performance of geopolymer concrete in fireeprints.uthm.edu.my/7737/1/ahmad_zurisman_mohd_ali.pdfthe...

Performance of Geopolymer Concrete in Fire

AHMAD ZURISMAN MOHD ALI

This thesis is presented as part of the requirement for the

Award of the Degree of

Doctor of Philosophy

Department of Civil and Construction Engineering

Faculty of Science, Engineering and Technology

Swinburne University of Technology

August 2015

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Abstract

Ordinary Portland Cement (OPC) concrete can be classified as a fire resistant

construction material. However, spalling may occur in fire especially in high strength

concretes. The need to address this spalling problem in fire has intensified since the

use of high rise buildings. Geopolymer is a cementless concrete binder which is based

on aluminosilicate reaction of fly ash, a power plant by-product and activated by

alkaline solution. Recent research has shown that geopolymer concrete has great

potential in resisting fire. In addition, without the presence of Portland cement in the

concrete has led to more sustainable construction material since cement is the second

highest CO2 emitter after fossil fuels.

In this research, the severity of large scale high strength concrete spalling under

hydrocarbon fire was investigated. The results show that high strength OPC concrete

severely spalled during the first 30 minutes of fire exposure in explosive manner. There

is a thermal diffusivity drop when the temperature is between 110oC and 155oC due to

water in concrete changing phase to steam. Maximum steam pressure corresponds to

155oC temperature is 0.44 MPa which shows that steam pressure alone is not a critical

factor for concrete spalling.

Further investigations on factors affecting concrete spalling show that larger specimen

spalled more than smaller scale specimen based on 3 m x 3 m walls, 1 m x 1 m walls,

columns and cylinders. Aggregates size effect was also observed with increasing

spalling with decreasing aggregate size. No obvious trend observed for different

aggregate types (granite and basalt).

For making geopolymer, fly ashes from Gladstone, Tarong and Microash were

examined for physical properties. Gladstone fly ash demonstrated the best workability

compared with Tarong and Microash. The reasons for workability differences were

investigated and the conclusion was agglomerated particle size distribution was the

cause

Effect of dry and wet condition on strength of geopolymer was investigated. Strength

reduction of 17% was observed.

The high strength geopolymer 1 m x 1 m wall panels and two sizes of cylinders (150,

100 mm) were tested. From hydrocarbon fire test, high strength geopolymer concrete

exhibited good fire resistance performance due to no explosive spalling observed. Two

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panels and all cylinders remained un-spalled. Less than 1% spalling (excluding

moisture loss) observed on 2 spalled panels. There are 11% - 65% of residual

strengths observed on fire tested specimens as compared to OPC which has no

remaining strength.

To investigate aggregate and geopolymer binder thermal incompatibility factor on

spalling, aerated geopolymer panels were tested. From hydrocarbon fire test, no

spalling observed was further proof of thermal incompatibility was the cause of spalling.

Under room temperature, bearing load, axial load, corner bearing and flexural tests on

aerated geopolymer panel were conducted. Results show that aerated geopolymer

panel has the capacity and strength to be used as structural wall in fire application.

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Table of Content

Abstract ....................................................................................................................... ii

Declaration ................................................................................................................. iv

Acknowledgement ...................................................................................................... v

Table of Content ........................................................................................................ vi

List of Figures ........................................................................................................... xii

List of Tables............................................................................................................ xvi

List of Abbreviations ............................................................................................. xviii

CHAPTER 1 ................................................................................................................. 1

Introduction ............................................................................................................... 1

1.1 Background ................................................................................................. 1

1.2 Aim of research ........................................................................................... 2

1.3 Research objectives .................................................................................... 2

1.4 Scope of the thesis ...................................................................................... 2

1.5 Thesis Organisation .................................................................................... 4

References ............................................................................................................ 6

CHAPTER 2 ................................................................................................................. 7

Literature Review ...................................................................................................... 7

2.1 Background ................................................................................................. 7

2.2 Geopolymer Binder in Concrete for Spalling Solution ................................ 11

2.3 Geopolymer Binder in Concrete for Environmental Benefits ...................... 12

2.4 Geopolymer History and Reaction Mechanisms ........................................ 13

2.5 Fly Ash ...................................................................................................... 17

2.6 Alkaline activator ....................................................................................... 20

2.7 Geopolymer workability ............................................................................. 21

2.8 Geopolymer compressive strength ............................................................ 22

2.9 Geopolymer under Environmental Exposure ............................................. 25

2.10 Geopolymer fire test .................................................................................. 26

References .......................................................................................................... 28

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CHAPTER 3 ............................................................................................................... 37

Hydrocarbon Fire testing of full size Portland Cement High Strength Concrete Wall

Panels ..................................................................................................................... 37

3.1 Introduction ............................................................................................... 37

3.2 Experimental Programme .......................................................................... 38

3.2.1 Material .............................................................................................. 38

3.2.2 Concrete Properties ........................................................................... 39

3.2.3 Test Setup ......................................................................................... 40

3.2.4 Compressive strength and moisture content ...................................... 41

3.2.5 Thermal Data Collection ..................................................................... 42

3.2.6 Spalling analysis ................................................................................ 44

3.2.7 Thermal diffusivity analysis ................................................................ 45

3.3 Result and Discussion ............................................................................... 46

3.3.1 Compressive Strength and Moisture Content ..................................... 46

3.3.2 Spalling .............................................................................................. 47

3.3.3 Temperature Result ........................................................................... 48

3.3.4 Thermal Diffusivity.............................................................................. 53

3.4 Conclusion ................................................................................................ 55

References .......................................................................................................... 56

CHAPTER 4 ............................................................................................................... 59

Specimen’s Size, Aggregate Size and Aggregate Type Effect on Spalling of Concrete

in Fire ...................................................................................................................... 59

4.1 Introduction ............................................................................................... 59

4.2 Experimental Programme .......................................................................... 60

4.2.1 Concrete Test Specimens .................................................................. 61

4.2.2 Hydrocarbon Fire Test ....................................................................... 65

4.2.3 Spalling Measurements ...................................................................... 67

4.2.4 Nominal Spalling Depth Analysis ........................................................ 67

4.3 Result and Discussion ............................................................................... 69

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4.3.1 Spalling .............................................................................................. 69

4.3.2 Nominal Depth ................................................................................... 71

4.3.3 Specimen’s size effect ....................................................................... 71

4.3.4 Aggregate Size Effect ........................................................................ 74

4.3.5 Aggregate Type Effect ...................................................................... 75

4.4 Conclusion ................................................................................................ 76

References .......................................................................................................... 78

CHAPTER 5 ............................................................................................................... 80

Investigation of the Effects of Fly Ash Types and Properties on the Workability of

Fresh Geopolymer................................................................................................... 80

5.1 Introduction ............................................................................................... 80

5.2 Experimental Program............................................................................... 82

5.2.1 Raw Material ...................................................................................... 82

5.2.2 Workability Test ................................................................................. 82

5.2.3 Investigation of the Relevant Physical Properties of Fly Ash .............. 83

5.2.4 Investigation of the Relevant Chemical Properties of Fly Ash ............. 85

5.3 Results and Discussions ........................................................................... 86

5.3.1 Workability Results............................................................................. 86

5.3.2 Analyses of the Measured Physical Properties of Fly Ash .................. 88

5.3.2.1 Particle Size Analyses .................................................................... 88

5.3.2.2 Particle Shape Analyses ................................................................. 94

5.3.3 Chemical Analyses............................................................................. 95

5.4 Conclusion ................................................................................................ 97

References ........................................................................................................ 100

CHAPTER 6 ............................................................................................................. 103

Strength of Geopolymers in Saturated and Dry Conditions.................................... 103

6.1 Introduction ............................................................................................. 103

6.2 Experimental Programme ........................................................................ 104

6.2.1 Material ............................................................................................ 104

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6.2.2 Specimens Details ........................................................................... 105

6.2.3 Drying and Saturation Method .......................................................... 105

6.2.4 Compressive Test ........................................................................... 106

6.2.5 Inductively Couple Plasma Test ...................................................... 106

6.3. Result and Discussion ............................................................................ 106

6.3.1 Compressive Strength ..................................................................... 106

6.3.2 Effect of Strength on Reduction of Strength in Saturated Geopolymer

109

6.3.3 Excess Sodium Silicate Factor ........................................................ 110

6.4 Conclusion .............................................................................................. 111

References ........................................................................................................ 112

