THE ROLE OF ALKALINE ACTIVATOR IN
GEOPOLYMERIZATION OF LOW-CALCIUM FLY ASH BASED GEOPOLYMERS.
OMAR A.K.A. ABDUL KAREEM
UNIVERSITI MALAYSIA PERLIS
2010
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
THE ROLE OF ALKALINE ACTIVATOR IN GEOPOLYMERIZATION OF LOW-CALCIUM
FLY ASH BASED GEOPOLYMERS.
BY
OMAR A.K.A. ABDUL KAREEM
(0730410193)
A thesis submitted
In fulfillment of the requirements for the degree of Master of Science (Research)
MATERIALS ENGINEERING UNIVERSITI MALAYSIA PERLIS
2010
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
i ACKNOWLEDGEMENT
ميحرلا نمحرلا ﷲ مسب
In The Name of Allah The Most Gracious and The Most Merciful.
With The Selawat and Salam to Prophet Mohammad SAW.
Alhamdullialh and thanks to Allah, who gives me the commitment and strength to finish this research. First and foremost, I would like to thank my parents for their love, understanding, patience and encouragement during my M.Sc. candidature. Their doa and blessing has allowed me to complete my thesis successfully.
I would like to express my gratitude to the spirit of my ex- supervisor Professor Dr.
Mohd. Nasir Zainal Arif for his encouragement and advice to complete my master work in field of geopolymers. My most sincere thanks go to my co-supervisor Professor Dr.
San Myint for her supervision, guidance, and encouragement throughout the course of this research. I also indebted to my supervisor Mr. Mohd. Mustafa Al-Bakri Abdullah for many insightful discussion and helpful criticism. Without their help, I would not have been able to achieve what I have achieved.
I dedicated special thanks to all doctors, lecturers, and technicians at school of Materials Engineering, University of Malaysia Perlis (UniMAP) for their supporting.
Last, but not least, my appreciation to my family and friends for their support during my study.
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
UNIVERSITY MALAYSIA PERLIS
NOTES : * If the thesis is CONFIDENTIAL or RESTRICTED, please attach with the letter from the organization with period and reasons for confidentially or restriction.
NOTES : * If the thesis is CONFIDENTIAL or RESTRICTED, please attach with the letter from the organization with period and reasons for confidentially or restriction.
DECLARATION OF THESIS
Author’s full name : OMAR A.K.A. ABDUL KAREEM...
Date of birth : 18/8/1983...………...
Title : THE ROLE OF ALKALINE ACTIVATOR IN
GEOPOLYMERIZATION OF LOW-CALCIUM FLY ASH BASED GEOPOLYMERS ………..
Academic Session : 2009-2010...………....
I hereby declare that the thesis becomes the property of Universiti Malaysia Perlis (UniMAP) and to be placed at the library of UniMAP. This thesis is classified as :
CONFIDENTIAL (Contains confidential information under the Official Secret Act 1972)*
RESTRICTED (Contains restricted information as specified by the organization where research was done)*
OPEN ACCESS I agree that my thesis is to be made immediately available as hard copy or on-line open access (full text)
I, the author, give permission to the UniMAP to reproduce this thesis in whole or in part for the purpose of research or academic exchange only (except during a period of years, if so requested above).
Certified by:
_________________________ ______________________________
SIGNATURE SIGNATURE OF SUPERVISOR
_________G2031828 _________ Mr. Mohd. Mustafa Al-Bakri Abdullah (NEW IC NO. / PASSPORT NO.) NAME OF SUPERVISOR
Date: 29/05/2010 Date: 29/05/2010
√
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
iii Peranan pengaktif beralkali dalam proses pengeopolimeran bagi fly ash rendah
kalsium berasaskan geopolymer
ABSTRAK
Polimer bukan organik atau geopolimer ringkas telah disintesis dalam kajian ini dengan pemangkin beralkali dari sisa abu pembakaran berkalsium rendah tempatan (Kelas F).
