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Experimental Study Of Fly Ash Based
Geopolymer Concrete with Robo Sand
V.V.S.S Chandra Sekhar1, K.Brahmani1, A.Rohit1, K.Mohan Krishna1,
C.Ravi Kumar Reddy2 1UG Student, Civil Engineering, Kallam Haranadha Reddy Institute Of Technology(KHIT), Guntur,A.P,INDIA 2Professor, Civil Engineering, Kallam Haranadha Reddy Institute Of Technology(KHIT), Guntur,A.P, INDIA
Abstract-We know that concrete is the most widely required
and used component in every construction. As concrete
requirement reach the peak, so as cement. The use of
Portland cement results in pollution to the environment due
to the release of major pollutant carbon dioxide (CO2). As
such, many alternate materials had been introduced to
exchange cement in the concrete. Fly ash which is end-
product from the coal industry is easily available material in
the world. Also, usage of fly ash is more environment-
friendly and economical compared to OPC. Fly being
sufficiently rich in silicate and aluminate reacts with
alkaline activators forming an alumino-silicate gel that
causes good binding with the aggregate resulting in the
production of good concrete. The compressive strength of
concrete increases with increase in fineness of fly ash which
leads to the decrease in permeability. Along with fly ash,
metakaolin is used. Another main component in concrete is
the fine aggregate (sand), replaced by robosand or
manufactured sand which is easily available and results in
good strength compared to normal sand. Chemicals, Sodium
Silicate (Na2SiO3) and Sodium Hydroxide (NaOH) are used
in preparing alkaline activators with a molarity of 12M. All
the cube specimens of 150X150X150 mm are cast and
cured by oven curing followed by open-air curing before
testing. These specimens are tested at different ages of 7 &
28 days.
Keywords: Geopolymerisation, fly ash, metakaolin,
robosand, alkaline activators.
I. INTRODUCTION
The present era we can observe over usage of natural
resources and environmental-friendly methods are
being developed for effective management of natural
resources which remain only 30% according to
studies. As we all know constructions now a day
reaching the sky with its advanced technologies. But
the base component of concrete remains same forever
and ever. As the requirement of concrete increases,
cement requirement increases. But the amount of
carbon dioxide produced during manufacturing
cement is 0.93 tons for a ton of cement. Hence,
definitely, an alternative material has to the used for
an eco-friendly construction. So, In 1978 Davidovits
proposed special concrete termed as "Geopolymer"
which acts as a perfect alternative for ordinary
concrete [1]. From this technology and known fact
that fly-ash, which is an end product of thermal power
plant abundantly. Tests have been made utilizing both
geopolymer technology and fly-ash. Hardjito et al
introduced the early work on fly-ash based polymer
concrete [6]. As there is an increasing demand for
high strength concrete, metakaolin came into
existence which is becomes very reactive in excess of
calcium hydroxide. High strengths can be achieved
depending upon color and quality of metakaolin. Due
to increase in construction practices demand for river
sand has been increased, as well as cost. Use of
robosand enhances the quality of concrete by reducing
the permeability as it contains perfect gradation. So, it
serves as the best alternative for river sand. Alkaline
activators are the solutions that play major role in geo
polymerization as they react with the aluminosilicates
present in fly ash.
II. LITERATURE REVIEW
G.Himali Kumari, N.Vidya Sagar et.al
studied the Strength characteristics of
concrete by partially replacing fine aggregate
with robo sand. The study is focused on
evaluating workability and strength by
incorporating robosand in proportions of
0%,50%,75% &100% for concrete grades
M25 and M35.It has been confirmed that the
strength resulted due to replacement is 8-
12% more than the similar mix with
conventional concrete.[2]
G. Hemanaag & SRK Prasad (2014)
conducted a study on Geo-polymer concrete
using Metakaolin, Fly ash replacing cement.
In this study, experiments are conducted on
fly ash and metakaolin based GPC with
various molarities of alkaline liquids. The
compressive strengths are compared for
different proportions. It is observed that
metakaolin based GPC attained higher
strengths compared to fly ash based GPC.
