Steel/basalt rebar reinforced Ultra-High Performance Concrete components against methane-air explosion loads
QingfeiMengaChengqingWuaJunLiaZhongxianLiubPengtaoWubYekaiYangbZhongqiWangc
Link:Steel/basalt rebar reinforced Ultra-High Performance Concrete components against methane-air explosion loads - ScienceDirect Abstract Ultra-High Performance Concrete (UHPC) is a relatively new construction material, which has been investigated over the past few decades. Despite its exceptional mechanical strength, UHPC still requires passive steel reinforcement to maximise its bending capacity and the overall material cost will be high. The basalt fibre rebar has a higher mechanical strength than steel rebar with lower cost. In addition, it also has better alkali resistance and good cost-effectiveness. The basalt fibre rebar is therefore considered as a potential alternative reinforcement in the structural member. In this study, a recently developed UHPC formula was adopted, the conventional steel rebar and basalt fibre rebar were used as reinforcement. The developed components were tested against static flexural and methane-air explosion loads. In the four-point flexural tests, the basalt fibre rebar reinforced specimen (400 mm × 100 mm × 100 mm) performed more ductile structural behaviour with higher flexural strength. Two large scale methane-air explosion tests were conducted in buried utility tunnels with different length (i.e., 12000 mm × 1800 mm × 600 mm and 20000 mm × 1800 mm × 600 mm). The experimental test in shorter tunnel yielded lower explosion pressure [1] with marginal structural response. The test in longer tunnel achieved a higher explosion pressure on concrete elements. The C30 and UHPC specimens (1800 mm × 400 mm × 90 mm) with steel/basalt fibre rebar reinforcement were tested. The pressure and deflection data revealed that basalt fibre rebar reinforced UHPC component had a more ductile structural behaviour against accidental gas explosion. Introduction Ultra-High Performance Concrete (UHPC) has been widely studied and used in research works and construction buildings due to its superior mechanical performances and durability. UHPC is generally a blend of silica fume, fine graded sand, steel fibre, Portland cement etc. The material features a high compressive strength of more than 150 MPa and good tensile performance due to fibre reinforcement [2]. To achieve the high compressive strength, the water to binder ratio should be well controlled below 0.2 in the UHPC binder. The high-temperature water bath, steam bath etc. were generally required during the material curing period, but in some literatures, non-heat curing was used instead [3,4]. It is also acknowledged that changing curing method, curing temperature and curing time may influence the early mechanical performance of UHPC [5,6]. Because of its outstanding structural performance, UHPC material has been widely investigated in resisting the extreme loading situations such as explosion [7]. Many studies have been conducted on UHPC at material level. The steel fibre reinforcement in UHPC is one of the most widely used fibre reinforcement options. It is found that the fibre volume and fibre length increment would lead to the higher ductility and damage resistance capacity in the compression tests [8]. In the literature [9], the fibre volume (i.e., 3%–5%) and orientation (i.e., parallel and orthogonal) variance in UHPC was found to influence the tensile rate sensitivity of UHPC. It is verified in another literature [10], the strain rate sensitivity of fibre reinforced concrete relies heavily on the fibre geometry and volume. A balance between the binder and volume of the fibre is decisive to the material properties of UHPC. Although the tensile strength of UHPC is higher than the conventional concrete, the passive flexural performance enhancement of structural component through rebar is still required in engineering practice. The steel rebar in infrastructural structures may corrode when subjected to the chloride penetration [11], alkali condition [12], etc. In recent years, fibre reinforced polymer (FRP) rebar emerges and it is considered an alternative to steel rebar reinforcement in the concrete elements. Compared to the steel rebar, the FRP rebar has advantages such as low cost, high strength, high resistance capacity to chemical and corrosion etc. [13]. It is proved that the FRP reinforcement can improve the ductility of the prestressed concrete beam under flexural loads [14]. Basalt fibre has been used in recent years because of its outstanding mechanical performance. It is made from the melted basalt rock