STRENGTH PROPERTIES OF FLY ASH BASED GEOPOLYMER CONCRETE
CONTAINING BOTTOM ASH
ALIREZA DEHGHAN NAJMABADI
A project report submitted in partial fulfilment of the
requirements for the award of the degree of
Master of Engineering (Civil – Structure)
Faculty of Civil Engineering
Universiti Teknologi Malaysia
JANUARY 2012
iii
To my beloved wife, Arshin
iv
ACKNOWLEDGEMENTS
First of all, I wish to express my appreciation to my supervisor,
Professor Ir. Dr. Mohd Warid Hussin, for his tireless support, critics and respect.
Meanwhile, I am also very thankful to Construction Material Research Group,
especially Assoc. Professor Dr. Muhammad Aamer Rafique Bhutta and Mr. Mohd.
Azreen Mohd. Ariffin, for their guidance, advices and cooperation. Without their
support, I might not be able to perform this project as it is.
I wish to express my gratitude to Universiti Teknologi Malaysia for support
by providing the research fund under Research University Grant (GUP) with Cost
Center no: Q.J130000. 7122.00H96.
I am grateful to all my family members, foremost my parents with their
endless support. My appreciation also extends to all who have provided assistance at
various occasions. Unfortunately, it is not possible to list all of them in this limited
space.
v
ABSTRACT
The most important purpose of this research is concerning about the
environment. Each year, vast amounts of natural resources are consumed to
manufacture
ordinary
Portland
cement
which
itself
causes
considerable
environmental problems. Geopolymer can be considered as the key factor which
does not utilize Portland cement, nor releases greenhouse gases. Sufficient data is
available about researches on fly ash based geopolymer concrete, but using both fly
ash and bottom ash has a new era. Bottom ash is another waste from the process of
combustion of coal and was used as partial replacement of sand in fly ash based
geopolymer concrete and the ideal percentage of this replacement was one of the
aims of this project. To find 7, 14 and 28 days compressive strength, three
100×100×100mm specimens with 0, 20, 40 and 60 percent replacement of bottom
ash were prepared and cured at ambient condition (28oC). Same condition of curing
was provided for 200×100mm cylinder specimens to determine 7-day and 28-day
tensile strength and 100×100×500mm prisms were tested to find flexural strength at
7-day and 28-day of the four mixtures. Sodium silicate (Na2SiO3) and sodium
hydroxide (NaOH) solution 14M with ratio of 2.5 were used as alkaline activator and
all other parameters were kept constant to ignore other unknown influences. The
optimum rate of replacement was 20% which produced geopolymer concrete with
28-day compressive strength of 26.5MPa, tensile strength of 2.81MPa and flexural
strength of 4.30MPa.
vi
ABSTRAK
Tujuan paling penting dalam penyelidikan ini adalah mangenai penjagaan
alam sekitar. Setiap tahun, sejumlah besar sumber asli digunakan untuk
mengeluarkan simen Portland biasa diamana innya juga menyebabkan masalah besar
pencemaran alam sekitar. Geopolymer boleh dianggap sebagai faktor utama bahan
yang tidak menggunakan Portland biasa, dan tidak embebaskan gas rumah hijau.
Data yang mencukupi boleh didapati tentang kajian konkrit geopolymer menjgankon
terbang, tetapi menggunakan kedua-dua abu terbang dan abu dasar adalah. Abu dasar
adalah sisa dari proses pembakaran arang batu diganaka sebagai bahan pengganti
separa pasir dalam konkrit geopolymer peratusan yang ideal penggantian adalah
matlamat projek ini. Untuk mendaptka kelwoton manpeten pada 7, 14 dan 28 hari,
tiga spesimen100×100×100mm dengan peratae abu desar sebangok 0, 20, 40 dan 60
pengaweton telah disediakan dan diawet pada keadaan ambien (28oC). Keadaan bagi
yang sama kekuton tegege pada umur disediakan untuk spesimen silinder
200×100mm menentukan mandoptic 7-hari dan 28hari, prisma 100×100×500mm
telah diuji untuk kekuatan lenturan pada 7 hari dan 28 hari. Sodium silikat (Na2SiO3)
dan natrium hidroksida (NaOH) degen 14M yang bernisbah 2.5 digunakan sebagai
alkali penggerak dan semua parameter yang lain adalah sama untuk mengabaikan
pengaruh-pengaruh lain yang tidak diketahui. Kadar optimum penggantian sebangok
20% telah menghasilkan konkrit geopolymer dengan kekuatan mampatan 26.5MPa,
kekuatan tegangan 2.81MPa dan lenturan 4.30MPa pada umur 28hari.
vii
TABLE OF CONTENTS
CHAPTER
1
TITLE
PAGE
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGMENTS
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
xii
LIST OF FIGURES
xiv
LIST OF SYMBOLS
xviii
INTRODUCTION
1
1.1
Introduction
1
1.2
Background of Study
3
1.3
Problem Statement
4
1.4
Objectives
4
1.5
Scope of Study
5
viii
2
LITERATURE REVIEW
7
2.1
Introduction
7
2.2
Environmental Issues and Sustainability
8
2.2.1
9
Sustainable Development
2.3
Blended Cement
11
2.4
Geopolymers
12
2.5
Constituents of Geopolymer
14
2.5.1
Source Materials
14
2.5.2
Fly Ash
15
2.5.3
Alkaline Liquid
18
2.5.4
Aggregates
18
2.5.4.1
20
Aggregates Classification
2.5.5
Bottom Ash
21
2.5.6
Water
24
2.5.7
Super Plasticizer
25
2.6
Mixture and Proportions
26
2.7
Curing of Geopolymer Concrete
28
2.8
Fresh Geopolymer Concrete Paste
29
2.9
Properties and Applications of Geopolymer Concrete
30
2.9.1
Shrinkage of Geopolymers
33
2.9.2
Density of Geopolymer Concrete
34
2.9.3
Velocity of Ultrasonic Pulses
35
2.9.4
Water Absorption of Geopolymer Concrete
38
2.9.5
Compressive Strength
39
ix
2.9.6
Tensile Strength
2.9.7
Factors Affecting the Relation Between
Tensile and Compressive Strength
2.9.8
Factors Affecting Geopolymer Concrete
Properties
2.9.9
3
Disadvantages of Geopolymers
42
43
45
47
METHODOLOGY
49
3.1
Introduction
49
3.2
Materials Preparation
50
3.2.1
Fly Ash
50
3.2.2
Alkaline Liquid
52
3.2.3
Aggregates
52
3.2.4
Bottom Ash
56
3.2.5
Super Plasticizer
62
3.3
Preliminary Works
63
3.4
Proportions, Mixing And Casting
64
3.5
Curing
71
3.6
Conclusive Tests
74
3.6.1
Density of Geopolymer Concrete
74
3.6.2
Ultrasonic Pulses Velocity (UPV) Test
75
3.6.3
Water Absorption Test
77
3.6.4
Compressive, Indirect Tensile Splitting and
Flexural Strengths Tests
79
x
4
RESULTS AND DISCUSSION
83
4.1
Introduction
83
4.2
Overview on the Mixing Water
84
4.3
Physical Properties of Bottom Ash And Natural Sand 85
4.4
Effect of Using Bottom Ash on Density of
Geopolymer Concrete
4.5
87
Velocity Of Ultrasonic Pulses For Geopolymer
Concrete
4.5.1
87
Relationship
Between
Velocity
of
Ultrasonic Pulses and Density
4.6
4.7
Water
Absorption
of
89
Geopolymer
Concrete
Containing Bottom Ash
90
Compressive Strength Results
91
4.7.1
Effect of Age on Compressive Strength of
Geopolymer Concrete
4.7.2
Relationship
Between
92
Compressive
Strength and Density
4.8
Indirect Tensile Splitting Strength
4.8.1
Flexural Strength Results
4.9.1
94
96
Ratio of Flexural Strength To compressive
Strength
5
93
Ratio of Tensile Splitting Strength to
Compressive Strength
4.9
93
97
CONCLUSIONS AND RECOMMENDATIONS
98
5.1
Summary
98
5.2
Significant Observations
100
5.2.1
Mould Preparation
100
5.2.2
Crystallization in the Alkaline Activator
101
xi
5.2.3
Physical Form of The Four Mixtures
101
5.3
Conclusions
102
5.4
Recommendations
104
REFERENCES
106
xii
LIST OF TABLES
TABLE NO.
TITLE
PAGE
2.1
Major producers of CO2 in 2003 (ORNL, 2006)
10
2.2
The quality of concrete in structures in terms of the
36
ultrasonic pulse velocity (Whitehurst, 1951)
3.1
Composition of Fly Ash as Determined by XRF
51
(mass %)
3.2
Grading of combined aggregates (50% coarse aggregate
54
+ 50% Sand)
3.3
Chemical composition of bottom ash from Tanjung Bin
57
3.4
Grading of Tanjung Bin bottom ash
58
3.5
Final mix designs (kg/m3)
65
3.6
Quantity estimation and planning of experiment
68
3.7
Assessment criteria for water absorption (CEB, 1989)
78
4.1
Discrepancy in the mixing water
84
xiii
4.2
Physical properties of sand and bottom ash
85
4.3
Density of geopolymer concrete specimens
86
4.4
Result of UPV test for mixtures with different
88
proportions of bottom ash
4.5
Corrected water absorption rate for the four mixtures
90
4.6
Compressive strength of geopolymer concrete containing
91
0, 20, 40 and 60% of bottom ash
4.7
Tensile splitting strength of geopolymer concrete
93
containing bottom ash
4.8
Relation between compressive, flexural, and tensile
96
strength of concrete
4.9
Flexural strength of geopolymer concrete containing 0,
20, 40 and 60% of bottom ash
96
xiv
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE
2.1
CO2 emissions in the BAU scenario
10
2.2
Fly ash figures before and after alkaline activation
17
(Nguyen, 2009)
2.3
Fresh geopolymer concrete paste (Hardjito and
30
Rangan, 2005)
2.4
Percentages of hazardous elements locked in the
32
geopolymer matrix (Davidovits, 1991)
2.5
Researches on concrete strength-UPV relationships
37
2.6
Effect of curing temperature on setting time of a
41
geopolymer concrete (Nguyen, 2009)
2.7
Room temperature setting for geopolymer concrete
42
and Portland cements concrete (Davidovits, 1991)
2.8
Relation between compressive strength and waterto-polymers solids (Nguyen, 2009)
42
xv
3.1
Process of collecting, delivering and storing the fly
51
ash
3.2
Sodium silicate in 10kg bottle
52
3.3
SSD condition preparation for sand and coarse
53
aggregates
3.4
Grading curve for combined aggregates
54
3.5
SSD specific gravity test procedure
55
3.6
Preparation process for dry bulk density
56
3.7
Tanjung Bin power stations’ bottom ash pound
57
3.8
Grading curve for bottom ash
59
3.9
Immersion of bottom ash in water
60
3.10
Drying process of bottom ash and sand for SSD
60
condition
3.11
Preparation of bottom ash for SSD bulk specific test
61
3.12
Preparation process for SSD bulk density
62
3.13
Applied super plasticizer in powder form
63
3.14
Prepared dry components of geopolymer concrete
67
before casting
3.15
Sealing alkaline activator in the tank
67
xvi
3.16
Mixing the geopolymer concrete in the pan mixer
67
3.17
Fresh geopolymer concrete containing 20% bottom
69
ash
3.18
Cube moulds after the compaction process
69
3.19
Prisms filled and compacted with the Mix40
70
3.20
Covering geopolymer concrete samples after casting
70
3.21
Geopolymer concrete containing 0% bottom ash at
71
7-day
3.22
One set of samples for strength tests
71
3.23
Mix20, Mix40 and Mix60 cubes at different ages
73
3.24
Weight measurement for density calculation
74
3.25
Checking the accuracy of UPV test apparatus with
75
reference bar
3.26
Measuring velocity of ultrasonic pulses by direct
75
transmission
3.27
Arrangement of specimens in the oven
77
3.28
Immersed geopolymer concrete cores in water
77
3.29
Geopolymer concrete cube placed in compressive
79
strength test machine
xvii
3.30
Placing the geopolymer concrete cylinder in
80
hydraulic machine for tensile splitting strength test
3.31
Geopolymer concrete prism placed in flexural
81
strength test
4.1
The influence of adding bottom ash on density of the
86
mixtures
4.2
Velocity of ultrasonic pulses against the age
87
4.3
Relationship between velocity of ultrasonic pulses
88
and density
4.4
Compressive strength development during 7 days
91
until 28 days
4.5
Ratio of compressive strength development between
93
age 7-day and 28-day
4.6
Tensile splitting strength at the age of 7 and 28days
94
4.7
Ratio of tensile splitting strength to compressive
92
strength at 7-day and 28-day
4.8
Flexural strength at 7-day and 28-day
96
4.9
Ratio of flexural strength to compressive strength at
97
7-day and 28-day
5.1
Mix20, Mix40 and Mix60 physical shape
101
xviii
LIST OF SYMBOLS
Al2O3
Alumina ( Aluminum oxide )
CaO
Calcium oxide
CO2
Carbon Dioxide
D, d
cross-sectional dimension
F
Maximum load
fc
Concrete compressive strength
Fe2O3
Iron oxide
ft
Concrete flexural strength
K2O
Potassium oxide
KOH
potassium hydroxide
L
Length
LOI
Loss on Ignition
M
Molar
MgO
Magnesium oxide
Na2O
Sodium oxide
Na2SiO3
Sodium silicate
P2O5
Phosphorus oxide
SiO2
Silica ( silicon oxide)
xix
T
Time of traverse
V
Velocity of ultrasonic pulses
CHAPTER 1
INTRODUCTION
1.1
Introduction
Due to growing of population and construction, subsequently, it is obvious
that the demand for space, natural resources, water, and energy will grow. The glory
years for Portland cement were during 20th century as a choice material for modern
construction. The production of ordinary Portland cement (OPC) is rising with a rate
of approximately 3% per year (McCaffrey, 2002). This huge production has two
main reasons, first of all, due to the availability of the materials for its production all
around the world and partly due to its versatile behavior which gave architectural
freedom. Nowadays, concrete industry is known to be the major consumer of natural
resources, such as water, sand and aggregates, and manufacturing Portland cement
also requires large amounts of each of them. Due to its high energy consumption and
environmental pollution rates, the Portland cement industry was the subject for many
investigations by regulatory agencies and the public. They have believed in
adjustment of the concrete industry into sustainable technology because of its role in
the infrastructure development and being the main consumer of energy and natural
resources. With this increasing request for infrastructural needs, it is a must for us to
make a balance between the human need for preserving the environment which is
endangered by the limitless use of natural resources and utilization of these natural
2
resources. The concern about environmental issues is becoming more important and
ignoring is not the solution any more.
For manufacturing each tone of the Portland cement as the primary
component of concrete about 1.5 tons of raw materials is needed. Furthermore; in
this process about one tone of Carbon Dioxide will be released into the atmosphere
(Roy, 1999). It is produced and used in large quantities, about 175 million tons in the
Europe and 1.75 billion tones worldwide. The involvement of ordinary Portland
cement production to greenhouse gas production in the world is estimated to be
approximately 1.35 billion tons per year or about 7% of the total greenhouse gas
emissions into environment (Malhotra, 2002). It was estimated that production of
OPC will increase the CO2 emissions by about 50% from the current levels by the
year 2020 (Naik, 2005). It is the main reason that many researchers believe that the
manufacture of Portland cement has a remarkable influence on the greenhouse gases
emission and consequently environmental impacts.
It would be a great success in case of manufacturing a concrete without any
ordinary Portland cement, this can be achieved by geopolymer concrete which does
not utilize any OPC in its process of production. In fact, geopolymer concrete results
from the reaction of a source material with large amounts of silica and alumina with
an alkaline liquid. Gourley (2003) estimated that production of a tone of geopolymer
would release 164 kg of Carbon Dioxide, which is approximately one-sixth of
conventional concrete emission (Alcorn, 2003).
To list the important factors in selection of the source materials to make
geopolymers we can mention to cost, availability, and type of application. A wide
range of mineral deposits and industrial by-products materials were became under
investigation to determine the materials that are suitable for the manufacture of
geopolymers. The source materials found to be suitable include natural minerals such
as metakaolin, clays, etc, which contains Si, Al and oxygen in their chemical
composition. Wallah and Rangan (2006) announced that by-product from other
3
industries, for instance, fly ash, silica fume, slag, rice-husk ash, and red mud could
also be applied in geopolymers as the source material.
1.2
Background of Study
The interest in the use of fly ash‐based geopolymer concretes has increased
since 2000 due to the environmentally sustainable option of using an industrial waste
to form a useful material. In the 1970s, Joseph Davidovits a French material scientist
applied the term Geopolymer for the first time, although similar materials had been
developed in the former Soviet Union since the 1950s with a different name as "soil
cements". The development of geopolymer concrete mix design has been carried out
previously at Curtin University, Western Australia. Hardjito and Rangan (2005)
investigated the effects of aspects such as alkaline parameters, water content and
curing conditions in “Development and Properties of Low‐Calcium Fly Ash‐Based
Geopolymer Concrete”. According to their studies, geopolymers are practically
shapeless to semi-crystalline three-dimensional alumino-silicate polymers similar to
zeolites. Geopolymers are composed of polymeric silicon-oxygen-aluminium
framework with silicon and aluminium tetrahedral alternately linked together in three
direction by sharing all the oxygen atoms. The negative charge created by aluminium
is balanced by the presence of positive ions such as Na+, K+, and Ca+. The empirical
formula of these mineral polymers is Mn [-(SiO2) z-AlO2] n·wH2O, where M is an
alkali cation such as potassium or sodium, the symbol - indicates the presence of a
bond, z is 1, 2 or 3, and n is the degree of polymerization. Geopolymerisation is an
exothermic process which consists of dissolution, transportation or orientation and
polycondensation. In Malaysia, few researches were conducted on geopolymer
concrete. Universiti Teknologi Malaysia (UTM) as a pioneer in advanced civil
engineering materials is researching on the geopolymer concrete due to its
environmentally friendly aspects and its high performances.
4
1.3
Problem Statement
More and more amounts of cement are manufacturing all around the world
which imposes a negative impact on our living environment. Due to absence of
cement in geopolymers mixture, many researchers believe that the geopolymer
concrete will be the future concrete. Several by-products have been tested to produce
geopolymer binders with high performances and finally, fly ash was introduced as
the choice material for this purpose due to its high availability and its low cost.
Although, fly ash will considerably solve problems associated with cement
production, still the enormous consumption of natural resources for construction has
not been solved.
Nowadays, people are aware of the consequences of the limitless utilization
of natural resources. But yet, no information is available on utilization of bottom ash
in geopolymer concrete. Its good properties as a fine aggregates replacement in
geopolymer concrete make it a great option for sand substitution.
1.4
Objectives
The objective of this project is to investigate the manufacturing process a
geopolymer concrete with different amounts of bottom ash as a replacement of fine
aggregates (sand) by various mix designs to develop a concrete mixture with higher
strength properties. The aim primarily is on achieving a proper mix design and a
mixing method that will provide a 28-day compressive strength of at least 25 MPa.
5
The aims of this study can be categorized as:
(i)
Studying the short term properties of fly ash based geopolymer concrete such
as workability, density and water absorption
(ii)
Probing the relation between velocity of ultrasonic in geopolymer concrete its
compressive strength
(iii)
Finding the suitable percentage of fine aggregates that can be replaced with
bottom ash without significant drop in compressive strength
(iv)
Investigating compressive strength development of geopolymer concrete
containing bottom ash in ambient curing condition
(v)
Exploring the effect of adding bottom ash on the tensile splitting strength
(vi)
Finding the effect of adding bottom ash on the flexural strength of
geopolymer concrete containing bottom ash
1.5
Scope of Study
This project report is investigating the short term properties of low calcium
fly ash based geopolymer concrete containing bottom ash and tests mixtures with
various percentages of bottom ash as fine aggregates replacement in order to find
their strength properties and will not be involved with the durability aspects of
geopolymer concrete. This research is only about geopolymer concrete and
geopolymer mortar will not be covered by this project. This study focused on
applicability of proposed methods to product concrete with adequate compressive
strength that can be used as structural components. Ambient curing was selected as
the method of curing which can find suitability of geopolymer concrete containing
bottom ash in real structural works.
6
Lack of adequate standards for fly ash and bottom ash and existence of
different materials with different compositions may lead to different results and
conclusions. In fact, source material with different chemical composition may cause
different properties in geopolymer which is a problem in comparing the results from
the researches from all around the world. Event small dosage of difference in fly ash
and bottom ash composition may produce large differences in results of one study to
another one.
CHAPTER 2
LITERATURE REVIEW
2.1
Introduction
In this chapter a background over the environmental impacts from the
manufacturing process of ordinary Portland cement and the main cement alternatives
will be represented and also research has been conducted into the previous
investigation about geopolymer and its mechanical properties resulting from mix
design and parameters which may have influences on geopolymer properties such as
curing time, curing temperature, chemical admixtures, alkali activators, extra water,
and its composition and any other factor might have impacts on geopolymer concrete
strength.
A brief review about its durability properties against sulfates and acids and its
behavior in high temperature will be performed, to show the advantages of
geopolymer concrete versus OPC concrete which has fewer advantages and imposes
much environmental pollution to the Earth.
8
2.2
Environmental issues and Sustainability
The need for truly sustainable options for 21st century is one of the most
important challenges facing the global community. Sustain is defined as to maintain
and to continue a process going on, and sustainability means that life on our planet
can be sustained for the foreseeable future. Since the environment is certainly the
most critical concern, and a civil engineer follows sustainability rules to do not
impact any negative effect on the environment. Therefore, the term sustainable has
come to be equivalent with environmentally friendly and “green technology.”
As a matter of fact, concrete is choice material in terms of sustainability and
the main reason to this claim are:

The raw materials (aggregates and water) required for concrete are amongst
the most abundant materials on the Earth and many countries are selfsufficient in these materials. It can be made on the site and there is no need
to deliver materials so it would reduce the economical and environmental
costs of the project. The main raw material for manufacturing cement is
limestone and it is the most abundant mineral on the earth.

By-products from other industries, for instance, fly ash, ground granulated
blast-furnace slag (GGBS) may be utilized as replacing cementitious
materials or even recycled aggregates in concrete that can reduce
environmental impacts of concrete manufacturing.

Ready-mixed concrete producers work under Quality Assurance schemes and
are committed to reduce waste and to improve efficiency and quality.
9

Many manufacturers reuse concrete waste and at the end of its service life,
the materials from a concrete and masonry structures can be crushed and be
reused as hardcore or aggregate.

Concrete saves energy by reflecting light due to its naturally brighter and
more reflective than asphalt. Furthermore, light-colored paving materials help
reduce the heat-island effect.

Generally, concrete structures and pavements are more durable. A correctly
installed concrete should stay in good condition for many decades.
2.2.1
Sustainable development
It was described by the world commission on environment and development
(1987) as “Meeting the needs of the present without compromising the ability of the
future generations to meet their own needs”. A structure that is constructed so the
total environmental impact during the whole life cycle is reduced to a minimum is an
environmentally sustainable structure. It means, the structure should be designed and
constructed in a manner which is tailor-made for the purpose or in other words the
right concrete for the right application. In order to achieve this, the environmentally
beneficial aspects of concrete such as high strength, good durability and high thermal
capacity shall be used. Unfortunately concrete production has two main negative
aspects with the term of sustainability:
The process of manufacturing OPC as the primary component of concrete is a
tremendously resource and energy consuming manner which every tone of cement
requires about 1.5 tons of raw materials.
01
Table 2.1: Major Producers of CO2 in 2003 (ORNL, 2006)
Country
Percent of world
production of CO2
United States
22
Russia
15
China
15
Russia
6
Japan
5
India
5
Figure 2.1: CO2 emissions in the BAU scenario (Szabo et al. 2003)
Energy use is an important factor in CO2 emission and cement production
plays a unique role in this field due to generating vast amounts of CO2 from clinker
production. Cembureau, the European Cement Association, reported the main
sources of CO2 emission by cement production:
1. De-carbonation of limestone in the kiln (about 525 kg CO2 / ton of clinker),
00
2. Burning of fuel in the kiln (about 335 kg CO2 / ton of cement),
3. Electricity consumption (about 50 kg CO2 / ton of cement)
When concrete is exposed to the environment it will be deteriorated, which
has significant influences on its serviceability, durability and safety. Cracking,
insufficient extent and quality of the cover, and the overall quality of the whole
structural concrete are the three main factors that speed up the transportation
phenomena of aggressive agents, such as chlorides and sulphate into the concrete.
2.3
Blended Cement
The first attempt to manufacture more environmentally friendly concrete was
producing concrete with blended cement. Suggestions have been put forward into
forming ‘blended cement’ where products such as pozzolans are added to OPC with
the purpose of decrease the environmental impacts of concrete. Commonly, a part of
OPC is replaced by by‐products from other industries, for instance, fly ash or ground
blast furnace slag (GBFS). Chindaprasirt (2008) reported that annually just in
Thailand, 4 million tons of fly bottom ashes are releasing into environment. Less
than half of this fly ash is utilized in the concrete industry as a pozzolanic material in
order to lessening the heat of hydration and enhancing the workability and durability
properties. Normally, ratio of the fly ash substitution with OPC is not as much as
40% of the mass of cement (Mehta, 1998).
Damtoft et al. (2008) reported that using Portland cement has a significant
impact on the environment and suggested techniques by which these environmental
impacts of manufacturing concrete can be reduced:
02

The addition of extra materials to the list of approved supplementary
cementious materials (SCM’s) within current standards.

Allowing more complex composite cements within current cement standards.
Greater attention must be paid to blending properties.

Development of methodology for the design of best performance for the use
of blended cements.
Damtoft et al. (2008) concluded that the use of blended cements in industry
will directly reduce the CO2 emissions to the atmosphere by means of replacing
volumes of OPC. Unfortunately, not very much information about blended cement is
available. Although results showed significant increase in properties of concrete with
blended cement, few researches were conducted on blast furnace slag or fly ash
based blended cement.
Up to this point, methods of manufacturing concrete with OPC were
discussed. A sustainable and more environmentally friendly method of construction
is Geopolymer concrete. Below, literature will be reviewed about this new material.
2.4
Geopolymers
Geopolymers are listed in the family of inorganic polymers. "Geopolymer"
was first introduced by Davidovits in 1979 as the mineral polymers resulting from
geochemistry. Geopolymers are the alkali alumino-silicates binders formed by the
alkali silicate activation of alumino-silicates materials (Duxson et al., 2005). They
are mostly admixion of silicon and aluminium materials from geological origin.
However, nowadays, geopolymers are manufactured from secondary raw materials
such as fly ash and slag. Fly ash utilization has many ecological benefits and much
lower cost than other source materials (Buchwald et al, 2009). They are ideal for
03
construction and repairing of infrastructures and also in precast industry, due to high
early strength, rapid and controllable setting time and durability aspect (Raijiwala
and Patil, 2011).
Geopolymers have the chemical composition similar to Zeolites, but have
amorphous microstructure. During the process of synthesizing, silicon and
aluminium atoms come together to form three dimensional polymeric chain and ring
structure that consists of Si-O-Al-O bonds which are similar to those that binds the
natural rocks (Sumajouw et al, 2005).
According to Sumajouw and Rangan (2005) report, the chemical composition
can consist of the steps mentioned below:

Dissolution of Si and Al atoms from the source material by the action of
hydroxide ions.

Transportation, orientation or condensation of precursor ions into monomers.

Polymerization of monomers into polymeric structures.
These steps may overlap with each other or occurs simultaneously,
consequently make it complicated to inspect each of them separately.
A geopolymer binder can take three different basic forms as list below
(Sumajouw & Rangan, 2005):

Poly (sialate), which has [-Si-O-Al-O-] as the repeating unit.

Poly (sialate-siloxo), which has [-Si-O-Al-O-Si-O-] as the repeating unit.

Poly (sialate-disiloxo), which has [-Si-O-Al-O-Si-O-Si-O-] as the repeating
unit.
04
The process of Polymerization is thought to include dissolution,
transportation and or orientation as well as re-precipitation. The dissolution of silica
and alumina requires the existence of an alkali metal or hydroxide. The coordination
of alumina in the source material increases the bonding strength of the matrix
(Soltaninaveh, 2008).
2.5
Constituents of Geopolymer
The main components of geopolymers are source materials and an alkaline
liquid. A comprehensive review about these constituents and any other admixtures
that may have positive effect on the behavior of geopolymers will be presented:
2.5.1
Source Materials
A wide range of minerals and industrial by-products materials were topics for
many researches in order to determine materials that are suitable for the manufacture
of geopolymers. Availability, price, application and demand of the users are the main
factors in the process of the selection of source materials. The source materials found
to be suitable include natural minerals such as metakaolin, clays, etc which contains
Si, Al and oxygen in their chemical composition. By-product from other industries
such as fly ash, silica fume, slag, rice-husk ash red mud, etc could be utilized
alternatively as the source materials (Wallah & Rangan, 2006).
Studies have been performed by many researches on source materials ,
through them low-calcium fly ash (Palomo et al. 1999; Swanepoel and Strydom
05
2002), Metakaolin (Davidovits 1999; Barbosa et al. 2000; Teixeira-Pinto et al. 2002),
natural Al-Si minerals (Xu and van Deventer 2000), mixture of calcined mineral and
non-calcined materials (Xu and van Deventer 2002), fly ash and kaolinite-based
geopolymer (Swanepoel and Strydom 2002; van Jaarsveld et al. 2002), and mixture
of granulated blast furnace slag and metakaolin (Cheng and Chiu 2003) can be
highlighted.
Davidovits (1999) found that calcined materials such as fly ash and slag
produced much higher compressive strength in comparison with those made from
non-calcined materials such as metakaolin clays. However, it was reported in order
to a large development in compressive strength and reduction in reaction time
calcined and non-calcined materials can be used together.
Metakaolin based geopolymers are more preferable by geopolymer
developers, since it yields higher rates of geopolymrisation, the white color and
controllable Si/Al ratio, but it is more expensive than other by-products (Gourley,
2003).
Natural Al-Si minerals have demonstrated great suitability to be utilized as
the source materials in geopolymers but few researches have focused on quantitative
suitability of a specific mineral as the source material due to the complex reaction
mechanisms involved (van Deventer et al, 2000).
2.5.1.1
Fly Ash
One of the most appropriate by-products for using in geopolymers as source
material is Fly ash which is the fine residue that comes through the combustion of
powdered coal and flue gases transport it from the combustion zone to the particle
06
removal system. Most of the ash has to be disposed on an open area near the power
station or by grounding both the ash and mixing it with water and pumping into
artificial lagoon or dumping yards and this leads to many serious environmental
problems. Annually, China produces about 100 million tones fly ash and Europe
produces 50 million tons of it. A small quantity of it is utilized as an additive to
cement and concrete, while the greater part is disposed of on dumps. Hardjito (2005)
reported that fly ash particles diameter ranges from less than 1µm up to 150µm
which were finer than OPC. The oxides of silicon, aluminum, iron and calcium are
available in its chemical composition. Other metal oxides present in small amounts
are magnesium, potassium sodium, and titanium and sulphur oxides. Composition of
fly ash is influenced by the type coal which is derived from. Generally, Fly ash and
slag are known as suitable by-product materials for geopolymers production.
Between these two, high reactivity which comes from finer particles makes Fly ash
as the better option. Possession of finer particles has another benefit, filling the voids
in the concrete will create denser and more durable concrete, and on the other hand,
by means of round shape of fly ash the workability of fresh concrete will be
improved. Amorphous content, morphology and the source of fly ash can be
mentioned as the other factors that affect the properties of geopolymers which have
fly ash as source material in their mixture.
ASTM has introduced to types of fly ash which are class F and class C.
Gourley (2003) concluded that low-calcium (ASTM Class F) fly ash had better
performance than high-calcium (ASTM Class C) fly ash as a source material in
geopolymers probably due to interfering of existence of calcium in high quantities
with the polymerization process. Low-calcium fly ash is more advantageous than
slag in production of geopolymer (Hardjito, 2005).
Fully fly ash made concrete is limited in industrial applications, partly as a
result of the cost of fly ash and, in contrast, the availability and convenience of OPC.
In fact, composition of fly ash is influenced by the type of coal which is derived
from.
01
Figure 2.2: Fly ash figures before and after alkaline activation (Nguyen,
2009).
Fernández-Jim nez and Palomo (2003) studied the appropriateness of
different types of fly ash as source materials in geopolymers and finally reported that
to manufacture ideal binding properties; these limits should be considered in the lowcalcium fly ash composition:

Unburned material (LOI) should be less than 5%,

The amount of Fe2O3 should not be more than 10%,

Low CaO content, but no limit was mentioned,

The amount of reactive silica should be between 40-50%,

And 80-90% of particles should be smaller than 45μm.
While van Jaarsveld et al (2003) claimed that the fly ash that had higher CaO
content in its composition developed higher compressive strength in the early ages. It
may properly cause by the development of calcium-aluminate-hydrate and other
calcium compounds in the geopolymer.
08
2.5.3
Alkaline Liquid
For reaction of source materials in the geopolymers mix design an alkaline
component is required. Alkaline activation of fly ash produces materials with
superior strength properties than the standard Portland cements. Many researches
were conducted and concluded that the most suitable type of the alkaline component
for this aim is to use it in liquid form. Generally, alkaline liquids are made from
soluble metals such as sodium and potassium or a combination of them. (Davidovits
1999; Palomo et al. 1999; Barbosa et al. 2000; Xu and van Deventer 2000;
Swanepoel and Strydom 2002; Xu and van Deventer 2002) utilized a combination of
sodium hydroxide (NaOH) or potassium hydroxide (KOH) and sodium silicate or
potassium silicate. Moreover, (Palomo et al. 1999; Teixeira-Pinto et al. 2002)
investigated the use of a single alkaline activator.
Generally, the alkaline liquids contain either sodium or potassium silicate
cause higher rates of reaction in comparison with alkaline liquids that have only
alkaline hydroxides. Xu and van Deventer (2000) reported that utilization of sodium
silicate solution to the sodium hydroxide solution as the alkaline liquid enhanced the
reaction between the source material and the solution. Moreover, they established
that the NaOH solution provided a higher level of dissolution of minerals than the
KOH solution which causes better performance for the geopolymer.
2.5.4
Aggregates
Normally the aggregates account for 70-77% of it the volume of concrete and
it is mined separately as coarse and fine aggregates. In fact, by-products of other
industries such as recycled concrete, bottom ash and slag might be used as aggregate
in concrete. Aggregates are usually storage by various sizes and sorted to be utilized
09
later for satisfaction of the grading requirements. To mention this process negative
impact, it is possible to state the production of wastes such as dust and water which
neither of them is principally damage the environment. Meanwhile, the dust may be
utilized in some other processes.
Normal concrete aggregates consist of sand and a range of sizes and shapes of
gravel or rocks. But it seems an increasing interest in substituting alternative
aggregate materials, largely using recycled materials and a new trend to use bottom
ash. Several materials such as blast furnace slag or various solid wastes including
fiberglass materials, plastics, paper and wood products are available as aggregate
substitutes, but not many researches were conducted on replacement of bottom ash
with sand in concrete which is the major aim of this study. This is essential to
distinguish the differences between cement and aggregate in view of the fact that
some materials have behavior like both cementitious material and aggregate (such as
certain GGBS and bottom ash). Although aggregate normally accounts for 70-77%
of the concrete volume, researches have shown that aggregate plays an important role
in concrete workability, strength, durability and stability. Furthermore, aggregate part
significantly influences the cost of the concrete mixture to make it economical.
Strength, hardness and durability are the three main characteristics of
aggregate that mentioned to be important for structural-use concrete. The aggregate
must be clean and with no undesirable chemicals, absorbed clay, and other fine
materials that might alter the hydration process and changing concrete properties.
Recycled aggregates that are polluted with sulfate and chloride ions should not be
utilized in concrete. Generally, recycled concretes aggregate has lower specific
gravities and higher absorption rates than conventional gravel aggregate. The
concrete which is manufactured with reused concrete aggregate possesses good
workability and durability, while the compressive strength depends on the
compressive strength of the original concrete and the water-cement ratio of the new
concrete.
21
Why do we still use natural aggregates? Lack of adequate and reliable data on
aggregate substitutes makes it nearly impossible to use it in concrete.
More
investigation must be conducted in order to account new sources of aggregate
suitable to design dense and durable recycled aggregate concretes.
Glass aggregate in concrete may lead to some problem by reason of the alkali
silica reaction (ASR) between the cement paste and the glass aggregate, which
weakens the concrete and decreases its durability as time passes on. Thus, further
researches are needed prior to waste glass cullet can be utilized in structural concrete
applications.
2.5.4.1
Aggregates Classification
In accordance with size, BS 882:1992 classified aggregates as:
a) Coarse aggregate: aggregate mainly retained on a 5.0 mm BS 410 test
sieve and containing no more finer material than is permitted for the various sizes in
this specification.
b) Sand: aggregate mainly passing a 5.0 mm BS 410 test sieve and containing
no more coarser material than is permitted for the various gradations in this
specification.
c) Fine aggregate: any solid material passing a 75 µm BS 410 sieve.
20
2.5.5
Bottom Ash
Bottom ash similar to fly ash, is a residue of coal combustion in power
generation stations. Bottom ash in many aspects is similar to manufactured
aggregates. Coal combustion at high temperatures in presence of high air flow
produces a porous material with low bulk densities. By providing gradation, it can be
utilized as light weight aggregate. Normally, the particle size of fly ash and bottom
ash are in the range of 0.001mm to 0.5mm, and 0.05mm to 50mm, respectively.
Hardjito and Shen Fung (2010) reported that in their studies the particle size of the
bottom ash was smaller than sand. Bottom ash by means of grinding to a proper
fineness can be utilized as a pozzolanic material to manufacture high strength
concrete (Jaturapitakkul and Cheerarot, 2003).
Since 1980s, bottom ash has successfully been applied as highway
embankment, highway pavement, cold bituminous application, highway roadbed,
structural backfilling (Huang, 1990), agricultural filter material (Butler, 1995), or
environmental pollution-prevention engineering (Sack, 1989).
The particle size
distribution of bottom ash is between that of sand and gravel which can hopefully
solve the disposal problem and achieving reuse benefits by use of bottom ash in
concrete.
It is expected that production of bottom ash will grow in the world. However,
there is no official report about the exact amount of coal ash production in Malaysia
due to the new technology of generating electricity with coal-fired system. In
Malaysia, there are six electric power plants with coal-fired system to generate
electricity. TNB imports high quality coal from Indonesia, Australia and also China
(Mahmud, 2003). Annas (2005) reported that coal utilization in Malaysia started in
1988 with consumption of 1.5 million ton coal per year and in 2001, the rate sharply
raised to 2.50 million tons coal per year. Tajuddin (2010) mentioned that the
dramatic increase followed to 20 million tons in 2008. Leo-Moggie (2002) estimated
that this amount will be reach to more than 25 million tons in 2011. To prevent fly
22
ash and dust from hovering in the environment, they installed electrostatic recipients
for trapping ash and dust. However, another waste material disposes in the bottom of
the furnaces is known as bottom ash which is in coarse shape, porous, glassy,
granular, grayish. Properties of bottom ash depend on the type of furnace and the
source of coal. Normally, after a process of combustion, 80% of coal will become in
form of fly ash and remain will be bottom ash. Quo et al. (2009) reported Taiwan
Power Company produces about 1.35 million tons of fly ash and 0.35 million tons of
bottom ash annually.
Few researches have been conducted on bottom ash, for example, as fine
aggregate in concrete (Ghafoori and Bucholc, 1997) or as fine aggregate in asphaltic
concrete (Churchill and Amirkhanian, 1999). However, good results were obtained
when bottom ash was used as fine aggregate in roller-compacted concrete (Ghafoori
and Cai, 1998). Bottom ash has large particles and porous surface which required
extra water to provide adequate workability and consequently reduced the
compressive strength. Bottom ash retained water by absorption, into and onto its
porous surface and irregular surface (Kasemchaisiri and Tangtermsirikul 2007).
Berg (1998), Jaturapitakkul and Cheerarot (2003) and Saikia et al. (2008)
reported the successful utilization of bottom ash as fine aggregate in producing
lightweight concrete masonry and as cement replacement in structural and masonry
works. The strength and drying shrinkage of concretes with different percentages of
replacement of furnace bottom ash (FBA) with sand were studied at fixed water–
cement ratio and fixed slump ranges (Bai et al, 2005). They found that, at a fixed
water–cement ratio, the compressive strength and the drying shrinkage decreased
with the increase in the FBA sand content. Kasemchaisiri et al. (2008) tested the
mechanical properties of self-compacting concrete (SCC) incorporating bottom ash
as partial sand replacement. They claimed that 10% replacement by weight of total
fine aggregate showed better durability, chloride penetration, carbonation depth and
drying shrinkage in comparison with control SCC mix. Hiroshi et al (2008) presented
that the artificial light-weight aggregate made from coal ash and shale fine powder
produced high-performance aggregate which possessed lightness, high strength and
23
high water retentivity. Another test was elaborated on mixes of ordinary sand,
bottom ash and mixes having equal natural sand and bottom ash contents. Mixtures
were designed by use super plasticizer. They found that the required mixing water
increased in case of usage of bottom ash in the concrete and also addition of bottom
ash did not considerably affect the entrapped air content and setting time of fresh
concrete. Since samples with bottom ash, either fully bottom ash replacement or
partially, required higher water, showed lower compressive strength properties than
those samples with 100% natural sand (Swamy et al., 1983).
Aggarwal et al. (2007) explored the effect of substitution of bottom ash as
fine aggregates on compressive, flexural and tensile splitting strengths of concrete.
They prepared various mixtures with a range of 0% to 50% of bottom ash as a
substitute of sand and finally found that:

The workability of concrete reduced when percentage of bottom ash
was increase

Increase in the percentage of bottom ash lowered the density of
concrete since the specific gravity of bottom ash was lower than
natural fine aggregates.

At all ages, compressive, tensile splitting and flexural strengths of
samples with higher bottom ash contents were lower than samples
without any bottom ash. Meanwhile, the discrepancies between
strengths were not significant after 28 days.

For all the mixtures the compressive, tensile splitting and flexural
strengths of samples were continued to enhance as they aged.

At 90 days, mixes containing 30% and 40% bottom ash, gained the
compressive strength equal to 108% and 105% of compressive
strength of normal concrete at 28 days and achieved the flexural
24
strength in the range of 113 to 118% at 90 days of flexural strength of
normal concrete at 28 days.

Bottom ash concrete attains tensile splitting strength in the range of
121-126% at 90 days of tensile splitting strength of normal concrete at
28 days.

According to the compressive strength more than 20 MPa at 28 days,
concrete with 50% bottom ash is suitable for most of structural
purposes.

Utilization of bottom ash in concrete as a waste material is in direct
relation with sustainability.
2.5.6
Water
The mixing water in concrete is normal tap water without any other process.
It is mentioned in BS EN 1008:2002 (Mixing water for concrete - Specification for
sampling, testing and assessing the suitability of water, including water recovered
from processes in the concrete industry, as mixing water for concrete) that " the
quality of the mixing water for production of concrete can influence the setting time,
the strength development of concrete and the protection of the reinforcement against
corrosion. When assessing the suitability of water of unknown quality for the
production of concrete, both the composition of the water and the application of the
concrete to be produced should be considered". Generally, the suitability of water for
the production of concrete depends upon its origin.
According to BS EN 1008:2002, portable water can only be used in mix
design of concrete without any test. Recovered water from other processes in the
25
concrete industry, water from underground sources or natural surface water and
industrial waste water should be tested before utilization in concrete. Sea water or
brackish water and Sewage water must not be used in reinforced concrete.
2.5.7
Super Plasticizer
They also are known as high range water reducers. Pirazzolli (2005) defined
them as linear polymers containing sulfuric acid groups attached to the polymer
backbone at regular intervals. Most of the commercially available formulations
belong to one of these four families:

Suffocated melamine-formaldehyde condensates

Suffocated naphthalene-formaldehyde condensates

Modified lignosulfonates

Polycarboxylate derivatives
By use of super plasticizer, it is possible to produce flowing concrete with
very high slump in the range of 175-225mm which can be used in heavily reinforced
structures where adequate consolidation cannot be achieved by vibration; producing
high-strength concrete with water-cement ratio of 0.3 to 0.4 is another benefit of
using super plasticizers in concrete. Plasticizers can raise the slump which depends
on its type, dosage, and time of addition of super plasticizer, water-cement ratio, and
type and amount of the cement. They can improve the workability of concrete for
most types of cement and also can affect other concrete properties.
26
2.6
Mixture and Proportions
According to literature, the majority of the investigations on geopolymer
material were about properties of small scale specimens. Palomo et al (1999)
researched the geopolymerisation of low-calcium fly ash (molar Si/Al=1.81) using
four different solutions with the solution-to-fly ash ratio by mass of 0.25 to 0.30. The
molar SiO2/K2O or SiO2/Na2O of the solutions was in the range of 0.63 to 1.23. The
sizes of specimens were 10x10x60 mm. By curing for 24 hours at 65oC, mixtures
with a combination of sodium hydroxide and sodium silicate solution could gain the
compressive strength of 60 MPa. Xu and Van Deventer (2000) reported that for
geopolymeric reactions the proportion of alkaline solution to alumino-silicate powder
by mass should be about 0.33. The specimen size was 200x200x200 mm, and the
maximum compressive strength achieved was 19 MPa after 72 hours of curing at
35oC with stilbite as the source material.
Van Jaarsveld et al (1998) presented the use of the mass ratio of the solution
to the powder of 0.39. They used 57% fly ash with 15% kaolin or calcined kaolin and
the alkaline liquid was a combination of 3.5% sodium silicate, 20% water and 4%
sodium or potassium hydroxide in their invetigation. Specimen size was of 50x50x50
mm. When they utilized fly ash and builders’ waste, the compressive strength of 75
MPa was achieved.
Barbosa et al (2000) followed the former work of Davidovits (1982) and used
calcined kaolin. According to their results, the optimal composition was the ratio of
Na2O/SiO2 = 0.25; H2O/Na2O =10.0, SiO2/Al2O3 = 3.3. A thin polyethylene film was
used as moulds.
Hardjito and Rangan (2005) found that for consistent results the ratio of
sodium silicate‐to‐sodium hydroxide ratio should be 2.5. They used the ratio of
alkaline solution‐to‐fly ash at about 0.35. Upon investigation of the affects of the
21
concentration of the sodium hydroxide solution, they realized that with higher
molarity of the sodium hydroxide solution, higher compressive strength can be
achieved. In their research work they used a range of molarity of the solution
between 8 molars to 14 molars. Liu et al. (2010) investigated the use of bauxite
residues in geopolymer concrete. In the production of unsintered construction and
building products, they suggested that the optimal proportions of raw materials can
be as below:
Bauxite Residue: 25 to 40%
Fly Ash: 18 – 28%
Sand: 30 ‐35%
Lime: 8 – 10%
Gypsum: 1 – 3%
Portland cement: 1%
This composition has been used to produce building materials that has
reached the 1st grade of Chinese standards for a brick (Liu et al. 2010).
Chindaprasirt et al. (2008) researched geopolymer mortars based on fly ash
and ground bottom ash. They used the Na2SiO3/NaOH mass ratio of 1.5 and three
different concentrations of 5, 10, and 15 M of NaOH. Finally, they found that both
fly ash and bottom ash were appropriate source materials for geopolymers. However,
fly ash was more reactive than bottom ash and caused a higher degree of
geopolymerisation. The NaOH solution with concentration of 10 M was established
to be a suitable and proper medium as alkaline liquid and produced fly ash and
bottom ash geopolymer mortars with the compressive strengths of 35 MPa and 18
MPa, respectively.
28
2.7
Curing of Geopolymer Concrete
Up to now, many researchers have investigated the effects of curing of
properties of concrete. Ambient conditions, steam curing and heat-curing were the
main objectives of their works. Unanimously, they reported that curing of
geopolymer concrete is one the most important parameters that influences the
durability and strength of geopolymers. Hardjito et al. (2004) found that the curing of
geopolymer concrete at higher temperatures, up to 60°C, would yield a higher
compressive strength than at a lower temperature, yet any increase in curing
temperature over this threshold made no substantial difference to its strength. A
proportional relationship was discovered between the length of curing time and
compressive strength. Hardjito et al. (2004) discovered the fast rate of
polymerization only stalled the strength gain when the concrete was cured for short
times, such as 24 hours. This contrasts with the strength development behavior of
OPC based concretes, which undergo a hydration process over a length of time when
being steam cured, therefore increasing in strength with age. This strength
development over time can be achieved with geopolymer concrete when curing time
is extended. It was discovered that increase in curing time in the range of 6 hours to
96 hours, the polymerization process would be improved and therefore produced
higher compressive strength. It is noted though, that the strength increase after 48
hours of steam curing is not significant.
It is recommended during the curing of geopolymer concretes at temperatures
up to 100°C; samples should be wrapped and then sealed to prevent excessive
evaporation of the samples during curing. Excessive evaporation may change the
mixture and would cause a less dense concrete with a weaker compressive strength.
It was also discovered that in wrapping the geopolymer concrete specimens, the mix
did not harden immediately under ambient conditions. Hardjito and Rangan (2005)
released that in their experiment the fly ash-based geopolymer concrete at room
temperatures below 30oC the sample did not set for at least 24 hours after casting.
29
Wallah and Rangan (2006) investigated the effects of conditions of curing on
the properties of geopolymer concrete. In May, July and September 2005, they
studied the influence of ambient conditions on a mixture. It was discovered that
specimens cured under ambient conditions exhibited significantly lower 7 day
compressive strengths than those cured under elevated temperatures for the first 24
hours. It was reported that under ambient curing conditions of geopolymer concrete,
the 7th day compressive strength and subsequent strength gain with respect to age lies
dependent upon the average ambient temperature at the time of curing. As the
ambient temperature at casting increased, as did the 7th day and subsequent
compressive strength’s tested at later dates. The compressive strength of the
geopolymer concrete during July exhibited 28 day strength of 31 MPa in comparison
to 47 MPa for the mix poured in May. The average temperature experienced within
July 2005 ranged from 8°C to 18°C, and 18°C to 25°C in May.
2.8
Fresh Geopolymer Concrete Paste
Information on the behavior and properties of the fresh geopolymers is
limited. Teixeira-Pinto et al (2002) recommended that geopolymer materials should
be mixed by the forced mixer due to possessing high viscosity and cohesive nature
and being dry during mixing. Meanwhile, found that Vicat needle apparatus is not
suitable to evaluate the setting time of fresh geopolymer concrete. In their researches
they found that the temperature of the fresh geopolymers was in direct relation with
the mixing time and increase in mixing time would raise the temperature of the paste
which consequently decreased the workability of geopolymer concrete. However,
one year later, Chen and Chiu (2003) measured the setting time of geopolymeric
material by mean of the Vicat needle. They reported that the initial setting time for
geopolymers cured at 60oC was very short and was between 15 to 45 minutes.
Barbosa et al (1999) presented that the viscosity of the fresh metakaolin-based
geopolymer paste increased with time.
31
Figure 2.3: Fresh geopolymer concrete paste (Hardjito and Rangan, 2005)
Cheng and Chiu (2003) also tested the effect of curing on geopolymer paste.
In fact, they mixed KOH and metakaolin for ten minutes, and then sodium silicate
and ground blast furnace slag were added and mixed for five minutes. It was reported
that setting was occurred in ambient conditions in a short period of time. However,
curing temperature and curing time have been reported to be significant parameters
in determination of the properties of the geopolymers, similar to that exists in
production of conventional concrete. Palomo et al. (1999) acknowledged that
increase in curing temperature of geopolymers caused higher compressive strength.
2.9
Properties and Applications of Geopolymer Concrete
Geopolymers and sustainability development are terms that are so close to
each other. The use of geopolymer, to date has only been limited to low strength
applications. This seems to remain the case, when in fact a lot of researchers praise
the characteristics of the product. Johnson (2007) reported that the heat, fire and acid
resistance of geopolymer concrete were be greater than that of Portland cement based
30
concrete. Johnson used the geopolymer fast setting characteristic as an advantage, as
he proposed that it be used in the production of concrete pipes and poles. Such
manufacturing requires concrete with zero slump, and processes that involve
centrifugal stages, roller suspension and vertical casting. It was discovered that by
manipulating the mix design, and therefore producing ‘no slump’ concrete, it was
possible to utilize geopolymer concrete in preparing pipes and other consolidated
moulded products. Duxson et al (2007) reported that depending on the composition,
curing conditions and properties of the constituents, geopolymer concrete can posses
these properties:

High compressive strength

Low shrinkage

Good abrasion resistance

Fast and controllable hardening

Fire resistance (up to 1000ºC)