CHAPTER 7 ............................................................................................................. 114

Hydrocarbon Fire testing of Geopolymer High Strength Concrete Wall Panels and

Cylinders ............................................................................................................... 114

7.1 Introduction ............................................................................................. 114


7.2.1 Material ............................................................................................ 115

7.2.2 Geopolymer Concrete Mix ................................................................ 117

7.2.3 Geopolymer concrete casting ........................................................... 118

7.2.4 Geopolymer concrete properties ...................................................... 123

7.2.5 Hydrocarbon fire test setup .............................................................. 125

7.2.6 Thermal diffusivity ............................................................................ 127

7.2.7 Compressive strength ...................................................................... 128

7.3 Results and Discussion ........................................................................... 129

7.3.1 Spalling ............................................................................................ 129

7.3.2 Temperature Results ........................................................................ 131

7.3.3 Thermal Diffusivity............................................................................ 135

7.3.4 Residual Compressive Strength After Fire Exposure ........................ 136

7.4 Conclusions ............................................................................................ 138

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References ........................................................................................................ 140

CHAPTER 8 ............................................................................................................. 142

Investigation on Aerated Geopolymer Wall Panels for Fire Applications ................ 142

8.1 Introduction ............................................................................................. 142


8.2.1 Material ............................................................................................ 143

8.2.2 Aerated Geopolymer Panel Properties ............................................. 145

8.2.3 Room Temperature Test .................................................................. 146

8.2.3.1 Bearing Load Test ........................................................................ 147

8.2.3.2 Axial Load Test ............................................................................. 148

8.2.3.3 Corner Bearing Test ..................................................................... 148

8.2.3.4 Flexural Load Test ........................................................................ 149

8.2.4 Hydrocarbon Fire Test ..................................................................... 150

8.2.4.1 Test setup..................................................................................... 150

8.3 Results and Discussion ........................................................................... 152

8.3.1 Room Temperature Test .................................................................. 152

8.3.1.1 Bearing Load Test ........................................................................ 152

8.3.1.2 Axial Load Test ............................................................................. 154

8.3.1.3 Corner Bearing Test ..................................................................... 157

8.3.1.4 Flexural Load Test ........................................................................ 158

8.3.2 Hydrocarbon Fire Test ..................................................................... 161

8.3.2.1 Spalling ........................................................................................ 161

8.3.2.2 Temperature Results .................................................................... 162

8.4 Conclusions ............................................................................................ 164

References ........................................................................................................ 165

CHAPTER 9 ............................................................................................................. 167

Summary, Conclusions and Recommendations .................................................... 167

9.1 Summary................................................................................................. 167

9.2 Conclusions ............................................................................................ 168

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9.3 Recommendations .................................................................................. 170

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List of Figures

Figure 2.1: Types of polysialates (Davidovits, 2002) ................................................... 15

Figure 2.2: Conceptual model for geopolymerisation (Duxson et al., 2007) ................. 16

Figure 2.3: SEM pictures (a) original fly ash, (b) fly ash activated with NaOH

(Fernández-Jiménez et al., 2005) ........................................................................ 16

Figure 2.4: Fly ash production (Flyash Australia, 2010) .............................................. 18

Figure 3.1: Reinforcement details of concrete wall panel (top view) ............................ 38

Figure 3.2: Concrete wall panel dimension and fire exposed area .............................. 39

Figure 3.3: Casting of Ordinary Portland Cement High Strength Concrete .................. 40

Figure 3.4: Casted Full-scale (3.36 m x 3.38 m) Portland Cement High Strength ........ 40

Concrete ..................................................................................................................... 40

Figure 3.5: TramexTM CME 4 moisture meter .............................................................. 42

Figure 3.6: Hydrocarbon and Standard Fire Temperature versus Time Profile ............ 42

Figure 3.7: Wall Panel and Furnace Setup .................................................................. 43

Figure 3.8: Hydrocarbon Fire Furnace ........................................................................ 43

Figure 3.9: Illustration of Thermal Couple’s Location................................................... 44

Figure 3.10: Thermal Couple Set Up ........................................................................... 44

Figure 3.11: Specimen After Fire Test ........................................................................ 47

Figure 3.12: Spalling Concrete Percentage ................................................................. 48

Figure 3.13: Temperature for specimens with 7 mm basalt aggregates ...................... 48

Figure 3.14: Temperature for specimens with 14 mm basalt aggregates .................... 49

Figure 3.15: Temperature for specimens with 20 mm basalt aggregates .................... 49

Figure 3.16: Temperature for specimens with 7 mm granite aggregates ..................... 50

Figure 3.17: Temperature for specimens with 14 mm granite aggregates ................... 50

Figure 3.18: Temperature across the thickness of the specimens with 7 mm basalt

aggregates........................................................................................................... 51


aggregates........................................................................................................... 51


aggregates........................................................................................................... 52

Figure 3.21: Temperature across the thickness of the specimens with 7 mm granite

aggregates........................................................................................................... 52

Figure 3.22: Temperature across the thickness of the specimens with 14 mm granite

aggregates........................................................................................................... 53

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Figure 3.23: Thermal diffusivity vs Temperature ......................................................... 54

Figure 4.1: Specimens’ dimension .............................................................................. 63

Figure 4.2: Casting of Ordinary Portland Cement High Strength Concrete .................. 63

Figure 4.3: Reinforcement bar details (a) large panel (b) medium panel (c) column .... 65

Figure 4.4: Specimen Fire Test Setup (a) Large panels (b) Medium panels (c) Columns

(d) Cylinders ........................................................................................................ 67

Figure 4.5: Fire Exposed Area (a) Large panels (b) Medium panels (c) Columns (d)

Cylinders ............................................................................................................. 69

Figure 4.6: Images of specimens after fire test (a) Large Panel (b) Medium Panel

(c) Column (d) Cylinder ........................................................................................ 71

Figure 4.7: Nominal Spalling Depth. ............................................................................ 73

Figure 4.8: Nominal Spalling Depth for Maximum Aggregate Size .............................. 75

Figure 4.9: Nominal Spalling Depth for Maximum Aggregate Type ............................. 76

Figure 5.1: Measurement of d1 and d2. ........................................................................ 82

Figure 5.2: CILAS Particle Size Analyzer .................................................................... 84

Figure 5.3: ZEISS Supra 40VP Scanning Electron Microscope ................................... 84

Figure 5.4: Belsorp Max Adsorption Measurement ..................................................... 85

Figure 5.5: Fly ash density measurement equipment .................................................. 85

Figure 5.6: Varian 720-ES inductively coupled plasma equipment .............................. 86

Figure 5.7: Geopolymers with alkaline solution to fly ash ratio of 0.4 for (a) Gladstone.

............................................................................................................................ 87

(b) Tarong. (c) Microash ............................................................................................. 87

Figure 5.8: Particle size distribution graphs for (a) Gladstone fly ash. (b) Tarong fly ash.

(c) Microash ......................................................................................................... 90

Figure 5.9: Adsorption and desorption curves for (a) Gladstone fly ash (b) Tarong fly

ash (c) Microash .................................................................................................. 92

Figure 5.10: Images of Gladstone fly ash in loose grainy form (left) and solid form

(right). .................................................................................................................. 93

Figure 5.11: Scanning Electron Microscope (SEM) Images comparison for Gladstone

Power Station fly ash and Tarong Power Station fly ash. ..................................... 95

Figure 5.12: Mixtures of demineralized water and fly ash from (a) Gladstone Power

Station. (b) Tarong Power Station. (c) Microash .................................................. 97

Figure 6.1: Compressive Strength of Dry and Saturated Geopolymer ....................... 110

Figure 7.1: Aggregate Particle Size Distribution Graph ............................................. 116

Figure 7.2: Sand Particle Size Distribution Graph ..................................................... 116

Figure 7.3: Alkaline activator’s mixer ......................................................................... 119

Figure 7.4: High shear concrete mixer ...................................................................... 119

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Figure 7.5: Dry components mixing process ............................................................. 120

Figure 7.6: Alkaline activator added into the mix ....................................................... 120

Figure 7.7: Geopolymer concrete in high shear concrete mixer ................................ 121

Figure 7.8: Geopolymer fresh concrete ..................................................................... 121

