International Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 04, April 2019, pp. 2294-2304. Article ID: IJCIET_10_04_239
Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=04
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
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INVESTIGATION ON STRUCTURAL
BEHAVIOUR OF GEOPOLYMER CONCRETE
INFLUENCED BY MICRO SILICA AND STEEL
FIBRE
A. Ravi
Assistant Professor (Sr. grade), Department of Civil Engineering
Mepco Schlenk Engineering College Sivakasi, Virudhunagar district, Tamilnadu
M. Aishwarya
PG Student, Department of Civil Engineering,
Mepco Schlenk Engineering College Sivakasi, Virudhunagar district, Tamilnadu
ABSTRACT
CO2 is released into the atmosphere in amount equal to the production of Ordinary
Portland Cement (OPC). Geopolymer concrete is an emerging technique in the
construction field where OPC is totally replaced by Fly ash. Fly ash is a waste residue
obtained from thermal power plant. Normally Class F fly ash based Geopolymer
concrete requires elevated temperature curing (above 60◦C), which make them
impossible for cast in situ construction. In this study the strength of geopolymer
concrete is achieved by sunlight curing by addition of Class C fly ash and Micro silica.
Sodium silicate solution (Na2SiO3) and sodium hydroxide solution (NaOH) with a ratio
(Na2SiO3/ NaOH) of 2.5 is used as an activator for geopolymer concrete. Main
objectives of the study are to investigate the effect of usability or replace ability of micro
silica with steel fibre based geopolymer concrete instead of OPC concrete in structural
applications. To achieve the goals, the optimum percentage of Micro silica, Class C fly
ash and steel fibres are found. Compressive strength and split tensile tests are
performed on specimens to evaluate the mechanical performance of the concrete.
Keywords: Class F fly ash, Micro Silica, Steel Fibre, Class C fly ash
Cite this Article: A. Ravi and M. Aishwarya, Investigation on Structural Behaviour of
Geopolymer Concrete Influenced by Micro Silica and Steel Fibre, International
Journal of Civil Engineering and Technology, 10(4), 2019, pp. 2294-2304.
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1. INTRODUCTION
There are numerous issues related with the generation of Ordinary Portland cement (OPC),
production of cement involves utilization of 5% of natural resources and release of 5– 7% of
worldwide carbon dioxide[1-4]. Geopolymer is the most recent usage of concrete, after
gypsum concrete and conventional Portland concrete (OPC)[5]. The reaction of a strong
aluminosilicate with hydroxide or silicate arrangement creates a manufactured aluminosilicate
material called as 'geopolymer'. Low-calcium fly ash is the most generally utilized material to
create geopolymer concrete. Fly ash is a byproduct coal power plant where burning of coal in
the coal-terminated heaters. Around one billion tons of fly ash remains are created every year
worldwide in coal-fired steam power plants. Analysts revealed that alkali-activated fly slag
concrete can accomplish compressive quality more than 60 MPa after curing at elevated
temperature[6-9]. Geopolymer concrete is termed as a Green Concrete since the usage of OPC
is neglected [11-14].Many research papers on geopolymer concrete mainly highlight the
elevated or high temperature curing, this make the geopolymer concrete not practical as cast in
situ[15]. Addition of fibre influences the workability of the geopolymer concrete. Addition of
large amount of fibre results in balling effects which reduces the workability of the geopolymer
concrete [16]. This research paper forms an idea for proposing geopolymer as a onsite concrete
and to overcome the requirement of elevated temperature for curing. This paper gives an outline
of the most recent elective restoring techniques for elimination of heat cured geopolymer
concrete to ensure commercial viability and for site usage.
