GPC Swamy

“PERFORMANCE OF GEOPOLYMER CONCRETE AT ELEVATED TEMPERATURE ” Dissertation submitted to

VISWESVARAIAH TECHNOLOGICAL UNIVERSITY, BELGAUM, KARNATAKA In partial fulfillment of the requirements for the award of the degree of

MASTER OF TECHNOLOGY IN CONSTRUCTION TECHNOLOGY By

KEDARA SWAMY .U Reg. No. 1BM05CCT07 Under the guidance of

Dr. SAKEY SHAMU Mr. M. S. SUDARSHAN

Department of Civil Engineering

B. M. S. COLLEGE OF ENGINEERING BANGALORE - 560 019 OCTOBER- 2007

“PERFORMANCE OF GEOPOLYMER CONCRETE AT ELEVATED TEMPERATURE ” Dissertation submitted to

VISVESWARAIAH TECHNOLOGICAL UNIVERSITY, BELGAUM, KARNATAKA In partial fulfillment of the requirements for the award of the degree of

MASTER OF TECHNOLOGY IN CONSTRUCTION TECHNOLOGY By

KEDARA SWAMY .U Reg. No. 1BM05CCT07 Under the guidance of

Dr. SAKEY SHAMU Mr. M. S. SUDARSHAN

Department of Civil Engineering

B. M. S. COLLEGE OF ENGINEERING BANGALORE - 560 019 OCTOBER- 2007

CERTIFICATE This is to certify that the dissertation entitled an “PERFORMANCE OF GEOPOLYMER CONCRETE AT ELEVATED TEMPERATURE ” being submitted by Mr. Kedara swamy .U to the Visveswaraya Technological University, Belgaum for the award of degree of Master of Technology in Construction Technology, is a record of bonafide work carried out by him during the year 2006-2007. Mr. Kedara Swamy U. has worked under my guidance and supervision and has fulfilled the requirements for the submission of this thesis, which to my knowledge has reached the requisite standards. Dr. Sakey Shamu

Dr. R. V. Ranganath

Professor Dept. of Civil Engg. B. M. S. College of Engg Bangalore

Professor & H.O.D Dept. of Civil Engg. B.M.S. College of Engg Bangalore

Mr. M. S. Sudarshan

Dr. M. K. Venkatesha

Director (Technical) Civil Aid Techno clinic Pvt. Ltd. Bangalore

Principal B. M. S.College of Engg. Bangalore

Examiners: 1. 2.

Signature with Date

DECLARATION I, the undersigned declare that this dissertation work entitled “PERFORMANCE OF GEOPOLYMER CONCRETE AT ELEVATED TEMPERATURE”, is a bonafide work carried out by me (during 2006 – 2007) in partial fulfillment of the requirements for the award of post graduate degree of Master of Technology in Construction Technology of Visveswaraiah Technological University, Belgaum and is based on the study carried out under the guidance of Dr. Sakey Shamu & Mr. M. S. Sudarshan in B. M. S. College of Engineering, Bangalore. I also declare that this thesis has not been submitted to any other university or institution for the award of any degree.

KEDARA SWAMY.U Reg. No. 1BM05CCT07 B. M. S. College of Engineering Bangalore.

ACKNOWLEDGEMENT I wish to express my sincere regards and heartfelt gratitude to Dr. Sakey Shamu, Professor Department of Civil Engineering & Mr. M. S. Sudarshan, Director, Civil Aid Techno Clinic Pvt. Ltd, under whose guidance, this study was carried out. Their constant encouragement, valuable suggestions and deep involvement were the source of inspiration and motivation for successful completion of this project. I am grateful to Dr. R. V. Ranganath, Head of the Civil Engineering Department, B. M. S. College, Bangalore, for his informative inputs during the course of this project. I am grateful to Dr. N. Suresh, Director, BFRC, NIE, Mysore, who has given me the opportunity to carry out work in his organization. I am also extremely thankful to staff of Civil Aid Techno Clinic Pvt. Ltd, Bangalore for their co-operation throughout the course of this study. I am thankful to Mr. C. V. Parthasarathy and all the technicians of concrete laboratory for helping me in the experimental work. I am deeply indebted to all the faculty members of Department of Civil Engineering, BMSCE, Bangalore for their knowledgeable advice throughout the course of this study. I wish to convey my special thanks to all the staff of Geo-Technical laboratory for their constant help and co-operation.

