Direct tensile behavior of ultra high performance fiber reinforced concrete subjected to impact loading

Direct Tensile Behavior of Ultra-High-Performance Fiber-Reinforced Concrete Subjected to Impact Loading Tran Ngoc Thanh February 2016 Department of Civil and Environmental Engineering The Graduate School Sejong University Dissertation Direct Tensile Behavior of Ultra-High-Performance FiberReinforced Concrete Subjected to Impact Loading 2016.02 Tran Ngoc Thanh Direct Tensile Behavior of Ultra-High-Performance Fiber-Reinforced Concrete Subjected to Impact Loading Tran Ngoc Thanh February 2016 Department of Civil and Environmental Engineering The Graduate School Sejong University Direct Tensile Behavior of Ultra-High-Performance Fiber-Reinforced Concrete Subjected to Impact Loading Tran Ngoc Thanh A dissertation submitted to the Faculty of the Sejong University in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Civil and Environmental Engineering February 2016 Approved by Major Advisor Professor Dong Joo KIM Direct Tensile Behavior of Ultra-High-Performance Fiber-Reinforced Concrete Subjected to Impact Loading by Tran Ngoc Thanh Approved Prof Jong Jae Lee, Chair of the committee Approved Prof Hyuk Chun Noh, Member of dissertation committee Approved Prof Su Tae Kang, Member of dissertation committee Approved Dr Sukhoon Pyo, Member of dissertation committee Approved Prof Dong Joo Kim, Advisor DEDICATION I would like to dedicate this dissertation to my parents, my brother and my sister who have supported me all the way ABSTRACT Ultra-high-performance fiber-reinforced concrete (UHPFRC) is much expected to enhance the resilience and sustainability of civil infrastructure under impacts or blasts owing to its outstanding tensile properties including high strength, ductility and energy absorption capacity at static rate; however, its tensile response at high strain rate is still not well understood In order to fill the knowledge gap, the objective of this research is to develop better understanding of UHPFRC tensile response at high strain rates The research is divided into three parts, as follows: In first part, the direct tensile stress versus strain response of UHPFRCs at high strain rates (5 to 24 /s) was investigated UHPFRCs exhibited tensile strain hardening behavior even at high strain rates and especially their tensile behavior was found to be very sensitive to the applied strain rates The tensile behavior of UHPFRCs at high strain rates was much influenced by the size of specimen and fiber type Unlike at static rate, UHPFRCs with smooth fibers produce higher tensile properties than those with twisted fibers at high strain rates In second part, the fracture energies including peak toughness and softening fracture energy of UHPFRCs at high strain rates (5–92 /s) was investigated and the UHPFRCs with 11.5% of fibers volume contents exhibited very high entire fracture energy (2871 kJ/m2) at high strain rates The peak toughness was highly sensitive to strain rate whereas the softening fracture energy was not In the investigation of UHPFRCs fracture energies, the un-notched specimens were more suitable than i notched specimens The effects of fiber type and fiber volume on the UHPFRCs fracture energies were found to be totally different between at static rate and at high strain rates Finally, a method for enhancing the tensile resistance of UHPFRCs at high strain rates (16 – 37 /s) was proposed by blending long and short steel fibers UHPFRCs blending small volume content of long and short steel fibers (total 1.5%) produced very high tensile resistance at high strain rates: post cracking strength up to 32.6 MPa, strain capacity up to 1.87%, peak toughness up to 412.6 kJ/m3 and softening fracture energy up to 31.3 kJ/m2 In particular, UHPFRCs with fibers blending, based on the synergistic performance, produced 86.4% higher strain capacity and 72.2% higher peak toughness than normal UHPFRCs with mono steel fibers The strain rate sensitivity model in tension of UHPFRCs based on the best fit of experimental test results was proposed and the tensile resistance of UHPFRCs was predicted even at high strain rates Keywords: Direct tensile