“PERFORMANCE OF GEOPOLYMER CONCRETE AT ELEVATED
TEMPERATURE ”
Dissertation submitted to
VISWESVARAIAH TECHNOLOGICAL UNIVERSITY,
BELGAUM, KARNATAKAIn partial fulfillment of the requirements for the award of the degree of
MASTER OF TECHNOLOGY
IN
CONSTRUCTION TECHNOLOGY
ByKEDARA SWAMY .U
Reg. No. 1BM05CCT07Under the guidance of
Dr. SAKEY SHAMU
Mr. M. S. SUDARSHAN
Department of Civil Engineering
B. M. S. COLLEGE OF ENGINEERING
BANGALORE - 560 019OCTOBER- 2007
“PERFORMANCE OF GEOPOLYMER CONCRETE AT ELEVATED
TEMPERATURE ”
Dissertation submitted to
VISVESWARAIAH TECHNOLOGICAL UNIVERSITY,
BELGAUM, KARNATAKAIn partial fulfillment of the requirements for the award of the degree of
MASTER OF TECHNOLOGY
IN
CONSTRUCTION TECHNOLOGY
ByKEDARA 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 019OCTOBER- 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 Professor & H.O.D
Dept. of Civil Engg. Dept. of Civil Engg. B. M. S. College of Engg B.M.S. College of Engg Bangalore Bangalore
Mr. M. S. Sudarshan Dr. M. K. Venkatesha Director (Technical) Principal
Civil Aid Techno clinic Pvt. Ltd. B. M. S.College of Engg. Bangalore Bangalore
Examiners: Signature with Date 1.
2.
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 CO2
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 3
1.3 Objective of the study 4
1.4 Scope of the study 4
1.5 Organization of the thesis 5
CHAPTER 2
LITERATURE REVIEW
6CHAPTER 3 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 14
CHAPTER 4
EXPERIMENTAL INVESTIGATIONS
4.1 Experimental investigation 18
4.1 Materials
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 Preparation of the specimens 21
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
RESULTS AND DISCUSSIONS
5.1 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. 51
5.10 - Shows the results of Modulus of Elasticity of Geopolymer Concrete. 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- Si- O-) 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
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 800 C for a further
24 hours. Temperature exposed specimens were subjected to temperature of 8000 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 Na2SiO3 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 <1 to 200 µm, and the particles are typically spherical in shape (Hemmings and Berry, 1988)
The types of coal determine the types of fly ash produced. Generally, anthracite and bituminous coals produce fly ashes which are classified as Class F fly ash. Class F – being mainly silica and alumina (80-85 weight %) and < 10 weight % CaO.Class C fly ash is produced by burning lignite or sub-bituminous coal. Class C fly ash has lower silica and alumina content, but higher CaO content (20-40 weight %).
3.1.2 ALKALINE LIQUID
In this experimental investigation a combination of sodium hydroxide and sodium silicate solution was chosen as the alkaline liquid. It is reported that mineral shows a higher extent of dissolution in sodium based solution than potassium based solution [1]. The sodium hydroxide was in the form of flakes (commercial grade), with 97% purity. The sodium hydroxide solution was prepared by dissolving flakes in distilled water (normal). The mass of NaOH solids used in the solution was of 16 molar. In this experiment 16 molar solution is used, NaOH solution with a concentration of 16M consisted of 16X40=640 grams of NaOH solids dissolved in one litre of water, where 40 is the molecular weight of NaOH. In this study 16M sodium hydroxide solution was used.
A commercially available sodium silicate solution was used. The specific gravity and chemical composition of such a sodium silicate solution was 1.53 and Na2o=27.62%,
SiO2=32.08%, H2o=40.3% by mass respectively
3.2 GEOPOLYMERISATION PROCESS:
The researchers have reported that binders could be produced by a polymeric reaction of alkaline liquids with the silicon and the aluminum in source materials of geological origin or by product materials such as flyash and rice husk ash, metakaoline, blast furnace slag, known as geopolymers.
Geopolymerisation is a geo synthesis (a reaction that chemically integrates minerals)that involves naturally occurring silico-aluminates. The silicon(Si)and aluminum(Al)atoms react to form molecules that are chemically and structurally comparable to those binding natural rock that allows for products to exhibits the most ideal properties of rock-forming elements namely, hardness, chemical stability and longetivity.