My deepest and utmost sincere thanks to my classmates Mr. Hanamanth Reddy G Furme and Mr. Mohammed Saleh for their constant help throughout the experimental work. I wish to express my heartfelt gratitude to my parents and family members for their moral support and valuable suggestions during my study. Last, but not the least, I thank my classmates and friends for the encouragement and support throughout my course. KEDARA SWAMY.U

ABSTRACT The increase in the green house effect causes ecological imbalance contributing to global warming which is at alarming rate. The cement industry is responsible for about 6% of all CO 2 emissions, because the production of one ton of Portland cement emits approximately one ton of CO2 into the atmosphere. In order to over come the green house effect caused by the manufacturing of the ordinary Portland cement an immediate need arise to find a suitable substitute for ordinary Portland cement. The discovery of geopolymers is a breakthrough which provides a cleaner and environmentally-friendlier alternative to Ordinary Portland Cement (OPC). Geopolymer is a new breed of fly ash which is an end product in thermal power plant. Geopolymer concrete is a revolutionary substitute to conventional ordinary Portland cement concrete with lot of advantages. Fire represents one of the most severe exposure conditions and hence provisions for appropriate fire resistance for structural members are major safety requirements in any building design. In order to predict the fire resistance of a structure, the temperatures in the structure must be determined. The fire resistance of structural members is dependent on the thermal and mechanical properties at elevated temperatures, of the materials of which the members are composed. This project aims at studying the performance of geopolymer concrete under elevated temperature. Performance of different GPC mixes were studied at varying test temperatures sustained for different durations. The specimens were heated for different temperatures namely 250 0 C, 400 0 C, 600 0 C,800 0 C sustained for duration of 2 hours and 4 hours. The mechanical properties like compressive strength, Young’s modulus, modulus of rupture were studied. A non destructive test was also conducted to assess the quality of the specimens exposed to different temperature ranges. SEM investigations were carried out to study the change in the microstructures at different temperatures.

Experimental investigations have shown that geopolymer concrete is likely to behave differently from

the conventional concrete when exposed to high temperatures. The

compressive strength exhibited by the geopolymer concrete was in the range of

(17.3- 94.93)

MPa. The ultra sonic pulse velocity (non-destructive test) of geopolymer concrete was in the range of (0.8-4.0) km/s. It is evident from the experimental research that the strength of the geopolymer concrete was greatly influenced by the curing temperature to which it is subjected and the duration, the chemical contents like sodium silicate to sodium hydroxide ratio is one of the governing factors.

CONTENTS CHAPTER 1

INTRODUCTION

1.1 General

1

1.2 Need for the present study 1.3 Objective of the study

3 4

1.4 Scope of the study

4

1.5 Organization of the thesis

5

CHAPTER 2

6

CHAPTER 3

LITERATURE REVIEW

GEOPOLYMER MATERIALS AND PROCESS

3.1 Geopolymer materials

13

3.1.1 Fly ash

13

3.1.2 Alkaline liquids

13

3.2 Geopolymerisation process

CHAPTER 4

14

EXPERIMENTAL INVESTIGATIONS

4.1

Experimental investigation

4.1

Materials

18

4.1.1 Flyash

18

4.1.2 Characteristics of aggregates used in the study

19

4.2 Proportioning of geopolymer concrete mix

21

4.3

21

Preparation of the specimens

4.3.1 Casting of the specimens

22

4.3.2 Curing of the specimens

23

4.4

Details of number of specimens

23

4.5

Exposing the specimens to Elevated Temperature

24

4.6

Test conducted

26

4.7

Physical Observation

26

4.7.1 Change in Colour

26

4.7.2 Aggregates

27

4.7.3 Cracks

27

4.7.4 Spalling

28

4.8

Compressive Strength test

28

4.9 Modulus of Elasticity test

29

4.10 Ultra Sonic Pulse Velocity test

31

4.11 Modulus of Rupture test

32

CHAPTER 5 5.1

RESULTS AND DISCUSSIONS

Physical observations

34

5.1.1 Discolouration

34

5.1.2 Aggregates

34

5.1.3 Cracking

35

5.1.4 Spalling

35

5.2

Results of Ultra Sonic Pulse Velocity test

36

5.3

Results of Compressive Strength test

43

5.4

Results of Modulus of Elasticity test

50

5.5

Results of Modulus of Rupture test

54

5.6

SEM results

62

CHAPTER 6

SUMMARY AND CONCLUSIONS

6.1 Summary

66

6.2 Conclusions

66

6.3 Scope for future study

68

LIST OF TABLES

4.1 - Physical characteristics of Fly Ash (RTPS)

17

4.2 - Chemical composition of Fly Ash

18

4.3 - Physical Characteristics of Aggregates

18

4.4 - Sieve Analysis Results of Fine Aggregate

19

4.5 - Sieve analysis results of Coarse Aggregate.