High resistance against acids and salt solutions

High resistance to alkali-aggregate reactions

Low thermal conductivity

Good adhesion to concrete surfaces, steel, glass and ceramics

Innate protection for steel reinforcement due to low chloride diffusion rates
Balaguru et al (1997; 1999) successfully utilized geopolymer composites with
the Si/Al ratio of more than 30 to strengthened concrete structures such as beam and
coating for transportation infrastructures. Finally, reported their excellent
performance in terms of fire resistance, durability against Ultra violet light, and did
not involve any toxic agents.
Fly ash-based geopolymer concrete railway sleepers were manufactured and
tested by Palomo et al (2004) which showed excellent engineering performances and
32
small drying shrinkage. Furthermore, they claimed that available concrete technology
to the date was sufficient for production of geopolymer concrete structural members.
Davidovits (1991) compared the behavior of geopolymers to that of Zeolitic
materials which are microporous crystalline solids that consist of silicon, aluminium
and oxygen in their framework and cations, water and other molecules within their
pores. They have the capability to adsorb toxic chemical wastes which is their
similarity with geopolymers. He declared that when waste materials are introduced
into mixture of a geopolymer, they locked into the three dimensional structure of the
geopolymeric matrix. Acid-resistant geopolymeric containment can significantly
lessen the leaching of mercury, iron, cobalt, cadmium, zirconium, nickel, zinc, lead,
arsenic, radium and uranium.
Figure 2.4: Percentages of hazardous elements locked in the geopolymer
matrix (Davidovits, 1991)
33
2.9.1
Shrinkage of Geopolymers
Generally, shrinkage is known as the gradual reduction in volume of concrete
with time and the external actions to the concrete does not influence it. Gilbert
(2002) categorized shrinkage into plastic shrinkage, chemical shrinkage, thermal
shrinkage and drying shrinkage. Plastic shrinkage normally takes place when the
concrete is still in plastic condition by means of excessive evaporation or absorption
of mixing water by soil or other absorptive materials. It is known as a significant
reason for cracking of concrete during hardening. However, temperature, ambient
relative humidity and wind velocity influence the extent of plastic shrinkage
considerably Neville (2000). It is also affected by the cement content of the mixture
and the water-cement ratio. In fact, for greater cement content and lower watercement ratio, the plastic shrinkage will be greater.
Chemical shrinkage can occur in the cement paste by various chemical
reactions, such as the hydration shrinkage. While, thermal shrinkage is normally
caused by release of the heat from hydration process of cement with water.
Drying shrinkage is the decrease in volume of concrete and caused by the loss
of water during the drying process and this type of shrinkage, the drying shrinkage,
comprises the largest part of the total long-term shrinkage.
Neville (2000) found that the aggregate part rolling a considerable influence
on the formation of shrinkage in concrete. Generally, higher aggregate content,
higher modulus and rougher surface aggregates will cause smaller shrinkage, while
higher water-cement ratio produces concrete with higher shrinkage. At higher
degrees of relative humidity, the shrinkage would be smaller. It is found that an
enlargement in the volume of concrete member will significantly decrease the level
of shrinkage due to requirement of further time for shrinkage to arrive at the interior
layers of the concrete (de Larrard et. al., 1994).
34
Wallah (2009) conducted an experiment on drying shrinkage of low calcium
fly ash based geopolymer. They used a combination of sodium hydroxide solution
and sodium silicate and finally heat-cured the specimens for 24 hours at 60oC.
Finally, they concluded that heat-curing of fly ash based geopolymer concrete
possessed good properties against drying shrinkage. In terms of the drying shrinkage
strains, they reported that the results for specimens with different compressive
strengths were almost the same and the values calculated according to Gilbert
method was about 5 to 7 times higher than these practical drying shrinkage strains.
2.9.2
Density of Geopolymer Concrete
The density of concrete is a determination of its unit weight which is related
to the amount and density of the aggregate, the amount of entrained air, and the water
and cement content. Density is a way to determine how compact one material is
compared to another one. Due to the different mix designs, different values were
reported for the density of concrete such as 1750–2400 kg/m3 for lightweight and
normal concrete ( Dorf, 1996) , 2403–2439 kg/m3 (Washington State Department of
Transportation), 2320 kg/m3 ( Portland Cement Association) and 2400 kg/m3
(McGraw-Hill Encyclopedia of Science and Technology) .
Vijai et al. (2010) investigated the density and compressive strength of fly ash
based geopolymer concrete by testing samples in ambient condition and heat-curing
at 60oC for 24 hours. They finally concluded that densities were in a range of 2251 to
2400 kg/m3 which were to some extent equal to the conventional concrete density.
There was a direct relation between the age of the geopolymer concrete and its
density. The average density of fly ash based geopolymer concrete is close to OPC
concrete density. In another investigation by Lloyd and Rangan (2010) on
geopolymer concrete with different aggregate types and grading, they found density
at 28 days for mixtures which were cured for 24 hours at 60oC was 2360 ±60 kg/m3.
35
Olivia and Nikraz (2011) conducted a research on low calcium fly ash geopolymer
concrete and reported that density of samples were in the range of 2248 to 2315
Kg/m3. Hardjito and Rangan (2005) reported that the density of fly ash based
geopolymer concrete depended on the unit mass of aggregate and the density of the
low-calcium fly ash-based geopolymer concrete ranged between 2330 to 2430 kg/m3.
2.9.3
Velocity of Ultrasonic Pulses in Geopolymer Concrete
Ultrasonic pulses velocity test (UPV) is a non-destructive test to assess the
quality of concrete, its uniformity, extension of cracks, and find the strength
according to correlations, modulus of elasticity and dynamic passion ratio. For this
purpose, the time of travel of an ultrasonic pulse passing through the concrete should
be measured. Higher velocity is obtained when concrete quality is good in terms of
density, uniformity and homogeneity, while low compaction, voids or damaged
material is present in the concrete under test, a corresponding reduction in the
calculated pulse velocity occurs. As concrete ages or deteriorates, it would be
reflected in either an increase or a decrease in the pulse velocity. Empirical
relationships may be established between the pulse velocity and both the dynamic
and static elastic modules and the strength of concrete. According to the BS. 1881:
Part203: 1986, it is essential that there be adequate acoustical coupling between the
concrete and the face of each transducer. Typical couplants are petroleum jelly,
grease, soft soap and kaolin/glycerol paste and it should be a very thin layer. It is
necessary to consider the various factors which can influence pulse velocity and its
correlation with various physical properties of the concrete, such as moisture content,
temperature of the concrete, path length and shape of the specimens. It is sometimes
helpful to use ultrasonic pulse velocity measurements to give an estimate of strength.
The mean pulse velocity and mean strength obtained from each set of three
nominally identical test specimens provide the data to construct a correlation curve.
36
Numerous experimental data and the correlation relationship between
strength and pulse velocity of concrete have been presented and proposed. Some
figures suggested by Whitehurst (1951) for concrete with a density of approximately
2400 kg/m3are given in Table 2.xxx. However, these lines of demarcation cannot be
sharply drawn, exceptions being noted in all but the extreme classifications.
Table 2.2: The quality of concrete in structures in terms of the ultrasonic
pulse velocity (Whitehurst, 1951)
Pulse Velocity ( m/s )
Concrete Quality
Above 4500
Excellent
3500 to 4500
Generally good
3000 to 3500
Questionable
2000 to 3000
Generally poor
Below 2000
Very poor
For the relationship with compressive strength, several parameters can
intervene so that there are not only one and simple relation between ultrasonic
velocity and the strength of concrete. Based on experimental results, Tharmaratnam
and Tan (1990) introduced the relationship between the ultrasonic pulse velocity in a
concrete (Vc) and concrete compressive strength (fc) as:
fc= a ebVc
Where a and b are parameters dependent upon the material properties.
(1.1)
31
Findings of different researchers' studies on the relationships between the
concrete strengths and UPV are shown in Figure2.5. The specimens used in these
researches were cubes and cylinders. Cylindrical concrete strengths were converted
into standard 150 mm cube. These researches have been processed on the different
specimens prepared in laboratory conditions and have different concrete mixture
ratios. As it is shown in Figure2.5, strength-UPV curves of these values are different
from each other.
A correlation is set up and showed in Figure 2.5 with the data obtained from
earlier experimental studies which are produced on specimens having dissimilar
concrete mixture ratios.
Figure 2.5: Researches on concrete strength-UPV relationships
There is no acceptable method at present for the non-destructive
determination of concrete strength. This is due to the complexity of the problem and
because oversimplified approaches have been used in the past to find a solution. The
novelty of this article is the recognition that concrete strength cannot be calculated
38
with acceptable accuracy from the longitudinal pulse velocity alone - supplementary
tests are needed. It also shows that the supplementary tests should measure material
characteristics of the concrete. That is, one approach for improvement is the use of
multivariable formulas. Preliminary tests demonstrate that the consideration of the
age of concrete as a supplement to the longitudinal pulse velocity does produce
improvement in the strength estimation. It is encouraging that not only the analysis
of past results but also preliminary tests seems to support the proposed approaches
(Popovics, 2001).
2.9.4
Water Absorption of Geopolymer Concrete
In some circumstances the water absorption or water permeability of the
material is a major factor, especially for durability criteria. Limited literature is
available on the water penetrability and absorption of fly ash geopolymer concrete
and according to them metakaolin based geopolymer concrete has permeability 1011 m/s (Davidovits, 1994a), while Shi (1996) found that permeability of slag based
geopolymer concrete is more than 10-12 m/s. Olivia al. (2008) had an experiment on
water absorption of low calcium fly ash based geopolymer concrete. Seven mixes
were casted in 100x200mm cylinders and cured for 24 hours at 60oC in the steam
cured. After 28days, the cylinders were cut into slices. According to their results,
geopolymer concrete had low water absorption, volume of permeable voids and
sorptivity. It is found that the fly ash based geopolymer concrete could be classified
as a concrete with an average quality according to water permeability value since its
water permeability was very low in comparison with OPC concrete. They concluded
that low water/binder ratio and a well-graded aggregate are the most important
factors in production of low water penetrability of geopolymer concrete. In another
study by Sathia, Ganesh Babu and Santhanam (2008) on fly ash based geopolymer
concrete, they concluded that absorption values of the geopolymer concretes at all
strength levels were lower than the limit of 3% specified for good concretes. The
final absorption results of these mixes shows that the geopolymer concretes were
39
having lower absorption rate compared to normal concretes, and also decreasing with
increasing strength.
2.9.5
Compressive Strength
Generally, the ultimate compressive strength and setting time of geopolymer
concrete were discovered to be dependent on curing temperature, water content and
type of alkaline activator and composition of source materials. Generally, fly ash
based concretes have slow reaction process which lead to the strength development
at later dates of age only and it is a barrier against using this kind of concrete in
precast concrete construction with ambient conditions of curing due to the low early
strength and formwork turnover routines.
Barbhuiya et al (2009) elaborated the influences of adding silica fume and
calcium hydroxide into concretes with a fly ash substitution of 30% of the OPC
based content. 5% silica fume by mass of the cement content was added as a final
addition when mixing the concrete. Hydrated lime on the other and was substituted at
a rate of 5% by mass of the total cementious materials. The first 24 hours were spent
at 20°C and then transferred to a moist curing room at 23°C and kept in water until
testing. Workability is seen to decrease upon the addition of hydrated lime, however
to improve this, a super plasticizer was added. The addition of silica fume to the mix
had no effect on the workability of a concrete mix. They found that the addition of
both silica fume and calcium hydroxide increased the early compressive strength of
the geopolymer concrete mixes. Testing at 3 days of age showed that the strength of
both silica fume and hydrated lime mixes were equally higher, (30 MPa) than the
standard concrete mix at 24 MPa. The major differences in compressive strengths
were apparent at 28 days with a constant progression from the standard mix (49
MPa), fly ash inclusive of hydrated lime (53 MPa) and then the concrete mix
incorporating silica fume with a 58 MPa 28 day compressive strength.
41
Vijai et al. (2010) also reported the heat curing would produce higher
compressive strength than curing under ambient conditions. The compressive
strength of heat-cured fly ash based geopolymer concrete did not improve
considerably after 7 days.
Temuujin, van Riessen and Williams (2009) tested the use of calcium based
additives into geopolymer pastes. To increase the gain of compressive strength and
accelerate the ambient curing (on average at 20°C) of the paste both calcium
hydroxide and calcium oxide were substituted into geopolymer pastes for fly ash.
Specimens were heat-cured at 70°C. They found that the addition of calcium
compounds enhanced the mechanical properties of geopolymers cured at ambient
temperatures, but decreased the strength of samples cured under elevated
temperatures. According to their studies, the addition of calcium hydroxide (Ca
(OH)2) improved the ambient curing strength more than calcium oxide (CaO) due to
involving of the calcium hydroxide with the reaction process in geopolymers. The
use of calcium hydroxide would appear to present incomplete hydration of the
product as it reacts with the alkaline solution in the formation of calcium hydroxide.
Specimens with CaO added presented compressive strengths approximately 20%
lower than those with calcium hydroxide. It is suggested that the lower compressive
strength in the pastes that is cured under elevated temperatures is due to the water
evaporation within the mix, exhibited by lower density and higher porosity. At
elevated temperatures, the presence of calcium prevented the formation of three
dimensional geopolymer networks due to the rapid dissolution of the paste.
Therefore, it reduced mechanical properties of the final product. Under ambient
conditions, it was established that by increasing the calcium compound of the
mixture, the compressive strength would be increased. With a 3% addition of
calcium hydroxide the compressive strength of 29 MPa compared to a geopolymer
paste with no calcium additive which exhibited strength of 12 MPa. In comparison,
geopolymer with a calcium hydroxide inclusion of 1% and 2% showed strength of 24
MPa and 28 MPa respectively (Temuujin, van Riessen and Williams, 2009).
40
Drechsler et al. (2005), Hardjito (2004) presented the use of super plasticizers
or increment in water contents improve the workability of the geopolymer concrete
which resulted in high slumps up to 240mm with excellent strength and without any
aggregate segregation.
Nguyen (2009) produced geopolymers using the similar batching processes to
OPC products. However, they announced that there was a significant dissimilarity
between geopolymer concrete and Portland cement concrete in the binder.
Figure 2.6: Effect of curing temperature on setting time of a geopolymer
concrete (Nguyen, 2009)
42
Figure 2.7: Room temperature setting for geopolymer concrete and Portland
cements concrete (Davidovits, 1991)
Figures 2.6 and 2.7 illustrate that the compressive strength of geopolymer
concrete is in a direct relation with curing time and curing temperature. In other
words, increase in curing time and curing temperature would yield higher
compressive strength.
Figure 2.8: Relation between compressive strength and water-to-polymers
solids (Nguyen, 2009).
43
This graph presents the effect of water-to-solids ratio on compressive strength
at 7days. As it can be seen, lower water-to-solids ratio in all curing temperatures
produces higher compressive strength, and also shows how temperatures affected the
compressive strength. By curing at 90oC and water-to-polymer solids ratio of 0.175,
the compressive strength achieved to more than 70 MPa at 7days.
2.9.6
Tensile strength
According to Harjito and Rangan (2005) report, similar to OPC concrete the
tensile strength splitting of geopolymer concrete was only a fraction of the
compressive strength. In fact, the tensile strength of fly ash-based geopolymer
concrete was larger than the values recommends by the Standards Australia (2001)
which is ft = 0.4√
and Neville (2000) that it is ft = 0.3 (fc)2/3 for OPC concrete.
According to literature, tensile strength of geopolymer concrete is a fraction
of its compressive strength. The tensile strength of concrete is relatively low, about
10 to 15% of the compressive, occasionally 20%. Thus, parameters that influence the
compressive strength will influence the tensile strength of geopolymer concrete.
2.9.7
Factor Affecting the Relation Between Tensile and Compressive Strength
Factors that influence the relation between compressive and tensile strengths
are:
44
a) Aggregate
The relation between the tensile strength and compressive strength depends
on the type of coarse aggregate used, except in high strength concrete, because the
properties of aggregate, especially its shape and surface texture, affect the ultimate
strength in compression very much less than the strength in tension or cracking load
in compression. In experimental concrete, entirely smooth coarse aggregate led to
lower compressive strength, typically by 10 percent, than when roughened. It seems
that the properties of fine aggregate also influence the ft/fc´ ratio. The ratio is
furthermore affected by the grading of aggregate. This is probably due to the
different magnitude of the wall effect in beams and in compression specimens: there
surface/volume ratios are dissimilar so that different quantities of mortar are required
for full compaction.
b) Age
Age is also a factor in the relation between ft and fc, beyond about one