under 1450–1500 °C temperature condition, with a similar manufacturing process to glass fibre, but the energy consumption is much less. The basalt fibre is manufactured under high temperature, the fire/high temperature resistant capacity of basalt fibre is higher than glass fibre (i.e., melting point 300–500 °C), aramid fibre (i.e., melting point 200 °C) and carbon fibre (i.e., melting point 800–1000 °C) [15]. The high temperature resistance capacity makes the basalt fibre composite rebar a potential reinforcement solution to resist loading with thermal variance such as accidental fire and blast. The simple manufacturing process of basalt fibre composite rebar without additional additives effectively reduces the material cost and ensures stable material properties. The mechanical properties of basalt fibre, such as tensile strength, elongation prior to fracture, etc., were found better than E-glass fibre [16]. The tensile strength ranging from 1.6 GPa to 4.8 GPa makes it competitive when compares to carbon fibre [17]. Dorigato and Pegoretti [18] noted the basalt fibre reinforced epoxy has similar performances to carbon fibre reinforced epoxy and it has a higher elastic modulus and strength value when compared to glass fibre reinforced epoxy. The laboratory tests were conducted to investigate the dynamic tensile strength of basalt fibre [19], the results revealed that the dynamic increase factor (DIF) of tensile strength is approximate 2 at a strain rate of 259 s−1. It is studied by Khuram et al. [20] that the basalt fibre composite demonstrated a better impact response as compared to the glass fibre composite due to its higher Young's modulus, compressive and bending strength. According to the competitive mechanical performances and low-cost characteristic, the basalt fibre rebar may be more suitable to apply as an alternate reinforcement in concrete elements as compared to other fibre rebars. Basalt fibre rebar reinforcement in concrete has been studied in a few literatures. Duic et al. [21] investigated the basalt fibre rebar reinforced concrete beams in flexural tests. It was found that the basalt fibre rebar reinforced concrete beam at a high reinforcement ratio demonstrated less shear cracking and steeper shear crack angles as compared to the steel rebar reinforced concrete beam. Tomlinson and Fam [22] and Lapko and Urbanski [23] conducted flexural tests on basalt fibre rebar reinforced concrete beams, and it was found the load-bearing capacity of the basalt rebar reinforced concrete beam was much higher as compared to steel rebar reinforced beam. But the deformation and deflection of basalt fibre rebar reinforced specimen were higher than the steel rebar reinforced specimen because of lower elastic modulus. Elgabbas el al [24]. also verified this point of view by conducting a flexural test on basalt fibre rebar reinforced concrete beam, finding that the cracks on basalt fibre rebar reinforced concrete beam were worse than the reference specimen. The low modulus of basalt rebar can be overcome by combining with the UHPC that typically has a higher modulus than conventional concrete, both materials can potentially apply their mechanical strengths to the maximum. The buried utility tunnel has been widely constructed around the world. Due to its easy accessibility and minimal interruption to the residents nearby during maintenance, many types of utility lines (e.g., general water supply pipes, steam pipe, electricity line etc.) are positioned along the tunnel. Natural gas supply line as one of the most significant resource supplies in the urban city is also included in the utility tunnels. The potential natural gas leakage, which may lead to gas explosions in the tunnel, is then considered as safety risk to the tunnel, infrastructures and residents nearby. There were some gas explosions occurring in the buried tunnel caused by the flammable gas-air mixture. In 2014, Kaohsiung experienced a flammable gas explosion in the buried storm drain [25], causing more than 30 death and injuries, in addition to massive damages to the road pavements. In 2015, Qingdao experienced a severe flammable gas explosion in a buried tunnel, neither the steel reinforced concrete slabs (i.e., the cover of the tunnel) nor road pavement survived in the explosion [26]. Li et al. [27] studied the masonry wall under natural gas explosion, and explored the gas explosion features and structural damage profile. Until now, there is rare study working on the structural elements subjected to the methane-air explosion in buried gas utility tunnels. In consideration of the severe structural damage in the