19

4.6 - Details of Geopolymer Concrete Mixtures

20

4.7 - Velocity criterion for Cement Concrete Quality Grading

31

5.1 - Physical Observation of the specimens in terms of Colour and Cracks.

34

5.2 - Ultra Sonic Pulse Velocity test results for the specimens subjected to different temperature and different sustained duration for mix 1.

36

5.3 - Ultra Sonic Pulse Velocity test results for the specimens subjected to different temperature and different sustained duration for mix 2.

38

5.4 - Ultra Sonic Pulse Velocity test results for the specimens subjected to different temperature and different sustained duration for mix 3.

40

5.5 - Ultra Sonic Pulse Velocity test results for the specimens subjected to different temperature and different sustained duration for mix 4.

42

5.6 - Compressive Strength test results for the specimens subjected to different temperature and different sustained duration for mix 1.

45

5.7 - Compressive Strength test results for the specimens subjected to different temperature and different sustained duration for mix 2.

47

5.8 - Compressive Strength test results for the specimens subjected to different temperature and different sustained duration for mix 3.

49

5.9 - Compressive Strength test results for the specimens subjected to different temperature and different sustained duration for mix 4. 5.10 - Shows the results of Modulus of Elasticity of Geopolymer Concrete.

51 54

5.11 - Modulus of Rupture test results for the specimens subjected to different temperature and different sustained duration.

57

5.12 - Shows the Compressive Strength and Ultra Sonic Pulse Velocity results.

58

5.13 - Shows the Compressive Strength and Young’s Modulus results.

60

5.14 - Shows the Compressive Strength and Flexure Strength results.

61

LIST OF FIGURES

4.1 - Details of the specimens subjecting to different temperature and different sustained duration.

23

5.1(a) - Ultra Sonic Pulse Velocity test of the specimens sustained for 2 hours Subjected to different temperature for mix 1.

36

5.1(b)Ultra Sonic Pulse Velocity test of the specimens sustained for 4 hours subjected to different temperature for mix 1.

37

5.1(c) Ultra Sonic Pulse Velocity test results for the specimens subjected to different temperature and different sustained duration for mix 1.

37

5.2(a)Ultra Sonic Pulse Velocity test of the specimen sustained for 2 hours subjected to different temperature for mix 2.

38

5.2(b)Ultra Sonic Pulse Velocity test of the specimen sustained for 4 hours subjected to different temperature for mix 2.

39

5.2(c) Ultra Sonic Pulse Velocity test results for the specimens subjected to different temperature and different sustained duration for mix 2.

39

5.3(a)Ultra Sonic Pulse Velocity test of the specimen sustained for 2 hours subjected to different temperature for mix 3.

40

5.3(b)Ultra Sonic Pulse Velocity test of the specimen sustained for 4 hours subjected to different temperature for mix 3.

40

5.3(c) Ultra Sonic Pulse Velocity test results for the specimens subjected to different temperature and different sustained duration for mix 3.

41

5.4(a)Ultra Sonic Pulse Velocity test of the specimen sustained for 2 hours subjected to different temperature for mix 4.

42

5.4(b)Ultra Sonic Pulse Velocity test of the specimen sustained for 4 hours subjected to different temperature for mix 4.

43

5.4(c) Ultra Sonic Pulse Velocity test results for the specimens subjected to different temperature and different sustained duration for mix 4.

43

5.5(a) Variation of the Compressive Strength of specimens sustained for 2 hours at different temperature for mix 1.

46

5.5(b) Variation of the Compressive Strength of specimens sustained for 4 hours at different temperature for mix 1.

46

5.5(c) Variation of the Compressive Strength of specimens sustained for different duration at different temperature for mix 1.

47

5.6(a) Variation of the Compressive Strength of specimens sustained for 2 hours at different temperature for mix 2.

48

5.6(b) Variation of the Compressive Strength of specimens sustained for 4 hours at different temperature for mix 2.

48

5.6(c) Variation of the Compression Strength at different temperature and different sustained duration for mix 2.

49

5.7(a) Variation of the Compressive Strength of specimens sustained for 2 hours at different temperature for mix 3.

50

5.7(b) Variation of the compressive strength of specimens sustained for 4 hours at different temperature for mix 3.

