BORANG PENGESAHAN STATUS TESIS

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1 UNIVERSITI TEKNOLOGI MALAYSIA PSZ 19:16 (Pind. 1/97) BORANG PENGESAHAN STATUS TESIS JUDUL: MECHANICAL PROPERTIES OF HIGH STRENGTH CONCRETE AT HIGH TEMPERATURE SESI PENGAJIAN: 2006/2007 Saya LUI POH CHING (HURUF BESAR) mengaku membenarkan tesis (PSM/Sarjana/Doktor Falsafah)* ini disimpan di Perpustakaan Universiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut: 1. Tesis adalah hakmilik Universiti Teknologi Malaysia. 2. Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk tujuan pengajian sahaja. 3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara institusi pengajian tinggi. 4. **Sila tandakan ( ) SULIT TERHAD (Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972) (Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan) TIDAK TERHAD Disahkan oleh (TANDATANGAN PENULIS) (TANDATANGAN PENYELIA) Alamat Tetap: BATU 18 ¾ SEBATU, SUNGAI RAMBAI, 77400, MELAKA. PM DR. MOHAMMAD BIN ISMAIL Nama Penyelia Tarikh: 23 APRIL 2007 Tarikh: 23 APRIL 2007 CATATAN: * Potong yang tidak berkenaan. ** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagai SULIT atau TERHAD. Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah dan Sarjana secara penyelidikan, atau disertasi bagi pengajian secara kerja kursus dan penyelidikan, atau Laporan Projek Sarjana Muda (PSM).

2 I hereby declare that I have read this thesis and in my opinion this thesis is sufficient in terms of scope and quality for the award of the degree of Bachelor of Civil Engineering Signature : Name of Supervisor : Associate Professor Dr. Mohammad Ismail Date : 23 April 2007

3 MECHANICAL PROPERTIES OF HIGH STRENGTH CONCRETE AT HIGH TEMPERATURE LUI POH CHING A report submitted in partial fulfillment of the partial requirement for the award of the degree of Bachelor Degree in Civil Engineering Faculty of Civil Engineering Universiti Teknologi Malaysia APRIL 2007

4 ii I declare that this thesis entitled Mechanical Properties of High Strength Concrete at High Temperature is the result of my own research except as cited in the references. The thesis has not been accepted for any degree and is not concurrently submitted in candidature of any other degree. Signature :... Name : Lui Poh Ching... Date : 23th April

5 To my beloved father, mother, brothers and sisters iii

6 iv ACKNOWLEDGEMENTS The author would like to express sincere appreciation to his supervisor, Ass. Prof. Dr. Mohammad Ismail, for invaluable encouragement and guidance during the preparation of this thesis. The author also would like to acknowledge Ms. Khairulnisa and the staffs at Material and Structural Laboratory, Environmental Laboratory and Faculty of Civil Engineering, Universiti Teknologi Malaysia (UTM) for their assistances in this research, especially in laboratory testing. Thanks also extended to the author s research partner Chong Pak Lim for providing the necessary data and additional information needed for this research. Last but not least, appreciation would go to the author s family and friends for their continuous encouragement and support.

7 v ABSTRACT To ensure concrete structure will be safe after being exposed to accidental fire, it is important and essential that the effect of heating and cooling condition on mechanical properties of various types of concrete be well understood. This research highlights the findings of performance of normal strength ordinary Portland cement (OPC) concrete (grade 40), high strength OPC concrete (grade 40) and palm oil fuel ash (POFA) concrete (grade 40) at elevated temperature of 100, 300, 500 and 800 o C. 57 concrete cubes were prepared for this research. The specimens were cooled differently in air and water after heated at prescribed temperatures. The properties of concrete were determined using unstressed residual compressive strength test, mass loss measurements and crack patterns observations. The results indicated that greater reduction of strength was occurred in specimens cooled in water as compare to specimens cooled in air. It was found that mass losses in high strength concrete were lower than normal strength concrete. POFA concrete showed better fire performances than OPC concrete.

8 vi ABSTRAK Untuk memastikan struktur konkrit kekal selamat dan stabil setelah terdedah kepada kebakaran, pengetahuan terhadap kesan pemanasan dan penyejukan kepada unsur mekanikal pelbagai jenis konkrit adalah penting dan perlu. Kajian ini menekankan penemuan ketahanan dan kekuatan normal konkrit ordinary Portland cement (OPC) gred 40, konkrit OPC kekuatan tinggi gred 80, dan palm oil fuel ash (POFA) gred 40 dengan suhu setinggi 100, 300, 500 dan 800 o C. 57 kiub konkrit telah disediakan untuk kajian ini. Spesimen-spesimen disejukkan dalam air dan udara secara berasingan setelah dipanaskan pada suhu yang ditentukan. Sifat-sifat fizikal konkrit diuji melalui ujian kekuatan mampatan tinggalan tanpa beban, ukur kehilangan jisim dan pemerhatian corak retak. Keputusan kajian menunjukkan bahawa spesimen yang disejukkan di dalam air mempamerkan kehilangan kekuatan yang ketara berbanding dengan spesimen yang didedahkan kepada udara. Didapati juga kehilangan jisim di dalam konkrit kekuatan tinggi adalah kurang berbanding dengan konkrit biasa. Konkrit POFA menunjukkan ketahanan api yang lebih baik berbanding konkrit OPC.

9 vii TABLE OF CONTENTS CHAPTER TITLE PAGE DECLARATION DEDICATION ACKNOWLEDGEMENTS ABSTRACT ABSTRAK TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF PHOTOS LIST OF ABBREVIATIONS LIST OF SYMBOLS LIST OF APPENDICES ii iii iv v vi vii x xi xvi xvii xviii xix 1 INTRODUCTION Background Objective Scope Importance of Research 4 2 LITERATURE REVIEW Effect of High Temperature on Concrete Stress-strain Relationship Tensile Strength Thermal Properties Elastic Modulus 13

10 viii Bending (Flexural) Strength Permeability Porosity Compressive Strength Mass Loss Cracking of Concrete Spalling of Concrete Factors Affecting Fire Performance of Concrete Specimen Dimensions Loading Conditions Moisture Content Type of Aggregate Heating Rate Concrete Density Concrete Strength Cooling Conditions Replacement of POFA in concrete Compressive strength test Stressed Test Unstressed Test Residual Unstressed Test 41 3 RESEARCH METHODOLOGY Variables Materials and Mix Proportions Test Specimens Apparatus Sieves and Mechanical Sieve Shaker Los Angeles Abrasion Machine Concrete Mixer Cube Moulds Slump Test Apparatus Dimension and Mass Measurement Device 46

11 ix Heating Device Compression Testing Machine Trial Mix POFA Preparation Sample Preparation Storing and Curing of Sample Experimental Procedure Testing Procedures 50 4 TEST RESULTS AND DISCUSSIONS Residual Compressive Strength of Concrete Effect of Cooling Regimes on Residual Compressive Strength of Concrete Residual Compressive Strength for Different Types of Concrete Mass Loss Spalling and Cracks 65 4 CONCLUSIONS AND RECOMMENDATIONS Conclusions Recommendations 70 REFERENCES 71 Appendices A-G 75-82

12 x LIST OF TABLES TABLE NO. TITLE PAGE 2.1 Table 2.1: C40 and C100 concrete mean permeability parameters (Gardner, D.R., Lark, R.J. and Barr, B., 2004) Test Matrix (Phan, L.T., 2002) Maximum compressive strength (MPa) of gravel concrete at different temperatures ( o C) using different cooling methods. (Sakr, K. and EL- Hakim, E., 2005) Mix proportion and compressive strength of concretes Mineralogical composition of Ordinary Portland Cement and POFA Cement Numbers of test specimens for each set of condition Numbers of specimens for trial mix Residual compressive strength of concrete at elevated temperatures Chemical composition and physical properties of binders (Salihuddin Radin Sumadi and Mohd. Warid Hussin, 1995) Mass loss of concrete at elevated temperatures 64

13 xi LIST OF FIGURES FIGURE NO. TITLE PAGE 1.1 Research Flow Chart Load-deformation relationship at different temperature for high strength concrete (Castillo and Durrani, 1990) Load-deformation relationship at different temperature for normal strength concrete (Castillo and Durrani, 1990) Stress-strain curves for carbonate aggregate HSC (Cheng, F.P., Kodur, V.K.R. and Wang, T.C., 2004) Stress-strain curves for siliceous aggregate HSC (Cheng, F.P., Kodur, V.K.R. and Wang, T.C., 2004) Tensile splitting strength of three grades of concrete subjected to different temperatures (Chan Y. N., Peng, G. F. and Anson, M., 1998) Splitting tensile strength after fire (Min Li, Chun Xiang Qian and Wei Sun, 2004) Residual tensile splitting of three grades of high strength and normal strength concrete versus temperatures (Noumowe, A.N., Clastres, P., Febicki, G. and Costaz, J. L., 1996) 11

14 xii 2.8 Temperature distribution at various depths during fire exposure in normal-strength concrete (NSC) and high-strength concrete (HSC) columns (Kodur, V.K.R., 1999)and high-strength concrete (HSC) columns Axial deformation of normal-strength concrete (NSC) and high-strength concrete (HSC) columns during fire exposure (Kodur, V.K.R., 1999) Normalized elastic modulus of HSC as a function of temperature (Cheng, F.P., Kodur, V.K.R. and Wang, T.C., 2004) Bending strength after fire (Min Li, Chun Xiang Qian and Wei Sun, 2004) Residual porosity of NSCs (Poon, C. S., Azhar, S., Anson, M. and Wong, Y.L., 2001) Residual porosity of HSCs (Poon, C. S., Azhar, S., Anson, M. and Wong, Y.L., 2001) Total porosity and average pore diameter of hardened cement paste in concrete (average pore diameters are marked on top of the columns in 10-2 µm) (Xu, Y., Wong, Y.L., Poon, C.S. and Anson, M., 2001) Summary of Compressive strength-temperature relationships for normal weight concrete, obtained by unstressed test (Phan, L. T., 2002) Summary of Compressive strength-temperature relationships for normal weight concrete, obtained by residual unstressed test (Phan, L. T., 2002) Summary of Compressive strength-temperature relationships for normal weight concrete, obtained by stressed test (Phan, L. T., 2002) 19