After lime and cement geopolymer is considered as the third-generation cement. It basically
consists of repeating unit of sialate and aluminate monomers (–Si–O–Al–O–). Various
aluminosilicate materials such as, kaolinite, feldspar and solid residue from industries such as
fly ash, metallurgical slag, mining waste etc. has been used as the soild raw materials in the
geopolymerization technology. The alkaline activators such as potassium hydroxide (KOH),
sodium hydroxide (NaOH), sodium silicate (Na2SiO3) and potassium silicate (K2SiO3) are used
to activate aluminosilicate materials. The reaction occurring in the geopolymerization process
is described as shown in Equation [3]
Figure 1 Geopolymerization process
(B.V. Rangan et al, GC1 – GC4)
From the equation, the water used in the geopolymer concrete is released during the
chemical reaction that occurs during the formation of geopolymer. Mixing time of the
geopolymer concrete also plays a vital role in the gain of compressive strength. Longer period
mixing reduces the slump value and increases the density and compressive strength of the
geopolymer concrete [17].
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2. RESEARCH SIGNIFICANE
Previous studies of the geopolymer concrete is mainly based on the heat cured geopolymer
concrete. Elevated temperature curing makes them restricted to precast construction.
Nowadays various research work has been under taken to study the structural behaviour of
ambient cured geopolymer concrete making them wide application in onsite construction.
Acceleration of geopolymerisation process can be achieved by the addition various
cementitious materials like OPC, GGBFS, Slaked lime which enhances the early stage
strength.[7]. Cracks due to drying and plastic shrinkage is arrested by the addition of fibres in
the concrete.[20]. Curing condition plays major role in the strength and micro structural
development of geopolymer concrete. Low calcium-based fly ash requires elevated
temperature curing in order to achieve designated strength. [10]. Setting time of the geopolymer
concrete also influenced by the addition of additives. In ambient curing setting time of the
geopolymer concrete is reduced comparing to the heat cured geopolymer concrete
3. MATERIALS USED
3.1. Class F Fly Ash
Class F fly ash is used as the base material for the ambient cured geopolymer concrete. Fly ash
with calcium content less than10 % is termed as Class F fly ash Table 2 shows that the calcium
content in class F fly ash is less than 10%. Class F fly ash used in this research work is collected
from Thermal Power Plant, Tuticorin.
3.2. Class C Fly Ash
Class C Fly ash is used as a replacement of F fly ash is smaller quantity. Fly ash with calcium
content more than 10 % is termed as Class C Fly ash. From table 2 it is verified that the class
C fly ash used in this research work has calcium content more than 10 %. Class C fly ash used
in this research work is collected from Neyveli Power plant.
3.3. Micro Silica
Pozzolanic material which is rich in silica content is termed as micro Silica. The term micro
denotes the average size of the silica particles should be under micro size category. From SEM
image of micro silica, it is confirmed that the size of the silica particles is 0.3µm which satisfies
the micro level particle size. Fig 2 shows the white coloured micro silica which is used in the
research work.
Figure 2 Photograph of Micro Silica
3.4. Alkaline Activator
The materials rich in silicate and hydroxide is used as the activator of the geopolymer concrete.
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Parameter I: Sodium silicate and sodium hydroxide is used as the alkaline activator in this
research work.
Parameter II: Sodium Silicate to Sodium hydroxide mass ratio is fixed as 2.5
Parameter III: Molar concentration of the sodium hydroxide solution is directly
proportional to the strength of the concrete and inversely proportional to the workability of the
concrete [18-19]. Molar concentration varying from 8M to 16 M is majorly used. In this
research work 10 M molarity of sodium hydroxide solution is used.
Parameter IV: Alkaline activator fly ash mass ratio is taken as 0.35.
3.5. Steel Fibre
Hooked End steel fibre is used in this research work.
Length of the steel Fibre = 30mm
Diameter of the steel fibre = 0.5mm
length
Aspect ratio = diameter = 60.
Figure 3 Photograph of Steel Fibre
3.6. Super Plasticizers
Workability of the geopolymer concrete is increased by the addition of naphathalene based
super plasticizers. Conplast SP430 is the super plasticizers of about 20 % of fly ash is used.