50

5.7(c) Variation of the compression strength at different temperature and different sustained duration for mix 3.

51

5.8(a) Variation of the Compressive Strength of specimens sustained for 2 hours at different temperature for mix 4.

52

5.8(b) Variation of the Compressive Strength of specimens sustained for 4 hours at different temperature for mix 4.

52

5.8(c) Variation of the compression strength of specimens at different temperature and different sustained duration of mix 4.

53

5.9 - Comparison of results of Modulus of Elasticity of different mixes at different temperature sustained for 4 hours.

54

5.10(a) - Stress Strain Curves for mix 1, at different temperature sustained for 4 hours.

55

5.10(b) - Stress Strain Curves for mix 2, at different temperature sustained for 4 hours.

55

5.10(c) - Stress Strain Curves for mix 3, at different temperature sustained for 4 hours.

56

5.10(d) - Stress Strain Curves for mix 4, at different temperature sustained for 4 hours.

56

5.11 - Modulus of Rupture of different mixes at different temperature.

59

5.12 - Shows the Compressive Strength and Ultra Sonic Pulse Velocity results.

59

5.13 - Shows the Compressive Strength and Young’s Modulus results.

62

5.14 - Shows the Compressive Strength and Flexure Strength results.

62

5.15 - Micrographs of Geopolymer Concrete of mix 4 at different temperatures sustained for 4 hours.

63

LIST OF PLATES

Plate 1: Preparation of the specimen

22

Plate 2: Specimens kept in Oven for heat curing.

23

Plate 3: Specimens kept in Electric Oven for Elevated Temperature.

25

Plate 4: Specimens showing the change in Colour.

27

Plate 5: Surface cracks, and change in Colour on the specimen.

28

Plate 6: Compression test arrangement.

29

Plate 7: Arrangement for Modulus of Elasticity test.

30

Plate 8: Ultra Sonic Pulse Velocity test.

31

Plate 9: Shows the Arrangement of Flexure Test

33

CHAPTER 1

1.1 INTRODUCTION Fire represents one of the most severe exposure conditions. So the provisions for appropriate fire resistance for structural members are major safety requirements in any building design. In order to predict the fire resistance of a structure, the temperatures in the structures must be determined. The fire resistance of the structural members is dependent on the thermal and mechanical properties, at elevated temperatures, of the materials of which the members are composed. In recent years, the construction industry has shown significant interest in the use of various newer generations concrete. These concretes are likely to behave differently from the conventional concrete when exposed to high temperatures. The exposure of concrete to elevated temperature affects the physical and mechanical properties. Elements could distort and displace, and under certain conditions, the surface could spall due to the build up of steam pressure. Because thermally induced dimensional changes, loss of structural integrity, an release of moisture resulting from the migration of free water could adversely affect the structures operation and safety, a complete understanding of the behavior of new generation concrete under long term elevated temperature exposure is essential for reliable design evaluations. The demand for cement concrete as a construction material is on the increase. Due to increase in infrastructure developments, the demand for concrete would increase in the future. It is estimated that the production of cement will increase from about from 1.5 billion tons in 1995 to 2.2 billion tons in 2010 (Malhotra, 1999). The global warming is caused by the emission of greenhouse gases, such as CO2, to the atmosphere by human activities. Among the greenhouse gases, CO2 contributes about 65% of global warming (McCaffrey, 2002). The cement industry is responsible for about 6% of all CO2 emissions, because the production of one ton of Portland cement emits approximately one ton of CO2 into the atmosphere (Davidovits, 1994c; McCaffrey, 2002). One of the efforts to produce more environmentally friendly concrete is to replace the amount of Portland cement in concrete with by-product materials such as fly ash. An important