Cecair pemangkin beralkali yang digunakan untuk proses pengaktifkan adalah campuran silikat sodium (waterglass) dan larutan natrium hidroksida (NaOH). Tujuan utama kajian ini adalah untuk mengkaji kesan kandungan dan unsur nisbah campuran pemangkin beralkali (silikat sodium dan larutan NaOH) pada kekuatan mampatan dan stuktur mikro hasil daripada geopolimer berkalsium rendah berasaskan sisa abu pembakaran. Geopolimer disediakan pada parameter operasi tetap, yang meliputi: kosentrasi larutan NaOH (15M), air tambahan (17%
daripada berat geopolimer), masa campuran (15 minit), masa pengembangan (24 jam), suhu curing (70° C), masa curing (24 jam) dan masa penuaan (24 jam). Kandungan pemangkin beralkali diverifikasi berdasarkan nisbah jisim Pemangkin/Sisa abu pembakaran digunakan di dalam kajian masa ini, iaitu (0.3, 0.35 dan 0.4), dan nisbah unsur campuran pemangkin beralkali atau nisbah silikat sodium/NaOH (0.6, 0.8, 1.0 and 1.2) disahkan. Kekuatan tekanan yang tertinggi dikekalkan pada kandungan pemangkin beralkali (Pemangkin/Sisa abu pembakaran = 0.4). Kekuatan mampatan dan data SEM menunujukkan bahawa bagi setiap nisbah Pemangkin/Sisa abu pembakaran (0.3, 0.35 dan 0.4), nisbah optimum silikat sodium/NaOH (masing-masing 0.8, 1.0 dan 1.0); memberikan kekuatan mampatan dan keseragaman paling tinggi, pengurangan liang pada struktur mikro dengan pengurangan tindak balas pada sisa abu pembakaran. Analisa XRD menunjukkan pembentukkan geopolimer pada nisbah optimum silikat sodium/NaOH terutama amorphous dengan kewujudan fasa penghabluran yang sedia ada di dalam sisa abu pembakaran dan sesetengah fasa zeolatik yang terbentuk semasa proses geopolimer. Kekuatan mampatan geopolimer optimum (8.61 Mpa, nisbah Pengaktif/Sisa abu pembakaran = 0.4 dan silikat sodium/NaOH = 1.0), menunjukkan kebolehan terma yang rendah pada 400° C, berdasarkan formasi daripada keretakan makro pada permukaan sampel yang disebabkan oleh pengewapan air dan kemerosotan akan berlaku serta proses pesinteran berlangsung pada suhu yang lebih tinggi iaitu 600°C dan 800°C.
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
The role of alkaline activator in geopolymerization process of Low-calcium fly ash based geopolymers.
ABSTRACT
Inorganic polymers or simply geopolymers were synthesized in this study by the alkaline activation of local low-calcium (Class F) fly ash. The alkaline activator liquid used for the activation process was a mixture of sodium silicate (waterglass) and sodium hydroxide (NaOH) solution. The main purpose of the research was to study the effect of the alkaline activator content and the alkaline activator constituents (Waterglass and NaOH solution) mixing ratio, on the compressive strength and on the microstructure of the resulted low- calcium (Class F) Fly ash-based geopolymer. The geopolymers were prepared at fixed operation parameters, which were including: the concentration of NaOH solution (15M), additional water (17% of the geopolymer weight), mixing time (15min), dilation time (24hr), curing temperature (70°C), curing time (24hr), and aging time of (24hr). The alkaline activator content was verified according to the Activator/Fly ash mass ratios utilized in the current research, which were (0.3, 0.35, and 0.4), and verified the mixing ratios of the alkaline activator constituents or waterglass/NaOH ratios were (0.6, 0.8, 1.00, and 1.2). The highest compressive strength was obtained at highest alkaline activator content (Activator/Fly ash
=0.4). The compressive strength and the SEM data also showed that for each Activator/Fly ash ratio (0.3, 0.35, and 0.4), an optimum waterglass/NaOH ratio of (0.8, 1.00, and 1.00 respectively); give the highest compressive strength and a homogenous, less porosity microstructure with less unreacted fly ash spheres. XRD analysis showed that the formed geopolymers at the optimum waterglass/NaOH ratios were mainly amorphous with presence of crystalline phases existed in the original fly ash and some zeolitic phases were formed during the geopolymerization process. The optimum compressive strength geopolymer (8.61 MPa, Activator/Fly ash ratio = 0.4, and waterglass/NaOH =1.00), shows low thermal durability at 400°C, by the formation of macrocracks on the sample surface due to the water evaporation and further deterioration and sintering process takes place at higher temperatures of 600 &
800°C.
