CHAPTER 1 - INTRODUCTION

Massive constructions are carried out all around the world. So that ordinary Portland cement (OPC) is
widely used. Production of Portland cement is currently topping 2.6 billion tons per year. When
making OPC, carbon dioxide is released to the atmosphere heavily. Approximately, one ton of carbon
dioxide is released when making one ton of OPC. It is directly caused to increase the global warming.
Also the extent of energy required to produce OPC is only next to steel and aluminum. Therefore, it is
essential to use an alternative to OPC. Then materials like fly ash and ground granulated blastfurnace
slag (ggbs) come in to the seen. Fly ash and ggbs are available excessively worldwide. Fly ash can be
taken from coal burning station while ggbs is a by-product at the steel industry. Both are by -products
(Ryu, et al., 2013).

In 1978, Joseph Davidovits (French scientist and Engineer) 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, ground granulated blastfurnace slag (ggbs)
and metakaolin. He termed these binders as geopolymers. In this scheme, the main contents to be
activated are silicon and aluminum. Sodium hydroxide and sodium silicate or potassium hydroxide and
potassium silicate can be used as alkaline activators (Nath and Sarker, 2015).

Figure 1.1 Joseph Davidovits

Some of geopolymer cement categories are mentioned below.

1. Slag – based geopolymer concrete

2. Rock – based geopolymer concrete
3. Fly ash – based geopolymer concrete

The fly ash and ggbs based geopolymer paste binds the loose coarse aggregate, fine aggregate together
to form the geopolymer concrete, with or without the presence of admixtures. The manufacture of
geopolymer concrete is carried out by using the usual concrete technology methods. Initially binder
should be made prior to make geopolymer concrete. To make binder, source material is mixed with
alkaline activator. Then, that binder is mixed with coarse and fine aggregate. After that
geopolymerisation reaction takes place. Eventually, that mixture can be used as normal concrete, but
there are some hurdles to use geopolymer concrete. That is why it is not still widely used for
construction purposes. Normally, heat curing (at 60 °C or more) is done for geopolymer concrete
products to get higher compressive strength. But for in-situ concreting, heat curing is not possible.

1
Cost is high because of using alkaline activators. If the concentration of alkaline activator is high then
it is not user friendly. Those are the shortcomings of using geopolymer concrete.

Geopolymer
concrete

Figure 1.2 Preparation of geopolymer concrete

1.1 Objectives

 To prepare the geopolymer concrete at room temperature

 To study the short-term engineering properties namely slump (of fresh geopolymer cement
concrete), cube and cylinder compressive strength splitting tensile strength ultrasonic pulse
velocity static and dynamic modulus of elasticity (of hardened geopolymer cement concrete)
subjected to ambient temperature curing

 To study the size effect on compressive strength

 To check the variation of compressive strength in water curing and air curing

 To check the variation of compressive and tensile strength with the age and concentration of
alkaline activator

 To check the variation of cube strength in water curing and air curing

 To obtain the regression models for the following relationships,

1. Tensile strength and Compressive strength

2. Static modulus and Compressive strength

1.2 Scope

Silicious fly ash and ggbs are used as the source materials while sodium hydroxide and sodium silicate
are used as alkaline activators. Six mix propositions are made by changing percentage of mass between
ggbs and fly ash (ggbs%:fly ash% = 0:100, 20:80, 30:70, 40:60, 50:50). Sodium hydroxide and sodium
silicate having concentration of 14M and 12M are used. Size effect and changing concentration of
sodium hydroxide (12M) are performed only for the sample which has 100% fly ash. Cubes are cast in
the sizes of 50 mm and 100 mm. Size effect is checked between 100 mm cubes and 50 mm cubes on
2
the compressive strength. Cylinders are cast 55 mm in diameter and 110 mm in height. Super
plasticizer is used as admixture. Water curing is started after 24 h of casting and also curing is done
under ambient temperature. Compressive and tensile strength are checked at the ages of 7, 14 and 28
days from casting. One sample is made to cure in air and compared its compressive strength with the
water curing.