Also observed that molarity is directly
proportional to compressive strength i.e.
increase in molarity resulted in increase of
compressive strength.[3]
M.Muthuanand, Dr.G.Dhanalakshmi (2015) on their study on metakaolin based geopolymer concrete, came to conclusion
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that the compressive capacity of concrete cubes gradually increases with the addition of 10% of metakaolin. Due to a good alkaline reaction between fly ash and metakaolin, mix with 70% fly-ash and 30% metakaolin shows good compressive strength. Also, the increase in metakaolin proportion results good compressive strength.[7]
Chunchu Bala Rama Krishna and M.Rama Krishna investigated compressive and flexural strengths for various combinations of fly ash and metakaolin with different molarities like 8M, 10M & 12M considering M30 grade concrete. Air dry curing is adopted. The results showed that there is a significant increase in strength when the molarity has increased. It is also found that the type of metakaolin used affected the strength of geopolymer concrete. Buff colored(Pink) Metakaolin has given higher strength, unlike white metakaolin.[4]
P.K.Jamdade & U.R.Kawde investigated the behavior of fly ash based geopolymer concrete at elevated temperature curing in an oven. The cubes cast are subjected to different curing temperatures i.e. 600C, 900C & 1200C. The observed results revealed that as curing temperature increases, compressive strength increases. But cubes cured at 600C attained greater compressive strength and cubes cured at 900C & 1200C has not shown a significant increase in the compressive strength.[5]
III. Materials
A. Coarse Aggregate
Coarse aggregates used in the study are crushed
stones of 20mm and 10mm size obtained from nearby
quarry site. As per IS 10262:2009,20mm aggregates
are taken 60% of total aggregate content and 10mm
aggregates are taken 40% of total content. The
specific gravity of coarse aggregate obtained is 2.69.
Figure No.1 Coarse Aggregates
B. Fine Aggregate
The fine aggregate adopted in the present study is
robosand. Robo sand or M-Sand is used as a
replacement of river sand. Robo sand is a purified
form of quarry dust and washed to remove the fine
rock dust to enhance the quality as per IS: 2386-
1975.It has proper gradation with particle size ranging
from 0-4.75mm. It is free from deleterious substances
which are likely to be present in the normal sand. It
makes the concrete cohesive with a low number of
voids due to perfect gradation. The specific gravity of
this robo sand obtained is 2.65 and fineness modulus
is 3.5
Figure No.2 Robo Sand
C. Flyash
It is a residue that is obtained from the combustion
of coal. They are in rich in silicates and alumina
which react with the alkaline activators to produce a
gel that can bind the constituents resulting in the geo
polymerization process. Fly ash is acquired from the
Thermal power plant, Vijayawada. The present is
carried out by using Class-F Fly ash. The fineness of
fly ash is 15%. The specific gravity of fly ash
obtained is 2.13.Bulk density of fly ash is 965 kg/m3
Figure No.3 Fly ash
D. Metakaolin
Metakaolin is obtained from the clay mineral
kaolin through calcination at 650-7500 c in an
externally fired rotatory kiln. It is a highly reactive
compound and pozzolanic in nature. It is available in
different forms such as white and buff colored. In the
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present study light, buff colored metakaolin is used. It
is acquired from Surat, Gujarat by Navapad Sales.
The specific gravity of metakaolin is 2.41
Figure No.4 Metakaolin
E. Alkaline Activators
Alkaline activator adopted in the present study is a
composite mix of Sodium Hydroxide (NaOH) and
Sodium Silicate (Na2SiO3). Sodium hydroxide, also
known as caustic soda is locally available in the form
of flakes and pellets. Sodium Silicate is available in
liquid form. Sodium Hydroxide dissolves in water to
form NaOH solution. These are the most important
components in the geopolymer mix as they enhance
several reactions with aluminosilicates that are
available in fly ash and metakaolin.
