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2024 Vol. 54, No. 6
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2024, 54(6): 1-12.
doi: 10.3724/j.gyjzG24043001
Abstract:
The serviceability of FRP prestressed concrete (FRP-PC) beams under sustained loading would be affected by the excessive long-term additional deflection, which is caused by the coupled effect of creep and relaxation of FRP tendons, and shrinkage and creep of concrete. A systematic review of the research progress on the long-term performance and design methods of FRP-PC beams was carried out. Firstly, the creep and relaxation properties of FRP tendons were introduced and the prediction methods were summarized. Secondly, the relevant results related to the past 20-year-research on the experiments of long-term performance of bonded prestressed concrete beams and externally prestressed concrete beams were concluded. The time-dependent finite element analysis method based on the age-adjusted effective modulus method (AEMM) or the integral-type creep model was summarized, and the corresponding parametric results were introduced. In addition, the similarities and differences of calculation theories and the simplified methods were analyzed. Finally, the future research on the long-term performance of FRP-PC beams was suggested.
The serviceability of FRP prestressed concrete (FRP-PC) beams under sustained loading would be affected by the excessive long-term additional deflection, which is caused by the coupled effect of creep and relaxation of FRP tendons, and shrinkage and creep of concrete. A systematic review of the research progress on the long-term performance and design methods of FRP-PC beams was carried out. Firstly, the creep and relaxation properties of FRP tendons were introduced and the prediction methods were summarized. Secondly, the relevant results related to the past 20-year-research on the experiments of long-term performance of bonded prestressed concrete beams and externally prestressed concrete beams were concluded. The time-dependent finite element analysis method based on the age-adjusted effective modulus method (AEMM) or the integral-type creep model was summarized, and the corresponding parametric results were introduced. In addition, the similarities and differences of calculation theories and the simplified methods were analyzed. Finally, the future research on the long-term performance of FRP-PC beams was suggested.
2024, 54(6): 13-21.
doi: 10.3724/j.gyjzG24032004
Abstract:
In order to determine the relaxation loss of prestressed carbon fiber reinforced polymer (CFRP) rods in the ground anchor abutment of Danjiangkou Reservoir Bridge of Shixi Expressway in Hubei Province, the stress relaxation of CFRP rods under different stress ratios was experimentally studied. Based on the axial tensile test of CFRP rod specimens anchored by bonded anchorage and mechanical crimping anchorage, the influence of different anchorage forms on the failure mode of CFRP rods and the material properties of CFRP rods were clarified; based on the 1 000 h stress relaxation test of CFRP rod specimens, the development laws of stress relaxation of CFRP rods at different stress levels were obtained. The results showed that the specimens anchored by bonded anchorage had an ideal bursting tensile failure under axial tension, but the strain of the specimens changed greatly during the stress relaxation test; the specimens anchored by mechanical crimping anchorage failed prematurely with the mode of the spallation and peeling of the CFRP rods under axial tensile, but the strain of the specimens changed little during the stress relaxation test, which could meet the relevant requirements of the stress relaxation test in GB/T 21839—2019. The stress relaxation of the CFRP rods increased with the increase of the initial stress ratio. The relaxation rates of specimens with initial stress ratios of 0.53, 0.63 and 0.82 were 1.06%, 1.65% and 2.31% after 1 000 h, respectively; the development of stress relaxation of CFRP rods converged rapidly and tended to be more stable with the increase of initial stress. The stress relaxation of specimens with initial stress ratios of 0.53, 0.63 and 0.82 at 24 h were 45.3%, 58.8% and 59.7% of that at 1 000 h, respectively. The stress relaxation of specimens with initial stress ratios of 0.53, 0.63 and 0.82 at 200 h were 78.3%, 81.2% and 82.7% of that at 1 000 h, respectively; based on the test results, the prediction model of stress relaxation in CFRP rods was established with high prediction accuracy, and the relaxation rates of prestressed CFRP rods in ground anchor abutment of Danjiangkou Reservoir Bridge in 10, 30, 50 and 100 years were 1.91%, 2.18%, 2.32% and 2.52%, respectively.
In order to determine the relaxation loss of prestressed carbon fiber reinforced polymer (CFRP) rods in the ground anchor abutment of Danjiangkou Reservoir Bridge of Shixi Expressway in Hubei Province, the stress relaxation of CFRP rods under different stress ratios was experimentally studied. Based on the axial tensile test of CFRP rod specimens anchored by bonded anchorage and mechanical crimping anchorage, the influence of different anchorage forms on the failure mode of CFRP rods and the material properties of CFRP rods were clarified; based on the 1 000 h stress relaxation test of CFRP rod specimens, the development laws of stress relaxation of CFRP rods at different stress levels were obtained. The results showed that the specimens anchored by bonded anchorage had an ideal bursting tensile failure under axial tension, but the strain of the specimens changed greatly during the stress relaxation test; the specimens anchored by mechanical crimping anchorage failed prematurely with the mode of the spallation and peeling of the CFRP rods under axial tensile, but the strain of the specimens changed little during the stress relaxation test, which could meet the relevant requirements of the stress relaxation test in GB/T 21839—2019. The stress relaxation of the CFRP rods increased with the increase of the initial stress ratio. The relaxation rates of specimens with initial stress ratios of 0.53, 0.63 and 0.82 were 1.06%, 1.65% and 2.31% after 1 000 h, respectively; the development of stress relaxation of CFRP rods converged rapidly and tended to be more stable with the increase of initial stress. The stress relaxation of specimens with initial stress ratios of 0.53, 0.63 and 0.82 at 24 h were 45.3%, 58.8% and 59.7% of that at 1 000 h, respectively. The stress relaxation of specimens with initial stress ratios of 0.53, 0.63 and 0.82 at 200 h were 78.3%, 81.2% and 82.7% of that at 1 000 h, respectively; based on the test results, the prediction model of stress relaxation in CFRP rods was established with high prediction accuracy, and the relaxation rates of prestressed CFRP rods in ground anchor abutment of Danjiangkou Reservoir Bridge in 10, 30, 50 and 100 years were 1.91%, 2.18%, 2.32% and 2.52%, respectively.