response, Fracture energy, Ultra-high-performance fiber-reinforced concrete, High strain rates, Fiber blending ii TABLE OF CONTENTS ABSTRACT i TABLE OF CONTENTS iii LIST OF FIGURES vii LIST OF TABLES ix CHAPTER INTRODUCTION 1.1 Motivation 1.2 Literature review and background 1.2.1 Development of UHPFRC 1.2.2 Tensile response of UHPFRC at high strain rates 1.3 Goal and objectives 12 1.4 Organization of Dissertation 13 PUBLICATIONS FROM DISSERTATIONS 16 References 17 CHAPTER INVESTIGATING TENSILE RESPONSE OF UHPFRC AT HIGH STRAIN RATE 22 2.1 Introduction 22 2.2 Experimental program 27 2.2.1 Materials and specimen preparation 28 2.2.2 Test setup and procedure 30 2.3 Test results 34 2.3.1 Static test results 34 iii 2.3.2 High strain rates test results 40 2.3.3 Strain rate sensitivities 43 2.4 Discussion 45 2.4.1 Effect of fiber type on the rate sensitive of UHPFRCs 45 2.4.2 Effect of specimen size on the rate sensitive of UHPFRCs 54 2.5 Conclusion 59 References 60 CHAPTER INVESTIGATING FRACTURE ENERGY OF UHPFRC AT HIGH STRAIN RATE 66 3.1 Introduction 66 3.2 Fracture energy of UHPFRC at high strain rates 69 3.3 Experimental procedure 73 3.3.1 Materials and specimen preparation 74 3.3.2 Test setup and procedure 75 3.4 Test results 78 3.4.1 Static test results 79 3.4.2 High-strain-rate test results 85 3.5 Discussion 90 3.5.1 Strain-rate effect on UHPFRC fracture resistance 90 3.5.2 Effect of fiber type and fiber volume content on UHPFRC fracture resistance 94 3.5.3 Effect of double edge notches on UHPFRC fracture resistance 97 3.6 Conclusions 101 iv Impact, Journal of Materials in Civil Engineering 17( 2) (2005) 143-152 [32] R Yu, P Spiesz, H.J.H F Brouwers, Static properties and impact resistance of a green Ultra-High Performance Hybrid Fibre Reinforced Concrete (UHPHFRC): Experiments and modeling, Construction and Building Materials 68 (2014) 158171 [33] S.G Millard, T.C.K Molyneaux, S.J Barnett, X Gao, Dynamic enhancement of blast-resistant ultra high performance fibre-reinforced concrete under flexural and shear loading, International Journal of Impact Engineering 37 (4) (2010) 405-413 [34] N.T Tran, T.K Tran, D.J Kim, High rate response of ultra-high-performance fiber-reinforced concretes under direct tension, Cement and Concrete Research 69 (2015) 72-87 [35] N.T Tran, T.K Tran, J.K Jeon, J.K Park, D.J Kim, Fracture energy of ultrahigh-performance fiber-reinforced concrete at high strain rates, Cement and Concrete Research (2015) [36] S.H Park, G.S Ryu, K.T Koh, D.J Kim, Effect of shrinkage reducing agent on pullout resistance of high-strength steel fibers embedded in ultra-highperformance concrete, Cement and Concrete Composites 49 (2014) 59-69 [37] D.J Kim, S El-Tawil, A.E Naaman, Rate-dependent tensile behavior of high performance fiber reinforced cementitious composites, Mater Struct 42(3) (2009) 399–414 150 [38] T.K Tran, D.J Kim, Investigating direct tensile behavior of high performance fiber reinforced cementitious composites at high strain rates, Cement and Concrete Research 50(0) (2013) 62-73 [39] J.J Kim, G.J Park, D.J Kim, J.H Moon, J.H Lee, High-rate tensile behavior of steel fiber-reinforced concrete for nuclear power plants, Nuclear Engineering and Design 266 (2014) 43-54 [40] V Mechtcherine, F Siva et al, Behavior of Strain-Hardening Cement-Based Composites Under High Strain Rates, Journal of Advanced Concrete Technology 9(10) (2011) 51-62 [41] T.K Tran, D.J Kim, High strain rate effects on direct tensile behavior of high performance fiber reinforced cementitious composites, Cement and Concrete Composites 45 (2014) 186-200 [42] A Caverzan, E Cadoni, M Di Prisco, Tensile behaviour of high performance fibre-reinforced cementitious composites at high strain rates, International Journal of Impact Engineering 45 (2012) 28-38 [43] K Fujikake, T Senga, N Ueda, T Ohno, M Katagiri, Effects of Strain Rate on Tensile Behavior of Reactive Powder Concrete, Journal of Advanced Concrete Technology (1) (2006) 79-84 [44] R Ranade, V.C Li, W.F Heard, Tensile Rate Effects in High Strength-High Ductility Concrete, Cement and Concrete Research 68 (2015) 94 – 104 [45] E Cadoni, A Meda, G.A Plizzari, Tensile behaviour of FRC under high