3
CHAPTER 2 - LITERATURE REVIEW

Literature review is mainly done by referring journals. There are many journal articles on geopolymer
concrete. Those include more information. Most of them are on preliminary properties of geopolymer
concrete cured at elevated temperature.

2.1 Introduction to geopolymer concrete

As the construction industry continues, its move towards the concept of sustainable development,
geopolymer concrete will eventually be used in several applications as an alternative for ordinary
Portland cement concrete. However, for geopolymer concrete to become a mainstream construction
material efforts need to be directed towards developing easy to use geopolymer concrete (Junaid, et al.,
2015). Recently, great concern for many researchers has been the development of cementless concrete
to reduce drastically the exhaustion of CO2. The theoretical basis of geopolymerization as a major
reaction mechanism of cementless concrete was established for the first time by the French researcher
Davidovits in 1978, who used kaolinite and alkaline activators. However, the recent rise of
environmental degradation as a social issue has reactivated research on alkali-activated concrete using
industrial by-products such as fly ash and blast furnace slag (Ryu, et al., 2013).

Fly ash is a suitable material for making geopolymeric binder because of its pertinent silica and
alumina composition and low water demand. The amount of currently unused fly ash is considerable
which can be utilized in manufacture of geopolymer products. For example, the annual generation of
ash is estimated to be about 580 million tons in China with 67% utilization and 200 million tons in
India with 50% utilization. Accumulation of the unused fly ash in these countries is huge and the
generation is estimated to increase in future. In Australia, though it is not as large, the annual
generation of fly ash is about 12 million tons. Low-calcium fly ash-based geopolymer concrete cured
in high temperature has been reported to have good mechanical properties in both short and long term
tests. The structural behavior of heat-cured fly ash geopolymer concrete was found to be similar or
superior to that of OPC concrete when tested for reinforced columns and beams bonding and fracture
properties (Nath and Sarker, 2015).

2.2 Fly ash based geopolymer concrete with alkaline activator (NaOH and Na2SiO3)

Fly ash is a byproduct of coal fired power station. Normally, there are two types of ash can be obtained
from coal burning. Those are fly ash and bottom ash. Fly ash consists of very fine particles, which are
transported by flue gases. This type of ash is collected by precipitators. Normally, those types of fly
ash had been used to prepare geopolymer concrete mostly. Ryu, et al. (2013) have shown that how the
mechanical properties of fly ash based geopolymer concrete were changed with alkaline activator.
Chemical compositions of fly ash were measured from X-ray fluorescence analysis. That analysis

4
showed that fly ash consisted of SiO2, Al2O3, CaO, Fe2O3, SO3, MgO, K2O and Na2O. Then different
types of geopolymer concrete samples were prepared by changing NaOH concentration as 6M, 9M and
12M. Then samples were prepared shown in Table 2.1.

Table 2.1 Mix proportion by Ryu, et al. (2013)

Mix proportion by mass (g)

Series Specimen Fly ash NaOH NaOH NaOH Na2Sio3 Sand
6M 9M 12M
FASH6SS50 1600 400 400 2400
1 FASH9SS50 1600 400 400 2400
FASH612SS50 1600 400 400 2400
FASH10SS100 1600 0 800 2400
FASH25SS75 1600 200 600 2400
2 FASH50SS50 1600 400 400 2400
FASH75SS25 1600 600 200 2400
FASH75SS25 1600 800 0 2400

Thus, the samples were made by changing SiO2/ Al2O3, SiO2/ Na2O, Al2O3/ Na2O and Si/Al mass
ratio. Having made concrete, cylinders were cast. Then heat curing was done under 60°C for 24 hrs.
This curing was done in different time period. Such that 1, 3, 7, 14, 28, 56 and 91 days. Then
compressive strength was checked of those different concrete samples. Graphs were drawn by using
those experimental details. Those were compressive strength versus age, compressive strength versus
tensile strength. Finally, relationship between the compressive strength and splitting tensile strength of
geopolymer concrete was obtained.

Diaz, Allouche and Vadiya, (2011) have carried out an investigation to find the properties of
geopolymer concrete such as density, compressive strength and elastic modulus. Initially, chemical
compositions and particle size distributions of fly ash samples were found by X-ray fluorescence
analysis. Then the mix proportion tabulated in Table 2.2 was used to prepare geopolymer concrete.

