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Mechanochemical investigation into bond performance of an NSM CFRP strengthening system at elevated temperatures

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Title:
Mechanochemical investigation into bond performance of an NSM CFRP strengthening system at elevated temperatures
Creator:
Siriwasrdanage, Trushara ( author )
Place of Publication:
Denver, CO
Publisher:
University of Colorado Denver
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Language:
English
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1 electronic file (199 pages). : ;

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Subjects / Keywords:
Fiber-reinforced concrete ( lcsh )
Fiber cement ( lcsh )
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bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

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Review:
Near surface mounted (NSM) fiber reinforced polymer FRP strengthening system is a promising strengthening technique that increases the flexural and shear strengths in concrete members. FRP rods or strips are embedded in concrete members using polymeric epoxy resin or cementitious materials. Polymeric materials are highly sensitive to high temperatures. Limited number of research studies have been conducted evaluating the bond performance of NSM FRP strengthened systems. Few references are available in the area of residual behavior of NSM System and fire protection systems for NSM strengthened concrete members. Two-phase experimental testing program was conducted to evaluate the mechanochemical performance of NSM CFRP strengthened concrete members. Material-level testing includes a Fourier transform infrared spectroscopy (FTIR) interpretation of bond degradation mechanism of polymeric adhesives and degradation of mechanical properties of polymeric materials. Used epoxy resin was exposed to elevated temperatures ranging from 25°C [77°F] to 200°C [392°F]. FTIR spectrums were collected for residual epoxy samples to examine the degradation of chemical bonds using a mid-range FTIR instrument. The effect of mechanical properties of epoxy resin was investigated from a coupon test. The element-level testing was conducted to investigate the bond performance of NSM CFRP strengthening system in fire. NSM CFRP strengthened concrete elements were exposed up to elevated temperatures of 200°C [392°F]. Monotonic tension test was conducted to evaluate the pull out strength, load-displacement behavior and different failure modes and cyclic loading was applied to examine the bond stiffness of NSM CFRP systems at elevated temperatures. Also, internal thermal propagation at the mid-span of the concrete element was examined using an Infrared (IR) thermal camera. Test results illustrate that the polymeric adhesives have significant influences on the mechanical properties of the epoxy resin that can reduced the overall strength of the NSM CFRP systems. Different failure modes were observed with decreased ultimate pull out strength at high temperatures. FTIR spectrums proved the effect on polymeric materials at high temperatures. Also, internal thermal propagation justify the observed failure modes and the strength degradation. This thesis presents the conducted experimental testing program and its results.
Thesis:
Thesis (M.S.)--University of Colorado Denver. Civil engineering
Bibliography:
Includes bibliographic references.
General Note:
Department of Civil Engineering
Statement of Responsibility:
Trushara Siriwardanage.

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University of Colorado Denver
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|Auraria Library
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All applicable rights reserved by the source institution and holding location.
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904622866 ( OCLC )
ocn904622866

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MECHANOCHEMICAL INVESTIGATION INTO BOND PERFORMANCE OF AN NSM CFRP STRENG THENING SYSTEM AT ELEVATED TEMPERATURES By THUSHARA SIRIWARDANAGE B.S., North Dakota State University, 2013 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment Of the requirements for the degree of Master of Science Civil Engineering 2014

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2014 SIRIWARDANAGE THUSHARA ALL RIGHTS RESERVED

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ii This thesis for the Master of Science degree by Thushara Siriwardanage h as been approved for the Civil Engineering program By Yail J immy Kim, C hair Nien Yin Chang Fredrick Rutz July 18, 2014

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iii Siriwardanage Thu shara (M.S., Civil Engineering) Mechacnochemical Investigation into Bond Performance of an NSM CFRP Strengthening System at Elevated Temperatures Thesis dir ected by Associate Professor Yail Jimmy Kim ABSTRACT Near surface mounted (NSM) fiber reinforced polymer FRP strengthening system is a promising strengthening technique that increase s the flexural and shear strengths in concrete members. FRP rods or strips are embedded in concrete members using polymeric epoxy resin or cementitious materials. Polymeric materials are highly sensitive to high temperatures. Limited number of research studies have been conducted evaluating the bond performance of NSM FRP strengthened systems Few references are available in the area of residual behavior of NSM System and fire protection systems for NSM strengthened concrete members. Two phase experimental testing program was conducted to evaluate the mechanochemical performance of NSM CFRP st rengthened concrete members. Material level testing includes a Fourier transform infrared spectroscopy (FTIR) interpretation of bond degradation mechanism of polymeric adhesives and degradation of mechanical properties of polymeric materials. Used epoxy re sin was exposed to elevat ed temperatures ranging from 25C [77F] to 200 C [392F] FTIR spectrums were collected for residual epoxy samples to examine the degradation of chemical bonds using a mid range FTIR instrument The effect of mechanical properties of epoxy resin was investigated from a coupon test. The element level testing was conducted to investigate the bond per formance of NSM CFRP strengthening system in fire. NSM CFRP strengthened concrete elements

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iv were exposed up to elevated temperatures of 2 00 C [392F] Monotonic tension test was conducted to evaluate the pull out strength, load displacement behav ior and different failure modes and c yclic loading was applied to examine the bond stiffness of NSM CFRP systems at elevated temperatures. Also, in ternal thermal propagation at the mid span of the concrete element was examined using an Infrared (IR) thermal camera. Test results illustrate that the polymeric adhesives have significant influences on the mechanical properties of the epoxy resin that can reduced the overall strength of the NSM CFRP systems. Different failure modes were observed with decreased ultimate pull out strength at high temperatures. FTIR spectrums prove d the effect on polymeric m aterials at high temperatures. Also, internal therma l propagation justify the observed failure modes and the strength degradation. This thesis presents the conducted experimental testing program and its results. The form and content of this abstract are approved. I recommend its publication. Approved : Jimmy Kim

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v ACKOWLEDGEMENT I had in a good university. There are a lot of people who helped me to reach that goal. First, I must take this chance to acknowledge my parents who wer e always with me. Their endless encouragements, helps and love have guide d me to be here in the first place. I believe that without my not have been able to come to this position today Therefore, I take this opportunity to thank my lovable parents. I offer my immense acknowledgement to my academic and research advisor Dr. Jimmy support I would not have been nver. His vision, advises and gu idance led to me pursue my goal in a relentless manner I would like to thank him for all things he had done for me and I cannot express my gratitude in word Also, I would like to acknowledge the department chair of civil engineering Dr. Kevin Rens for his great support by accepting me as a MS student and letting me continuing my higher education at UC Denver. It should be noted that the support I received from the civil engineering faculty was at its best and I thank all the faculty members. Also, I acknowledge all the professors whom I had classes with. Within this short period of time a lot of people supported me should pay my tributes to Mr. Tom Thu is, Jack, Shahlaa Alwakeel and Denny who helped me in many ways to complete my lab testing. Also, I take the chance to acknowledge Denise Davis for helping me to complete the chemical testing at chemistry department. I thank all the people who helped me in this short period of time.

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vi This research was supported by the US Department of Transportation through the Mountain Plains Consortium Program

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vii TABLE OF CONTENTS Chapter 1. Introduction ................................ ................................ ................................ ...................... 1 1.1 General ................................ ................................ ................................ ........................... 1 1.2 Research significance and objectives ................................ ................................ ............. 4 1.3 Scope ................................ ................................ ................................ .............................. 6 1.4 Thesis organization ................................ ................................ ................................ ........ 7 2. Literature Review ................................ ................................ ................................ ............. 9 2.1 Strengthening systems for concrete structures ................................ ............................... 9 2.2 FRP ................................ ................................ ................................ .............................. 10 2.2.1 FRP applications ................................ ................................ ................................ ....... 11 2.3.1 NSM techniques ................................ ................................ ................................ ........ 13 2.3.2 Previous applications on NSM ................................ ................................ .................. 14 2.3.3 Previous research studies on NSM FRP strengthening system ................................ 15 2.4 Fire endurance of concrete Structures ................................ ................................ .......... 16 2.5 NSM strengthened concrete structures exposed to fire ................................ ................ 18 2.6 FTIR ................................ ................................ ................................ ............................. 19 2.6.1 FTIR applications ................................ ................................ ................................ ...... 21 2.7 The glass transition temperature ................................ ................................ .................. 22 3. FTIR Interpretation of Epoxy Adhesive at Elevated Temperatures .............................. 29 3.1 General overview ................................ ................................ ................................ ......... 2 9 3.2 Experimental program ................................ ................................ ................................ 29 3.2.1 Materials ................................ ................................ ................................ ................... 29

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viii 3.2.2 Sample preparation for FTIR ................................ ................................ .................... 30 3.2.3 FTIR instrument setup ................................ ................................ .............................. 31 3.3 Assumptions of chemical reaction of epoxy and epoxy compound ............................ 31 3.4 Spectrum changes of epoxy samples over elevated temperature ................................ 33 3.5 Physical changes of epoxy under fire ................................ ................................ .......... 35 3.6 Conclusions ................................ ................................ ................................ .................. 36 4. Thermo mechanical Behavior of an Adhesive and CFRP ................................ ............. 56 4.1 General overview ................................ ................................ ................................ ......... 56 4.2 Materials ................................ ................................ ................................ ...................... 57 4.3.1 Sample Preparation ................................ ................................ ................................ ... 58 4.3.2 Instrument Setup ................................ ................................ ................................ ....... 58 4.4 Test results ................................ ................................ ................................ ................... 59 4.4.1 Influence of elevated temperatures on epoxy adhesive ................................ ............ 59 4.4.2 Influence of high temperatures on CFRP strips ................................ ........................ 61 4.5 Summery and conclusions ................................ ................................ ........................... 62 5. Performance of NSM CFRP concrete Interface Subjected to Elevated Temperatures 74 5.1 General ................................ ................................ ................................ ......................... 74 5.2 Experimental program ................................ ................................ ................................ 75 5.2.1 Materials ................................ ................................ ................................ ................... 76 5.2.2 Specimen preparation ................................ ................................ ................................ 77 5.2.3 Heat application ................................ ................................ ................................ ........ 78 5.2.4 Instrumentation and testing procedure ................................ ................................ ...... 79 5.3 Test results ................................ ................................ ................................ ................... 80

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ix 5.3.1 Pullout capacity ................................ ................................ ................................ ......... 80 5.3.2 Load displacement behavior ................................ ................................ ..................... 81 5.3.3 Failure mode ................................ ................................ ................................ ............. 82 5.3.4 Thermal propagation along the bond line ................................ ................................ 83 5.3.5 Bond stiffness of the NSM CFRP strengthening system at elevated temperatures .. 84 5.3.6 Thermal propagation at mid span of the concrete block ................................ .......... 85 6. Summery and Conclusions ................................ ................................ .......................... 125 Referen ces ................................ ................................ ................................ ........................ 131 Appendix A ................................ ................................ ................................ ................................ ....... 136 B ................................ ................................ ................................ ................................ ....... 147 C ................................ ................................ ................................ ................................ ....... 157 D ................................ ................................ ................................ ................................ ....... 170

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x LIST OF TABLES Table 2.1. Properties of FRP types (ACI 440.2R 08) ................................ ................................ .. 24 3.2. Ingredients of resin ................................ ................................ ................................ ..... 37 3.2. Ingredients of hardener ................................ ................................ ............................... 37 3.3 Identified FTIR vibrational modes ................................ ................................ .............. 38 4.1 Test results of epoxy coupons exposed to elevated temperatures ............................... 63 4.2 Ultimate tensile strength of CFRP coupons exposed to elevated temperatures .......... 64 4.3 Displacement at the ultimate load of CFRP coupons exposed to elevated temperatures ................................ ................................ ................................ ....................... 64 5.1. Concrete mix design ................................ ................................ ................................ ... 89 5.2. 30 days compressive strength of concrete cylinders ................................ ................... 89 5.3. Monotonic tension test results ................................ ................................ .................... 90

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xi LIST OF FIGURES Figure 2.1. Deterioration of concrete due to : (a) a ggression by ca rbon dioxide; (b) aggression by sulphates; (c) aggression by chlorides; (d) a lkali aggregates reaction [ MAPEI, 2011] ... 25 2.2. Exam ples of externally bonded strengthening system ................................ ................ 26 2.3 Typical cross sections NSM strengthened members ................................ .................. 26 2.4. Dimensions of NSM FRP system specified by ACI 440.2R 08 ................................ 27 2. 5. Previous application of NSM system (De Lorenzis, 2000) ................................ ........ 27 2.6. Concrete deterioration due to fire ................................ ................................ ............... 28 2.7. Fourier transform infrared spectrometer (FTIR) [Introduction to spectroscopy, 2008] ................................ ................................ ................................ ................................ ............ 28 3.1. IR vibrations modes (Infrared Spectral Interpretation, 1999). ................................ ... 39 3.2 Sample preparation : (a) epoxy specimens; (b) heat exposure; (c) electronic furnace 40 3.3 Epoxy adhesive: (a) resin ; (b) hardener ; (c) 1 hour cured epoxy ............................... 41 3. 4 Instrumentation: (a) mid range FTIR machine; (b) test setup; (c) test configuration 42 3.5 Epoxy colors at elevated temperatures of : (a) 25C; (b) 50C; (c) 75C; (d) 100C; (e) 125C; (f) 150C; (g) 175C; (h) 200C ................................ ................................ ...... 43 3.6 Color change comparison of: (a) 150 C; (b) 175 C; (c) 200 C .............................. 44 3.7 FTIR Spectrum of resin ................................ ................................ .............................. 45 3.8 FTIR Spectrum of hardener ................................ ................................ ........................ 45 3.9 FTIR Spectrum of one hour cured epoxy ................................ ................................ ... 46 3.10 FTIR Spectrum of epoxy adhesive at room temperature ................................ .......... 46 3.11 (a) FTIR Spectrum epoxy samples at 50 C, (b) enlarge d spectrum of section I, (c) enlarge d spectrum of section II, ( d) thermocouple reading ................................ ............... 47

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xii 3.12 (a) FTIR Spectrum epoxy samples at 75 C, (b) enlarge d spectrum of section I, (c) enlarge d spectrum of section II, (d) thermocouple reading ................................ ............... 48 3.13 (a) FTIR Spectrum epoxy samples at 100 C, (b) enlarge d spectrum of section I, (c) enlarge d spectrum of section II, (d ) thermocouple reading ................................ ............... 49 3.14 (a) FTIR Spectrum epoxy samples at 125 C, (b) enlarge d spectrum of section I, (c) enlarge d spectrum of section II, (d) thermocouple reading ................................ ............... 50 3.15 (a) FTIR Spectrum epoxy samples at 150 C, (b) enlarge d spectrum of section I, (c) enlarge d spectrum of section II, (d ) thermocouple reading ................................ ............... 51 3.16 (a) FTIR Spectrum epoxy samples at 175 C, (b) enlarge d spectrum of section I, (c) enlarge d spectrum of section II, (d ) thermocouple reading ................................ ............... 52 3.17 (a) FTIR Spectrum epoxy samples at 200 C, (b) enlarge d spectrum of section I, (c) enlarge d spectrum of section II, (d ) thermocouple reading ................................ ............... 53 3.18 (a) Spectrum comparison at section I : (a) 1 hour exposed; (b) 2 hour exposed; (c) 3 hour exposed ................................ ................................ ................................ ...................... 54 3.1 9 Spectrum comparison at section II : (a) 1 hour exposed; (b) 2 hour exposed; (c) 3 hour exposed ................................ ................................ ................................ ...................... 55 4.1. Epoxy sample preparation and instrumentation : (a) mold; (b) p repared epoxy sample; (c) used heating pads; (d) heat application on epoxy samples ................................ ........... 65 4.2. CFRP strip test : (a) prepared CFRP strip; (b) heat application using two heating pads; (c) CFRP failure at 25 C; (d) CFRP failure at 200 C ................................ ............ 66 4.3. Epoxy coupon test results : (a) stress decreasing rate s at elevated temperatures; (b) stan dard deviation and COV of stress decreasing rates ................................ ..................... 67 4.4. CFRP strip test result s: (a) Ultimate load (b) standard deviation and COV of ultimate load (c) displacement at ultimate load; (d) standard deviation and COV of disp lacement ................................ ................................ ................................ ...................... 67 4.5. Stress decreasing rate a t elevated temperatures: (a) 25C; (b) 50 C; (c) 75C; (d) 100C; (e) 125 C; (f) 150C; (g) 175C; (h) 200 C ................................ .......................... 69 4.6. Thermocouple rea ding of epoxy samples: (a) 50 C; (b) 75 C; (c) 100 C; (d) 125 C; (e) 150 C; (f) 175 C; (g) 200 C ................................ ................................ ............... 71 4.7. Stress decreasing rate comparison of epoxy samples at: (a) EC I; (b) EC II; (c) EC III ................................ ................................ ................................ ................................ ............ 72