strainrate, Mater Struct 42 (2009) 1283-1294 151 [46] T.K Tran, D.J Kim, Investigating direct tensile behavior of high performance fiber reinforced cementitious composites at high strain rates, Cement and Concrete Research 50(0) (2013) 62-73 [47] S Pyo, K Wille, S El-Tawil, A.E Naaman, Strain rate dependent properties of ultra high performance fiber reinforced concrete (UHP-FRC) under tension, Cement and Concrete Composites 56 (2015) 15–24 [48] K Wille, M Xu, S El-Tawil, A.E Naaman, Dynamic impact factors of strain hardening UHP-FRC under direct tensile loading at low strain rates, Materials and Structures (2015) [49] M Xu, K Wille, Fracture energy of UHP-FRC under direct tensile loading applied at low strain rates, Composites Part B: Engineering 80 (2015) 116-125 [50] S Pyo, Characteristics of Ultra High Performance Concrete Subjected to Dynamic Loading, Dissertations and Theses, 2014 [51] K Wille, S El-Tawil, A.E Naaman, Properties of strain hardening ultra high performance fiber reinforced concrete (UHP-FRC) under direct tensile loading, Cement and Concrete Composites 48 (2014) 53-66 [52] P Tjiptobroto, W Hansen, Mechanism for tensile strain hardening in high performance cement-based fiber reinforced composites, Cement and Concrete Composites 13(4) (1991) 265-273 [53] P Tjiptobroto, W Hansen, Model for Predicting the Elastic Strain of FRC Containing High Volume Fractions of Discontinuous Fibers, ACI Materials Journal 90 (1993) 134-142 152 [54] K Kosa, A E Naaman, Corrosion of Steel Fiber Reinforced Concrete, ACI Materials Journal 87 (1990) 27-37 153 Chapter SUMMARY, CONCLUSIONS AND RECOMMENDATIONS 5.1 Summary and Conclusions The overall of this research is to develop better understanding of tensile response of UHPFRC at high strain rates In order to accomplish the purpose, three objectives including (1) investigating tensile response of UHPFRC at high strain rate, (2) investigating fracture energy of UHPFRC at high strain rate and (3) enhancing tensile resistance of UHPFRC at high strain rates, have been achieved as follow: 1) UHPFRCs exhibited tensile strain hardening accompanied to multiple microcracks at high strain rates and their tensile behavior was very sensitive to the applied strain rates The tensile behavior of UHPFRCs was much influenced by the size of specimen and fiber type 2) UHPFRCs produced very high entire fracture energy (2871 kJ/m2) at high strain rates Their peak toughness were highly sensitive to the applied strain rates, whereas their softening fracture energies were not The fracture energies were strongly depended on the fiber type, fiber volume and specimen shape 3) The ductility and energy absorption capacity of UHPFRC at high strain rates were significantly improved by blending small volume of long and short steel fibers The tensile resistance of UHPFRCs at high strain rates showed reasonable agreement between experiment and theory Detail conclusions of each objectives in this dissertation are as follows: 154 5.1.1 Conclusions related to the investigating direct tensile response of UHPFRC at high strain rate An extensive experimental program was performed to investigate the direct tensile response of UHPFRCs at high strain rates UHPFRCs with three fiber types (long smooth, twisted and short smooth fibers) and two specimen sizes (25x25 and 25x50 mm2) were tested under static and high strain rates Based on the experimental results, following conclusions could be drawn:  The UHPFRCs maintained tensile strain hardening behavior accompanied with multiple fine cracks even at high strain rates (5 - 24 /s) Their tensile behavior was sensitive to the applied strain rates and the tensile resistance of UHPFRCs at high strain rates was much higher than at static rate  Long smooth fibers, among fiber types, produced the highest tensile resistance including post cracking strength, strain capacity and peak toughness at high strain rates between and 24 /s whereas twisted fibers generated the highest tensile resistance at static rate owing to the breakages of twisted fibers observed at high strain rates Moreover, long smooth fibers showed the highest rate sensitivity of post cracking strength, whereas the short smooth fibers