15 xiii 2.18 Normalized compressive strength of HSC as a function of temperature (Cheng, F.P., Kodur, V.K.R. and Wang, T.C., 2004) Compressive strength of concrete after high temperature (Min Li, Chun Xiang Qian and Wei Sun, 2004) Ratio of residual compressive strength to initial strength (Noumowe, A.N., Clastres, P., Debicki, G. and Costaz, J.-L., 1996) Compressive strength of three grades of concrete subjected to different peak temperatures (Chan, Y. N., Peng, G. F. and Anson, M., 1998) Percentage of residual compressive strength of three grades of concrete subjected to different peak temperatures to the original compressive strength (Chan, Y. N., Peng, G. F. and Anson, M., 1998) Relative residual compressive strength of high strength concrete (Poon, C. S., Azhar, S., Anson, M. and Wong, Y.L., 2001) Relative residual compressive strength of normal strength concrete (Poon, C. S., Azhar, S., Anson, M. and Wong, Y.L., 2001) Residual compressive strength and percentage to original value (Xu, Y., Wong, Y.L., Poon, C.S. and Anson, M., 2001) Relative residual compressive strength of limestone concretes (Savva, A.; Manita, P. and Sideris, K.K., 2005) Relative residual compressive strength of siliceous concretes (Savva, A.; Manita, P. and Sideris, K.K., 2005) Residual compressive strength of OPC/PFA pastes- 2 inch cubes (Khoury, G.A., 1992) 27

16 xiv 2.29 Weight variations (Noumowe, A. N., Clastres, P., Febicki, G and Costaz, J. L., 1996) Effect of specimen size on compressive strength after high temperature (Min Li, Chun Xiang Qian and Wei Sun, 2004) Comparison of design curves and experimental loss of strength curves (Metin Husem, 2005) The compressive strength before and after exposure to 800 C (Xin Luo, Wei Sun and Sammy Yin Nin Chan, 1999) The compressive strength before and after exposure to 1100 C (Xin Luo, Wei Sun and Sammy Yin Nin Chan, 1999) Effect of replacement levels on strength (Salihuddin Radin Sumadi and Mohd. Warid Hussin, 1995) Coefficient of permeability of OPC/POFA mortar (Salihuddin Radin Sumadi and Mohd. Warid Hussin, 1995) Calcium hydroxide depletion for OPC and OPC/AA samples (Salihuddin Radin Sumadi and Mohd. Warid Hussin, 1995) Effect of ash content on compressive strength of concrete (Abdul Awal, A.S.M. and Hussin, M.W., 1996) Effect of fineness of ash on compressive strength of concrete (Abdul Awal, A.S.M. and Hussin, M.W., 1996) Comparison of compressive strength of concrete mixed with ground palm oil fuel ash (Vanchai Sata, Chai Jaturapitakkul and Kraiwood Kiattikomol, 2004) 40

17 xv 4.1 Residual compressive strength of concrete 52 subjected to different temperatures 4.2 Loss of strength curves for OPC Loss of strength curves for OPC Loss of strength curves for POFA Comparison of research results (air cooling and water cooling) with Metim Husem s (2006) curves Loss of strength curves for test cubes cooled in air Loss of strength curves for test cubes cooled in water Comparison of research results (air cooling) with Noumowe, A.N. et. al. s (1996) curves Comparison of research results (air cooling) with Chan, Y. N. et. al. s (1999) curves Comparison of research results (air cooling) with Poon, C. S. et. al. s (2001) curves Comparison of research results (air cooling) with Phan, L. T. s (2002) curves Comparison of research results (air cooling) with Poon, C. S. et. al. s (2001) curves Comparison of research results (air cooling) with Savva, A. et. al. s (2005) curves Comparison of research results (air cooling) with Xu, Y. et. al. s (2001) curves Mass loss of concrete subjected to different temperatures 64

18 xvi LIST OF PHOTOS TABLE NO. TITLE PAGE 4.1 Crack patterns observed at 500 o C and 800 o C Crack patterns observed for OPC-80 specimens cooled in air (left) and cooled in water (right) at 800 o C Surface spalling observed at 500 o C for OPC-80 specimen 68

19 xvii LIST OF ABBREVIATIONS NSC - Normal strength concrete HSC - High strength concrete POFA - Palm oil fuel ash OPC - Ordinary Portland cement SF - Silica fume FA - Fly ash BS - Blast furnace slag PFA - Pulverized fly ash GGBS - Granulated blast furnace slag CSF - Condensed silica fume

20 xviii LIST OF SYMBOLS f c - Residual compressive strength after subjected to certain temperature f c(room) - Compressive strength at room temperature C-S-H - Calcium-silicate-hydrate SiO 2 - Silicon dioxide Ca(OH) 2 - Calcium hydroxide

21 xix LIST OF APPENDICES APPENDIX TITLE PAGE A Completed concrete mix design form for OPC concrete grade 40 MPa 75 B Completed concrete mix design form for OPC concrete grade 80 MPa 76 C Completed concrete mix design form for OPC/POFA concrete grade 40 MPa 77 D Completed additional mix design form for OPC/POFA concrete grade 40 MPa 78 E Residual compressive strength of concrete subjected to different temperatures 79 F Mass loss of concrete subjected to different temperatures 81 G Calculation of mineralogical composition 82

22 CHAPTER 1 INTRODUCTION 1.1 Background High strength concrete is often considered a relatively new material to construction industry. However, over many years of gradual development, the production of high strength concrete is now economically and technically practicable. Now high strength concrete starts to become popular around the world with its increased use in structural applications. Due to its many advantages over normal strength concrete, high strength concrete has been used in bridges, columns and shear wall of high-rise buildings, offshore structures, and in construction where durability and strength is critical. High strength concrete provides a higher level performance in strength and durability compared to conventional concrete. High strength concrete allows for the use of smaller size of concrete structure which increases the amount of usable space and decrease the construction cost because of its ability to carry larger loads. Also, a variety of additives such and water reducing admixtures are easily available in the production of high strength concrete and this had increased the popularity of uses of high strength concrete in structural buildings [1]. Pozzolanic concrete containing natural or artificial pozzolans are used widely due to their good structural performance, economic advantages, and environmental friendliness. During the last few years, several types of agricultural wastes have been investigated by many researchers to seek the availability of them to be used as new

23 2 cement substitutes for environmental and economic purposes. In Malaysia, Palm oil fuel ash (POFA), a waste material from burning of palm oil shell and husk began to gain attention for its availability to replace a certain proportion of cement in the production of concrete [2]. Previous studies have proved that POFA fulfilled the requirement by ASTM C618 92a as a good pozzolanic material [3]. According to Danupon Tonnayopas et. al. (2006) [4], pozzolanic reaction between the POFA and cement matrix could have effect on the development of concrete strength. Fire safety is very important in designing structures. Cases related to fire has caused both the loss of life and loss of property. The risk of pozzolanic concrete exposed to fire is higher than the other types of concrete by considering their increased usages in structural applications with high temperature such as the oil, gas, nuclear, and power industries [5]. To improve the workability, the lower amount of water and certain admixtures is required in the production of high strength concrete. Due to its lower water/cement ratio and lower porosity, high strength concrete have less fire endurance as compared to normal strength concrete. Knowledge on thermal properties of high strength concrete and pozzolanic concrete is limited. Concrete is a composite of several materials that have different thermal properties and its properties depend on moisture content and porosity. Therefore, concrete are more complex than the other material and it is hard to predict its thermal behavior [6]. Recent studies have shown that high strength concrete behavior at high temperature and pozzolanic concrete may significantly different from that of pure normal strength concrete. There are almost no design rules and recommendations for the design of structures using high strength concrete and pozzolanic concrete and most of them are based on the pure normal strength concrete. As a result, in many cases, engineers and constructor lack the background and knowledge to predict the behavior and performance of high strength concrete and pozzolanic concrete during and after exposed to high temperature. Understanding of the behavior of concrete during extinguishing of accidental fires is important. It is believed that use of water spray to extinguish fire will cause certain damages to concrete. With the increased usage of

24 3 high strength concrete and pozzolanic concrete, fire performance of these concrete needs to be determined. 1.2 Objective The objective of this research is to study the effect of transient high temperature on the mechanical properties of high strength concrete and effect of POFA substituted in concrete. The followings are detailed objective of this study: To determine the effect of high temperature on compressive strength of high strength concrete and POFA concrete and compare to that of normal strength concrete and that observed at room temperature. To investigate the effect of different cooling methods on relative strength of high strength concrete, normal strength concrete and POFA concrete after exposed to high temperature. To find effect of high temperature on the mass loss and surface appearance of high strength concrete, normal strength concrete and POFA concrete. To study the factors that affect the behavior of high strength concrete, normal strength concrete and POFA concrete at high temperature. 1.3 Scope Information about the materials and test are given as follow: The experimental phase of this study included three types of concrete, normal strength OPC concrete (40Mpa); high strength OPC concrete (80Mpa) and POFA concrete (40Mpa). Conventional materials which include cement Portland cement, crushed granite, sand and water were used for production of concrete specimens. POFA collected from a local palm oil mill was used to product POFA concrete.

25 4 Testing of concrete specimens was conducted at elevated temperatures (room temperature, 100, 300, 500, and 800 o C) for all types of concrete. Tests were carried out on cube specimens according to British Standard BS Unsealed concrete specimens was used in heating process, which mean that the moisture content of concrete specimens are allowed to evaporate freely. The residual unstressed property test was carried out to measure mechanical properties of concrete at room temperature after heating and cooling. 1.4 Importance of Research The increasing use of high strength concrete and POFA concrete in structural construction has led to concerns about its fire performance. To ensure these structures will be safe after being exposed to accidental fire, it is important and essential that the effect of heating and cooling condition on mechanical properties of these concrete be well understood. This research provided findings of a study on the behavior of high strength concrete and POFA concrete after exposed to extreme temperature or accidental fire and verified the different behaviors of high strength concrete, normal strength concrete and POFA concrete at high temperature.

