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AIP Conference Proceedings 2385, 100004 (2022); https://doi.org/10.1063/5.0070991 2385, 100004
© 2022 Author(s).
Experimental investigation of geopolymer
concrete
Cite as: AIP Conference Proceedings 2385, 100004 (2022); https://doi.org/10.1063/5.0070991
Published Online: 06 January 2022
M. Saravanan, C. Aravindhan and S. Ramakrishnan
Experimental InvHstigation of Geopolymer Concrete
M.Saravanan1, a), C. Aravindhan2, b), and S. Ramakrishnan3, c)
1Department of Civil Engineering, Marri Laxman Reddy Institute of Technology and Management,
Hyderabad, Telangana, India
2Department of Civil Engineering, Bannari Amman Institute of Technology, Tamilnadu, India
3Department of Civil Engineering, Sri Krishna College of Engineering and Technology, Tamilnadu,
India
a)Corresponding author: saravananm@mlritm.ac.in
b)aravindanc@bitsathy.ac.in
c)ramakrishnans@skcet.ac.in
Abstract. Portland cement is a worldwide major building material. In addition to deforestation and the burning of fossil
fuels, the cement manufacturing sector is one carbon dioxide source. The emission to the atmosphere of greenhouse gases
like CO2 causes global warming. CO2 accounts for around 65% of global warming among greenhouse gases. Around 7% of
greenhouse gas emissions in the atmosphere of earth are contributed by the global cement industry. Alternative binders for
concrete production are needed to address environmental effects of Portland cement. For the construction of the geopolymer
horn, this project work uses low-calcium (Class F) ash based geopolymers from the National Heat Power Plant. As an
alkaline solution for the activation of fly ash, the combination of sodium silicate and sodium hydroxide solutions was
utilised. The fly-ash solution varied between 0.35, 0.40 and 0.45. Sodium hydroxide solution concentration was held at 8M
(Molars). Geopolymer concrete was different for the treatment at 60°C and 100°C as ambient curing and oven curing. The
geopolymers were tested for compressive strength at different ages, including 7, 14 and 28 days. Based on the test results, (a)
the compressive strength of geopolymer concrete is also increased as the fly ash solution increases. (b) Oven-cured
concrete's compressive strength was more than the ambient concrete. (c) Concrete compressive strength increases with the
curing temperature rising from 60°C to 100°C.
INTRODUCTION
Concrete is a widely used material for the construction of best foundations, architectural buildings,
bridges, roads, block walls, fences and pole shops. Portland cement production emits about one tonne of carbon
dioxide to the atmosphere. CO2 contributes approximately 65 percent of global warming among greenhouse
gases. Approximately 1,35 trillion tonnes/year or 7 per cent of total greenhouse gas emissions to the earth's
atmosphere is the world's share of ordinary Portland concrete (OPC) production [1]. The cement industry is
nevertheless extremely energised. After aluminium and steel, the manufacturing of Portland cement is the most
energy intensive process as it Eats 4GJ of power per tonne. The Indian cement industry is the third largest coal-
fired user in the country after thermal and iron and steel facilities. The capacity of the industry was
approximately 198 million tonnes at the beginning of 2008-09. Cement demand in India, driven by housing,
infrastructure and capital expenditures, is projected to increase by 10% annually in the medium term. Taking into
account an expected growth in production and consumption of 9-10%, the cement industry will continue to
improve its supply position in 2008-09 [1] (Ragan & Hardjito, 2006).
Ground granulate blast furnace slag (GGBS) is a by-product of iron-producing blast furnaces. GGBS is
a glassy, granular, non-metallic material composed mainly of calcium silicates and aluminates. The particle size
of GGBS is nearly the same as cement. GGBS, often blended as low-cost filler with Portland cement, increases
concrete workability, density, durability and alkaline reaction resistance [3].
MOTIVATION
The use of regular cement (silica and alumina) is high, and the daily use of cement is growing throughout the
whole world. Therefore, fly ash is an alternative innovative material. It has high cement properties and fly ash
is made out of coal which is available in thermal power station. It is a large quantity of Si-Al materials [6].
A geopolymer cement is replaced by fly ash with a more compressive strength of the concrete compared with
normal concrete, and has many further advantages. Also, fly ash is less expensive than cement as the fly ash is a
waste and can be used again [7].
International Conference on Advances in Materials, Computing and Communication Technologies
AIP Conf. Proc. 2385, 100004-1–100004-10; https://doi.org/10.1063/5.0070991
Published by AIP Publishing. 978-0-7354-4161-3/$30.00
100004-1
Geopolymer concrete's principal benefits are that normal concrete produces more CO2 to boost global warming
so as to avoid this carbon emission, as the emission of CO2 is very low, geopolymer concrete came into use.