achievement in this regard is the development of high volume fly ash (HVFA) concrete that utilizes up to 60 percent of fly ash, and yet possesses excellent mechanical properties with enhanced durability performance. The test results show that HVFA concrete is more durable than Portland cement concrete (Malhotra 2002). Another effort to make environmentally friendly concrete is the development of inorganic alumina-silicate polymer, called Geopolymer, synthesized from materials of geological origin or by-product materials such as fly ash, metakaolin, silica fume, granulated blast furnace slag and rice husk ash, that are rich in silicon and aluminum (Davidovits 1994, 1999). In 1978, Davidovits introduced the word geopolymer which was used to describe an environmentally friendly material which possesses excellent strength and chemical properties. It also exhibits ceramic like properties with superior resistance to fire at elevated temperature. The low energy requirements of production from common raw materials and their inflammability at high temperatures, the geopolymers are attracting increasing interest as ecologically friendly fire proof building material, sound and heat insulators and materials for encapsulating hazardous wastes for storage or disposal. In this respect, the geopolymer technology proposed by Davidovits (1988a; 1988b)shows considerable promise for application in concrete industry as an alternative binder to the Portland cement. In terms of reducing the global warming, the geopolymer technology could reduce the CO2 emission to the atmosphere caused by cement and aggregates industries by about 80% (Davidovits, 1994c). Fly ash, one of the source materials for geopolymer binders, is available abundantly world wide, but to date its utilization is limited. From 1998 estimation, the global coal ash production was more than 390 million tons annually, but its utilization was less than 15% (Malhotra 1999). It is estimated that by the year 2010 the production of the fly ash will be about 780 million tones annually (Malhotra 2002). Accordingly, efforts to utilize this by-product material in concrete manufacture are important to make concrete more environmentally friendly. For instance, every million tons of fly ash that replaces Portland cement helps to conserve one million tons of lime stone, 0.25 million tons of coal and over 80 million units of power, not withstanding the abatement of 1.5 million tons of CO2 to atmosphere (Bhanumathidas and Kalidas 2004).

The motivation for using fly ash as the main raw material is driven by various factors: (1) It is cheap and available in bulk quantities (2) It is currently under-utilized except for its use as an additive in OPC (3) It has high workability and (4) It requires less water (or solution) for activation.

1.2 NEED FOR THE PRESENT STUDY It is evident from the present scenario that ordinary Portland cement is causing much of the environmental hazards such as Increasing green house gases.  Enormous consumption of power for the manufacture of cement.  Economic point of view. So considering all above points there is a need to find some alternative material. Any material which contains silicon and aluminum in amorphous state can be a source of binding material, and Fly ash which contains this is considered to be a waste product which can be utilized effectively to overcome the effects caused by Ordinary Portland Cement. Long term application of any material can be taken up only when it is tested for the drastic conditions, and one among the severe or extreme case is susceptible to fire. When geopolymer concrete is subjected to high temperatures as in a fire, there is likely deterioration in its properties. Of particular importance are loss in compressive strength, loss of elastic modulus, cracking and spalling of the concrete. To ascertain whether a structure can be repaired rather than demolished after a fire, an assessment of structural integrity must be made. Assessment of fire damaged concrete usually starts with visual observation of colour change, crazing, cracking, and spalling. So there exists a need to find the fire resistance of the Fly ash based Geopolymer concrete.

1.3 OBJECTIVE OF THE STUDY:The objective of the present investigation is to study the effect of elevated temperatures on the fire performance of Fly ash based Geopolymer concrete. Four different mixes were prepared by varying the aggregate and Fly ash ratio and are subjected to elevated temperatures of 250°C, 400°C, 600°C and 800°C with a sustained duration of 2 hours and 4 hours. The present investigation is carried out with the following objective: To study the residual properties of Geopolymer concrete in terms of compressive strength, modulus of elasticity and modulus of rupture.  To carry out a non-destructive test for determining the homogeneity of the matrix and aggregates at different temperatures.  To study the micro-structure of the specimens subjected to different temperatures and sustained duration. 1.4 SCOPE OF THE STUDY The experimental work was conducted to obtain the residual strength of the Fly ash based Geopolymer concrete at elevated temperature. In the experimental work only one source of dry low-calcium Fly ash (class F) from local power station was used. The tests and analytical methods that were available for Ordinary Portland Cement were used to predict the results.

1.5 ORGANISATION OF THE THESIS

The second chapter deals with the various investigations carried out by research workers in the field of study of the performance of geopolymer concrete at elevated temperatures. Chapter three comprises of the brief introduction of geopolymer materials and the geopolymerisation process. Chapter four deals with the materials and the tests carried out on the materials used and the experimental procedure followed. The fifth chapter deals with the results and discussion of the experiments. The sixth chapter includes the important conclusions and scope for future study.