Figure 7.9: Cast geopolymer concrete panel ............................................................. 122

Figure 7.10: Geopolymer concrete panel being steam cured .................................... 122

Figure 7.11: Demoulded hardened geopolymer concrete panels .............................. 123

Figure 7.12: Geopolymer concrete dimensions (a) panel (b) cylinders ...................... 124

Figure 7.13: TramexTM CME 4 moisture meter .......................................................... 124

Figure 7.14: Reinforcement details for geopolymer concrete panel ........................... 125

Figure 7.15: Geopolymer concrete panels and cylinders furnace setup illustration ... 126

Figure 7.16: Images of panels (left) and cylinders (right) hydrocarbon fire test setup 126

Figure 7.17: ProceqTM SilverSchmidt rebound hammer ............................................ 128

Figure 7.18: Geopolymer concrete panels after 2 hours hydrocarbon fire exposure .. 129

Figure 7.19: Geopolymer concrete cylinders after 2 hours hydrocarbon fire exposure

.......................................................................................................................... 130

Figure 7.20: Temperature for panel 1 (P1) ................................................................ 131



Figure 7.23: Temperature across thickness for panel 1 ............................................. 133



Figure 7.26: Temperature across thickness comparison between geopolymer concrete

and Portland cement HSC ................................................................................. 135

Figure 7.27: Thermal diffusivity vs Temperature ....................................................... 136

Figure 7.28: Fire tested geopolymer concrete cylinders 150 mm diameter (left) and 100

mm diameter (right) after compressive strength test .......................................... 138

Figure 8.1: Sand Particle Size Distribution Graph ..................................................... 144

Figure 8.2: Aerated geopolymer panel cross section ................................................ 146

Figure 8.3: Reinforcement details for aerated geopolymer panel .............................. 146

Figure 8.4: TramexTM CME 4 moisture meter ............................................................ 147

Figure 8.5: Bearing load test setup ........................................................................... 147

Figure 8.6: Axial load test setup ................................................................................ 148

Figure 8.7: Corner bearing test setup ........................................................................ 149

Figure 8.8: Flexural load test setup ........................................................................... 149

Figure 8.9: Hydrocarbon temperature versus time curves ......................................... 150

Figure 8.10: Aerated geopolymer concrete panels furnace setup illustration ............. 151

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Figure 8.11: Image of aerated geopolymer panels fire test setup .............................. 151

Figure 8.12: Bearing load vs displacement graph for panel 1 .................................... 153



Figure 8.15: Photos of panels’ shear failure after bearing load test ........................... 154

Figure 8.16: Axial load vs displacement for panel 1 .................................................. 155



Figure 8.19: Buckling failure of panel 1 ..................................................................... 156

Figure 8.20: Localised failure at bottom of panels after axial load test ...................... 157

Figure 8.21: Photos of panels after corner bearing test ............................................. 158

Figure 8.22: Flexural load versus displacement for panels with Crust up .................. 159

Figure 8.23: Flexural load versus displacement for panels with Crust down .............. 159

Figure 8.24: Photos of panels’ cracks after flexural load test..................................... 161

Figure 8.25: Aerated geopolymer panels after 30 minutes hydrocarbon fire exposure

.......................................................................................................................... 162

Figure 8.26: Temperature for aerated geopolymer panel .......................................... 163


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List of Tables

Table 2.1: Bibliographic history of some important events/articles about alkali-activated

cements (Li et al., 2010) ...................................................................................... 13

Table 2.2: Chemical requirement for Class F and Class C fly ashes according to ASTM

618 (1994) ........................................................................................................... 18

Table 2.3: Average chemical content for fly ashes in Australia (Heidrich, 2003) .......... 19

Table 3.1: Concrete (per cubic meter) mix summary ................................................... 39

Table 3.2: Concrete Casting and Fire Test Details ...................................................... 41

Table 3.3: Compressive strength and moisture content summary ............................... 46

Table 4.1: Concrete (per cubic meter) mix summary ................................................... 61

Table 4.2: Specimens’ fire test details ......................................................................... 64

Table 4.3: Spalling Percentage Summary for All Specimens....................................... 72

Table 5.1: Relative slump summary ............................................................................ 88

Table 5.2: Average Diameter Summary ...................................................................... 89

Table 5.3: Adsorption test (BET Theory) results summary .......................................... 92

Table 5.4: Bulk density of fly ash ................................................................................ 93

Table 5.5: Water Absorption Test Results ................................................................... 93

Table 5.6: Chemical Component and slump-flow of Fly Ash ....................................... 96

Table 5.7: Chemical concentration for water filtered from fly ash and demineralized

water mixture ....................................................................................................... 97

Table 6.1: Chemical composition of fly ash (Kong and Sanjayan, 2010) ................... 105

Table 6.2: Result summary of geopolymers with 0.4 alkaline solution to fly ash ratio and

2.5 Na2SiO3 to NaOH ratio ................................................................................. 107


1.75 Na2SiO3 to NaOH ratio ............................................................................... 107


1.0 Na2SiO3 to NaOH ratio ................................................................................. 108

Table 6.5: Result summary of geopolymers with 0.57 alkaline solution to fly ash ratio

and 2.5 Na2SiO3 to NaOH ratio .......................................................................... 109

Table 6.6: ICP Test Results ...................................................................................... 110

Table 7.1: Chemical composition of Gladstone fly ash .............................................. 115

Table 7.2: Sodium silicate specification .................................................................... 117

Table 7.3: Geopolymer concrete mixture proportions ................................................ 118

Table 7.4: Moisture content and testing date details ................................................. 124

Table 7.5: Geopolymer concrete spalling summary .................................................. 130

Table 7.6: Compressive Strength and Density Summary .......................................... 136

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Table 7.7: Residual compressive strength summary ................................................. 137

Table 8.1: Chemical component of Gladstone fly ash ............................................... 144

Table 8.2: Sodium silicate specification .................................................................... 145

Table 8.3: Panels weight and density summary ........................................................ 152

Table 8.4: Results of Bearing Load Tests ................................................................. 152

Table 8.5: Results of Axial Load Tests ...................................................................... 156

Table 8.6: Results of Corner Bearing Tests .............................................................. 157

Table 8.7: Results of Flexural Load Tests ................................................................. 159

Table 8.8: Calculated Maximum Loads for various d, f’c and fy ................................. 160

Table 8.9: Aerated geopolymer panel spalling summary ........................................... 162

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List of Abbreviations

ft - tensile strength of concrete

fy - compressive strength of concrete

HSC - high strength concrete

ICP - inductively couple plasma

K - thermal diffusivity

LOI - loss on ignition

PS - polysialate

PSS - polysialate-siloxo

PSDS - polysialate-diloxo

PC - pulvarized coal

rp - relative slump

SEM - scanning electron microscopic

SF - slump-flow

t - time (minutes)

T - temperature (oC)

XRF - X-Ray fluorescence

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CHAPTER 1

Introduction

1.1 Background

Concrete structures were designed to withstand various types of environmental

conditions categorised as from mild to very severe conditions. Fire represents one of

the most severe environmental conditions to which concrete structures may be

subjected to such as close conduit structure like tunnel (Kim et al., 2010; Khaliq and

Kodur, 2011). There are many reasons that can trigger fire event in a tunnel or high

rise building. Fire event in Tunnel Mont Blanc in 1999 was initiated from a breakdown

of a truck carrying margarine and flour. In 2010, a 28-story high-rise apartment caught

on fire ignited from welding spark killing at least 50 people. A recent fire event occurred

in 2012, when two buses collided in the 12.9 km Hsuehshan Tunnel, Taiwan causing a

passenger bus to catch fire after it was rear-ended by another bus. Generally,

concrete is regarded as a fire resistant construction material, especially when

compared to the alternatives such as steel and timber. However, concrete is

susceptible to a less known phenomenon termed spalling in fire. Spalling normally

occurs on concrete exposed to fire especially high strength concrete structure in which

widely used nowadays in high rise buildings and tunnels. (Sanjayan and Stocks, 1993).

The new breed of concrete binder considered to be the binder of the future due to less

CO2 emission, geopolymer is a cementless concrete binder. The name geopolymer

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was coined by Davidovits in 1975 (Davidovits, 1991; Van Jaarsveld et al., 2002).