The synthesis of geopolymer is believed to consist of three steps:
First the dissolution of alumino-silicate under strong alkali solution, second, the reorientation of ion clusters, and the third, polycondensation. But each step may include many pathways. Different pathway can create different ion cluster, which directly determine the final properties of geopolymer. Thus, it is very important to under stand the actual pathway for producing geopolymer in order to gain insight into the mechanism of geopolymerisation. However, until now, these mechanisms are not well documented due to rapid rate of formation of geopolymer. Experimentally it is very difficult to separate out these steps.
Poly(sialates) are chain and ring polymers with Si4+and AL3+in coordination
with oxygen and range from amorphous to semi-crystalline with the empirical
formula:
Mn (-(SiO2) z–AlO2)n . wH2O (2-1)
Where “z” is 1, 2 or 3 or higher up to 32; M is a monovalent cation such as potassium
or sodium, and “n” is a degree of polycondensation (Davidovits, 1984, 1988b, 1994b,
1999). Davidovits (1988b; 1991; 1994b; 1999) has also distinguished 3 types of
polysialates, namely the Poly(sialate) type (-Si-O-Al-O), the Poly(sialate-siloxo) type
(-Si-O-Al-O-Si-O) and the Poly(sialate-disiloxo) type (-Si-O-Al-O-Si-O). The structures of these polysialates can be schematized as in Figure .
A geopolymer can take one of the three basic forms.
Poly(sialate), which has[-Si-O-Al-O-] as the repeating unit.
Poly(sialate-siloxo), which has [-Si-O-Al-O-Si-O-] as the repeating unit.
Poly(sialate-disiloxo), which has [-Si-O-Al-O-Si-O-Si-O-] as the repeating unit.
Geopolymerization involves the chemical reaction of alumino-silicate oxides (Si2O5,Al2O2) with alkali polysilicates yielding polymeric Si – O – Al
bonds. Polysilicates are generally sodium or potassium silicate supplied by chemical industry.
(-)
(Si2O5, Al2O2)n + nSiO2 + nH2O NaOH, KOH n(OH)3 -Si-O-Al-O-Si-(OH)3
(OH)2 (-) (-)
n(OH)3 -Si-O-Al-O-Si-(OH)3 NaOH, KOH (Na,K)(+)–(-Si-O-Al-O-Si-O-) + nH2O
(OH)2 O O O
Unlike ordinary Portland/pozzolanic cements, geopolymers do not form calcium
silicate-hydrates (CSHs) for matrix formation and strength, but utilize the
polycondensation of silica and alumina precursors and a high alkali content to attain structural strength. Therefore, geopolymers are sometimes
referred to as alkali activated alumino silicate binders (Davidovits, 1994a; Palomo et. al., 1999; Roy,1999; van Jaarsveld et. al., 2002a).
CHAPTER 4
4.1 EXPERIMENTAL INVESTIGATION
The present experimental work deals with the study of the performance of fly ash based geopolymer concrete at different elevated temperatures namely 2500 C, 4000 C, 6000 C, 8000 C,
At different sustained durations of 2 hours and 4 hours.
The details of the materials used in the present work, the mix design, method of mixing, casting of specimen, curing and heating to different temperatures along with the tests carried out on the heated specimens are explained in this chapter.
4.2 MATERIALS 4.2.1 FLY ASH
Fly ash used in this experimental work is brought from Raichur thermal power station (RTPS) Karnataka. It is a class F fly ash (the fly ash which contains less than 10 % of the calcium) which is called low calcium fly ash. The physical characteristics of fly ash was conducted and the results are tabulated in Table 4.1
Table 4.1 – Physical Characteristics of Fly Ash (RTPS)
Sl No Details Results
1. Specific Gravity 2.05
2. Fineness (Blaine’s air permeability
(m2/kg) 439
Chemical test on fly ash
The chemical test was conducted o the fly ash and the results were tabulated in the Table 4.2 Table 4.2 Chemical Composition of Fly Ash
SL
NO TEST CONDUCTED RESULTS
1
Silicon dioxide plus aluminum oxide plus iron oxide, percent
by mass
94.40
2 Silicon dioxide percent by mass 60.88
3 Magnesium oxide percent by mass 0.98
4
Total sulphur as sulphur trioxide. percent by mass,
(maximum)
0.20
5 Loss on ignition, percent by mass 1.13
4.2.2 Aggregates
The type of fine aggregate used in this study is locally available sand. The type of coarse aggregates used for this study is crushed granite (Angular) which is locally available. Maximum size of aggregate used is 12.5 mm. Physical characteristics of the sand used are presented in Table 4.3, 4.4, 4.5.