month, the tensile strength increases more slowly than the compressive strength. So
the ft/fc decreases with time.
c) Curing
The tensile strength of concrete is more sensitive to inadequate curing than
the compressive strength; possibly because the effects of non-uniform shrinkage of
flexure test beams are very serious. Thus air-cured concrete has a lower ft/fc ratio
than concrete cured in water and tested wet.
45
d) Air-Entrainment
Air-entrainment affects the ft/fc ratio because the pressure of air lowers the
compressive strength of concrete more than the tensile strength, particularly in the
case of rich and strong mixes. The influence of incomplete compaction is similar to
that of entrained air.
e) Light-weight concrete
Light-weight concrete conforms broadly to the pattern of the relation between
the ft and fc for ordinary concrete. At very low strength (300psi) the ratio ft /fc can
be as high as 0.3, but at higher strengths it is the same as ordinary concrete.
However, drying reduces the ratio by some 20% so that in the design of light-weight
concrete a reduced value of ft/fc is used.
f) Method of Test
As stated above, the tensile strengths of concrete measured by different tests
produce results of varying value. Incidentally, the value of the compressive strength
is also not unique but is affected by the shape of the test specimen. So the numerical
value of the ratio of the tensile strength to the compressive strength is not the same.
For these reasons, in expressing the ratio of the tensile to compressive strengths, the
test method must be explicitly stated. If the value of flexural strength is of interest, a
factor relating the splitting strength to flexural strength needs to be applied.
46
2.9.8
Factors Affecting Geopolymer Concrete Properties
Many parameters have been recognized that influence the properties of
geopolymers. Palomo et al (1999) reported that the curing temperature, curing time
and the type of alkaline liquid significantly affected the mechanical properties of fly
ash-based geopolymer concrete. Elevated curing temperature and longer curing time
were yielded in higher compressive strength. Moreover, alkaline liquid that had
soluble silicates in their composition increased the rate of reaction in comparison
with alkaline solutions that contained only hydroxide.
Van Jaarsveld et al (2002) reported that properties of geopolymers were
significantly varied with the water content and the curing and calcining condition of
kaolin clay. Meanwhile, they noted cracking and negative effects in geopolymers in
case of curing at too high temperature and recommended the use of mild curing.
van Jaarsveld et al (2003) elaborated another investigation and mentioned that
properties of geopolymers were derived from the source materials ,especially the
CaO content, and the water-to-fly ash ratio.
Barbosa et al (1999; 2000) concluded that the important parameters in
formation of geopolymers are the molar composition and the water content. They
illustrated that the hardened geopolymers were in amorphous microstructures and
their bulk densities were about 1.3 to 1.9.
Xu and van Deventer (2000) had a comprehensive experiment on natural SiAl geopolymers and finally listed the factors that significantly affected the
compressive strength of these materials such as the CaO and K2O content, the molar
Si-to-Al ratio of the source material, alkali liquid, the extent of dissolution of Si, and
the molar of Si-to-Al ratio in solution.
41
2.9.9
Disadvantages of Geopolymers
Many advantages were mentioned above; still geopolymer concrete has not
been successfully marketed as a modern and sustainable binder. In fact, the main
reason is that large cement companies are against the change from what they are
professional in to what they have to learn and find it risky. From the construction
industries point of view, ‘green cement’ has yet to establish itself as a viable,
recognised or proven technology (Duxson et al., 2007).
Yet, no exact estimation on the cost of the manufacture of geopolymer
concrete has been reported. Hardjito and Rangan (2005) estimated that low-calcium
fly ash based geopolymer concrete is cheaper than normal concrete; while
Pacheco‐Torgal et al. (2007) reported that the cost of ‘green cement’ is 62% more
expensive than Portland cement. Without accurate values for the cost of manufacture
of geopolymers, it is obvious that investors will not spend their money where they
have no idea about the project capital return.
Another barrier for geopolymers marketing is that specifications have been
set as acceptable standard and these standards only cover cement based products.
Thus, lack of standards and specifications for geopolymers must be consider as a
major barrier for mass utilization of them.
It is logical to mention that the manufacture process of geopolymers is very
complex for the general public who know little about this technology and need to
know either this new ‘green concrete’ is safe and stable enough to trust or not.
Geopolymers have been around since the 1950’s in the Soviet Union where Professor
Glukhovsky originally discovered geopolymers. In fact, they used only slag instead
of fly ash to construct the majority of buildings in the Ukraine back which are still
servicing without any significant signs of deterioration.
48
The author estimates that in the near future the global environmental rules in
regards to CO2 productions will impose the OPC companies to be adjusted to more
sustainable standards and without any doubt one of the answers shall be geopolymer
products.
Dehghan, Hussin and Falahati (2011) investigated the issues that prevent
geopolymer concrete to be marketed and be used in the structural works. They
reported that complexity in the procedure of manufacturing geopolymer binder is the
main barrier against their mass production. In addition to this, lack of standard and
lack of skilled labours have ceased their introduction to the market.
CHAPTER 3
METHODOLOGY
3.1
Introduction
Limited experience on fly ash‐based geopolymer concrete without any OPC
imposed several preliminary experimental works to familiarize with the mix
proportions and procedure of preparing the samples. According to literatures,
utilization of sodium silicate solution to the sodium hydroxide solution as the
alkaline liquid enhanced the reaction between the source material and the solution.
Thus, initial mix designs for the production of geopolymer concrete using sodium
hydroxide (NaOH) and sodium silicate (Na2SiO3) to form the alkaline solution were
prepared. However, cost of potassium based solution was another factor that
influences the decision making of using alkaline liquid. A trial and error process was
used for fine tuning the strength of the mixes, including different bottom ash
contents.
In this project the compressive and tensile and flexural strengths were the
main aspects of the investigation. To familiarize with the short-term strength
51
development of fly ash based geopolymer concrete, tests were conducted at 7, 14 and
28 days after casting.
Methods and standards for manufacturing and testing of OPC concrete were
followed in the production of geopolymer concrete. Meanwhile, it could help with a
relevant comparison between the two products. Aggregates proportion as an
important factor in properties of concrete was fixed at 70% by weight within the mix
and its size, moisture content, shape and fineness modulus were observed carefully in
order to investigate the effect of replacement of bottom ash and the aggregates were
used only from one source.
3.2
Materials Preparation
Mix proportion has known to be the most important parameter on geopolymer
concrete properties and strength. Thus, preparation of the constituents of geopolymer
concrete required more attention than any other factor. Below, the preparation of the
main components of the geopolymer in this experiment was discussed:
3.2.1
Fly ash
Dry low calcium fly ash was provided from Kapar power station, Malaysia.
Ten bags of fly ash with average weight of 20 kg were obtained from the Kapar
power station’s ash silo and stored in a dry and cool storage. Figure3.1. shows the
process of collecting, delivering and storing the fly ash.
50
Figure 3.1: Process of collecting, delivering and storing the fly ash
For chemical analysis, fly ash was sieved to particle size less than 75μm and
sent to Allied chemists laboratory SDN. BHD. The chemical composition of fly ash
is given in table 3.1.
Table 3.1: Composition of Fly Ash as Determined by XRF (mass %)
Element
Mass (%)
SiO2
46.7
Al2O3
35.9
Fe2O3
5.0
CaO
3.92
MgO
0.84
Na2O
0.58
K2O
0.5
P2O5
0.383
LOI
1.0
52
3.2.2
Alkaline Liquid
As it was mentioned above, a combination of sodium hydroxide and sodium
silicate solution was used as alkaline liquid in this experiment. Sodium hydroxide
(NaOH) in liquid form with a concentration of 14M (mass molar 4000gr/mol) and
pH 14 at 50g/L in 20oC was used in this experiment. Sodium silicate relative density
was 2.13gr/cm3. Another component of alkaline activator was sodium silicate and
was provided from R&M chemicals.
Figure 3.2: Sodium silicate in 10kg bottle
3.2.3
Aggregates
Aggregates were provided from local resource, stored uncovered outside of
the laboratory in storage divisions. In this research work coarse aggregate with
nominal sizes of 10mm, and fine aggregates in the form of sand were used.
Aggregates were prepared in saturated-surface-dry (SSD) condition and then were
sealed in plastic bags about one month before the mixing. For this purpose, coarse
53
aggregates and sand were soaked separately in clean water, and then distributed on a
plastic sheet until their surface become dry. SSD condition for geopolymer concrete
must be prepared to avoid the absorption of the alkaline solution by the aggregates
which reduce the polymerization of the fly ash. This process was very time
consuming and aggregates were prepared in more than 10 days. During preparation
room temperature, thickness of aggregate layers and volume of aggregates were
different, thus at the end of the process of preparing SSD condition, all bags were
combined together to make them uniform.
Figure 3.3: SSD condition preparation for sand and coarse aggregates
Sieve analyses on the natural sand were carried out based on BS 812103.1:1985. It was discovered that the optimum proportion was a combination with
50% of each of them. Following BS. 882:1992: Table5, there are lower limit and
upper limit for passing percentages for all-in aggregates through each sieve.
54
Table 3.2: Grading of combined aggregates (50% coarse aggregate+ 50%
Sand)
Sieve size(mm)
Combination
BS. 882:1992
(50%coarse+50%sand)
10
97.0
95-100
5.0
55.0
30-65
2.38
42.3
20-50
1.18
17.3
15-40
600
16.3
10-30
300
14.5
5-15
150
2.0
0-8
Thus, the grading curve of combined aggregates is presented in Figure3.2 and
it met the requirement of the standard.
100
100 95
Percentage passing ( % )
90
80
65
70
60
50
50
Combination
40
40
Lower limit
30
30
20
10
Upper limit
30
15
8
0
0
150
10
5
300
600
15
1.18
20
2.36
5
10
BS. Sieve sizes
Figure 3.4: Grading curve for combined aggregates
As it can be seen, combination of 50% coarse aggregate with 50% sand met
the requirement for standard grading curves of BS 882:1992.
55
SSD bulk specific gravity of sand which is the ratio of the weight in air of a
unit volume of aggregate, including the weight of water within the voids to the
weight in air of an equal volume of gas-free distilled water was measured in
accordance with ASTM C 128 – 01” Standard Test Method for Density, Relative
Density (Specific Gravity), and Absorption of Fine Aggregate’’ with use of 500 gr
SSD sand. Figure3.5 shows the process of preparation of sample to calculate SSD
bulk specific gravity.
Figure 3.5: SSD specific gravity test procedure
After drying the sample at 110oC and weighting the dried sample, SSD bulk
specific gravity of sand was measured as 2.47 and its dry bulk specific density was
2.41.
Moisture content and absorption was computed as a percentage by
subtracting the oven-dry mass from the saturated surface-dry mass, dividing by the
oven-dry mass, and multiplying by 100. In concrete technology, aggregate moisture
is expressed as a percent of the dry weight of the aggregate. Absorption natural sand
measured on 500 gr SSD sand and it was calculated to be 2.7 %. Moisture content of
coarse aggregate was also determined as 1.9%.
56
ASTM C 29/C 29M - 97’’ Standard Test Method for Bulk Density (“Unit
Weight”) and Voids in Aggregate’’ was selected as the code of practice to measure
dry and SSD bulk density of sand. Sand was filled in the cylinder at three layers and
for each layer 25 strokes was used for rodding. Figure3.6 illustrates the process of
preparing the sand for dry bulk density. Dry bulk density was calculated as 1641
Kg/m3 and its SSD bulk density was calculated with use of absorption (2.7 %) to be
1685Kg/m3.
Figure 3.6: Preparation process for dry bulk density
Void content was measured according to ASTM C 29/C 29M - 97, density of
water was reported in this standard in26.7oC as 996.6Kg/m3. Thus, void content of
normal sand was 31.3 %.
3.2.4
Bottom Ash
Bottom ash was obtained from Tanjung Bin power station, Johor, Malaysia.
Ten bags with average weight of 20 kg were delivered from Tanjung Bin power
51
station’s ash pond to UTM laboratory and stored in a safe place. Figure3.7 shows the
Tanjung Bin power stations’ bottom ash pond.
Figure 3.7: Tanjung Bin power stations’ bottom ash pond
To find bottom ash chemical composition, a sample of bottom ash which was
sieved through sieve 75μm was sent to ALLIED CHEMISTS LABROTARRY SDN.
BHD for chemical analysis and result from this analysis is tabulated in Table3.3.
Table 3.3: Chemical composition of bottom ash from Tanjung Bin
Element
Mass (%)
SiO2
45
Al2O3
30
Fe2O3
11
CaO
8.4
MgO
<0.1
Na2O
<0.1
K2O
0.9
P2O5
<0.1
LOI
27.4
58
Since bottom ash was selected as a replacement for sand, its size gradation
was also a major parameter. Thus, sieve analysis was elaborated for it to find out its
grading curve which is presented in Table3.4 and Figure3.8. Sieve test on bottom ash
was carried out based on BS 812-103.1:1985. Bottom ash had large particles even
larger than 20mm, to make it a suitable substitute for sand, initially, it was sieved
through sieve 5mm to become in the same range with sand.
Table 3.4: Grading of Tanjung Bin bottom ash
Sieve size(mm)
Passing
BS. 882:1992
percentage ( % )
Additional limit
(C)
10
100
100
-
5.0
98.7
89-100
-
2.38
64.6
60-100
60-100
1.18
49.0
30-100
30-90
600
38.8
15-100
15-54
300
26.6
5-70
5-40
150
12.2
0-15
-
75
6.4
-
-
According to BS. 882:1992, the grading of the sand shall comply with the
overall limits given in Table3.8. Additionally, not more than one in ten consecutive
samples shall have a grading outside the limits for any one of the gradations C, M or
F.
59
100
100
100
100
100
98.8
Passing percentage ( % )
90
89
80
70
70
64.4
60
60
50
Bottom ash
49
40
Lower limit
38.8
30
20
100
100
15
15
12.2
10
Upper limit
30
26.6
5
0
0
150
300
600
1.18
2.36
5
10
BS. Sieve
Figure 3.8: Grading curve for bottom ash
The fineness modulus of bottom ash was calculated based on the results of
bottom ash sieve analysis which was tabulated in Table3.4. The fineness modulus
was measured by summation of the cumulative percentage retained on the sieve
series of 150, 300, 600μm, 1.18, 2.36 and 5.0 mm. The calculated fineness modulus
of bottom ash was 3.25 which showed coarser nature of this material.
Bottom ash was also prepared in saturated surface dry (SSD) condition. This
process was performed about one month before the casting with a similar method for
sand. For preparation of bottom ash, it was sieved through sieve 5mm which lead to
upper limit grading as it is for sand. Figure 3.9 shows the method of soaking bottom
ash in water which took 24 hours. As it can be seen in the photo, after filling the
bucket with water, large air bubbles released which showed bottom ash has a porous
nature.
61
Figure 3.9: Immersion of bottom ash in water
During discharging the extra water, BS sieve 75μm was used. According the
literature, this process of washing was named as washing the bottom ash and the
produced was named as washed bottom ash (WBA). The process was continued by
distributing the wet bottom ash on plastic sheets to become in surface dry mode.
Figure3.10 shows drying process of bottom ash for SSD condition. The left material
is natural sand and the right one is bottom ash which was darker than natural sand.
Figure 3.10: Drying process of bottom ash and sand for SSD condition
60
SSD bulk specific gravity of washed bottom ash was also measured in
accordance with ASTM C 128 – 01” Standard Test Method for Density, Relative
Density (Specific Gravity), and Absorption of Fine Aggregate’’ with use of 500 gr
SSD bottom ash. Figure3.11 shows the process of preparation of bottom ash for SSD
bulk specific test.
Figure 3.11: Preparation of bottom ash for SSD bulk specific test
After drying the sample at 110oC and weighting the dried sample, SSD bulk
specific gravity of bottom ash was measured as 1.74.
Water absorption was computed as a percentage by subtracting the oven-dry
mass from the saturated surface-dry mass, dividing by the oven-dry mass, and
multiplying by 100. In concrete technology, aggregate moisture is expressed as a
percent of the dry weight of the aggregate. Absorption natural sand measured on 500
gr SSD bottom ash and it was calculated to be 10.81 %.
ASTM C 29/C 29M – 97’’ Standard Test Method for Bulk Density (“Unit
Weight”) and Voids in Aggregate’’ was selected as the code of practice to measure
dry and SSD bulk density of sand. Sand was filled in the cylinder at three layers and
62
for each layer 25 strokes was used for rodding. Figure3.12 illustrates the process of
preparing the sand for SSD bulk density. Dry bulk density was calculated as
957.7kg/m3 and its SSD bulk density was calculated with use of absorption (10.81
%) to be 1061.2 kg/m3.
Figure 3.12: Preparation process for SSD bulk density
Void content was measured according to ASTM C 29/C 29M – 97, density of
water was reported in this standard in 26.7oC as 996.6kg/m3. Thus, void content of
bottom ash was 44.7 %.
3.2.5
Super plasticizer (SP)
As it was mentioned above, workability of mixtures was not proper to cast in
the moulds, so extra water and superplasticizer were added to the mixtures to provide
a moderate slump. Commercially available SP in powder form was added to the
mixtures by 2% of weight of fly ash to improve workability. According to British
63
Standard BS EN 206-1:2000, concrete specification, performance, production and
conformity, The total amount of admixtures, if any, shall not exceed the maximum
dosage recommended by the admixture producer and not exceed 50 g of admixture
(as supplied) per kg cement unless the influence of the higher dosage on the
performance and the durability of the concrete is established. Admixtures used in
quantities less than 2 g/kg cement are only permitted if they are dispersed in part of
the mixing water. However, this was not a major problem since the amount of SP
was more than that ratio.
Figure 3.13: Applied super plasticizer in powder form
3.3
Preliminary Works
To start geopolymer concrete without bottom ash was produced to familiarize
with the process and behavior of the material. The first two mixes were prepared in
the middle of September, 2011, with the use of a pan mixer. Samples were poured in
100x100x100mm cubes for compression strength test. Heat-curing in oven was the
method to cure trial mixes to speed up the process and another two trial mixes were
casted in the end of September, 2011 and another two were made in August, 2011.
64
The main objectives to perform those pre-investigations were:

Familiarizing with the process of manufacturing fly ash based
geopolymer concrete and optimizing the mix design

Discovering the most suitable combination of aggregates for the
mixture

Investigating the amount of extra water that was required for
workability by means of slump test

Finding suitable temperature for curing of fly ash based geopolymer
concrete containing bottom ash

Exploring the setting time in order to prevent flash set in the mixer
Mix proportions, method of mixing and casting were based on the results of
trial mixes which were discussed below:
3.4
Proportions, Mixing, and Casting
The mixing phase had a notable influence in the production of geopolymer
concrete, because a wrong and unbalanced mixture may cause flash set or even
prevent hardening process which both are failures for the designer and waste of time
and materials are its consequences.
65
According to the literature which was reported in Chapter 2 and also results
based on trial mixes, a brief review on the type, size and content of constituents of
the final mix designs were presented:

Low calcium fly ash was obtained from Kapar power station, Malaysia

Bottom ash was attained from Tanjung Bin power station, Johor, Malaysia

Alkaline liquid was a mixture of sodium silicate solution and sodium
hydroxide solution with the ratio of 2.5. Sodium hydroxide solution was in
molarity of 14M.

Ratio of alkaline liquid/fly ash was kept on 0.4 by mass.

70% of the weight of the mixtures was aggregates in the size of 10 mm and
sand

Bottom ash was replaced by 0, 20, 40 and 60 percent of fine aggregate by
mass
It was assumed that the average unit-weight of geopolymer concrete was
2350 kg/m3and the mass of combined aggregates was 70% of the whole mass of
concrete which 0.70×2350= 1645 kg/m3. The aggregate size shall be selected to
satisfy the standard grading curves used in the design of OPC concrete mixtures. The
aggregate part consisted of 822.5 kg/m3 (50%) of 10 mm aggregates and
822.5 kg/m3 (50%) of sand to meet the requirements of standard grading curves. All
specifications were in accordance with British Standard BS882:1992.
By decreasing the unit-weight of geopolymer concrete from the aggregates
content, the mass of low-calcium fly ash and the alkaline liquid were equal to
66
705kg/m3 (2350 – 1645 = 705 kg/m3). As it was mentioned, the alkaline liquid/ fly
ash ratio by mass was taken as 0.4. Therefore, the mass of fly ash became 503 kg/m3
which is (705/ (1+0.4) =503 kg/m3) and the mass of alkaline liquid was 202 kg/m3
according to (705 - 503 = 202 kg/m3). In this project, the ratio of sodium silicate
solution/sodium hydroxide solution by mass was selected as 2.5; the mass of sodium
hydroxide solution = 202/ (1+2.5) = 58 kg/m3, while the mass of sodium silicate
solution was equal to 144 kg/m3 that (202 – 58 =144 kg/m3). Commercially available
super plasticizer with amount of approximately 2% of mass of fly ash,
503 × (2/100) = 10 kg/m3was added into the mixture to assist the placement of fresh
concrete. Water was also added to mixtures to improve the workability and produce a
desirable moderate slump value.
It was decided to fix the slump value of all mixtures to a specific amount to
compare the strengths of them. According to the BS EN: 206-1:2000, class S2 with
80mm slump value was the target. These proportions were tabulated in Table3.5 as
below:
Table 3.5: Final mix designs (kg/m3)
Item
Mix0
Mix20
Mix40
Mix60
503
503
503
503
Coarse aggregate 10mm
822.5
822.5
822.5
822.5
Sand
822.5
658
493.5
329
Bottom Ash
0
164.5
329
493.5
Sodium Hydroxide (14M)
58
58
58
58
Sodium Silicate
144
144
144
144
Super plasticizer
10
10
10
10
Extra water
9.1
4.5
1.8
0
Fly ash
61
Figure3.14: Prepared dry components of geopolymer concrete before casting
Davidovits (2002) recommended that the mixture of the sodium silicate
solution and the sodium hydroxide solution should be prepared at least one day
before addition into the solid constituents. Following this recommendation, the
sodium hydroxide solution was mixed with sodium silicate solution one day before
the mixing and then sealed in a tank as showed in Figure3.15.
Figure 3.15: Sealing alkaline activator in the tank
68
Nine cubes for 7, 14 and 28 days compressive strength were casted. Six
200×100mm cylinders were prepared for tensile splitting strength test at the age of
7-day and 28-day, meanwhile six 100×100×500mm prisms were also prepared for
calculation of flexural strength at the age of 7-day and 28-day and one extra prism to
measure water absorption Detailed calculation for required amount of concreting is
tabulated in Table3.6 which must be prepared four times.
Table 3.6: Quantity estimation and planning of experiment
Test
Description
Size (mm)
No. of
specimens
Age of testing
Volume (m3)
Total (m3)
Compressive
Tensile
Flexural
Water
strength
strength
strength
absorption
100×100×100
200×100
100×100×500
100×100×500
3
3
3
1
7 and 28
7 and 28
28
0.009
0.03
0.005
7, 14 and 28
0.009
0.053+10%=0.058 for each mix design
At first, all dry constituents such as aggregates, fly ash and bottom ash
(except for the first mixture) were combined for about 5 minutes. Then, the alkaline
solution was inserted into the dry mix gradually. Mixing was continued until
formation of a homogenous combined paste which was about another 5±1 minutes. It
was observed from trial mixes that addition of 2% of the weight of fly ash as super
plasticizer would not provide the workability solely, thus extra water was added to
mixes for providing slump value of 80-90 mm. Figure3.16 shows mixing the
geopolymer concrete in the pan mixer.
69
Figure 3.16: Mixing the geopolymer concrete in the pan mixer.
It was observed that geopolymer concrete physical shape was different from
OPC concrete. In fact, fresh geopolymer concrete was very dark and shiny and had
an extremely sticky and cohesive nature and pouring geopolymer concrete needed
more time and energy due to the difficulty of moving. Figur3.17 demonstrates fresh
geopolymer concrete containing 20% bottom ash.
Figure 3.17: Fresh geopolymer concrete containing 20% bottom ash
For the first step in the casting stage, moulds were prepared for concreting by
lubricating with a polymeric wax. For the use of geopolymer concrete, the usual
grease or oil is not suitable and a polymeric mould releaser material must be used.
11
The next step was performed by filling the half of moulds with the prepared
paste. The compaction process was performed by twenty five manual strokes per
layer as well as ten seconds of vibration on vibration table to vanish the air bubbles
and for the next layer the same procedure was utilized. Figure3.18 and Figure3.19
shows the cubes and prisms on the vibration table. The duration and type of vibration
was chosen in accordance with preliminary experiments.
Figure 3.18: Cube moulds after the compaction process
Figure 3.19: Prisms filled and compacted with the Mix40
10
3.5
Curing
It was found that strength properties of geopolymers significantly increase
with the increase in the temperature of curing. Ambient curing in indoor temperature
(28oC) was used as the regime of curing and there was no need to seal the specimens
and samples were only covered by plastic sheets for 1-2 days as can be seen in
Figure3.20.
Figure 3.20: Covering geopolymer concrete samples after casting
After 3 days of curing in indoor temperature, the moulds of Mix0, Mix20 and
Mix40 were opened. After 3 days, these mixtures were set and it was applicable to
move, but Mix60 moulds were opened on the 4th day after casting since it needed
more time to harden. Thus, all moulds were removed and striped samples were put in
a safe corner with indoor temperature of 28oC and average humidity of 85%.
Figure3.21 shows the geopolymer concrete containing 0% bottom ash at the age of
7days, and Figure3.22 is one set of samples for each strength test, while Figure3.23
shows Mix20, Mix40 and Mix60 at various ages.
12
Figure 3.21: Geopolymer concrete containing 0% bottom ash at 7-day
Figure 3.22: One set of samples for strength tests
13
Figure 3.23: Mix20, Mix40 and Mix60 cubes at different ages
3.6
Conclusive Tests
After finishing all preliminary tests on trial mixtures which were more than
10 mix designs and also performing tests on the raw materials to acquire information
about their physical properties and chemical compositions, conclusive tests on
strength properties of the final samples were elaborated. Methods of testing were
mentioned as below:
3.6.1
Density of Geopolymer Concrete
Density of geopolymer concrete was calculated based on the method that
have been used for OPC concrete. BS. 1881: Part 114: 1983 was selected as code of
practice which described density as the mass of a unit volume of hardened concrete
14
and expressed in kilograms per cubic meter (kg/m3). For determination of volume,
dimension of the cubes were measured and cubes were weighted as-received in air.
Figure3.24. shows the process of weighting by balance in indoor temperature.
Figure 3.24: Weight measurement for density calculation
3.6.2
Ultrasonic Pulses Velocity (UPV) Test
To investigate the effect of replacing sand with bottom ash on geopolymer
concrete uniformity, UPV test was conducted on specimens at the age of 7, 14 and
28days. This was performed by measuring the velocity of ultrasonic pulses for two
pairs of cube side for three times by direct transmission which means six reading for
each cube. The electronic timing apparatus’s accuracy needed to be checked with the
reference bar. Checking the accuracy with the reference bar was shown in
Figure3.25.
15
Figure 3.25: Checking the accuracy of UPV test apparatus with reference bar
Before starting the measurement, center of cube faces were marked. Green
grease was used as couplant for both transmitters. For each face three measurements
were conducted and for each cube two faces were tested for velocity of ultrasonic
pulses. The process of measurement was shown in Figure3.26.
Figure 3.26: Measuring velocity of ultrasonic pulses by direct transmission
16
The process was followed by averaging the three values of each face and
reported as velocity of ultrasonic pulses for the geopolymer concrete at the age of 7,
14 and 28days. Electronic timing circuits enable the transit time T of the pulse to be
measured. The ultrasonic pulse velocity V (m/s) was calculated according to BS.
1881: Part 203:1986:
(3.1)
where
L is the path length;
T is the time taken by the pulse to traverse that length.
3.6.3
Water Absorption Test
To investigate water absorption of fly ash based geopolymer concrete
containing different percentages of bottom ash, for each mixture one prism was
prepared from the same batch with similar method of curing. Following the BS.
1881: Part 122: 1983, this test should be conducted when the age of samples is in the
range of 28 to 32 days. Thus at the age of 28 days, it was cored with the diameter of
75mm. Density and dimension of specimens were measured in accordance with BS.
118: Part 114. Then the cores were dried in the oven at 110oC until their mass
become constant.
11
Figure 3.27: Arrangement of specimens in the oven
After removal from the oven, the cores were put in an airtight vessel for 24
hours to cool. The process was followed by weighting the specimens and then they
were immersed in water tank for 30 minutes with its longitudinal axis horizontal and
at a depth such that there was 25 mm of water over the top of the specimens. Process
of immersion is presented in Figure3.28.
Figure 3.28: Immersed geopolymer concrete cores in water
18
Then, they brought out the water tank and wiped with a cloth and again they
were weighted. The increase in mass resulting from immersion expressed as a
percentage of the mass of the dry specimen for water absorption of geopolymer
concrete. Results of water absorption were checked with the assessment criteria of
CEB (1989) which was presented in Table3.7.
Table 3.7: Assessment criteria for water absorption (CEB, 1989)
Absorption (%)
Absorption rating
Concrete quality
at 30 minutes
< 3.0
Low
Good
3.0 to 5.0
Average
Average
> 5.0
High
Poor
Since length of samples were 100mm, a correction factor based on BS 1881Part 122-83 should be applied to the results.
3.6.4
Compressive, Indirect Tensile Splitting and Flexural Strengths Tests
As it was stated above, the compressive, tensile and flexural strengths of
geopolymer concrete were the main targets of this investigation. Therefore, tests
were conducted on the hardened geopolymer concrete cubes at 7, 14 and 28 days
while cylinders and prisms were tested at 7 and 28 days after concreting. The tests
were elaborated by use of hydraulic testing machines for compressive, splitting
tensile and ultimate flexural strengths tests.
Compressive strength test was elaborated based on BS. 1881: Part116: 1983
by means of three 100x100x100 mm geopolymer concrete cubes. Sizes on the
19
specimens were measured to calculate their cross-sectional area. In the next step,
load was applied without shock and continuously at a nominal rate of 0.3 N/ (mm² .s)
which was in the range that the standard suggested. Figure3.29 shows the process of
loading by hydraulic strength machine.
Figure 3.29: Geopolymer concrete cube placed in compressive strength test
machine
Compressive strength calculation of each cube was performed by dividing the
maximum load applied to it by the cross-sectional area and results were reported to
the nearest 0.5 N/mm².
The tensile splitting strength test was performed based on BS. 1881: 117:
1983 on three 200x100 mm cylinders at 7 and 28 days after casting. Since the
cylinder was fully covered by steel loading surfaces, no extra plate was used and
loading with pace rate of 0.02 N/ (mm2.s). Method placing the cylinders in the
machine was presented in Figure3.30.
81
Figure3.30: Placing the geopolymer concrete cylinder in hydraulic machine
for tensile splitting strength test
The tensile splitting strength (
in N/m² is calculated by the formula:
(3.2)
where
F is the maximum load (in N);
L is the length of the specimen as shown (in mm);
d is the cross-sectional dimension of the specimen (in mm).
The tensile splitting strength was expressed to the nearest 0.05 N/mm².
BS. 1881: Part 118: 1983 was selected as code of practice to measure flexural
strength of geopolymer concrete containing different percentages of bottom ash as
replacement of sand. To measure the flexural strength of geopolymer concrete,
100×100×500mm prisms were tested with pace rate of 0.06 N/ (mm².s). Figure3.31
shows the arrangement of supports and loading rolls on a geopolymer concrete prism
in the flexural strength test machine.
80
Figure 3.31: Geopolymer concrete prism placed in flexural strength test
machine
The flexural strength of geopolymer concrete fcf (N/mm²) was calculated by:
(3.3)
Where
F is the breaking load (N)
d1 and d2 are the lateral dimensions of the cross-section (mm)
L is the distance between the supporting rollers (mm).
And final results were expressed to the nearest 0.1 N/mm².
CHAPTER 4
RESULTS AND DISCUSSION
4.1
Introduction
In this chapter, it is going to report and discuss about the results which were
achieved in accordance with the methods that were mentioned in the previous
chapter. For each item, three specimens were tested and mean value of the data are
plotted in figures and tables to analyze. The standard deviations are calculated on the
test results as the error bar. Significant observations and occurrences are reported
with discussion about the possible reasons.
In this chapter, the effects of replacement of bottom ash instead of natural
sand on the strengths and a number of basic properties of fly ash based geopolymer
concrete are discussed. The concentration is on the density, velocity of ultrasonic
pulses, water absorption, compressive strength, tensile splitting strength and flexural
strength of geopolymer concrete.
83
4.2
Overview on the Mixing Water
It was observed that by increase in the amount of bottom ash in the mixture,
workability improved without requirement to extra water in Mix40 and Mix60.
According to investigations which were stated in Chapter 3, moisture contents of
natural sand and bottom ash were 2.7% and 10.81%, respectively. Table4.1 shows
the difference of mixing water in each mixture as the sum of moisture content of
sand and bottom ash plus the extra water which was added to mixture to improve the
workability to a moderate slump.
Table 4.1: Discrepancy in the mixing water
Water content ( kg/m3)
Mix0
Mix20
Mix40
Mix60
Sand
22.2
17.7
13.3
8.8
Bottom ash
0
17.7
35.5
53.3
Extra water
9.1
4.5
1.8
0
Total
31.3
39.9
50.6
62.1
As it can be seen in Table4.1, with the increase in bottom ash, the mixing
water in the mixture increased. In fact, absorption of bottom ash was 4 times more
than natural sand. Moisture highly retained into and onto the bottom ash due to the
high porosity and irregular surface. According to literature about usage of bottom ash
in normal concrete, the same behaviour was reported.
84
4.3
Physical Properties of Bottom Ash and Natural Sand
To compare physical properties bottom ash and sand, tests were conducted on
these two materials and results are presented in Table4.2.
Table 4.2: Physical properties of sand and bottom ash
Property
Natural sand
Bottom ash
Fineness modulus
2.36
3.25
SSD bulk specific gravity
2.47
1.74
Dry bulk specific gravity
2.41
1.57
Absorption ( % )
2.7
10.81
Dry bulk density (kg/m3)
1641
957.7
SSD bulk density (kg/m3)
1685
1061.2
Void content ( % )
31.3
44.7
Bottom ash had a higher fineness modulus in comparison with natural sand,
which shows it was coarser than sand. By investigations on bulk specific gravity and
also bulk density of bottom ash it was discovered that bottom ash was lighter and had
a higher void content than normal sand. This can reduce the unit weight of the end
product and consequently may deduct the strength properties.
85
4.4
Effect of Using Bottom Ash on Density of Geopolymer Concrete
Densities of all the four mixtures were calculated at the age of 7, 14 and
28days to investigate variation on the density by time and also understanding how
replacement of bottom ash would affect the density. Meanwhile, physical shapes of
the end products were similar except Mix60 which needed more time to harden and it
was not physically stable like the other samples. Table4.3 shows the densities Mix0,
Mix20, Mix40 and Mix60 at age of 7, 14 and 28days.
Table 4.3: Density of geopolymer concrete specimens
Density (kg/m3)
Mixture
7-day
Standard
Deviation
14-day
Standard
Deviation
28-day
Standard
Deviation
Mix0