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xiii 4.8. CFRP strip test results: (a) 25C; (b) 200C; (d) thermocouple reading at 200C ..... 73 5.1. Compression test: (a) concrete cylinders; (b) tested sample ................................ ....... 91 5.2. Concrete block specimen dimensions: (a) concrete block with groove; (b) NSM strengthening system; (c) thermocouple location ................................ .............................. 92 5.3 Sample preparation : (a) mold fabrication; (b) concrete filling; (c) concrete block fabrication for NSM system; (d) prepared concrete specimen ................................ .......... 93 5.4. Instrumentation for monotonic tension test : (a) concrete block located on MTS machine; (b) prepared sample for heating; (c) testing procedure ................................ ...... 94 5.5. Monotonic tension test results : (a) Interfacial capacity; (b) standard deviation and COV; (c) weibull distribution ................................ ................................ ............................ 95 5.6. Load displacement behavior of tested concrete blocks at elevated temperatures of : (a) 25 C; (b) 50 C; (c) 75 C; (d) 100 C; (e) 125 C; (f) 150 C; (g) 175 C; (h) 200 C ................................ ................................ ................................ ................................ ............ 97 5.7. Failure modes of tested concrete blocks at elevated temperatures of: (a) 25C epoxy concrete interface failure; (b) 25 C epoxy CFRP interface failure (c) 50C; (d) 75C epoxy concrete interface failure; (e) 75C epoxy CFRP interface failure (f) 100C; (g) 125C; (h) 150Cpartial epoxy CFRP interface failure; (i) 150C complete epoxy CFRP interface failure; (j) 175C; (k) 2 00C ................................ ................................ ............. 100 5.8. Thermocouple reading of concrete blocks tested with monotonic tension test at elevated temperatur es of: (a) 50C; (b) 75C; (c) 100C; (d) 125C; (e) 150C; (f) 175C; (g) 200 C ................................ ................................ ................................ .......................... 102 5.9. Internal temperature (thermocouple II) increment of monotonic tension test specimens exp osed to : (a) 50C; (b) 75C; (c) 100 C; (d) 125C; (e) 150C; (f) 175C; (g) 200 C ................................ ................................ ................................ .......................... 104 5.10. Internal temperature increment comparison of (a) specimen 1; (b) specimen 2; (c) specimen 3 ................................ ................................ ................................ ....................... 104 5.11 Load displacement behavior of cyclic loading specimens 1 at : (a) 25C; (b) 50C; (c) 75C; (d) 100C; (e) 125C; (f) 150C; (g) 175C; (h) 200C.. ................................ 106 5.12 Normalized load displacement behavior of cyclic loading specimen 1 at : (a) 25C; (b) 50C; (c) 75C; (d) 100C; (e) 125C; (f) 150C; (g) 175C; (h) 200C. ................. 108 5.13. Bond stiffness of NSM strengthened concrete blocks at: (a) 25C; (b) 50C; (c) 75C; (d) 100C; (e) 125C; (f) 150C; (g) 175C; (h) 200C. ................................ ....... 110

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xiv 5.14. Average stiffness comparison of each category ................................ ...................... 110 5.15 Thermo couple readings of cyclic loading specim ens 1 of each category at : (a) 50C; (b) 75C; (c) 100C; (d) 125C; (e) 150C; (f) 175C; (g) 200C ................................ .. 112 5.16. Comparison of thermocouple readings of specimen 1: (a) thermocouple I; (b) thermocouple II ................................ ................................ ................................ ................ 112 5.17 IR image testing: (a) IR thermal camera; (b) specimen setup for the testing ......... 113 5.18 IR thermal images of concrete block expose d to 50 C at : (a) 0; (b) 5; (c) 10; (d) 15; (e) 20; (f) 25; (g) 30 minutes ................................ ................................ ............................ 1 14 5.19 IR thermal images of concrete block exposed to 75 C at : (a) 0; (b) 5; (c) 10; (d) 15; (e) 20; (f) 25; (g) 30 minutes ................................ ................................ ............................ 115 5.20 IR thermal images of concrete block exposed to 100 C at : (a) 0; (b) 5; (c) 10; (d) 15; (e) 20; (f) 25; (g) 30 minutes ................................ ................................ ............................ 1 16 5.21 IR thermal images of concrete block exposed to 125 C at : (a) 0; (b) 5; (c) 10; (d) 15; (e) 20; (f) 25; (g) 30 minutes ................................ ................................ ..................... 117 5.22 IR thermal images of concrete block exposed to 150 C at : (a) 0; (b) 5; (c) 10; (d) 15; (e) 20; (f) 25; (g) 30 minutes ................................ ................................ ..................... 118 5.23 IR thermal images of concrete block exposed to 175 C at : (a) 0; (b) 5; (c) 10; (d) 15; (e) 20; (f) 25; (g) 30 minutes ................................ ................................ ..................... 119 5.24 IR thermal images of concr ete block exposed to 200 C a : t (a) 0; (b) 5; (c) 10; (d) 15; (e) 20; (f) 25; (g) 30 minutes ................................ ................................ ..................... 120 5.25 Thermal propagation of each category based on the IR images at the internal epoxy concrete surface (a) 50 C; (b) 75 C; (c) 100 C; (d) 125 C; (e) 150 C; (f) 175 C; (g) 200 C ................................ ................................ ................................ .............................. 1 22 5.26 Thermal propagation comparison of each category ................................ ................ 1 22 5.27 Thermo couple reading at the heated surface of each category of (a) 50 C; (b) 75 C; (c) 100 C; (d) 125 C; (e) 150 C; (f) 175 C; (g) 200 C ................................ ....... 124

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1 1 I ntroduction 1.1 General Use of FRP materials in structural strengthening systems has significantly increased over the last decade. FRP is available in many different sizes and shapes which is manufactured for different applications. FRP structural strengthening systems have become very popular all over concrete, steel and masonry structures. Also, it is widely accepted in many countries due to its ultimate performances such as high er resistance to corrosion, light weight, hi gher tens ile strength and etc. T wo common types of strengthening systems can be named as externally bonded and near surface mounted strengthening systems. Externally boned strengthening system can be further divided into two common systems called as wet lay up FRP systems and pultruded FRP laminate systems. Wet lay up FRP systems consist fiber fabrics saturated with resin and rigid FRP plates are used in pultruded FRP lami nate systems (Petri and Blaszak ). Near surface mounted system was later introduced to the engineering field (Hassan, Rizkalla, 2004). Only few research studies have been performed on NSM strengthened systems. FRP strips and rods are widely use in NSM applications (De lorenzis et all. 20 04; Kotynia 2005; teng et all 2006; Aniello et all. 2012). Precut grooves are made in tension flange of the concrete structures to place the FRP rods and strips. Grooves fill with epoxy resins or cementatious material and place FRP rods or strips to establ ish the NSM strengthened system. Hassan and Rizkalla, (2004) conducted a research study to demonstrate the different between externally bonded strengthening system and near surface mounted system. The behavior and the effectiveness of these two systems was observed by testing 8 different concrete T beams under a

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2 monotonically increasing concentrated load applied at mid span. Research results intend that the NSM strengtheni ng system significantly improves the stiffness and the flexural capacity of the concre te beam than externally bonded concrete beam. This indicate that NSM strengthened system is more effective than externally bonded systems in concrete structures. Concrete structures are usually exposed to different environmental conditions and hazards. Th erefore, the functionality of FRP strengthened materials under different conditions are important. Fire is the one of the crucial hazard that can affect the composite strengthening system. Fire is an important factor should be concerned in concrete buildin gs design Bridges and other outside structures have less effect by fire due to its less possibility of a fire event. But it is required to consider about other crucial conditions such as chemical hazards and critical weather conditions for these structure s. Fire can affect the material bond strength of the composite system, losses in stiffness, creep resistance can be expected (Aniello et all. 2012; Kodur et all. 20 07; Eang et all. 2007; Foster et all 2008; Katz 2012; Mouritz et all. 2009). Therefore, fire risk cannot be ignored for structural building members strengthened with FRP strengthening systems. The glass transition temperature (Tg ) is one of the most important material property of polymer materials that should be concerned under fire exposure. Below the Tg material behaves brittle. When the material reach es its glass transition temperature, the material becomes soft and the materi al temperature above Tg, material acquires an elastic behavior. FRP material has a higher glass transition temperature compared to bonding adhesive. Epoxy resins have been widely used for both external and NSM strengthening systems

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3 which have a typical gla ss transition temperature range of 50 C to 90 C (Blontrock et all. 1999). A large number of research studies have been done to investigate the behavior of FRP strengthened concrete structures. Most of the studies have conducted for externally strengthene d structures (Foster a nd Bisby 2008). Late introduction of NSM system limited the research studies for few number of resources under fire exposure. Although the findings for NSM system are important to investigate further studies under fire exposure. Zhu et all (2013) conducted an experimental research study of fire resistance of RC beam strengthened with NSM using high Tg BFRP bars. Experimental program conducted with 108 effective tensile test specimens and 7 four point bending beam specimens. Results in dicate that the higher Tg NSM FRP systems can acquire improved fire resistance. F ire protections for NSM strengthening systems are important. Few studies have b een conducted to excavate the new and better fire insulations for NSM systems Mou rtiz et all. ( 2009) presents a critical review of research progress in modelling the structural response of polymer matrix composites exposed to fire. Aniello et all (2011) conducted a research study on NSM strengthened insulated concrete beams to investigate the fire e ndurance and residual strength. They examined the performance of six full scale NSM strengthened beams exposed to 1 hour of fire. Test results imply that properly insulated beams can achieve a satisfactory fire endurance of 1 hour. As discussed above, most research studies have focused on the transition temperature of the CFRP bars used in NSM system and fire insulation system for NSM systems. Also, a significant number of studies have been conducted on NSM strengthened systems evaluating the bond performan ce under normal condition. Therefore, the fire endurance and the bond performance of the NSM strengthened concrete structures during a fire event

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4 need more attention. Abdul Rahman (2013) conducted a research program inves tigating the performance of the NSM strengthened concrete structures subjected to high temperature under residual condition He observed the adhesive bond concrete interface of residual specimens exposed to elevated temperature s up to 200C Also, the mechanical properties and characterization of different type of adhesives for the use of bonding NSM FRP strengthening applications have been ex a mine under the same condition. This thesis report presents further findings on the performance of NSM FRP strengthened concrete structure s at elevated temperatures So that it is possible to predict the behavior of NSM FRP strengthened system under fire. 1.2 Research significance and objectives Most research studies have been conducted in the area of fire endurance of insulated NSM strengthened concrete structures. Many studies have focused on finding better fire insulation systems for NSM FRP strengthening system and strength behavior of high glass t ransition temperature FRP material application s for NSM FRP strengthening systems. Also, earlier research studies investigat ed failure capacity, failure mode, interfacial bond behavior of adhesive concrete at room temperature (Abdul, 2013). Minimal number of the research study can be found in data base in the area of investigating the interfacial bond behavior between adhesive concrete and adhesive FRP of NSM FRP system. Also it should be noted that the glass transition temperature of polymers is crucial factor that has to concern under fire exposer at or above the Tg Because the material shows typical changes in mechanical properties of the polymer. Iwashita and Yagashiro (2004) investigated the debonding fracture energy, failure mode and effective bondi ng length of

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5 different types of epoxy resins used to wrap the FRP over concrete specimens. An e xperimental program was conducted near and above the Tg of the epoxy resin. Test results imply a decrease in debonding fracture energy and increase in bon d ing length near and above the Tg. Gamage et all (2005) conducted a shear test method experimental program to evaluate the bond strength of CFRP strengthened concrete members at eleva ted temperatures. Results show a rapid loss of strength when epoxy temper ature increased beyond 60 C. These research studies illustrate that the Tg is a critical factor that should be concerned. Lack of resources i mply that predicting the behavior of NSM FRP strengthened concr ete structures is more challenging at high temperatu res. Therefore, it is required to pay more attention in the for the material and bond behavior of NSM FRP strengthened structures under fire. So that the catastrophic events can be avoided. This research program consists a two phase experimental program co nducted at elevated temperatures Material behavior and interfacial bond behavior of adhesive concrete and adhesive CFRP was observed. Also, a FTIR chemical testing was done for residual species of epoxy resin investigating the chemical structural changes over elevated temperatures. Following chapters of this thesis report include further descr iptions of the testing program The research objectives are listed as below: 1: I nvestigating the chemical reactions of epoxy resin which was used to bond the CFRP st rip into the groove. Epoxy species were exposed to elevated tempe rature ranging from 25C to 200 C with a an elevated time period of 1 hour up to maximum exposer time of 3 hours. FTIR spectrum were obtained to analyze the chemical reaction over elevated te mperatures and time periods. Observations were directly combined with the changes of mechanical changes of the material at high temperatures.

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6 2: I nvestigating the changes of mechanical behavior of epoxy resin and CFRP strips at high temperatures. Displacement controlled tension test and a monotonic tension test were conducted for epoxy resin and CFRP strips, respectively. 3: O bserve the interfacial bond behavior between adhesive concrete and ad hesive CFRP strips over elevated temperatures under fire. Two element level testing programs were conducted. Also, the attention was paid examining the internal thermal propagation at the mid span of the strengthening system. 1.3 Scope The research stud y described in this thesis was carried out investigating the performance of NSM FRP strengthening systems. The bond performance of NSM CFRP strengthening system was examine by conducting material level and element level testing programs including a FTIR spectrum interpretation Total of 24 e poxy and 10 CFRP coupons were tested at elevated temperatures. FTIR spectrum s were collected using a mid range FTIR instrument. 2 mm square epoxy samples were exposed up to elevated temperatures of 200 C. Also epoxy s amples were exposed up to 3 hours with a typical time period of 1 hour at the desired temperatures Collected FTIR spectrums were used to examine the chemical degradation of polymeric structure and the results were used to prove the mechanical degradation of the polymeric adhesives at high temperatures. Heat was applied to pretension epoxy coupons and recorded the stress degradation. Material level testing was used to observe the influence into polymeric adhesives used in NSM CFRP systems at high

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7 temperatures. T he first part of the thesis consis t s the material level testing program and its results. The second part of the thesis describes the element level testing program which was conducted to investigate the bond performance of NSM CFRP strengthe ning system. Monotonic tension and cyclic loading tests were carried out. Used concrete elements are 150 X 100 X 75 mm (6 X 4 X 3 inches) by length, width and height, respectively CFRP stripes were embed in to a precut groove that is 150 mm (6 inches) long, 13 mm (0.51 inches) wide and 25 mm (1 inches) height. Two part epoxy adhesive was used in the NSM CFRP strengthening system as the bonding agent The epoxy resin has a lower gla ss transition temperature of 71 C. Elements were preheat about 5 mi nutes before the testing by using a heat ing pad Different failure modes, ultimate pullout strength, and bond stiffness were used to examine the bond behavior of NSM strengthening system in fire. Also thermal propagation at the mid span of the bond line was imaged using an IR camera. Thermal profiles were plots in the second section of the thesis. 1.4 T hesis organization Chapter 02 consists of a literature review of NSM FRP strengthening system. The section includes a description of FRP strengthening systems, FRP applications, NSM method, fire endurance of concrete structures, and FITR testing. Previous research studies ar e summarized and details are given to support the understanding this thesis work. FTIR interpretation of the polymeric adhesive (epoxy) at high temperatures is described in chapter 03 Spectrum changes and new chemical bonds were examine to describe the mechanical property degradatio n of polymeric (epoxy) adhesive

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8 Chapter 04 describes the material level testing program that was conducted to evaluate the mechanical pro per ty changes of epoxy adhesive and CFRP stripes. Stress degradation of epoxy adhesive at high temperature was observed by applying heat t o pre loaded epoxy coupon s Monotonic tension was applied to preheated CFRP strips. Testing procedure and results are described in the section Element level testing program is described in chapter 05 This c hapter describes the testing procedures of monotonic tens ion test and cyclic loading test and their results. Also, thermal propagation profiles are included in the chapter which was collected from IR thermal camera. Chapter 06 is the summery of the research program which was carried out to investigate the performance of NSM CFRP strengthening systems under fire exposure. Conclusions are summarized in the chapter. Extra figure s and data are enclosed in appendixes.