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
v TABLE OF CONTENTS
Page
ACKNOWLEDGEMENT……… i
APPROVAL AND DECLARATION……….. ii
ABSTRAK……….. iii
ABSTRACT………... iv
TABLE OF CONTENTS……….. v
LIST OF TABLES……… x
LIST OF FIGURES……….. xi
LIST, OF SYMBOLS, ABBREVIATIONS OR NUMENCLATURE ……… xv
CHAPTER 1- INTRODUCTION 1.1 Background……….. 1
1.2 Problem Statement ……….. 3
1.3 The Geopolymerization Mechanism ………... 4
1.4 Low-Calcium Fly(Class F) ash Based Geopolymer ………. 5
1.5 Objectives Of The Research ……….……… 6
CHAPTER 2 -LITERATURE REVIEW 2.1 Introduction ………... 8
2.2 Fly Ash ……… 8
2.3 Introduction Of Geopolymers ……….………. 10
2.4 Constituent Of Geopolymers ………... 12
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
2.4.1 Source Materials ………... 12
2.4.2 Alkaline Activator Liquid …………..……….………… 14
2.5 Synthesis Of Fly Ash-Based Geopolymer ……… 15
2.5.1 Mixture Proportion ……….…………... 15
2.5.1.1. The mass mixing ratio of Activator/Fly ash ……… 17
2.5.1.2. The mass mixing ratio of waterglass/NaOH ……… 19
2.5.2 Factors influencing the fly ash-based geopolymer synthesis …. 20 2.6 Structure Of Geopolymers ………... 24
2.7 Microstructure Of Geopolymers ………... 26
CHAPTER 3- RESEARCH METHODLOGY 3.1 Raw Materials ………. 28
3.1.1 Sodium hydroxide solution (NaOH) ……… 28
3.1.2 Sodium silicate liquid (waterglass) ……….…….. 28
3.1.3 Fly ash………. 29
3.2 Fly Ash Analysis ……… 29
3.2.1 (XRF) analysis of the fly ash………. 29
3.2.2 The fly ash particle size distribution……… 29
3.3 Preparation Of The Alkaline Activators Solution……….... 29
3.3.1 Preparation of 15M NaOH ……….. 30
3.3.2 Procedure………... 30
3.4 Synthesizing The Fly Ash-Based Geopolymers With Different Activator/Fly Ash Ratios………... 31
3.4.1 Mixing ………..………. 31
3.4.2 Molding, Curing and Aging……….. 33
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
vii 3.5 Synthesis Of Fly Ash-based Geopolymer With Different
waterglass/NaOH Ratio At Different Activator/Fly ash Ratio ……. 36
3.5.1 Mixing, Molding, Curing and Aging………... 37
3.5.2 Optimization of waterglass/NaOH mixing ratio in mass……….. 37
3.6 Analysis Method………. 37
3.6.1 Mechanical compressive strength………. 37
3.6.2 Morphology analysis……….. 39
3.6.2.1. X-Ray Diffraction (XRD) ……… 39
3.6.2.2 Scanning Electron Microscopy (SEM)………. 40
3.7 SEM Study On Fly Ash-Based Geopolymer At Elevated Temperatures ………... 40
3.7.1. Procedure………. 40
3.7.2. Scanning electron microscopy (SEM) analysis ……… 41
CHAPTER 4- RESULT AND DISCUSSION 4.1 Analysis Of The Fly Ash ………... 42
4.1.1 The composition of the fly ash ……… 42
4.1.2 Particle size distribution of the fly ash ………... 43
4.2 The Effect Of Different Activator/Fly ash Mass Mixing Ratio On The Workability Of The Fresh Fly Ash-Based Geopolymer Mixture At Constant waterglass/NaOH Ratio ………. 44
4.3 The Effect Of Activator/Fly ash Mass Mixing Ratio On the Compressive Strength Of The Fly Ash-Based Geopolymer At Constant waterglass/NaOH Ratio ……….. 46
4.3.1 Total water content (based water+ additional water) …………... 47
4.3.2 SiO2 species content ……….. 48
4.3.3 Na2O species content ……… 50
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
4.3.4 Waterglass content ………... 52
4.4 The Influence Of waterglass/NaOH Mass Mixing Ratio On The Compressive Strength Of Fly Ash Based-Geopolymers Synthesized At Different Activator/Fly ash Ratio ……... 54