Table 4.3 - Physical Characteristics of Aggregates
Physical properties Fine aggregate Coarse aggregate
(sand) (12.5 mm down)
Specific gravity 2.60 2.61
Fineness modulus 2.78
-Loose bulk density (kg/m3) 1536 1290
Dry rodded bulk density
(kg/m3) 1640 1500
Table 4.4 - Sieve Analysis Results of Fine Aggregate
Sieve Size Weight Retained (gm) Cumulative % Retained Cumulative % Passing
Zone - Specifications as per IS:383-1970 for % Passing
I II III IV 4.75 mm 33 3.3 96.7 90-100 90-100 90-100 95-100 2.36 mm 36 6.9 93.1 60-95 75-100 85-100 95-100 1.18 mm 186 25.5 74.5 30-70 55-90 75-100 90-100 600µ 313 56.8 43.2 15-34 35-59 60-79 80-100 300µ 202 87 13 5-20 8-30 12-40 15-50 150µ 122 99.2 0.8 0-10 0-10 0-10 0-10 Pan 8 - - --- --- ---
---The fine aggregate tested conforms to Zone-II as per IS:383. Table 4.5 – Sieve Analysis results of Coarse Aggregate.
Sl. No. Sieve size (mm) Wt. retained (gm) retained% Wt.
Cum. %Wt. retained % Passing 1. 16 0 0 0 100 2. 12.5 200 4 4 96 3. 10 1280 25.6 29.6 70.4 4. 4.75 3200 64 93.6 6.4
5.
Pan 320 6.4
-Coarse aggregate tested confirms to the size of 12.5 mm of nominal size of aggregate as per IS 383 – 1970.
4.3 PROPORTIONING OF GEO POLYMER CONCRETE MIXES
The different concrete mixes were obtained by absolute volume method assuming the wet density of the geopolymer concrete as 2400 Kg/m3 based on the preliminary tests in our
laboratory.
The water content was fixed at 140 Kg/m3. the fly ash content was varied in range of 315
Kg/m3 (15% of total particulate matter) to 566 Kg/m3 (27% of total particulate matter)
considering workability criteria and desired compressive strength of geopolymer concrete. The alkaline solution used was the combination of sodium hydroxide and sodium silicate solution where the concentration of the sodium hydroxide solution was kept constant at 16 molarities, ratio of sodium silicate solution to sodium hydroxide solution was kept constant at 2.5 respectively. The details of the mix proportions are shown in the Table 4.6
Table 4.6: Details of Geopolymer Concrete Mixtures
MIX No.
AGGREGATE Fly ash (F)
Kg/m³ NaOH Kg/m³ Na2SiO3 Kg/m³ Water/Fly ash (W/F) coarse fine 1 1016 767 315 86.56 216.41 0.44 2 980 739 377 86.56 216.41 0.37 3 944 712 441 86.56 216.41 0.32 4 872.6 658 566 86.56 216.41 0.25
4.4 PREPARATION OF THE SPECIMEN
All the ingredients were mixed in the laboratory using pan mixer. The capacity of the pan mixer is 60 liters. Initially all the dry ingredients such as the fly ash, fine aggregates, coarse aggregates were mixed for 3 minutes, after which, the alkaline solutions were added which were prepared one day prior and then all the ingredients were mixed thoroughly for 4 minutes.
4.4.1 Casting of the specimen
The mixed concrete is cast in 100X100X100 mm cube, 150X300mm cylinders and 400X75X75mm beams. All specimens were prepared in accordance with IS 516:1959. The casting of cubes is done in 3 layers. Each layer is given 25 blows with tamping rod and after completing all the layers, the cube mould was vibrated for 30 seconds on vibrating table. Similarly, cylinders are cast in 3 layers. Each layer is given 30 blows and after completing the layers, it is vibrated for 30 seconds. In a similar way beams are also cast and vibrated.
After casting, the specimens were wrapped with a thick plastic cover, to cover the surface, in order to avoid the evaporation of water during high temperature curing.