2024, 54(6): 22-30.
doi: 10.3724/j.gyjzG24041601
Abstract:
Through the pull-out test of Glass Fiber Reinforced Polymer(GFRP) bent bars reinforced Ultra High Performance Concrete(UHPC), the mechanical performance and damage mechanism of GFRP bars in bending zone were studied. The cooperative performance of GFRP bent bars and UHPC was revealed. The stress model of specimens was established. The study variables include: diameter of GFRP bars, anchoring length of the tail end of bent bars, shapes of the tail ends of bars and types of bar matrix. The results showed that the diameter of GFRP bars had a great influence on the bending strength due to the influence of the fold in the bending area and the stress concentration on the shoulder. The increase of the anchoring length at the tail of the GFRP bars had an positive effect on the bending strength of GFPR bars within a certain range, while the shape of tail end (L-shaped and U-shaped) bars had a little influence on the bending strength. The failure mechanism of GFRP bars under tension in the bending zone was presented, and three stages of fracture process of GFRP bars were revealed: the matrix cracking at the inside of stressed shoulders of bars, the inner fiber cracking and the outer fiber cracking. A stress analysis model was established for the bending area of GFRP-UHPC in the pull-out state.
Through the pull-out test of Glass Fiber Reinforced Polymer(GFRP) bent bars reinforced Ultra High Performance Concrete(UHPC), the mechanical performance and damage mechanism of GFRP bars in bending zone were studied. The cooperative performance of GFRP bent bars and UHPC was revealed. The stress model of specimens was established. The study variables include: diameter of GFRP bars, anchoring length of the tail end of bent bars, shapes of the tail ends of bars and types of bar matrix. The results showed that the diameter of GFRP bars had a great influence on the bending strength due to the influence of the fold in the bending area and the stress concentration on the shoulder. The increase of the anchoring length at the tail of the GFRP bars had an positive effect on the bending strength of GFPR bars within a certain range, while the shape of tail end (L-shaped and U-shaped) bars had a little influence on the bending strength. The failure mechanism of GFRP bars under tension in the bending zone was presented, and three stages of fracture process of GFRP bars were revealed: the matrix cracking at the inside of stressed shoulders of bars, the inner fiber cracking and the outer fiber cracking. A stress analysis model was established for the bending area of GFRP-UHPC in the pull-out state.
2024, 54(6): 31-45.
doi: 10.3724/j.gyjzG24040301
Abstract:
To study the seismic performances of a novel of GFRP-confined FRP bar-reinforced concrete piers, also called FCFRC piers which were constructed of GFRP rebars, CFRP stirrups, GFRP sheets, and concrete, a numerical simulation model for FCFRC piers under the monotonic and cyclic horizontal loads was developed based on software OpenSee. By the model, taking axial compressive ratios, shear-span ratios, longitudinal reinforcement ratios, confining levels of CFRP stirrups and external wrapped sheets, strength degrees of concrete and sizes of cross sections of piers as variables, pushover analysis was conducted on 5 184 FCFRC pier specimens. The effect of the above variables on key parameters of the trilinear resilience model with the yield bearing capacity, the peak bearing capacity, the elastic and elastic-plastic stiffness, and the ultimate drift angle was obtained. Analysis results indicated that the yield and ultimate bearing capacities all could be improved by increasing axial compressive ratios, longitudinal reinforcement ratios, strength degrees of concrete and sizes of cross sections, however, the confining levels of CFRP stirrups and external wrapped sheets had a little effect on them relatively. Based on the results of parameter analysis, the formulas for key parameters of the resilient model were obtained. In addition,the loading-unloading hysteresis regulation between horizontal force and displacement of FCFRC piers was proposed. Combining the skeleton curve and the hysteresis regulation, a resilient model for horizontal force and displacement of FCFRC piers was presented, simultaneously, compared with the test results, the adaptability of the model was verified.
To study the seismic performances of a novel of GFRP-confined FRP bar-reinforced concrete piers, also called FCFRC piers which were constructed of GFRP rebars, CFRP stirrups, GFRP sheets, and concrete, a numerical simulation model for FCFRC piers under the monotonic and cyclic horizontal loads was developed based on software OpenSee. By the model, taking axial compressive ratios, shear-span ratios, longitudinal reinforcement ratios, confining levels of CFRP stirrups and external wrapped sheets, strength degrees of concrete and sizes of cross sections of piers as variables, pushover analysis was conducted on 5 184 FCFRC pier specimens. The effect of the above variables on key parameters of the trilinear resilience model with the yield bearing capacity, the peak bearing capacity, the elastic and elastic-plastic stiffness, and the ultimate drift angle was obtained. Analysis results indicated that the yield and ultimate bearing capacities all could be improved by increasing axial compressive ratios, longitudinal reinforcement ratios, strength degrees of concrete and sizes of cross sections, however, the confining levels of CFRP stirrups and external wrapped sheets had a little effect on them relatively. Based on the results of parameter analysis, the formulas for key parameters of the resilient model were obtained. In addition,the loading-unloading hysteresis regulation between horizontal force and displacement of FCFRC piers was proposed. Combining the skeleton curve and the hysteresis regulation, a resilient model for horizontal force and displacement of FCFRC piers was presented, simultaneously, compared with the test results, the adaptability of the model was verified.
2024, 54(6): 46-53.
doi: 10.3724/j.gyjzG23051401
Abstract:
In the context of the "dual-carbon goals" strategy, the use of green and low-carbon geopolymer concrete instead of high-carbon emission Portland cement concrete is currently a hot research topic. This paper focused on fly ash-based geopolymer concrete and conducted a beam test to study the interfacial bonding performance between geopolymer concrete and glass fiber reinforced polymer (GFRP) bas under bending and tensile loads. The influence of different concrete strengths or types on the interfacial bonding performance between geopolymer concrete and GFRP bars was determined. The results showed that due to the difference in mechanical properties between geopolymer concrete and Portland cement concrete, although they showed similar failure modes in the tests with GFRP bars, the failure mechanism at the interface varied with different concrete strengths, and the bonding stiffness and strength also changed accordingly. Finally, the XUE model and Bimodal model were modified for shape factor, and a bond-slip constitutive model suitable for the interface between geopolymer concrete and GFRP bars was established through comparative analysis.
In the context of the "dual-carbon goals" strategy, the use of green and low-carbon geopolymer concrete instead of high-carbon emission Portland cement concrete is currently a hot research topic. This paper focused on fly ash-based geopolymer concrete and conducted a beam test to study the interfacial bonding performance between geopolymer concrete and glass fiber reinforced polymer (GFRP) bas under bending and tensile loads. The influence of different concrete strengths or types on the interfacial bonding performance between geopolymer concrete and GFRP bars was determined. The results showed that due to the difference in mechanical properties between geopolymer concrete and Portland cement concrete, although they showed similar failure modes in the tests with GFRP bars, the failure mechanism at the interface varied with different concrete strengths, and the bonding stiffness and strength also changed accordingly. Finally, the XUE model and Bimodal model were modified for shape factor, and a bond-slip constitutive model suitable for the interface between geopolymer concrete and GFRP bars was established through comparative analysis.