showed the highest rate sensitivity of both strain capacity and peak toughness  The tensile behavior of UHPFRCs at higher strain rates strongly depended on the size of cross section area Specifically, the post cracking strength of UHPFRCs at high strain rates reduced significantly, whereas that at static rate 155 slightly changed as the size of the specimen decreased Moreover, larger specimens showed the higher rate sensitivity than that of smaller specimens 5.1.2 Conclusions related to the investigating fracture energy of UHPFRC at high strain rate An extensive experimental process was conducted to investigate the fracture energies including peak toughness and softening fracture energy of UHPFRCs at high strain rates UHPFRCs with three fiber types (smooth and twisted fibers), two fiber volume content (1 and 1.5%) and two specimen shape (notched and un-notched) were tested under static and high strain rates Based on the results of this study, the following conclusions can be drawn:  All the UHPFRCs exhibited tensile strain-hardening behavior accompanied by multiple micro-cracks with very high entire fracture energies (28-71 kJ/m2), even at high strain rates (5-92 /s) The peak toughness of the UHPFRCs were highly sensitive to the applied strain rates, whereas the softening fracture energies of the UHPFRCs were not  Smooth fibers exhibited higher fracture energies at high strain rates than twisted fibers, whereas twisted fibers generated higher peak toughness at static rates As the fiber volume content increased, the peak toughness and softening fracture energies of the un-notched specimens at high strain rates decreased, whereas those of both the un-notched and notched specimens at the static rate increased Moreover, Smooth fibers also generated higher rate sensitivity than twisted fibers and the UHPFRCs with greater fiber volume content exhibited 156 lower rate sensitivity  Notched specimens generally exhibited higher fracture energies than unnotched samples at both static and high rates Un-notched specimens may be suitable for investigating UHPFRC fracture resistance, but further research is still required to determine the appropriate gauge length 5.1.3 Conclusions related to the enhancing tensile resistance of UHPFRC at high strain rate An experimental program was conducted to investigate the tensile resistance of UHPFRCs with blended fibers at high strain rates UHPFRC blending 1% one of three types long steel fibers, long smooth, long hooked and long twisted fibers, and 0.5% one of two types short steel fibers, medium smooth and short smooth fibers, were tested under direct tension at static and high strain rates Based on the results of this study, the following conclusions can be drawn:  All the UHPFRCs with fiber blending exhibited tensile strain-hardening behavior accompanied to multiple micro-cracks with very high tensile resistance: post cracking strength up to 32.6 MPa, strain capacity up to 1.87%, peak toughness up to 412.6 kJ/m3 and softening fracture energy up to 31.3kJ/m2 at high strain rates Their post cracking strength, strain capacity and peak toughness were sensitive to the applied strain rates, whereas the softening fracture energy was not 157  The tensile resistance of UHPFRCs with fiber blending strongly depended on the long fiber types and short fiber types: long smooth fibers generally produced higher tensile resistance at high strain rates than hooked and twisted fibers, while medium smooth fiber produced higher tensile resistance than short smooth fiber And consequently, UHPFRC blending long smooth fibers and medium smooth fibers generate the highest tensile resistance as well as rate sensitivity at high strain rates  The strain capacity and peak toughness of UHP-HFRCs at high strain rates showed excellent synergistic response, whereas the post cracking strength and softening fracture energy were not clear UHPFRC blending long smooth fibers and medium smooth demonstrated maximum synergy especially in term of strain capacity (0.864) and peak toughness (0.722) at high strain rates  A strain rate sensitivity model in tension of UHPFRC was proposed based on the best fit of 143 test results at wide range of