Table 2.2 Mix proportion by Diaz, Allouche and Vadiya, (2011)

Material Quantity (Kg/m3)

Fly ash 494
Sand 691
Gravel 858
Activator Solution 198-464
High range water reducing
15
admixture
.

Then 50mm cubes were cast and cured at 60°C. After 28 days, tests were carried out and obtained
results.
5
A recent research by Chindaprasirt and Chalee (2014) has been carried out to check the effect of
sodium hydroxide concentration on chloride penetration and steel corrosion of fly ash based
geopolymer concrete at a marine site. Long term durability of geopolymer concrete under sea water
was investigated. Initially chemical composition of fly ash was obtained by doing X- ray fluorescence
analysis. Samples were prepared by changing the concentration of the NaOH. Fly ash, fine aggregate,
coarse aggregate, NaOH and Na2SiO3 weight were maintained constant. Then concrete samples were
made for different concentrations of NaOH. The Following mix proportion was used to prepare
concrete, see table 2.3.

Table 2.3 Mix proportion by Chindaprasirt and Chalee (2014)

Mixture proportion (Kg/m3)

Mix Fine Coarse
FLY ASH NaOH Na2SiO3
aggregate aggregate
8M 390 585 1092 67 167
10 M 390 585 1092 67 167
12 M 390 585 1092 67 167
14 M 390 585 1092 67 167
16 M 390 585 1092 67 167
18 M 390 585 1092 67 167

Having made concrete, 200mm cubes were cast and cured at ambient temperature. Then compressive
strength was checked after 28 days and 3 years. it was observed that during 3-year exposure in
seawater, fly ash-based geopolymer concrete with a high NaOH concentration continuously gain
strength faster than that with a low NaOH concentration.

Prabir, Sean and Zhitong (2014) have carried out a research to identify the effect of fire exposure on
some properties such as cracking, spalling and residual strength of GPC against OPC. Initially GPC
was prepared by using fly ash. That was done according to Table 2.4. Ingredients are in kg/m3.

Table 2.4 Mix proportion by Prabir, Sean and Zhitong (2014)

Coarse aggregate
Fly Sodium Sodium
Cement Water Sand
Mixture ash hydroxide silicate
10 20
(mm) (mm)

OPC 334 - 177 - - 643 404 860

GPC - 408 20 41 103 647 554 647

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Then water curing was done for OPC and steam curing was done at 600C - 80 0C for GPC. Then both
concrete samples were exposed to heat after 28 days from casting. Samples were heated up to 1000 0C.
Then they were cooled down to room temperature. Then it was observed parameters like compressive
strength, cracking and spalling for both samples.

There is another type of coal ash called as bottom ash. Bottom ash means large particles settled to
bottom of the furnace when burning the coal. This type of fly ash can also be used to prepare
geopolymer concrete. Xie and Ozbakkaloglu (2015) presented the results of an experimental study on
the behavior of fly ash and bottom ash based geopolymer concrete (GPC) were cured at ambient
temperature. A total of 10 batches of GPC and a single batch of ordinary Portland cement concrete
(OPC) were manufactured. Tests on compressive strength, elastic modulus, flexural strength,
workability, drying shrinkage and absorption capacity were carried out to determine the properties of
fresh concrete and mechanical and durability-related properties of hardened concrete. Test parameters
were included the mass ratio of fly ash to bottom ash, liquid alkaline to coal ash binder ratio, coal ash
content and concrete type. The results indicate that the selected parameters significantly affect the
microstructure and the behavior of GPC. It shows that higher drying shrinkage compared to that of
OPCs’ due to the large amount of unreacted coal ash particles in the hardened GPC. Also GPC with a
lower fly ash to bottom ash mass ratio develop higher drying shrinkage due to the lower degree of
geopolymerization. It is also observed that no significant exothermic reactions were observed during
the curing of the GPCs’ at the ambient temperature. This indicates that GPCs’ cured at ambient
temperature do not undergo exothermic processes to the extent that are experienced by conventional
OPCs’.