Geopolymer concrete is known as very high fire resistance material due to its ceramic-

like properties (Davidovits and Davidovics, 1991). Geopolymer concrete strength after

elevated temperature exposure can increase due to further geopolymerisation (Pan et

al., 2009). However, there is decrease in strength of geopolymer concrete after

elevated temperature exposure especially geopolymer concrete with coarse aggregate

due to thermal incompatibility between aggregates and binder which can contribute to

the decline in geopolymer concrete strength (Kong and Sanjayan, 2008).

To-date, the chemistry of geopolymer has been extensively focused by many studies.

Some investigations have been undertaken to study the material properties of

geopolymer concrete and structural behaviour of geopolymer concrete structural

elements such as beams and columns, high performance geopolymer concrete and

steel fibre reinforced geopolymer concrete. Only a few have investigated the

performance of geopolymer concrete in fire, let alone large scale size geopolymer

concrete and hydrocarbon fire exposure.

1.2 Aim of research

The aim of the research is to develop a fire resistant geopolymer concrete when

exposed to hydrocarbon fire.

1.3 Research objectives

The objectives of the research are listed below:

1) To investigate the performance of large scale high strength geopolymer

concrete panels and aerated geopolymer concrete in hydrocarbon fire.

2) To investigate the severity of large scale high strength Portland cement

concrete spalling when exposed to hydrocarbon fire.

3) To investigate several issues affecting high strength geopolymer concrete

casting in mass production.

1.4 Scope of the thesis

This research was undertaken in two main parts; Portland cement high strength

concrete part and geopolymer concrete part. In Portland cement high strength part, the

severity of high strength Portland cement concrete spalling was investigated by

exposing large scale 3 m square wall panel to hydrocarbon fire. The weight loss of

panels after fire test was measured and the spalling percentage was calculated based

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on the weight loss. The panel’s temperatures were measured at several depths of wall

for further thermal properties analysis.

In addition, specimen size effect on spalling was investigated by comparing the spalling

of 3 m square panels with 1 m square panels, columns and cylinders. All panels were

cast with different maximum aggregate size (7 mm, 14 mm and 20 mm) and type

(basalt and granite) for investigation on aggregate size and type effect on spalling.

In geopolymer concrete part, 3 types of fly ash were initially selected as aluminosilicate

source of geopolymer concrete namely Gladstone fly ash (from Gladstone power

station), Tarong fly ash (from Tarong power station) and Microash. Since the

geopolymer concrete were cast in large scale production, workability of fresh

geopolymer was used as main criteria in selecting the fly ash. Therefore, Gladstone fly

ash was selected because fresh geopolymer exhibited the best workability compared to

Tarong and Microash. Factors affecting the workability of these fly ashes were

investigated out by examining the physical properties of the fly ashes such as mean

particle size, particle size distribution, pore volume, water absorption and density. The

effect of water to geopolymer mortar was investigated by examining the strength of

geopolymer paste in saturate and dry conditions. The high strength geopolymer

concrete mix was determined based on the outcome of fly ash workability and water

effect investigation.

The investigation on the performance of high strength geopolymer concrete was

carried out by exposing 1 m square wall panels and 2 sizes of cylinders (100 mm and

150 mm diameter) to hydrocarbon fire. Concrete spalling, temperature profile and

residual strength were measured. Thermal incompatibility between aggregate and

geopolymer effect on spalling was also investigated. Aerated geopolymer concrete

(without coarse aggregate) wall panels were tested for hydrocarbon fire exposure. In

addition, investigation on the suitability of aerated geopolymer concrete to be used as

structural member was carried out by testing the panels for axial load capacity, bearing

capacity, flexural strength and corner bearing capacity. The overview of the research is

illustrated in Figure 1.1

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Performance of

Geopolymer Concrete In

Fire

Portland

Cement High

Strength

Concrete

Hydrocarbon Fire

testing of full size

Portland Cement

High Strength

Concrete Wall

Panels

Geopolymer

Concrete

Specimen’s

Size, Aggregate

Size and

Aggregate Type

Effect on

Spalling of

Concrete in Fire

Investigation of

the Effects of

Fly Ash Types

and Properties

on the

Workability of

Fresh

Geopolymer

Strength of

Geopolymers

in Saturated

and Dry

Conditions

Hydrocarbon

Fire testing of

Geopolymer

High Strength

Concrete Wall

Panels and

Cylinders

Investigation on

Aerated

Geopolymer

Wall Panels for

Fire

Applications

Figure 1.1: Research Overview

1.5 Thesis Organisation

This thesis consists of nine chapters. Chapter 1 describes the motivation of

developing fire resistant geopolymer concrete, the aim of the research, objectives of

the research and brief description on the research content. Chapter 2 of the thesis

covers literature review of the general scenario of concrete performance in under high

temperature. Several fire events which cause devastating effect on concrete

structurally, the potential of geopolymer concrete as fire resisting material and the

benefits of geopolymer concrete environmentally are mentioned in this chapter. In

addition, literature on geopolymer concrete including fundamental chemistry of

geopolymer, investigation on geopolymer compressive strength, investigation on

geopolymer workability and fire exposure on geopolymer concrete investigation are

also presented.

Chapter 3 of the thesis presents the results of the severity of full size 3 m square

Portland cement high strength concrete spalling when exposed to hydrocarbon fire. In

addition, thermal diffusivity values for the concrete are also determined.

Chapter 4 of the thesis presents the investigation on factors affecting high strength

concrete spalling. Factors that have been investigated are specimen’s size, aggregate

size and aggregate type.

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Aluminosilicate source (fly ash) for geopolymer was investigated and reported in

Chapter 5. This chapter presents the effect of physical properties of fly ash on

workability of geopolymer. The source of fly ash used in this research was decided

based on the outcome of this chapter.

Chapter 6 of the thesis presents the strength of geopolymer paste in both saturated

and dry condition. Geopolymer is basically an aluminosilicate reaction to produce gel

and hardening process through polymerization. Unlike hydration process in Portland

cement binder, geopolymer’s reaction does not involve free water during mixing stage.

Therefore, strength reduction when geopolymer immersed in water for saturation

process was investigated.

Chapter 7 of the thesis presents the performance of high strength geopolymer concrete

exposed to hydrocarbon fire. High strength geopolymer mix calculation and casting

procedure are also presented. High strength geopolymer concrete spalling,

temperature profile, thermal diffusivity graphs and residual strength are discussed and

reported in this chapter.

Chapter 8 of the thesis describes the investigation of aggregate and geopolymer binder

thermal incompatibility effect on spalling and the suitability of aerated geopolymer

concrete wall to be used as structural member in fire application. Aerated geopolymer

concretes wall without coarse aggregate were tested under room temperature (flexural,

bending, axial load and corner bearing) and in fire conditions.

Finally in Chapter 9 of the thesis, overall conclusions made in this research are

provided. In addition, recommendations of future work and discussions on enhancing

geopolymer concrete research are also presented.

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References

Davidovits, J. (1991). "Geopolymers - Inorganic polymeric new materials." Journal of

Thermal Analysis 37(8): 1633-1656.

Davidovits, J. and Davidovics, M. (1991). Geopolymer. Ultra-high temperature tooling

material for the manufacture of advanced composites. International SAMPE

Symposium and Exhibition (Proceedings).

Khaliq, W. and Kodur, V. K. R. (2011). "Effect of High Temperature on Tensile Strength

of Different Types of High-Strength Concrete." ACI Materials Journal 108(4):

394-402.

Kim, J. H. J., Mook Lim, Y., Won, J. P. and Park, H. G. (2010). "Fire resistant behavior

of newly developed bottom-ash-based cementitious coating applied concrete

tunnel lining under RABT fire loading." Construction and Building Materials

24(10): 1984-1994.

Kong, D. L. Y. and Sanjayan, J. G. (2008). "Damage behavior of geopolymer

composites exposed to elevated temperatures." Cement and Concrete

Composites 30(10): 986-991.

Pan, Z., Sanjayan, J. G. and Rangan, B. V. (2009). "An investigation of the

mechanisms for strength gain or loss of geopolymer mortar after exposure to

elevated temperature." Journal of Materials Science 44(7): 1873-1880.

Sanjayan, G. and Stocks, L. J. (1993). "Spalling of high-strength silica fume concrete in

fire." ACI Materials Journal 90(2): 170-173.