26 5 Selecting Topic Defining Problem Identifying Objective and Scope of Research Literature Review Finding Suitable Literature Materials and Evaluating Literatures Thesis Internet Textbooks Journal Articles Research Reports Reference Books Conference Papers Research Design and Experimental Process Analyzing Data and Discussion Conclusion Figure 1.1: Research Flow Chart

27 CHAPTER 2 LITERATURE REVIEW 2.1 Effect of High Temperature on Concrete Many investigations on the effect of high temperature on high strength concrete have been reported. Temperature is one of the factors that affect the properties of concrete. Felicetti, R., Gambarova, P.G., Rosati, G.P., Corsi, F. and Giannuzzi, G. [7] (1996) investigated the residual mechanical properties of high strength concrete subjected to high temperature cycles by tested 100 x 200 mm cylinders (72 95 MPa) at a cycle of high temperature ranging from 105 to 500 o C. They found that residual mechanical properties of high strength concrete such as compressive and tensile strength are greatly influenced by long exposure to high temperature. For temperature below 500 o C, heating effect on the structural behavior of concrete is quite limited because the material becomes softer and high temperature has less influence on the reinforcement Stress-strain Relationship The structural differences between normal strength concrete and high strength concrete result in different stress-strain relationship after subjected to high temperature. Castillo and Durrani [8] (1990) investigated the effect of temperatures ranging from 23 C to 800 C on concrete cylinders with size mm and strength ranged from 31 MPa to 89 MPa and found that steepness and linearity of

28 7 stress-strain curves increases as the strength of concrete increases, as shown in Figure The steeper stress-strain curves are mainly because high strength concrete has more brittle behavior. Due to the higher bond strength between cement paste and aggregates, internal cracking in high strength concrete is reduced and this contributes to the elastic and brittle behavior of high strength concrete. Figure 2.1: Load-deformation relationship at different temperature for high strength concrete (Castillo and Durrani, 1990) Figure 2.2: Load-deformation relationship at different temperature for normal strength concrete (Castillo and Durrani, 1990)

29 8 Research done by Cheng, F. P., Kodur, V.K.R. and Wang, T.C. [9] (2004) shows those high strength concrete exhibit brittle properties below 600 C and ductility above 600 C, as shown in Figure They also founded that high strength concrete made of carbonate aggregate underwent larger strain than that made of siliceous concrete. Figure 2.3: Stress-strain curves for carbonate aggregate HSC (Cheng, F.P., Kodur, V.K.R. and Wang, T.C., 2004)

30 9 Figure 2.4: Stress-strain curves for siliceous aggregate HSC (Cheng, F.P., Kodur, V.K.R. and Wang, T.C., 2004) Tensile Strength From Chan Y. N., Peng, G. F. and Anson, M. s [10] (1998) study, there is a sharp loss of tensile splitting strength for both high strength and normal strength concrete after exposed to high temperatures, compared to the more gradual loss of compressive strength as shown in Figure 2.5. When specimens were subjected to high temperatures, thermal incompatibility induced the production of macro-cracks in the concrete. The existence of such cracks reduces the valid area of cross-sections. Therefore, the tensile strength is more sensitive to macro-cracks produced in concrete than compressive strength. The results are supported by research done by Min Li, Chun Xiang Qian and Wei Sun [11] (2004), as shown in Figure 2.6. Noumowe, A. N., Clastres, P., Febicki, G. and Costaz, J.L. [12] (1996) who conducted both the direct tensile and splitting tensile test also show that the tensile

31 10 strength of concrete after subjected to high temperatures were not affected by the initial compressive strength of concrete significantly, as shown in Figure 2.7. Figure 2.5: Tensile splitting strength of three grades of concrete subjected to different temperatures (Chan Y. N., Peng, G. F. and Anson, M., 1998) Figure 2.6: Splitting tensile strength after fire (Min Li, Chun Xiang Qian and Wei Sun, 2004)

32 11 Figure 2.7: Residual tensile splitting of three grades of high strength and normal strength concrete versus temperatures (Noumowe, A.N., Clastres, P., Febicki, G. and Costaz, J. L., 1996) Thermal Properties In year 1999, Kodur, V.K.R. [13] investigated the different fire performance between normal strength concrete and high strength concrete by exposed loaded NSC and HSC columns to fire in a specially built furnace. Large cracks were observed in HSC columns. The lower permeability of high strength concrete prevent the internal temperature from releases to atmosphere and causes the increase of internal pressure in concrete until cracking and spalling occurred. The report also thermal expansion of high strength concrete is lower than normal strength concrete due to its compactness, as shown in Figure 2.8. Figure 2.9 shows that the deformation of high strength concrete is lower than that of the normal strength concrete.

33 12 Figure 2.8: Temperature distribution at various depths during fire exposure in normal-strength concrete (NSC) and highstrength concrete (HSC) columns (Kodur, V.K.R., 1999) Figure 2.9: Axial deformation of normal-strength concrete (NSC) and high-strength concrete (HSC) columns during fire exposure (Kodur, V.K.R., 1999)

34 Elastic Modulus The elastic modulus defined as the ratio of elastic modulus (taken as the tangent to the stress-strain curve at the origin) at a specified temperature to that at room temperature. The elastic modulus of high strength concrete will decrease under high temperature. Study by Cheng, F.P., Kodur, V.K.R. and Wang, T.C. [9] (2004) shows that elastic modulus of high strength concrete decreases to about 50% of its original values after exposed to temperature up to about 400 C, as shown in Figure The study also shows that the rate of decrease in elastic modulus of steel fiber reinforced high strength concrete is much higher than that of normal high strength concrete in temperature range 400 C to 600 C. However, the type of aggregate does not affect the modulus of elasticity of high strength concrete at high temperature. Figure 2.10: Normalized elastic modulus of HSC as a function of temperature (Cheng, F.P., Kodur, V.K.R. and Wang, T.C., 2004)

35 Bending (Flexural) Strength Min Li, Chun Xiang Qian and Wei Sun Sun [11] (2004) in their testing of the specimens with the size of mm show that bending strength of concrete decreased with increased of temperature. High strength concrete underwent greater rate of strength loss than normal strength concrete, especially at temperatures ranged from 200 C to 400 C, as shown in Figure They also stated that the reduction of bending strength is much higher than that of compressive strength and splitting tensile strength. Figure 2.11: Bending strength after fire (Min Li, Chun Xiang Qian and Wei Sun, 2004) Permeability Gardner, D.R., Lark, R.J. and Barr, B. [14] (2004) conducted a research by tested 100 mm cubes with strength 40 MPa and 100 MPa at temperatures of 85 and 105 C. Relative gas permeability test have been conducted to measure the permeability of concrete. The results show that the effect of concrete grade on permeability on concrete is obviously greater than the influence of conditioning

36 15 temperature, as shown in Table 2.1. There is no significant different in permeability results for concrete of same grade tested in different temperatures. Table 2.1: C40 and C100 concrete mean permeability parameters (Gardner, D.R., Lark, R.J. and Barr, B., 2004) Temperature of conditioning ( C) Maximum mean percent (%) weight loss Mean value of m ( 10-5 ) Mean t1/2 (min) C40 concrete C100 concrete Porosity The pore structure of concrete is responsible to influence the properties of the concrete such as the strength, durability and permeability [5, 18]. Poon, C. S., Azhar, S., Anson, M. and Wong, Y.L. [5] (2001) conducted porosity analysis using mercury intrusion porosimetry (MIP) technique, which has a measuring pressure ranging from 0.01 to 207 MPa. The test was conducted on specimens subjected to temperatures of 600 and 800 o C. The test results indicate that porosity of concrete increase with the increase in temperature. In the research, pulverized fly ash (PFA) concretes had the lowest porosity and average pore diameter at all test temperatures, as shown in Figure The research results are consistent with the results of research done by Xu, Y., Wong, Y.L., Poon, C.S. and Anson, M. [18] (2001) who conducted porosity analysis at temperatures of 450 and 650 o C. Xu, Y. et. al. [18]

37 16 (2001) reported that the coarsening of pore structure of concrete became obvious when the exposure temperature was 450 o C and became even more severe after exposure to a temperature of 650 o C, as shown in Figure However, high PFA dosage in concrete had a beneficial effect in reducing pore structure coarsening at elevated temperatures. Figure 2.12: Residual porosity of NSCs (Poon, C. S., Azhar, S., Anson, M. and Wong, Y.L., 2001) Figure 2.13: Residual porosity of HSCs (Poon, C. S., Azhar, S., Anson, M. and Wong, Y.L., 2001) Note: CC is control concrete; FA is fly ash; BS is blast furnace slag; SF is silica fume.

38 17 Figure 2.14: Total porosity and average pore diameter of hardened cement paste in concrete (average pore diameters are marked on top of the columns in 10-2 µm) (Xu, Y., Wong, Y.L., Poon, C.S. and Anson, M., 2001) Note: C means concrete with pulverized fly ash (PFA) replacement ratio of 25% and water cement ratio of Compressive Strength Many researchers have stated that compressive strength of concrete decreases with temperature. Phan, L. T. [15] (2002) tested 100 x 200 mm cylinders with initial compressive strength ranged from 51 to 98 MPa using unstressed, stressed and residual unstressed test method under high temperatures ranged from 100 C to 600 C and reported that compressive strength of concrete are adversely affected by temperature, as shown in Figure Loses between 10 to 20% of original compressive strength were observed in normal strength concrete when heated to 300 C and between 60 to 75% at 600 C. For high strength concrete, a higher rate of strength loss than normal strength concrete were observed, which is about 40% loss of strength were observed at temperatures below 450 C.

39 18 Figure 2.15: Summary of Compressive strength-temperature relationships for normal weight concrete, obtained by unstressed test (Phan, L. T., 2002) Figure 2.16: Summary of Compressive strength-temperature relationships for normal weight concrete, obtained by residual unstressed test (Phan, L. T., 2002) Note: Mixture I, II and III are HSC; Mixture IV is NSC.

40 19 Figure 2.17: Summary of Compressive strengthtemperature relationships for normal weight concrete, obtained by stressed test (Phan, L. T., 2002) Cheng, F.P., Kodur, V.K.R. and Wang, T.C. [9] (2004) studied the effect of temperature ranged from 100 C to 800 C on four different type of 100 mm x 200 mm unstressed concrete cylinders under hot condition. The study reported that the strength of high strength concrete decreased as the temperature increased to 100 C, as shown in Figure Concrete specimens regained part of its strength at 200 C. The strength at 200 C is about 80% of the original strength at room temperature. At the temperatures range from 400 C to 800 C, the strength of the concrete specimens dropped sharply, reaching to about 20 and 40 percent of original strength at 600 C and 800 C respectively.

41 20 Figure 2.18: Normalized compressive strength of HSC as a function of temperature (Cheng, F.P., Kodur, V.K.R. and Wang, T.C., 2004) Min Li, Chun Xiang Qian and Wei Sun [11] (2004) investigated the residual properties of high-strength concrete after fire by tested prismatic specimens with grade of C40, C60, and C70 under temperatures ranged from 200 C to 1000 C. Figure 2.19 shows that high strength concrete has greater strength loss as compared to normal strength concrete and the difference is significant at temperature ranged from 25 C to 400 C.

42 21 Figure 2.19: Compressive strength of concrete after high temperature (Min Li, Chun Xiang Qian and Wei Sun, 2004) In a study done by Saemann and Washa [16] (1957) for normal strength concrete, reduction of 15% strength occurred as temperature increased to 125 C. For temperature of 125 to 250 C, a gain of strength of about 10% of the initial strength was observed. Further increase in temperature caused the strength drops rapidly. At 700 C, specimens experienced about 20 percent loss of its original strength. According to Gluekler, E.L. [17] (1979) in an investigation of the thermal behavior of concrete, failure of concrete at high temperature are affected by reduction of concrete strength and pressurization of concrete pores. At high temperatures, gradual cracking of concrete occurred due to the loss of water in cement paste. Shrinkage of cement paste and expansion of aggregate weakens the bond between the aggregate and the cement, thus reducing the strength of the concrete. Pressurization of concrete pores is cause by the expansion of water and gases in concrete during heating. Concrete spallation occurred when the internal pressure exceed the tensile strength of concrete.

