INFLUENCE OF FLY ASH AND NANO- SILICA ON
STRENGTH PROPERTIES OF CONCRETE
Dr. D. V. Prasada Rao1
, M. Pavan Kumar2
1
(Associate Professor, Department of Civil Engineering, Sri Venkateswara University
College of Engineering, Tirupati, Andhra Pradesh, India)
2
(PG Student, Department of Civil Engineering, Sri Venkateswara University
College of Engineering, Tirupati, Andhra Pradesh, India)
ABSTRACT
This aim of the experimental investigation is to find the influence of Nano-Silica (NS) and
Fly Ash (FA) on strength properties of concrete. Fly Ash and Nano-Silica are used as partial
replacement of cement. In the present experimental investigation the cement is partially replaced by
20% and 30% of Fly Ash and Nano-Silica 1.5%, 3% and 4.5% by weight. The influence of combined
application of Fly Ash and Nano-Silica on compressive strength, split tensile strength, flexural
strength and modulus of elasticity of M25 grade of concrete is investigated. The test results of
concrete prepared using the different proportions of Fly Ash and Nano-Silica are compared with that
of controlled concrete. The variation of different test results of concrete prepared with various
proportions of Fly Ash and Nano-Silica indicates the same trend. Based on the test results, it can be
observed that concrete prepared with 20% Fly Ash and 3% Nano-Silica combination possesses
improved properties compared to the controlled concrete. The increase in the various strength
characteristics of concrete prepared using Fly Ash and Nano-Silica can be attributed to the effective
particle packing and the also the availability of additional binder in the presence of Fly-Ash and
Nano-Silica.
Keywords: Fly-Ash, Nano-Silica, Partial Replacement, Particle Packing and Strength of Concrete.
1.0 INTRODUCTION
Concrete can be considered as the most widely used in the construction industry. In the
present day construction practice along with the strength equal importance is given to the durability
INTERNATIONAL JOURNAL OF ADVANCED RESEARCH
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ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
Volume 5, Issue 7, July (2014), pp. 94-102
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of concrete. The Indian Standard Code of practice for plain and reinforced concrete recommends the
minimum cement content to satisfy the strength and durability. Hence, the utilization of cement is
increased. But, the cement production consumes large amount of energy and emits carbon dioxide
results in environmental pollution. Hence, one of the solutions to these problems is to reduce the
consumption of cement and utilise Pozzolana materials for the preparation of concrete. Previous
studies indicates that the use of Fly Ash, Micro Silica, Matakaoline, Ground Granulated Blast
Furnace Slag as partial replacement of cement, reduces the cement consumption and also increases
the strength and durability of concrete. To improve the performance of concrete further, Nano
materials are now being introduced as supplementary materials.
Recent developments in Nano-technology and the availability of nano-silica made the use of
such materials in concrete. Nano-Silica (NS) is a Nano-sized, highly reactive amorphous silica. Due
to the smaller particles size and high surface areas compared to the other pozzolanic materials, the
use of nano-silica possibly enhances the performance of concrete more effectively. As the nano-silica
particles are very fine and they tend to agglomerate due to high surface interaction, uniform
dispersion of nano-silica is an important issue to get its beneficial effects. The influence of combined
application of fly ash and nano-silica is to be investigated.
2.0 OBJECTIVE
The objective of the present research work is to find the influence of the combined
application of fly ash and nano-silica on various strength properties of M25 grade of concrete. 20%
and 30% of fly ash and 1.5%, 3% and 4.5% of nano-silica are adopted as cement replacement by
weight. Compressive strength, split tensile strength, flexural strength and modulus of elasticity of
concrete with the addition of various proportions of fly ash and nano-silica are to be obtained and the
results are to be compared with the controlled concrete.
3.0 EXPERIMENTAL PROGRAMME
3.10 Properties of Materials
3.11 Cement
In the present investigation Ordinary Portland cement (OPC) of 43 Grade confirming to IS
specifications was used. The properties of cement are shown in Table 1.