Coal ash is also used to make geopolymer concrete as same as bottom ash. This research was carried
out to study effect of sodium silicate and sodium hydroxide on the strength of aggregates made from
coal fly ash using the geopolymerisation method. Fansuri, et al. (2010) have investigated that
geopolymerisation of coal fly ash to produce synthetic aggregates as a potential means of utilizing coal
combustion by-product. It has been revealed that the geopolymerisation strongly depends on the
physicochemical properties of fly ash, the availability of soluble silicates and aluminates, and the
concentration of added sodium hydroxide. Initially chemical composition of fly ash was found. Then
geopolymer concrete was made by using that fly ash. Different samples were made by changing the
weight of Na2O, SiO2, NaOH and water. The presence of sodium hydroxide increases the amount of
soluble silicates and aluminates in the mixture through fly ash solubilisation. Solubility tests on
various fly ash samples have been shown that solubility increases as the concentration of sodium
hydroxide in the fly ash increases, which also increases the strength of the resulting geopolymer
aggregates. The compression strength of the geopolymer aggregates also increases to a maximum
before decreasing again as the amount of sodium silicate is increased. Finally, it was observed that the

7
geopolymerisation strongly depends on the physicochemical properties of the fly ash, the availability
of soluble silicates and aluminates, and the concentration of added sodium hydroxide, which is able to
increase the amounts of soluble silicates and aluminates in the mixture through fly ash solubilisation.
The amount of water required for fly ash geopolymerisation strongly depends on the nature of the fly
ash.

In this research, a mix design procedure for low calcium alkali activated fly ash based concrete was
obtained. This is useful to build up a new proportion for any condition. Junaid, et al. (2015) presented
a systematic approach for selecting mix proportions for alkali activated fly ash based geopolymer
concrete (GPC). The proposed mix design process was developed for low calcium (class F fly ash)
activated geopolymers using sodium hydroxide and sodium silicate as alkaline activator solution. A
review of the literature reveals that there are no published comprehensive approaches in designing
mixes for GPC. The ratios between water to geopolymer solid (W/GPC) and alkaline liquid to fly ash
(AL/FA) ratios were considered as direct measures of strength and workability. The ratio of alkaline
liquid to water (AL/W) was identified to be most closely linked to the strength of OPC mixes. These
ratios were accompanied by other equally important parameters, namely; the molarity of the alkali, the
composition of sodium silicates, the ratio of the silicates to the hydroxides, and the temperature and
duration of curing. Most importantly, relationships have been established between these important
parameters in order to achieve a certain level of strength together with desired workability. More than
500 mixes were made and resulted in establishing easy to use graphs. These graphs have been referred
to as G – graphs.

Eventually, it can be concluded that, a higher molarity of NaOH used as an alkaline activator appeared
to provide higher compressive strength together with a considerable effect on the early strength.
However, that geopolymer concrete was mainly more suitable for precast concrete products because
the compressive strength of geopolymer concrete can be developed at temperatures that higher than
60°C. Geopolymer concrete also seems to possess a similar mechanical behaviour to that of OPC
concrete. The relationship between the elastic modulus and the compressive strength of GPC is similar
to that of ordinary concrete. However, their relationship is linear, whereas for ordinary concrete it
follows a power curve. The elastic modulus of GPC may be better expressed as function of both
density and compressive strength. The density of GPC can be accurately predicted by the fineness of
fly ash. It was found that GPC was suffered less comparing to OPC. Residual strength of OPC was
decreased with increasing temperature but it was increased with GPC. OPC had more cracks due to
rapid moisture loss but GPC had less moisture loss so it had no cracks at all. GPC can take peak
temperature very quickly. That means it has high thermal conductivity.

8
2.3 Geopolymer concrete curing under ambient temperature

Usually, geopolymer concrete products are being cured at high temperature. Mostly, it is above 60 °C.
That is why geopolymer concrete is still used for precast concrete products. Higher compressive
strength can be achieved by curing at higher temperature. But, it is better to know the properties of
gepolymer concrete under ambient temperature curing as well.