Van Jaarsveld, J. G. S., Van Deventer, J. S. J. and Lukey, G. C. (2002). "The effect of

composition and temperature on the properties of fly ash- and kaolinite-based

geopolymers." Chemical Engineering Journal 89(1-3): 63-73.

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CHAPTER 2

Literature Review

2.1 Background

Generally, concrete is regarded as a fire resistant construction material,

especially when compared to the alternatives such as steel and timber. However,

concrete is susceptible to a well-known phenomenon termed spalling in fire. Spalling is

a physical process of the breakdown of surface layers of concrete which crumble into

small pieces in response to high temperatures and/or mechanical pressure. Spalling of

concrete in fire is dislodgement of small pieces of concrete (chips up to 50 mm)

popping out from the surface of concrete, often explosive in nature. Explosive spalling

may have a very severe impact on the surrounding environment. Pieces of smashed

concrete can fly with high speed and explosive energy causing severe casualty (Ali et

al., 2001). For example, a fire in Channel tunnel (35 km railroad tunnel connecting

England and France) in 1996 caused severe damage to concrete tunnel rings owing to

the spalling of concrete and resulted in six-month closure for repairs costing US$1.5

million per day (Ulm et al., 1999). On 24 March 1999, a cargo truck carrying margarine

and flour in the Mont Blanc tunnel connecting France and Italy caught fire and stopped

at Kilometre 6.7 causing 39 human deaths and severely damaging 900 m long tunnel

roof due to spalling (Roh et al., 2008). A fire occurred in the Great Belt tunnel in

Denmark in 1995 also causing severe spalling of concrete tunnel rings (Hertz, 2003).

Steam pressure build-up in the pores of concrete in fire is believed to cause moisture

clog spalling, first proposed by Shorter and Harmathy (1961). Spalling was not

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considered a major problem until the advent of high strength concrete (HSC) and its

widespread use since 1990’s. HSCs are significantly more vulnerable to spalling in fire.

Sanjayan and Stocks (1993) is the first published research work in international journal

identified this problem. Since HSC has become the dominant construction material,

there has been a renewed interest in spalling research. Highly reputed researchers in

the field of concrete have now cast doubts on the moisture clog spalling hypothesis.

Bazant (1997) hypothesized that spalling results from restrained thermal dilation close

to the heated surface, which leads to compressive stresses parallel to the heated

surface, leading to brittle fractures of concrete. This hypothesis is further developed by

Ulm et al. (1999) - chemoplastic softening model, Stabler and Baker (2000a and

2000b) - coupled thermo-mechanical damage model and Nechnech et al. (2002) -

elasto-plastic damage model.

National Research Council of Canada (NRC), as well as a number of organizations

world-wide, reported that factors affecting fire performance of high strength concrete

are concrete strength, concrete density, load intensity, moisture content, fire intensity,

aggregate type and specimen’s dimension (Kodur, 2000)

Spalling may also result from the thermal incompatibility between the aggregates and

the cement paste, in particular in concrete with silicious aggregates (Kong and

Sanjayan, 2010; Pan et al., 2012). The exact mechanism of spalling is still hotly

disputed.

Experimental results published by Crozier and Sanjayan (2000) showed that areas of

concrete surfaces under compressive stresses are more prone to spalling than the

ones under tensile stresses. This evidence supports the hypothesis of brittle fracture of

concrete under compressive stresses due to restrained thermal dilation. The fact that

HSC is highly brittle also supports this theory. HSC is predominantly used in structural

elements subjected high level of compressive stresses, e.g., the tunnel’s rings and

columns in high-rise buildings.

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Due to the highly publicized events such as Channel and Great Belt fires, many

infrastructure owners are demanding the spalling issue to be addressed at the design

stage. Currently, it is addressed by providing some sort of fireproofing to concrete

tunnel rings and columns in high-rise buildings. These fireproofing add significant

expense to the construction costs due to materials cost and high manpower needed for

complicated installation procedures. In addition, sprayed type fire proofing on exposed

structural member does not enhance the architectural design of a building.

Spalling occurs in the initial stages of the fire, i.e., within 15 to 30 minutes (Sanjayan

and Stocks, 1993; Crozier and Sanjayan, 2000) – a critical period for fire control and

escape. Hydrocarbon fire in a tunnel can have catastrophic consequences due to the

tunnel collapse caused by concrete spalling, while fire fighters are assisting people to

escape.

Further, the large columns in lower storeys of high-rise buildings constructed during the

last decade are almost always constructed with high strength concrete, which are

susceptible to spalling of concrete in a fire (Sanjayan and Stocks, 1993). Lower storey

columns virtually carry the entire building and destruction of these columns in a fire can

have catastrophic consequences. Spalling results in rapid loss of the surface layers of

the concrete columns exposing the steel reinforcement, which quickly loses strength

when exposed to fire. Ali et al. (2001) reported that 17 out of 18 columns tested for fire

test spalled explosively.

Chan et al. (1999) conducted fire tests using standard’s fire curve on 100 mm cubic

concrete cube made with silica fume. All specimens spalled explosively and Chan et al.

(1999) concluded that moisture content and strength are the two main factors

governing explosive thermal spalling of concrete. Moisture content has a dominant

influence on spalling.

Noumowe et al. (2006) reported that 160 mm diameter cylinders and 100 x 100 x 400

mm prism self-compacted high strength concrete spalled during low heating rate

(0.5oC/min) with maximum 400oC temperature while normal high strength (vibrator

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compacted) concrete remained un-spalled. Normal high strength concrete recorded

55% residual strength after the heating cycle. However, both self-compacted high

strength and normal high strength concrete spalled explosively when exposed to

standard fire curve.

Hernández-Olivares and Barluenga (2004) also reported similar outcome when 200 x

300 x 50 prism high strength concrete made with silica fume spalled when exposed to

standard fire temperature curve.

Noumowe et al. (2009) reported that 160 × 320 mm specimens of lightweight

aggregate concrete spalled during the heating phase. The explosion took place when

the temperature at the surface of the specimens was between 290 and 430°C and

concluded that combination of high thermal gradient (which induces high thermal

stresses) and low permeability (which induces high vapour pressure) is main concern

in the concrete spalling at high temperature.

Arioz (2007) reported that surface cracks of 70×70×70 mm concrete became visible

when the temperature reached 600°C. The cracks were very pronounced at 800°C and

increased extremely when the temperature increased to 1000°C. The weight of the

concrete specimens reduced significantly as the temperature increased. This reduction

was gradual up to 800°C. A sharp reduction in weight was observed beyond 800°C.

The increments of crack and weight reduction are due to chemical degradation of OPC

cement binder at 800°C temperature.

Most of researches investigated the damage of fire exposure to concrete on small lab

scale specimens and fire exposure are based on Standard Fire (or cellulosic fire)

specified by ISO 834 (International Standard, 1999). The size of these specimens are

not representing the level of concrete deterioration in terms of spalling and other

thermal properties when exposed to fire in actual condition. In addition, risk of spalling

is significantly raised when the rate of temperature rise is rapid (Copier, 1983). In a

hydrocarbon fire according to EN 1991, rate of heating is twice as the standard fire

(room temperature to 1000oC within 10 minutes) (BSI, 2005). Hydrocarbon fire

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simulates fire event in a tunnel, petrochemical refineries plant, combustible chemical

storage warehouse, etc. Therefore, in this research, the performance of high strength

concrete exposed to fire was conducted in large scale high strength concrete wall

panels and results from large scale specimens were compared with small scale ones.

Fire temperature curve for fire exposure was based on hydrocarbon fire to maximise

the spalling risk. This research also investigates the size effect as discussed above

where there is no consensus as to how the size effects the spalling of concrete.

2.2 Geopolymer Binder in Concrete for Spalling Solution

During the last decade, remarkable achievements have been made through

geosynthesis and geopolymerisation. It is an excellent alternative to Portland cement

binder concrete due to the elastic properties of hardened geopolymer concrete and the

behaviour and strength of reinforced geopolymer concrete structural members are

similar to those observed in the case of Portland cement concrete (Rangan, 2008)

Geopolymers are very-low viscosity inorganic resins, hardened like thermosetting

resins, but have very high strength and fire resistance, and are ceramic-like in their

properties (Davidovits, 1991). An ultra-high temperature tooling material for the

manufacture of advanced composites was made using geopolymers, which performed

better than the ceramic tooling materials (Davidovits and Davidovics, 1991). During the

Grand Prix season 1994 and 1995, Benetton-Renault Formula 1 Sport Car designed a

unique thermal shield made out of carbon/geopolymer composite. It helped Michael

Schumacher to win twice the world championship and offered to his technical team to

become World Champion of car builders during these two years. Since then, most

Formula 1 teams are using geopolymer composite materials (www.geopolymer.org).