Plate 1: Preparation of the specimen
4.4.2 Curing
The curing of the specimens is carried out by subjecting the specimen to a temperature of 65° C for 20 hours along with the mould. After subjecting the specimen to temperature curing, the specimens were allowed to cool down to ambient temperature and then de moulded and wrapped in thick polythene bags and kept for air curing for further 7 days.
Plate 2: Specimens kept in Oven for Heat Curing
4.5 DETAILS OF SPECIMENS
For each mix of geo polymer concrete and each test temperature and each sustained duration 3 specimens are considered. To compare the properties of geo polymer concrete before and after subjecting to elevated temperature. For each mix 3 controlled specimens were also cast.
GPC MIX 1 45.9 MPa MIX 4 94.9 MPa MIX 3 86.9 MPa MIX 2 49.2 MPa 250 DEG 800 DEG 600 DEG 400 DEG
Figu
re 4.1: Details of the specimens subjecting to different temperature and different sustained duration.4.6
4.6 EXPOSING THE SPECIMENS TO ELEVATED TEMPERATURE
The specimens were subjected to elevated temperature for specified duration in a special heating chamber of size 2.1 X 1.1 X 1 m. the chamber is heated through electrical coil and is capable of attaining a max temperature of 10000 C.
The oven is installed below the ground with top sliding cover at ground level. Electrical sensors are provided in the oven to measure the temperature inside the oven. The temperature is controlled in the control panel in which the temperature can be set to required degree and can be maintained to required time without any increase or decrease in the temperature.
The specimens were heated in electric oven and were kept in such a way, leaving equidistance from each sample, so that all the sides of the samples could be exposed to heat. As the heat reached to the testing temperature, this temperature is maintained constantly for the required period such as 2hours and 4 hours, the rate of temperature rise was set as 50 C per minute.
3 specimens
from each mix
After exposing the samples to the required temperature and for required duration the heating of the samples was stopped and was allowed in the electric oven to cool down. Later on when oven cooled down to ambient temperature, the specimens were taken out and were wrapped in the plastic bag and kept for observation and testing. Three specimens were tested for each exposed and for each sustained duration, only the average values are reported.
Plate 3: Specimens kept in Electric Oven for Elevated Temperature 4.7 TEST CONDUCTED
The tests proposed are such that they indicate the degradation, changes in strength properties due to exposure to elevated temperature. The residual properties were measured in terms of compressive strength, modulus of elasticity and modulus of rupture. In addition, ultra-sonic pulse velocity test was conducted and densities of concrete were also measured to observe the possible variations.
4.8 PHYSICAL OBSERVATIONS
Before the specimens were subjected to various tests, the physical changes after exposing the specimen to different temperature and for different sustained duration were observed. The
observation includes change in dimensions, colour, development of cracks etc. The observations are furnished in the Table. 5.1.
4.8.1 Change in colour
Similar to Portland cement concrete, geopolymer concrete exhibits change in colour, when exposed to elevated temperature the change in colour observed is as follows:
Upto 250° C, which was sustained for 2 hours and 4 hours, there was no change in colour, the colour remained the same as that of unheated specimen.
@ 400° C which was sustained for 2 hours and 4 hours, in these specimens exhibit slight pink colouration.
@ 600° C which was sustained for 2 hours and 4 hours, the change in the colour of the specimen was quite prominent. The specimen turned pink mixed with brown colour.
@ 800° C which was sustained for 2 hours and 4 hours, the specimen exhibits brown
colour. The colour of the aggregates and the matrix had turned into brown colour, as observed from the crushed specimen.
Plate 4: Specimens showing the change in Colour 4.8.2 Aggregates
Commonly used aggregates are thermally stable up to 650° C. At higher temperature when the specimen was subjected to compression test, it was observed that the failure occurs not only in the interfacial vicinity between aggregates and geopolymer but failure occurs through the aggregates. These aggregates were so weak that they could be crushed very easily by hand. This shows that the aggregates at higher temperatures was unstable and become very weak. 4.8.3 Cracks
The specimen which was subjected to 250° C and 400° C temperature for 2 hours and 4 hours did not show any cracks. Where as specimens that was subjected to 600° C and 800° C for 2 hours and 4 hours sustained duration showed surface cracks, and these cracks were predominantly in the matrix. The micro cracks observed on the surface were in the form of map cracking.