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9 2 L iterature R eview 2.1 Strengthening systems for concrete structures Concrete is widely used in constructions of building, bridges, dams, parking garages and etc. With the evolution of cement, new constructions were widely increased. Reinforced concrete was introduced in mid nineteenth century and it has become a major component in th e construction field. Prestress ed concrete is another technique which is introduced in late nineteenth century that is utilized in many bridge constructions, parking ga rages, concrete slabs and etc. T he main issue with concrete structures is concrete deter ioration over the time due to the weathering effect, steel rebar corrosion and severe env ironmental conditions [Figure 2.1] This increases the cost of maintenance and reduce the lifespan of the structure. Therefore, the engineers were interested in findin g new methods for strengthening deteriorated concrete structures. Over last decade, an emerging material call fiber reinforced polymer (FRP) has taken the attention for strengthening concrete structures. The high resistance to corrosion and high tensile s trength of FRP material led the material to use for structural strengthening systems and internal reinforcement in concrete members (ISIS, 2004). Externally bonded FRP strengthening systems [Figure 2.2] is the most common system that is used in many concre te structures (Aboubakr et all, 2014). Near surface mounted (NSM) was later introduced to the engineering field (Hassan, Rizkalla, 2004). Detailed descriptions of these two methods are given in following sections.

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10 2.2 FRP Fiber reinforced polymer is an emer ging material which is widely used in construction field. FRP is made of different types of fibers and the name of the FRP is given based on the fiber type used Three major types of FRP materials can be found in the market. Carbon fiber reinforced polymer (C FRP), Aramid fiber reinforced polymer (AFRP) and glass fiber reinforced polymer (GFRP) are the main FRP types that can find in the market. In few countries, basalt fiber reinforced polymer (BFRP) is used as strengthening material (Sindri, 2012). FRP is highly resistant to corrosion. Also. FRP has a light weight with a higher tensile strength. All the FRP types are available in many different sizes and shapes. A ramid and C arbon FRP are pref erred in ACI 440.4R 04 standard Typical properties of diff erent types of F RP material are given in table 2.1. CFRP is m ade of carbo n fiber. CFRP has higher strength, high stiffness, excellent fatigue properties, and high moisture, higher thermal and chemical resistance compared to other FRP materials (ISIS 2009 ). ARAMID is formed from the term of AROmatic polyAMIDe (synthetic organic fiber). AFRP has lower weight than CFRP. Also the cost of the material is lower than CFRP. Six different fiber types have been used in AFRP industry called Kevlar, Twaron, Technora , Aropree, FiBRA, Rarafil (ISIS, 2009 ). GFRP is made using different types of glass fibers. E glass fibers widely used in FRP industry than C and D glass fibers. GFRP is has a better resistance to chemicals and has a lower cost than CFRP (Mattock an d Babaci, 1989).

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11 2.2.1 FRP applications Because of the lower weight, high strength, and higher resistances to corrosion, FRP material is becoming a leading material for many applications. Engineers are interested on FRP rods, bars and tendons as intern al reinforcement in RC structures and pre stressing tendons in pre stressed concrete structures becaus e of the high resistance to corrosion. A large number of research studies have been conducted in this area. As an example, Xue and Tan (2012) conducted a research study finding the behavior of FRP bars used as reinforcing bars in pre stressed with a combination of bonded CFRP tendons and steel/GFRP reinforcements investigating the cracking behavior of the beams. Test results inte nd ed a reduced crack width for beams with combined reinforcements of Steel/GFRP. As discussed in early sections, FRP materials have been used as strengthening agents for deteriorated concrete structures. Because of the cost effectiveness for repairing dama ge structures using conventional material, engineers are interested in the use of FRP (NCHRP, 2003). Externally bonded and near surface mounted strengthening systems are the two strengthening systems that are used in construction field to enhance the flexu ral strength of the deteriorated structures. Detailed information about NSM strengthening system are given in later sections. 2.2.2 FRP techniques The e xternally bonded and NSM strengthening systems are widely used in structural rehabilitation industry. This section covers different techniques which are used in these two systems. Near surface mounted (NSM) system is later introduced and researchers are

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12 focusing on NSM sy stem to improve the system with new techniques for strengthening concrete structures (Abdul, 2013). Externally bonding strengthening systems was early introduced to strength the deteriorations structures. Two main techniques are used in externally bonded strengthening system. First technique is called as wet lay up FRP system which bonds dry and flexible FRP fabrics with epoxy resins on site (Petri and Blaszak; BASF, 2007; Abdul, 2013). BASF (2007) illustrates that this technique provides flexibility, shor ter installation time and lower installation cost as the benefits. Pultruded (pre cured system) FRP system is the second technique which is formed by bonding a rigid FRP sheet to the tension zone. FRP sheets are saturated and pre cured before the site appl ication (Petri and Blaszak; BASF, 2007; Abdul, 2013). Premature debonding failure is common on externally bonded FRP strengthened structures due to the stress at the cut of point (Abdul, 2013: Kim et all, 2005; Merdas and Benzaid, 2013). 2.3 NSM FRP stre ngthening system NSM FRP strengthening system was later introduced. Therefore few research studies can be found in the data base (Hassan and Rizkalla, 2004; Abdul, 2013; Palmieri et all, 2010). However, NSM is becoming an emerging technique that can be use d to improve the load caring capacity of concrete members (Sena Cruz et all 2012) as well as unreinforced masonry walls (Tumialan et al. 2001). The origin al methods was found in Europe for bars were used with cement mortar as reinforcement and adhesive (De Lorenzis et all 2000; Burke, 2008; Abdul; 2013). In 1948, NSM technique used to upgrade the negative moment region of a RC bridge deck (Parretti and Nanni, 2004; Asplund et all, 1949) No wadays, FRP rods and strips are used

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13 as reinforcement with an epoxy adhesive or relative cemtetitous material. NSM FRP strengthening systems is an attractive method that increases the flexural strength and shear strength of deficient RC and PC members (Par retti and Nanni, 2004; Alkhrdaji et al., 1999, De Lorenzis et al., 2000). Therefore, researchers have paid more attention to find out the effectiveness of this system. Lorenzis and Teng (2007) illustrate a critical review of existing research studies and p rovide an outline for future researches. 2.3.1 NSM techniques FRP rod or strips have been used as reinforcement and conventional epoxy resin or cementitious adhesive as bonding agent. Grooves are precut on the tension flange with specified dimensions. After cleaning the grooved properly FRP reinforcement is embedded with an appropriate bonding agent. Figure 2.3 shows a typical cross sectional view of NSM FRP strengthened members NSM groove spacing and the depth of the NSM strengthened specimen are critical factors because the spalling of concrete corners can occur with the closer spacing with the edge of the co ncrete element (Blaschko, 2003; Abdul, 2013). ACI 440.2R 08 specifies a minimum clear groove spacing of two times the groove depth to avoid the overlapping of the tensile stress around the NSM bars and four times for the clear edge distance to avoid the ed ge effect (ACI 440.2R). Also ACI 440.2R specifies the minimum groove dimensions a s shown the Figure 2.4 It indicates a minimum groove width of 1.5 times the diameter of the FRP bars and three times the thickness of the FRP strip. The minimum depth of the groove is recommended to be 1.5 times the diameter of the FRP bar and 1.5 time the width of the FRP strip. De Lorenzis and Galati (2009) conducted a

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14 research investigating the performance of NSM FRP bars. Different groove dimensions were used and obtained that increasing the groove dimensions increases the bond strength of the NSM bar. Oehlers et all (2008) indicated that increased dimensions can achieve higher debonding strains and greater ductility. 2.3.2 Previous applications on NSM Early 1950s, NSM steel rods have been used to strength en concrete structures. In 1948, NSM rods were used to upgrade the negative moment region of a RC bridge deck in Sweden (Parretti and Nanni, 2004; Asplund et all, 1949). Since the FRP application on strengthening system s is a modern technique, there are not many references available. In 1997 1998, the structural floor of Myriad Convention Center, Oklahoma City, OK (USA) was strengthened by using NSM CFRP rods. Also, externally bonded plates and CFRP sheets were adopted i n this system (De Lorenzis, 2000; Hogue et al., 1999). Two RC circular structures were strengthened using CFRP rods embedded in epoxy filled grooves in USA in 1998 (Nanni, 1998; De Lorenz is, 2000). Brige J 857, Phelps C ounty MO (USA) was strengthened with NSM in 1998. One of the three solid decks and two columns were strengthened to increase the flexure capacity (Alkhrdaji et al., 1999; De Lorenzis, 2000). Tumialan et al., 1999 conducted a strengthening and load testing program at the decommissioned Malcolm Bliss Hospital in St. Louis, MO (USA) (De Lorenzis, 2000). Some pictures of previous applicat io ns of NSM in given in Figure 2.5 However, many number of laboratory level research studies have conducted to elevate the performance of NSM FRP system. Therefo re, reasonable number of references can be found related to element level lab testing and few numbers for full scale testing in the data base. De Lorenzis

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15 (2000) conducted a full scale beam test investigating the characterization at the material and sub sy stem. 2.3.3 Previous research studies on NSM FRP strengthening system A lot of research studies have conducted on element level. Many of them used pull out test to investigate the interfacial capacity, interfacial bond behavior and different failure modes. Also, in some element level testing programs have used three point bending and four point bending testing. As mentioned early, only a few full scale testing was conducted evaluating the performance of the NSM system. In this section, the performance s of NSM FRP strengthened concrete will be described based on the past research studies. Also, Different testing methods are described. Hassan and Rizkalla (2004) tested total of nine beams strengthened with NSM CFRP bars to determine the development lengt h of the FRP reinforcement. Different embedment lengths of 150, 550, 800, and 1200 mm were used to strengthen beams. Three point bending testing was used to load the beams. Beams strengthened with longer embedment lengths (550, 800, and 1200 mm) showed hig her ultimate loads. All the beams strengthened with NSM CFRP bars failed due to the concrete surface splitting at the concrete epoxy interface. De Lorenzis et all (2000) carried out a coupon test with different FRP rebars, bonding l engths and groove sizes, Also, a t otal of four T beams were tested to investigate the full scale structural performances. Direct pull out testin g has used to test the coupons and s plitting of epoxy cover was observed. With increase of groove size coupons showed increased bond str ength with a higher resistance to splitting. T beams were loaded using

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16 four point bending loading method. NSM strengthened beams showed increase in capacity with an increased stiffness. Chikh et all (2013) conducted a pullout bending testing on concrete s pecimens strengthened with NSM method. They were interested investigating the influences of the concrete strength, reinforcement configuration, embedment length and the interfacial bond behavior between concrete, epoxy and CFRP. Testing was conducted using both CFRP rod and plates with three different strengthening configurations. Test results imply that CFRP plate shows better performance than rods. Also, pull out force increased with increasing bond length and the increasing concrete strength. Sena Cruz e t all (2012) conducted a direct pull out testing program evaluating the bond behavior of NSM strengthened concrete element under wet dry cycles. Total of 35 specimens were tested with different groove sizes. The influence of the bond length, the groove wid th and depth, and the number of wet dry cycles on the bond performance were observed during the test. Double bond shear testing program was conducted on NSM FRP strengthened structures by Palmieri et all (2012). Total of 18 specimens were tested with diff erent types of FRP materials (CFRP, GFRP, BFRP) and different shapes (rods and stripes). Test results indicated two different failure modes of debonding at the resin/FRP interface for sand coated and ribbed bars and pullout of NSM FRP bars for smooth bars. 2.4 Fire endurance of concrete Structures Fire is an important factor that can reduce the performance of any structure. In many cases, most buildi ng showed sudden collapse at a fire event. This is because of the reduction in

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17 strength and the elastic modulus of b oth concrete and steel with the increase of the temperature This can cause to loss many number of lives or critical damages and injuries. The concrete deterioration mechanism due to the fire is shown in Figure 2.6 Therefore, it is required to ensure that a structure has the ability to ensure adequate rescue time at a fire event At least 2 hour fire endurance is required (N. Bilow and E. Kamara, 2008). Over last 60 years, many testing and analytical models have been conducted to prove the e xcellent fire resistance of concrete. Also, there are many simplify methods that have been used to ensure a better fire endurance of a concrete structure. In USA, prescriptive approach has used to design structures for fire safety (N. Bilow and E. Kamara, 2008). Prescriptive designs are derived from fire testing experiences and provide minimum dimensions and thicknesses of concrete cover that can ensure the fire resistance of the structure. It is be noted that the prescriptive methods are not always economi cal (Green et all, 2007). Also, performance based fire safety design has become more common ( P. Begley 2004) Many codes permit design guidelines for fire protection. The section 720 of the 2006 International Building Code (IBC) (1) describes prescriptive design requirements for buildings. ACI 216.1M 07 / TMS 216 resistance of a building which are not specified by ACI 318 or ACI 530/ASCE 5/TMS 402. However, all these codes have created to ensure a better fire endurance of a building at least with the minimum design requirements. Thus, the ensured fire protection design will prevent critica l haza rds and save many lives.

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18 2.5 NSM strengthened concrete structures exposed to fire In this section, m ore attention is paid to the area of the performances of NSM strengt hened concrete members in fire. F ew research documents are available in this area due to the late introduc tion of this strengthening system. Many research studies have conducted investigating the residual performances of NSM system after exposed to fire. However, it is required to endure the performance of NSM FRP strengthened member be cause this technique is becoming an emerging technique with better performances in both flexural and shear capacities than externally bond FRP strengthened members. Epoxy adhesives are widely used with FRP rods or strips to form the NSM strengthening syste m. Both FRP and epoxy are highly sensitive to high t emperatures due to the changes of the polymer matrix at high temperatures. Therefore, more attention is needed examining the behavior of NSM FRP strengthened structures. Stratford et all (2010) conducted a real fire test to compare the performances of a slab FRP strengthened with both externally bonded and near surface mounted systems. Strengthening was applied to the ceiling of the structure and the strengthening system was protected with intumescent coa ting and gypsum boards. One side of the ceiling w as unprotected. Test results were obtained from a real fire test and results indicate that the portion strengthened with NSM FRP and gypsum boards showed better performances. An experimental program was car ried out by Palmieri et all (2012) to examine the performance NSM FRP strengthened concrete beams. Six beams were tested with 1 hour exposure time. All beams were preloaded to the service load before the heat applied. NSM strengthened beams showed a satisf actory fire endurance for 1 hour of fire. Also, the test

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19 results indicate that the strengthened beams can retain up to 92% of its capacity if the insulation system can maintain the adhesive temperature at a low valve ( T Tg, where Tg is the glass transition temperature of the adhesive ) Burke (2008) tested twenty three NSM FRP strengthened concrete slabs strips to examine the flexural performance at high temperatures (200 C) and low temperatures ( 26 C). Also, the effect of two different NSM gro ove widths and two different bonding agents (epoxy and cementitious adhesives) were studied. A numerical model was used to compare the experimental test results. Test results indicate that the low temperatures have no effect on the strengthening system. At high temperatures, cementitious material allowed the strengthening system to retain its full capacity more than 5 hours at 100 C. As well as above research studies many other research studies have focused on the residual mechanical properties or flexural strength of the NSM FRP strengthened structure. Therefore, it shows the requirement of the new findings in the area of the bond beh avior of the NSM FRP strengthened concrete structures in fire. 2.6 FTIR FT IR (Fourier transform infrared spectrometer) is the most modern spectrometer (Intro. to Spectroscopy, 2008) This operates on a different principle than Dispersive Infrared spec trometer. Interferogram is a complex signal that contains all the infrared spectrum frequencies. Interferogram is a pattern produced by the optical pathway. Fourier transform is used to separate the individual absorption frequencies from the interferogram. This instrument acquires the interferogram in less than a second. Also, it has the opportunity to

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20 collect multiple interferograms of the same sample. Therefore, FT IR is greater in speed and sensitivity than the dispersive infrared spectrometer (Intro. to Spectroscopy, 2008). An interferometer is used to process the energy to send to the sample. The energy source passes through a mirror (45 degree angle) called beam splitter. The beam splitter split s the incoming energy source in to two beams. One beam pas ses the beam splitter with a 90 degree angle to a fixed mirror and return back to the beam splitter [Figure 2.7 ] The o ther beam goes to a moving mirror and return back. The moving mirror causes to vary the path length of the beam. At the beam splitter, those two beam recombine and make the interferogram. The difference of those combined beams cause both constructive and d estructive interferences. Then the interferogram forwards to the sample. The sample absorbs all the frequencies that are found in its infrared spectrum. This modified interferogram is detected with all the information about the amount of energy that was ab sorbed at every frequency. The computer compares this modified interferogram with the reference laser beam and represent the final interferogram including all the information in one time domain signal. The computer extract the individual frequencies which w ere absorbed and plot it as absor bance wave number (frequency). This is called as infrared spectrum (Intro. to Spectroscopy, 2008). Before obtaining a spectrum of a compound, it is required to obtain the back ground interferogram. This contains the infra red active atmospheric gases, carbon dioxide and water vapor. Oxygen and nitrogen are not infrared active. After obtaining the spectrum for the compound which also contains back ground spectrum, the computer automatically deduct s the back ground spectrum f rom the original sample interferogram and analyze s the final reconstructed spectrum for the compound.