Somna, et al. (2011) have carried out curing under ambient temperature. Geopolymer concrete was
made by using fly ash. It was done by changing NaOH concentration from 4.5 – 16.5M (4.5, 7, 9.5, 12,
14, 16.5). Here Na2SiO3 and NaOH were used as alkaline activator. Initial molar ratios of SiO2, Al2O3,
Na2O and H2O are shown in Table 2.5.

Table 2.5 Mix proportion by Somna, et al. (2011)

NaOH
Mix concentration SiO2 / Al2O3 Na2O /Al2O3 H2O / Na2O
/(M)
4.5 NaOH 4.5 2.81 0.47 16.85
7.0 NaOH 7.0 2.81 0.63 11.64
9.5 NaOH 9.5 2.81 0.77 8.78
12.0 NaOH 12.0 2.81 0.91 6.97
14.0 NaOH 14.0 2.81 1.01 5.94
16.5 NaOH 16.5 2.81 1.12 4.97

Then curing was done under room temperature. Compressive strength was checked after 7, 14, 28, 42
and 60 days. Microstructure was observed using SEM and EDX tests. An increase in NaOH
concentration from 4.5 to 14M increased the compressive strength of geopolymer concrete paste.
Microstructure studies indicated that NaOH concentration of 12-14 M created new crystalline products
of sodium aluminosilicate. The highest compressive strength value could be achieved when NaOH
concentration is 14M. When increasing concentration more than that the strength values started to
decrease.

Properties of geopolymer concrete can vary under curing condition. If curing is done under high
temperature, strength values are high but in curing under ambient temperature compressive strength
values are low. This research was carried out to find effect of mechanical activation of fly ash on the
properties of geopolymer cured at ambient temperature. Temuujin, Williams and Riessen (2009) have
also been carried out curing under ambient temperature. Initially, chemical composition was found by
X-ray fluorescence (XRF) test. 14M NaOH and Na2SiO3 were used as alkaline activator. GPC was

9
made by using fly ash. Then components were mixed and de formed in a high velocity centrifuge
mixer and placed in 25mm diameter cylindrical plastic moulds. Samples were kept at room
temperature for 21 days then demoulded. Compressive strength testing was done 28 days after
processing. Mechanical activation of fly ash results in particle size and morphology changes with
concomitant increase in eactivity with alkaline liquid. Addition of water in the reaction mix decreases
mechanical properties of the geopolymer samples. After 28 days, compressive strength of the room
temperature cured samples were between 16 MPa and 45 MPa for unmilled and mechanically activated
fly ash based samples. Those values are less when comparing with compressive strength values at 70
°C.

Most previous works on fly ash based geopolymer concrete were focused on concrete subjected to heat
curing. Development of geopolymer concrete that can be set and hardened at normal temperature will
be widened its applications beyond precast concrete. Nath and Sarker (2015) have focused on a study
of fly ash based geopolymer concrete suitable for ambient curing condition. A small proportion of
ordinary Portland cement (OPC) was added with low calcium fly ash to accelerate the curing of
geopolymer concrete instead of using elevated temperature. Samples were prepared according to Table
2.6.

Table 2.6 Mix proportion by Nath and Sarker (2015)

Mortar Mix (Kg/m3) Mortar ratio

Mix Designation Fly W/S
Sand OPC Na2SiO3 NaOH Na2O/SiO2 H2O/Na2O Si/Al
ash
1 P0 1178 730 0 208.6 834 0.118 11.730 1.765 0.200
2 A40/P5 1178 693.5 36.5 208.6 834 0.115 11.737 1.975 0.202
3 P8 1178 671.6 58.4 208.6 834 0.117 11.730 1.994 0.202
4 P10/R2.5 1178 657 73 208.6 834 0.118 11.725 2.008 0.202
5 P12 1178 642.4 78.6 208.6 834 0.120 11.731 2.018 0.204
6 A35 1214.5 693.5 36.5 182.5 73 0.103 11.651 1.940 0.182
7 A45 1141.5 693.5 36.5 234.6 93.9 0.126 11.801 2.009 0.223
8 R2.0 1178 657 73 194.7 97.3 0.126 11.228 1.989 0.202
9 R1.5 1178 657 73 175.2 116.8 0.136 10.608 1.961 0.203

Then, samples were cured in room environment (about 23 °C and RH 65 ± 10%) until they were
tested. Inclusion of OPC as little as 5% of total binder was reduced the setting time to acceptable
ranges and caused slight decrease of workability. The early-age compressive strength was improved
significantly with higher strength at the age of 28 days. Geopolymer microstructure was shown
considerable portion of calcium-rich aluminosilicate gel resulting from the addition of OPC.