43 22 Noumowe, A.N., Clastres, P., Debicki, G. and Costaz, J.-L. [12] (1996) investigated the properties and the behaviors of 160 mm 320 mm and 110 mm x 220 mm cylinders ordinary concrete and high strength concrete made with the same calcareous aggregates at high temperature up to 600 o C. They concluded that high temperature leads to a reduction of residual strength of both normal and high strength concretes, as shown in Figure The changes of residual compressive strength for both concrete are not significant at temperatures up to about 200 C. However, the strength drops rapidly after 350 C. From their research, both ordinary and high strength concrete exhibited the similar residual compressive strength curves. Figure 2.20: Ratio of residual compressive strength to initial strength (Noumowe, A.N., Clastres, P., Debicki, G. and Costaz, J.-L., 1996) Chan, Y. N., Peng, G. F. and Anson, M. [10] (1998) tested 100 mm cube specimens with compressive strengths of 39, 76 and 94 MPa under temperatures ranged from 400 C to 800 C. From the study, only a small amount of original strength was lost at temperature up to 400 C, as shown in Figure Both high strength concrete and normal strength concrete lost most of their strength at

44 23 temperature between 400 C and 800 C. According to them, the temperature range can be regarded as the critical temperature range to the strength loss of concrete. Figure 2.21: Compressive strength of three grades of concrete subjected to different peak temperatures (Chan, Y. N., Peng, G. F. and Anson, M., 1998) Figure 2.22: Percentage of residual compressive strength of three grades of concrete subjected to different peak temperatures to the original compressive strength (Chan, Y. N., Peng, G. F. and Anson, M., 1998) In a research done by Poon, C. S., Azhar, S., Anson, M. and Wong, Y.L. [5] (2001), the unstressed residual compressive strength of normal strength and high

45 24 strength pozzolanic concretes incorporating silica fume (SF), fly ash (FA) and blast furnace slag (BS) in 100mm concrete cubes at temperatures up to 800 C was investigated. They reported that high strength concrete suffer smaller loss of strength than normal strength concrete at high temperatures, as shown in Figure In high strength concrete, the pulverized fly ash (PFA) concretes showed the better fire resistance at elevated temperatures than granulated blast furnace slag (GGBS), ordinary Portland cement (OPC) and condensed silica fume (CSF) concretes. In normal strength concrete, the GGBS concretes gave better performance than PFA and OPC concretes. Figure 2.23: Relative residual compressive strength of high strength concrete (Poon, C. S., Azhar, S., Anson, M. and Wong, Y.L., 2001) Figure 2.24: Relative residual compressive strength of normal strength concrete (Poon, C. S., Azhar, S., Anson, M. and Wong, Y.L., 2001) Note: CC is control concrete; FA is fly ash; BS is blast furnace slag; SF is silica fume.

46 25 Xu, Y., Wong, Y.L., Poon, C.S. and Anson, M. [18] (2001) investigated the residual properties of pulverized fly ash (PFA) concrete with mm specimens at temperatures up to 800 C. They found that all concrete specimens showed a peak residual compressive strength higher than the original strength when exposed to temperature of 250 C, as shown in Figure Figure 2.25: Residual compressive strength and percentage to original value (Xu, Y., Wong, Y.L., Poon, C.S. and Anson, M., 2001) Note: C means concrete with pulverized fly ash (PFA) replacement ratio of 25% and water cement ratio of 0.5. Savva, A., Manita, P. and Sideris, K.K. [19] (2005) studied the influence of elevated temperatures on the mechanical properties of concretes containing pozzolanic materials: Milos earth (ME), Ptolemaida fly ash (PFA) and Megalopolis fly ash (MFA)) at temperatures of 100, 300, 600 and 750 C with 150 mm concrete cubes. They concluded that concretes with pozzolanic materials show better strength results than the pure OPC concretes at temperatures up to 300 C, as shown in Figure However, at temperature above 300 C, a higher decrease in strength is observed for the PFA (siliceous aggregates) concretes and ME (limestone aggregates) concretes.

47 26 Figure 2.26: Relative residual compressive strength of limestone concretes (Savva, A.; Manita, P. and Sideris, K.K., 2005) Figure 2.27: Relative residual compressive strength of siliceous concretes (Savva, A.; Manita, P. and Sideris, K.K., 2005)

48 27 In a reassessment done by Khoury, G.A. [20] (1992), strength losses in pulverized fuel ash (PFA) or slag are lower than that in OPC concrete. In some cases, the increase in strength was observed in blended cement concrete at temperatures up to 550 C, as shown in Figure Figure 2.28: Residual compressive strength of OPC/PFA pastes- 2 inch cubes (Khoury, G.A., 1992) Mass Loss In the research done by Noumowe, A. N., Clastres, P., Febicki, G. and Costaz, J. L. [12] (1996), mass loss was higher in normal strength concrete than in high strength concrete, as shown in Figure Between 120 and 350 C, the maximum loss rate (more than 7% weight loss) was observed.

49 28 Figure 2.29: Weight variations (Noumowe, A. N., Clastres, P., Febicki, G and Costaz, J. L., 1996) Cracking of Concrete According to Noumowe, A. N., Clastres, P., Febicki, G. and Costaz, J. L. [12] (1996), the surface cracking were more noticeable on high strength concrete than on normal strength concrete. The results is supported by Poon, C. S., Azhar, S., Anson, M. and Wong, Y.L. [5] (2001) who stated that the surface crack pattern is a good indication about the internal pore structure of the concrete. Generally, pozzolanic concrete such as Pulverized fly ash (PFA) concretes are less susceptible to cracking during heating [5, 18] Spalling of Concrete

50 29 Rapid heating will cause the occurrence of explosive spalling in high strength concrete, which has became one of the major concerns with high strength concrete in construction industry. Besides laboratory fire conditions, spalling has been observed under actual fire conditions. An example of them is a railcar fire in the English Channel tunnel on 18 November The spalling of concrete has caused severe damage to tunnel s concrete liner and cause dangers to rescue and fire fighting activities [21]. Spalling is the phenomenon when pieces of the hardened concrete surface exposed to fire break away explosively during rapid heating of concrete to high temperature. As the result of loss of the surface layers of the concrete during a fire, the core concrete is more vulnerable to high temperatures. The rate of transmission of heat to the reinforcement increases as the core concrete is no longer protected by concrete cover [13]. Bending of soften reinforcement will cause failure in concrete structures. Investigation on thermal properties of concrete specimens shows that spalling can be occurred as progressively break away of concrete pieces which causing a gradual reduction in mass or sudden disintegration of concrete into fine pieces, followed by the release of energy in violent manner and projection of the concrete pieces to all direction at high velocity. Investigation of Phan, L.T. [15] (2002) indicated that high strength concrete is believed to be more susceptible to explosion failure because of its low permeability, compared to normal strength concrete. Because of the high density and low permeability of concrete, the extremely high water vapor pressure will be generated in high strength concrete during exposure to fire. Occurrences of spalling have been observed but not consistently. In the study, explosive spalling has only occurred to a few specimens from a group of specimens that were subjected to certain testing conditions. The result shows that explosive spalling in high strength concrete is difficult to predict. In the report, explosive spalling occurred at temperature ranged from 300 C to 450 C, as shown in Table 2.2. The report

51 30 suggested that internal pressure is the primary cause of explosive spalling while secondary impact in this failure is thermal stresses. Table 2.2: Test Matrix (Phan, L.T., 2002) 2.2 Factors Affecting Fire Performance of Concrete Fire performance of high strength concrete is influenced by several factors Specimen Dimensions Specimens with larger size are more prone to explosive spalling than specimens with smaller size. Larger structures have capacity to store more energy

52 31 and lower ability to release heat and moisture to atmosphere. Energy stored in concrete cause an internal pressure that contributes to explosive spalling of concrete when exposed to high temperature. Normally small size specimens are used in the fire test of concrete. This may give misleading results as compared to actual fire condition on structures with far larger sizes [13]. Min Li, Chun Xiang Qian and Wei Sun [11] (2004) investigated the compressive strength loss of two grade 40 specimens with sizes of 100 x 100 x 100 mm and 150 x 150 x 150 mm. Figure 2.30 shows that specimens with larger size have lesser strength loss. Concrete is poor in heat transmission. Therefore specimen with larger size is less affected by temperature and will have higher strength. Figure 2.30: Effect of specimen size on compressive strength after high temperature (Min Li, Chun Xiang Qian and Wei Sun, 2004) Loading Conditions Loading conditions on concrete structures influence their fire performance at high temperatures. The effect of loading conditions on high strength concrete was

53 32 studied by Phan, L.T. [15] (2002) using three test methods (i.e.: stressed test, unstressed test, and unstressed residual test). The study shows that the three test methods have different strength losses results. For temperatures of 100 C and 200 C, strength loss of 20 % obtained in residual unstressed test, which are lower than 25 % to 30 % of strength losses obtained in stressed and unstressed test. For temperature up to 450 C, residual unstressed test displayed highest strength loss of 50 %, compared with 25 % to 30 % of strength losses for stressed and unstressed test methods. Generally, high strength concrete with preload stress is more prone to explosive spalling when exposed to high temperatures Moisture Content The moisture content influences the strength of concrete. Castillo and Durrani [8] (1990) found that higher moisture content in concrete leads to lower strength and greater possibility of spalling. He stated that denser internal microstructure in high strength concrete result in slower escape of moisture from concrete. Significant destructive spalling occurs when the moisture content is higher than 80%. According to Lankard, D.R. et. al. [22] (1971), the moisture content has a great effect on the strength of concrete as temperature increases. Reduction of the strength of concrete can be caused by water in concrete that weakens the bonding forces between gel particles by softens the cement gel Type of Aggregate Fire resistance of concrete is affected by several mineral groups in the aggregate used in production of concrete. In a research done by Sullivan and Shanshar [23] (1992), concrete using siliceous aggregate (such as quartz and calcite) experienced higher strength loss than that using carbonate aggregate (such as limestone and marble) after exposed to high temperature. This can be explained by Dolar Mantuani, Ludmila [24] (1983) that the thermal expansion coefficient of