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21 2.6 .1 FTIR applications FTIR interpretations have been used successfully in many applications. Most epoxy related research studies have used FTIR spectrums to monitor the curing, phase preparation and chemical changes due to environmental effects or due to any other chemical reac tion. In chemistry, FTIR uses to characterize the chemical compound with peak values indicated by IR spectrum. In engineering testing, FTIR is used to identify the specific changes of the spectrum to show the predicted chemical reaction due to a desired fa ctor. Nikolic et all (2010) used FTIR technology to analyze a new epoxy formulation based on the use of polyamine adducts as the hardener. They were interested on crosslinking reactions of different stoichiometric mixtures of the unmodified GY250 resin wi th the aliphatic EH606 and the cycloaliphatic EH637 polyamine adducts. Seven different samples of epoxies were tested by W, Brittan (1991) to study the prehardneed epoxies with different hardener and resign ratios. ATR FTIR (Attenuated Total Reflectance F ourier Transform Infrared Spectroscopy) was used in this study. Test results indicated that the FTIR is much simpler than traditional methods. N, Poisson et all (1996) has used mid range FTIR to observe the curing and reactions of epoxy. A pre polymer ( di glycidyl ether of bisphenol A) was mixed with dicyandiamide as a hardener. Fountional group was determined by analyzing about 20 peaks. S, Lin et all (1978) used FTIR to analy the degradation of cured epoxy samples due to thermal and oxidation. Different epoxy samples were studied using three different types of epoxies. FTIR spectrums of thermal, oxidative and photo degradation was compared with the spectrum of natural degradation of epoxy

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22 2.7 The glass transition temperature The glass transition temperature (Tg) of a polymeric material is defined as the temperature at which the mechanical properties of a polymeric material radically changed due to the internal movement of the polymer chains that form the polymeric material [Adhesives & glues & sea lants 2014] The glass transition temperature directly affect s the mechanical properties of the polymeric material such as strength, hardness, brittleness, elongation and etc at a temperature below the glass transition temperature polymeric materials (ad hesives or plastics) acquire a hard/brittle behavior. When the polymeric material exposed to a temperature high er than the glass transition temperature of the material, polymeric materials show elastic behavior. Therefore it is required to pay more attention to the Tg of epoxy adhesive which are used in strengthening systems at high temperatures. 2.8 Summery and Conclusions This chapter discuses a brief literature review of the available data on FRP strengthening systems, FRP applications, NSM method, fire endurance of concrete structures, and FITR testing. Existing research references have listed to support the understanding of the NSM FRP strengthening systems and its behavior. Based on the discussion following were conc luded. NSM strengthening system showed better performance than the externally bonded strengthening system. FRP rod or strips are embedded using an appropriate bonding agent in to precut grooves to form the NSM system. Only few research

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23 studies have been con ducted in the area of NSM strengthening system due to the late introduction of the system. Most research studies have focused on investigating the bond capacity, determining groove size requirement and other dimensional properties at room temperature. Som e of the researches were conducted to examine the residual performance of the NSM strengthening system at elevated temperatures. Also, few tests were conducted investigating the fire insulation system for NSM FRP strengthen systems. Epoxy or any appropria te cementitious material uses to embed the FRP rod or strips in to the groove. Epoxy adhesives are polymeric materials which can be affected its mechanical properties by high temperature. Mid range FTIR instrument is widely used to examine the chemical changes of chemical compounds. The glass transition temperature is a crucial factor that defines the chemical behavior of polymeric materials. Therefore, it is important to investigate the b ehavior of polymeric materials which is used in strengthening systems under high temperature. Lack of research references in the area of NSM FRP strengthening system shows the requirements of new finding s to examine the structural behavior of NSM FRP stren gthened concrete structures.

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24 Table 2.1. Properties of FRP types (ACI 440.2R 08) FRP Type Young's Modulus Ultimate Tensile Strength CFRP (Carbon) 100 140 Gpa 1,020 2,080 Mpa [15,000 21,000 ksi] [150 350 ksi] GFRP (Glass) 20 40 GPa 520 1,400 MPa [3,000 6,000 ksi] [75 200 ksi] AFRP (ARAMID) 48 68 Gpa 700 1,720 Mpa [7,000 10,000 ksi] [100 250 ksi]

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25 (a) (b) (c) (d) Figure 2.1. Deterioration of concrete due to : (a) a ggression by carbon dioxide; (b ) aggression by sulphates; (c ) aggression by chlorides; (d) a lkal i aggregates reaction [ MAPEI, 2011]

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26 Figure 2.2. Examples of externally bonded strengthening system (BASF,2007) Figure 2.3 Typical cross sections NSM strengthened members (Aslen 500)

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27 Figure 2.4. Dimensions of NSM FRP system s specified by ACI 440.2R 08 Figure 2.5. Previous application of NSM system (De Lorenzis, 2000)

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28 Figure 2.6 Concrete deterioration due to fire [ MAPEI, 2011] Figure 2.7. Fourier transform infrared spectrometer (FTIR) [Introduction to spectroscopy, 2008]

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29 3 FTIR Interpretation of Epoxy Adhesive at Elevated T emperature s 3.1 General overview Total of 22 epoxy coupons (8 categories ) which were exposed to different temperatures and time periods were used to observe the chemical changes of epoxy adhesive at high temperatures. Epoxy samples were prepared with an average thickness of 2 mm and samples were exposed to elevat ed temperatures ranging from 25 C to 200 C with a typical interval of 25 C. Also, each category was exposed to different time periods with a typical period of 1 hour. Mid range Fourier transform infrared spectrometer was used to collect the spectrums for each epoxy category. FTI R spectrums have been used to interpret the chemical changes of the epoxy compounds. FTIR is one of the modern technique whi ch operates on Fourier transform mathematical operation. Also, color change s of epoxy adhesive was observed at elevated temperatures. This section covers the observed spectrum changes and color changes of epoxy adhesive at high temperatures. 3.2 Experimental program 3.2.1 Materials A conven tional epoxy adhesive were used Used epoxy is a low viscosity adhesive and 100 % solid after the full curing. Epoxy adhesive has two parts, a blue color resin and a clean hardener. The resin is named as MBrace saturant PTA and the hardener is MBrace saturant PTB [Figure 3.3 (a) and (b)]. Both these solutions are polymeric solutions which have made

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30 from organic compounds. MBrace saturant PTA (resin/blue) and MBrace saturant PTB (hardener/clear) that has to blend together. The resin and hardener have to blende 3:1 by weight [M brace, 2007]. Minimum of 7 seven days curing is required to ensure the ultimate strength of the material. The thermal c onductivity of this material as 1.45 Btuin/hrft2F (0.21 W/mK) and the glass tr ansition temperature (Tg) is 71C (163 F) (MBreace 20 07). Cured epoxy adhesive has a tensile strength ( f epx ) of 55.2 MPa with a corresponding modulus ( E epx ) of 3034 MPa 3.2.2 Sample preparation for FTIR Mbrace epoxy adhesive mixed as recommended by the manufacture (3:1 by the weight of resin and hardener respectively, Mbrace 2003). Mixed epoxy adhesive was laid in an aluminum pan with an average thickness of 2 mm. Adhesive cured for seven days and cut in to sma ll pi eces of 2 X 2 mm squares. [Figure 3.2 (a) ]. These small pieces w ere exposed to elevated temperatures ranging from 25C [77F] to 200C [392F] at a typical interval of 25C [77F] and elevated time periods ranging from 1 hour to 3 hours at a interval of 1 hour. A digital control electric furnace used to expose these small s amples to desired temperature [F ig ure 3.2 (b) and (c) ]. Samples were removed from the furnace after exposing for the desired time periods and cooled down to room temperature. Then af ter all samples were placed in dry plastic covers to avoid contact with moisture until the FTIR test is done. Also the resin [Figure 3.3 (a)] hardener [Figure 3.3 (b)] and 1 hour cured mixed epoxy [Figure 3.3 (c)] samples were prepared for the FTIR test These samples were tested at the room temperature.

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31 3.2.3 FTIR instrument setup IR spectrums were obtained using a mid range Fourier transform i nfrared spectrometer [Figure 3.4 (a)]. As shown in Figure 3.4 (b) prepared sample (2 X 2 mm) placed on the sample slot and pressured by pressure tower. Before placing the sample on the sample slot it is requir ed to clear the plat form with an alcohol cleaning wiper and dry the plat form well. This is to remove any kind of organic or in organic compounds from the plat form and to ensure a better spectrum. Absorbance was obtained instead of transmittance w ith a re solution of 4 [Figure 3.4 (c) ]. Therefore, the final spectrum obtained is absorbance verse wave numbers. Also spectrums were taken for resin and hardener and 1 hour cured adhesive samples. These were in the form of liquid. Therefore, after placing the sample on the platform it is required to cover it with a disc and take the back ground spectrum to calibrate inst rument before collected the spectrums 3.3 Assumptions of chemical reaction of epoxy and epoxy compound Actual chemical compound of the epoxy adhesive is unkn own. However, chemical Ingredients that include in the resin and the hardener lead to assume the chemical str ucture through the FTIR. Table 3.1 and 3. 2 show the Ingredients of the resin and the hardener CAS number and the chemical structure of the related compound are taken from the material safety data sheets of virgin materials of the resin and the hardener [Mbeare MSDS, 2010] These saturants ar e result s of chemical solution s of all these chemicals. As recommended by manufacture r these saturants were mixed in a ratio of 3:1 by the weight of the resin and the hardener respectively. Therefore, the cured epoxy adhesive is a result

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32 of a reaction between these two saturants. FTIR spectrums saturants, 1 hour cured epoxy and fully cured epoxy sample at room temperature used to assume the final chemical structure of the cured epoxy adhesive. Figure 3.7 is the spectrum obtained from FTIR for the resin Peak range of 4000 2000 used to identify the main chemical compound identifications. Based on the spectrum representation, it was noted that the resin consist s with an ether gro up. Eithers are organic compound that has replaced with an oxygen for CH 2 grou p i n an aliphatic chain [Figure 3.7 ] [IR spectroscopy, Helmut]. Also it was confirmed by the peak values at 1105, C O C. Peaks between 3100 2800 illustrate CH, CH 2 and CH 3 stretc hing [Figure 05]. Spectrum of the hardener [Fig ure 3.7 ] showed peaks at 3166 and 3350 proving that the chemical compound contain N H bands (Nitrogen compounds, Amines). This is because the hardener contains m ore amines as listed in Table 3.2 Also the broad peak of 3600 2800 indicate the presence of O H band (Hydroxyl) in the chemical structure. This is because of the presence of b enzyl alcohol that used to manufacture the hardener [Table 3.3 ] Also it consists with ether band (C O C) present ing the peak value at 1105 in the spectrum [Figure 3.8 ]. Figure 3.9 demonstrates the spectrum of 1 hour cured epoxy adhesive sample. Peaks at 3350 and 3166 that was noted in the hardener showed less absorbance in th e spectrum. This proves the presentence of N H band in the chemical structure of mixed adhesive but the band saturation is less compared to the hardener The broad band between 3600 2800 presents the O H band. This band showed a small peak range because at this stage it only contains few hydroxyl bands ( O H) in the solution [Figure 3.9 ]. It should be noted that t he peak values of O H and N H bonds overlap at this range This solution becomes a solid

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33 with the time. Minimum of seven day curing is required to achieve the ultimate strength of the material [Mbrace, 2003] With these spectrum readings, it is assumed that the cured epoxy adhesive contain s ether, hydroxyl and amine bands. Peaks observed at 1105 and 3345 are indications of ether and amine band s and the broad bang of wave numbers ranging from 3600 2850 indicates the hydroxyl band [Figure 3.10 ]. Peak values of 25 C epoxy spectrum are identifie d and band names are listed in Table 3. 3. Peaks at 29 60, 2923, 2868 and 2858 are CH 3 asymmetric CH 3 symmetric and CH 2 asymmetric and CH 2 symmetric, respectively. These bands are identi cal in all samples. Some sample readings showed two peaks around 2376 and 2348 due to the air disturbance of carbon dioxide (CO 2 ). Peak numbers in finger print region are identi fied as mentioned in T able 3. 3 and Figure 3.1 illustrates the described IR vibrations modes in Table 3.3 As di scussed in early sections peaks at 1105 and 3345 used to identify ether (C O C asymmetric stretching) and amine (N H stretching) bands in the compound structure of cured epoxy adhesive. 3.4 Spectrum changes of epoxy samples over elevated temperature Figures 3.11 to 3.17 indicate the IR spectrums of epoxy adhesive at elevated temperature ranging 50 C to 200 C with an exposed time periods of 1, 2 and 3 hours. IR spectrum of 1 hr. and 2 hr. 50 C d C sample which was exposed to 3 hours showed a broad peak values around 920 and 875 with a small shifting [Figure 3.11 and 3.19 ]. All epoxy samples exposed to high temperatures ranging from 75 C to 200 C demonstrated the simil ar change to 3 hour exposure 50 C epoxy sample [Figure 3.19 ].

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34 With the in crease of the exposure time epoxy samples exposed to 125C st arted showing a new band at 1654 Formation of this new band is C=C bond and indicates a typical change in structural cha ng e in epoxy compound [Figure 3.14 ].The intensity of the new band at the peak of 1654 ( C=C bond) which observed at 125 C increased with of the exposure temperature from 125 C to 200 C [Figures 3.15 to 3.17 ]. Also spectrums showed higher intensities for higher exposure time [ Figures 3.18 ]. This is because of the increment of the bands which is related to that peak value with time. As shown in F igure 3.16 epoxy sample at 200C showed a higher intensity for 3 hour exposure time at the peak value of 1654 Also, intensity at the wave number of 1730 was increased with the exposure time. Visible changes of absorbance at 1730 pea k was observed for 175 C 2 hour category and for higher temperature. This implies that the C=O bo nd in the epoxy compound increases with the increase of the temperature and exposure times. FTIR spectrums of epoxy samples prove that the adhesive complex changes with the temperature. Also the exposure time is critical because the influence on the adhesive increase with the time. Peak ba nd which was observ ed at 875 was dissipated at 200 C after exposed to 3 hours [Figure 3.17 and 3.19 ]. Even though the glass transition tempera ture (Tg) of Mbrace epoxy is 71 C, adhesive show ed a chemical change in the epoxy compound fo r 3 hours exposed samples at 50 C. This is because FTIR spectrum s were taken for res idual epoxy samples after exposing to material behavior in fire. But the results prove that the hig h temperatures has affected the chemical structure of the epoxy adhesive. Therefore, it is valid to predict the possible chemical changes in epoxy adhesive at high er temperature at high temperatures.

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35 3.5 Physical changes of epoxy under fire Color change of a compound is another parameter that indicate the chemical changes of a substance In chemistry, the color change of a substance defines as a chemical change of a compound. This is because most compounds contain with a unique color and any changes of that compound may be show n by color changes Epoxy samples that were exposed to high temperature showed color changes with increased time. Figure 3.5 and 3.6 illustrate s the co lor change over increased temperature and time. Visible colo r changes were observed for 175 C and 200 C epoxy categories [Figure 3.5 (g) and (h) ] Epoxy adhesive showed darker color compared to the epoxy adhesive at room temperature. Original epoxy showed clear blue co lor at room temperature [Figure 3.4 (a) ]. 50 C 75C, 100C, 125C and 150 C demonstrate visible color ch anges. But FTIR spectrum of 125 C and 150 C epoxy categories showed new visible spectrum changes at the wave number of 1654 forming new C=C bond. But the intensity of these catego ries were lower compared to 175C and 200 C categories. 175C and 200 C epoxy categories showed higher intensities for the band at 1 730 wave number compared to 125C and 150 C categories Therefore, the color change of the epoxy adhesive may be due to the formation of the new C=C bond and increase of C=O bond in the compound structure. As shown in the Figure 3.5 and 3.5 175C and 200 C epoxy categories showed darker color with the increase of exposure time proving the described reason for the color chang e.

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36 3.6 Conclusions This chapter discuss es the collected FTIR spectrum changes and colo r changes of epoxy category at elevated temperatures. A mid range Fourier transform infrared spectrometer was used to collect the IR spectrums and the color changes of samples were physically observed. Based on the results following s were concluded. Epoxy adhesive started showing chang es in IR spectrum at 50 C for 3 hours exposer time. The glass transition temperature of the Mbrace epoxy adhesive is 71 C [MBrace, 2007] But the observed spectrum change at 50 C indicates that the chemical compound of epoxy adhesive can be affected by high er temperatures which can affect the mechanical properties of the adhesive. Epoxy adhesive showed new bond at 1654 wave number. The intensity of that band increased with the increased temperatures. The intensity of the band at 1730 wave number increased with the increased time for 1 75C and 200 C epoxy categories. Visible color changes were observed in 175C and 200 C epoxy categories.