Plate 5: Surface Cracks, and change in Colour on the specimen 4.8.4 Spalling
Spalling was not observed in any of the specimens which were subjected to different high temperatures at different sustained temperature.
The physical observation of the specimens in terms of colour and cracks are shown in the Table.5.1.
4.9 COMPRESSIVE STRENGTH TEST
Tests were carried out to find out the effect of elevated temperatures on the residual compressive strength. The compressive strength of the cubes exposed to elevated temperatures are tested after 7 days curing.
Concrete cubes, 100X 100 X 100 mm in size were tested for compressive strength as per IS: 516-1959. The cubes were centrally placed in the compression testing machine of capacity 3000 KN and load was applied gradually and uniformly without shock. The loading rate was adjusted to 140Kg/cm2/min. The load was applied until the specimen fails and the maximum
load carried by each specimen during the test was recorded. From the failure load compression strength of each specimen is calculated. The results obtained are presented in Tables 5.6-5.9 and Figures 5.5-5.8.
Plate 6: Compression test arrangement
4.10 MODULUS OF ELASTICITY IN COMPRESSION
The cylindrical specimens of 150X300 mm dimensions were used to test modulus of elasticity in compression, the test was performed with universal testing machine which has a capacity of 3000 KN. The test is carried out based on the guide lines in IS 516-1959. The aluminum angles were attached to the cylinder surface to measure the average strain. These were attached at the distance of gauge length to hold the dial gauge. An electronic dial gauge capable of measuring deformation up to 0.001mm was used. Loading was done in three cycles the loading rate was 140 kg/sq cm/min until an average stress of (C+5) kg /sq cm is reached where C is one third of average compressive strength of the cube calculated to the nearest 5 kg/sq cm. The load is maintained for one minute and then reduced gradually to 1.5 kg/sq cm till the reading is noted. The same rate of loading is carried on to the second cycle of loading until an average stress of (C+1.5) kg/sq cm is reached and the load is reduced gradually to 1.5 kg/sq cm. The third cycle of loading and unloading is done similar to second cycle. Unusual behavior of any, was
corrected during the second and third loading. The applied load and longitudinal deformation was noted. These readings were plotted on stress vs. strain graph. The slope of the initial linear portion of the curve is taken as the modulus of elasticity.
Plate 7: Arrangement for Modulus of Elasticity test
4.11 ULTRA SONIC PULSE VELOCITY TEST
To assess the change in microstructure of the geopolymer concrete subjected to high temperature, the Specimens were subjected to Pulse velocity test as per 13311-Part 1. The equipment used - PUNDIT has a time measurement capability of 0.1 micro seconds. The time taken by the ultrasonic pulse to travel through the specimen between transducer and receiver held in contact with the specimen was noted. The path length divided by the time taken gives the pulse velocity. The quality grading of the cement concrete based on the values are given in the Table 4.7.
Plate 8: Ultra Sonic Pulse Velocity test
Table 4.7 Velocity Criterion for Cement Concrete Quality Grading (Ref. 13311-Part -1:1992)
Sl.No UPV for cement concrete (Km/Sec) Concrete Quality grading 1 Above 4.5 Excellent 2 3.5 to 4.5 Good 3 3.0 to 3.5 Medium 4 Below 3.0 *Doubtful
This table is used as a guide line to verify the UPV values and quality grading of geopolymer concrete.
4.12 MODULUS OF RUPTURE
The flexure test was carried out on the specimens of 75X75X400 mm dimensions. The test was performed with two points loading in the flexure testing machine. In the bed of testing machine two steel rollers of 38 mm dia are provided on which the specimen is placed which serves as support point. The load is applied through two similar rollers mounted at the third points of the supporting span, the load was divided equally between two rollers. The load is applied axially and without subjecting the specimen to any torsional stress or restraints and the maximum load (P)at failure is noted.
The modulus of rupture was calculated using the formula 2PL/bd2.
• Where , P= the applied load.
• L= length of the specimen.
• B= breadth of the specimen.
• D= depth of the specimen.
The results are furnished in the Table 5.11. and in Figure 5.14.