54 33 siliceous aggregate is higher than carbonate aggregate. A higher thermal expansion coefficient is caused by the higher rate of heat transmission which results in lower resistance to fire exposure. Blundell, R. [25] (1969) found that strength of concrete will reduce with the increase of the ratio of modulus of elasticity of aggregate to the coefficient of thermal expansion of aggregate. He also stated that reduction in strength is caused by the stresses generated between the aggregate and hardened cement paste due to different thermal expansion of the cement paste and aggregate when subjected to heating. This can result in micro cracking and disruption of the cement-aggregate bond and thus causing the reduction of strength Heating Rate Quantitative report about the effect of heating rate is quite limited. Diederichs, U. et. al. [26] (1989) tested concrete at heating rate of 2 C and 32 C to simulate slow and rapid heating condition on concrete. The results of study show that higher heating rate caused the concrete more prone to thermal explosive spalling Concrete Density Compared with high strength concrete made of normal weight aggregates, high strength concrete made of lightweight aggregate are more susceptible to explosive spalling. It is believed due to the higher vapor pressure in the lightweight aggregate when at high temperature as the lightweight aggregate contains more water content than normal weight aggregates [13] Concrete Strength

55 34 Concrete with higher original compressive strength experiences higher rate of strength loss after exposed to high temperature. Concrete strengths higher than 55 MPa have lower fire endurance and more prone to explosion failure [13] Cooling Conditions Based on the previous studies, cooling systems used by fire fighting activities during accidental fire have significant effect on the properties of concrete. Metin Husem [27] (2005) studied the effect of cooling method (cooled in air and cooled in water) on the residual strength of concrete by tested prismatic micro-high performance (HPMC) and ordinary micro-concrete (OMC) concrete with dimension mm after exposed to temperature ranged from 200 C to 1000 C. According to the results, residual flexural and compressive strength for both high strength and normal strength concrete decrease as temperatures increase and the rate of reduction is greater in concrete that used water cooling method, as shown in Figure The results are supported by Sakr, K. and EL-Hakim, E. [28] (2005) in a study of the effects of air, foam and water cooling methods on mechanical properties of concrete specimens with dimension mm. He stated that greater reduction of compressive strength occurred in water cooling method compared to air or foam cooling methods because water caused a big damage to concrete, as shown in Table 2.3.

56 35 Figure 2.31: Comparison of design curves and experimental loss of strength curves (Metin Husem, 2005) Table 2.3: Maximum compressive strength (MPa) of gravel concrete at different temperatures ( o C) using different cooling methods. (Sakr, K. and EL-Hakim, E., 2005) Xin Luo, Wei Sun and Sammy Yin Nin Chan [29] (1999) examined the effect of heating and cooling regimes on normal strength and high strength concrete after exposed mm specimens to peak temperatures of 800 C and 1100 C. They found that the effect of cooling regimes became less significant at higher temperatures, as shown in Figure Figure 2.32: The compressive strength before and after exposure to 800 C (Xin Luo, Wei Sun and Sammy Yin Nin Chan, 1999)

57 36 Note: Series of NP are NSC; series of HS, HF1S and HF2S are HSC Figure 2.33: The compressive strength before and after exposure to 1100 C (Xin Luo, Wei Sun and Sammy Yin Nin Chan, 1999) 2.3 Replacement of POFA in Concrete Salihuddin Radin Sumadi and Mohd. Warid Hussin [2] (1995) investigated the possibility of POFA to replace cement by tested 50mm mortar cubes containing various proportions of POFA with fineness of 725 m 2 /kg. They reported that POFA satisfied the requirement of ASTM C to be classified as Class F pozzolanic material. From the research, it is possible to replace POFA up to 20% of cement without affecting the strength of mortar, as shown in Figure According to permeability analysis in the research, permeability of POFA mortar is higher than OPC mortar at early ages, as shown in Figure However the permeability of POFA mortar reduces with age due the formation of additional gel as the result of pozzolanic reaction of POFA with cement. Lower permeability of concrete will result in a more durable material. Figure 2.36 illustrated the reduction of calcium hydroxide content in POFA samples with age and the trend of depletion is similar with samples containing PFA.

58 37 Figure 2.34: Effect of replacement levels on strength (Salihuddin Radin Sumadi and Mohd. Warid Hussin, 1995) Figure 2.35: Coefficient of permeability of OPC/POFA mortar (Salihuddin Radin Sumadi and Mohd. Warid Hussin, 1995)

59 38 Figure 2.36: Calcium hydroxide depletion for OPC and OPC/AA samples (Salihuddin Radin Sumadi and Mohd. Warid Hussin, 1995) The replacement of POFA in cement in concrete is examined by Abdul Awal, A.S.M. and Hussin, M.W. [3] (1996) by tested concrete cubes (mix proportion of 1: 2:3 for cement, fine and coarse aggregates with water cement ratio of 0.5) containing POFA at replacement level of 10, 20, 30, 40, 50 and 60% of cement weight. The research shows that it is possible to replace 40% POFA in concrete without adverse effect on compressive strength and the maximum strength was achieved for concrete with 30% POFA replacement, as shown in Figure Based on the research, the strength of concrete became higher with the increase of POFA fineness, as shown in Figure 2.38.

60 39 Figure 2.37: Effect of ash content on compressive strength of concrete (Abdul Awal, A.S.M. and Hussin, M.W., 1996) Figure 2.38: Effect of fineness of ash on compressive strength of concrete (Abdul Awal, A.S.M. and Hussin, M.W., 1996)

61 40 In a research done by Vanchai Sata, Chai Jaturapitakkul and Kraiwood Kiattikomol [30] (2004), utilization of POFA in high strength concrete was investigated by tested concrete cylinders with 100 mm in diameter and 200mm in height. They reported that concrete containing up to 20% of POFA gave the maximum compressive strength, as shown in Figure From the research, POFA with high fineness of 1244 cm 2 /g (median particle size of 10.1 µm) can be used to produce high-strength concrete. According to them, the POFA with higher fineness had greater pozzolanic reaction with cement and the small particles of POFA could also fill in the voids of concrete mixture, result in increasing of the compressive strength of concrete. Figure 2.39: Comparison of compressive strength of concrete mixed with ground palm oil fuel ash (Vanchai Sata, Chai Jaturapitakkul and Kraiwood Kiattikomol, 2004) 2.4 Compressive strength test Three types of compressive strength test are commonly used to study the effect of high temperature exposure on the compressive strength of concrete. The

62 41 purpose of these test methods is to provide properties data of concrete by stimulating the real loading and fire condition Stressed Test A preload (a fraction of the ultimate compressive strength at room temperature) is applied to the specimen and sustained during heating to the test temperature. When the desired temperature is reached, the load increased until the specimens fail Unstressed Test The specimens are heated to an elevated temperature without any initial load and maintained until a steady state is reached. Steady state is defined as a constant situation when the center of the specimen achieves temperature around 10 C of the target temperature, and the difference between the surface and internal temperatures is less than 10 C [31]. When the steady-state temperature is reached, load will applied to the specimens until failure Residual Unstressed Test The specimens are heated without any initial load to desired temperature and allowed to cool to room temperature. When the specimens reached room temperature, they will be loaded until failure.

63 CHAPTER 3 RESEARCH METHODOLOGY 3.1 Variables There are two primary variables in this study: 1) the temperature, 2) the compressive strength of concrete. Testing of concrete specimens was conducted at different temperatures (room temperature, 100, 300, 500, and 800 o C) for normal strength concrete, high strength concrete and POFA concrete. The specimens were 28 days age at the time of the tests. Mechanical properties of these concrete specimens were compared with each other and then compared with the samples which had not been heated. For comparison purposes, all types of concrete specimens were subjected to identical heating and cooling conditions. Two cooling conditions of heated concrete were performed. First condition is gradually cooling: natural cooling of concrete in air until the room temperature was reached. Second condition is rapid cooling: the hot specimens at the peak temperature were immersed into water until the room temperature was reached. Effects of the type of cooling on compressive strength of concrete specimens were examined. 3.2 Materials and Mix Proportions The materials used in this study were: ordinary Portland cement (ASTM Type I), sand (fine aggregate) and crushed aggregate with maximum sizes of 10 mm (coarse aggregate) conforming to BS 882:1983 [32]. Cube specimens were prepared

64 43 for three types of concrete named grade 40 ordinary Portland cement (OPC) concrete, grade 80 OPC concrete and grade 40 POFA concrete respectively. The grade 40 OPC concrete was considered to be normal strength concrete (NSC), consisting of ordinary Portland cement (OPC), aggregates and water. The grade 80 OPC concrete was considered to be high strength concrete (HSC). Grade 40 POFA concrete was an addition to this research in order to compare the POFA blended concrete with pure OPC concrete at high temperatures. The POFA was conformed to ASTM C618-92a [33]. The research by Abdul Awal, A.S.M. and Hussin, M.W. [3] stated that it is possible to replace POFA in 1:2:3 mix concrete (a mix proportion of 1:2:3 for cement, fine and coarse aggregates with water cement ratio of 0.5 which produced average strength of 45MPa ) up to 40% of total weight of cement without worsening the strength of concrete. However, a 20% replacement of cement with POFA in the mix proportion of 80MPa high strength concrete in this study had merely achieved average strength of 41MPa at 28 th day. According to Vanchai Sata et. al. [30], high strength POFA concrete required very fine POFA to achieve the desired strength at early age. Thus, further investigations are required in order to obtain high strength POFA concrete. In producing this high-strength mix and POFA mix, liquid superplasticizer (1 litre per 100kg of cement) was used to achieve the desired workability and 28 days compressive strength. The method of mix design applied is according to the method published by the Department of Environment UK [34] (1988). The mix proportions and concrete strength at 28 th day are reported in Table 3.1. Mineralogical composition of Ordinary Portland Cement and POFA Cement is shown in Table 3.2.

65 44 Table 3.1: Mix proportion and compressive strength of concretes Grade (MPa) 40 (OPC ) 40 (POFA) 80 (OPC) Cement (kg/m 3 ) POFA (kg/m 3 ) Coarse aggregate (kg/m 3 ) 10 mm Fine aggregate (kg/m 3 ) Water (kg/m 3 ) Superplasticizer (L) Cube strength at 28 days Table 3.2: Mineralogical composition of Ordinary Portland Cement and POFA Cement Percentage (%) Phase OPC 80%OPC+20%POFA C 3 S C 2 S C 3 A C 4 AF Test Specimens 100 mm cube specimens were prepared. At least four cubes were tested for a given set of temperature condition. For each grade of concrete, 3 cube specimens were kept at room temperature as control cubes and the other 16 cube specimens were put in the oven until desired temperature was reached. For each selected temperature condition, two cubes were cooled in water and the other two were cooled in air until they reach room temperature. Numbers of test specimens are reported in Table 3.3.