CHAPTER 2

LITERATURE REVIEW

It has been reported very good heat resistant properties of material prepared using sodium silicate, potassium silicate and metakaolin; having thermal stability up to 1200-1400°C. Kovalchuk. Investigated heat resistant geopolymer materials manufactured using class F fly ash, which had good thermal resistance properties up to 800° C. Geopolymer prepared using either fly ash or metakaolin have frame work structures originating from condensation of tetrahedral aluminosilicate units varying Al/Si ratio such as (Al- O- SiO-) M, (Al-O-Si-O-Si-O-)M,(Si-O-Al-O-Si-O-Si-O-)M etc. M is an alkali ion, typically Na or K, which balances the charge of the tetrahedral Al [1]. Geopolymer prepared using class F fly ash are largely amorphous in nature. Two series of test samples were made, differing in their composition and method of moulding. In series I samples were prepared using sodium hydroxide, potassium silicate and sodium silicate solutions, providing 8-9% Na or K in mixtures and water binder ratios of 0.27-0.35. Water/binder ratio given in this paper was calculated as a ratio of total mass of water to mass of fly ash. The pastes were cast in plastic cylinders and sealed with the lid. Because of low flow ability of mixes hand compaction using cylinder plunger was utilized at a filling stage. In series 2 fly ash samples were prepared using 8-9% Na or K in mixtures and water/binder of 0.09-0.166. In series 2 mixes of very dry consistency were used, thus some of the samples were pressure compacted. It was shown that prolonged initial curing of samples at room temperature before the application of heat was beneficial for strength development of geopolymer samples prepared using fly ash. The method of curing mixtures of series 1 and 2 was the same, initially samples were cured for 24 hours at room temperature, after that the mixtures were ramped wither to 80° or 100° C series cured respectively, at 80° -100° C, and cured at this temperature for 24 hours. The 25X50mm diameter cylinder samples were exposed to firing at 800°, 1000° and 1200° C for 4 hours at a heating rate 10° C/min. The polished specimens were used for the SEM examinations. To prepare the polished specimens, 1mm thick slices were cut from the cylinder samples using a low diamond saw, impregnated with ultra low viscosity resin and then

polished. For the examination using SEM the polished specimens were carbon coated. X-ray diffraction analysis of powdered specimen was made using a Rigaku Giegerflex D-max II automated diffractometer with following conditions: 40kV, 22.5mA, Cu-Kα radiation. The XRD patterns were obtained by scanning at 0.1° per minute and in steps of 0.05°. The slow scanning rate was used to improve resolution of peaks. The materials were also analyzed using mercury intrusion porosimeter to study porosity and average pore diameter before and after firing. The strength evolution in geopolymer specimens prepared using sodium containing activator and w/b in a range of 0.09-0.3. The experiment showed that the specimen prepared at w/b= 0.09 developed shrinkage cracking when exposed to 800 0 C. shrinkage cracking increased with increase of w/b ratio. After exposure to temperature above 800 0 C strength of all the specimens prepared using Na-containing activator deteriorated rapidly. The specimens cured at 100

0

C

had initial strength 50-100% higher than that of the specimens cured at 80 0 C. All specimens had a tendency of increasing strength upon firing. After firing the compressive strength of the pressure compacted specimens was lower than that of the hand compacted specimen. On firing, specimens manufacture using pressure 1-3 MPa increased strength up to 30 %, while other non compacted specimen had strength increased 44%. However, after exposure to temperature above 8000 C strength of specimen prepared using Na-containing activator rapidly deteriorated. strength loss was rapid in specimens prepared using heat curing at 1000 C, which had higher initial strength than specimens cured at 800 C. The compressive strength of the specimens prepared using potassium silicate and fly ash at w/b=0.166-0.345 and cured at 800 C to 1000 C. Specimens manufactured using w/b=0.166 were compacted using applied pressure of 2,6and 10 MPa. The initial strength of 2-5 MPa was measured for materials prepared at w/b =0.166 and 0.345 and cured at 800 C, while for the materials prepared at w/b=0.166 and cured at 1000 C the highest compressive strength of 12 MPa was achieved. Materials prepared at w/b= 0.345 and 0.166 and cured at 800 C had a similar strength evolution after exposure to 8000 ,10000, and 12000 C, achieving maximum strength of 53 MPa after firing at 10000 C, while further increasing of firing temperature caused deterioration of strength. The specimen w/b= 0.166 compacted by hand and cured at