previous accidents, the UHPC slabs with steel and basalt fibre rebar reinforcements are considered in the present study against methane-air explosion.In this study, a newly developed UHPC was adopted and investigated with basalt fibre rebar reinforcement. The UHPC and basalt fibre rebar material were investigated under static compressive, flexural and tensile loads. A total of 3 different types of UHPC specimens were manufactured and tested under four-point bending in the laboratory. Different damage modes and ductility index were obtained. The basalt fibre rebar reinforced UHPC specimen was found has higher ductility. In the subsequent field methane-air explosions test, 3 different types of concrete structural slabs in two full-scale tunnels setup were tested. The pressure data was captured and analysed. The steel reinforced C30 concrete and steel reinforced UHPC were used as reference slabs to compare with the basalt fibre rebar reinforced UHPC slab against the gas explosion. The displacements on each specimen were captured, analysed and compared. Section snippets UHPC In this study, a previously developed UHPC composition was used [28], and the material compositions are listed in Table 1. The 52.5 grade Portland cement [28] and the natural sand (i.e., size between 0.16 mm and 2.5 mm) were used in the mixture. The coarse aggregate was eliminated to achieve a more homogeneous mixture binder of UHPC. Fine aggregates addition such as silica fume and silica flour (i.e., quartz powder) were used to enhance the granular composition [29]. Pozzolanic additive silica Static bending test Both the steel and basalt fibre rebar reinforcements in UHPC specimens were investigated and compared in this section.Methane-air explosion test Based on the outstanding structural behaviours of UHPC with steel/basalt fibre rebar reinforcements, large scale slab specimens were made and tested under 9.5% methane-air explosion in two large scale tunnels. The methane-air explosion resistant capacity of different rebar reinforced UHPC slabs is investigated and compared in this section. Conclusion This study investigated the structural responses of basalt fibre reinforced UHPC specimens against static flexural test and 9.5% methane-air explosion tests. Higher flexural strength and ductility index were observed on the basalt fibre rebar reinforced prism specimen as compared to the steel rebar reinforced specimen in the static flexural test. In addition, the basalt rebar reinforced UHPC specimen may experience the rebar reinforcement debonding during the loading period, which results in a CRediT authorship contribution statement Qingfei Meng: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Writing - original draft. Chengqing Wu: Conceptualization, Methodology, Formal analysis, Resources, Writing - review & editing, Visualization, Supervision, Project administration, Funding acquisition. Jun Li: Methodology, Formal analysis, Writing - review & editing. Zhongxian Liu: Investigation. Pengtao Wu: Investigation. Yekai Yang: Investigation. Zhongqi Wang: Investigation, Data curation. Declaration of competing interest The authors declare that there is not any conflict of interest in this manuscript. Acknowledgements The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (Grant No. 51978186) and the Australian Research Council Discovery Project DP160104661.References (49)• Z. Wang et al.Experimental investigation of gas explosion in single vessel and connected vessels
J Loss Prev Process Ind(2013)• Q. Ma et al.Effects of premixed methane concentration on distribution of flame region and hazard effects in a tube and a tunnel gas explosion
J Loss Prev Process Ind(2015)• M. Cooper et al.On the mechanisms of pressure generation in vented explosions
Combust Flame(1986)• G. Tomlin et al.The effect of vent size and congestion in large-scale vented natural gas/air explosions
J Loss Prev Process Ind(2015)• Q. Bao et al.Effects of gas concentration and venting pressure on overpressure transients during vented explosion of methane–air mixtures
Fuel(2016)• B. Nie et al.The roles of foam ceramics in suppression of gas explosion overpressure and quenching of flame propagation
J Hazard Mater(2011)• D.-Y. Yoo et al.Structural performance of ultra-high-performance concrete beams with different steel fibers
Eng Struct(2015)• I.H. Yang et al.Structural behavior of ultra high performance concrete beams subjected to bending
Eng Struct(2010)• D. Shen et al.Influence of strain rate on bond behavior of concrete members reinforced with basalt fiber-reinforced polymer rebars