Very much more valuable than the other types of material, geopolymer concrete has motivated us to carry on
this project [3]. The aim of the project is to study the influence of parameters such as alkaline solution to
binder ratio, curing condition on compressive strength of fly ash based geopolymer concrete at various ages.
Scope of the Study
¾
To study the effect of alkaline solution to binder ratio, concentration of sodium hydroxide solution and
curing conditions on fly ash based geopolymer concrete.
¾
Ratio of alkaline solution to binder by mass varies as 0.35, 0.40 & 0.45.
¾
Ambient curing and oven curing (60oC & 100oC) was adopted.
¾
To determine the compressive strength of fly ash based geopolymer concrete at various ages such as
7days, 14 days and 28 days.
LITERATURE REVIEW
In 1978, Davidovits proposed that binders could be produced by a polymeric reaction of alkaline liquids with
the silicon and the aluminum in source materials of geological origin or by-product materials such as fly ash
and rice husk ash. These binders were termed as geopolymers, because the chemical reaction that takes place in
this case is a polymerization process. geopolymers are members of the family of inorganic polymers. The
chemical composition of the geopolymer material is similar to natural zeolitic materials, but the microstructure
is amorphous instead of crystalline. The polymerization process involves a substantially fast chemical reaction
under alkaline condition on Si-Al minerals, that results in a three-dimensional polymeric chain and ring
structure consisting of Si-O-Al-O bonds are formed. The schematic formation of geopolymer material can be
described by the following equations[1] (Ragan & Hardjito 2006).
Hardjito and Rangan [1] had investigated the use of fly ash as binder to make concrete with no cement.
The experimental work has been done using low calcium fly ash as binder and sodium hydroxide and sodium
silicate solution as activators. The effect of salient parameters like concentration of sodium hydroxide solution,
ratio of sodium silicate solution to sodium hydroxide solution, curing temperature, curing time, handling time,
addition of super plasticizer, water content in the mixture and mixing time on the properties of fresh and
hardened concrete were discussed. Based on the compressive strength of geopolymer concrete, the recommended
values for test variables are the following (i) The concentration of sodium hydroxide solution was in the range
between 8 M and 16 M. (ii) The sodium silicate solution-to-sodium hydroxide solution ratio by mass was in the
range of 0.4 to 2.5. (iii)The alkaline solution-to-fly ash ratio by mass was approximately 0.35 to 0.45.
Vijai et. al [2] described the effect of curing types such as ambient curing and hot curing on the
compressive strength of fly ash based geopolymer concrete. For hot curing, the temperature was maintained as
60oC for 24 hrs in hot air oven. The compressive strength of hot cured concrete was higher than the ambient
cured concrete. In ambient curing, the compressive strength increases about five times with age of concrete from
7days to 28 days. The compressive strength of hot cured fly ash based geopolymer concrete has not increased
substantially after 7 days
METHODOLOGY
The physical and chemical properties of materials, mixture proportions, the mixing process and the curing
conditions of geopolymer concrete
x
Fly ash
x
Fine Aggregate
x
Coarse aggregate
x
Alkaline solution
x
Super plasticizer
x
Water content of mixture
100004-2
FIGURE 1. Flow chart
Properties of Materials
Fly ash: The fly ash used in this study was obtained from National Thermal power plant. It falls in the category
of class F grade and its chemical composition, The physical properties of fly ash were determined as per IS:
1727-1967
TABLE 1. Ingredients of fly ash (chemicals)
s. no
Ingredients
Valve
1
SiO
2
56.88%
2
Al2o3 27.65%
3
Fe
2
O+FeO
6.28%
4
TiO2 0.31%
5
CaO 3.6%
6
MgO 0.34%
7
SO4 0.27%
8
LOI
4.46%
9
Specific gravity of fly ash 2.13
TABLE 2. Physical properties of Fly ash
S.no
Ingredients
Valves
1
Specific gravity of fly ash
2.13
2
Fineness, Percentage
passing on 150 m sieve
99.6%
3
Fineness, Percentage
passing on 90 m sieve
98.1%
Results and Disucussion Experimental works
Properties of materials
Data collected
Conclusions
100004-3
Fine aggregate: The locally available river sand, passing through 4.75 mm was used in this experimental work.