Table 1: Properties of Cement
S.No Property Value
1 Specific Gravity 3.15
2 Normal Consistency 33 %
3
Setting Time
i)Initial Setting time
ii) Final setting time
40 Min
6 hours
3.12 Fine Aggregate
Locally available river sand confirming to IS specifications was used as the fine aggregate in
the concrete preparation. The properties of fine aggregate are shown in Table 2.

96
Table 2: Properties of Fine Aggregate
S.No Property Result
2 Fineness Modulus 2.8
3 Bulk Density (Loose) 15.75 kN/m3
4 Grading of Sand Zone - II
3.13 Coarse Aggregate
Coarse aggregate of nominal size 20 mm and 10 mm, obtained from the local quarry
confirming to IS specifications was used. The properties of coarse aggregate are shown in Table.3.
The coarse aggregate used for the preparation of concrete is a mixture of 20 mm and 10 mm size
aggregates in ratio 1.5: 1.0.
Table 3: Properties of Coarse Aggregate
S.No Property Result
2 Bulk Density (Loose ) 14.15 kN/m3
3 Water Absorption 0.5%
4 Fineness Modulus 7.2
3.14 Fly Ash
In the present experimental investigation ‘Class F’ Fly ash obtained from a Thermal Power
Plant is used. Cement is replaced by 20% and 30% of fly ash by weight of cement. The properties of
fly ash are shown in Table 4.
Table 4: Properties of Fly Ash
S.No. Ingredient Value
1 Silica (SiO2) 56.88 %
2 Aluminum trioxide (Al2O3) 27.65 %
3 Ferric oxide (Fe2O3 + Fe3O4) 6.28 %
4 Titanium dioxide (TiO2) 0.31 %
5 Calcium oxide (Cao) 3.6 %
6 Magnesium oxide (MgO) 0.34 %
7 Sulphate (SO4) 0.27 %
8 Loss of ignition (LOI) 4.46 %
9 Specific gravity of Fly Ash 2.12
3.15 Nano-Silica
Nano-silica is a new pozzolanic material commercially available in the form of water
emulsion of colloidal silica. It is potentially better than the other pozzolanic materials because of
high content of amorphous silica (>99%) and the reduced size of its spherical particles of order 5-
10nm. In this experimental investigation cement is replaced by 1.5%, 3% and 4.5% of nano-silica by
weight. The properties of nano-silica are shown in the Table 5.

97
Table 5: Properties of Nano-Silica
S.No. Property Actual Analysis
1 Active nano Silica Content 35-40%
2 PH 9.3 -9.6
3 Specific Gravity 1.08-1.11
4 Texture Milky White Liquid
5 Dispersion Water
3.16 Water
Water used for casting and curing of concrete test specimens is free from impurities which
when present can adversely influence the strength of concrete.
3.20 CONCRETE MIX PROPORTION
M25 grade of concrete was designed as per the Indian Standard code of practice. The various
ingredients for one cubic meter of concrete are shown in the Table 6. As the nano-silica is available
in the colloidal form, the quantity of water is adjusted to account for the water available in colloidal
nano-silica.
Table 6: Quantities of Ingredients per cum of M25 Grade Concrete
S.No
Cement
(% )
Fly
Ash
(%)
Nano-
Silica
(%)
Water
(lit)
Cement
(kg)
Fly Ash
(kg)
Colloidal
Nano-
Silica
(kg)
Fine
Aggregate
(kg)
Coarse
Aggregate
(kg)
1 100 0 0 160 320 0 0 725 1220
2 80 20 0 160 256 64 0 725 1220
3 78.5 20 1.5 152.8 251.2 64 12 725 1220
4 77 20 3 145.6 246.4 64 24 725 1220
5 75.5 20 4.5 138.4 241.6 64 36 725 1220
6 70 30 0 160 224 96 0 725 1220
7 68.5 30 1.5 152.8 219.2 96 12 725 1220
8 67 30 3 145.6 214.4 96 24 725 1220
9 65.5 30 4.5 138.4 209.6 96 36 725 1220
3.30 TEST SPECIMENS
Concrete test specimens consist of 150 mm × 150 mm × 150 mm cubes, cylinders of 150 mm
diameter × 300 mm height and prisms of 100 mm × 100 mm × 500 mm. Concrete cubes were tested
at different curing periods (3, 7, 28 and 56 days) to get the compressive strength. Cylindrical
specimens were also tested at the age of 28 days to obtain the compressive strength, the split tensile
strength and the modulus of elasticity of concrete. The prisms were tested at the age of 28 days to
obtain the flexural strength of concrete. The rate of loading is as per the Indian Standard
specifications.