4.4.1 The effect of the SiO2/Al2O3 molar ratio ………... 56
4.4.2 The effect of Na2O/SiO2 molar ratio ………... 58
4.4.3 The effect of Na2O/ Al2O3 molar ratios ………... 60
4.4.4 The effect of H2O/Na2O molar ratio ………... 63
4.4.5 The effect of percent waterglass content in geopolymers ……... 65
4.5 Microstructure Study On The Fly Ash And Resulted Geopolymers ... 68
4.5.1 Microstructure of original fly ash ……… 69
4.5.2 Microstructure of geopolymers synthesized at waterglass/ NaOH =0.6 ……….. 70
4.5.3 Microstructure of geopolymers synthesized at waterglass / NaOH =0.8 ……….. 72
4.5.4 Microstructure of geopolymers synthesized at waterglass/ NaOH =1.00 ………... 73
4.5.5 Microstructure of geopolymers synthesized at waterglass/ NaOH =1.2 ……….. 75
4.6 X-ray Diffraction Of The Original Fly Ash And Optimum Compressive Strength Geopolymers………... 78
4.7 SEM Study Of The Optimum Compressive Strength Fly Ash-Based Geopolymer At Evaluated Temperatures ………. 81
CHAPTER 5 CONCLUSION AND FUTURE WORK 5.1 Conclusions ……… 85
5.2 Future Work ……….……... 87
REFERENCE……… 89
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
ix
APPENDIX A ………... 96
APPENDIX B ………... 97
APPENDIX C ……… 98
APPENDIX D ……… 99
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
LIST OF TABLES
Table No. Page
2.1 Composition of geopolymers prepared from fly ash and bottom ash
(Chindaprasirt et al. 2009) ………. 18
2.2 Effect of waterglass/NaOH solution and NaOH concentration of (Class F) fly ash-based geopolymers. (Hardjito & RaNgan 2005) ... 19
2.3 Dramatic difference of fly ash-based geopolymer (Jaarsveld et al. 1998, Swanepoel & Strydom 2002)………... 21
2.4 Curing regimes on fly ash-based geopolymer development……….. 23
3.1 Details of mixtures proportion ……….. 31
3.2 Details of mixture proportions ……….. 38
4.1 XRF analysis data of Fly ash composition ……… 43
4.2 Fly ash particle size analysis data ………. 44
4.3 Effect of the Activator/Fly ash ratio on the workability and water content in geopolymer ………... 45
4.4 Effect of the Na2O content on the molar ratios of Na2O/Al2O3 and Na2O/SiO2 ………. 52
4.5 Increasing the H2O/Na2O molar ratio of the resulted geopolymers with increasing in waterglass/NaOH ratio from (0.6-1.2) at different Activator/Fly ash ratios (0.3, 0.35, and 0.4) ………... 64
4.6 Increasing the waterglass percentage of the resulted geopolymers with increasing in waterglass/NaOH ratio from (0.6-1.2) at different Activator/Fly ash ratios (0.3, 0.35, and0.4) ……… 68
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
xi LITS OF FIGURES
Figure No. Page
2.1 The poly (sialates) structures according to Davidovits (2005)…….. 11
2.2 Effect of H2O/Na2O molar ratio on compressive strength (Hardjito & Rangan 2005) ………. 17
2.3 Influence of curing temperature on strength development (Hardjito et al., 2002) ……… 22
2.4 XRD patterns of the base materials and Na-poly (sialate-siloxo, PSS) polymers (Barbosa et al. 2000). PSS1(SiO2/Al2O3=3.3), Na2O/SiO2=0.25,H2O/Na2O=10), PSS2(SiO2/Al2O3=3.3, Na2O/ SiO2=0.25,H2O/Na2O=25) and PSS7SiO2/Al2O3=3.8,Na2O/SiO2= 0.30, H2O/Na2O=17.5 ... 25
2.5 XRD patterns of alkali activated fly ash mortars (Fernandez- Jimenez and Palomo 2005). Q= quartz from fly ash and sand aggregate; M= Mullite; F= hematite; C= CaO; H= herchelite; X=hydroxysodalite; T=trona; N= nahcolite ………... 26