66 45 Table 3.3: Numbers of test specimens for each set of condition Mixture\Temperature Room 100 o C 300 o C 500 o C 800 o C Total cubes 40MPa OPC MPa POFA MPa OPC Apparatus Sieves and Mechanical Sieve Shaker Standard sieves size of 10 mm, 5 mm, 1.18 mm, 600 µm and 300 µm were used to sieve the POFA. Sieves were placed in order of decreasing apertures size from top to bottom. Electrically operated mechanical sieve shaker was used to create vibration of the sieves Los Angeles Abrasion Machine Los Angeles Abrasion Machine with steel bars of 12 mm diameter and 800 mm long were used to grind the POFA Concrete Mixer Concrete mixer used is laboratory type and electrically operated pan mixer with maximum recommended capacity of 112 liters. The amount of mixing batch is between 50 % and 90 % of the maximum capacity carried by the mixer to avoid

67 46 incomplete mixing and spillage of concrete. Before using the mixer, any fresh concrete in the mixer from previous batch was completely cleaned off Cube Moulds Standard steel cube mould with mm dimension was used. To prevent loss of water, the joints between the sides of the mould and between the sides and the base plate were thinly coated with mould oil before assembled. The whole assembly of mould was positively located and firmly held together to prevent leakage from the mould. A standard steel rod with mm dimension was used to compact the concrete Slump Test Apparatus This apparatus used for the determination of workability of fresh concrete mix. The apparatus comprises of a steel cone with foot pieces fitted on a base with wing bolts. The slump cone is 300 mm high, with diameter at base 200 mm and at top 100 mm. A tamping rod was used to compact the concrete specimen. The interior of slump cone was made sure clean of any concrete before the test Dimension and Mass Measurement Device Vernier caliper with measurement resolution to 0.1 mm was used to measure the dimension of concrete cube and an electrical balance with accuracy to 1g was used to determine the mass of specimens. Dimension measurements were made only before the specimens are heated. Mass measurements were done before and after specimens are heated in order to determine mass loss of specimens after exposure to high temperature.

68 Heating Device In order to dry the POFA before it can be sieved, an oven with temperature range from 100 to 110 o C was used. A high temperature electrical chamber furnace with maximum operating temperature of 1000 o C was used as heating device to test the concrete specimens at high temperatures. The furnace is using a digital temperature control system and both the inner and outer case of furnace is constructed from zinc coated steel. It is heated by resistance wire resting on refractory formers and has a power setting of 7000 watt Compression Testing Machine Electrically operated compression testing machine which works on hydraulic system was used. The machine is provided with digital display of load indicators and suitable for testing concrete cubes of size 100 x 100 x 100 mm. 3.5 Trial Mix Production of trial mix was done before preparation of test specimens. It will ensure that the strength, workability, density and other properties of concrete made from the mix design are as required and predicted. Compression tests were conducted at 7, 14 and 28 days age of concrete. Numbers of concrete specimens for trial mix are reported in Table 3.4. Table 3.4: Numbers of specimens for trial mix Mixture\Days 7 28 Total cubes 30MPa MPa MPa 3 3 9

69 POFA Preparation Preparation of POFA was conducted according to the procedures mentioned in the research report done by Abdul Awal, A.S.M. and Hussin, M.W. [3]. POFA, the product of burning palm oil husk and shell was collected form a local oil mill. After collection, the POFA was dried in oven at temperature of 105 ± 5 o C for 24 hours to remove its moisture content. After that the dried POFA was sieved through 300µm sieve by mechanical sieve shaker for a sufficient period to remove any foreign material and bigger size particles. The sieved POFA (maximum 4 kg each time) was ground in Los Angeles Abrasion Machine for at least 7 hours. Steel bars of 12 mm diameter and 800 mm long were used in Los Angeles Abrasion Machine to grind the ashes. 3.7 Sample Preparation Mixing of fresh concrete was conducted according to BS1881:Part125:1983 [35]. Firstly, half the coarse aggregate was added in the mixer, followed by the fine aggregate, the cement and the remaining coarse aggregate. The mixture was spread evenly over the pan and then the mixer was started with adding all of the water during the first 30 s of mixing. Mixing was continued for another 2 min to 3 min. Slump tests were conducted for the resulting concrete to determine the workability of concrete. The procedures of slump test are according to BS1881:Part102:1983 [35]. Three layers of concrete with same thickness were filled into coned mould and compacted by using a standard steel rod. Each layer of concrete was tamping 25 strokes with the steel rod. After that, the top surface of concrete was level using a trowel. The mould was removed slowly by raising it vertically in 5s to 10s. The slump was measured immediately after the mould was removed by determining the difference between the height of the mould and of the highest point of the specimen being tested.

70 mm concrete cubes were cast after mixing of concrete. The procedures of making concrete cubes are as given in BS1881:Part108:1983 [35]. The interior surfaces of cube moulds were coated with mould oil to prevent adhesion of concrete before placing the concrete. Concrete cubes casting was done by filling each mould with three layers of concrete. Each layer was compacted by using a 25 mm steel bar. 35 strokes per layer will be applied and the strokes will be ensuring that distribute uniformly over the cross-section of the mould. Preparation of concrete cubes for each category of concrete was done in the same batch. 3.8 Storing and Curing of Sample After casting, the samples in steel mould were stored for 24 hours at room temperature and covered with wet gunny sacks to ensure a relative humidity of higher than 90%. After 24 hours, the samples were removed from mould and cured in water. At the age of 27 days, the specimens were taken out of the tank, wiped off water on the specimen surfaces and kept at room temperature for 24 hours in order to achieve a surface dry condition. 3.9 Experimental Procedure Heating of concrete was conducted at the age of 28 days. Mass and dimension measurements were made before the specimens were placed into center of electric furnace for heating at a rate of 10 o C/minute. After the desired temperature was reached, the specimens were placed in the furnace and maintained for 1 hour to attain a steady condition and then allowed to cool down gradually and rapidly. In gradually cooling, the hot specimens were cooled naturally in air to the room temperature (approximately 24 hours of cooling time). In rapid cooling, the hot specimens at the peak temperature were taken out of the oven and immediately dipped into a water tank until the room temperature was reached. Appearances of hot concrete specimens at different temperature were observed.

71 Testing Procedures Compressive strength test was carried out after the cubic specimens were stabilized at room temperature. Concrete specimens that exposed to high temperatures were weighed before the compressive strength test was conducted. The residual compressive strengths of concrete cubes were determined according to BS1881:Part116:1983 [35]. The compressive strength tests on all concrete samples were performed with a constant loading rate. The reason of choosing a constant rate of compression is to provide a moderate rate of loading which will produce consistent results that represent more accurately the true compressive strengths of the specimens. The load was applied continuously without shock until the specimen fails, and the maximum load carried by the specimen during the test was recorded.

72 CHAPTER 4 TEST RESULTS AND DISCUSSIONS 4.1 Residual Compressive Strength of Concrete The residual compressive strength of test cubes after heating at different temperatures was determined and the test results were shown in Table 4.1 and Figure 4.1. Grade 40 ordinary Portland cement concrete, grade 80 ordinary Portland cement concrete and grade 40 POFA concrete are regarded as OPC 40, OPC-80 and POFA- 40 respectively. Table 4.1 Residual compressive strength of concrete at elevated temperatures Temperature Average compressive Normalized strength ( o C) Concrete strength, f c (MPa) f c /f c(room) Air Water Air Water OPC Room OPC POFA OPC OPC POFA OPC OPC POFA OPC OPC POFA OPC OPC POFA

73 Residual Compressive strength (Mpa Temperature ( o C) Water cooling(opc-40) Air cooling(opc-40) Water cooling(opc-80) Air cooling(opc-80) Water cooling(pofa-40) Air cooling(pofa-40) Figure 4.1: Residual compressive strength of concrete subjected to different temperatures Effect of Cooling Regimes on Residual Compressive Strength of Concrete For better comparison of results, a ratio f c /f c(room) was calculated to give expression for the residual compressive strength of concrete after subjected to elevated temperatures. f c is the residual compressive strength after subjected to certain temperature and f c(room) is the strength of concrete at room temperature. The effects of cooling regimes on residual compressive strength of concrete are as shown in Figure

74 Normalized strength, fc/fc(room) Water cooling Air cooling Temperature( o C) Figure 4.2: Loss of strength curves for OPC Normalized strength, fc/fc(room) Water cooling Air cooling Temperature( o C) Figure 4.3: Loss of strength curves for OPC-80

75 Normalized strength, fc/fc(room) Water cooling Air cooling Temperature( o C) Figure 4.4: Loss of strength curves for POFA-40 As shown in Figure , cooling conditions did not cause a significant difference in residual strength of concrete at temperature up to 100 o C and the differences of strength losses between air cooling and water cooling were not more than 4%. From Figure , the effect of cooling regimes began to take place when the temperature was increased from 200 to 700 o C. It was observed that strength loss in concrete cooled in water was more than concrete cooled in air. The additional strength losses caused by water cooling regime when compared to air cooling regime were 13% at 300 o C and 11% at 500 o C for OPC-40. For OPC-80, the additional strength losses were 18% at 300 o C and 21% at 500 o C. The additional strength losses of 10% and 34% were observed for POFA-40 at 300 and 500 o C respectively. The results are consistent with the research results from previous study that water cooling on heated concrete caused more decrease in strength as compared to air cooling [27, 28, 29]. Figure 4.5 shows the comparison of loss of strength curves obtained in this research with curves obtained by Metin Husem [27] (2006). In Metin Husem s [27] (2006) study, for ordinary micro-concrete at 400 and 600 o C, compressive strength losses after water cooling were both 17% more than compressive strength losses after air cooling. For high performance micro-concrete, compressive strength of water cooling showed a greater drop of 6% and 8% at 400

76 55 and 600 o C respectively compared to compressive strength of air cooling. Metin Husem [27] (2006) concluded that internal pressure in the concrete may increase when the heated aggregate is rapidly cooled in water and this pressure may cause the damages in concrete. He also stated the expansion of cement in its composition in water is the cause for deterioration of concrete. When concrete are cooled in water, calcium oxide, which decomposed from calcium hydroxide (exist in hydrated Portland cement) at high temperature is wetted and transforms into calcium hydroxide again. This will cause the changes in volume and thus results in deterioration of concrete (refer to Photo 4.2 which showed that greater cracks occurred in concrete cooled in water). According to Ivan Janotka and Terezia Nurnbergerov [36] (2005), strength loss are related with crack expansion in concrete specimens due to the rapid cooling of heated concrete. Noumowe, A.N. et. al. [27] (1996) stated that thermal shock produced by rapid water cooling could results in deterioration of the concrete structure. OPC-40 - air OPC-80 - air OPC-40 - water OPC-80 - water Figure 4.5: Comparison of research results (air cooling and water cooling) with Metim Husem s (2006) curves Note: OMC is ordinary micro-concrete (NSC); HPMC is high performance micro-concrete (HSC).