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37 Table 3 .1 Ingredients of resin CAS Number Chemical name 25085 99 8 Oxirane, 2,2' [(1 methylethylidene)bis(4,1 phenyleneoxymethylene)]bis homopolymer 68609 97 2 Oxirane, mono[(C12 14 alkyloxy)methyl] derivs. 17557 23 2 Oxirane, 2,2' [(2,2 dimethyl 1,3 propanediyl)bis(oxymethylene)]bis 100 41 4 ethylbenzene Table 3.2 Ingredients of hardener CAS Number Chemical name 9046 10 0 alpha (2 Aminomethylethyl) omega (2 aminomethylethoxy) poly(oxy(methyl 1,2 ethanediyl)) 2855 13 2 3 aminomethyl 3,5,5 trimethylcyclohexylamine 25620 58 0 1,6 Hexanediamine, C,C,C trimethyl 25085 99 8 Oxirane, 2,2' [(1 methylethylidene)bis(4,1 phenyleneoxymethylene)]bis homopolymer 100 51 6 Benzyl alcohol 288 32 4 Imidazole

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38 Table 3.3 Identified FTIR vibrational modes P eak value Bond Name 3345 1 O H stretch and N H stretch 2960 1 CH 3 asymmetric stretch 2923 1 CH 2 asymmetric stretch 2868 1 CH 3 symmetric stretch 2858 1 CH 2 symmetric stretch 2376 1 2348 1 CO 2 1607 1 R ing modes 1581 1 1508 1 1457 1 CH 2 bend 1382 1 CH 3 umbrella bend 1361 1 1295 1 C N stretch 1244 1 C C O C Stretch 1181 1 1105 1 C O C asymmetric Stretch 1034 1 C O C symmetric Stretch 933 1 =C H bend 916 1 N H wag 826 1 N H wag 767 1 Out of plane C H bend 735 1 Split CH2 r ock 727 1 697 1 Ring modes 669 1 Out of plane C H bend 638 1 C H wag

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39 Figure 3.1. IR vibrations modes (Infrared Spectral Interpretation, 1999).

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40 (a) (b) (c ) Figure 3.2. Sample preparation for FTIR: (a) epoxy specimens; (b) heat exposure; (c) electronic furnace

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41 (a) (b) (c) Figure 3.3. Epoxy adhesive: (a) resin ; (b) hardener ; (c) 1 hour cured epoxy

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42 (a) (b) (c) Figure 3.4. Instrumentation : (a) mid range FTIR machine; (b) test setup ; (c) test configuration Pressure tower Epoxy sample Sample slot

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43 (a) (b) (c) (d ) (e ) (f) (g ) (h ) Figure 3.5 Epoxy colors at elevated temperatures of : (a) 25C; (b) 50C; (c) 75C; (d) 100C; (e) 125C; (f) 150C; (g) 175C; (h) 200 C

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44 (a) (b) (c) Figure 3.6 Color change comparison of : (a) 150 C; (b) 175 C; (c) 200 C

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45 Figure 3.7. FTIR Spectrum of resin. Figure 3.8. FTIR Spectrum of hardener. CH 2 and CH 3 stretching ( 2980 275 0) N H stretching ( 3350 3166 ) O H band ( 3600 280 0) CH, CH 2 and CH 3 stretching (3100 2800) C O C Stretching Either bang (1105)

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46 Figur e 3.9. FTIR Spectrum of one hour cured epoxy Figure 3.10. FTIR Spectrum of epoxy adhesive at room temperature CH, CH 2 and CH 3 stretching (3100 2800) C O C Stretching Either bang (1105) 767 733 727 697 669 638 1382 1361 1244 1181 1105 1034 933 916 826 2868 2858 2868 2858 2923 2960 3345 1607 1581 1508 1457

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47 (a) (b) (c) (d ) Figure 3.11. (a) FTIR Spectrum epoxy samples at 50 C ; (b ) enlarge spectrum of section I; (c) enlarge spectrum of section II; (d ) t hermocouple reading of 50 C epoxy category I I I

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48 (a) (b) (c) (d) Figure 3 .12. (a) FTIR Spectrum epoxy samples at 75 C; (b ) enlarge spectrum of section I; (c) enlarge spectrum of section II ; (d) thermocouple reading of 75 C epoxy category I I I

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49 (a) (b) (c) (d) Figure 3.13. (a) FTIR Spectrum epoxy samples at 100 C, (b) enlarge spectrum of section I, (c) enlarge spectrum of section II (d) t hermocouple reading of 100 C epoxy category. I I I

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50 (a) (b) (c) (d) Figure 3.14. (a) FTIR Spectrum epoxy samples at 125 C; (b ) enlarge spectrum of section I; (c) enlarge spectrum of section II ; (d) t hermocouple reading of 125 C epoxy category I I I

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51 (a) (b) (c) (d) Figure 3. 1 5. (a) FTIR Spectrum epoxy samples at 1 50 C; (b ) enlarge spectrum of section I; (c) enlar ge spectrum of section II; (d) t hermocouple reading of 150 C epoxy category I I I

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52 (a) (b) (c) (d) Figure 3.16. (a) FTIR Spectrum epoxy samples at 175 C; (b ) enlarge spectrum of section I; (c) enlarge spectrum of section II ; (d) t hermocouple reading of 175 C epoxy category I I I

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53 (a) (b) (c) (d) Figure 3.17. (a) FTIR Spectrum epoxy samples at 20 0 C; (b ) enlarge spectrum of section I; (c) enlarge spectrum of section I I; (d) t hermocouple reading of 200 C epoxy category I I I

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54 (a) (b) (C) Figure 3.18. (a) Spectrum comparison at section I : (a) 1 hour exposed; (b) 2 hour exposed; (c) 3 hour exposed

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55 (a) (b) (C) Figure 3.19 Spectrum comparison at section II : (a) 1 hour exposed ; (b) 2 hour exposed ; (c) 3 hour exposed

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56 4 Thermo mechanical Behavior of an Adhesive and CFRP 4.1 General overview Epoxy adhesive are widely used in many applications. M any NSM FRP strengthening systems use epoxy adhesive as a bonding agent to embed the FRP rod or the strip in the groove. Cementitous material is one of the other option s that are use d in NSM applications. Epoxy material is a polymer which is a combination of few different organic compounds. FRP material is also a polymer that is made of different types of fibers (Carbon, Glass and Aramid FRP). At high temperatures, these material show changes in polymer matrix. This is because of the glass transition temper ature (Tg) of these polymers. Near the glass transition temperature or the above temperatures polymers shows elastic behavior. The refore, the mechanical properties of these materials can be affected by high temperatures. The elastic behavior of epoxy or FR P may result in reduced strength of the material. Therefore, it is required to analyze the behavior of epoxy and FRP materials at high temperatures which help predicting the performance of NSM F RP strengthening systems at high temperatures. Total of 24 epo xy dog bone coupons and 6 C FRP strips were tested at elevated temperatures. Epoxy coupons were prepared as recommended by the manufacture and tested at elevat ed temperatures ranging from 25C to 200 C. The behavior of epoxy coupons were observed through a displacement controlled test. Tested C FRP stripes were only exposed to 25C and 200 C. Monotonic tension was applied until the complete failure occurred. Thermo mechanical behavior of the materials were observed through the stress decreasing rate (MPa/sec) and the ultimate tensile capacity of C FRP strips The results of this experiment are described in this chapter.

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57 4.2 Material s Low viscous conventional e poxy used as adhesive in this research experiment. The adhesive is easy to apply and after curing it creates a high performance composite system with fiber reinforced polymer (BASF). This a low viscous material that is 100 % solid after cured. Therefore, this adhesive can be u sed in vertical and ov erhead applications (MBrace 2007 ). This epoxy contains two parts called MBrace saturant PTA (resin/blue) and MBrace saturant PTB (hardener/clear) t hat has to blend together The resin and the hardener have to blende 3:1 by volume or 100:30 by weight [Mbrace, 2007] Minimum of 7 seven days curing is required to ensure the ultimate strength of the material. Cured epoxy adhesive has a tensile strength ( f epx ) of 55.2 MPa with a corresponding modulus ( E epx ) of 3034 MPa. Manufacture specifies the Thermal Conductivity of this material as 1.45 Btuin/hrft2F (0.21 W/mK) and the glass transition temperature (Tg) is 71 C (163 F) (MBreace 2003). CFRP tapes were used in the NSM system and the tapes are pre cur ed rectangular bars. Surface texture is provided on each face to improve the bonding (Aslan 500, 2011). Used CFRP strips have an ultimate tensile capacity of 70.8 kN (15.92 ksi) with an elastic modulus of 124 GPa (18000 ksi). The nominal area of the tape i s 31.67 mm 2 (Aslan 500, 2011). Manufacture indic ate the glass transition as 110 C (230 F). 4.3 Experimental program Total of 24 epoxy coupons and 6 CFRP coupons were tested at high temperatures. This section describes the sample preparation and the experimental program.

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58 4.3.1 Sample Preparation As recommended by manufacture epoxy was blended at a ratio of 3:1 by the weight of resin and hardener, respectively. A m old with 11 coupon frames [F ig ure 4.1 (a) ] was filled with well blended epoxy to make epoxy coupons of 100 mm long X 6.7 mm thick X 12.2 mm wide by average All the coupons cured at room temperature more than seven days as recommended by the manufacture to ensure the ultimate strength of the material. Total of 30 dog bone coupons [Figure 4.1 (b)] were prepared. The average cross section of a coupon is 81.7 mm 2 Total of six CFRP strips were cut with 5 inches length [Figure 4.2 (a)] Desired length was selected to ensure at least 1 inch grip at both terminals. 4.3.2 Instrument Setup 20 kips MTS testing instrument and two heating pads [Figure 4.1 (c)] used to proceed the coupon test. Heat release was manually controlled due to the absence of temperature controllers on h eating pads. As shown is Figure 4.1 (b) epoxy coupon was placed in between tensions grips and tighten. Two heating pads were attached to the both sides of the epoxy coupon covering about 2 inches. Two thermo couples were attached to measure the temper ature of each heating pad [Figure 4.1 (d)] The epoxy coupon was pre tensioned to 1 kN with a rate of 16.67 N per second Procedure was set up as a displacement controlle d to hold the tension at 1 kN. Once the epoxy coupon achieved the desired tension (1 kN) heat was applied with an elevated tempera ture ranging from 25 C to 200 C. Stress reduction of epoxy coupons was recorded until the tensile strength reache s 0 N. Tensile stress reduction rate was observed through a tensile stress verse time plot.

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59 Prepared CFRP strips were tested applying monoto nic tension until the complete failure occurred. 20 ki ps MTS instrument was used. CFRP strips were tighten in between grips. At least 1 inch grip was ensured at each grip to prevent the slipping of CFRP strip at the terminals CFRP strips was exposed to 20 0 C for 3 hours before tensioning. Heat was applied using two heat pads and the temperature was recorded of each heat ing pad by two thermo couples [F igure 4.2 (b) ]. After exposing to the desired time period monotonic tension was applied with a rate of 1mm per minute. 4.4 Test results Epoxy and CFRP coupon test results are described in this section. 4.4.1 Influence of elevated temperatures on epoxy adhesive Results of the epoxy coupons over elevated t emperatures are given in table 4.1. Three epoxy coupons were tes ted at room temperature (25 C) ( the control specimens ) and showed an average stress decreasing rate of 0.004 MPa per second with a coefficient of variation of 0.364. The glass transition te mpe rature of MBrace epoxy is 71 C (Mbrace 2003). Howev er, epoxy coupons exposed to 50 C showed an average stress decreasing rate of 0.029 MPA which is 625 % higher than the con trol with a COV of 0.048 (Table 4.1 ). Epoxy co upons exposed to 75 C showed a signif icant increment in stress decreasing rate compared to control and coupons exposed to 50 C. The a verage stress decreasing rate is 0.082 MPa per second with a 0.048 COV. This is because EC 75 category has passed the glass transition temperature of the materi al. Therefore, 75C category lost its total stress

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60 carrying capacity 207 times quicke r than 50 C category [Figure 4.5 (c) and 4.6 ]. Since the glass transition temperat ure of the epoxy material is 71 C, temperatures after 75 C was not critical but the heat releasing rates governed the stress decreasing rate of e ach category. However, 125 C [Figure 4.5 (e)] and 150 C [Figure 4.5 (f)] categories behaved similarly with a stress decreasing rate of 0.168 and 0.165 MPa per sec, respectively. The standard deviatio ns are 0. 007 in both categories [Table 4.1] with a COV of 0.039 and 0.044 for 125 C and 150 C, respectively. The slope of th e stress decreasing rate of 125 C and 150 C cate gory was similar to each other [Figure 4.6] Epoxy coupons exposed to 100 C showed a stress decreasing rate of 0.126 MPa per sec with a standard deviation of 0.024 and a COV of 0.197 [Figure 4.3] An increased stress decreasing rate was showed by epoxy coupons exposed to 175C and 200 C categories [Figure 4.6] Each category showed an ave rage stress decreasing rate of 0.217 MPa and 0.221 MPa, respectively with the similar standard deviation of 0.020. The coefficients of variation of 175C and 200 C categories are 0.090 a nd 0.093, respectively. Figure 4.6 show s the comparison of stress decr easing rates o f each category ranging from 25 C to 200 C. The decreasing rate of epoxy coupons exposed to 200 C is 55.25 times greater than the 25 C category. Chapter 3 was an illustration of chemical changes of epoxy adhesive and the results indicated tha t there are significant changes in the chemical structure of the epoxy adhesive at elevated temperatures. However, FTIR spectrums were collected for residual epoxy samples. Significant chemical changes were ob served for epoxy samples at 125 C and greater. Coupon test results indicated that applied heat has a significant effect on the mechanical properties of the epoxy adhesive. Epoxy adhesive lost its s trength within 10 minutes at 50 C and the strength decreasing time

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61 was reduced with the increased heat [Fi gure 4.6 ]. It should be noted that the used epoxy adhesive a low glass transi tion temperature and that is 71 C [MBrace 2007] 4.4.2 Influence of high temperatures on CFRP strips Total of six CFRP stri ps were tested at 25C and 200 C. Summar y of the results are listed in T able 4.2, 4.3 and Figure 4.4. Tested coupons at room temperature showed an av erage ultimate capacity of 41.41 kN w ith a standard deviation of 7.92. The COV is 0.19 At 200 C, coupons showed 10.2 % reduction in ultimate capacity. The a verage ultimate strength recorded is 37.17 kN. The standa rd deviation and the COV at 200 C are 3.34 and 0.09, respectively. Also, the recorded displacement that was recorded shows that there is effect on CFRP ma terial at high temperatures. 25 C showed an average displacement of 8.47 mm and 200 C coupons demonstrated an average displacement of 9.01 m m. Standard deviation of the 25 C and 200 C categories are 0.70 and 0.06, respectively. Manufacturer indicates the glass transition tempe rature of the CFRP resin as 110 C (230 F). However, tested CFRP coupons shows that CFRP material is capable to retain its strength at a heat of 200 C for 3 hours. This indicate that the CFRP material is highly resistance to temperatures. Failure mode of each categor y was similar. Fiber failure a t mid span was observed [Figure 4.2 (c) ]. Also, some coupons showed slipping between grip and the CFRP strip interface. It should be noted that the recorded displacement is the cumulative of the MTS instrument. Therefore, the actual displacement of the coupon may be less than the recorded.

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62 4.5 Summery and conclusions In summary, total of 24 epoxy coupons and 6 CFRP coupons were tested to examine the thermo mechanical behavior of CFRP and epoxy materials at high temperatures. Displacement control testing was used for epoxy and monotonic tension test was performed until the complete failure was occurred for CFRP coupons. Based on the test results followings were concluded. Even though the glass transition temperat ure of the epoxy adhesive is 71 C, epoxy adhesive showed strength reduc tion at 50 C temperature. Epoxy coupon lost its strength within 10 minutes of exposure time at 50 C. This indicate s that an adhesive can have an effect on its mechanical properties at a temperature near the specified glass transition temperature of the resin. With the increase of the heating r ate adhesive showed increased stress decreasing rates. This demonstrate s that the adhesive increase s the strength losing rate with the increase of the heat releasing rate. Tested CFRP coupons showed that the high tem perature (200 C) has no significant eff ect on the CFRP material properties. Coupons show similar failures to the coupons tested at 25 C. Therefore, in a conjunction of CFRP and epoxy strengthening system epoxy adhesive control the overall strength of the system. Adhesive properties such as glass transition temperature, flash point are critical factors that should be concerned.