1000 C had an increasing strength up to 12000 C. Observation of strength evolution of the specimens compacted at 2-10 MPa show that pressure compaction does not induce significant improvement of initial strength, but can be detrimental for strength development on firing. Materials prepared using K-containing activators had significantly increased their initial strength, while materials prepared using Na-containing activators had very high loss of strength at temperature exceeding 8000 C. Previously materials prepared using metakaolin showed thermal resistance up to 13000 C for sodium polysialate geopolymers and up to 13000C–14000C for potassium polysialite geopolymers (V.F.F.Barbosa, K.J.D.Mackenzie, 2003) they reported that increased amounts of water and/or sodium and silicon could cause reduced thermal resistance of geopolymer material when exposed to firing. The curing at the elevated temperature increased the initial strength and fire resistance of the geopolymer materials. Loss of strength on firing was possibly connected to the deterioration of aluminosilicate gel. After decomposition of the aluminosilicate gel free sodium, silicon, and aluminum produced Na-feldspars. Presence of the Na- feldspars is responsible for the increase of porosity and deterioration of strength. here the experimental results indicated that a loss of compressive strength in materials prepared using Na- containing activator when exposed to firing was associated with a significant increase of the average pore size and shrinkage cracking. The presence of significant amounts of iron oxide in the fly ash used for materials preparation and poor polymerization of geopolymers in samples utilizing fly ash causes degradation of fire resistance properties of the geopolymer materials. Densification reduced shrinkage of materials on firing in case of materials activated by Na and K containing activators. Curing at 800 and 1000 C was utilized in the specimen preparation. Curing at 1000 C lead to an increased initial compressive strength, and improved fire resistance, which were attributed to improved activation of fly ash at elevated temperature. The additional tests need to be performed to verify heat conduction through the layer of geopolymer when exposed to standard heating curve. This investigation showed that prepared geopolymer materials compare favorably with organic polymers, they are non flammable, do not release toxic fumes and have very low weight loss 5-

12 % as compared to 50- 80 % for fire resistant polymer nano composites when heated up to 10000 C. The geopolymer materials were found superior to Portland cement concretes in their thermal properties when exposed to 8000- 10000 C. Volume expansion was observed in some of the geopolymer mixes with increased content of silica it was attributed to expansion on heating of un-combined silica. In this case the expansion increased with an increase of firing temperature to a point, when a large volume of foam was produced at 12000 C. The flyash used in another paper [5], the fly ash used was glassy with some crystalline inclusions of mullite, hematite and quartz. The chemicals used were sodium silicate solution and potassium hydroxide flakes of 90% purity, potassium hydroxide solution. The chemicals were combined to obtain a molarity of 7 molar. The specimens were cured undisturbed for 24 hours at room temperature before being subjected to elevated temperature of 80 0 C for a further 24 hours. Temperature exposed specimens were subjected to temperature of 800 0 C at an incremental rate of 4.40 C per minute from room temperature. Once the temperature of 8000 C was attained, it was maintained for a further 1 hour before the specimens were allowed to cool naturally to room temperature. The compressive strength assessment of concrete specimens were conducted using load control regime with a loading rate of 20 MPa/min, the specimens were tested for 3 day strength. Effect of Sodium Silicate to Potassium Hydroxide on Geopolymer Concrete. The 3 day compressive strength measurements for fly ash based binder prepared at various sodium silicate to potassium hydroxide ratios. Ratios ranged from 0.5-2.5 there was a noticeable improvement in strength with increasing ratio. The curing temperature selected was 800 C. However the observed strength of fly ash-based binder increased after temperature exposure. This means that the fly ash activation was incomplete within the introduced curing regime. (24 hour precuring at room temperature and 24 hour elevated curing at 80o C). The geopolymerisation of the fly ash was only completed as it was exposed to elevated temperature. Unexposed strengths may be improved by increasing the elevated curing temperature or by prolonging the curing period.

Fly Ash to Alkaline Silicate Activator Ratio Influence on Geopolymer Paste The strength performances in terms of fly ash to activator ratio similar to water to cement ratio typically used as a fundamental method of quantifying compressive strength in OPC. There was a general decrease in strength when the amount of activator introduced into the system was increased. The mass of activators is a sum of masses for Na 2SiO3 and KOH. The solids/liquid ratio contributes to the porosity level of the hardened geopolymer paste. Thus, the solids/ liquids ratio affects the volume of voids in the pastes which directly influences the strength of the geopolymer. However, the trends were reversed when the activator content was increased. Consequently lowering the fly ash-to- activator ratio. It was find that the strength of the binder with lower fly ash-to activator ratio (FA/act = 2.0) decreased after elevated temperature exposure, unlike previous relations where strength increased after exposure (FA/act = 3.0). This trend is similar to that of metakaolinite-based binder investigated in the previous work. Influence of Binder Age on Geopolymer Paste In order to study the effect of the binder age influence on compressive strengths, the pastes were prepared at various Na2SiO3 /KOH ratios and tested for 3-day and 7-day strengths. It was found that there was an insignificant increase in strength when the age at which the specimens were tested was increased. The chemical reaction of a geopolymer paste is a rapid geopolymerisation process, the compressive strength does not vary with the age of concrete when heat accelerated cured for 24 hours. This observation is in contrast to the well known behavior of a Portland cement, which requires a hydration process and under goes strength gain over time.(A.M. Neville(1990) properties of concrete).