Lyon et al. (1997) reported that geopolymer composites is ideally suited for

construction, transportation and infrastructure where fire endurance is part of needed

requirement .

Low cost geopolymer resins can be produced by activation of fly ash. Geopolymer

concrete is produced by combining these resins with coarse and fine aggregates using

the conventional concrete technology methods. Since fly ash is an industrial by-product

from coal power stations (largely wasted by dumping in landfills), the cost of

manufacturing this concrete can be potentially lower than the conventional Portland

cement based concrete.

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Research works reported so far in the literature indicate that geopolymers have

superior fire resistance when compared to conventional concretes (Kong et al., 2008;

Kong and Sanjayan, 2008; Pan et al., 2009). The superior fire resistance properties are

attributed to the ceramic-like properties of geopolymers, including the way it looks:

smooth, glassy and shiny (Palomo et al., 1999).

2.3 Geopolymer Binder in Concrete for Environmental Benefits

Production of 1 ton of Portland cement consumes 1½ tons of raw materials and

is responsible for the release of about 0.75 ton of CO2 into the atmosphere. Portland

cement production releases 6.5 million tons of CO2 in Australia. Worldwide,

greenhouse gas emission from the Portland cement production is about 3 billion tons

annually or about 7% of the total greenhouse gas emissions to the earth’s atmosphere.

Further, the production of Portland cement worldwide is increasing 3% annually

(Collins and Sanjayan, 2002; Hardjito et al., 2004). The amount of CO2 emissions due

to concrete using conventional Portland cement is the fourth largest contributor to

global carbon emissions after oil, coal and natural gas. Portland cement was found to

be the primary source of CO2 emissions generated by typical commercially produced

concrete mixes, being responsible for 74% to 81% of total Portland cement concrete

CO2 emissions (Flower and Sanjayan, 2007).

Utilisation of unused industrial by-products such as fly-ash, which otherwise are

dumped in landfills and contribute to land pollution, to make concrete without the use of

any Portland cement will not only reduce the cost of construction materials but also

reduce the greenhouse gas emissions arising from Portland cement manufacture.

Power stations around the world are currently still using coal as fuel to generate

electricity. These power stations produce enormous quantities of fly-ash residues every

year. In 2011, about 13 million tons per annum of fly ash is produced in Australia

(Cement Australia, 2011), in which only small quantity is used for cementitious

applications (e.g. Portland cement/fly ash blended cements, road stabilisation, low

strength fills, asphaltic fillers etc) (Heidrich, 2003). Worldwide, the production of fly ash

is 390 million tons per annum, but its utilisation was less than 14%. In the future, fly ash

production will increase, especially in countries such as China and India (Hardjito et al.,

2005). From China alone, 2.1Gt produced in 2011 which accounting for 58% of world

total cement production (Oss, 2011). Therefore, utilizing the fly ash in geopolymer

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concrete as fire resistance construction materials in this research will not only have a

huge impact on concrete in fire development, but also provided a better sustainable

environment.

2.4 Geopolymer History and Reaction Mechanisms

Alkali-activated cement researches begin in 1939 with the work of Feret (slags

used for cement) and alkali-slag combinations work by Purdon in 1940 (Roy, 1999).

Glukhovsky (1959) used “soil cement” term for concrete binder which using “soil

silicates” In 1979, Davidovits introduced “geopolymer” terms for alkaline activated

material and the term is generally accepted to-date. Table 2.1 summarises the history

of alkali-activated cement (Roy, 1999; Li et al., 2010).

Table 2.1: Bibliographic history of some important events/articles about alkali-activated cements (Li et al., 2010) Author Year Significance

Feret 1939 Slags used for cement

Purdon 1940 Alkali-slag combination

Glukhovsky 1959 First called “alkaline cements”

Davidovits 1979 “Geopolymer” term

Forss 1983 F-cement (slag-alkali-superplastizer)

Davidovits and Sawyer 1985 Patent of “Pyrament’ cement

Krivenko 1986 DSc thesis, R20-RO-SiO2-H20

Deja and Maloplepsy 1989 Resistance to chlorides shown

Roy and Langton 1989 Ancient concretes analogs

Talling and Brandstetr 1989 Alkali-activated slag

Wu et al. 1990 Activation of slag cement

Roy et al. 1991 Rapid setting alkali-activated cements

Wang and Scivener 1995 Slag and alkali-activated microstructure

Fernandez-Jimenez and Puertas 1997 Kinetic studies of alkali-activated slag cements

Davidovits 1999 Chemistry of geopolymeric system

Palomo 1999 Alkali-activated fly ash – a cement for the future

Palomo and Palacios 2003 Immobilization of hazardous waste

Duxson 2007 Geopolymer technology: the current state of art

Provis and Deventer 2009 Geopolymers: structure, processing, properties

and industrial application

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Table 2.1 only lists the major works in the chemical aspects of the alkali activated

cements and have missed some contributions by our group. Alkali activated research

commenced in Melbourne in 1995 with the investigation on microstructure and

durability of alkali activated cementitious paste (Bakharev and Patnaikuni, 1997). In

1997, Collins and Sanjayan (1998) used alkali activated cement primarily to find a way

to increase early age strength characteristics of slag concrete . The slag blended

cement with Portland cements are notoriously low in early age strength and therefore

have difficulty being used in precast applications. The group has also demonstrated

that alkali activated cements have superior sulphate resistance (Bakharev et al., 2002)

and acid resistance (Bakharev et al., 2003). Fire resistance properties of geopolymer

using fly ash showed excellent results. Some of the major publications in this area are:

Kong et al. (2008), Kong and Sanjayan (2010) and Pan and Sanjayan (2010). The

mechanical properties of geopolymer show that the properties are comparable to

Portland cement concretes (Pan et al., 2011).

The polymerisation process involves a chemical reaction under highly alkaline

conditions on Al-Si minerals (e.g. fly ash, kaolin, metakaolin), yielding polymeric Si-O-

Al-O bonds, as described by Davidovits (1991): Mn [ – ( Si – O2 ) z – Al – O ] n . wH2O,

where M is the alkaline element, the symbol – indicates the presence of a bond, z is 1,

2 or 3, and n is the degree of polymerisation.

Sialate is an abbreviation for silicon-oxo-aluminate in which the alkali is sodium (Na+),

potassium (K+), lithium (Li+) or calcium (Ca2+). Polysialates are chain and ring polymers

with Si4+ and Al3+ in IV-fold coordination with oxygen and range from amorphous to

semi-crystalline (Davidovits, 1991). Types of polysialates identified in geopolymer are

polysialate (PS), polysialate-siloxo (PSS), polysialate-disiloxo (PSDS) as shown in

Figure 2.1

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Figure 2.1: Types of polysialates (Davidovits, 2002)

The hardening processes of geopolymer normally occur through polymerisation

process. General mechanism of alkali activation for primarily comprising silica and

reactive alumina as proposed by Glukhovsky in 1950’s consist three main processes

namely destruction-coagulation stage, coagulation-condensation stage and

condensation-crystallisation stage. The first step (destruction-coagulation stage)

consists of a breakdown of the covalent bonds Si–O–Si and Al–O–Si, which happens

when the pH of the alkaline solution rises, so those groups are transformed into a

colloid phase. Then in coagulation-condensation stage, destroyed products accumulate

and interact among them to form a coagulated structure. Finally, condensed structure

generated and crystallized (Li et al., 2010).

More comprehensive review of the current state of knowledge on inorganic polymers

was compiled by Duxson (2007) in which a further enhancement on general

mechanism proposed by Glukhovsky in 1950’s. A conceptual model for inorganic

polymerisation illustration with high level of simplification (excluding raw material

processing such as fine grinding, heat treatment etc.) as shown in Figure 2.2.

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Figure 2.2: Conceptual model for geopolymerisation (Duxson et al., 2007)

Dissolution of the solid aluminosilicate source by alkaline hydrolysis (consuming water)

produces aluminate and silicate species started by the alkaline solution attack on the

fly ash (Fernández-Jiménez et al., 2005). Figure 2.3 shows the scanning electron

microscopic (SEM) images of fly ash before and after dissolution.

