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Experimental Investigation on Geopolymer Bricks

Subharajit Roy1, Sanjith J2,Jagath H R3, Chethan G4
1Research Scholar, Dept. of Civil Engineering, Adichunchanagiri Institute of Technology, Karnataka, India.
2,3,4Assistant Professor, Dept. of Civil Engineering, Adichunchanagiri Institute of Technology, Karnataka, India.
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Abstract - Fly ash, also known as “pulverized fuel ash” in coal (65% of India’s coal production annually). This hefty
many countries such as England, Northern Ireland, and amount of produced fly ash in India covers nearly 15,000
Scotland etc. is a coal combustion product. It is composed of hectares of useful land as only 3% to 4% of the produced fly
fine particles of burnt fuels and fuel gases emitted from coal- ash is being recycled, whereas countries like China, America,
fired boilers. Though it was causing severe air pollution, in the and European nations utilize 40% of their produced fly ash.
past, fly ash was usually released into the atmosphere as it is
mainly a thermal waste of coal firing thermal plants. But With the above-stated complications from brick
presently, according to air pollution control standards, it is manufacturing, fly ash production and urbanization, it is
captured prior to release by fitting pollution control extremely important to rethink about the possibilities of
equipment. Due to its pozzolanic nature, recycled fly ash is alternative raw materials for brick manufacturing and
usually used as the production of hydraulic cement and a sustainable development to protect the further land
complete and/or partial replacement for Portland cement in degradation. Concrete is still one of the most popular
concrete production. Potential of fly ash as a material is not construction materials on earth. The cement manufacturing
only restricted to cement and concrete industries. It can be industries usually use fly ash as a partial and/or complete
utilized as a raw material for brick production, which will be a replacement to make Portland cement. Ordinary Portland
positive answer towards both environmental and economic cement (OPC) typically produces a large amount of carbon
complications. The purpose of this particular study is to dioxide (CO2) in the nature that significantly contributes to
explore the performance of Geopolymer brick consists of fly greenhouse gas emissions. Geopolymer solid brick is an
ash as one of its chief material. The bricks were casted with innovative building material, normally produced by the
clay soil to fly ash in the different proportion of 100:0, 80:20, chemical reaction of inorganic particles which has a huge
70:30, 60:40 and 50:50. Sodium fume solution was applied as potential to deplete the greenhouse emission by 80%. This
an alkaline-activator and a ratio 1:2 of water to NaOH study is to present the technology behind the producing of
solution was used as the binder solution. With an optimum geopolymer solid bricks using low-calcium (Class-F) dry fly
water/binder ratio of 0.416 and adopted dimension of (200 X ash as its main source material and to discover and evaluate
100 X 100) mm. The experimental outcomes were compared of the physical and durable properties of it.
with locally available conventional bricks.
1.1 Geopolymer
Key Words: Light weight bricks, clay soil, fly ash (class-
F), geopolymer, compressive strength, water absorption. In the 20th century, Viktor Glukovsky of Kiev developed a
concrete material which was then known as “Soil Cement or
1. INTRODUCTION soil silicate concrete”. When a French material scientist
named Joseph Davidovits introduced geopolymer concept,
India, a country over a billion of its population and a total both the definition and terminology of geopolymer became
geographical area of 328.73 million hectares (MH), of which very diverse and often contradictory. With ongoing
approximately 32% (105 MH) of its facing land degradation. innovations in the polymer science, the definition of
With a whopping 82.6 million hectares as its gross irrigated geopolymer became different for different groups of
crop area, India stands at the top of the world in agriculture, scientists (chemists, geopolymer material chemists, alkali-
defeating countries such as The United States and China. cement scientists, geopolymer ceramic chemists and ceramic
Currently, India produces over 360 billion bricks annually scientists etc.). Generally, geopolymers are a typically
for which the net consumption is over fifteen thousand inorganic and alumino-silicate (Si-O-Al) based ceramic
hectares of land with a serious adverse impact on soil material similar to zeolites. The formation of geopolymers is
erosion and unprocessed emissions. To produce a quick reaction of the alkaline activated solution with silica-
conventional bricks, brick manufacturing industries nearly alumina minerals which further forms a three-dimensional
uses 2,200 m3 per billion bricks per annum of soil. polymeric long chain of an amorphous covalent bond
Oversimplification of the data can be inferred as, for network. The polymer study constitutes a diverse group
production of only millions of clay bricks, 0.75 hectares of which consists of polymer science, chemistry, and
land is required annually. Furthermore, concern arises as the engineering. Polymers are of two kinds, either organic
Thermal Power Plants (TPP) of India produces over 120 (carbon-based) or inorganic (Ex. Silicon-based). The organic
millions of fly ash annually from approx. 260 million tons of polymers further classified as natural polymers (rubber,

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cellulose etc.), synthetic organic polymers (textile fibers,

plastics, films etc.) and natural biopolymers (biology,
medicine etc.). The name geopolymer derived from the rock-
forming raw materials which are of geological origin and
used in the synthesis process for silicon-based polymers.