2.6 Microstructure of the fly ash-based geopolymer (Palomo et al., 1999 a) ………... 27
3.1 The fresh geopolymer during mechanical mixing ………. 32
3.2 Standard steel mold used for samples casting (50×50×50mm) …… 34
3.3 Molded and wrapped geopolymers samples ……….. 34
3.4 Curing the geopolymers in the furnace ……….. 35
3.5 Demolding the geopolymer samples from molds ……….. 35
3.6 Geopolymers samples after 7 days of aging ……….. 36
3.7 Geopolymer samples on compression testing. (A) Before testing and (B) After ………... 39
4.1 Particle size distribution of the fly ash ………... 43
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
4.2 Effect of different Activator/Fly ash ratio on the compressive strength of Fly ash-based geopolymer at constant waterglass/NaOH
ratio of 1.00 ……… 46
4.3 Effect of SiO2/Al2O3 molar ratio on the compressive strength of fly ash-based geopolymer at different Activator/Fly ash ratio ………… 49 4.4 Effect of Na2O content on the compressive strength of fly ash based
geopolymers at different Activator/Fly ash ratio ………... 51
4.5 Effect of the percent waterglass for each Activator/Fly ash ratio on the compressive strength of the fly ash-based geopolymer at
constant Activator/Fly ash ratio ………. 53
4.6 The effect of different waterglass/NaOH ratio on the compressive strength of the fly ash-based geopolymers at each different Activator/Fly ash ratio (0.3, 0.35 and 0.4)……….. 54 4.7 The increased in the SiO2/Al2O3 molar ratio of the fly ash based
geopolymers with increased in waterglass/NaOH ratio from 0.6 to
1.2 ……….. 56
4.8 The effect the SiO2/Al2O3 molar ratio and the compressive strength of the resulted geopolymers with increased in waterglass/NaOH ratio from 0.6 to 1.2 ………... 57 4.9 Decreased in Na2O/ SiO2 molar ratio with increased in
waterglass/NaOH ratios of the fly ash based geopolymers synthesized at different Activator/Fly ash ratio (0.3, 0.35, and 0.4).. 60 4.10 The effect of Na2O/SiO2 molar ratio with increased
waterglass/NaOH ratio (0.6 to 1.2) of geopolymers on the compressive strength of the resulted geopolymers synthesized at Activator/Fly ash ratios of (0.3, 0.35 and 0.4) ………... 60 4.11 Decreased in Na2O/Al2O3 molar ratio with increased
waterglass/NaOH mass ratio of the fly ash based geopolymers at different Activator/Fly ash ratio (0.3, 0.35, and 0.4 ……….. 62 4.12 Figure 4.12: The effect of Na2O/Al2O3 molar ratio with increased in
waterglass/NaOH ratio from (0.6 to 1.2) on the compressive strength of the resulted geopolymers synthesized at Activator/Fly
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
xiii ash ratios of (0.3, 0.35 and 0.4) ………. 62 4.13 The effect of the different waterglass/NaOH ratios on the H2O/
Na2O molar ratio and the compressive strength of the resulted geopolymers synthesized at Activator/Fly ash ratios of (0.3, 0.35
and 0.4) ……….. 63
4.14 The effect of the different waterglass/NaOH ratios on the waterglass% and the compressive strength of the resulted geopolymers synthesized at Activator/Fly ash ratios of (0.3, 0.35
and 0.4) ……….. 67
4.15 SEM micrograph of the base material (fly ash) ………. 69 4.16 SEM micrographs of the original fly ash and the resulted
geopolymers at Activator/Fly ash ratios of (0.3, 0.35, and 0.4), synthesized at waterglass/NaOH of 0.6 ………. 71 4.17 SEM micrographs of the original fly ash and the resulted