2024, 54(6): 54-60.
doi: 10.3724/j.gyjzG24032001
Abstract:
Large diameter shield tunnel is the main construction form of long and large tunnels that cross sea and river, which has the advantages of safety, economy, efficiency, and intelligence. Fiber Reinforced Polymer (FRP) possess the advantages of light weight, high strength, corrosion resistance, fatigue resistance and design-ability, which can be used to replace steel to address engineering problems in complex underground service environments. The research and applications of FRP at home and abroad were presented from four typical projects of large-diameter shield tunnel construction, such as deep foundation excavation supporting structure, underground diaphragm wall, shield tunnel internal structure, and mud circulation pipe. The results showed that the mechanical and service properties of FRP could meet the requirements in the application of underground foundation excavation supportings, shield tunnels and other structures. Finally, the application of FRP materials in the underground engineering structures was prospected according to the research and application states and current problems of FRP.
Large diameter shield tunnel is the main construction form of long and large tunnels that cross sea and river, which has the advantages of safety, economy, efficiency, and intelligence. Fiber Reinforced Polymer (FRP) possess the advantages of light weight, high strength, corrosion resistance, fatigue resistance and design-ability, which can be used to replace steel to address engineering problems in complex underground service environments. The research and applications of FRP at home and abroad were presented from four typical projects of large-diameter shield tunnel construction, such as deep foundation excavation supporting structure, underground diaphragm wall, shield tunnel internal structure, and mud circulation pipe. The results showed that the mechanical and service properties of FRP could meet the requirements in the application of underground foundation excavation supportings, shield tunnels and other structures. Finally, the application of FRP materials in the underground engineering structures was prospected according to the research and application states and current problems of FRP.
2024, 54(6): 61-71.
doi: 10.3724/j.gyjzG23071211
Abstract:
The prestressed concrete cylinder pipe (PCCP) may fail at each structural layer under internal pressure. Carbon fiber reinforced polymer (CFRP) lining is one of the most commonly used methods for repairing PCCPs. However, the failure mechanism of CFRP-lined PCCP under internal pressure remains to be fully understood. The paper presents a multilayer ring model of CFRP-lined PCCP under internal pressure. Analytical expressions for the radial displacement, stress and strain of CFRP-lined PCCP were obtained. The analytical results were in good agreement with existing experimental results, which verified the accuracy of the model. The parametric study results showed that the bearing capacity of PCCP under internal pressure increased with the increase of steel cylinder thickness and concrete core thickness. In addition, increasing the prestressing level could improve the cracking resistance capacity. The bearing capacity of CFRP-lined PCCP under internal pressure increased with the increase of CFRP thickness.
The prestressed concrete cylinder pipe (PCCP) may fail at each structural layer under internal pressure. Carbon fiber reinforced polymer (CFRP) lining is one of the most commonly used methods for repairing PCCPs. However, the failure mechanism of CFRP-lined PCCP under internal pressure remains to be fully understood. The paper presents a multilayer ring model of CFRP-lined PCCP under internal pressure. Analytical expressions for the radial displacement, stress and strain of CFRP-lined PCCP were obtained. The analytical results were in good agreement with existing experimental results, which verified the accuracy of the model. The parametric study results showed that the bearing capacity of PCCP under internal pressure increased with the increase of steel cylinder thickness and concrete core thickness. In addition, increasing the prestressing level could improve the cracking resistance capacity. The bearing capacity of CFRP-lined PCCP under internal pressure increased with the increase of CFRP thickness.
2024, 54(6): 72-80.
doi: 10.3724/j.gyjzG23111328
Abstract:
Carbon fiber-reinforced polymer (CFRP) has been widely used in structural strengthening due to its light weight, high strength and anti-corrosion. Specifically, in strengthening RC beams, various strengthening techniques, such as external bonding, near-surface mounting and prestressing, have been developed so far. However, due to the brittle nature of the CFRP material and the interface of concrete bonded with CFRP plates, strengthened beams used to exhibit brittle failure at low ductility. Therefore, a novel strengthening method with high ductility and prestressed CFRP plates was proposed based on previous findings on the mid-span-supported strengthening technique by changing the mid-span deviators to elastic-plastic devices. The effectiveness of the proposed strengthening method was verified by finite element analysis. The finding indicated the new method could maintain the CFRP at a high stress level and increase the ultimate deflection up to 137% in limited loss of ultimate strength. The results could be reference to further development of structural strengthening methods.
Carbon fiber-reinforced polymer (CFRP) has been widely used in structural strengthening due to its light weight, high strength and anti-corrosion. Specifically, in strengthening RC beams, various strengthening techniques, such as external bonding, near-surface mounting and prestressing, have been developed so far. However, due to the brittle nature of the CFRP material and the interface of concrete bonded with CFRP plates, strengthened beams used to exhibit brittle failure at low ductility. Therefore, a novel strengthening method with high ductility and prestressed CFRP plates was proposed based on previous findings on the mid-span-supported strengthening technique by changing the mid-span deviators to elastic-plastic devices. The effectiveness of the proposed strengthening method was verified by finite element analysis. The finding indicated the new method could maintain the CFRP at a high stress level and increase the ultimate deflection up to 137% in limited loss of ultimate strength. The results could be reference to further development of structural strengthening methods.
2024, 54(6): 81-90.
doi: 10.3724/j.gyjzG24042801
Abstract:
Fatigue cracking is one of the most common issue that damages the serviceability of steel bridges. Prestressed carbon fiber-reinforced polymer (CFRP) materials can effectively inhibit crack propagation, thereby extending the service life of structures. In prestressed CFRP-reinforced steel beams, the interface between CFRP and steel interface serves as the primary load transfer path, ensuring the mechanical properties and durability of the reinforced structure. However, under the influence of fatigue and hygrothermal environments, the bonding performance of the interface between CFRP and steel may tend to degrade, leading to the degradation of mechanical properties in the reinforced structure. This paper summarized the results of static and fatigue performance tests of steel beams with different prestressed strengthening system design schemes, as well as the degree of influence of environmental factors on structural performance, based on existing research. Additionally, this paper compiled formulas for calculating the interface principal stress and energy release rate of damaged steel beams reinforced with prestressed CFRP, and proposed methods for predicting the bearing capacity reduction coefficient and service life of reinforced steel beams under fatigue loading and hygrothermal environments, as well as structural reinforcement design strategies considering interface durability.
