Geopolymer concrete is a cement less concrete gaining popularity globally towards the sustainable development. It is a type of amorphous alumino-silicate cementitious material which can be synthesized by polycondensation reaction of geopolymeric precursor and alkali polysilicates. Beside fly ash, alkaline solution is utilized to make geopolymer paste which binds the aggregates to form geopolymer concrete. In this experiment an attempt is made to study the compressive, flexural and split tensile strength properties of geopolymer concrete. Concrete cubes of size 100 x 100 x 100 mm or 150 x 150 x 150 mm, beams of size 100 x 100 x 500 mm and cylinders of 150 mm diameter x 300 mm length are prepared and cured under ambient curing. The compressive strength was found out at 7 days and 28 days.

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 6, Issue 11, Nov 2015, pp. 149-155, Article ID: IJCIET_06_11_015
Available online at
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=6&IType=11
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication
___________________________________________________________________________
STUDY ON STRENGTH PROPERTIES OF
LOW CALCIUM BASED GEOPOLYMER
CONCRETE
K Venkateswara Rao
Civil Engineering, Gudlavalleru Engineering College, Andhra Pradesh, India
A.H.L.Swaroop
Civil Engineering, Gudlavalleru Engineering College, Andhra Pradesh, India
Dhanasri K
Civil Engineering, Gudlavalleru Engineering College, Andhra Pradesh, India
Sailaja K
Civil Engineering, Gudlavalleru Engineering College, Andhra Pradesh, India
ABSTRACT
Geopolymer concrete is a cement less concrete gaining popularity globally
towards the sustainable development. It is a type of amorphous alumino-
silicate cementitious material which can be synthesized by polycondensation
reaction of geopolymeric precursor and alkali polysilicates. Beside fly ash,
alkaline solution is utilized to make geopolymer paste which binds the
aggregates to form geopolymer concrete. In this experiment an attempt is
made to study the compressive, flexural and split tensile strength properties of
geopolymer concrete. Concrete cubes of size 100 x 100 x 100 mm or 150 x 150
x 150 mm, beams of size 100 x 100 x 500 mm and cylinders of 150 mm
diameter x 300 mm length are prepared and cured under ambient curing. The
compressive strength was found out at 7 days and 28 days.
Key words: Compressive Strength, Flexural Strength, Fly Ash, Geopolymer
and Split Tensile Strength.
Cite this Article: K Venkateswara Rao, A.H.L.Swaroop, Dhanasri K and
Sailaja K, Study on Strength Properties of Low Calcium Based Geopolymer
Concrete. International Journal of Civil Engineering and Technology, 6(11),
2015, pp. 149-155.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=6&IType=11

2. K Venkateswara Rao, A.H.L.Swaroop, Dhanasri K and Sailaja K
http://www.iaeme.com/IJCIET/index.asp 150 editor@iaeme.com
1. INTRODUCTION
Ordinary Portland cement (OPC) is the primary binding material used in the
preparation of concrete. As we know cement is the backbone for global infrastructural
development, it was estimated that 7% of the world’s carbon dioxide is attributable to
Portland cement industry. Because of the significant contribution to the environmental
pollution & to the high consumption of natural resources like limestone etc., we can’t
go producing more and more cement.
Amount of the carbon dioxide released during the manufacture of OPC due to the
calcinations of limestone and combustion of fossil fuel is in the order of one ton for
every ton of OPC produced. In addition, the extent of energy required to produce OPC
is only next to steel and aluminium. So there is a need to economise the use of
cement. One of the practical solutions to economise cement is to replace with
supplementary cementations materials like fly ash, slag and Metakaolin. On the other
hand, the abundant availability of fly ash worldwide creates opportunity to utilise this
by-product of burning coal, as a substitute for OPC to manufacture concrete. The total
production of fly ash is nearly is as same as that of cement (75 million tons). But our
utilisation of fly ash is only 5% of the production. Therefore, the use of fly ash must
be popularised.
Flyash, When used as a partial replacement of OPC, in the presence of water and
in ambient temperature, reacts with the calcium hydroxide during the hydration
process of OPC to form the calcium silicate hydrate (C-S-H) gel. The development
and application of high volume fly ash concrete, which enabled the replacement of
OPC up to 60% by mass, is a significant development.
In 1978, Davidovits (1999) proposed that binders could be produced by a
polymeric reaction of alkaline liquids with the silicon and the aluminium in materials
of geological origin or by-product materials such as fly ash and rice husk ash. He
termed these binders as geopolymers.
Palomo et al (1999) suggested that pozzolana such as fly ash might be activated
using alkaline liquids to form a binder and hence totally replace the use of OPC in
concrete.
In 2001, when this research began, several publications were available describing
geopolymer pastes and geopolymer coating materials (Davidovits 1991;
Davidovits1994; Davidovits. 1994; Balaguru,. 1997; van Jaarsveld,. 1997; Balaguru
1998; van Jaarsveld. 1998; Davidovits 1999; Kurtz. 1999; Palomo. 1999; Barbosa.
2000). However, very little was available in the published literature regarding the use
of geopolymer technology to make low calcium (ASTM Class F) fly ash-based
geopolymer concrete.
This research was therefore dedicated to the development, the manufacture, and
the engineering properties of the fresh and hardened low-calcium (ASTM Class F)
flyash-based geopolymer concrete.
2. EXPERIMENTAL PROGRAM
Sodium Hydroxide flakes are dissolved in distilled water to make solution of desired
concentration. To this solution calculated amount of sodium silicate in gel form is
added and thoroughly mixed. This alkaline solution is prepared 24 hours prior to use.
Fly ash and the aggregates are mixed together in a tray for about three minutes (dry
material mix). Sodium hydroxide and sodium silicate solution is mixed with the dry
material mix. Mixing is done for five to ten minutes. The fresh concrete is then casted