geopolymers at Activator/Fly ash ratios of (0.3, 0.35, and 0.4), synthesized at waterglass/NaOH of 0.8 ………. 73 4.18 SEM micrographs of the original fly ash and the resulted
geopolymers at Activator/Fly ash ratios of (0.3, 0.35, and 0.4), synthesized at waterglass/NaOH of 1.00 ………... 75 4.19 SEM micrographs of the original fly ash and the resulted
geopolymers at Activator/Fly ash ratios of (0.3, 0.35, and 0.4), synthesized at waterglass/NaOH of 1.2 ………. 77 4.20 X-ray diffraction pattern of the original fly ash. Q = quartz, M =
mullite ……… 79
4.21 X-ray diffraction pattern of geopolymer synthesized at Activator/Fly ash ratio 0.3, waterglass/NaOH 0.8. Q = quartz, M = mullite, S = hydroxysodalite, H = herschelite ………... 80 4.22 X-ray diffraction pattern of geopolymer synthesized at
Activator/Fly ash ratio 0.35, waterglass/NaOH 1.00. Q = quartz, M
= mullite, S = hydroxysodalite, H = herschelite ……… 80 4.23 X-ray diffraction pattern of geopolymer synthesized at
Activator/Fly ash ratio 0.4, waterglass/NaOH 1.00. Q = quartz, M =
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
mullite, S = hydroxysodalite, H = herschelite ………... 81 4.24 The optimum Fly ash-based geopolymers with optimum
compressive strength of 8.61 MPa, Activator/Fly ash ratio= 0.4 and waterglass/NaOH ratio = 1.00, after heat treatment at (400, 600,
and 800°C respectively) ………. 82
4.25 SEM micrographs of fly ash-based geopolymers (Activator/Fly ash ratio= 0.4, waterglass/NaOH ratio = 1.00), before heat treatment and after heat treatment at (400, 600, and 800°C respectively) ……. 84
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
xv LIST OF SYMBOLS, ABBREVIATIONS OR NUMENCLATURE
OPC Ordinary Portland Cement
Si Silicon
Al Aluminum
O Oxygen
Na Sodium
K Potassium
Ca Calcium
Mg Magnesium
M+ Alkali Ion
CO2 Carbon dioxide
CaO Calcium Oxide
H2O Water
Na2O Sodium Oxide
Al2O3 Aluminum Oxide
SiO2 Silicon Oxide
Fe2O3 Iron Oxide
NaOH Sodium hydroxide
KOH Potassium hydroxide
Waterglass Sodium Silicate Solution Class F Low-calcium Fly ash Class C High-calcium Fly ash
XRD X-ray Diffraction
ACI American Concrete Institute
LOI Loss On Ignition
% Weight percent
SEM Scanning Electron Microscopy
m Meter
Al-Si Aluminosilicate
M Molar
MPa. Mega Pascal
θ Theta
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
RT Room Temperature
PSS Polymer(sialate-siloxo)
cP Centipoise
cc Centimeter Cubic
gm Gram
hr Hour
°C Degree Celsius
min Minute
mm Millimeter
ASTM American Standard Testing Material
KN Kilo Newton
kV Kilo Volt
Å Angstrom
S Second
Mam Milliampere
µm micrometer
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
1 CHAPTER 1
INTRODUCTION
1.1Background
Concrete usage around the world is second only to water. Ordinary Portland cement (OPC) is conventionally used as the primary binder to produce concrete. The environmental issues associated with the production of OPC are well known (Hardjito et al., 2005). The amount of carbon dioxide released during the manufacture of OPC due to the calcination of limestone and combustion of fossil fuel is in the order of one ton for every ton of OPC production. In additional, the extent of energy required to produce OPC is only next to steel and aluminum.