Fatigue cracking is one of the most common issue that damages the serviceability of steel bridges. Prestressed carbon fiber-reinforced polymer (CFRP) materials can effectively inhibit crack propagation, thereby extending the service life of structures. In prestressed CFRP-reinforced steel beams, the interface between CFRP and steel interface serves as the primary load transfer path, ensuring the mechanical properties and durability of the reinforced structure. However, under the influence of fatigue and hygrothermal environments, the bonding performance of the interface between CFRP and steel may tend to degrade, leading to the degradation of mechanical properties in the reinforced structure. This paper summarized the results of static and fatigue performance tests of steel beams with different prestressed strengthening system design schemes, as well as the degree of influence of environmental factors on structural performance, based on existing research. Additionally, this paper compiled formulas for calculating the interface principal stress and energy release rate of damaged steel beams reinforced with prestressed CFRP, and proposed methods for predicting the bearing capacity reduction coefficient and service life of reinforced steel beams under fatigue loading and hygrothermal environments, as well as structural reinforcement design strategies considering interface durability.
2024, 54(6): 91-99.
doi: 10.3724/j.gyjzG24013001
Abstract:
To explore the fatigue performance of surface-cracked bent steel plates with different reinforcing materials, fatigue loading tests were conducted on Q345 steel plates with surface cracks using Carbon Fiber Reinforced Polymer (CFRP) plates and steel plates as reinforcement schemes. The effects of initial crack size, reinforcing plate thickness, and bonding methods on the reinforcement performance were analyzed. During the tests, the depth and length of crack propagation were measured using an ultrasonic flaw detector, and the crack propagation process in the steel plates was simulated by using the Extended Finite Element Method (XFEM). The results showed that both CFRP plates and steel plates could effectively extend the fatigue life of the damaged steel plates and suppress crack propagation. When double-layered reinforcing plates were used, delamination failure occurred, affecting the reinforcement effect. Therefore, it was recommended to use a single-layer bonding method for reinforcement. The reinforcement effect of CFRP plates was superior to that of steel plates, and increasing the thickness of the reinforcing plates further enhanced the reinforcement effect. Reinforcement was significantly more effective on damaged steel plates with larger initial cracks compared to those with smaller initial cracks. The fatigue life and crack length obtained from XFEM simulation of crack propagation were consistent with the experimental results.
To explore the fatigue performance of surface-cracked bent steel plates with different reinforcing materials, fatigue loading tests were conducted on Q345 steel plates with surface cracks using Carbon Fiber Reinforced Polymer (CFRP) plates and steel plates as reinforcement schemes. The effects of initial crack size, reinforcing plate thickness, and bonding methods on the reinforcement performance were analyzed. During the tests, the depth and length of crack propagation were measured using an ultrasonic flaw detector, and the crack propagation process in the steel plates was simulated by using the Extended Finite Element Method (XFEM). The results showed that both CFRP plates and steel plates could effectively extend the fatigue life of the damaged steel plates and suppress crack propagation. When double-layered reinforcing plates were used, delamination failure occurred, affecting the reinforcement effect. Therefore, it was recommended to use a single-layer bonding method for reinforcement. The reinforcement effect of CFRP plates was superior to that of steel plates, and increasing the thickness of the reinforcing plates further enhanced the reinforcement effect. Reinforcement was significantly more effective on damaged steel plates with larger initial cracks compared to those with smaller initial cracks. The fatigue life and crack length obtained from XFEM simulation of crack propagation were consistent with the experimental results.
2024, 54(6): 100-107.
doi: 10.3724/j.gyjzG23112405
Abstract:
Through conducting axial compression tests on 13 RC stub columns with corroded stirrups strengthened by grouted GFRP Jackets reinforced with CFRP grids, the effects of the number of CFRP grid layers and stirrup corrosion rate on the load-axial displacement curve,ultimate bearing capacity and damage pattern of the specimens were investigated.The results indicated that: the overall performance of the reinforced columns was brittle failure; the fiberglass sleeve reinforcement increased the ultimate bearing capacity of the stirrup-corroded RC columns by 59.4%, and the CFRP grids as a reinforcing material increased the ultimate bearing capacity of the reinforced columns by 87%;the number of CFRP grid layers had a greater influence on the load-axial displacement curves of reinforced columns than the corrosion rate of stirrups, and the more the number of layers, the more obvious the strengthening degree of the curves in the elastoplastic stage; the ultimate bearing capacity increased with the increase of the number of CFRP grid layers; the ultimate bearing capacity increased with the increase of the corrosion rate of stirrups, and the increase of the ultimate bearing capacity showed a decreasing trend.The research results of the experiments could provide an experimental basis for the reinforcement of bridge abutments with corroded stirrups in practical engineering.
Through conducting axial compression tests on 13 RC stub columns with corroded stirrups strengthened by grouted GFRP Jackets reinforced with CFRP grids, the effects of the number of CFRP grid layers and stirrup corrosion rate on the load-axial displacement curve,ultimate bearing capacity and damage pattern of the specimens were investigated.The results indicated that: the overall performance of the reinforced columns was brittle failure; the fiberglass sleeve reinforcement increased the ultimate bearing capacity of the stirrup-corroded RC columns by 59.4%, and the CFRP grids as a reinforcing material increased the ultimate bearing capacity of the reinforced columns by 87%;the number of CFRP grid layers had a greater influence on the load-axial displacement curves of reinforced columns than the corrosion rate of stirrups, and the more the number of layers, the more obvious the strengthening degree of the curves in the elastoplastic stage; the ultimate bearing capacity increased with the increase of the number of CFRP grid layers; the ultimate bearing capacity increased with the increase of the corrosion rate of stirrups, and the increase of the ultimate bearing capacity showed a decreasing trend.The research results of the experiments could provide an experimental basis for the reinforcement of bridge abutments with corroded stirrups in practical engineering.
2024, 54(6): 108-117.
doi: 10.3724/j.gyjzG23022014
Abstract:
The mechanical properties of CFRP-concrete interface are important factors affecting the seismic performance of CFRP reinforced structures. A bilinear cohesive force unit based on nonlinear softening mechanical behavior was established to simulate the bonding interface of CFRP reinforced structures. Considering the material nonlinearity of concrete and rebars, the seismic performance of CFRP reinforced concrete composite torsional columns was analyzed by finite element method. In order to verify the rationality of the method and improve the arrangement of CFRP, the stress variation, the failure mechanism of the interface and the bearing capacity of the structure were analyzed. The results were compared with the experimental results and the finite element analysis results without considering the interface bonding slip. The results of finite element analysis showed that the tensile stress, bonding interface stress and damage variables of CFRP were large in the middle and corners of the section, but small at the junction of CFRP. The stripping failure expanded from the edge of CFRP with large stress to the middle during the loading process. The structural failure process obtained by finite element analysis was basically consistent with the experimental results, which revealed the influence of bonding interface degradation on the seismic performance of CFRP reinforced concrete columns. The relative error between the maximum load obtained at each stage and the experimental results was less than 10%. Without considering the degradation of bond interface properties and the stripping of CFRP, the contribution of CFRP to the bearing capacity in the strengthening stage was overestimated. The cohesive force model of bond interface could provide a reference for seismic performance analysis of CFRP reinforced concrete composite torsional columns.