10
CHAPTER 3 – MATERIALS AND METHODS

3.1 Procedure

Source materials (Flyash,

GGBS) and aggregate
Sample 1.2 Sample 1.1 to Sample 6

12M NaOH +Na2SiO3 14M NaOH +Na2SiO3

Preparing concrete mixture Preparing concrete mixture

Sample 1.3 to Sample 6

Sample 1.1

Casting (Cube50/Cylinder) Casting (Cube100) Casting (Cube50/Cylinder)

Curing (Starting after 24 h from casting)

Testing (Cube test and Splitting

tensile test, After 7, 14 and 28
days)

Obtaining results

Analyzing the obtained results

LEGEND

Cube50 - 50 mm Cube

Cube100 - 100 mm Cube

Cylinder - Cylinder which has diameter = 55 mm and height = 110 mm

Figure 3.1 Procedure

11
3.2 Sample designation system

We have named sample such as sample 1, sample 2 etc, to identify them easily. But sometimes that
may lead to a misunderstanding as well. Therefore we have presented designation system also to
identify the ingredients of samples easily according to Table 3.1. That defines about the sample a lot.

Table 3.1 Sample designation system

Sample number Description Sample Designation

1.1 100F:100mm 1.1(100F:100mm)
1.2 100F:12M 1.2(100F:12M)
1.3 100F:14M 1.3(100F:14M)
2 90F:10S 2(90F:10S)
3 80F:20S 3(80F:20S)
4 70F:30S 4(70F:30S)
5 60F:40S 5(60F:40S)
6 50F:50S 6(50F:50S)

Here after when we mention the sample, it is done 1.1(100F:100mm), 6(50F:50S), 1.2(100F:12M) etc.
1.1(100F:100mm) describes, it includes 100% fly ash and it was only used to produce 100 mm cubes.
When considering 6(50F:50S), it includes both fly ash and slag (ggbs) 50% each. 1.2(100F:12M)
describes, it includes 100% of fly ash and concentration of alkaline activator is 12 M. Except sample
1.2, 14 M concentration of alkaline activator was used for other samples.

3.3 Materials

1. Fly ash

Fly ash was taken from the coal – fired power stations. And also low calcium fly ash (class F) was
used as a base material because the presence of calcium in high amount may interfere with the
polymerisation process and alter the microstructure. It was sieved through 75 μm sieve.

2. Ground granulated blastfurnace slag

It was taken from as a byproduct of iron making process. Ggbs was ground and sieved through 75 μm
sieve.

3. Alkaline activator

Sodium hydroxide and sodium silicate were used as the alkaline activator. 14 M and 12 M sodium
hydroxide and sodium silicate solution were used.

12
4. Aggregate

Both coarse and fine aggregate were in saturated surface dry (SSD) condition. Uncrushed sand was
used for fine aggregates. Course aggregates were taken which are passed through 14 mm sieve and
retained on 6.3 mm sieve.

5. Super plasticizer

Rheobuild 1000 was used as high range water reducing admixture. Because of geopolymer concrete is
very cohesive. Therefore high range water reducing admixture was used to have sufficient workability
of the samples.

3.4 Mix proportion

Mix proportion given in the Table 3.2 was used to make geopolymer concrete. Having gone through
literature review, this proportion had been selected. Trial mixes also had been done using that mix
proportion.

Table 3.2 Mix proportion

Material Amount / (kg/m3)

Combined (fly ash+ggbs) 500

Fine aggregate 650
Coarse aggregate 800
Alkaline activator (NaOH + Na2SiO3) 300
High range water reducing admixture 10

The ratio between Na2SiO3 to NaOH is 2.5. It was also preferable to mix the sodium silicate solution
and the sodium hydroxide solution together at least one day before adding the liquid to the solid
constituents.