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63 Table 4.1 Test results of epoxy coupons exposed to elevated temperatures Temperature, C Specime n Stress decreasing rate, MPa/ sec Average Rate, MPa/ Sec Standard deviation Coefficients of variation 25 EC 25 1 0.005 0.004 0.002 0.364 EC 25 2 0.003 EC 25 3 0.005 50 EC 50 1 0.029 0.029 0.001 0.048 EC 50 2 0.031 EC 50 3 0.028 75 EC 75 1 0.082 0.082 0.006 0.069 EC 75 2 0.088 EC 75 3 0.076 100 EC 100 1 0.104 0.126 0.024 0.194 EC 100 2 0.122 EC 100 3 0.153 125 EC 125 1 0.168 0.168 0.007 0.039 EC 125 2 0.180 EC 125 3 0.179 150 EC 150 1 0.173 0.165 0.007 0.044 EC 150 2 0.161 EC 150 3 0.160 175 EC 175 1 0.199 0.217 0.020 0.090 EC 175 2 0.238 EC 175 3 0.216 200 EC 200 1 0.216 0.221 0.020 0.093 EC 200 2 0.203 EC 200 3 0.243

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64 Table 4.2 Ultimate tensile strength of CFRP coupons exposed to elevated temperatures Temperature, C Specimen Ultimate load, kN Average load kN Standard deviation Coefficient of variation 25 25 CS 1 32.69 41.41 7.92 0.19 25 CS 2 48.15 25 CS 3 43.40 200 200 CS 1 37.46 37.17 3.34 0.09 200 CS 2 33.69 200 CS 3 40.35 Table 4.3 Displacement at the ultimate load of CFRP coupons exposed to elevated temperatures Temperature, C Specimen Displacement at ultimate load, mm Average displacement, mm Standard deviation Coefficient of variation 25 25 CS 1 8.95 8.47 0.70 0.08 25 CS 2 7.67 25 CS 3 8.80 200 200 CS 1 9.00 9.01 0.06 0.01 200 CS 2 9.08 200 CS 3 8.96

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65 (a) (b) (c) (d) Figure 4.1. Epoxy sample preparation and instrumentation : (a) mold; (b) p repared epoxy sample; (c) used heating pads; (d) heat application on epoxy samples

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66 (a) (b) (c) (d) Figure 4.2. CFRP str ip test (a) prepared CFRP strip: (b) heat application using two heating pads; (c) CFRP failure at 25 C; (d) CFRP failure at 200 C

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67 (a) (b) Figure 4.3 Epoxy coupon test results : (a) stress decreasing rates at elevated temperatures; (b) standard deviation and COV of stress decreasing rates (a ) (b ) (c ) (d ) Figure 4.4 CFRP strip test results: (a ) u ltimate load ; (b ) standard deviation and COV of ultimate load ; (c ) displacement at ultimate load ; (d) standard deviation and COV of d isplacement

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68 (a ) (b ) (c ) (d ) (e ) (f )

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69 (g ) (h ) Figure 4.5 Stress decreasing rate at elevated temperatures of: (a ) 25 C; (b ) 50 C; (c ) 75C; (d) 100C; (e) 125 C; (f) 150C; (g) 175C; (h) 200 C

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70 (a ) (b ) (c ) (d ) (e ) (f )

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71 (g ) Figure 4.6 Thermo couple reading of epoxy samples at: (a) 5 0 C; (b) 75 C; (c) 100 C; (d) 125 C; (e) 150 C; (f) 1 75 C; (g) 200 C

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72 (a ) (b ) (c) Figure 4.7 Stress decreasing rate comparison of epoxy samples : (a) EC I; (b) EC II; (c) EC III

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73 (a) (b) (c) Figure 4.8 CFRP strip test results: (a) 2 5 C; (b) 200C; (d ) t hermocouple reading at 200 C

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74 5 Performance of NSM CFRP concrete Interface Subjected to Elevated Temperatures 5.1 General Near surface mounted (NSM) CFRP strengthening system is a promising technique that is used to enhance the flexural and shear strength of deteriorated concrete structures. CFRP rods or strips are embedded i n to the pre cut groove with an epoxy adhesive or cementit i ous material to form the NSM system. All the epoxy adhesive are polymeric materials which can be affected by the high temperature. Fire is a crucial hazard that can affect the strength of concrete structures as well as the mechanical properties of polymeric materials in the strengthening system An experimental research program was conducted to invest igat e the effect of NSM CFRP strengthened concrete structures at high temperatures due the fire The experimental program consists a monotonic tension test and a cyclic loading test. Also an infrared thermal images were taken to ensure the thermal propaga tion at the mid span of the strengthening system. Monotonic tension test and the cyclic loading test were carried ou t using concrete block which are 150 mm long, 100 mm wide and 75 mm height. A conventional epoxy resin was used to embed the rectangular CF RP strip in to the groove. The glass transition temperature o f the used epoxy adhesive is 71 C [MBrace, 2007] Monotonic tension test results indicate that the heat exposure time and the heat releasing rate are crucial factors that can affect the strength of the strengthening systems and the failure mode of the concrete structure. Different types of failures were observed including CFRP strip failure at the mid line of the Strip. Also, a significant strength reduction was recorded for th e concrete block exp osed to 100 C. Bond stiffness was examined from the

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75 cyclic loading test and test results indicate that the bond stiffness can be affected by high temperatures. However, a numerical comparison was not conducted due to the displacement singularity of the tes ted specimens. The internal thermal propagation at the mid span was recorded using a thermocouple attached to the internal surface of the strengthening system. Also IR images were collected to ensure the thermal propagation at the mid span of the concrete block. It was noted that the heat release rate is a crucial factor that influences the strength and failure mode of the strengthening system. The behavior of the NSM CFRP strengthening system was examined by the pullout strength, different failure modes, bond stiffness and the thermal propagation. 5.2 Experimental program Thermal effect of the NSM strengthened concrete blocks were observed from two different types of testing methods. A m onotonic tension test was conducted to investigate the ultimate pullout strength, failure modes, and the load displacement behavior of NSM CFRP strengthened sys tems at elevated temperatures. C yclic load was applied to examine the stiffness changes of the NSM CFRP strengthened system under fire. Also, IR thermal images were collected to analyze the thermal propagation of the Strengthening system at elevated temperatures. This secti on covers the material details, sample preparation, instrumentation and testing procedures of these three testing programs.

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76 5.2.1 Materials 30 Mpa [4351 p si] concrete mixed design was used to mix the concrete [Table 5.1 ]. The water cement ratio of the mix design is 0.65. Concrete was mixed in the laboratory using an elect r ic concrete mixture The compressive strength of the concrete was tested using prepare d cylindrical specimens. The radius and the height of the specimens are 100 X 200 mm (4 X 8 inches) respectively [Figure 5.1 (a)] The average strength of concrete was measured to be 30.40 Mpa [4409 psi]. The results of the tested spe cimens are l isted in Table 5.2 and the F igure 5.1 (b) shows the failure of tested specimens. Mbrace epoxy resin was used to embed the CFRP strips in the groove. Epoxy adhesive is a common bonding agent that is used in many different CFRP applications. The e poxy adhesive u sed is a conventional epoxy adhesive with a low glass transition temperature. The glass transition temperat ure of the adhesive is 71 C [160 F] [Mbrace, 2007]. The adhesive has two parts, a resin (blue) and a hardener (clear). The resin and hardener has to ble nd 3:1 ratio by weight, respective. Mixed blend should cure at least 7 days to achieve its ultimate strength ( f epx ) of 55.2 MPa [8006 psi] The cured adhesive has an elastic modulus ( E epx ) of 3034 MPa [440 ksi] [Mbrace, 2007]. Manufacture r specifies the Thermal Conductivity of this material as 1.45 Btuin/hrft2F (0.21 W/mK). The u sed c arbon fiber reinforced polymer (CFRP) strips has a nominal area of 31.67 mm 2 The ultimate tensile strength of the strips is 70.8 kN (15.92 ksi) and has an elastic modulus of 124 GPa (18000 ksi) [Aslen, 2011]. The glas s transition temperature is 110C (230 F) as recommended by the manufacturer. Wider surface of the CFRP strip was texture d to develop the bond mechanism.

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77 5.2.2 Specimen preparation Concrete was prepared with the specified mix design in table 5.1 measured cement, sand, aggregate and water insert in to a concrete mixture and mi xed the concrete well Total of 8 cylindrical contains with a radius of 100 mm (4 inches) and aheight of 200 m m (8 inches) was greased before placing mixed concrete in to the container. After concrete is placed in containers, all the prepared samples were air dried for 24 hour and placed in a water tank for 8 days. Thr ee specimens were tested after 7 days curing. Rest of the specimens were cured for 28 days and tested. MTS compressive testing [ASTM C39] machine was used for the test. Test results are indicated in table 5.2 and Figure 5.1 (b) shows the failure of a tested specimens. Total of 48 specimens were fabri cated to examine the behavior of NSM CFRP strengthening systems. Two different testing programs were conducted using 24 specimens for each test program. Each specimens has a 150 mm (6 inches) length, 100 mm (4 inches) width and 75 mm (3 inches) height [Fig ure 5.2 (a)] 1500 mm (6 inches) long groove was configured with a 25 mm (1 inch) height and a (1/2 inch) width [Figure 5.2 (b) The groove dimension s were used as recommended by ACI 440.2R 08. The specimen con figuration is shown in Figure 5.2 with dimens ions. Steel molds (400 X 100 X 75 mm) were used to prepare the concrete blocks [Figure 5.3 (a)] Each mold was configured with forms to specified configuration described. One thermocouple was located as shown in the Figure 5.3 (b) to measure the temperature inside the bond. After the preparation, each mold was filled with concrete and compacted to fill the voids. All the specimens were cured for 28 days. Cured concrete blocks were removed from the molds and the cleaned the grooves with a steel brush and hig h pressured air. This is to clean the weak oxidized cement on the

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78 concrete surface and make the interface rough enough to make a perfect bond. Clean ed concrete blocks were fabricated for NSM CFRP strengthening syste m application a s shown Figure 5.3 (a) 4 inches bonding length was provided to each concrete block [Figure 5.2 (b)] Epoxy adhesive was prepared blending blue colored resin and the clear hardener with ration of 3:1 by the weight. 6.5 inches long CFRP strips was used with a 3.5 inches of bonded length in the groove. CFRP was place in the groove with the specified dimensions and the groove was filled with epox y adhesive [Figure 5.3 (b) ]. All the blocks were cured 7 days to achieve the ultimate strength of the epoxy adhesive as recommended by the manufacturer. Another 8 specimens were prepared to investigate the thermal propagation of the specimens under heat application. Concrete blocks were prepared in the similar condition as discussed early. After epoxy adhesive cured, con crete block cut at the mid span to make the ep oxy concrete interface [Figure 5.17 (b ) ]. All the concrete blocks were air dried before test s 5.2.3 Heat application All the well cured concrete block specimens were exposed to elevat ed temperatures ranging from 25C [77F] to 200C [392F] at a typical interval of 25 C. 150 X 100 mm (6 X 4 inches) heating pad was used to apply the heat on the concrete block surface Heat was applied on the N SM strengthened surface [Figure 5.4 (b) ]. All the specimens were pr eheated for five minutes at the desire d temperature before the loading Heat was applied until the concrete blocks failed completely. Two thermo couples were attached to the concrete blocks to measure the surface temperature and the internal temperature of the

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79 e pox y concrete interface [Figure 5.2 (c ) ]. IR images collected up t o 30 minutes of heat application from the beginning. 5.2.4 Instrumentation and testing procedure Monotonic tension test and cyclic loading test were conducted using 20 kip s MTS testing machine A pull out tensioning mold was used to carry out the tension test. As shown in F igure 5.4 (a) the mold was placed in between two grips and tied the bottom grip well Concrete block was located on the mold stage and tied the bolds to ensure the stress transformation along the bond line. Then after top grip was tied well and attached the thermocouples to read the temperature [Figure 5.4 (b)]. As shown in Figure 5.2 (b) heating pad was attached to the NSM strengthened surface to apply the desi red temperature. After the concreted block installed, the block was preheated for five minutes at the desired temperatures before the tension applied. Once the pre heating completed monotonic tension was applied at a rate of 0.5 mm per minute [Figure 5.4 ( c)] The test was run until the complete failure occurred and the heat was applied until the test is completed. Load, displacement and temperature were recorded. Instrumentation for the cyclic loading in similar to the monotonic tension test. After preheat ing completed cyclic load was applied. Cyclic loading was ranging from 10% to 100% of the average pull out capacity recorded from the monotonic test. Cyclic load was applied at a rate of 0.5 mm per minute and the heat was applied until the complete failure occurred. Thermal propagation at the mid span of the concrete block was imaged using an IR thermal camera [Figure 5.17 (a )] Heat was applied using the same heating pad which described early. Thermal images were taken up

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80 to 30 minutes of heat application at a typical period of 5 minutes. Th ermal propagation was graphed in Figure 5.25 5.3 Test results 5.3.1 Pullout capacity Pull out strength was taken by conducting the monotonic tension test. The summary of the results are indicated in Table 5.3 and F igure 5.5 illustrate the average pullout capacity, standard deviation and the COV of the tested concrete blocks. Three control specimens were tested at room temperature and the ultimate pullout capacity was recorded as 36.20 kN. The standard deviation and the coefficient of variation (COV) of the control specimens were 7.86 and 0.22, respectively. Tested concrete block at 50 C heating showed 11.57 % decrease in strength with a higher standard deviation and COV of 10.21 a nd 0.32, respectively. The pull out capacity was 32.01 kN. However, CB 50 category showed lower capacity than CB 75 category. This is because of the CB 50 1 specimen failed with a lower pullout capacity of 21.28 kN. Only 6.27 % reduction of pullout capacity was reco rded f or concrete blocks heated at 75 C. The standard deviation and the COV of CB 75 category were 4.60 and 0.14, respectively. The pullout capacity is slightly higher than the CB 50 category. A significant capacity reduction was notes for CB 100 category. The recorded ultimate pullout strength was 12.29 kN. This is about 66 % capacity reduction compared to the control specimens. This is because the applied heat was greater than the glass transition temperature of the epoxy adhesive and a large portion of t he epoxy adhesive was soften. This implies that the heat releasing rate is a crucial factor that can affect the

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81 strengthening system. All the categories which were exposed to higher temperatures than 100 C showed a lmost linear strength reduction behavior This is because the heat releasing rate governed the bond strength of the strengthening system. CB 125 category showed 70.52% strength reduction compared to the control specimens with a standard deviation of 2.18 and COV of 0.20. The ultimate pullout capac ity of CB 150 is 7.47 kN which is 161.2% greater than that of CB 200 category. Concrete blocks exposed to 175 C showed a pullout capacity of 3.04 kN with a standard deviation of 0.40 and 0.13 of COV. These results indicate that the bond strength of the NS M strengthening system depends on the glass transition temperature of the bonding agent and the heat releasing rate. Weibull distribution was established for the monatomic tension test [Figure 5.5 (c)]. Shape factor was obtain from the slope and the intercept of the curve function shown in the Figure 5.5 (c). Scale factor of the weibull distribution is 18.65 and shape factor is 0.0044. The coefficient of determination (R 2 ) of the weibull function is 0.8448. 5.3.2 Load displacement behavior Pullout strength vs displacement plots were recorded during from the monotoni c tension test and the F igure 5.6 shows the plotted graphs. As shown in F igure 5.6 (a) and 5.6 (b) concrete block tested at room temperature and e xposed to 50 C failed suddenly after reaching the ultimate pullout strength. However, CB 75 I also showed the sudden failure at the ult imate pullout strength [Figure 5.6 (c) ]. This is because a large portion of epoxy adhesive was able to retain the mechanical properties of the adhesive. Two specimens that sh owed load softening in Figure 5.6 (c) due to the CFRP slip after the CFRP strip failure. This will be discussed later in failure mode section. Due to different failure modes, concrete