The mechanical properties of CFRP-concrete interface are important factors affecting the seismic performance of CFRP reinforced structures. A bilinear cohesive force unit based on nonlinear softening mechanical behavior was established to simulate the bonding interface of CFRP reinforced structures. Considering the material nonlinearity of concrete and rebars, the seismic performance of CFRP reinforced concrete composite torsional columns was analyzed by finite element method. In order to verify the rationality of the method and improve the arrangement of CFRP, the stress variation, the failure mechanism of the interface and the bearing capacity of the structure were analyzed. The results were compared with the experimental results and the finite element analysis results without considering the interface bonding slip. The results of finite element analysis showed that the tensile stress, bonding interface stress and damage variables of CFRP were large in the middle and corners of the section, but small at the junction of CFRP. The stripping failure expanded from the edge of CFRP with large stress to the middle during the loading process. The structural failure process obtained by finite element analysis was basically consistent with the experimental results, which revealed the influence of bonding interface degradation on the seismic performance of CFRP reinforced concrete columns. The relative error between the maximum load obtained at each stage and the experimental results was less than 10%. Without considering the degradation of bond interface properties and the stripping of CFRP, the contribution of CFRP to the bearing capacity in the strengthening stage was overestimated. The cohesive force model of bond interface could provide a reference for seismic performance analysis of CFRP reinforced concrete composite torsional columns.
2024, 54(6): 118-129.
doi: 10.3724/j.gyjzG23042605
Abstract:
In order to study the seismic performance of CFRP reinforced recycled aggregate concrete composite torsional columns, two specimens reinforced by CFRP and one specimen not reinforced by CFRP were designed and carried out pseudo-static tests under composite torsional conditions, and the strain, crack development law and failure mode were analyzed. The results showed that two CFRP reinforced specimens had undegone torsional failure, and one unreinforced specimen had undergone bending and torsional failure.CFRP reinforced column specimens had better seismic performance, the peak torque and ductility coefficient increased by 44.68% and 71.41%, respectively, and the strength attenuation, stiffness degradation, energy dissipation and cumulative damage were significantly improved.The ratio of longitudinal reinforcement has little effect on the seismic performance of the specimen, the peak torque is increased by 5.45%, and the stiffness degradation and cumulative damage were improved.
In order to study the seismic performance of CFRP reinforced recycled aggregate concrete composite torsional columns, two specimens reinforced by CFRP and one specimen not reinforced by CFRP were designed and carried out pseudo-static tests under composite torsional conditions, and the strain, crack development law and failure mode were analyzed. The results showed that two CFRP reinforced specimens had undegone torsional failure, and one unreinforced specimen had undergone bending and torsional failure.CFRP reinforced column specimens had better seismic performance, the peak torque and ductility coefficient increased by 44.68% and 71.41%, respectively, and the strength attenuation, stiffness degradation, energy dissipation and cumulative damage were significantly improved.The ratio of longitudinal reinforcement has little effect on the seismic performance of the specimen, the peak torque is increased by 5.45%, and the stiffness degradation and cumulative damage were improved.
2024, 54(6): 130-140.
doi: 10.3724/j.gyjzG23092008
Abstract:
Axial compressive tests of 14 short circular concrete columns strengthened with woven carbon fiber mesh and polypropylene fiber-reinforced cement-based composite materials were conducted. The ultimate bearing capacity and damage pattern of each specimen were obtained, the curves between average compressive stress and concrete strain, the curves between average compressive stress and strain of woven carbon fibers mesh, and the ultimate bearing capacity histogram of each specimen were given. The effects of parameters such as the polypropylene fiber content in the reinforced cement-based composite material, the number of layers and the grid sizes on the axial compressive performances and damage mechanisms of specimens were analyzed. The test results showed that the ultimate bearing capacity of the short circular columns reinforced with woven carbon fiber mesh and polypropylene fiber-reinforced concrete could be significantly improved; in the case of a small mass content, the changes in the polypropylene fiber content (with a mass content of 0.05%, 0.15%, 0.25%) in the reinforced layer had a little effect on the bearing capacity of specimens; the bearing capacity of specimens in a certain range increased with the number of layers of woven carbon fiber mesh. The bearing capacity of specimens increased with the increase in the number of wrapped layers of woven carbon fiber mesh; compared with the mesh with the grid of 2 cm×2 cm, the mesh with the grid of 1 cm×1 cm was more effective in improving the bearing capacity of specimens. By introducing four reasonable basic assumptions and two strength models, the calculation method of the axial compressive bearing capacity for composite reinforced columns with woven carbon fiber mesh and polypropylene fiber-reinforced cement-based composite materials was proposed. The theoretical calculated values obtained by the proposed method and the calculation methods from related literatures were compared with the test results, and the results showed that the theoretical values calculated by the proposed method were in good agreement with the test results, and the theoretical values were smaller than the test values. It was indicated that the proposed formula had certain safety reserve.
Axial compressive tests of 14 short circular concrete columns strengthened with woven carbon fiber mesh and polypropylene fiber-reinforced cement-based composite materials were conducted. The ultimate bearing capacity and damage pattern of each specimen were obtained, the curves between average compressive stress and concrete strain, the curves between average compressive stress and strain of woven carbon fibers mesh, and the ultimate bearing capacity histogram of each specimen were given. The effects of parameters such as the polypropylene fiber content in the reinforced cement-based composite material, the number of layers and the grid sizes on the axial compressive performances and damage mechanisms of specimens were analyzed. The test results showed that the ultimate bearing capacity of the short circular columns reinforced with woven carbon fiber mesh and polypropylene fiber-reinforced concrete could be significantly improved; in the case of a small mass content, the changes in the polypropylene fiber content (with a mass content of 0.05%, 0.15%, 0.25%) in the reinforced layer had a little effect on the bearing capacity of specimens; the bearing capacity of specimens in a certain range increased with the number of layers of woven carbon fiber mesh. The bearing capacity of specimens increased with the increase in the number of wrapped layers of woven carbon fiber mesh; compared with the mesh with the grid of 2 cm×2 cm, the mesh with the grid of 1 cm×1 cm was more effective in improving the bearing capacity of specimens. By introducing four reasonable basic assumptions and two strength models, the calculation method of the axial compressive bearing capacity for composite reinforced columns with woven carbon fiber mesh and polypropylene fiber-reinforced cement-based composite materials was proposed. The theoretical calculated values obtained by the proposed method and the calculation methods from related literatures were compared with the test results, and the results showed that the theoretical values calculated by the proposed method were in good agreement with the test results, and the theoretical values were smaller than the test values. It was indicated that the proposed formula had certain safety reserve.