The following properties of fine aggregates were determined as per IS: 2386-1963
TABLE 3. Experimental results on fine aggregate
Sl. No
Properties
Test
results
1
Specific gravity
2.65
2
Fineness modulus 2.49
3
Bulk density 1260
Kg/m3
4
Water absorption 1%
Coarse aggregate: The locally available crushed granite stone aggregate of 20mm maximum size was used as
coarse aggregate. The coarse aggregate passing through 20mm and retaining 4.75mm was used for this
experiment works. The following the properties of coarse aggregate were determined as per :2386-1963
TABLE 4. Experimental results on Coarse aggregate
Sl. No
Properties
Test results
1
Specific gravity
2.68
2
Fineness modulus 8.65
3
Bulk density 1540 Kg/m3
4
Water absorption 0.5%
Alkaline solution: As alkaline solution, a combination of sodium silicate and sodium hydroxide was used. The
sodium silicate solution A53 was used with SiO2 to Na2O mass ratios of around 2, ie (Na2O = 14.7%, SiO2 =
29.4% and water 55.9% by mass). Sodium in the form of flake or pellet was used with purity of 97-98 percent.
To achieve the required concentration, the solids must be dissolved in water. Sodium hydroxide solution
concentrations as eight molars. The sodium silicate solution ratio was fixed by mass by 2.5 to sodium hydroxide
solution. The reason was that the solution of sodium silicate was lower than that of sodium hydroxide [3].
Super Plasticizer: A sulphonated, naphthalene formaldehyde super plasticizer based on condensate was used
for the operational capabilities of fresh concrete as water-reducing agents in the concrete mixtures. A dark
brown solution containing 42 percent solids was the super plasticizer.
Water Content of Mixture: The water in the mixture reacts chemically with cement to produce a paste which
binds together the aggregates in ordinary Portland cement (OPC). By contrast, water does not cause a chemical
reaction in a low-calcium fly ash-based concrete blend. The chemical reaction in geopolymers actually produces
water which is eventually produced
MIX PROPORTIONS
The coarse and the fine aggregates, as in the case of the Portland cement concrete, occupy around 75 to 80% of
the geopolymer concrete mass. The criteria of performance depend on the application of a geopolymer concrete.
The compressive strength of hardened horn and the working capacity of fresh firms are the criteria for their
performance. The liquid to binding ratio by mass, the water-to-geopolymer solids relation by mass, the heat
curing temperature and the heat curing time shall be selected as parameters to meet the performance criteria.
Proposed guidance for design of geopolymer-based concrete heat-coated low-calcium fly ash. Data from the
design of low-calcium fly ash based geopolymer concrete were proposed in the basis of results obtained from
numerous microbials produced in the lab over a period of four years [9].
100004-4
This project work adopted the above-mentioned method for designing the mixture proportion. The mixture
ratios are 0.35 and 0.40 to 0.45 for different alkaline solutions. Mix design for low calcium ashes for alkaline
solution with a 0.35 fly ash ratio geopolymer concrete
Mix Proportions
TABLE 5. Mixture proportion per m3 of geopolymer concrete
Materials
Mass( Kg/m3)
Alkaline solution /fly ash (by mass)
0.35
0.4
0.45
Coarse aggregate
1260
1260
1260
Fine aggregate
540
540
540
Fly ash
444
429
414
Sodium hydroxide solution
45
49
53
Sodium silicate solution
111
122
133
MANUFACTURE OF GEOPOLYMER CONCRETE
Preparation of Liquids
To make the solution the solids of sodium hydroxide (NaOH) were solved in water. The mass of NaOH solids in
a solution varied depending on the level of the molar solution, M. For example, 8 M NaOH solution consisted of
8x40 = 320 grammes of NaOH (pellet-flake), per litre of solution, where 40 is NaOH's molecular weight. NaOH
solution is also used as an alternative solution. The weight of NaOH solids was measured at a concentration of
262 grammes per kg NaOH solution. It should be noted that NaOH solid mass is a fraction of the NaOH
solution's mass and water is the principal component [3].
At least one day before use to prepare the alkaline liquid, the sodium silicate solution and the sodium hydroxide
solution have been combined. On the day of the casting of the specimens, the alkaline fluid and the extra water
were mixed together to make the fluid mixture.
Manufacture of Fresh Concrete and Casting
By applying conventional techniques used in the production of Portland cement concrete, geopolymer concrete
can be constructed. In the lab the pan-mixer was used for about 3 minutes to mix fly ash and aggregates. In dry
condition the aggregates were saturated. Then the dry materials were added to the alkaline solution and the
mixture continued to produce fresh concrete for about 4 minutes. Without any sign of setting or any deterioration
in compressive strength, fresh concrete can be handled in up to 120 minutes. The fresh concrete was cast into the
moulds immediately after mixing, in three layers for cubical specimens of size 100mm x 100mm x 100mm (Fig.