As early as the 1980s Davidovits proposed a controversial theory that some of the Pyramids in Egypt were not built by mining limestone blocks and moving them into place but were cast in place and allowed to set, creating an artificial zeolitic rock. This theory, which gained acceptance, culminated in a book “The Pyramids An Enigma Solved”, written together with Magie Morris and published in 1988. Intensive research, initiated by Davidovits and co-workers, to prove this theory has resulted in the rediscovery of a new family of mineral polymers, which they called alkali -activated aluminosilicate geopolymer or simply geopolymers. This name was chosen because of the similarities with organic condensation polymers in regards to their hydrothermal synthesis conditions (Davidovits, 1982; Davidovits & Sawyer, 1985; Davidovits, 1988;
Davidovits, 1994a).
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
Over the last twenty years, geopolymer also known as mineral polymer or inorganic polymer glasses, have received much attention as a promising new form of inorganic polymer material that could substantially substitute for conventional or ordinary Portland cement, plastics and many mineral-based products. However, to date the exact mechanisms that cavern geopolymerization are still not fully understood (Hardjito et al., 2005).
Geopolymers are members of the family of inorganic polymers. The chemical composition of the geopolymer material is similar to natural zeolitic materials, but the microstructure is amorphous. Zeolites composition is based on aluminosilicate framework and three dimensional network inorganic polymers built up of (Si, Al) O4
tetrahedra linked by sharing oxygen atoms into rings and cages. The polymerization process (geopolymerization) involves a substantially fast chemical reaction under alkaline condition on Si-Al minerals that result in a three dimensional polymeric chain and ring structure consisting of Si-O-Al-O bonds (Davidovits, 1994a).
Moreover, as the geopolymers synthesizing technology is basing on the alkaline activation of source materials contains mostly Silicon (Si) and Aluminum (Al) in amorphous form (Hardjito et al., 2004), the similarity of some fly ashes to natural aluminosilicates (due to the presence of SiO2 and Al2O3 in the ash) has encouraged the use of geopolymerization as a possible technology solution in the making of special cement (Silvestrim et al., 1997, 1999). The successful stabilization and immobilization of some toxic heavy metals in geopolymeric material by Jaarsveld et al. (1998), Jaarsveld & Deventer (1999), has also encouraged the use of this fairly new technology.
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
3 1.2Problem Statement
Most researches done on the fly ash-based geopolymers were focusing on the manufacturing of fly ash-based geopolymers, and study the operation parameters influencing on the mechanical properties of the resulted concrete like mixing time, NaOH solution concentration, curing temperatures, curing time, aging conditions, chemical resistance property, aggregate materials content, and the Microstructure characterization of the produced geopolymer at range of Activator/Fly ash ratios 0.25 to 0.45( Palomo et al., 1999a; Jaarsveld et al, 1998; Jaarsveld & Deventer, 1999; Xu &
Deventer, 2000; Bakharev, 2005; Hardjito & Rangan, 2005 and Fernandez-Jimenez &
Palomo, 2003). These others used low-calcium (Class F) fly ash as based materials for making geopolymers. The alkaline activator used in the activation process was mixture of sodium waterglass and NaOH solution mixed at constant waterglass/NaOH.
However, very little was available in the published literature regarding to the effect of the waterglass/NaOH mass ratio on the mechanical compressive strength and microstructure of low-calcium (Class F) fly ash-based geopolymer.
Whereas, Chindaprasirt et al. (2007), reported the effect of the mass mixing ratio of waterglass/NaOH, on the workability and compressive strength of geopolymers synthesized using high-calcium (Class C) fly ash. They used range of waterglass/NaOH ratios of 0.67, 1.00, 1.5, and 3.0.
This research was therefore dedicated on study the role of the alkaline activator (waterglass + NaOH solution) content and mixing procedure on the mechanical
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
compressive strength and microstructure properties of low-calcium fly ash based geopolymers synthesized at different Activator/Fly ash ratios.