4.0 RESULTS AND DISCUSSION
4.1 Compressive Strength
The variation of the cube compressive strength of M25 grade concrete with age for various
proportions of fly ash and nano-silica is shown in Fig.1. The cube compressive strength indicates the

98
average of three test results. It can be observed that the compressive strength of concrete prepared
using fly ash and nano-silica exhibits more strength than the control concrete up to 3% of nano-silica
if the percentage of fly ash is 20% and with further increase in nano-silica the compressive strength
decreases. But, if the percentage of fly ash is increased to 30% irrespective of the content of nano-
silica the compressive strength is less than the control concrete.
(i) 20% Fly Ash (ii) 30% Fly Ash
Fig. 1: Variation of Cube Compressive Strength of M25 Grade Concrete with Age for Different
Percentages of Fly Ash and Nano-Silica.
The variation of 7 days and 28 days cube compressive strength of M25 grade of concrete
prepared with different proportions of nano-silica and fly ash is shown in Fig.2. The compressive
strength of concrete initially increases up to 3% nano-silica and then the strength decreases with
further increase in nano-silica for 20% and 30% of fly ash content. The 7 days and 28 days cube
compressive strength of control concrete is 22.37 N/mm2
and 32.12 N/mm2
respectively. The
increase in 7 days and 28 days cube compressive strength concrete with 3% nano-silica and 20% fly
ash combination is 4.6% and 6.1% respectively.
(i) 7 days Cube Compressive Strength (ii) 28 days Cube Compressive Strength
Fig. 2: Variation of Cube Compressive Strength of M25 Grade of Concrete with Nano-Silica for
various percentages of Fly Ash
Comparison is also made between the cube compressive strength and cylindrical compressive
strength of concrete containing various percentages of fly ash and nano-silica at the age of 28 days.
The test results are shown in Table 7. The ratio of cube compressive strength and cylinder
compressive strength is found to be around 0.88

99
Table 7: Comparison between 28 days Cube and Cylinder Compressive Strength of Concrete
Prepared with Fly Ash (FA) and Nano-Silica (NS)
S.No. Concrete Cube
Compressive
Strength (N/mm2
)
σCube
Cylinder
Compressive Strength
(N/mm2
)
σCylinder
σCube/ σCylinder
1 Control Concrete 32.12 27.36 0.85
2 FA 20 % + NS 0 % 27.53 24.50 0.89
3
FA 20 % + NS 1.5
%
29.10 25.90 0.89
4 FA 20 % + NS 3 % 34.07 30.66 0.90
5
FA 20 % + NS 4.5
%
31.55 27.76 0.88
6 FA 30% + NS 0 % 25.62 21.88 0.85
7
FA 30 % + NS 1.5
%
26.51 22.83 0.86
8 FA 30% + NS 3% 28.00 24.32 0.87
9 FA 30% + NS 4.5 % 26.51 23.85 0.90
4.20 Split Tensile Strength
The variation of split tensile strength of M25 grade of concrete with Nano-Silica for various
percentages of fly ash is shown in Fig. 3. The split tensile Strength of control concrete is 3.73
N/mm2
. The split tensile strength of concrete initially increased up to 3% of Nano silica for any
given percentage of fly ash and beyond which the strength decreases with increase in the Nano-silica.
It can also be observed that at a combination of 3% of Nano silica and 20% fly ash maximum split
tensile strength can be obtained. The increase in split tensile strength of concrete with 3% Nano-
Silica and 20% fly ash content is 3%.