77 56 At temperature above 500 o C, the effect of cooling regimes became less pronounced with the increase of temperatures, as shown in Figure This result is similar with the statement made by Xin Luo et al. [29] (2000) that effect of cooling rate is less significant when concrete is exposed to higher temperatures. From Figure 3.2, compressive strength gain of 3% was observed in OPC-80 cooled in air when temperature was increased from 100 to 300 o C. Figure 3.3 shows that POFA-40 regained 12% of its strength when temperature was increased from 100 to 500 o C. There was no strength gain observed in concrete cooled in water, as shown in Figure According to the result obtained by Metin Husem [27] (2006), compressive strength gains are 13% for the specimens cooled in air and 5% for specimens cooled in water from 200 to 400 o C, as shown in Figure 4.5. The increment of strength may caused by removal of absorbed water from the cement paste at certain temperature, which contributes to the increase of Van der Waals forces between cement gel particles [9, 12, 18, 20, 27]. The specimens cooled in water don t show any strength gain or show lower strength gain because some of the evaporated water is regained when they are cooled in water [27] Residual Compressive Strength for Different Types of Concrete The comparison of residual compressive strength of OPC-40, OPC-80 and POFA-40 is shown in Figure The temperature range can be divided into three regions as room temperature to 100 o C, o C and o C. Each temperature range shows a different pattern of strength changes.

78 Normalized strength, fc/fc(room) OPC 40 MPa OPC 80 MPa POFA 40 MPa Temperature( o C) Figure 4.6 Loss of strength curves for test cubes cooled in air 1.20 Normalized strength, fc/fc(room) OPC 40 MPa OPC 80 MPa POFA 40 MPa Temperature( o C) Figure 4.7 Loss of strength curves for test cubes cooled in water At temperature up to 100 o C, there were drops in residual strengths for all types of concrete, as shown in Figure For OPC-40, the strength losses was 10% when cooled in air and 11% when cooled in water, while OPC-80 lost about 20% and 16% of strength when cooled in air and water respectively. POFA-40 showed losses of strength of 7% for both water and air cooling regimes. This finding is similar with the research done by Noumowe, A.N. et. al. [12] (1996) which

79 58 reported that the decrease of strength at this temperature is caused by localized boundary cracking in concrete due to thermal vapor pressure, as shown in Figure 4.8. OPC 40 MPa OPC 80 MPa Figure 4.8: Comparison of research results (air cooling) with Noumowe, A.N. et. al. s (1996) curves OPC 40 MPa OPC 80 MPa Figure 4.9: Comparison of research results (air cooling) with Chan, Y. N. et. al. s (1999) curves

80 Normalized strength, fc/fc(room) NSC- Poon, C.S. et al. HSC- Poon, C.S. et al. OPC-40-air OPC-80-air Temperature( o C) Figure 4.10: Comparison of research results (air cooling) with Poon, C. S. et. al. s (2001) curves OPC 40 MPa OPC 80 MPa Figure 4.11: Comparison of research results (air cooling) with Phan, L. T. s (2002) curves Note: Mixture I, II and III are HSC; Mixture IV is NSC.

81 60 As shown in Figure , losses of strength for OPC-40 at 300 o C and 500 o C were 22% and 33% respectively for air cooling regime and 35% and 44% respectively for water cooling regime. From Figure 4.6, a slight strength gain of 3% was observed for OPC-80 at temperatures range from 100 to 300 o C when cooled in air and the strength loss was increased back to about 20% of its original strength at 500 o C. Figure 4.7 shows that residual strength of OPC-80 cooled in water decreased until achieved strength loss of 41% at 500 o C. The results are similar with findings reported by Chan, Y. N. et. al. [10] (1999), as shown in Figure 4.9. They indicated that coarsening of concrete pore structure is the reason for strength loss of concrete at temperature below 600 o C. Figure indicated that high strength concrete was more resistant to elevated temperatures in term of residual compressive strength at temperature higher than 200 o C. This is consistent with the results obtained by Poon, C. S. et. al.5, as shown in Figure Poon, C. S. et. al. [5] (2001) reported that the lower residual compressive strength of normal strength concrete is due to greater coarsening of pore structure in normal strength concrete at elevated temperature. In Poon, C. S. et al s [5] (2001) study, a decrease of 19% to 26% of the original strength was observed in normal strength concrete at temperatures range from 200 to 400 o C, while most of the high strength concrete still maintained their original strength, as illustrated in Figure From Figure , it is observed that the results obtained for normal strength and high strength OPC concrete in this research is similar with the previous researches. POFA-40 exhibited better fire resistance than other concrete by achieved maximum strength of 100% of its original strength at 500 o C for air cooling regime, as shown in Figure 4.6. The strength gain of POFA concrete can be explained by the formation of tobermorite gel as a result of the pozzolanic reaction of calcium hydroxide, Ca(OH) 2 in OPC with reactive silica in pozzolanic material. [5, 18, 19]. Table 4.2 shows that silicon dioxide (SiO 2 ), which may contribute to the formation of tobermorite gel, is 43.6% of chemical compositions in POFA compared to 20.2% of chemical compositions in OPC. According to Poon, C. S. et. al. [5] (2001), it is believed that tobermorite is three times stronger than the calcium-silicate-hydrate (C- S-H) gel.

82 61 Table 4.2: Chemical composition and physical properties of binders (Salihuddin Radin Sumadi and Mohd. Warid Hussin, 1995) OPC POFA PFA Chemical composition (%) Silicon dioxide SiO Aluminum oxide Al 2 O Ferric oxide Fe 2 O Calcium oxide CaO Magnesium oxide MgO Sulphur trioxide SO Sodium oxide Na 2 O Potassium oxide K 2 O Loss on ignition Physical properties Specific surface (m 2 /kg) Specific gravity Normalized strength, fc/fc(room) % PFA- Poon, C.S. et al. POFA Temperature( o C) Figure 4.12: Comparison of research results (air cooling) with Poon, C. S. et. al. s (2001) curves Note: 30% PFA is normal strength concrete with 30% pulverized fly ash (PFA) replacement level.

83 62 POFA 40 MPa Figure 4.13: Comparison of research results (air cooling) with Savva, A. et. al. s (2005) curves Note: OPC is ordinary Portland cement; MFA is Megalopolis fly ash; PFA is Ptolemaida fly ash; ME is Milos earth. POFA 40 MPa Figure 4.14: Comparison of research results (air cooling) with Xu, Y. et. al. s (2001) curves Note: C means concrete with pulverized fly ash (PFA) replacement ratio of 25% and water cement ratio of 0.5.

84 63 Figure illustrate the comparisons of strength changes of POFA concrete at elevated temperatures obtained in this research with strength changes of PFA concrete obtained from previous researches. It was observed that strength gains of POFA concrete in this research occurred at temperature up to 500 o C, which is inconsistent with previous researches that the increase in strength was observed in PFA concrete at temperatures up to C. Thus further investigations are needed to verify this result. From Figure , residual compressive strength was dropped sharply in temperatures range from 500 to 800 o C for all types of concrete. Again, POFA-40 performed better at these temperatures. At 800 o C, OPC-40, OPC-80 and POFA-40 underwent strength losses of 78%, 71% and 52% respectively when cooled in air and strength losses of 77%, 73% and 64% respectively when cooled in water. At 800 o C, the strength losses is mainly due to serious cracking and chemical decomposition (decomposition of calcium-silicate-hydrate (C-S-H) gel which cause the loss of binding property of cement gel) of concrete [5, 12, 18, 19, 20]. 4.2 Mass Loss Table 4.3 and Figure 4.15 showed the mass loss of concrete subjected to different temperatures. The mass losses of concrete were less significant at 100 o C, which were 0.468%, 0.178% and 0.366% for OPC-40, OPC80 and POFA-40 respectively. These results are in harmony with the research done by Noumowe, A.N. et. al. [12] (1996). They found that large amount of moisture still retain in concrete when temperature reached 100 o C.

85 64 Table 4.3 Mass loss of concrete at elevated temperatures Temperature ( o C) Concrete Average % Mass Loss OPC OPC POFA OPC OPC POFA OPC OPC POFA OPC OPC POFA Percentage of mass loss (%) Temperature ( o C) OPC 40 Mpa OPC 80 Mpa POFA 40 Mpa Figure 4.15 Mass loss of concrete subjected to different temperatures

86 65 Between 100 and 500 o C, the maximum rate of mass loss was observed. When temperature reached 500 o C, 6.292%, 5.290% and 6.347% of mass losses for OPC-40, OPC80 and POFA-40 respectively were obtained. The rate of mass loss decreased after 500 o C and resulted in mass losses of 7.804%, 6.219% and 7.179% for OPC-40, OPC80 and POFA-40 respectively at 800 o C. These mass losses are mainly due to the drying process (evaporation of free water) at temperatures up to 200 o C and dehydration of the main hydrates (C-S-H) at temperatures range from 200 to 600 o C [12]. Mass losses in high strength concrete are lower than normal strength concrete due to its denser microstructure [12, 14]. The mass loss after 700 o C is caused by the decomposition in concrete. Both normal strength OPC and POFA concrete had similar trend in the reduction of mass. 4.3 Spalling and Cracks Each type of concrete showed different pattern of cracks when subjected to elevated temperatures. For OPC-80, surface cracks started to appear at 500 o C and became greater with the increase of temperature, as shown in Photo 4.1(c) (d). As indicated in Photo 4.1(a) (b) and Photo 4.1(e) (f), surface cracks only occurred at 800 o C for OPC-40 and POFA-40. From Photo 4.1(b), some major cracks were observed in OPC-40 specimens. For OPC-80 specimens, more major cracks were observed when compared to OPC-40 specimens, as shown in Photo 4.1(d). Photo 4.2 shows that OPC-80 specimens cooled in water exhibited larger sizes of cracks when compared to specimens cooled in air. As shown in Photo 4.1(f), there were no major cracks for POFA-40 specimens, but minor cracks were observed. Poon, C. S. et. al. [5] (2001) stated that more surface cracking indicates that the internal structure of the concrete is denser. Concrete with denser internal structure such as high strength concrete suffer greater cracks at higher temperatures due to the internal pressure produced by evaporable water and expanded aggregates. Although POFA concrete has denser microstructure as stated by previous researchers [2, 4, 30], but it is reasonable to believe that the depletion of Ca(OH) 2 in POFA concrete due to pozzalanic reaction [2] could lead to reduced cracking at

87 66 elevated temperatures. According to Xu, Y. et. al. [18] (2001), cracking observed during cooling of heated concrete is related to the rehydration of dissociated calcium hydroxide (Ca(OH) 2 ). Ca(OH)2 would dissociate at temperatures above o C. In this study, no explosive spalling was observed for any types of concrete during heating. Compared to previous researches, explosive spalling normally occurred in high strength concrete at temperatures above o C [10, 15, 27]. No occurrence of explosive spalling in this research can be explained by Phan, L. T. [15] (2002) who indicated that explosive spalling in high strength concrete is difficult to predict due to the difference in specimen dimensions, moisture content, heating rate, loading condition etc. However, surface spalling occurred in OPC-80 specimens at 500 o C, as shown in Photo 4.3. According to Phan, L. T. [15] (2002), high strength concrete is more susceptible to spalling at high temperatures due to the buildup of pore pressure by water vapors because of its high density and low permeability.