4. MIX PROPORTION AND CASTING
The geopolymer mix design proportion is based on the various works on fly ash based
geopolymer concrete [3]. Various proportion of Micro Silica, Class c fly ash and Steel fibre is
fixed and mix design is done. Mix ratio for the geopolymer concrete is calculated as below
Fly ash: NaOH: Na2SiO3: FA: CA: SP
1: 0.1 : 0.25 : 1.21 : 2.83 :0.02
As per the mix design calculation table 1 shows the quantity of various materials required
for one cube casting.
Table 1 Quantity calculation of materials for 1 cube
Fly Ash
1.5Kg
Fine aggregate
1.82Kg
Coarse aggregate
3.45Kg
Super plasticizer
30g
Concrete cube of Size 150mm x 150mm x0150mm is cast to find the compressive strength
of the geopolymer concrete for various proportion. After demould the cubes are kept
undisturbed for 28 days in room temperature for curing purpose
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Figure 4 Cube Casting
Figure 5 Cubes at curing
Figure 6 Testing of Concrete
Fig 4 and 5 represents the cubes at casting and curing periods. After 28 days of curing cubes
are tested in Universal testing machine which is shown in fig 6 to find the compressive strength
of the concrete. Concrete cylinder of Size 150 mm x 300mm is cast to find the split tensile
strength of the geopolymer concrete for various proportion. After demould the specimens are
kept undisturbed for 28 days in room temperature for curing purpose.
Figure 7 Testing of Cylinder
After 28 days of curing specimens are tested in Universal testing machine which is shown
in fig 7 to find the split tensile strength of the concrete.
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5. MATERIAL CHARACTERISTICS
5.1. SEM Image of micro silica
In order to ensure the size of the cementitious material Scanning Electron Microscopic image
is taken to study the size and shape of micro silica. The SEM image is taken from Nano
technology Research Centre, Mepco Schlenk Engineering College.
Figure 8 SEM image of Micro Silica
From fig 8 it is inferred that the size of the average silica particles is about 0.3µm.
5.2. X-RAY Fluorescence Spectroscopy Of Fly Ash
Elemental analysis of fly ah is done by X-RAY Fluorescence spectroscopy. The XRF result
of both fly ash is taken from CECRI, Karaikudi. Table 2 shows the chemical composition of
both class C and class F fly ash. chemical composition of the fly ash should satisfy the ASTM
C 618 standard specification.
Figure 9 XRF images for class F and class C fly ash
Table 2 chemical composition of fly ash
Class F
Class C
Al2O3
7.15
10.47
SiO2
36.20
12.58
CaO
4.59
53.69
SO3
0.27
3.0
Fe2O3
43.27
9.85
TiO2
8.54
10.36
6. RESULT AND DISCUSSION
6.1. Compressive Strength of Concrete.
To find the optimum replacement of Class C fly ash and micro Silica with steel fibre,
geopolymer concrete cube is cast with the varying proportions of 2%,3% and 4% class C fly
ash, 3%,4% and 5% b Micro Silica with 0.1%,0.2%and 0.3% of steel fibre. Fig 10 shows the
28 days compressive strength of the geopolymer concrete of nominal mix design G25. The
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Compressive strength of 22.5 N/mm2 is achieved for conventional geopolymer in ambient
curing with 100% fly ash
30
0.1% steel
Compressive strength N/mm2
25
0.2 %
steel
20
15
0.3% steel
10
5
0
3% MS 4% MS 5% MS
+ 4% C + 3% C + 2%C
Figure 10 28 Days Compressive strength of Concrete
From fig 10 it is inferred that the geopolymer concrete with mix proportion of 4% micro
Silica + 3 % class C fly ash + 0.3% steel fibre shows the higher strength with 28 % of increase
in strength comparing to the conventional geopolymer concrete
6.2. Split Tensile Strength
Split tensile strength N/mm2
To study the tensile strength of the geopolymer concrete split tensile strength is done. The
cylindrical specimen of size 150mmx300mm is cast for varying proportions of 2%,3% and 4%
class C fly ash, 3%,4% and 5% Micro Silica with 0.1%,0.2%and 0.3% of steel fibre. Fig 11
shows the 28 days split tensile strength of the geopolymer concrete of nominal mix design G25.