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82 blocks exposed to 1 00 C and higher [figures 5.6 (d ) to 5.6 (g) ] showed load softening after the failure. This because of the epoxy softening with temperature and the friction between each surfaces (concrete epoxy and epoxy CFRP) and it depends on the failure mode. 5.3.3 Failure mode Different failure modes were noticed during the monotonic tension test. The summery of all the failure modes are summarized in Figure 5.7 all the categories showed their own uniq ue failure mode. As shown in F i gure 5.7 (a) concrete blocks tested at room temperature shown con crete epoxy interface failure. Also, one control specimens showed epoxy CFRP interface slippin g at the ultimate load [Figure 5.6 (b) ]. Epoxy CFRP interface was able to transfer the stress to the concrete epoxy interface but it is also possible to occur the epoxy CFRP interface failure Cracks were observed on the concrete block specimens. Epoxy specimens. However, epoxy adhesive failure was observed on th is category [Figur e 5.7 (c) ]. This is because of the effect of heat applied to the specimen. Complete concrete epoxy interface failure was observed on concrete block exposed to 75 C. Also, failure of this category includes adhesive failure at the bottom of the bond and CFRP strip failure at the mi d line of the strip [Figure 5.7 (d) ]. Strengthening bond was failed at the mid line of the bo nd with CFRP failure Epoxy CFRP interface failure was also observed on CB 75 category [Figure 5.7 (e) ]. Due t o the adhesive softening at 100 C, CB 100 category showed partial epoxy CFRP interface failure. CFRP failure also observed at the mid line of the strip [Figure 5.7 (f) ]. Concrete epoxy interface failure was not observed for the categ ories exposed to 100 C and higher. As shown in Figu re 5.7 (h) CB 125 category showed epoxy

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83 interface failure with CFRP strip failure at the mid line similar to the CB 100 category. Concrete blocks exposed to 150 C showed two different types of failure. CB 50 I showed complete epoxy CFRP interface failure [ F igure 5.7 (h ) ] and other two specimens showed partial epoxy CFRP interface failure [Figure 5.7 (i) ] similar to CB 100 and CB 125 categories. Failure modes of the concrete blocks exposed to 175 C an d 200 C were complete epoxy CFRP interfac e failure. As sho wn in F igur e 5.7 (j) and (k) specimens failed with epoxy adhesive crushing at the ultimate load. This because a large portion of bond was affected by the applied heat due to the higher heat releasing rate. As discussed early, heat releasing rate is an impo rtant factor considering the strength and the failure of the NSM strengthening system. F ailure mode s of each category indicate the bonding behavior at elevated temperatures. It should be noted that the most specimens showed CFRP slipping after the CFRP fa ilure. 5.3.4 Thermal propagation along the bond line Thermal propagation along the bond line was recorded using a thermocouple attached inside the internal concrete epoxy interface of each specimen. Thermal readings were used to compare the each the strengthening system. Collected thermal re adings are summarized in Figure 5.8 and Figure 5.9 shows the comparison of thermal conduction at different t emperatures. As shown in Figure 5.8 all the specimens showed similar thermal conduction for all three specimens of each category. This proves that the applied heat is same in each category. However, CB 100 2 specimens showed increased conduction rate compared to other two

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84 specimens [ Fig ure 5.8 (c) ]. The thermal conduction was increased with the i ncreasing heating rate [Figure 5.9 ]. This implies the proof of the discussed test results. 5.3.5 Bond stiffness of the NSM CFRP strengthening system at elevated temperatures The bond stiffness of NSM CFRP system at elevated temperatures was examined from the cyclic loading test. Cyclic loading test results are summarized in Figure 5.11, 5.12 and 5.13. Figure 5.12 is an interpretation of normalized load of the cyclic load which is normalized to the average ultimate pullout load of each category. Also, recorded thermo couple readings are given in Figure 5.14. Three control specimens were tested at room temperature and the results indicate that the stiffness was increased up to the 4 th loading cycle and then after a decreasing was observed [Figure 5.13 (a)] Specimens failed at 9 th 10 th and 8 th cycles [Figure 5.11 (a) and 5.12 (a)]. Similar stiffness behavior was observed for 50 C 75 C and 100 C categories [Figure 5 .13 (b), (c) and (d)] However, all the three specimens of 100 C category failed at the 7 th cycle [Figure 5.11 (d)] and 75 C failed around the 6 th cycle [Figure 5.11 (c)] Therefore, the complete stiffness behavior was not recorded The number of cycles to th e complete failure was smaller compared with the other categories and it was unique for 75 C and 100 C categories Concrete blocks which were exposed to 125C showed a reduction in stiffness until the complete failure [Figure 5. 13 (e)] The failure of these specimens were occurred around the 9 th cycle [Figure 5.11 (e)] The complete failure of 150 C category was occurred around 9 th cycle [F igure 5.11 (f)] and the stiffness was similar to the 125 C category except the stiffness at the 5 th cycle [Figure 5.13 (e)] Stiffness at the 9 th cycle was recorded for only one specimens. S o that the increase

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85 of the stiffness was ignored at the 9 th cycle of the 150 C category. Concrete block which were exposed to 175C showed similar behavior to the control specimens with a relatively lower stiffness than the control specimens [Figure 5.13 (g)] 200 C category showed higher stiffness at the beginning than other categories and sudden showed sudden drops in stiffness with in first 4 cycles [Figure 5.13 (h)] This can be because of the lower cyclic load at the beginning. However, low stiffness was recorded after the 4 th cycle. It sh ould be noted that the described stiffness of the NSM CFRP system at elevated temperatures based on the average s tiffness as shown in Figure 5.13 Also, it should be noted that a numerical comparison was not carried out due to the displacement singularity. However, the recorded data show some stiffness reduction with the increase of temperature. More figure s are summarized in appendix D. 5.3.6 Thermal propagation at mid span of the concrete block Thermal propagation of concrete blocks at the mid span was collected using an IR thermal camera and the re sul ts are summarized in Figure 5.18 to 5.2 IR images were ta ke n for each category [Figure 5.18 to 5.24 ]. Thermal increment near the internal epoxy concrete interface was plotted [Figure 5.24 ] All the specimens showed linear temp erature increment [Figure 5.26 ]. The thermal increasing rate was increased with the increased heat application. As shown in Figure 5.18 to 5.23 with time temperature was propagated along the mid span of the concrete block. Heat releasing rate was crucial because it governed the internal therma l in crement. As sh own in Figure 5.25 (a), (b) and (c) 50, 75 and 100 C categories showed thermal increments below the glass transition temperature of the epoxy resin. However, F igure 5.20 indicates that the 100 C specimens have a higher thermal

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86 effect on the strengthening bond near the surface than CB 50 and 75 categories Therefore it is possible to have a higher temperature than the glass transition of epoxy resin. This is the reason that the CB 100 category showed a decreased pullout strength with CFRP failure and epoxy adhesive failure. Al l the cate gories which was exposed to 125 C and higher temperatures showed higher temperature increments than the glass transition temperature of the epo xy resin at 30 minutes [F igure 5.19 to 5.24 ]. However, 125C [Figure 5.19 ] and 150 C [Figure 5.22 ] cate gory showed thermal increments near the glass transition temperature resulting different failure modes and reductions in str ength. As discussed in section 5.3.4 CB 125 showed CFRP failure at mid line o f the strip and epoxy failure [Figure 5.7 (a) ] while CB 150 showed complete epoxy CFRP interface failure as well as the mid line CFRP fai lure and epoxy failure [Figure 5.7 (h) and (i) ]. Concrete b loc k exposed to 175C [Figure 5.23 ] and 200 C [Figure 5.24 ] showed a higher thermal increasing rates than others an d the thermal increment was greater than the glass transition temperature of the epoxy resin. Higher thermal increment of these two categories resulted about 95 % of strength reduction and complete epoxy CFRP failur e with epoxy crushing [Figure 5.7 (j) to (k) ]. Temperature at the concrete heating pad was recorded by thermo couples and given in Figure 5.27 5.4 Summary and Conclusions Near surface mounted (NSM) strengthening system is a promising strengthening technique that is formed by embedding CFRP rods or strips in to a precut groove with an appropriate bonding agent. Two experimental testing were conducted to examine the bond beha vior of NSM system at high temperatures due to fire event. The monotonic tension test was carried

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87 out investigating the ultimate pullout strength, load displacement behavior and different failure modes. Bond stiffness was examined from the cyclic load test Also, mid span thermal propagation was observed by taking IR thermal images and thermocouples attached to the internal epoxy concrete interface. Followings were concluded from the test results. Pull out strength of the concrete blocks which were exposed room temperature, 50C and 75 C showed a higher pullout strength. A significant pullout reduction was observed for the CB 100 category and a linear pullout r eduction was examined up to 200 C. Complete epoxy CFRP interface and epoxy concrete interface fai lures were observed for control specimens. Concrete block exposed to 50C and 75 C showed adhesive failure at the bottom end of the bond. CFRP failure was observed for CB 75 category. Concret e blocks exposed to 100 C and higher temperatures showed adhesiv e crushing, CFRP failure at mid line of the strip and epoxy CFRP interface failure. Complete epoxy CFRP interface failure was observed for CB 175 and 200 categories. Brittle failure was observed for CB 25, 50 and 75 categories and load softening was exami ned for other categories after the failure. Bond stiffness was examine from the cyclic loading test. 75 C and 100 C categories failed at a low number of loading cycles. An increment of stiffness was recorded up to the 4 th cycle for 25, 50, 75 and 100 C categories and after that specimens showed a reduction in stiffness.

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88 Numerical comparison was not done due to the displacement singularity. But it was possible to see small deviations in stiffness with the increased temperatures. Thermal propagation of CB 150, 175 and 200 categories at 30 minutes were higher than the glass transition temperature of the epoxy adhesive. Thermal propagation controlled the failure mode of the strengthening system.

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89 Table 5.1 Concrete mix design W/C 65% Cement (kg/m 3 ) 332 Water (kg/m 3 ) 216 Aggregate (kg/m 3 ) 1050 Sand (kg/m 3 ) 757 Table 5.2 30 days compressive strength of concrete cylinders Specimen Compressive Load (kN) Compressive Stress(Mpa) M1 261 33.25 M2 215 27.39 M3 240 30.57 Average CS (Mpa) 30.40

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90 Table 5.3. Monotonic tension test results Temperature, C Specimen Maximum t ensile strength, kN Average t ensile Strength, kN Standard deviation Coefficients of variation 25 CB 25 1 27.82 36.20 7.86 0.22 CB 25 2 37.39 CB 25 3 43.40 50 CB 50 1 21.28 32.01 10.21 0.32 CB 50 2 41.60 CB 50 3 33.16 75 CB 75 1 38.94 33.93 4.60 0.14 CB 75 2 29.90 CB 75 3 32.96 100 CB 100 1 10.10 12.29 2.66 0.22 CB 100 2 11.53 CB 100 3 15.25 125 CB 125 1 13.18 10.67 2.18 0.20 CB 125 2 9.618 CB 125 3 9.224 150 CB 150 1 8.318 7.47 0.84 0.11 CB 150 2 7.46 CB 150 3 6.63 175 CB 175 1 3.48 3.04 0.40 0.13 CB 175 2 2.71 CB 175 3 2.92 200 CB 200 1 3.69 2.86 0.91 0.32 CB 200 2 3.01 CB 200 3 1.88

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91 (a) (b) F igure 5.1 Compression test: (a) c oncrete cylinders ; (b) tested sample

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92 (a) (b) (c) Figure 5.2 Concrete block specimen dimensions : (a) c oncrete block with groove; (b) NSM strengthening system; (c) thermocouple location.

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9 3 (a) (b) (c) (d) Figure 5.3 Sample preparation (a) mold fabrication; (b) concrete filling; (c ) concrete block fabrication for NSM system; (d) prepared concrete specimen

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94 (a) (b) (c) Figure 5.4 Instrumentation for monotonic tension test : (a) concrete block located on MTS machine; (b) prepared sample for heating; (c) testing procedure

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95 (a) (b) (c) Fi gure 5.5 Monotonic tension test results : (a) Interfacial capacity; (b) standard deviation and COV; (c) weibull distribution

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96 (a) (b) (c ) (d ) (e ) (f )

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97 (g ) (h ) Figure 5.6 Load displacement behavior of tested concrete blocks at elevated temperatures of : (a) 25 C; ( b) 50 C ; (c) 75C; (d) 100C; (e) 125C; (f) 150C; (g) 175C; (h) 200 C

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98 (a) (b) ( c ) (d )

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99 (e ) (f ) (g ) (h )

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100 (i ) (j ) ( k ) Figure 5.7 Failure modes of tested concrete blocks at elevated temperatures of : (a) 25 C e poxy concrete interface failure ; (b ) 25C e poxy CFRP interface failure ( c ) 50C; (d ) 75C epoxy concrete interface failure; (e ) 75C epoxy CFRP interface failure (f) 100C; (g) 125C; (h) 150Cpartial epoxy CFRP interface failure; (i ) 150 C complete epoxy CFRP interface failure ; (j) 175C; (k ) 200 C.

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101 (a) (b) (c) (d) (e) (f)

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102 (g) Figure 5.8. Thermocouple reading of concrete blocks tested of monotonic tension t est at elevated temperatures of: (a) 50C; (b) 75C; (c) 100C; (d) 125C; (e) 150C; (f) 175C; (g) 200C

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103 (a) (b) (c) (d) (e) (f)

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104 (g) Figure 5.9. Internal temperature (thermocouple II) increment of monotonic tension test specimens exposed to : (a) 50 C; ( b) 75 C; (c ) 100C; (d) 125 C; (e) 150C; (f) 175C; (g) 200 C (a) (b) (c) Figure 5.10. Internal temperature increment comparison of : (a) specimen 1; (b) specimen 2; (c) specimen 3

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105 (a) (b) (c ) (d ) (e ) (f )

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106 (g ) (h ) Figure 5.11 Load displacement behavior of cyclic loading specimen 1 at : (a) 25C; (b) 50C; (c) 75C; (d) 100C; (e) 125C; (f) 150C; (g) 175C; (h) 200C.

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107 (a) (b) (c ) (d ) (e ) (f )

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108 (g ) (h ) Figure 5.12 Normalized load displacement behavior of cyclic loading specimen 1 at : (a) 25C; (b) 50C; (c) 75C; (d) 100C; (e) 125C; (f) 150C; (g) 175C; (h) 200C.

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109 (a) (b) (c) (d) (e) (f)

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110 (g) (h) Figure 5.13 Bond stiffness of NSM strengthened concrete blocks at: (a) 25C; (b) 50C; (c) 75C; (d) 100C; (e) 125C; (f) 150C; (g) 175C; (h) 200C. Figure 3.14. Average s tiffness comparison of each category.

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111 (a) (b) (c ) (d ) (e ) (f )

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112 (g ) Figure 5.15 Thermo couple readings of cyclic loading specimens 1 of each category at : (a) 50C; (b) 75C; (c) 100C; (d) 125C; (e) 150C; (f) 175C; (g) 200C. (a) (b) Figure 5.16 Comparison of thermocouple readings of specimen 1: (a) thermocouple I; (b) thermocouple II.