Construct Build Mater(2019)• M. Baena et al.Experimental study of bond behaviour between concrete and FRP bars using a pull-out test
Compos B Eng(2009)
Link:Steel/basalt rebar reinforced Ultra-High Performance Concrete components against methane-air explosion loads - ScienceDirect Abstract Ultra-High Performance Concrete (UHPC) is a relatively new construction material, which has been investigated over the past few decades. Despite its exceptional mechanical strength, UHPC still requires passive steel reinforcement to maximise its bending capacity and the overall material cost will be high. The basalt fibre rebar has a higher mechanical strength than steel rebar with lower cost. In addition, it also has better alkali resistance and good cost-effectiveness. The basalt fibre rebar is therefore considered as a potential alternative reinforcement in the structural member. In this study, a recently developed UHPC formula was adopted, the conventional steel rebar and basalt fibre rebar were used as reinforcement. The developed components were tested against static flexural and methane-air explosion loads. In the four-point flexural tests, the basalt fibre rebar reinforced specimen (400 mm × 100 mm × 100 mm) performed more ductile structural behaviour with higher flexural strength. Two large scale methane-air explosion tests were conducted in buried utility tunnels with different length (i.e., 12000 mm × 1800 mm × 600 mm and 20000 mm × 1800 mm × 600 mm). The experimental test in shorter tunnel yielded lower explosion pressure [1] with marginal structural response. The test in longer tunnel achieved a higher explosion pressure on concrete elements. The C30 and UHPC specimens (1800 mm × 400 mm × 90 mm) with steel/basalt fibre rebar reinforcement were tested. The pressure and deflection data revealed that basalt fibre rebar reinforced UHPC component had a more ductile structural behaviour against accidental gas explosion. Introduction Ultra-High Performance Concrete (UHPC) has been widely studied and used in research works and construction buildings due to its superior mechanical performances and durability. UHPC is generally a blend of silica fume, fine graded sand, steel fibre, Portland cement etc. The material features a high compressive strength of more than 150 MPa and good tensile performance due to fibre reinforcement [2]. To achieve the high compressive strength, the water to binder ratio should be well controlled below 0.2 in the UHPC binder. The high-temperature water bath, steam bath etc. were generally required during the material curing period, but in some literatures, non-heat curing was used instead [3,4]. It is also acknowledged that changing curing method, curing temperature and curing time may influence the early mechanical performance of UHPC [5,6]. Because of its outstanding structural performance, UHPC material has been widely investigated in resisting the extreme loading situations such as explosion [7]. Many studies have been conducted on UHPC at material level. The steel fibre reinforcement in UHPC is one of the most widely used fibre reinforcement options. It is found that the fibre volume and fibre length increment would lead to the higher ductility and damage resistance capacity in the compression tests [8]. In the literature [9], the fibre volume (i.e., 3%–5%) and orientation (i.e., parallel and orthogonal) variance in UHPC was found to influence the tensile rate sensitivity of UHPC. It is verified in another literature [10], the strain rate sensitivity of fibre reinforced concrete relies heavily on the fibre geometry and volume. A balance between the binder and volume of the fibre is decisive to the material properties of UHPC. Although the tensile strength of UHPC is higher than the conventional concrete, the passive flexural performance enhancement of structural component through rebar is still required in engineering practice. The steel rebar in infrastructural structures may corrode when subjected to the chloride penetration [11], alkali condition [12], etc. In recent years, fibre reinforced polymer (FRP) rebar emerges and it is considered an alternative to steel rebar reinforcement in the concrete elements. Compared to the steel rebar, the FRP rebar has advantages such as low cost, high strength, high resistance capacity to chemical and corrosion etc. [13]. It is proved that the FRP reinforcement can improve the ductility of the prestressed concrete beam under flexural loads [14]. Basalt fibre has been used in recent years because of its outstanding mechanical performance. It is made from the melted basalt rock under 1450–1500 °C temperature condition, with a similar manufacturing process to glass fibre, but