88 67 (a) OPC-40 at 500 o C (b) OPC-40 at 800 o C (c) OPC-80 at 500 o C (d) OPC-80 at 800 o C (e) POFA-40 at 500 o C (f) POFA-40 at 800 o C Photo 4.1: Crack patterns observed at 500 o C and 800 o C

89 68 Photo 4.2: Crack patterns observed for OPC-80 specimens cooled in air (left) and cooled in water (right) at 800 o C Photo 4.3: Surface spalling observed at 500 o C for OPC-80 specimen

90 CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS 5.1 Conclusions Based on the results obtained, the conclusions drawn from this study are as follows: Cooling regimes affected the residual strength of concrete at temperatures range from 200 to 700 o C. The rate of strength loss is more in concrete cooled in water as compared with concrete cooled in air. For air cooling regime, compressive strength gains were observed in high strength OPC concrete from o C and normal strength POFA concrete from o C. No strength gain was observed in concrete cooled in water. High temperature can be divided into different ranges according to residual strength of concrete. From room temperature to 100 o C, there were drops in residual strengths for all types of concrete. High strength OPC concrete cooled in air regains part of their strength after 100 o C, while normal strength OPC concrete continued to loss its strength with the increase of temperature. At temperature higher than 200 o C, high strength OPC concrete is more resistant to elevated temperatures in term of residual compressive strength when compared to normal strength OPC concrete. POFA concrete showed better fire resistance than OPC concrete at elevated temperatures. Mass losses in high strength concrete are lower than normal strength concrete due to its denser microstructure. Mass of normal strength OPC concrete decreased in the similar manner to that of normal strength POFA concrete.

91 70 More surface cracking was observed in high strength concrete than normal strength concrete. Minor cracks only occurred in normal strength POFA concrete and this indicated that POFA concrete is able to retain their properties better at high temperatures. Specimens cooled in water exhibited larger sizes of cracks compared to specimens cooled in air. High strength concrete is more susceptible to spalling at high temperatures. 5.2 Recommendations Recommendations for the future study are as bellows: Conduct stress test and unstressed test for concrete at high temperatures in order to study the more actual situation of concrete in structural building. Besides compressive strength, investigate the effect of high temperatures on the other mechanical properties of concrete such as stress-strain relationship, tensile strength, flexural strength, elastic modulus, porosity and permeability. Increase the numbers and sizes of specimens to obtain more accurate result. Study the properties of concrete at higher temperature and closer temperature range to find every distinct change in properties of concrete when temperature increases. For example, temperatures at 100, 200, 300, 400, 500, 600, 700, 800, 900 and 1000 are recommended. Study the behavior of high strength POFA concrete at high temperature instead of normal strength POFA concrete. Cure the concrete for longer period of time until a stable strength condition is achieved.

92 71 REFERENCES 1. Phan, L. T. and Carino, N. J.. Fire Performance of High Strength Concrete: Research Needs. Proceedings of ASCE/SEI Structures Congress 2000: Advanced Technology in Structural Engineering. Philadelphia, USA Salihuddin Radin Sumadi and Mohd. Warid Hussin. Palm Oil fuel Ash (POFA) as a Future Partial Cement Replacement Material in Housing Constructiuon. Journal of Ferrocement. Vol.25 (1) Abdul Awal, A.S.M. and Hussin, M.W.. Properties of Fresh and Hardened Concrete Containing Palm Oil Fuel Ash. 3rd Asia Pacific Conference on Structural Engineering and Construction Danupon Tonnayopas, Fukit Nilrat, Kanung Putto and Jakathep Tantiwitayawanich. Efffect of Oil Palm Fiber Fuel Ash on Compressive Strength of Hardening Concrete. Proceedings of the Fourth Thailand Materials Science Technology Conference. Thailand Poon, C. S., Azhar, S., Anson, M. and Wong, Y.L.. Comparison of the Strength and Durability Performance of Normal- and High-Strength Pozzolanic Concretes at Elevated Temperatures. Cement and Concrete Research 31. pp Shah, S. P. and Ahmad, S. H.. High Performance Concrete, Properties and Applications. MC Graw-Hill. New York, USA. pp Felicetti, R., Gambarova, P.G., Rosati, G.P., Corsi, F. and Giannuzzi, G. Residual Mechanical Properties of High-Strength Concretes Subjected to High-Temperature Cycles. Proceedings of 4th International Symposium on Utilization of High-Strength/High-Performance Concrete. Paris, France. pp Castillo, C. and Durrani, A. J.. Effect of Transient High Temperature on High-Strength Concrete. ACI Materials Journal. Vol.87 (1). pp Cheng, F-P., Kodur, V.K.R. and Wang, T-C. Stress-Strain Curves for High Strength Concrete at Elevated Temperatures. Journal of Materials in Civil Engineering. Vol. 16(1). pp Chan, Y. N., Peng, G. F. and Anson, M.. Residual strength and pore structure of high-strength concrete and normal strength concrete after

93 72 exposure to high temperatures. Cement and Concrete Composites. Vol. 21. pp Min Li, Chun Xiang Qian and Wei Sun. Mechanical Properties of High- Strength Concrete after Fire. Cement and Concrete Research. Vol. 34. pp Noumowe, A. N., Clastres, P., Febicki, G. and Costaz, J. L.. Thermal Stresses and Water Vapor Pressure of High Performance Concrete at High Temperature. Proceedings of 4th International Symposium on Utilization of High-Strength/High-Performance Concrete. Paris, France Kodur, V.K.R.. Fire Performance of High-Strength Concrete Structural Members. Construction Technology Update. No Gardner, D.R., Lark, R.J. and Barr, B.. Effect of conditioning temperature on the strength and permeability of normal- and high-strength concrete. Cement and Concrete Research. Vol. 35. pp Phan, L.T.. High-Strength Concrete at High Temperature: An Overview. Proceedings of 6th International Symposium on Utilization of High- Strength/High-Performance Concrete. Leipzig, Germany. Vol. 1. pp Saemann, J. C. and Washa, G. W.. Variation of Mortar and Concrete Properties with Temperature. ACI Journal, Proceeding. Vol.54 (5). pp Gluekler, E.L.. Local thermal and structural behavior of concrete at elevated temperatures. Transaction of the 5th International Conference on Structural Mechanics in Reactor Technology, Vol. A. International Congress Center Berlin, Berlin, Germany. pp Xu, Y., Wong, Y.L., Poon, C.S. and Anson, M.. Impact of High Temperature on PFA Concrete. Cement and Concrete Research 31. pp Savva, A., Manita, P. and Sideris, K.K. Influence of elevated temperatures on the mechanical properties of blended cement concretes prepared with limestone and siliceous aggregates. Cement & Concrete Composites. Vol. 27. pp Khoury, G.A.. Compressive Strength of Concrete at High Temperatures. Magazine of Concrete Research. Vol. 44. pp

94 Comeau, Ed and Wolf, Alisa. Fire in the Chunnel. NFPA Journal. National Fire Protection Association, Quincy, MA. Vol. 91 (2). pp Lankard, D.R., Birkimer, D.L., Fondfriest, F.F. and Synder, M.J. Effects of Moisture Content on the Structure Properties of Portland Cement Concrete Exposed to Temperatures up to 500 o F. Temperature and Concrete, SP-25, American Concrete Institute, Detroit. pp Sullivan, P. J. E. and Shanshar, R.. Performance of concrete at elevated temperatures as measured by the reduction in compressive strength. Fire Technology. Vol. 28 (3). pp Dolar Mantuani, Ludmila. Handbook of Concrete Aggregate: a Petrographic and Technological Evaluation. Noyes Publications. Park Ridge, New Jersey, USA. pp Blundell, R.. Discussions on Structure, Solid Mechanics and Engineering Design. Proceeding of a conference on civil Engineering Materials. Southampton Diederichs, U., Jumppanen, U.M., and Penttala, V.. Behavior of High Strength Concrete at High Temperatures. Report 92. Helsinki University of Technology Metin Husem. The Effects of High Temperature on Compressive and Flexural Strengths of Ordinary and High-Performance Concrete. Fire Safety Journal. Vol. 41. pp Sakr, K. and EL-Hakim, E.. Effect of High Temperature or Fire on Heavy Weight Concrete Properties. Cement and Concrete Research. Vol. 35. pp Xin Luo, Wei Sun and Sammy Yin Nin Chan. Effect of heating and cooling regimes on residual strength and microstructure of normal strength and high-performance concrete. Cement and Concrete Research. Vol. 30. pp Vanchai Sata, Chai Jaturapitakkul and Kraiwood Kiattikomol. Utilization of Palm Oil Fuel Ash in High-Strength Concrete. Journal of Materials in Civil Engineering, ASCE, Vol. 16 (6) Phan, L. T. and Carino, N. J.. Effects of Test Conditions and Mixture Proportions on Behavior of High-Strength Concrete Exposed to High Temperature. ACI Materials Journal. Vol. 99 (1). pp

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96 APPENDIX A 75

97 APPENDIX B 76

98 APPENDIX C 77

99 APPENDIX D 78

100 79 APPENDIX E Residual compressive strength of concrete subjected to different temperatures OPC Concrete Grade 40 Temperature Cooling Specimen Strength Average Strength Normalized strength ( o C) Method (Mpa) (Mpa) f c /f c(room) Water Air Water Air Water Air Water Air OPC Concrete Grade 80 Temperature Cooling Specimen Strength Average Strength Normalized strength ( o C) Method (Mpa) (Mpa) f c /f c(room) Water Air Water Air Water Air Water Air

101 80 POFA Concrete Grade 40 Temperature Cooling Specimen Strength Average Strength Normalized strength ( o C) Method (Mpa) (Mpa) f c /f c(room) Water Air Water Air Water Air Water Air

102 81 APPENDIX F Mass loss of concrete subjected to different temperatures OPC Concrete Grade 40 Temperature Specimen Mass (g) % Mass Average ( o C) Before Heating After Heating Loss % Mass Loss OPC Concrete Grade 80 Temperature Specimen Mass % Mass Average ( o C) Before Heating After Heating Loss % Mass Loss POFA Concrete Grade 40 Temperature Specimen Mass % Mass Average ( o C) Before Heating After Heating Loss % Mass Loss

103 82