3. Study on Strength Properties of Low Calcium Based Geopolymer Concrete
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into the moulds immediately after mixing, in three layers. Each layer is tamped 35
times with a standard tamping rod. Three types of mixes are mixed with varying
concentration of Sodium Hydroxide i.e., mixes of 10 Molar, 14 Molar and 16 Molar
concentrated alkaline solution. Mud oil is applied to the inside surfaces of moulds
carefully since Geopolymer concrete is very highly sticky material. The moulds after
casting should be placed in a closed room at night time and should be shifted to a
place of enough sunlight at day time. They are demoulded after placing them under
sunlight for 3 to 4 days.
Based on earlier research conducted in Materials testing lab by the author, the
following parameters were maintained constant throughout the Experimental work.
The parameters are
• The ratio of sodium silicate to sodium hydroxide =2.5
• Ratio of Fine aggregate to total Aggregate = 0.35
2.1. Fly ash
In the present experimental work, low calcium, Class F (American Society for Testing
and Materials 2001) dry fly ash obtained from the silos of NTTPS, Vijayawada,
Andhra Pradesh was used as the base material
Table 1 Chemical Composition of Flyash
S. No Test Parameters Result (%)
1 Sio2 66.80
2 Al2O3 24.50
3 Fe2O3 4.00
4 CaO 1.50
5 MgO 0.45
6 Na2O 0.40
7 K2O 0.22
8 MnO 0.03
9 TiO2 0.75
10 Cl <0.01
11 P2O5 0.40
12 ZnO 0.01
13 LOI 0.65
Table 2 PhysiTcal Properties of aggregates
S.No
Type of
Aggregates
Specific
Gravity
Crushing
value,%
Fineness
modulus
Water
Absorption,%
1 Coarse aggregate 2.78 27.5 6.65 1.14
2 Fine aggregate 2.67 _ 2.55 1.07
IS 383:1970 2.6-2.8 45% 5.5-8.0 <10

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2.2. Alkaline Liquids
In the present study we have used a combination of sodium hydroxide (NaOH) and
sodium silicate (Na2SiO3) solutions. The sodium hydroxide solids were either a
technical grade in flakes form (3 mm), 98% purity, and obtained from National
scientific company, Vijayawada, or a commercial grade in pellets form with 97%
purity, obtained from National Scientific, Vijayawada. The sodium hydroxide
(NaOH) solution was prepared by dissolving either the flakes or the pellets in water.
The mass of NaOH solids in a solution varied depending on the concentration of the
solution expressed in terms of molar, M. Molar concentration or molarity is most
commonly in units of moles of solute per litre of solution. For use in broader
applications, it is defined as amount of solute per unit volume of solution. For
instance, NaOH solution with a concentration of 16M consisted of 16x40 = 640 grams
of NaOH solids (in flake or pellet form) per litre of the solution, where 40 is the
molecular weight of NaOH. The mass of NaOH solids was measured as 262 grams
per kg of NaOH solution of 16M concentration. Sodium silicate solution obtained
from National scientific company, Vijayawada was used. The chemical composition
of the sodium silicate solution was Na2O=14.7%, SiO2=29.4%, and water 55.9% by
mass.
These solutions were prepared one day before the casting day because for a better
chemical reaction between them and in order to obtain a better binding nature.
Specific gravity of Sodium Hydroxide (NaOH) = 1.47
Specific gravity of Sodium Silicate (Na2SiO3) = 1.6
2.3. Mixing and Compaction
The aggregates in saturated surface dry condition and the dry fly ash were mixed in a
tray manually for 3-4 minutes. At the end of this mixing, the liquid component of the
geopolymer mixture, i.e. the combination of the alkaline solution, was added to the
solids, and the mixing continued for a specified period of time.
Hand compaction- The standard tamping bar of 600 mm length and 16mm
diameter is used and the strokes of the bar shall he distributed in a uniform manner
over the cross-section of the mould. For cubical specimens, concrete is casted in 3
layers and each layer is subjected to 35 strokes for 15 cm cubes. Cylindrical
specimens are casted in three layers and each layer is subjected to 30 stokes. The top
surfaces of specimens are finished thoroughly.
2.4. Curing
Curing is a procedure that is adopted to promote the hardening of concrete under
conditions of high temperature and humidity. In this experiment curing was carried
out at an open atmosphere in sunlight for early setting and hardening of Geopolymer
concrete. Sunlight curing has a major influence on the properties of GPC compared to
other types of curing. The test specimens were left in the mould for about four to five
days. The samples were then removed from the moulds and placed in sunlight for 28
days before testing.