1.2 Development of Geopolymer Bricks

Generally, fly ash of class F is rich with silica and alumina
content. When fly ash (class-F) is used in the brick
manufacturing, the high amount of silica and alumina reacts
Fig-1: Clay Soil (Source: Chikkamagaluru, Karnataka)
with alkali activated pre-mixed solution of sodium hydroxide
and sodium silicate. This reaction activity results in gel 3.2 Fly Ash
formation which is known as the binder hence there is no
requirement of cement in this brick production. Fly ash is generated as a by-product in the thermal power
plants due to the combustion process of pulverized coal. The
2. OBJECTIVES low-calcium (ASTM Class F) fly ash was collected from
Ennore thermal power plant, Tamil Nadu and used in this
The objectives of this study is,
experiment. The chemical and physical properties are as
i. To introduce substantial light weighted bricks in the follows.
field of construction.
Table-2: Chemical Composition of Fly ash (Class-F)
ii. To develop and study salient properties of
geopolymer bricks. Chemical composition of Fly ash Weight in %
iii. To implement and investigate a process of casting Silica 55-65
and curing, which doesn’t require an enormous
amount of water. Aluminium oxide 22-25
Iron oxide 5-7
3. MATERIALS and IT’S PROPERTIES
Calcium oxide 5-7
3.1 Clay Soil
Magnesium oxide <1
For this experimental study, clay soil is excavated and Titanium oxide <1
gathered from the site in Chikkamagaluru, Karnataka and
sieved with 4.75mm IS sieve. The physical properties of used Phosphorous <1
clay soil are shown in the table below. Sulphates 0.1
Table-1: Physical properties of Clay soil Alkali oxide <1
Loss of ignition 1-1.5
Characteristics Value Unit
Specific gravity 2.20 - Table-3: Physical Properties of Fly ash (Class-F)
Moisture content 1.80 %
Sieve Size Weight Retained
Liquid limit 30 % % Passing
(micron) (Grams)
Plastic limit 14.58 % 90 95 92
Grain size distribution analysis 75 122 83
30
i. Gravel
53 % 45 704 62
ii. Sand
17 Specific Gravity 1.8
iii. Silt & Clay
Fineness 519 m2/Kg
Standard Proctor Test
i. Maximum Dry Density (MDD) g/cc
2.88
ii. Optimum Moisture Content %
12
(OMC)

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4.2 Mix Proportioning and Material Quantity

The various proportions of materials were used and mixed
for the casting of geopolymer bricks that are as follows-

1. 100% soil +0% fly ash +water

2. 50% soil +50% fly ash + Alkaline solution (NaOH +

Na2SiO3) +water

3. 60% soil +40% fly ash + Alkaline solution (NaOH +

Fig-2: Fly ash (Source: Ennore Thermal Power Plant, Na2SiO3) +water
Tamil Nadu)
4. 70% soil +30% fly ash + Alkaline solution (NaOH +
3.3 Water Na2SiO3) +water

Locally available portable water confirming to Indian 5. 80% soil +20% fly ash + Alkaline solution (NaOH +
standard code IS: 456-2000 is used. Na2SiO3) +water