Table No.1 Chemical Composition of Fly Ash
IV. METHODOLOGY
A. Alkaline Solution Preparation
The alkaline solutions are to be prepared
24hours prior to use in concrete. Sodium hydroxide
and Sodium silicate are used in preparing alkali
solution. Sodium hydroxide is present in the form of
flakes which are to be dissolved in water to make
Sodium Hydroxide solution. In the present study 12M
(12 Molarity) is considered. So, for making a 12Molar
solution 480grams of sodium hydroxide flakes are to
be dissolved in water to make a one-litre solution.
Heat is evolved when both solutions are mixed. So,
they are mixed in concrete separately.
Molarity=moles of solute/litre of solution
12M=12 molarity
=2 x molecular weight
=12 x40
=480 gm
B. Mix Design
As there are no confined codal practices for an
optimum geopolymer mix, quantities of constituents
are calculated by trail method and assuming the
density of concrete as 2400 kg/m3 and rest of the
calculation is carried out by considering the density of
concrete.
Benny Joseph and George Mathew has proved
that total volume occupied by fine & coarse aggregate
is taken as 70% which resulted in appreciable
strengths [8]. Then the occupancy of geopolymer
binders i.e., fly-ash, metakaolin& alkaline activators
is obtained as 30% of volume. The alkaline liquid to
powder content (FA & MK) ratio is adopted as 0.45.
The ratio of Na2SiO3 to NaOH is taken as 2.5.
In order to verify the feasibility of robo sand over
river sand in strength point of view, a sample mix is
done and the test results are observed
Table No.2 Mix Proportions for GPC with
Robo Sand
Table No.3 Mix Proportion for GPC with
River Sand
Oxides Percentage %
SiO2 60.53
Al2O3 26.21
Fe2O3 5.8
CaO 1.94
MgO 0.39
K2O+Na2O 1.01
SO3 0.28
Loss on Ignition 2.0
Mix No Mix Proportion
GPC 1 100%+0%MK
GPC 2 80%+20%MK
GPC 3 60%FA+40%MK
GPC 4 50%FA+50%MK
Mix No Mix Proportion
GPC 5 50%FA+50%MK
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Table No.4 Quantities of Materials
V. Test Procedure
A. Mixing and Casting
Mixing and casting of geopolymer based
concrete are similar to normal concrete.
Firstly a dry mix is prepared consisting of
coarse aggregate, robo sand, powder
content i.e., fly ash and metakaolin as per
different proportions in required
quantities. Then sodium hydroxide and
sodium silicate are added to the dry mix
separately. Proper mixing is done for 5-7
min to attain good bond between the
constituents. Then the mix is filled into
150*150*150mm moulds and to attain
uniform filling of concrete, compaction is
done at the rate of 25blows for 3 layers.
As the setting time is very slow, the cubes
are allowed to rest in the mould for 1 or 2
days. Then the cubes are removed from
the moulds for curing.
B. Curing
Curing is carried out in 2 stages. In the
first stage, the cubes are kept in the oven
for 24-48 hrs at 600c. In the second stage,
the cubes are allowed to be cured in open
atmosphere i.e., AMBIENT CURING.
C. Testing
The cubes are tested for 7 & 28 days after
curing. The compressive strength value
can be obtained by subjecting the cubes
after desirable curing period to gradual
loading under a compressive testing
machine which has a capacity of
subjecting 1000KN load.
Figure No.5 Compressive testing machine
VI. Results and Discussion
For the mix proportion 100% fly-ash and 0%
metakaolin with robosand, compressive
strength at 7days is 4.416 N/mm2 and 28
days compressive strength is 6.84 N/mm2.
For the mix proportion 80% fly-ash and 20%
metakaolin with robosand, the compressive
strength at 7days is 5.5 N/mm2 and 28 days
compressive strength is 8.36 N/mm2.
For the mix consisting 60% fly-ash and 40%
metakaolin with robosand, the compressive
strength at 7days is 6.85 N/mm2 and 28 days
compressive strength is 10.53 N/mm2.