FIGURE 2. Fresh Geopolymer concrete
2). For compaction of the specimens, each layer was given 60 to 80 manual strokes using a Roding bar [7].
100004-5
Curing of Geopolymer Concrete
It is generally recommended to heat low-calcium fly ash ash-based geopolymer concrete. The chemical reaction
in a geopolymer paste is significantly assisted by heat curing. The compressive strength of the geopolymer
concrete depends on curing time and curation temperature. The duration of the healing was between 4 and 96
hours. The polymerization process improved longer curing time, leading to a higher compressive strength. The
strength rates were rapid to 24 hours and the strength gain was only moderate beyond 24 hours. Increased
geopolymer concrete curing temperature resulted in increased compression force. Either steam curing or dry
curing can achieve heat treatment. Approximately 15 percent higher than steam cured geopolymer concrete, dry
cured geopolymer concrete has a compressive strength. The required temperature can be as low as 30° for heat
curing. In tropical climates, the ambient conditions can provide for this range of temperatures. In addition, heat
heat heating can be delayed for several days for geopolymer concrete. There was no compressive strength
deterioration due to the delay in heat heat treatment until 5 days. In fact, such a delay in the start of heat curing
substantially increased the compressive strength of geopolymer concrete. This may be due to the
geopolymerisation that occurs prior to the start of heat curing.
Curing of Test Specimens
Following casting, specimens of geopolymer concrete were immediately cured. In this study two types of
healing, namely oven treatment and ambient curing, were used. The test specimens were healed in the oven for
the oven curing and kept at a room temperature for ambient healing. Examples were oven-cured 24 hours in the
oven at 60oC and 100oC. After the treatment period, test specimens were laid in the moulds for at least 6 hours,
so that the environmental conditions were not changed drastically. The specimens had been left in the laboratory
for air-dry until the day of testing after demolding. The oven heals the samples and under the ambient healing
RESULTS AND DISCUSSIONS
Test for compressive strength: The compressive strength test on hardened fly ash based geopolymer concrete
was performed on standard compression testing machine of 3000kN Capacity, as per IS: 516-1959. Totally 81
number of cubical specimens of size 100mm x 100mm x 100mm was casted and tested for the compressive
strength at the age of 7days, 14days and 28days. The compressive strength test was performed as shown in
of three test concrete cubes.
Compressive strength = ܮܽ݀ ܽݐ݂݈ܽ݅ݑݎ݁
ܣݎ݁ܽ ݂ܿݑܾ݁ (1)
FIGURE 3. Specimens under ambient curing
process (Fig. 3).
Figure 4. Each of the compressive strength test data corresponds to the mean value of the compressive strength
100004-6
TABLE 6. Compressive Strength of geopolymer concrete for Alkaline solution to fly ash ratio of 0.35
Curing condition
Concentration
of
NaOH liquid(in
Molars)
Compressive strength at
various
ages (N/mm2)
7 days
14 days
28 days
Ambient curing
8M
3.2
8.5
4
14.
Oven curing at
8M
14.6
16.7
20.
60oC
2
Oven curing
8M
16.9
18.7
22.