the energy consumption is much less. The basalt fibre is manufactured under high temperature, the fire/high temperature resistant capacity of basalt fibre is higher than glass fibre (i.e., melting point 300–500 °C), aramid fibre (i.e., melting point 200 °C) and carbon fibre (i.e., melting point 800–1000 °C) [15]. The high temperature resistance capacity makes the basalt fibre composite rebar a potential reinforcement solution to resist loading with thermal variance such as accidental fire and blast. The simple manufacturing process of basalt fibre composite rebar without additional additives effectively reduces the material cost and ensures stable material properties. The mechanical properties of basalt fibre, such as tensile strength, elongation prior to fracture, etc., were found better than E-glass fibre [16]. The tensile strength ranging from 1.6 GPa to 4.8 GPa makes it competitive when compares to carbon fibre [17]. Dorigato and Pegoretti [18] noted the basalt fibre reinforced epoxy has similar performances to carbon fibre reinforced epoxy and it has a higher elastic modulus and strength value when compared to glass fibre reinforced epoxy. The laboratory tests were conducted to investigate the dynamic tensile strength of basalt fibre [19], the results revealed that the dynamic increase factor (DIF) of tensile strength is approximate 2 at a strain rate of 259 s−1. It is studied by Khuram et al. [20] that the basalt fibre composite demonstrated a better impact response as compared to the glass fibre composite due to its higher Young's modulus, compressive and bending strength. According to the competitive mechanical performances and low-cost characteristic, the basalt fibre rebar may be more suitable to apply as an alternate reinforcement in concrete elements as compared to other fibre rebars. Basalt fibre rebar reinforcement in concrete has been studied in a few literatures. Duic et al. [21] investigated the basalt fibre rebar reinforced concrete beams in flexural tests. It was found that the basalt fibre rebar reinforced concrete beam at a high reinforcement ratio demonstrated less shear cracking and steeper shear crack angles as compared to the steel rebar reinforced concrete beam. Tomlinson and Fam [22] and Lapko and Urbanski [23] conducted flexural tests on basalt fibre rebar reinforced concrete beams, and it was found the load-bearing capacity of the basalt rebar reinforced concrete beam was much higher as compared to steel rebar reinforced beam. But the deformation and deflection of basalt fibre rebar reinforced specimen were higher than the steel rebar reinforced specimen because of lower elastic modulus. Elgabbas el al [24]. also verified this point of view by conducting a flexural test on basalt fibre rebar reinforced concrete beam, finding that the cracks on basalt fibre rebar reinforced concrete beam were worse than the reference specimen. The low modulus of basalt rebar can be overcome by combining with the UHPC that typically has a higher modulus than conventional concrete, both materials can potentially apply their mechanical strengths to the maximum. The buried utility tunnel has been widely constructed around the world. Due to its easy accessibility and minimal interruption to the residents nearby during maintenance, many types of utility lines (e.g., general water supply pipes, steam pipe, electricity line etc.) are positioned along the tunnel. Natural gas supply line as one of the most significant resource supplies in the urban city is also included in the utility tunnels. The potential natural gas leakage, which may lead to gas explosions in the tunnel, is then considered as safety risk to the tunnel, infrastructures and residents nearby. There were some gas explosions occurring in the buried tunnel caused by the flammable gas-air mixture. In 2014, Kaohsiung experienced a flammable gas explosion in the buried storm drain [25], causing more than 30 death and injuries, in addition to massive damages to the road pavements. In 2015, Qingdao experienced a severe flammable gas explosion in a buried tunnel, neither the steel reinforced concrete slabs (i.e., the cover of the tunnel) nor road pavement survived in the explosion [26]. Li et al. [27] studied the masonry wall under natural gas explosion, and explored the gas explosion features and structural damage profile. Until now, there is rare study working on the structural elements subjected to the methane-air explosion in buried gas utility tunnels. In consideration of the severe structural damage in the previous accidents, the UHPC slabs with steel and basalt fibre rebar reinforcements are considered