Fig.3: Variation of Split Tensile Strength of M25 Grade of Concrete with different percentages of
Nano-Silica and Fly Ash

100
4.30 Flexural Strength
The variation of flexural strength of M25 grade of concrete containing various proportions of
fly ash and nano-silica is shown in Fig.4. The flexural strength of control concrete is 5.03 N/mm2
.
The flexural strength of concrete initially increases up to 3% percentage of Nano-Silica for different
percentage of fly ash and then with further increase in the Nano-Silica the flexural strength
decreases. The recommended combination for maximum split tensile strength is 3% of Nano-silica
and 20% fly ash. The increase in the flexural strength concrete with 3% nano-silica and 20% fly ash
content is 3.4%.
Fig.4: Variation of Flexural Strength of M25 Grade of Concrete with Different Percentages of Nano-
Silica and Fly Ash
4.40 Modulus of Elasticity
Fig.5 shows the variation of modulus of elasticity of M25 grade concrete with various
percentages of nano-silica and fly ash. It can be observed that the modulus of elasticity of concrete
increases with nano-silica for the given content of fly ash. The maximum value is obtained at 3%
nano-silica for the given content fly ash.
Fig.5: Variation of Modulus of Elasticity of M25 Grade of Concrete with Nano-Silica for different
percentages Fly Ash

101
The M25 grade control concrete has modulus of elasticity of 24.90 GPa. The presence of
20% fly ash the modulus of elasticity is decreased to 22.82 GPa and with 30% fly ash the value is
further decreased to 22.27 GPa. The modulus of elasticity of fly ash concrete increases in the
presence of nano-silica. The modulus of elasticity of M25 grade concrete attains maximum value at a
combination of 3% nano-silica and 20% fly ash by weight of cement. The increase in the modulus of
elasticity of concrete with 3% nano-silica and 20% fly ash content is 3.1%. .
5.0 CONCLUSIONS
The results of the experimental investigation indicate that the fly ash and nano-silica can be
adopted as Ordinary Portland cement replacement for concrete preparation. Using the test results, it
can be concluded that with the increase in the percentage of nano-silica the various strength
characteristics of concrete increased up to 3%, with further increase in the nano-silica the strength
characteristics of concrete are decreased for the given percentages of fly ash. It is very interesting to
note that the variation of compressive strength, split tensile strength, flexural strength and modulus
of elasticity of M25 grade fly ash concrete with nano-silica indicates the similar trend.
The increase in various strength characteristics of concrete containing fly ash with increase in
the nano-silica content can be due to the availability of additional binder in the presence of nano-
silica. Nano silica has high amorphous silicon dioxide content. The Portland cement in concrete
releases calcium hydroxide during the hydration process. The nano silica and fly ash reacts with the
calcium hydroxide to form additional binder material. The availability of additional binder leads to
increase in the paste-aggregate bond, results improved strength properties of the concrete prepared
with nano-silica and fly ash combination. The decrease in the strength characteristics of concrete
with increase in the nano-silica content beyond 3% is due to the poor quality of binder formed in the
presence of high content of nano-silica and fly ash. The various strength characteristics of concrete
can be improved by the addition of 3% nano-silica and 20% fly ash content. It can be concluded that
the cement content can be reduced without compromising the strength of concrete by the use of fly
ash and nano-silica combination at an appropriate proportion.
REFERENCES
1. Gengying Li., (2004). “Properties of High-Volume Fly Ash Concrete incorporating Nano-
SiO2”, Cement and Concrete Research, pp. 1043-1049.
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Concrete Design” pp. 47–53.
3. Belkowitz, J. and Armentrout, D. L. (2009). The Investigation of Nano Silica in the Cement
Hydration Process. ACI Special Publication 267(8): 87-100.
4. Sanchez, F., and Sobolev, K. (2010). “Nano-Technology in Concrete – A Review”,
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5. G. Quercia and H.I.H. Browwers, (2010). ‘Applications of Nano Silica in Concrete Mixtures’,
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9. IS: 10262-2009. Concrete Mix Proportioning – Guidelines (First Revision). Bureau of Indian
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