3.4 Sodium Hydroxide (NaOH) Sodium hydroxide and sodium silicate solutions were mixed
together with an extra amount of water (if required) to
Sodium hydroxide is an inorganic compound, used as a base prepare the alkaline solution. This compound alkaline
in chemical reactions. It can easily dissolve in water and solution was prepared just before it was mixed with the dry
forms series of hydrates (NaOH.nH2O). For this experiment, materials. During the early stages, for all of the above
several concentrated NaOH solutions (in terms of molarity) different material proportions, the molar ratio of the alkaline
were prepared by using sodium hydroxide pellets. solution was kept constant at 1:10. In later stages of the
experiment and with the help experimental data, soil to fly
3.5 Sodium Silicate (Na2SiO3) ash ratio 70:30 was selected as the best combination among
the rest. With the constant soil to fly ash ratio, the molar
Sodium silicate is colourless transparent solids or white
ratios of the alkaline solution were varied as 1:8, 1:12, 1:14.
powders, adhesive in nature and soluble in water in various
degrees. Usually stable as a chemical compound, sodium Table-4: Quantity of materials (With a constant molar ratio
silicate produces alkaline solution when it dissolves in water. of 1:10)
In this research activity, various concentrated (in terms of
molarity) sodium silicate solutions were made out of its Soil Fly ash Molar Na2SiO3 NaOH
powder form. Proportion
(kg) (kg) ratio (ml) (ml)
4. MIX DESIGN and PROPORTIONING 100:0 3.3 0 1:10 10 40
50:50 1.65 1.65 1:10 10 40
4.1 Preparation of Alkaline Solution (For Molar ratio-
1:10) 60:40 1.98 1.32 1:10 10 40

i. Sodium Silicate (Na2SiO3) Solution- 70:30 2.2 1.1 1:10 10 40

80:20 2.7 0.6 1:10 10 40
As we know, the molecular weight of Na2SiO3 powder is
212.14 gm. For 1M solution, 212.14 gm of Na2SiO3 needs to
be dissolving into 1000 ml of distilled water. So for 1M Table-5: Quantity of materials (With a constant soil to fly
solution, if we use a smaller quantity of water, (for example ash ratio)
100 ml of water) the required amount of Na2SiO3 powder Soil Fly ash Molar Na2SiO3 NaOH
will be 2.12 gm. Proportion
(kg) (kg) ratio (ml) (ml)
ii. Sodium Hydroxide (NaOH) Solution- 70:30 2.2 1.1 1:10 10 40

Similarly, the molecular weight of NaOH pellets is 40 gm. For 70:30 2.2 1.1 1:8 20 60
1M solution, 40 gm of NaOH needs to be dissolving into 1000 70:30 2.2 1.1 1:14 30 70
ml of distilled water. So for the preparation of 10M solution,
40 gm of NaOH dissolved in 100 ml of distilled water. 70:30 2.2 1.1 1:12 20 80
70:30 2.2 1.1 1:10 10 50

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5. MIXING, CASTING and CURING

Rectangular moulds with a cross section of 20 cm x 10 cm x
10 cm were prepared. Initially, clay soil and fly ash were
weighed according to the selected ratio. After that, both of the
materials were mixed with dry hands until the uniform
colour appeared (approximately for 3 minutes).
Simultaneously, the alkaline solution was prepared with the
help of sodium silicate and sodium hydroxide solutions. The
final mix was prepared by mixing dry mixed material with the
alkaline solution until a uniform mix was developed (approx.
3 to 4 minutes). During the casting process, a limited amount
of water was added up to the level of requirement. This mix
then immediately casted into moulds, the required amount of
compaction was done and surface finishing was given to each
moulds. The specimen then dry cured at an optimum
temperature of 60oC inside an oven. After completion of the Fig-5: Geopolymer Bricks with Material Ratio 70:30
required curing period inside the oven, the brick specimens
were kept inside the moulds for at least six hours in order to
avoid a drastic change in the environmental conditions. After
six hours, the specimens were finally de-moulded and were
left to air-dry in the laboratory until the day of the test.

Fig-6: Geopolymer Bricks with Material Ratio 80:20

6. TESTS and RESULTS

Fig-3: Dry Hand Mixing of Materials 6.1 Compressive Strength Test

Compressive strength of the bricks is tested with the help of
compression testing machine. The compression testing
machine is having a capacity of 2000 KN, and loaded at a
constant rate of loading at 200kg/cm2/min as per Indian
standard procedure for clay bricks and fly ash bricks (IS:
1077-1992 and IS: 12894-2002). The compressive strength
check is done for both 7 and 14 days specimens with
combinations of different material ratios and different molar
ratios of the alkaline solution. The results are as follows-

Fig-4: Dry Hot Oven Curing

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Table-6: Compressive Strength of Geopolymer Bricks

(Keeping molarity of alkaline solution as 1:10)

Chart-2: Compressive Strength of Geopolymer Bricks

(Keeping material ratio constant as 70:30)