Plate 9: Arrangement of flexure test
CHAPTER 5
RESULTS AND DISCUSSION
5.1 PHYSICAL OBSERVATION
The physical observation made on the geo polymer concrete specimens regarding the colour, propagation of cracks and spalling soon after heating the specimens to high temperatures are reported below
5.1.1 Discolouration
The discolouration in geopolymer concretes exposed to elevated temperatures can be attributed to the changes in iron compounds present in the constituent materials such as fly ash, fine aggregates and coarse aggregates. Flyash being present in significant quantities contributes considerable amount of iron compounds into the mix and hence, the discoloration is prominently observed in geopolymer concretes.
The duration of the temperature exposure seems to have no effect on the discolouration, since the samples exposed to duration of 2 hours and 4 hours do not exhibit any difference in discolouration.
The change in colour can be used as a tool to arrive at the probable temperature exposure in geopolymer concrete, as in the case of Portland cement concrete.
5.1.2 Aggregates
The aggregates, when exposed to high temperature were found to be unstable and were very weak this is due to the action of heat on the aggregate. As the aggregate composed of many minerals, which may under go crystal transformation at high temperatures and also may under go expansion causing cracks making the aggregate very weak and unstable.
5.1.3 Cracks
The appearance of the cracks can be attributed to the contraction of the mortor due to water evaporation. The contraction is higher than that of cement concrete due to higher fine content present in geopolymer concrete.
5.1.4 Spalling
No Spalling was observed in any of the specimens which were subjected to different high temperatures at different sustained temperature. This is because of the formation of the micro cracks which were seen on the specimens. Since there will be a lot of water pressure inside the specimen when it is heated to high temperature, the formation of micro cracks will reduce the pressure. These micro cracks create the path for the water vapour to escape from the specimen. But where as in Portland cement concrete the spalling can be seen. This is because there may not be micro cracks at the higher temperature, which results in the built up of water pressure inside the specimen. This pressure causes the spalling of specimen as the temperature is raised. Table.5.1. Physical Observation of the specimens in terms of Colour and Cracks.
Temperature Duration Change in
Colour
Cracks
2500 C 2 H No change No cracks
2500 C 4 H No change No cracks
4000 C 2 H Slight pink No cracks
4000 C 4 H Slight pink No cracks
6000 C 2 H Pink mix brown Surface cracks
6000 C 4 H Pink mix brown Surface cracks
8000 C 2 H brown Surface cracks
8000 C 4 H brown Surface cracks
5.2 RESULTS OF ULTRA SONIC PULSE VELOCITY TEST
The pulse velocity transmission depends on the quality of concrete such as density, presence of micro cracks, pores etc., in geopoymer concrete the increase in temperature causes degradation in the matrix due to formation of micro cracks. Further at higher temperatures coarse aggregates also cracks, increasing micro cracks in concrete. This is clearly shown in the UPV readings. Apart from this more pores are observed at a temperature of 600° C and above, as a result the ultra sonic pulse velocity values are also less. The period of sustain temperature of 2 hours and 4 fours has no effect on ultra sonic pulse velocity readings.
The continuous decrease in pulse velocity values are almost same for the specimens which were subjected to increasing temperature @ different sustained durations. The graph shows that the UPV values are increasing as the compression strength increase. Where as, the UPV values when compared with the different temperatures shows the variation. The results are tabulated in the Tables 5.2- 5.5 and Figures 5.1-5.4.
The results of the specimen when subjected to a elevated temperature of 800° C shows the lesser values of UPV when compared to the results of the specimens subjected to the increasing temperatures of 250° C,400° C, and 600° C . This is because at 800° C the matrix will become very porous which results in the poor values of UPV.
Note: The value zero in the X-axis is referred as ambient temperature in the Figures 5.1- 5.4.
Table 5.2 Ultra Sonic Pulse Velocity test results for the specimens subjected to different temperature and different sustained duration for mix 1.
UPV TEST 0 0.5 1 1.5 2 2.5 3 3.5 4 0 200 400 600 800 1000 TEMPERATURE DEGREES U P V K m /s 2 HOUR
Figure 5.1(a)Ultra Sonic Pulse Velocity test of the specimen sustained for 2 hours subjected to different temperature for mix 1.
Mix 1
(45.90 N/mm2)
Temperature in 0 C Pulse velocity in KM/S
Duration 2 hours 4 hours Controlled 3.7 3.7 250 2.1 1.8 400 1.5 1.6 600 1.0 1.0 800 0.8 0.8