1.3The Geopolymerization Mechanism
The exact reaction mechanism which explains the setting and the hardening of alkali-activated geopolymers is not yet quit understood, although it is thought to be depended on the prime material as well as on the alkali activator. According to Glukhovsky et al. (1980), the mechanism of alkali- activation is composed of conjoined reactions of destruction-condensation ,that include the destruction of the prime material in to low stable structural units ,their interaction with coagulation structures and creation of condensation structures . The first steps consist of breakdown of covalent bounds Si-O-Si and Al-O-Si, which happened when the PH of the alkali solution rises, so those groups are transformed in a colloid phase. Then an accumulation of the destroyed products occurs, which interacts among them to form a coagulated structure, leading in a third phase to the generation of a condensed structure.
However, Zuhua et al. (2009) reported that the geopolymerization process occurred approximately into two periods: the dissolution- hydrolysis period and the hydrolysis-polycondensation period. But the fact, these two steps probably occur simultaneously once the solid material mixed with the alkaline activator (Hongling &
Deventer, 2003). The exact separation of these two steps is hard and the partition here is only from the point of view of thermodynamics, the period (I) including the dissolution of the SiO2 and Al2O3 species and hydrolyses it, as indicated in the equations (1.1) to (1.3), (Zuhua et al., 2009).
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
5
_
OH
–Si – O – Si– + H2O 2–Si – OH (Eq.1.1) _
OH
–Al – O – Al – + H2O 2– Al – OH (Eq.1.2)
_ OH
–Si– O –Al – + H2O – Si – OH + –Al –OH (Eq.1.3)
_ OH OH OH / /
– Si – OH + – Al – OH HO – Si – O – Al – OH + H2O (Eq.1.4) / /
OH OH
NaOH / /
n (OH)3– Si – O – Al(OH)3 Na+ ….(Si – O – Al – O)n +3n H2O (Eq.1.5) / /
OH OH / / NaOH / /
n(OH)3– Si – O – Al – O– Si – (OH)3 Na+...( – O –Si – O – Al – O – Si – )n + / / / /
OH OH 3nH2O (Eq.1.6)
The water is the reactant in this period, if the (OH-) concentration is high enough; more water will accelerate the dissolution and hydrolysis period. In the meantime, the water plays as product in the period (II), as indicated in equations (1.4) to (1.6). If the water content is too much, will hinder the geopolymerization kinetically (Zuhua et al., 2009).
1.4Low-calcium (Class F) Fly Ash Based Geopolymer
In this research, the Low-calcium (Class F) fly ash is used as binder, instead of OPC or any hydraulic cement paste. The alkaline activator used for activated the fly ash,
© T hi s it em is p ro te ct ed by o rig in al co py rig ht
was a mixture of sodium waterglass and sodium hydroxide solution NaOH. The preparation procedure was aiming to verify the alkaline activator content as well as the mixing procedure of the activator liquid constituents, in order to investigate the influence of the changing parameters on the mechanical compressive strength and the microstructure of the prepared geopolymers. Therefore, the operation parameters including (NaOH solution concentration, mixing time, dilation time, curing temperature, curing time, and aging period) were fixed during the preparation processes. And no aggregate materials or admixtures were used in the preparation process. The geopolymers materials were prepared at Activator/Fly ash ratios of (0.3, 0.35, and 0.4) following the recommended range of Activator/Fly ash ratios (0.3-0.45), suggested by Rangan (2008).
1.5Objectives Of The Research
This research have been done in order to investigate the effect of the alkaline activator content and mixing procedure on the mechanical compressive strength and the microstructure of low-calcium (Class F) fly ash based geopolymers. Regarding to this scope the following objectives has been taken for this research:
1. To identify the effect of Activator/Fly ash ratio on the workability of fresh paste and on the mechanical compressive strength of the hardened low-calcium (Class F) fly ash based geopolymer.
2. To study the effect of alkaline activators (waterglass/NaOH ) mass ratio on the compressive strength and the microstructure of low-calcium (Class F) fly ash