It was expected to make 6 mix proportions by changing the mass ratio between fly ash and ggbs while
keeping other materials constant. After that, tests of concrete were carried out for each mix proportion
type separately according to Table 3.2.

13
 Table 3.3 Mixing proportion for each sample

Source
Source Aggregate / Alkaline activator
material Super
material % (kgm-3) / (kgm-3)
Sample /(kgm-3) plasticizer
Fly Fly NaOH / (kgm-3)
Ggbs Ggbs Fine Coarse Na2siO3
ash ash 12M 14M
1(1.1,1.2,1.3) 100 0 500 0 690 860 85.7 85.7 214.3 10

2 90 10 450 50 690 860 0 85.7 214.3 10

3 80 20 400 100 690 860 0 85.7 214.3 10

4 70 30 350 150 690 860 0 85.7 214.3 10

5 60 40 300 200 690 860 0 85.7 214.3 10

6 50 50 250 250 690 860 0 85.7 214.3 10

3.5 Sample preparation

Initially binder was prepared in order to prepare the geopolymer concrete. Source material and alkaline
activator were added together and mixed well. Source materials include fly ash and ggbs. Alkaline
activator includes sodium hydroxide and sodium silicate. Super plasticizer was added as the admixture
to increase the workability. Then, aggregates (both coarse and fine) were added in to that binder. Wet
mixing was done well. Hand mixing was used because sizes of the samples are small.

3.6 Checking consistence

Mini slump test was carried out to check the consistence for all the samples.

14
3.7 Casting

Cubes and cylinders were cast prior to do the necessary tests. Sizes of the moulds to cast cubes will be
50 mm and 100 mm. And also 55 mm diameter and 110 mm height moulds were used to cast the
cylinders. Steel rod was used to compact concrete.

Figure 3.3 Moulds to cast cubes and cylinders

Geopolymer concrete is not hardened immediately at room temperature if fly ash is used as a source
material. When the room temperature is less than 30 °C, hardening may not occur for at least for 24
hours. Therefore mould should be removed after concrete hardening.

Table 3.4 Data of casting cubes and cylinders (14M of alkaline activator)

Cubes Cylinders /( height =

Sample 110 mm, diameter =
50mm 100mm
55 mm)
1.1(100F:100mm)
1.2(100F:12M) 18 9 54
1.3(100F:14M)
2(90F:10S) 9 - 27
3(80F:20S) 9 - 27
4(70F:30S) 9 - 27
5(60F:40S) 9 - 27
6(50F:50S) 9 - 27

Table 3.5 Data of casting cubes and cylinders (12M of alkaline activator)

Cylinders /( height = 110

Sample Cubes / (50 mm)
mm, diameter = 55 mm)
1 9 27

15
Casting of cubes and cylinders

 Initially the faces of cube and cylinders moulds were cleaned and coated with grease.

 The mould was filled with concrete in three layers, each layer was tamped 15 times by the
tamping rod in both cubes and cylinders

 All mould should be kept there for 24 hours without moving. But for sample one it should be
kept 48 hours, because it was taken 48 hours to get hardened.

 All moulds were removed and the concrete specimens were placed into a water bath.

3.8 Curing

Although heat curing is preferred for geopolymer concrete, here water curing was done under ambient
temperature. Curing was done for 7 days, 14 days and 28 days. Curing was started after 24 hours from
casting. All the specimens were kept in a water bath. For another sample 6(50F:50S), air curing was
done.

3.9 Tests which were carried out

1. Mini Slump test

The slump test is useful to check the workability of concrete. The required amount of concrete is very
less. Therefore we performed mini slump test rather than doing conventional slump test. The main
apparatus which were used in this test are,

 Mini slump cone

 Smooth flat Plate

 Tamping rod

50 mm

150 mm

100 mm

Figure 3.4 Apparatus for mini slump test

First this cone was placed on a smooth leveled surface. Then the cone was filled with concrete in three
layers. Each layer was compacted by applying 10 blows from the steel rod. Then the cone was

16
removed carefully. When removing the cone, the concrete slupmed down. Then the diameter was
measured form the top of the slumped concrete mix. This averaged diameter was taken as the slump
flow value of the concrete.