at100oC
4
30
25
20
15
10
5
0 7 days 14 days 28 DAYS
GRAPH 1. Variation of Compressive Strength with Curing Conditions for alkaline solution to fly ash ratio of 0.35
TABLE 7. Compressive Strength of geopolymer concrete for Alkaline solution to fly ash ratio of 0.40
Curing condition
Concentration
of
NaOH liquid (in
Molars)
Compressive strength at
various
ages (N/mm2)
7 days
14 days
28 days
Ambient curing
8M
5.8
11.5
16.3
Oven curing
at 60o
C
8M 16.2
20.3
21.5
Oven
curing at100o
C
8M 17.7
21.8
24.2
18.7
22.4
20.2
16.9
14.4
14.6
16.7
8.5
3.2
Compressive strength
N/mm
2
FIGURE 4. Compressive Strength of cube specimen
100004-7
30
25
20
15
10
5
0 7 Days 14 Days 28Days
Ambient curing Oven curing- 60oC Oven curing- 100oC
GRAPH 2. Variation of Compressive Strength with Curing Conditions for alkaline solution to fly ash ratio of 0.40
TABLE 8. Compressive Strength of geopolymer concrete for Alkaline solution to fly ash ratio of 0.45
Curing condition
Concentration
of
NaOH liquid(in
Molars)
Compressive strength at
various
ages (N/mm2)
7 days
14 days
28 days
Ambient curing
8M
9.4
12.9
18.5
Oven curing at 60 oC 8M 17.4
22.5
24
Oven curing at 100oC
8M 22.4
24.1
27
30
25
20
15
10
5
0 7 Days 14 days 28 days
Ambient curing Oven curing- 60oC Oven curing- 100oC
GRAPH 3. Variation of Compressive Strength with Curing Conditions for alkaline solution to fly ash ratio of 0.45
TABLE 9. Effect of alkaline solutions on Compressive Strength
Concentration of
NaOH sol (in
molars)
Ratio of alkaline
solution to fly ash
(by
mass)
Compressive strength at 28th
day
(N/mm
2
)
Ambient
Curing
Oven
cured
at
60°C
Oven cured
at 100°C
8M
0.35
14.4
20.2
22.4
8M
0.4
16.3
21.5
24.2
8M
0.45
18.5
24
26
24.2
20.3
21.5
16.3 16.2
21.8
17.7
11.5
5.8
24.1 27
22.5
24
22.4
18.5
17.4
12.9
Compressive strength
N/mm
2
Compressive strength
N/mm
2
100004-8
30
25
20
15
10
5
Ambient curing Oven curing- 60oC Oven curing- 100oC
GRAPH 4. Effect of curing temperature on Compressive strength
CONCLUSION
¾
The compressive strength of oven cured concrete, regardless of age, was higher than the ambient
cured concrete solution of fly ash.
¾
A compressive force of 28 days of oven cured specimens at 600&1000C for alkaline fly ash ratios
of 0.35 is 25 percent and 35 per cent greater than that of ambient cured specimens.
¾
The compressive strength of the oven-curing specimens for the period of 28 days is 1.3 times 1.4
times higher than for the ambient fly-ash ratio of the specimens cured at 600&1000C.
¾
The compression capacity of 28 days for the 600&1000C oven cured specimens is 1.3 times and
1.1 times higher than for the cured ambient samples for alcaline fly ash ratios of 0.45.
¾
Fly ash-based geopolymer concrete cured in the laboratory ambient conditions gains compressive
strength with age.
¾
In ambient curing, compressive strength at 28 days is about 3 times and 1.4 times higher than 7
and 14 days respectively.
¾
Increase in alkaline solution to fly ash ratio by mass, results in increase in the compressive strength
of fly ash-based geopolymer concrete.
o
When compressive strength was plotted against alkaline solution to fly ash ratio, 0.4 &
0.45 ratio was seen to be
1.8 & 2.9 times respectively greater than the 0.35 ratio and by percentage it was 44%
&66% higher during the initial 7 days.
o
Similarly, after 14 days for 0.4 & 0.45 ratio was seen to be 1.3 & 1.5 times respectively
greater than the 0.35 ratio and by percentage it is 26% &34% higher comparatively.
o
Likewise at the interval of 28 days for 0.4 & 0.45 ratio was seen to be 1.1 & 1.3 times
respectively greater than the 0.35 ratio and by percentage it is 11%&22% higher
comparatively.
¾
The maximum compressive strength achieved in this project work for low calcium fly ash based
geopolymer concrete is 27MPa.
¾
There is no substantial gain in the compressive strength of oven-cured geopolymer concrete with age
beyond 7days.
o
During ambient curing the compressive strength was increased by 77% from 7
days to 28 days.
o
Similarly, during oven curing the compressive strength was increased by 24%
from 7 days to 28 days.
¾
Increase in curing temperature in the range of 60°C to 100°C, causes marginal increase in
27
24
24.2
22.4
18.5
16.3
21.5
20.2
14.4
AL/FA
=0.35
AL/FA
=0.4
100004-9
compressive strength of fly ash-based geopolymer concrete.
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1.
D. Hardjito. and B. V, Rangan, Development and properties of low calcium fly ash based geopolymer,
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2.
K. Vijay, R. Kumutha , and B. G. Vishnuram, Influence of curing types on strength of Geopolymer
concrete, International Conference on Advances in Materials and Techniques in civil Engineering
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3.
D. Ravikumar, S. Peethamparan and N. Neithalath, Structure and strength of NaOH activated concretes
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4.
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D. Hardjito and M. Z., Tsen, Strength and Thermal stability of fly ash based geopolymer mortar, The
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7.
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8.
IS: 1727 – 1967, “Methods of test for Pozzolanic materials”, Bureau of Indian Standards, New Delhi.
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IS: 2386 – 1963, “Methods of test for aggregates for concrete”, Bureau of Indian Standards, New
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100004-10