Influence of Curing Period The results have indicated that a longer curing period does not significantly affect strength performances. The authors believe the geopolymerisation of fly ash binder was complete within the 24 hours of accelerated curing. Van Jaarsveld et al. claimed that curing for longer

periods of time at elevated temperatures appear to weaken the structure. However, the experimental findings in this section proved other wise within the time frames investigated. Elevated Temperature Performance of Geopolymer Concrete The fly ash to activator and Na2SiO3 /KOH ratios were kept constant at 3.0 and 2.5 respectively. Qualitative observations were recorded only after temperature exposure. All specimens performed very well under exposure to temperature. Apart from decolourisation, which was similar to the effect observed in the paste, there was no Spalling observed on any of the concrete cylinders. Residual strength The compressive strength of fly ash-based concrete was higher than those recorded in the fly ash-based paste. The introduction of the aggregates to the geopolymer paste increased the room temperature strengths from 59.0 MPa to 70.5 MPa and 61.8 MPa for basalt and slag aggregates respectively. However the strength of the geopolymer concrete decreased after exposed to elevated temperature. The temperature exposed specimens were weaker than their unexposed counterparts. The results show a 58 % droop of strength in the basalt based concrete. And a 65 % drop in slag based concrete after temperature exposure. As observed, the phenomenon of temperature exposed strengths being higher than unexposed strengths does not exist as in the previous pure paste mixture. Comparison of geopolymer concrete with the OPC concrete fire performance The findings above do not necessary substantiate that the geopolymer concrete performed poorly when exposed to elevated temperature. In fact , the 3-day strength geopolymer concrete which degraded to 42 % of the original strength was considered to be an improvement compared the 67-day strength of the high strength concrete (HSC) which reduced to 22 % of the original strength when subjected to an elevated temperature of 8000 C. So, the performance of fly ash based binder at elevated temperature declined with the inclusion of aggregates to make concrete. It is hypothesized that this is caused by the incompatibility and differential thermal expansion between the aggregates and the binder.

Thermal expansion of geopolymer paste There was a length change of the geopolymer paste with respect to its original length, lo. When initially heated upto 1500C, the hardened geopolymer paste expanded. Between 1500C and 2200 C, no further expansion occurred. The geopolymer paste then shrunk between 2200 C and 8000 C. Shrinkage occurred due to the mass loss when subjected to elevated temperature. The TGA was able to measure the mass loss as a function of temperature. Rapid dehydration occurred at the peak of the 1200 C to 1300 C heating range. Generally , the total percentage of mass remaining after being heated to 8000 C averaged at 88.8%. All specimens experienced a rapid decline in percentage within the first 2000 C and stabilized after until approximately 7000 C. After 7000 C, there was little change in the percentage of mass remaining. The expansion of concrete at elevated temperature is strongly affected by the aggregates because aggregates generally occupy 75-80 % of the volume of the concrete. The expansion of aggregates predominates over the contraction of the geopolymer paste subjected to temperature beyond 2200 C, which produces a net result of expansion in concrete. Meanwhile, a differential thermal expansion exists between the aggregates and the paste. The results prove the hypothesis that the thermal incompatibility relating to the paste and aggregates is the primary reason for the performance loss at elevated temperatures between the geopolymer paste and concrete specimens.

CHAPTER 3 GEOPOLYMER MATERIALS AND PROCESS: 3.1 GEOPOLYMER MATERIALS

3.1.1 FLY ASH: Fly ash is a finely divided residue resulting from the combustion of ground or powdered coal in electricity generating plant. Fly ash consists of earthly minerals, which include silicon, aluminum, iron, calcium, magnesium and traces of titanium and organic matter, such as carbon. The fly ash is solidified while it is being suspended in he exhaust gases, and is collected from the exhaust gases by electrostatic precipitators. Therefore, fly ash particles are generally spherical in shape because the solidification process occurs while the solid is in gas suspension. Furthermore, the collision between particles results in some larger particles or particles made up of several smaller ones bonded together. The particle size of fly ashes ranges from