strain rate between 0.0001 and 150 /s The tensile resistance of UHPFRCs showed reasonable agreement between experiment and theory 5.2 Recommendations Based on the results of this dissertation, recommendations for further research are as follow:  The tensile response of UHPFRCs in this dissertation was investigated at 158 impact rates (lower than 100 s-1) and further research should investigate the tensile response of UHPFRCs at very high strain rates corresponding to blast rates (more than 100 s-1)  Fiber orientation, one of important parameters effect on the tensile response of UHPFRCs even at high strain rates, should be considered In addition, the effects of temperature and humidity on the tensile response of UHPFRCs at high strain rates should be studied  Besides the tensile response, other mechanical response, such as compressive, flexural and shear response of UHPFRCs at high strain rates should be understood  The addition of nano-materials including carbon nanotube, graphene oxide, nano cement, nano SiO2 … are expected to improve the packing density and mechanical properties of UHPFRCs even at high strain rates  A standard test method for investigating tensile response of UHPFRCs at high strain rates should be proposed to achieve uniform result across laboratories  The behavior of UHPFRC structure under impact or blast loading should be explored 159 국문초록 충격시 초고강도 섬유보강 콘크리트의 직접 인장거동 세종대학교 대학원 건설환경공학과 Tran Ngoc Thanh 초고강도 섬유보강 콘크리트의 매우 높은 강도, 연성 그리고 에너지 흡수능력을 가지고 있어 이 재료를 적용할 경우, 사회기반 시설물의 충격 및 폭발하중 하에서의 저항성 향상에 큰 도움이 될 것으로 기대되고 있다 하지만, 이러한 우수한 저항성능은 충격 및 폭파 시와 같이 고속의 변형률 속도에서 얻어진 결과가 아니라 매우 저속의 정적 변형률 속도에서 얻어진 결과로서, 실제로 초고강도 섬유보강 콘크리트의 충격 및 폭파하중 하의 고속 변형률 속도에서의 인장거동은 아직 명확하기 이해되지 않고 있다 160 따라서, 본 연구는 고속변형률 속도에서의 초고강도 섬유보강 콘크리트의 인장거동 조사에 그 목적을 가지고 있고 아래와 같은 세 부분의 세부 연구를 진행하였다 우선, 고속 변형률 속도 (5 to 24 /s)에서의 초고강도 섬유보강 콘크리트의 인장 응력 – 변형률 선도를 조사하였다 초고강도 섬유보강 콘크리트는 고속 변형률 속도에서도 인장 변형경화 거동을 나타내었으며, 변형률 속도에 매우 민감한 변화를 나타내었다 이 고속 변형률 속도에서의 인장거동은 시험체의 크기와 사용된 섬유의 종류에 따라서 매우 다르게 나타났다 특이할 점은, 일반적으로 비틀림 강섬유가 정적 변형률 속도에서 더 높은 인장 저항성능을 유발한 반면에, 고속 변형률 속도에서는 무변형 강섬유가 더 높은 인장 저항성능을 나타내었다 그리고, 고속 변형률 속도 (5 to 92 /s)에서의 초고강도 섬유보강 콘크리트의 경화 파괴에너지와 연화 파괴에너지를 포함한 즉 파괴 인성치에 대하여 조사하였다 11.5% 만의 섬유 보강량을 사용한 초고강도 섬유보강 콘크리트가 고속 변형률 속도에서 매우 높은 파괴에너지 (2871 kJ/m2)를 나타내었다 경화 파괴에너지가 변형률 속도의 변화에 매우 민감하기 변화되는 반면에 연화 파괴에서는 변형률 속도의 변화에 큰 영향을 받지 않았다 이러한 변형경화 거동을 보이는 초고강도 섬유보강 콘크리트의 파괴에너지 조사를 위해서는 노치가 없는 시험체를 사용하여 161 조사하는 것이 바람직하다고 판단되었다 섬유의 종류와 보강량에 따라서 초고강도 섬유보강 콘크리트의 파괴에너지가 정적 및 고속 변형률 속도에서 매우 상이하였다 마지막으로, 고속 변형률 속도에서의 초고강도 섬유보강 콘크리트의 인장 저항성 향상을 위하여 길이가 긴 장섬유와 짧은 단섬유를 혼입하여 사용하는 방법에 대하여 조사하였다 그 결과 1%의 장섬유와 0.5%의 단섬유를 보강한 초고강도 섬유보강 콘크리트의 경우,장섬유 또는 단섬유 만을 사용한 초고강도 섬유보강 콘크리트와 비교하여, 매우 높은 인장 저항성능을 나타내었다: 최종균열 인장강도는 32.6 MPa, 변형능력은 1.87%, 그리고 412.6 kJ/m3의 경화 파괴에너지, 그리고 31.3 kJ/m2의 연화 파괴 에너지를 나타내었다 이러한 섬유의 혼합 사용을 통하여, 한 종류의 섬유만을 사용한 초고강도 섬유보강 콘크리트와 비교하여 86.4% 높은 변형능력과 72.2% 높은 에너지 흡수능력 (경화 파괴에너지)를 나타내었다 또한, 실험결과를 바탕으로 변형률 속도에 따른 인장 저항 성능을 예측할 수 있는 관계식을 제안하였다 주요어: 직접 인장 거동, 파괴 에너지, 초고강도 섬유 보강 콘크리트, 고속 변형률 속도, 섬유 혼합 162 ACKNOWLEDGEMENTS Foremost I would like to express my deeply gratitude and sincere appreciation to my advisor, Prof Dong Joo KIM, for his guidance, tremendous support, patience and encouragement throughout my doctoral studies The great knowledge, the vision and 163 passion from him helped me have more confident to complete the work I would also like to thank my dissertation committee members, Prof Jong Jae Lee, Prof Hyuk Chun Noh, Prof Su Tae Kang, Dr Sukhoon Pyo, for their time, knowledge and valuable comments during my work Special thanks are due to Sejong university and Advanced Cementitious Composites Laboratory for the financial support and sponsors Besides, I would like to thank my Vietnamese and Korean friends for their friendship and help Finally, I express my wholehearted thanks to my family, especially my parents, for their continuous support, encouragement, and boundless love throughout my life Seoul, February 2016 Tran Ngoc Thanh 164 ...Dissertation Direct Tensile Behavior of Ultra- High- Performance FiberReinforced Concrete Subjected to Impact Loading 2016.02 Tran Ngoc Thanh Direct Tensile 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