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113 (a) (b) Figure 5.17 IR image testing : (a) IR thermal camera; (b) specimen setup for the testing

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114 (a) (b) (c) (d) (e) (f) (g) Figure 5.18 IR thermal images of concrete block exposed to 50C at : (a) 0; (b) 5; (c) 10; (d) 15; (e) 20; (f) 25; (g) 30 minutes 22.7 C 77.7C 23.3C 65.5C 22.2C 67.7C 64.4C 22.7C 22.2C 62.7C 22.2C 69.4C 22.2C 59.4C

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115 (a) (b) (c) (d) (e) (f) (g) Figure 5.19 I R thermal images of concrete block exposed to 75C at : (a) 0; (b) 5; (c) 10; (d) 15; (e) 20; (f) 25; (g) 30 minutes 22.2C 84.4C 22.2C 88.8C 22.2C 92.2C 93.8C 22.2C 22.7C 88.3C 22.2C 87.2C 22.2C 89.4C

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116 (a) (b) (c) (d) (e) (f) (g) Figure 5.20 IR thermal images of concrete block exposed to 100C at : (a) 0; (b) 5; (c) 10; (d) 15; (e) 20; (f) 25; (g) 30 minutes 22.7 C 137C 22.7 C 130C 21.6C 132C 124C 22.7 C 22.2C 112C 22.2C 122C 21.6C 118C

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117 (a) (b) (c) (d) (e) (f) (g) Figure 5.21 IR thermal images of concrete block exposed to 125C at : (a) 0; (b) 5; (c) 10; (d) 15; (e) 20; (f) 25; (g) 30 minutes 22.7 C 180C 22.7 C 184C 22.2C 176C 177C 22.7 C 22.2C 160C 22.7 C 167C 22.7 C 171C

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118 (a) (b) (c) (d) (e) (f) (g) Figu re 5.22 IR thermal images of concrete block exposed to 150C at : (a) 0; (b) 5; (c) 10; (d) 15; (e) 20; (f) 25; (g ) 30 minutes 21.6C 220C 22.2C 198C 21.6C 205C 199C 21.6C 22.7 C 220C 22.7 C 190C 22.7 C 185C

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119 (a) (b) (c) (d) (e) (f) (g) Figure 5.23 IR thermal images of concrete block exposed to 175C at : (a) 0; (b) 5; (c) 10; (d) 15; (e) 20; (f) 25; (g) 30 mi nutes 22.7C 205C 22.7C 206C 22.7C 209C 194C 21.6C 22.2C 198C 22.7 C 188C 22.7 C 198C

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120 (a) (b) (c ) (d) (e) (f ) (g) Figur e 5.2 4 IR thermal images of concrete block exposed to 200C at : (a) 0; (b) 5; (c) 10; (d) 15; (e) 20; (f) 25; (g) 30 minutes 23.3C 227C 23.3C 215C 23.8C 221C 223C 23.3C 23.8C 223C 24.4C 221C 24.4C 227C

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121 (a) (b) (c) (d) (e) (f)

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122 (g) Figure 5.25 Thermal propagation of each category based on the IR images at the internal epoxy concrete surface : (a) 50C; (b) 75C; (c) 100C; (d) 125C; (e) 150C; (f) 175C; (g) 200C Figure 5.26 Thermal propagation comparison of each category

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123 (a) (b) (c) (d) (e) (f)

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124 (g) Figure 5.2 7 Thermo couple reading at the he ated surface of each category at : (a) 50C; (b) 75C; (c) 100C; (d) 125C; (e) 150C; (f) 175C; (g) 200C

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125 6 Summery and Conclusions This thesis report presents an investigation of the performance of near surface mounted (NSM) strengthened system under fire. NSM strengthening system is an emerging technique which has better performance that externally bond strengthening system. Chapter 02 of this thesis report discuss es about the NSM strengthening system as well as new finding in the area of fire exposure of NSM strengthened concrete structures. Based on the literature review followings were concluded. Only a few research studies have been conducted in the area of NSM strengthening system due to the late in troduction of the system. NSM strengthening system showed better performance than the externally bonded strengthening system. Most research studies have focused on investigating the bond capacity, determining groove size requirement and other dimensional properties at room temperature. Some of the researches were conducted to examine the residual performance of the NSM strengthening system at elevated temperatures. Also, few tests were conducted investigating the fire insulation system for NSM FRP streng then systems. Epoxy or any appropriate cementitious material uses to e mbed the FRP rod or strips in to the groove. Epoxy adhesives are polymeric materials which can be affected its mechanical properties by high temperature.

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126 Lack of research references in the area of NSM FRP strengthening system shows the requirements of new finding to examine the structural behavior of NSM FRP strengthened concrete structures. Mid range FTIR instrument is widely used to examine the chemical changes of chemical compounds The glass transition temperature is a crucial factor that defines the chemical behavior of polymeric materials. Therefore, it is important to investigate the behavior of polymeric materials which is used in strengthening systems under high temperature. Two phase experimental testing program conducted to examine the material level performances and the element level performances. Material level testing includes a Fourier transform infrared spectrometer (FTIR) interoperation of epoxy adhesive at elevated te mperatures. The bond behavior of NSM CFRP system was investigated through the element level testing program. Chemical changes of epoxy adhesive was investigated through FTIR spectrums and chapter 03 consists the carried out experimental program. Test resu lts lead to conclude the followings. Chemical changes of residual epoxy samples exposed to elevated temperatures and elevated time periods up to 3 hours were examined thorough a mid range FTIR instrument. Spectrum changes were observe d for epoxy samples a fter exposing 3 hours under 50 C of temperature at the 875 peak value.

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127 All the epoxy samples exposed to 75 C and higher temperatures at each time periods showed a consistence in spectrum changes observed at 50 C. Visible chemical changes were observed near the 1654 wave number on epoxy samples exposed to 125 C. The intensity of the spectrum at the 1654 and 1730 was increase with the time and the temperature. Even though, the test was carried out for residual epoxy samples it was possible to conclude the chemical changes at high temperatures. This proves that the polymeric adhesive can be affected by high temperature resulting any mechanical property changes of adhesive. Also, color changes were observed at elevated temperatures to prove the chemical changes of epoxy samples. Visible color changes were observed in epoxy samples exposed to 175 C and 200 C. Material level testing was conducted to examine the behavior of epoxy adhesive and CFRP strips at high temperatures. Both are polymeric materials which are highly sensitive to temperature due to the glass transition temperature of each material. Displacement control tension test was conducted for epoxy coupon investigating the stress reduction rate at high temperatures. Monotonic tension was applied to CFRP stripes which were exposed to 200 C for 3 hours. Chapter 04 describes the material level testing program and it results. Based on the results following can be concluded. Even though the glass transition temperature of epoxy adhesive is 71C, epox y adhesive showed a significant stress decreasing rate at 50 C. Since the heat was

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128 just below the Tg, epoxy coupon at 50 C stress reduction rate was lower than other categories. The stress decreasing rate of epoxy coupons exposed to 75 C and higher was controlled by the heat releasing rate. This implies that the mechanical properties of a polymeric adhesive can be controlled by the heat releasing rate. Stress decreasing rate was increased with the increase of the temperature. Six CFRP strips were teste d at 25 C and 200 C. CFRP strips were preheated at 200 C for 3 hours and then monotonic tension was applied until the complete failure occurred. However, tested coupons showed about 10 % load reduction than that of control specimens. Displacement at u ltimate load was also checked and found about 6 % increment in displacement. Either this displacement increment may be a result of the temperature effect or due to the CFRP slipping. show a significant load reduction, displacement increment or different failure mode. Both categories failure similar to each other. Chapter 5 discusses the element level testi ng program and its result which was conducted to investigate the performance of NSM CFRP strengthening systems in fire. A monotonic tension test and a cyclic loading test were performed. Also this section includes an IR thermal image testing which was carr ied out to draw the thermal propagation at the mid span of the strengthening system. Test results indicated the followings. Concrete block exposed to 25, 50 and 75 C showed higher pullout strength compared to other specimens. A significant strength reduc tion was observed for the

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129 concrete block exposed to 100 C. The strength decreasing was almost liner for the block exposed to higher temperatures than 100 C. Brittle failure was observed for CB 25, 50 and 75 categories. Two specimens of CB 75 category an d greater heat exposure categories showed load softening after the first failure. This is due to the epoxy softening at higher temperature than the glass transition temperature of the epoxy adhesive. Concrete epoxy interface failure was observed for CB 25 and 50 and 75. Also, one specimen of CB 25 category showed epoxy CFRP interface failure. Epoxy adhesive failure was common in both CB 50 and 75 categories. CFRP failure was observed at the mid line of the strip for CB 75 category. Also, partial epoxy CFRP failure was examined at 75 C. Concrete blocks exposed to 100 C greater showed epoxy CFRP interface failure including epoxy crushing. Completer epoxy CFRP failure was common in CB 175 and 200 categories. Bond stiffness was examine from the cyclic loadin g test. 75 C and 100 C failed at a low number of loading cycles. An increment of stiffness was recorded up to the 4 th cycle for 25, 50, 75 and 100 c categories and after that specimens showed a reduction in stiffness. Numerical comparison was not done due to the displacement singularity. But it was possible to see small deviations in stiffness with the increased temperat ures. IR images s how the thermal propagation at the mid span of the NSM str engthening system. Results indicate that the internal temperature increment was controlled by the heat releasing rate.

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130 CB 50, 75 and 100 categories showed less internal temperatur e increments than the glass transition temperature. However, near the concrete surface the temperature was higher than the Tg. This was the reason for different failure modes the strength decreasing at 100 C. Therefore, it should be noted that the heat r eleasing rate and the glass transition temperatures of polymeric material are crucial factors that should be concerned.

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131 REFERENCES Elements Rerofitted with NSM Composite Colorado Denver (2013). ACI. 2008. Guide for the design and construction of externally bonded FRP systems for strengthening concrete structures (ACI.440.2R 08), American Concrete Institute, Farmington Hills, MI. Adhesives & glues & sealants http://www.adhesiveandglue.com/glass transition temperature.html 2014 Alkhrdaji, T., Nanni, A., Chen, G., and Baker, M. 1999. Upgrading the transportation infrastructure: soild RC decks strengthened with FRP, Concrete International, 21(10), 37 41. Aniello Palmieri Fire endurance and residual strength of Journal of Com posites for Construction October 13, 2012. 210 N. 13th Street Seward NE. Brothers, Inc. 210 N. 13th Street Seward NE. FRP Composites in Civil Engineering September 27 29, 2010 Asplund, S.O. (1949), Strengthening Bridge Slabs with Grouted Reinforcement Journal of the American Concrete Institute, Vol. 20, No. 6, January, pp. 397 406. ASTM E 119 ASTM C39/C39M st Method for Compressive Strength of Cylindrical ASTM International. Bnichou, N., Kodur, V., Chowdhury, E., Bisby, L., and Green, M., Results of Fire Resistance Experiments on FRP strengthened Reinforced Concrete S labs and Beam Slab Assemblies Report no. 2. IRC RR 234 (2007).

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132 Bilotta, Antonio, et al. "Experimental bond test on concrete members strengthened with NSM FRP systems: influence of groove dimensions and surface treatment." Proceedings of the 6th international conference on FRP composites in civil engineering (CICE 2012), Rome, Italy 2012. Blaschko, M. 2003. Bond behavior of CFRP strips glued into slits, Proceedings of Fiber Reinforced Polymer Reinforcement for Concrete Structures (FRPRCS 6), 205 214. Blontrock H, Taerwe L, Matthys S. Properties of fibre reinforced plastics at elevated temperatures with regard to fire resistance of reinforced concrete members. ACI Structural Journal, 188(5) 43 54 (1999). Burke, P.J. 2008. Low and high temperature performance of near surface mounted FRP De Lorenzis, L., and J. G. Teng. "Near surface mounted FRP reinforcement: An emerging technique for strengthening structures." Composites Part B: Engineering 38.2 (2007): 119 143. April 2002,pp. 123 133. De Lorenzis, L., A. Nanni, and A. La Tegola, "Strengthening of Reinforced Concrete Structures with Near Surface Mounted FRP Rods" bibl. International Meeting on Composite Materials, PLAST 2000, Milan, Italy, May 9 11, 2000 Washington University, Washington (2008). Foster, S. K., and L. A. Bisby. "Fire survivability of ext ernally bonded FRP strengthening systems." Journal of Composites for Construction 12.5 (2008): 553 561. Foster, S. K., and L. A. Bisby. "High temperature residual properties of externally bonded FRP systems." ACI Special Publication 230 (2005). Gu, Xiaohong, et al. "Microstructure and morphology of amine cured epoxy coatings before and after outdoor exposures An AFM study." JCT research 2.7 (2005): 547 556. Hassan, T. and Rizkalla, S. 2004. Bond mechanism of near surface mounted fiber reinforced pol ymer bars for flexural strengthening of concrete structures, ACI Structural Journal, 101(6), 830 839.

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133 4, C.W. Dolan, S. Rizk alla and A. Nanni, Editors, ACI, Baltimore, MD, pp. 1145 1161. International Building Code, International Code Council, Inc., Falls Church, VA, 2006, pp. 109 155 (2006). J.C.P.H. Gamage, M.B. Wong and R. Al Performance of CFRP Strengthened International Institute for FRP in Construction (2005). Joint ACI Concrete and Masonry Construction Ass emblies (ACI 216.1 07/TMS 0216.1 American Concrete Institute, Farmington Hills, MI, 2007, 28 pp. J. Sena elements strengthened with NSM CFRP laminate strips under wet d New Materials and under Severe Conditions, Bond in Concrete (2012). Liew, JY Richard, L. K. Tang, and Y. S. Choo. "Advanced analysis for performance based design of steel structures exposed to fires." Journal of Structural Engineering 128.12 (2002): 1584 1593. L"PEZ, Cristina, et al. "Fire protection systems for reinforced concrete beams and slabs strengthened with CFRP laminates." Proceedings of the 6th international conference on FRP composites in civil engineering (CICE). Rome 2012 erature on Bond Strength of FRP J. Compos. Constr. ,ASCE, 3(2), 73 81. Kang, J Y., et al. "Analytical evaluation of RC beams strengthened with near surface mounted CFRP laminates." ACI Special Publication 230 (2005). Kim, S.E., Choi, S., and Ma S. 2003. Performance based design of steel arch bridges using practical inelastic nonlinear analysis, Journal of Constructional Steet Research 59, 91 108. Kodur, V. K. R., et al. "Fire endur ance of insulated FRP strengthened square concrete columns." ACI Special Publication 230 (2005). Kotynia, R. 2005. Strain efficiency of near surface mounted CFRP strengthened reinforced concrete beams. Proc. of CCC conference, 11 13, Lyon, France. N. Beam Strengthened with NSM

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134 and mid Infrared spectroscopy studies of an ep 247. Nol, Martin. Behaviour of Post Tensioned Slab Bridges with FRP Reinforcement under Monotonic and Fatigue Loading Diss. University of Waterloo, 2013. Nikolic, Goran, et al. "Fast fou rier transform IR characterization of epoxy GY systems crosslinked with aliphatic and cycloaliphatic EH polyamine adducts." Sensors 10.1 (2010): 684 696. manuals. MBrace Saturant, BASF Corporation Building Systems (2013) BASF Construction Chemicals (UK) Ltd (2007). Mustafa, Ridzuan, et al. "Synthesis and characterization of rigid aromatic based epoxy resin." Malaysian Polymer Journal 4.2 (2009): 68 75. Palmieri, Aniello, Stijn Matthys, and Luc Taerwe. "Double bond shear tests on NSM FRP strengthened members." Strain 35 (2012): 35. Palmieri, Aniello, Stijn Matthys, and Luc Taerwe "Fire Endurance and Residual Strength of Insulated Concrete Beams Strengthened with Near Surface Mounted Reinforcement." Journal of Composites for Construction 17.4 (2012): 454 462. Parretti, Renato, and Antonio Nanni. "Strengthening of RC members using near surface mounted FRP composites: design overview." Advances in Structural Engineering 7.6 (2004): 469 483. Petri, P., Blaszak, Gregg, Rizkalla, Sami, and P. Eng. "Structural Fire Endurance of an RC Slab Strengthened with High Tg Near Surface Mounted CFRP Bars." Raafat El ISIS Educational Module 9 (2009). Raafat EI Near Surface Mounted Fiber Reinforced Polymer Reinforcements fo ACI Structural Journal (09 10/2004). Safety Data Sheet, MBRACE SATURANT PTA, BASF (2010). Safety Data Sheet, MBRACE SATURANT PTB, BASF (2010).

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135 s of Fourier Transform IR to 3148. Teng, J.G., De Lorenzis, L., Wang, B., Li, R., Wong, T., and Lam, L. 2006. Debonding failures of RC beams strengthened with near surfa ce mounted CFRP strips, Journal of Composites for Construction, 10(2), 92 105. Tumialan, G.; Tinazzi, D.; Myers, J.; and Nanni, A. (1999), "Field Evaluation of Masonry Walls Strengthened With FRP Composites at the Malcolm Bliss Hospital", Report CIES 99 8 University of Missouri Rolla, Rolla, MO. square analysis Williams, Brea, et al. "Fire insulation schemes for FRP strengthened concrete slabs." Composites Part A: Applied Science and Manufacturing 37.8 (2006): 1151 1160. Xue, Weichen, and Yuan Tan. "Cracking Behavior and Crack Width Predictions of Concrete Beams Prestressed with Bonded FRP Tendons." Proceedings of the 6 th International Conference on Composites in Civil Engineering, Rome, Italy, June 2012. Zhu, H., Wu, G., Zhang, L., Zhang, J., Hui, D., Experimental Study on the Fire Resistance of RC Beams Stre ngthened with Near Surface Mounted High Tg BFRP bars, Composites: Part B (2014).

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136 Appendix A More figures of FTIR spectrums are summarized in appendix A.

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147 Appendix B More figure of epoxy coupon test and CFRP strip test are given in this section. Thermo couple reading of each category is also listed. Epoxy coupon test.

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157 Appendix C Monotonic tension test figure are summaries in this section. Thermo couple reading and more figure of failure mode in listed. Sample preparation, instrumentation and failure modes of monotonic tension test

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162 Pullout capacity displacement behavior and thermo couple readings

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170 Appendix D More figure of cyclic loading are summarized in this section. Summary includes load displacement behavior, Normalized load displacement behavior, thermo couple readings and failure of each specimen. Load displacement behavior

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174 Normalized load displacement behavior

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178 Thermo couple readings

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182 Failures of specimens

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