The split tensile strength of 2.4 N/mm2 is achieved for conventional geopolymer in ambient
curing with 100% fly ash
3
0.1%
steel
2
0.2 %
steel
1
0.3%
steel
0
3% MS 4% MS 5% MS
+ 4% C + 3% C + 2%C
Figure 11 28 Days Split tensile strength of Concrete
From fig 12 it is inferred that the geopolymer concrete with mix proportion of 4% micro
Silica + 3 % class C fly ash + 0.3% steel fibre shows the higher strength with 20 % of increase
in strength comparing to the conventional geopolymer concrete.
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6.3. Flexural Behavior of geopolymer Beam.
Ability of a beam or lab to resist failure in bending is called flexural strength of the specimens.
Flexural strength of the specimen is expressed as Modulus of Rupture (MPa). Fig 12 shows
the sketch of two point loading in the beam. Two point loading is done to study the behaviour
of the beam under flexural failure.
Figure 12 Sketch of Two Point loading in beam
Flexural Strength
=
Pl
bxdxd
Beam of the size,
Length
= 1200mm
Depth
= 150mm
Breadth
= 100mm and
4 nos of 12 mm dia bar for main reinforcement and 8 mm dia for vertical stirrups spacing
of 140 mm c/c is cast and cured for 28 days in sunlight. After de moulding the cast beam is
kept in sunlight for 28 days for curing purpose. Fig 13 (a) & (b) shows the testing of
conventional GPC beam and optimized proportion of GPC beam with mix proportion
of 3% class C fly ash, 4% Micro Silica and 0.3 % steel fibre.
(a)
(b)
Figure 13 (a) Two point loading test on conventional GPC beam & (b) Two point loading test on
optimized GPC beam
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Load vs Deflection
Load vs deflection
deflection(mm)
Deflection (mm)
6
4
2
0
0
5
6
4
2
0
0
10
5
10
15
load(tonne)
load kN
(a)
(b)
Figure 7.14 (a) Load Vs deflection curve for conventional GPC beam & (b) Load Vs deflection curve
for optimized GPC beam.
Table 3 Result comparison for GPC beam
Beam Specimen
Initial
Crack
Load
(Tonne)
Ultimate
Load
(Tonne)
Ulitimate
Moment
(Knm)
Flexural
Strength
N/Mm2
Flexural
Rigidity
Nmm2
Conventional
Gpc Beam
3.5
8.45
26.64
42.59
5.44x1011
Optimum Gpc
Beam
5
9.85
32.20
51.53
7.24x1011
7. CONCLUSION
1. Elimination of heat curing can be achieved by the addition of class C fly ash is smaller
proportion. Formation of C-S-H gel generates hydration which is sufficient for the
curing purpose.
2. Mix proportion of 4% micro Silica + 3 % class C fly ash + 0.3% steel fibre shows 28
% of increase in compressive strength.
3. Mix proportion of 4% micro Silica + 3 % class C fly ash + 0.3% steel fibre shows the
higher strength with 20 % of increase in split tensile strength.
4. Addition of steel fibre reduces the crack propagation and helps in increase of the
compressive strength.
5. Ultimate load carrying capacity of GPC beam of proportion 3% C , 4% M and 0.3%
steel fibre increase 16.5% compare to conventional beam.
6. Onsite application of geopolymer concrete opens wide application of geopolymer
Concrete in structural application.
From the above research work it is concluded that ambient curing in geopolymer concrete
leads to a new pavement for the onsite structural application with complete elimination of
Ordinary Portland Cement (OPC).
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