2024, 54(6): 141-148.
doi: 10.3724/j.gyjzG24040701
Abstract:
In order to investigate the seismic performance of concrete-filled square steel tubular columns with CFRP(C-CFST), three columns with CFRP were tested under quasi-static load with steel ratio as the parameter. The changing parameter of the composite columns is steel ratio. The loading process and failure modes of the composite columns were described. ABAQUS finite element analysis software was used to establish a numerical analysis model on the basis of rational selection of material constitutive relations. Compared with the experimental results, the accuracy of the model and its modeling method were verified. By establishing a large number of refined numerical models, considering different parameters such as yield strength of steels, compressive strength of concrete, steel ratio, slenderness ratio, and whether I-shaped CFRP profiles are built in, the influence of these parameters on the load-displacement hysteretic curve, load-displacement skeleton curve, stiffness, bearing capacity and other performance indicators of composite columns was studied. The results showed that the hysteretic curve of the new composite column was relatively full, there was no obvious pinch phenomenon, and it showed a good seismic performance; compared with ordinary CFST tubular columns, the new composite columns had better ductility, bearing capacity and energy dissipation capacity; the change of concrete compressive strength had little effect on the ultimate bearing capacity of composite columns, and the ultimate bearing capacity would increase significantly with the increase of steel yield strength and steel ratio; when the wall thickness of square steel pipe increased by 1 mm, the ultimate bearing capacity increased by 14.3%, 8.3%, and the energy dissipation value increased by 14.3%, 10.7%; when the slenderness ratio increased from 32.33 to 50.81, the ultimate bearing capacity and energy dissipation decreased by 41.2% and 60.8%, respectively. Therefore, it is suggested that the slenderness ratio should be reasonably controlled.
In order to investigate the seismic performance of concrete-filled square steel tubular columns with CFRP(C-CFST), three columns with CFRP were tested under quasi-static load with steel ratio as the parameter. The changing parameter of the composite columns is steel ratio. The loading process and failure modes of the composite columns were described. ABAQUS finite element analysis software was used to establish a numerical analysis model on the basis of rational selection of material constitutive relations. Compared with the experimental results, the accuracy of the model and its modeling method were verified. By establishing a large number of refined numerical models, considering different parameters such as yield strength of steels, compressive strength of concrete, steel ratio, slenderness ratio, and whether I-shaped CFRP profiles are built in, the influence of these parameters on the load-displacement hysteretic curve, load-displacement skeleton curve, stiffness, bearing capacity and other performance indicators of composite columns was studied. The results showed that the hysteretic curve of the new composite column was relatively full, there was no obvious pinch phenomenon, and it showed a good seismic performance; compared with ordinary CFST tubular columns, the new composite columns had better ductility, bearing capacity and energy dissipation capacity; the change of concrete compressive strength had little effect on the ultimate bearing capacity of composite columns, and the ultimate bearing capacity would increase significantly with the increase of steel yield strength and steel ratio; when the wall thickness of square steel pipe increased by 1 mm, the ultimate bearing capacity increased by 14.3%, 8.3%, and the energy dissipation value increased by 14.3%, 10.7%; when the slenderness ratio increased from 32.33 to 50.81, the ultimate bearing capacity and energy dissipation decreased by 41.2% and 60.8%, respectively. Therefore, it is suggested that the slenderness ratio should be reasonably controlled.
2024, 54(6): 149-159.
doi: 10.3724/j.gyjzG24032002
Abstract:
Biochar can be served as a lightweight aggregate material and its partial incorporation into concrete can realize internal curing and filling effects, thereby enhancing the mechanical properties of cementitious materials. It represents a potential carbon capture and sequestration technique. However, due to the high porosity of biochar’s microstructure, biochar concrete faces challenges such as low strength, poor corrosion resistance, and instability. This study proposed the use of Glass Fiber Reinforced Polymer (GFRP) tubes to confine biochar concrete, and the axial compression tests on GFRP tube-confined biochar concrete were performed, with design parameters including GFRP tube thickness (number of layers), biochar content, and biochar water absorption rate. Emphasis was placed on analyzing the axial stress-strain curves, circumferential strain-axial strain curves, yielding stress, ultimate strain, and circumferential fracture strain of each specimen. The results indicated that, under the premise of same biochar content and water absorption rate, the ultimate compressive strength of GFRP-confined biochar concrete specimens increased by 490.4% to 563.3% compared to that of unconfined specimens. The ultimate strain of confined specimens also significantly increased, and the yielding stress and strain of the confined specimens were much greater then those of unconfined specimens, indicating that GFRP confinement significantly improves the bearing capacity and deformation performance of biochar concrete. With increasing biochar content, the peak stress of confined specimens decreased while the axial ultimate strain increased. On the other hand, an increase in biochar water absorption rate led to an increase in the yielding load of confined specimens but a decrease in the ultimate strain. Additionally, an increase in the number of layers of GFRP tubes enhanced the secondary stiffness of confined specimens. The circumferential strain-axial strain curve exhibited no obvious transition point between the elastic segment and the linear segment, indicating that three was a good synergy between FRP tubes and biochar concrete.
Biochar can be served as a lightweight aggregate material and its partial incorporation into concrete can realize internal curing and filling effects, thereby enhancing the mechanical properties of cementitious materials. It represents a potential carbon capture and sequestration technique. However, due to the high porosity of biochar’s microstructure, biochar concrete faces challenges such as low strength, poor corrosion resistance, and instability. This study proposed the use of Glass Fiber Reinforced Polymer (GFRP) tubes to confine biochar concrete, and the axial compression tests on GFRP tube-confined biochar concrete were performed, with design parameters including GFRP tube thickness (number of layers), biochar content, and biochar water absorption rate. Emphasis was placed on analyzing the axial stress-strain curves, circumferential strain-axial strain curves, yielding stress, ultimate strain, and circumferential fracture strain of each specimen. The results indicated that, under the premise of same biochar content and water absorption rate, the ultimate compressive strength of GFRP-confined biochar concrete specimens increased by 490.4% to 563.3% compared to that of unconfined specimens. The ultimate strain of confined specimens also significantly increased, and the yielding stress and strain of the confined specimens were much greater then those of unconfined specimens, indicating that GFRP confinement significantly improves the bearing capacity and deformation performance of biochar concrete. With increasing biochar content, the peak stress of confined specimens decreased while the axial ultimate strain increased. On the other hand, an increase in biochar water absorption rate led to an increase in the yielding load of confined specimens but a decrease in the ultimate strain. Additionally, an increase in the number of layers of GFRP tubes enhanced the secondary stiffness of confined specimens. The circumferential strain-axial strain curve exhibited no obvious transition point between the elastic segment and the linear segment, indicating that three was a good synergy between FRP tubes and biochar concrete.