2230
10
2242
11
2247
34
Mix20
2187
8
2192
26
2216
27
Mix40
2112
25
2114
39
2122
40
Mix60
2098
11
2099
22
2102
18
86
2250
2230
Density (kg/m3)
2210
2190
2170
Mix0
2150
Mix20
2130
Mix40
2110
Mix60
2090
2070
2050
7
14
28
Age ( Days )
Figure 4.1: The influence of adding bottom ash on density of the mixtures
As it can be seen, density dropped dramatically by addition of bottom to the
geopolymer concrete mixture, on the other hand, similar to normal concrete with
increase in the period of curing density of samples increased. The highest density for
a mixture with bottom ash was 2216 kg/m3 at 28 days, while at the same age for
normal geopolymer concrete density gained to 2247 kg/m3. For the last mixture,
density remained approximately constant during age 7-day and 28-day.
4.5
Velocity of Ultrasonic Pulses for Geopolymer Concrete
Direct UPV as a non-destructive test was conducted and mean values for each
mixture are shown in Table4.4 and Figure4.2.
81
Table 4.4: Result of UPV test for mixtures with different proportions of
bottom ash
Velocity of Ultrasonic Pulses ( m/s )
Mixture
7 Days
Standard
Deviation
14 Days
Standard
Deviation
28 Days
Standard
Deviation
Mix0
3745
0.21
3981
0.25
4213
0.35
Mix20
3331
0.14
3685
0.86
3797
0.47
Mix40
3053
1.3
3212
1.02
3268
0.63
Mix60
2195
1.6
2339
0.65
2340
0.59
Velocity of ultrasonic pulses (m/s)
4500
Velocity of ultrasonic pulses vs. Age
4000
3500
Mix0
Mix20
3000
Mix40
Mix60
2500
2000
7
14
28
Age ( Days )
Figure 4.2: Velocity of ultrasonic pulses against the age
Adding bottom ash significantly reduced velocity of ultrasonic pulses and
homogeneity of geopolymer concrete. However, according the quality assessment of
concrete by Whitehurst (1951), both Mix0 and Mix20 can be categorized as
generally good quality concrete since their pulse velocity inside them were more than
3500 m/s, while Mix4 was in the range of questionable quality and Mix60 was
generally poor.
88
4.5.1
Relationship between Velocity of Ultrasonic Pulses and Density in
Geopolymer Concrete
There was a direct relationship between density and velocity of ultrasonic
pulses; however, more investigation is required to plot and introduce a correlation
with high accuracy which was not in the scope of this project.
2260
2240
Density ( kg/m3)
2220
2200
2180
2160
2140
2120
2100
2080
2060
2000
2500
3000
3500
4000
4500
Velocity of ultrasonic pulses ( m/s )
Figure 4.3: Relationship between velocity of ultrasonic pulses and density
As it can be seen in the above figure, with the increase in density, pulses
velocity increased inside the geopolymer concrete specimens.
89
4.6
Water Absorption of Geopolymer Concrete Containing Bottom Ash
Water absorption for all the four mixtures were measured at the age of 28-day
and were corrected by correction factor of 1.09 since their lengths were 100mm and
results are presented in Table4.5.
Table 4.5: Corrected water absorption rate for the four mixtures
Mixture
Water absorption (%)
Quality in Accordance
with CEB 1989
Mix0
2.1
Good
Mix20
4.0
Average
Mix40
4.8
Average
Mix60
5.9
Low
According to results, water absorption increased with higher contents of
bottom ash in geopolymer concrete. The ratio of 2.1% increased to 4% by addition of
20% bottom ash to the mixture, which changed the quality status of the samples from
good quality to average quality. In Mix40, the water absorption reached 4.8% which
was so close the 5% as the limit for average quality concrete, while water absorption
of Mix60 dropped to 5.9% which shows its high porosity and low quality.
91
4.7
Compressive strength results
To investigate the effect of using bottom ash in geopolymer concrete instead
of natural sand, three cubes were tested at the age of 7, 14 and 28 days and results are
shown in Table4.6 and Figure4.4.
Table 4.6: Compressive strength of geopolymer concrete containing 0, 20, 40
and 60% of bottom ash
Compressive strength (MPa)
Mixture
7 Days
Standard
Deviation
14 Days
Standard
Deviation
28 Days
Standard
Deviation
Mix0
24.5
1.2
32.0
0.6
37.4
3.5
Mix20
16.0
1
19.5
0.95
26.5
2
Mix40
8.0
1.8
9.5
1.5
11.5
1.4
Mix60
5.0
1.1
6.5
1.1
6.0
0.5
45
Compressive strength
Compressive strength (MPa)
40
35
30
25
Mix0
20
Mix20
Mix40
15
Mix60
10
5
0
7
14
28
Age ( Days )
Figure 4.4: Compressive strength development during 7 days until 28 days
90
In all the mixture, with increase in the period of curing the compressive
strength improved. For Mix0, it increased from 24.5 MPa at 7-day to 37.5 MPa at 28day, and for Mix20, it increase from 16MPa to 26.5 MPa. With 20% replacement of
sand, 30% of 28-day compressive strength decreased. In other words, by 7% change
in the whole mass of geopolymer concrete, 30% of 28 days compressive strength
decreased.
When the ratio of replacement reached 40%, the compressive strength
increased from 8 MPa to 11.5MPa. Development of compressive strength in Mix60
which had the highest amount of bottom ash was from 5MPa to 6.5MPa.
4.7.1
Effect of Age on Compressive Strength of Geopolymer Concrete
Investigations of compressive strength development of the samples were
performed based on the ratio of compressive strength at 7 days and 28 days.
100
90
80
70
60
50
28 days
40
7 days
30
20
10
0
Mix0
Mix20
Mix40
Mix60
Figure 4.5: Ratio of compressive strength development between age 7-day
and 28-day
92
At 7-day, mixture without bottom ash gained 65% of its 28-day compressive
strength, while this ratio decreased to 61% for Mix20. However, with higher bottom
content, the ratio increased to 70% and 79% for Mix40 and Mix60, respectively.
4.7.2
Relationship between Compressive Strength and Density
Similar to normal concrete, there was a direct relationship between
compressive strength and density of geopolymer concrete. With increase in density,
compressive strength was also increased.
4.8
Indirect Tensile Splitting Strength
Results from testing cylinders and prisms for indirect tensile splitting strength
of geopolymer concrete are categorized in Table4.7 and explained by Figure 4.6.
Table 4.7: Tensile splitting strength of geopolymer concrete containing
bottom ash
Tensile splitting strength (MPa)
Mixture
7 Days
Standard
Deviation
28 Days
Standard
Deviation
Mix0
2.15
0.28
3.55
0.21
Mix20
1.80
0.20
2.45
0.13
Mix40
1.05
0.04
1.55
0.2
Mix60
0.70
0.01
0.90
0.12
93
Tensile splitting Strength (MPa)
4
Tensile splitting strength
3.5
3
2.5
Mix0
2
Mix20
1.5
Mix40
1
Mix60
0.5
0
7
28
Age ( Days )
Figure 4.6: Tensile splitting strength at the age of 7 and 28days
As it can be seen in Figure4.6, tensile strength of geopolymer decreased with
replacing sand with bottom ash. Tensile strength of geopolymer concrete without
bottom ash at the age of 7-day was 2.15MPa and increased to more 3.5MPa at 28day, while the same trend for Mix20 was from 1.8MPa to 2.45MPa. For Mix60 the
28-day tensile strength dropped to less than 1.0MPa.
4.8.1
Ratio of Tensile Splitting Strength to Compressive Strength
According to results from section 4.8 and 4.9, ratio of tensile splitting
strength to compressive strength of geopolymer concrete with different proportions
of bottom ash was calculated at the age of 7-day and 28-day.
94
Tensile splitting strength/compressive strength
15
14
13
12
7
11
28
10
9
8
Mix0
Mix20
Mix40
Mix60
Mixture
Figure 4.7: Ratio of tensile splitting strength to compressive strength at 7day and 28-day
Mehta and Monteiro (1993) conducted a research on strength properties of
normal concrete and results of their works is tabulated Table4.7.
Table 4.8: Relation between compressive, flexural, and tensile strength of
concrete
95
According to their work, with increase in compressive strength from 1000psi
to 9000psi the ratio of tensile strength to compressive strength decreased from 11%
to 7%. In cement concrete, age is a significant factor in the relation between ft and
fc, beyond about one month, the tensile strength increases more slowly than the
compressive strength. So the ft/fc´ decreases with time. But in this experiment, with
decrease in the compressive strength from Mix0 to Mix60, the ratio of tensile
splitting strength-to-compressive strength increases. In fact, it increased from 8% to
13% at 7-days and from 9% to 14% at 28-day.
4.9
Flexural Strength Results
Flexural strength of Mix0, Mix20, Mix40 and Mix60 were calculated and
mentioned in Table4.9 and discussion was conducted by Figure4.8.
Table 4.9: Flexural strength of geopolymer concrete containing 0, 20, 40 and
60% of bottom ash
Flexural strength (MPa)
Mixture
7 Days
Standard
Deviation
28 Days
Standard
Deviation
Mix
4.4
0.1
6.7
0.27
Mix20
3.0
0.1
4.7
0.11
Mix40
1.6
0.27
2.3
0.12
Mix60
1.2
0.2
1.4
0.12
96
8
Flexural strength
Flexural Strength (MPa)
7
6
5
Mix0
4
Mix20
3
Mix40
2
Mix60
1
0
7
28
Age ( Days )
Figure 4.8: Flexural strength at 7-day and 28-day
Similar to other strength properties, flexural strength of geopolymer concrete
decreased with usage of bottom ash in the mixture. Flexural strength of Mix0
developed from 4.4MPa to 6.7MPa which was considerably high. However, for
mixtures containing bottom ash the highest result was 4.7MPa for Mix20 at 28-day
which was slightly higher than 7-day flexural strength of Mix0.
4.9.1
Ratio of Flexural Strength to Compressive Strength
According to results from section 4.8 and 4.10, ratio of flexural strength to
compressive strength of geopolymer concrete with different proportions of bottom
ash was calculated at the age of 7-day and 28-day.
91
Flexural strenghth / compressive strength
25
24
23
22
21
20
7
19
28
18
17
16
15
Mix0
Mix20
Mix40
Mix60
Mixture
Figure 4.9: Ratio of flexural strength to compressive strength at 7-day and
28-day
According to Mehta and Monteiro (1993) results, with the increase in
compressive strength from 1000psi to 9000psi, the ratio of flexural strength to
compressive strength decreased from 23% to 11.2%. In this experiment, as the period
of curing increased the ratio decreased. Although with increase in the amount of
bottom ash in the mixture compressive strength decreased, the ratio increased. This
trend was not similar to normal concrete trend which may due to better performance
of mixtures with bottom ash in flexure.
CHAPTER 5
CONCLUSIONS AND RECOMMENDATIONS
5.1
Summary
This chapter presents a summary of the research work and also the major
observations and conclusions from the conducted results. The main aim of this study
was to investigate the effect of using bottom ash in geopolymer concrete as a
replacement for natural sand and find applicability of using geopolymer concrete
containing bottom ash in structural works. After production of many trial mixes and
also following the works of other researchers in Universiti Teknologi Malaysia
(UTM), a mix design was achieved for geopolymer concrete without any bottom ash
and then investigations were elaborated by replacing partials of sand with bottom ash
and influences of this parameter was monitored in terms of workability, density,
water absorption, velocity of ultrasonic, compressive strength, tensile splitting
strength and also flexural strength. The two material (geopolymer concrete with and
without bottom ash) differed by more than just replacement of sand and it was found
that bottom ash which absorbed more water in its pores significantly reduced the
extra water. The magnitude was occurred in Mix60 which there was no need to extra
water. In order to maintain constant approaches between the mixtures, consideration
was taken about material preparation, ratio of alkaline liquid-to-fly ash, ratio of
sodium silicate-to-sodium hydroxide, workability, mixing procedures, compaction,
99
storage and curing condition to keep them constant for all the mixtures. Thus, for all
of the mixtures the dry mixing was 5minutes and wet mixing was 5±1min. The
process of compaction was performed both with tamper and vibration table and then
the samples were cured at ambient condition.
Workability was monitored as the only characteristic of fresh geopolymer
concrete to investigate the effect of using bottom ash in geopolymer concrete. After
3days of casting the moulds were opened and samples were kept at ambient
condition with average temperature of 28oC until the date of testing. At the age of 7
and 28 days, density, velocity of ultrasonic pulses, compressive strength, tensile
splitting strength and flexural strength were measured. While at the age of 14days,
only density, velocity of ultrasonic pulses and compressive strength was measured.
At the age of 28days, water absorption was also measured by making three cores on
a prism.
Conclusive tests were compressive strength test on 100×100×100mm cubes,
tensile splitting strength test on 200×100mm cylinders and flexural strength test on
100×100×500mm prisms. Detailed results of the tests and the relations between
them are tabulated and plotted in Chapter4.
5.2
Significant observations
5.2.1
Mould preparation
One of the most difficult tasks in the process of making the samples was
mould preparation. Since normal oil is not suitable for making geopolymer concrete,
after each time casting, internal surfaces of the moulds were not smooth and
011
hardworking was required to prepare the mould for the next casting. It is highly
recommended to use new moulds with smooth surface to avoid waste of time.
5.2.2
Crystallization in the alkaline activator
It was observed that five days after the mixing of the alkaline solution
consisting of sodium hydroxide and sodium silicate crystallization was started and on
the sixth day after mixing large solid particles were appeared in the solution. With a
sudden movement of the container the hardening was speeded up. Prepared alkaline
solution shall not be used after 3 days of mixing, unless it was tested by a trial mix.
5.2.3
Physical form of the four mixtures
After adding 20, 40 and 60 bottom ash into the mixture, no visual outcome
was observed during the mixing process. The only occurrence was the decrease in
the requirement of extra water with the increase of bottom ash in the mixtures.
Mix60 kept one day more than other mixtures in moulds, since the samples were not
completely set. After striping the moulds, the surface of Mix0 samples were smooth
and surface voids were not intensive. While, for Mix20, Mix40 and Mix60 intensive
small voids were observed on the surface of the samples. Sample Mix20, Mix40 and
Mix60 are presented in Figure5.1.
010
Figure 5.1: Mix20, Mix40 and Mix60 physical shape
5.3
Conclusions
After performing the tests on the four mixtures with various percentages of
bottom ash, the following conclusions are drawn:
1.
Although the growth in density of geopolymer concrete with
age was not significant, density of all the four mixtures increased with period
of curing. As the amount of replacement of bottom ash increases, density
decreases. In fact, the density of geopolymer concrete without bottom ash
was 2247 Kg/m3 at 28-day, while at the same age this amount was 2216
kg/m3 for Mix20 which was the highest density among the mixtures with
bottom ash.
012
2.
Velocity of ultrasonic pulses increases with the age
geopolymer concrete, but decreases as the percentage of bottom ash
increases. It increased 12.5 % from 7-day to 28-day for geopolymer concrete
without bottom ash, while it improved by 14% for mixture with 20% bottom
ash.
3.
According to Whitehurst (1951), quality of Mix0 and Mix20
can be categorized as generally good quality concrete. By increase in the
amount of bottom ash in the mixture, the quality becomes poor and poorer
due to higher porosity and lower homogeneity.
4.
Water absorption increases with the increase in amount of
bottom ash of the mixture. As a matter of fact, normal geopolymer concrete
has a low ratio of water absorption, while this ratio increases as the bottom
ash increases in the mixture. Normal geopolymer concrete water absorption
was less than 3% which causes good durability properties.
5.
There is a direct relation between compressive strength of
geopolymer concrete (with and without bottom ash) with period of curing.
However, by replacing more bottom ash with sand, compressive strength
decreases.
6.
With increase in bottom ash of the mixtures, the ratio of 7-day
to 28-day compressive strength increases, which means it improves the early
strength.
7.
Tensile splitting strength decreases with growth in the
proportion of bottom ash in geopolymer concrete. On the other hand, the ratio
of tensile splitting strength-to-compressive strength increases with higher
013
amounts of bottom ash in the mixture and also age of the mixture, which
shows good behaviour of bottom ash geopolymer concrete in tension.
8.
With the increase in amount of bottom ash, flexural strength
decreases. But ratio of flexural strength-to-compressive strength increases
with increase in the proportion of bottom ash, while it decreases in one
mixture as the time passes.
5.4
Recommendations
For acquiring more knowledge on the strength and durability properties of
geopolymer concrete containing bottom ash in order to be used in structural works,
more investigations are needed to be conducted on the properties of this material.
The scope of this research extends to very limited variables due to time restraints.
However, there are recommendations to be investigated in further research on
geopolymer concrete mix design.
1.
As it can be seen in Figure4.1 and 4.4 the density and compressive
strength development of geopolymer concrete extends for a period beyond 28 days.
More samples were prepared for 60 days compressive strength test, but due to time
restrictions the results of conducted tests were not mentioned in this report. The
investigation should not be limited to this period of curing and more tests on strength
development of geopolymer concrete containing bottom ash for long term periods
after pouring must be elaborated.
2.
In this project, trial mixes were designed to find the optimum
proportions for highest rates of compressive strength and then it was used as a
014
control mix to investigate the effect of replacement of bottom ash on strength
properties and finding the best ratio of replacement. Probably, by further
investigations higher rates of strength can be achieved for Mix20, if different mix
designs were prepared specially for this kind of geopolymer concrete.
3.
Investigation was performed on the relationship between compressive
strength and UPV result to find a correlation between these two properties in order to
estimate the strength of geopolymer concrete during age of 7 days to 60 days.
However, limitation of time was a barrier against this objective and it needed long
term data.
015
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