Mix Mass Of Materials in Kg/m3
Coarse
Aggregates
Fine Aggregates Fly-ash Metakaolin NaOH Na2SiO3
20
MM
10
MM
River
Sand
Robo
Sand
GPC 1 705.6 470.4 - 504 496.551
- 63.84 159.6
GPC 2 705.6 470.4 - 504 397.2 99.351 63.84 159.6
GPC 3 705.6 470.4 - 504 297.93 198.62 63.84 159.6
GPC 4 705.6 470.4 - 504 248.27 248.27 63.84 159.6
GPC 5 705.6 470.4 504 - 248.27 248.27 63.84 159.6
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For the mix proportion 50% fly-ash and 50%
metakaolin with robosand, the compressive
strength at 7days is 8.52 N/mm2 and 28 days
compressive strength is 12.75 N/mm2.
For the mix proportion 50% fly-ash and 50%
metakaolin with river sand, the compressive
strength at 7days is 3.48 N/mm2 and 28 days
compressive strength is 5.125 N/mm2.
Table No.5 Compressive Strengths for
Different Mix Proportions
Table No.6 Compressive Strength comparison for
river and robo sand
Figure No.6 Compressive Strength At 7
days
Figure No.7 Compressive Strength At 28
days
Mix
No
Mix Proportion Compressive
Strength in N/mm2
7 Days 28 Days
GPC 1 100%FA+0%MK 4.416 6.84
GPC 2 80%FA+20%MK 5.52 8.36
GPC 3 60%FA+40%MK 6.85 10.53
GPC 4 50%FA+50%MK 8.52 12.75
Type
Of
Sand
Mix Proportion Compressive
Strength in N/mm2
7
Days
28 Days
River
Sand
50%FA+50%MK 3.485 5.125
Robo
Sand
50%FA+50%MK 8.52 12.75
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Figure No.8 Compressive Strengths at 7&28 days
Figure No.9 Compressive Strengths at 7&28 days for
river sand and robo sand
VII. CONCLUSIONS
The compressive strength of geopolymer
concrete specimens at 7 days has achieved
65% of its final strength at 28days.
For every 20% addition of metakaolin, there is an
increase of 25% in compressive strength.
For proportion containing 50%Flyash and
50%Metakaolin with robo-sand, there is an
increase of 44-48% in compressive strength
compared to that of river-sand.
There is an increase in compressive strength
as metakaolin content increases.
Low compressive strength values are resulted
due to the use of light buff colored
metakaolin and fly ash used which brought a
drastic decrease in the compressive strength.
So, metakaolin being a material that can
attain higher strengths can regulate the
strength to get lowered which is dependent
on many conditions including the color of
metakaolin used, type of curing and weather
conditions as it requires high temperatures to
get processed to result in desired strength.
The variation of strength can be observed as
a linear variation representing the peak
strength for GPC 4
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VIII. References
[1] J.Davidovits "Geopolymers Inorganic Polymeric
New Materials" 1991 Journal of Thermal Analysis 37;
1633-1656
[2] RukmangadharaRao.S et al. Int. Journal of
Engineering Research and Applications IJERA ISSN:
2248-9622, Vol No. 5, Issue 12, (Part - II) Dec 2015,
PP.84-88
[3]G.Hemanaag, S.R.K Prasad, “Geopolymer
Concrete Using Metakaolin, Fly ash and their
comparison", IJERT, Volume.3, Issue No 8, Aug
2014
[4] Chunchu Bala Rama Krishna & M.Rama Krishna
2015,”An Experimental Study on Geopolymer
Concrete with fly ash and metakaolin as source
materials", IJMETMR, Vol.2, Issue No:12
[5] P.K.Jamdade, U.R Kawade, “Evaluate Strength of
Geopolymer Concrete by Using Oven Curing” IOSR
Journal of Civil Engineering, Volume No. 11, Issue 6,
PP: 63-66, e-ISSN: 2278-1684/p-ISSN: 2320-3340,
November-December 2014.
[6] Hardjito et al., 2005 Fly Ash Based Geopolymer
Concrete, Australian Journal of Structural
Engineering, 2005. 6: pp 1-9.
[7] M.Muthuanand, G.dhanalakshmi 2016
“Metakaolin Based Geopolymer Concrete, ICCEET
2016, IJARMATE, VOLUME NO.2, Special Issue 2