2024, 54(6): 160-168.
doi: 10.3724/j.gyjzG23011501
Abstract:
To investigate the restoring force characteristics of T-joints between PVC-CFRP confined concrete columns and RC ring beams, eleven exterior joint specimens under quasi-static loading were tested. The experimental results showed that the enlarged ring beam joints could effectively connect the PVC-CFRP confined concrete columns and RC beams, and the joint specimens showed favorable seismic performance. On the basis of the experimental study, the material constitutive relations were reasonably selected, the fiber model method was adopted, the nonlinear analysis program was compiled, and the quasi-static tests of the exterior joint specimens were simulated numerically. The model predicted results agreed well with the experimental data. Based on the numerical model verified by experiments, the effects of concrete strength, height of ring beam, longitudinal reinforcement ratio of beam, column diameter and yield strength of longitudinal reinforcement on skeleton curves were analyzed, and reasonable design suggestions were proposed. The numerical simulation results showed that when the concrete strength of the ring beam joint increased from 20 MPa to 60 MPa, the peak bending moment increased by 13.7%, while the ultimate displacement decreased by 8.0%. As the longitudinal reinforcement ratio of beam increased from 2% to 5%, the peak bending moment increased by 26.3%, while the ultimate displacement decreased by 19.9%. As the yield strength of beam longitudinal reinforcement increased from 400 MPa to 600 MPa, the peak bending moment increased by 56.3%, while the ultimate curvature decreased by 17.9%. When the height of ring beam increased from 350 mm to 450 mm, the peak bending moment showed little influence, while the ultimate displacement decreased by 11.0%. When the column diameter increased from 200 mm to 300 mm, the peak load increased by 56.3%, and the ultimate displacement increased by 28.5%.
To investigate the restoring force characteristics of T-joints between PVC-CFRP confined concrete columns and RC ring beams, eleven exterior joint specimens under quasi-static loading were tested. The experimental results showed that the enlarged ring beam joints could effectively connect the PVC-CFRP confined concrete columns and RC beams, and the joint specimens showed favorable seismic performance. On the basis of the experimental study, the material constitutive relations were reasonably selected, the fiber model method was adopted, the nonlinear analysis program was compiled, and the quasi-static tests of the exterior joint specimens were simulated numerically. The model predicted results agreed well with the experimental data. Based on the numerical model verified by experiments, the effects of concrete strength, height of ring beam, longitudinal reinforcement ratio of beam, column diameter and yield strength of longitudinal reinforcement on skeleton curves were analyzed, and reasonable design suggestions were proposed. The numerical simulation results showed that when the concrete strength of the ring beam joint increased from 20 MPa to 60 MPa, the peak bending moment increased by 13.7%, while the ultimate displacement decreased by 8.0%. As the longitudinal reinforcement ratio of beam increased from 2% to 5%, the peak bending moment increased by 26.3%, while the ultimate displacement decreased by 19.9%. As the yield strength of beam longitudinal reinforcement increased from 400 MPa to 600 MPa, the peak bending moment increased by 56.3%, while the ultimate curvature decreased by 17.9%. When the height of ring beam increased from 350 mm to 450 mm, the peak bending moment showed little influence, while the ultimate displacement decreased by 11.0%. When the column diameter increased from 200 mm to 300 mm, the peak load increased by 56.3%, and the ultimate displacement increased by 28.5%.
2024, 54(6): 169-176.
doi: 10.3724/j.gyjzG23061204
Abstract:
Six precast geopolymer concrete sandwich panels enabled by glass fiber reinforced polymer (GFRP) hexagonal tubular connectors were fabricated and tested under axial compression. The effects of three key parameters, including the connector spacing, panel height and wythe thickness, on the failure mode, bearing capacity and deformation of the specimens under axial compression were studied and discussed. The results showed that all specimens exhibited large eccentric compression failure due to the second-order effect, which was characterized by the concrete crushing and horizontal cracking in the two wythes, respectively; with the increase of the distance between the connectors, the composite performance of the wall panel was reduced, the area of the concrete crushing area decreased, the lateral deformation increased, and the bearing capacity of the specimens decreased gradually (when the distance between the connectors increased from 300 mm to 600, 900 mm, and without connectors, the bearing capacity decreased by 17.1%, 42.0%, 49.5%, respectively). With the decrease of the height of the wall panel or the increase of the thickness of the wythes, the slenderness ratio and the second-order effect of the specimens gradually decreased, the area of the concrete crushing zone increased, the out-of-plane deformation decreased, and the bearing capacity of the specimen increased (when the thickness of the wythes increased from 50 mm to 75 mm or the height decreased from 2 100 mm to 1 500 mm, the bearing capacity of the specimen increased by 34.3% and 5.9%, respectively).
Six precast geopolymer concrete sandwich panels enabled by glass fiber reinforced polymer (GFRP) hexagonal tubular connectors were fabricated and tested under axial compression. The effects of three key parameters, including the connector spacing, panel height and wythe thickness, on the failure mode, bearing capacity and deformation of the specimens under axial compression were studied and discussed. The results showed that all specimens exhibited large eccentric compression failure due to the second-order effect, which was characterized by the concrete crushing and horizontal cracking in the two wythes, respectively; with the increase of the distance between the connectors, the composite performance of the wall panel was reduced, the area of the concrete crushing area decreased, the lateral deformation increased, and the bearing capacity of the specimens decreased gradually (when the distance between the connectors increased from 300 mm to 600, 900 mm, and without connectors, the bearing capacity decreased by 17.1%, 42.0%, 49.5%, respectively). With the decrease of the height of the wall panel or the increase of the thickness of the wythes, the slenderness ratio and the second-order effect of the specimens gradually decreased, the area of the concrete crushing zone increased, the out-of-plane deformation decreased, and the bearing capacity of the specimen increased (when the thickness of the wythes increased from 50 mm to 75 mm or the height decreased from 2 100 mm to 1 500 mm, the bearing capacity of the specimen increased by 34.3% and 5.9%, respectively).