2. Compressive strength test

The cubes were used to find the compressive strength of the concrete. 9 cubes will be checked for each
mixture. Cubes testing were done under 3 curing stages. Those were 7, 14 and 28 days having started
curing. Three cubes were checked for each curing stage and average values were taken as compressive
strength of the samples. 50 mm and 100 mm cubes were used for checking compressive strength.

 After 7, 14 and 28 days cubes (3 cubes) were taken out from water and testing was done

 Then compressive strength of cubes can be calculated

Same procedure was followed to find the compressive strength of cylinders as well.

3. Splitting tensile test

The height and the diameter of the cylinders were 110 mm and 55 mm respectively. 9 cylinders were
checked for each mix. Testing was done after 7, 14 and 28 days.

Testing procedure,

 After 7, 14 and 28 days, cylinders (3 cylinders) were taken out from water and testing could be
done by using universal testing machine

 Then tensile strength of the cylinders could be calculated

4. Pulse velocity

The main objective of this test is to determine void pattern and determine the dynamic and static
modulus of elasticity of concrete. The ultrasonic pulse velocity is influenced by some properties of
concrete such as elastic stiffness and mechanical strength. Ultrasonic velocity equipment measures the
transit time of a pulse between transducers placed on the surface of a body of concrete. The pulse
velocity can then be calculated using the measured path length through the concrete. The velocity of an
ultrasonic pulse is influenced by those properties of concrete which determine its elastic stiffness and
mechanical strength. The variation obtained in set of pulse velocity measurements made along
different path in a structure. When a region of low compaction under test a corresponding reduction in
the calculated pulse velocity occurs and this enables the approximate extent of the imperfection to be
determined.

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The received signal and transit time is affected by the coupling of the tranducerces to concrete surface.
Sufficient coupling agent and pressure must be applied to the tranducerces to ensure stable transit
times. The strength of received signal is also affected by the travel path length and by pressure and
degree of cracking or deterioration in concrete. Pulse generator, Pair of transducers, Amplifier, The
time measuring circuit, Time displaying unit, connecting cables are used as instruments.

Initially 54 kHz transducers were connected to the socket and marked TRAN and REC before the
pundit was switch on. Then the instrument was calibrated using the reference bar. Then the couplet
was applied to the suitable points on the surface and the time was recorded. After that the transducers
which contact surfaces were occupied with grease, were held until a consisting reading appear. Finally,
Time was recorded when the constant reading appear and Path length was measured.

Figure 3.5 Measuring transit time

5. Static modulus and Dynamic modulus

Testing was done for cured samples after 7, 14 and 28 days. Cylinders were used for testing.
Compression testing machine, Strain measuring apparatus were used to measure the modulus of GPC.
For cylindrical specimen the surface of the concrete must be leveled otherwise capping was done.
Then test specimen was placed with measuring instruments or fixing points attached axially, centrally
in the machine. First basic stress was applied on the specimen and strain gauge readings were taken.
Then stress was increased steadily at a constant rate until stress equal to one-third of compression
strength of GPC. Then strain gauge readings were taken. Dynamic modulus was found by using pulse
velocity values and static modulus was calculated the graphs (Ciccotti.M and Mulargia.F, 2004).

The relationship between elastic modulus and the velocity of an ultrasonic pulse travelling in isotropic
elastic medium is given by

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 E = ƿV2 (1+ ⱱ) (1-2ⱱ) / (1- ⱱ)

E = Dynamic modulus

V = Pulse velocity

ⱱ = Poisson’s ratio

ƿ = Density

 Poisson’s ratio of GPC is 0.05 – 0.45

So here it was used as 0.2. Therefore

E = ƿV2 /1.1

The value of modulus of elasticity, poission’s ratio and density all vary from point to point in concrete.
So, it is possible to use empirical relationships to estimate the values of the static and dynamic
modulus of elasticity from pulse velocity.

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