6.2 Water Absorption Test

Water absorption test is conducted to check the durability
property (such as degree of burning, quality and behaviour
under weathering action etc.) of the bricks (IS: 3495, Part-II).
Initially, the dry brick specimen is kept inside the oven
(105oC to 115oC) till it reaches its constant mass. Then, the
specimen kept for cooling at room temperature. After it
attains the room temperature, its weight is noted (W1). The
dry sample then immersed in clean water at a temperature
(27+2)oC for 24 hours. Finally, the specimen was removed
from the water and wiped with damp cloth to remove the
surface water. The final weight of water absorbed brick is
noted (W2). The formula for calculating water absorption (%
by mass) is as follows-
Chart-1: Compressive Strength of Geopolymer Bricks
(Keeping molar ratio of alkaline solution as 1:10) Water Absorption= [(W2- W1) / W1] X 100

Table-7: Compressive Strength of Geopolymer Bricks Table-8: Water Absorption of Geopolymer Bricks (Keeping
(Keeping material ratio as 70:30) molarity of alkaline solution as 1:10)

Material Ratio (Clay Soil : Fly ash) = 70:30

Molar Ratio of Alkaline Solution (1:10)
Results for 7 days Results for 14 days Initial Final
Molar
Specimen Specimen Dry Weight
Ratio Material Ratio % of Water
Weight after water
Weigh Weigh (Soil : Fly ash) Absorption
of Compressiv Compressiv (W1) in absorption
t of t of Kg (W2) in kg
Alkaline e Strength e Strength
bricks bricks
Solution (N/mm2) (N/mm2) 100:0 3.14 3.65 16.24 %
(Kg) (Kg)
50:50 2.65 2.98 12.45%
1:8 2.82 2.70 2.75 3.25
60:40 2.76 3.20 15.94%
1:10 2.82 2.85 2.70 3.45
70:30 2.70 3.02 11.85%
1:12 2.80 2.63 2.78 3.10 80:20 2.88 3.23 12.15%
1:14 2.80 2.68 2.80 3.30

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6.3 Efflorescence Test

Efflorescence is a whitish crystalline salt compound, consists
of magnesium sulphate, calcium sulphate and carbonate of
sodium and potassium. Usually, efflorescence originates due
to moist condition, condensation and low temperature etc
and deposits on the surface of the bricks. The presence of
efflorescence in bricks is reported as nil, slight, moderate,
heavy and serious (IS: 3495, Part-III). From the day of de-
moulding, till now no white patches are observed hence
efflorescence is reported as nil.

6.4 Dimension Test

For dimension test, few sample bricks are selected randomly
and their dimensions (length, width, height) are measured.
These dimensions are checked in one or two lots of ten each
as shown in fig.6. Allowed variations in brick dimensions are
kept limited, within ±3% for class one bricks and ±8% for
Chart-3: Water Absorption of Geopolymer Bricks other classes (IS: 1077).
(Keeping molarity of alkaline solution as 1:10)

Table-9: Water Absorption of Geopolymer Bricks (Keeping

material ratio as 70:30)

Material Ratio (Soil : Fly ash) = 70:30

Final
Molar
Initial Dry Weight
Ratio of % of Water
Weight after water
Alkaline Absorption
(W1) in Kg absorption
Solution
(W2) in kg
1:8 2.75 3.22 17.09%
1:10 2.70 3.00 11.11%
1:12 2.78 3.12 12.23% Fig-7: Dimension Test on Geopolymer Bricks
1:14 2.80 3.18 13.57% 7. CONCLUSONS
Based on the experimental studies carried out on
geopolymer bricks with different material ratios and
different ratios of alkaline solution, the following inferences
are drawn-

i. The weight of geopolymer bricks is relatively lower

than the conventional clay bricks (reduction up to
25%).

ii. In case of both 7 and 14 days, the highest

compressive strength is exhibited by the
geopolymer bricks with the material ratio of 70:30
(with a constant alkaline solution of 1:10),
compared to other combinations.

iii. With varying percentages of alkaline solution, the

Chart-4: Water Absorption of Geopolymer Bricks (Keeping highest compressive strength is recorded in case of
material ratio constant as 70:30) geopolymer bricks with the alkaline solution of 1:10
(with a constant material ratio of 70:30). This
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pattern is similar in the case for both 7 days and 14 CONCRETE & STRUCTURES, 14 - 16 August 2011.
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