2024, 54(6): 177-189.
doi: 10.3724/j.gyjzG24041713
Abstract:
9 concrete-filled steel tubular columns with an inner FRP tube (CFT-GT), 1 concrete-filled steel tubular column (CFT) and 9 FRP tube confined concrete columns were tested subjected to axial compression. The results showed that the ultimate bearing capacity of CFT-GT was higher than that of CFT. With the decrease of the diameter-to-wall thickness ratios of the inner FRP tube (d/t2) or the diameter ratios of the steel tube to the FRP tube (D/d), the ultimate bearing capacity increased. The circumferential and longitudinal peak strains of CFT-GT increased with the decrease of d/t2. With the D/d increasing, the circumferential peak strains of the inner FRP tube of CFT-GT increased. However, D/d had little influence on the longitudinal peak strains of the inner FRP tube. In addition, it showed that all the ultimate circumferential strains of the inner FRP tube of CFT-GT were smaller than that of FRP tube confined concrete columns while the ultimate longitudinal strains of the inner FRP tube of CFT-GT was higher than that of FRP tube confined concrete column specimens. Based on the experimental study above, it was pointed out that the relations between circumferential strain and longitudinal strain in all current FRP confined concrete constitutive models were not appropriate for CFT-GT composite columns. Hence, a new constitutive model was proposed for CFT-GT composite columns.
9 concrete-filled steel tubular columns with an inner FRP tube (CFT-GT), 1 concrete-filled steel tubular column (CFT) and 9 FRP tube confined concrete columns were tested subjected to axial compression. The results showed that the ultimate bearing capacity of CFT-GT was higher than that of CFT. With the decrease of the diameter-to-wall thickness ratios of the inner FRP tube (d/t2) or the diameter ratios of the steel tube to the FRP tube (D/d), the ultimate bearing capacity increased. The circumferential and longitudinal peak strains of CFT-GT increased with the decrease of d/t2. With the D/d increasing, the circumferential peak strains of the inner FRP tube of CFT-GT increased. However, D/d had little influence on the longitudinal peak strains of the inner FRP tube. In addition, it showed that all the ultimate circumferential strains of the inner FRP tube of CFT-GT were smaller than that of FRP tube confined concrete columns while the ultimate longitudinal strains of the inner FRP tube of CFT-GT was higher than that of FRP tube confined concrete column specimens. Based on the experimental study above, it was pointed out that the relations between circumferential strain and longitudinal strain in all current FRP confined concrete constitutive models were not appropriate for CFT-GT composite columns. Hence, a new constitutive model was proposed for CFT-GT composite columns.
2024, 54(6): 190-196.
doi: 10.3724/j.gyjzG24040601
Abstract:
With the advancement of material science and industrial technology, composite materials have gained rapid development and been widely used in multiple fields. Currently, the railway has been booming in China, with the increase in railway mileage each year, the railway network has been becoming denser. Technical difficulties may arise in both the construction and service stages of railway, and the use of composite materials provides a new solution. Based on rational optimization of materials and structures, composite materials have solved some difficulties and gradually been used in railway infrastructure. However, due to the special requirements of railway infrastructure, the application of composite materials has still been restricted and their potential has not been fully unleashed. To promote the further development of composite materials in railway infrastructure, the state-of-the-art of the research and application of composite materials in railway infrastructure were reviewed, their development prospects and the problems hindering their development were analyzed. Finally, the development directions for future were proposed.
With the advancement of material science and industrial technology, composite materials have gained rapid development and been widely used in multiple fields. Currently, the railway has been booming in China, with the increase in railway mileage each year, the railway network has been becoming denser. Technical difficulties may arise in both the construction and service stages of railway, and the use of composite materials provides a new solution. Based on rational optimization of materials and structures, composite materials have solved some difficulties and gradually been used in railway infrastructure. However, due to the special requirements of railway infrastructure, the application of composite materials has still been restricted and their potential has not been fully unleashed. To promote the further development of composite materials in railway infrastructure, the state-of-the-art of the research and application of composite materials in railway infrastructure were reviewed, their development prospects and the problems hindering their development were analyzed. Finally, the development directions for future were proposed.
2024, 54(6): 197-205.
doi: 10.3724/j.gyjzG24041501
Abstract:
To study the mechanical properties of chopped basalt fiber-reinforced cement-based composites, 84 compressive specimens, 72 flexural specimens and 140 tensile specimens were designed and tested. The effects of water-cement ratio, fiber content, fiber length and surface alkali resistant coating treatment on the basic mechanical properties of chopped basalt fiber-reinforced cement-based composites were studied. The results showed that the addition of chopped basalt fibers could effectively improve the compressive, flexural and tensile failure modes of cement-based composites. The compressive strength of the composite decreased with the increase of the content of chopped basalt fibers and the decrease of fiber length. The 28 d compressive strength of the experimental group with the fiber length of 12 mm and the volume content of 2% decreased by 28.8%. In addition, the inclusion of chopped basalt fibers could significantly improve the flexural strength and tensile strength of cement-based composites. When the fiber length was small, the low content had a more significant effect on the flexural strength and tensile strength of the composites, and when the fiber length was large, the high content was more significant. The flexural strength and tensile strength of 28 d composites with 2% volume content of 12 mm fibers and 0.5% volume content of 6 mm fibers increased by 97.6% and 41.4%, respectively, and the tensile strength increased by 200.7% and 230%, respectively.
To study the mechanical properties of chopped basalt fiber-reinforced cement-based composites, 84 compressive specimens, 72 flexural specimens and 140 tensile specimens were designed and tested. The effects of water-cement ratio, fiber content, fiber length and surface alkali resistant coating treatment on the basic mechanical properties of chopped basalt fiber-reinforced cement-based composites were studied. The results showed that the addition of chopped basalt fibers could effectively improve the compressive, flexural and tensile failure modes of cement-based composites. The compressive strength of the composite decreased with the increase of the content of chopped basalt fibers and the decrease of fiber length. The 28 d compressive strength of the experimental group with the fiber length of 12 mm and the volume content of 2% decreased by 28.8%. In addition, the inclusion of chopped basalt fibers could significantly improve the flexural strength and tensile strength of cement-based composites. When the fiber length was small, the low content had a more significant effect on the flexural strength and tensile strength of the composites, and when the fiber length was large, the high content was more significant. The flexural strength and tensile strength of 28 d composites with 2% volume content of 12 mm fibers and 0.5% volume content of 6 mm fibers increased by 97.6% and 41.4%, respectively, and the tensile strength increased by 200.7% and 230%, respectively.