in the present study against methane-air explosion.In this study, a newly developed UHPC was adopted and investigated with basalt fibre rebar reinforcement. The UHPC and basalt fibre rebar material were investigated under static compressive, flexural and tensile loads. A total of 3 different types of UHPC specimens were manufactured and tested under four-point bending in the laboratory. Different damage modes and ductility index were obtained. The basalt fibre rebar reinforced UHPC specimen was found has higher ductility. In the subsequent field methane-air explosions test, 3 different types of concrete structural slabs in two full-scale tunnels setup were tested. The pressure data was captured and analysed. The steel reinforced C30 concrete and steel reinforced UHPC were used as reference slabs to compare with the basalt fibre rebar reinforced UHPC slab against the gas explosion. The displacements on each specimen were captured, analysed and compared. Section snippets UHPC In this study, a previously developed UHPC composition was used [28], and the material compositions are listed in Table 1. The 52.5 grade Portland cement [28] and the natural sand (i.e., size between 0.16 mm and 2.5 mm) were used in the mixture. The coarse aggregate was eliminated to achieve a more homogeneous mixture binder of UHPC. Fine aggregates addition such as silica fume and silica flour (i.e., quartz powder) were used to enhance the granular composition [29]. Pozzolanic additive silica Static bending test Both the steel and basalt fibre rebar reinforcements in UHPC specimens were investigated and compared in this section.Methane-air explosion test Based on the outstanding structural behaviours of UHPC with steel/basalt fibre rebar reinforcements, large scale slab specimens were made and tested under 9.5% methane-air explosion in two large scale tunnels. The methane-air explosion resistant capacity of different rebar reinforced UHPC slabs is investigated and compared in this section. Conclusion This study investigated the structural responses of basalt fibre reinforced UHPC specimens against static flexural test and 9.5% methane-air explosion tests. Higher flexural strength and ductility index were observed on the basalt fibre rebar reinforced prism specimen as compared to the steel rebar reinforced specimen in the static flexural test. In addition, the basalt rebar reinforced UHPC specimen may experience the rebar reinforcement debonding during the loading period, which results in a CRediT authorship contribution statement Qingfei Meng: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Writing - original draft. Chengqing Wu: Conceptualization, Methodology, Formal analysis, Resources, Writing - review & editing, Visualization, Supervision, Project administration, Funding acquisition. Jun Li: Methodology, Formal analysis, Writing - review & editing. Zhongxian Liu: Investigation. Pengtao Wu: Investigation. Yekai Yang: Investigation. Zhongqi Wang: Investigation, Data curation. Declaration of competing interest The authors declare that there is not any conflict of interest in this manuscript. Acknowledgements The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (Grant No. 51978186) and the Australian Research Council Discovery Project DP160104661.References (49)• Z. Wang et al.Experimental investigation of gas explosion in single vessel and connected vessels
J Loss Prev Process Ind(2013)• Q. Ma et al.Effects of premixed methane concentration on distribution of flame region and hazard effects in a tube and a tunnel gas explosion
J Loss Prev Process Ind(2015)• M. Cooper et al.On the mechanisms of pressure generation in vented explosions
Combust Flame(1986)• G. Tomlin et al.The effect of vent size and congestion in large-scale vented natural gas/air explosions
J Loss Prev Process Ind(2015)• Q. Bao et al.Effects of gas concentration and venting pressure on overpressure transients during vented explosion of methane–air mixtures
Fuel(2016)• B. Nie et al.The roles of foam ceramics in suppression of gas explosion overpressure and quenching of flame propagation
J Hazard Mater(2011)• D.-Y. Yoo et al.Structural performance of ultra-high-performance concrete beams with different steel fibers
Eng Struct(2015)• I.H. Yang et al.Structural behavior of ultra high performance concrete beams subjected to bending
Eng Struct(2010)• D. Shen et al.Influence of strain rate on bond behavior of concrete members reinforced with basalt fiber-reinforced polymer rebars
Construct Build Mater(2019)• M. Baena et al.Experimental study of bond behaviour between concrete and FRP bars using a pull-out test
Compos B Eng(2009)