Figure 2.3: SEM pictures (a) original fly ash, (b) fly ash activated with NaOH

(Fernández-Jiménez et al., 2005)

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Once in solution the species released by dissolution are incorporated into the aqueous

phase, which may already contain silicate present in the activating solution. A complex

mixture of silicate, aluminate and aluminosilicate species is thereby formed.

Supersaturated aluminosilicate solution is created at high rate due to rapid dissolution

of amorphous aluminosilicate at high pH. This supersaturated aluminosilicate solution

resulted in gel formation. The system continues to rearrange and reorganize after the

gel formation resulting in the three-dimensional aluminosilicate network commonly

attributed to geopolymers (Duxson et al., 2007).

2.5 Fly Ash

Fly ash also known as pulverised fuel ash, is a fine grey powder consisting

mostly of spherical glassy particles. It is residue product from burning coal in coal fired

power station. Fly ash is collected from the exhaust gases from the combustion

chambers with electrostatic precipitators or bag houses before the gases are released

to atmosphere (Flyash Australia, 2010; Cement Australia, 2011). Explanation of fly ash

production at a power station is shown in Figure 2.4.

Coal is injected into the furnace and ignited while in suspension. During combustion,

minerals in coal become fluid at high temperature and are then cooled. In a pulverized

coal (PC) fired boiler, the furnace operating temperatures are typically in excess of

1400°C. As the particles are heated, volatile matter is vaporized and combustion

occurs. Minerals undergo thermal decomposition, fusion, disintegration and

agglomeration. The final products of combustion are usually spherical ash particles,

which may subsequently undergo other processes such as coalescence with other

particles or expansion due to internal gas release. The formation of molten ash droplets

marks the highest temperature, and a significant fraction of the volatile forms of

elements will exist in the gas phase. The main formation mechanism for coarse ash

particles (>2 micrometer) is carryover of a proportion of the mineral matter in the feed

coal. A portion of the incombustible material is retained in the furnace as bottom ash.

The rest of the inorganic material leaves in the flue gases as fly ash. Rapid cooling in

the post-combustion zone results in the formation of spherical, amorphous (non-

crystalline) particles (Clarke, 1993; Kutchko and Kim, 2006).

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Figure 2.4: Fly ash production (Flyash Australia, 2010)

The fly ashes produced in Australian power stations are light to mid-grey in colour and

have the appearance of cement powder. The particle sizes range from less than 1 to

200 micrometer (Heidrich, 2003). According to the ASTM C 618, there are two classes

of fly ash; Class C and Class F. Class C fly ash, contains more than 20% of calcium

oxide (CaO) in its composition, is produced from burning lignite or sub-bituminous coal

and is sometimes called high-calcium fly ash. Meanwhile, class F fly ash is also known

as low calcium fly ash. The Loss on Ignition (LOI) is also an important characteristic for

fly ash, especially when it is used in concrete production. LOI indicates the amount of

unburned carbon present in the fly ash. Table 2.2 summarizes the chemical

requirement of Class F and Class C fly ashes according to ASTM C618 .

Table 2.2: Chemical requirement for Class F and Class C fly ashes according to ASTM 618 (1994)

Chemical Properties Class F Class C

Silicon dioxide (SiO2) plus aluminum

oxide (Al2O3) plus iron oxide (Fe2O3) Minimum 70% Minimum 50%

Sulfur trioxide (SO3) Maximum 5% Maximum 5%

Moisture content Maximum 3% Maximum 3%

Loss on ignition (LOI) Maximum 6% Maximum 6%

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The use of Class F pozzolan containing up to 12.0% loss on ignition may be approved

if either acceptable performance records or laboratory test results are made available.

The Loss on Ignition (LOI) is also an important characteristic for fly ash, especially

when it is used in concrete production. LOI indicates the amount of unburned carbon

present in the fly ash.

In terms of mineral composition, fly ash consists of a glassy matrix with noticeable

crystalline phases of quartz (SiO), magnesioferrite (MgFe2O4), hematite (Fe2O32),

anhydrite (CaSO), lime (CaO), and portlandite (Ca(OH)) (Hanjitsuwan et al., 2011).

In Australia, majority of fly ash produced is categorised as Class F mainly due to the

amount of silica and alumina range between 80 – 85%. Class F fly ash is pozzolanic

and reacts with various cementitous materials. Most of the fly ash being used to

enhance the properties of concrete (as admixture), OPC replacement as concrete

binder, road base binders and asphalt filler (Heidrich, 2003). Average chemical content

of 10 fly ashes in Australia is summarised in Table 2.3.

Most researches in Australia used fly ash from power plants in Western Australia and

Gladstone power plant in Queensland (Hardjito et al., 2004; Hardjito et al., 2005; Kong

and Sanjayan, 2008; Kong and Sanjayan, 2010; Pan et al., 2012; Giasuddin et al.,

2013; Deb et al., 2014; Nematollahi and Sanjayan, 2014)

Table 2.3: Average chemical content for fly ashes in Australia (Heidrich, 2003)

Chemical Component Weight (%)

SiO2 61.1

Al2O3 26.2

Fe2O3 4.2

CaO 1.7

MgO 0.9

Na2O 0.8

K2O 1.1

SO3 0.2

Loss on Ignition (LOI) 2.6

In this research, there are fly ashes from Gladstone power plant and Tarong power

plant were initially used as geopolymer aluminosilicate source. Based on workability

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test and further investigation on physical properties effect on workability, fly ash from

Gladstone power plant was used.

2.6 Alkaline activator

Basically, geopolymer can be produced by any strong alkali solution as the

alkaline activators (Rowles, 2004). Glukhovsky et al. (1980) classified alkaline activator

into six groups according to their chemical composition : (1) Caustic alkalis: MOH; (2)

Non-silicate weak acid salts: M2CO3, M2SO4, M3PO4, MF, etc; (3) Silicates: M2O·nSiO2

(4) Aluminates: M2O.nAl2O3; (5) Aluminosilicates M2O·Al2O3·(2-6)SiO2; and (6) Non-

silicate strong acid salts: M2SO4.

The type of alkaline solution plays an important role in the geopolymerisation process.

An investigation on three alkaline solutions are sodium hydroxide (NaOH), sodium

carbonate (Na2CO3) and sodium silicate solutions concludes that NaOH has the

highest compressive strength followed by sodium silicate solution and higher

concentration of Na2O corresponds to higher compressive strength (Fernández-

Jiménez et al., 2005).

Xu and Van Deventer (2000) reported that the ionic sizes of alkali-metal cation also

affect the dissolution rate when NaOH solution exhibits a higher dissolution rate with

aluminosilicate source materials as the smaller Na+ cation even though Na+ and K+

have the same electric charge. This is due to cation-anion pair interaction becoming

less significant as the cation size increases (Xu and Van Deventer, 2000).

Alkaline activator can be a single material such as sodium hydroxide, sodium silicate,

calcium hydroxide or combination of any silicate and hydroxide (Brough and Atkinson,

2002; Buchwald and Schulz, 2005).

NaOH is used because it is cheap, has low viscosity and is the most widely available

alkaline hydroxide. Also, the hydroxyl ion - in NaOH is an important element in starting

the geopolymerisation process (Provis and Van Deventer, 2009).

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Sodium silicate (Na2SiO3) is a high viscosity chemical in liquid or powder form. It

influences the geopolymer mixture workability when a highly concentrated one is used

in liquid and a powder form. Na2SiO3 in the geopolymer system increase the final

strength of the paste and bind the material together to produce a dense paste (Jo et al.,

2007).

NaOH plus sodium silicate have been found to produce the fastest setting time and

promotes the collapse of both micropores and mesopores, thus increasing density and

strength (Jiang, 1997). The majority of research has found that activation with sodium

silicate or sodium silicate blended with NaOH has given the best strength (Pimraksa et

al., 2008; Adam et al., 2010; Guo et al., 2010; Nazari et al., 2011; Zhao and Sanjayan,

2011).

Therefore, this research used the combination of sodium silicate and sodium hydroxide

as alkaline activator.

2.7 Geopolymer workability

Workability is often referred as the ease with which a concrete can be

transported, placed and consolidated without any loss of stability or homogeneity. It is

greatly affected by the characteristics of the constituent materials of concrete (Leite et

al., 2013). The workability properties are measured for fresh concrete before it has set

and hardened.