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Table 3 Test results of Geopolymer Concrete
Mix
Molarity
of NaOH
solution
Curing
Method
Compressive
Strength (N/mm2
)
Split Tensile
Strength
(N/mm2
)
Flexural
Strength
(N/mm2
)
7days 28days 7days 28days 7days 28days
M1 10M
Ambient
curing
20.70 26.95 2.22 2.50 2.94 3.98
M2 14M
Ambient
curing
25.15 32.10 2.76 2.97 3.39 4.52
M3 16M
Ambient
curing
27.23 34.67 2.91 3.48 3.55 4.73
Figure 1 Compressive strength of Geopolymer Concrete vs Days
Table 4 Test results of Conventional Concrete
Type of Test 28 Days Strength in MPa
Compressive Strength 36.3
Flexural Strength 4.88
Split Tensile Strength 4.23
Table 5 Comparison of GPC with CC
Type of Test Geopolymer Concrete in MPa Conventional Concrete in MPa
Compressive Strength 34.67 36.3
Flexural Strength 4.73 4.88
Split Tensile Strength 3.48 4.23
0
5
10
15
20
25
30
35
40
3 7 14 28
StrengthinMPa
Days
10 Molar
14 Molar
16 Molar

6. K Venkateswara Rao, A.H.L.Swaroop, Dhanasri K and Sailaja K
http://www.iaeme.com/IJCIET/index.asp 154 editor@iaeme.com
Figure 2 Comparison of GPC with CC
3. CONCLUSION
1. With increase in concentration of NaOH, the strength of GPC increases ( i.e.,
compressive, flexural and split tensile strengths increases)
2. With evaporation of water from GPC in sunlight, concrete gets harder.
3. On comparison with conventional concrete, GPC takes more time to get harder i.e.,
initial and final setting times of GPC are very high.
4. Current research is focusing on the strength properties of geopolymer in aggressive
high temperatures of sunlight.
5. From the experimental investigation it can be concluded that Geopolymer concrete
can perform well even under ambient conditions of Sunlight.
6. To attain better strengths even at the early age of concrete inclusion of steel fibers is
recommended
7. As GPC is dense concrete, use of light weight aggregate is recommended.
8. The Geopolymer Concrete showed satisfactory performance in comparison to
conventional concrete
REFERENCES
[1] Hardjito, D. and Rangan, B. V. (2005), Development and Properties of Low-
Calcium Fly Ash-based Geopolymer Concrete, Research Report GC1, Faculty of
Engineering, Curtin University of Technology, Perth, available at espace@curtin.
[2] Modified guidelines for geopolymer concrete mix design using indian standard
by R. Anuradha, V. Sreevidhya, R. Venkatasubrahmani and B.V Rangan, dept of
civil eng. Vlb janakiammal college engineering and technology, kovaipudur,
coimbatore.
[3] IS 383-1970 Specification for coarse and fine aggregates from natural sources for
concrete.
[4] Vijaya Rangan B. Mix design and production of fly ash based geopolymer
concrete The Indian Concrete Journal, May (2008)7-14.
[5] IS 10262-2009 Recommended guidelines for concrete mix design.
[6] IS 516 -1959 Methods of tests for strength of concrete.
0
5
10
15
20
25
30
35
40
Split Tensile
Strength
Flexural Strength Compressive
Strength
StrengthinMPa
Conventional Concrete
Geopolymer Concrete

7. Study on Strength Properties of Low Calcium Based Geopolymer Concrete
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