High viscosity of sodium silicate and sodium hydroxide made geopolymer concrete less

workable compared to Portland cement concrete. Since geopolymer is based on

aluminosilicate reaction for producing gel and hardening, no free water were added into

fresh concrete and reduced the workability. Sathonsaowaphak et al. (2009) reported

that main factors affecting fresh geopolymer mortar workability were sodium

silicate/hydroxide ratio and sodium hydroxide concentration. The increase of both

sodium silicate/hydroxide ratio and sodium hydroxide concentration resulted in less

workable mortar mixes due to higher viscosity of sodium silicate and sodium hydroxide.

The setting time of geopolymer paste was found out to increase proportionally with the

increasing of sodium hydroxide concentration because of hardening and setting of the

paste is governed by geopolymerisation process. The geopolymerisation process

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which usually occurred in a slower rate as compared with C-S-H and C-A-H dependent

cementitious system (Hanjitsuwan et al., 2014).

Even though there are a lot of commercial superplasticizers in the market that are

suitable that can be used in Portland cement concrete to improve the workability, only

polycarboxylate (PC) based superplasticizers were effective in increasing the

workability. This is due to its ether chain in its structure which resulted in steric

repulsion (Nematollahi and Sanjayan, 2014).

Most of researches on geopolymer workability focus on chemical reaction of alumina

and silica in which the basic of geopolymerisation process. However, there is still no

firm conclusion on the ratios of silicate/hydroxide, liquid/fly ash, the amount of water or

the concentration on hydroxide needed to obtained high workability. In this research,

the focus on factors affecting fly ash workability based on physical properties of fly ash

particle such as particle sizes, particle distribution, pore volume etc.

2.8 Geopolymer compressive strength

Compressive strength is the one of most important concrete property from

structural engineering point of view. In geopolymer concrete, there are several factors

affecting its compressive strength. Sukmak et al. (2013) studied the effect of sodium

silicate/sodium hydroxide and alkaline activator solution/fly ash ratios on compressive

strength of geopolymer bricks. With curing regime of 75oC for 48 hours, results showed

that optimum values for sodium silicate/sodium hydroxide and alkaline activator

solution/fly ash ratios are 0.7 and 0.6 respectively.

Ryu et al. (2013) studied on hydroxide concentration, hydroxide/silicate and curing

method and curing period influences on compressive strength of geopolymer mortar.

The results show that the combination of highest concentration of NaOH which is 9 M,

hydroxide/silicate ratio of 1 and 60oC for 24 hours curing regime provides the highest

compressive strength of geopolymer mortar. Further investigation on pore size of

geopolymer paste at 28 days indicates that the number of small pores increases with

higher molarity of the alkaline activator. The reduction of the porosity accompanying

the lowering strength observed in fly ash-based geopolymer can be explained by the

geopolymerisation process, which is the hardening mechanism of geopolymer based

on coal ash rich in Al and Si components.

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Pimraksa et al. (2011) reported that concentration on NaOH and KOH as alkaline

activator directly influence the strength of geopolymer. Higher concentration on alkaline

activator molarity in which represents higher Na2O/Al2O3 and Na2O/SiO2 ratios

promoted the strength enhancement. The strengths increased with the increases in

curing temperature and time. Optimum curing regime suggested is 75oC for 5 days.

There was a significant increase in strength between Na2O/SiO2 ratio 0.75 and 1.0 but

strength increment was reduced when the ratio reached 1.25. The increase in strength

observed is attributed to an increase in the dissolution process, thus resulting in a

higher reaction rate and in fewer unreacted FA particles (Law et al., 2014).

Gorhan and Kurklu (2014) investigated the influence of sodium hydroxide (NaOH)

solution concentration, curing time and temperature on geopolymer mortars. NaOH

concentrations of 3, 6 and 9 M were used throughout the laboratory work. Based on

compressive strength results, NaOH concentration of 6 M with 85oC curing temperature

and 2 – 5 hours curing time produced the best compressive strength for geopolymer

mortars.

Ahmari and Zhang (2012) studied the feasibility of utilizing copper mine tailings for

production of eco-friendly bricks based on the geopolymerisation technology found out

that geopolymer bricks made from NaOH concentration of 15 M compressive strength

is higher than geopolymer bricks made from 10 M NaOH. The authors also reported

compressive strength increase for brick with higher NaOH/mining tailings ratio. This is

due to higher Na/Al and Na/Si ratio for those bricks which produced much thicker

geopolymer binder gels and bind the unreacted particles.

While many research papers reported on compressive strength increment with higher

hydroxide concentration particularly NaOH, research done by He et al. (2013) shows a

total contrast in compressive strength development. Several reasons such as Si and Al

ions leaching disruption due to high viscosity of NaOH and premature precipitation of

geopolymeric gels because of excessive OH- concentration are postulated for the

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decrease of geopolymer composites compressive strength in higher NaOH

concentration.

Apart from hydroxide concentration effect on compressive strength of geopolymers,

ratio of silicate to hydroxide influence was investigated by some researches. Ridtirud et

al. (2011) reported that geopolymer mortars with sodium silicate/sodium hydroxide

ratio of 1.5 provide the highest compressive strength (45 MPa) compared to mortars

made with lower sodium silicate/sodium hydroxide ratios. The increasing trend is

mainly attributed to the increasing Na content in the mixture where Na+ ion plays a

critical role in the formation of geopolymer by acting as a charge balancing ions.

However, the authors also reported that the compressive strength of mortars with ratio

of sodium silicate/sodium hydroxide of 3 decreased as excess sodium silicate

hampered the evaporation of water and also disrupt the formation of three dimensional

networks of aluminosilicate geopolymers.

Some other researches highlighted the need of proper adjustment of silicate/hydroxide

ratio to improve the compressive strength of geopolymer concrete/mortar/brick

(Sathonsaowaphak et al., 2009; Guo et al., 2010; Nazari et al., 2011).

Kromjlenovic et al., (2010) concluded that the physical characteristic of fly ash, the

fineness, or particle size distribution was the key parameter in compressive strength of

geopolymer mortar. The compressive strength of geopolymers predominantly

depended on the content of FA fine particles (smaller than 43 um). In all cases, the

highest mortar compressive strength showed the FA which had the highest amount of

fine particles.

In this research, further investigation on various silicate/hydroxide ratios, liquid/fly ash

ratio, hydroxide concentration and fly ash source was carried out in order to achieve

high strength geopolymer concrete more than 50 MPa. This is because most of

literatures reported compressive strength of geopolymer concrete is less than 50 MPa.

The high strength classification of geopolymer concrete is based on high strength of

Portland cement concrete classification in accordance to IS EN 206 (European

Standard, 2013).

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2.9 Geopolymer under Environmental Exposure

Concrete structures were designed to be able to withstand aggressive

environmental exposure. Fly ash-based geopolymer concrete is better than Portland

cement concrete in many aspects such as compressive strength, exposure to

aggressive environment, workability and exposure to high temperature (Al Bakri et al.,

2011). Giasuddin et al. (2013) discovered that geopolymer binder has the potential to

replace traditional oil well cements in CO2 geo-sequestration in saline aquifier. Results

show that the saline water cured geopolymer exhibited higher compressive strength

compared to normal water cured geopolymer.

Main phases of blended ash geopolymer concrete such as sodalite, gmelite and

natrolite were still intact even after 18 months of acid sulphuric exposure. This is due to

no ettringite detected as the Al ions participated in the formation of N-A-S-H gels, thus

making the available Al ions insufficient to form ettringite as in Portland cement binder

system (Ariffin et al., 2013).

There are compressive strength losses ranging from 53.3% to 78.4% when geopolymer

bricks are exposed to nitric acid (pH 4). The losses are caused by incomplete

geopolymerisation, modification of chemical composition of geopolymer gels and high

degree of unreacted alkali specimen (Ahmari and Zhang, 2013).

Other than acidic exposure, water (wetting and drying cycles) can introduce

deterioration problems in geopolymer. Unlike OPC, geopolymer reaction in producing

aluminosilicate gel and geopolymerisation hardening process do not involve any

hydration process. Therefore, water play no roles in hardened geopolymer structure

(Davidovits, 1989). Further investigation on strength reduction due to saturation

process was carried out in this research.

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