Polymer Bars Research Articles

Non-Destructive Inspection Method Using Elastic Waves for Quality Management in the Bending Process Region of BFRTP

In order to establish a sustainable infrastructure, structures must maintain their minimum required performance for an extended period. Typically, existing concrete structures are reinforced with steel, but the susceptibility of steel reinforcements to corrosion, attributed to factors such as carbonation and chlorides, can lead to performance degradation, rendering the specified requirements unmet. As a remedy, there has been a growing interest in using lightweight and corrosion-resistant fiber-reinforced polymer (FRP) bars as an alternative to traditional steel reinforcement in concrete structures. Particularly noteworthy is the use of FRP bars manufactured with thermoplastic resins (FRTP) due to their ease of processing and convenient applicability on construction sites. This study delves into the mechanical behavior evaluation by examining the propagation characteristics of elastic waves in the curved section of basalt FRTP (BFRTP). Multiple BFRTP bars underwent a 180-degree bending process, subject to various conditions, including heat and twist variations. Subsequent measurements focused on the propagation characteristics of elastic waves in the curved sections, emphasizing wave attenuation, frequency features, and propagation velocity. Additionally, bending tensile tests were conducted on the curved bars, and a comparative analysis was performed between the tensile strength and the aforementioned elastic wave propagation characteristics. The results affirm a consistent correlation between the propagation characteristics of elastic waves (amplitude ratio, centroid frequency, velocity) during the traversal of the curved BFRTP section and its tensile strength. Notably, both centroid frequency and velocity exhibited correlation coefficients exceeding 0.7, suggesting their potential efficacy as reliable indicators for estimating tensile strength.

Bond durability between geopolymer-based CFRP composite and OPC concrete substrate in seawater environments

Geopolymer binders are regarded as promising environmentally-friendly approaches for repairing damaged structures because of their excellent bonding and durability. The interfacial bonding properties between the geopolymer and the damaged structures are critical to the effectiveness of the repair, however, the durability of this interfacial bonding in complex environments remains poorly understood, impeding the application of the aforementioned repair methods. Therefore, this study investigates the durability of the interfacial bond between geopolymer and ordinary Portland cement (OPC) concrete in seawater environments, providing valuable insights for engineering applications of geopolymer-based repair techniques. The adoption of OPC concrete as the substrate was based on its widespread use as a cementitious material in existing structures. Additionally, geopolymer repair mortars and epoxy resin were utilized as the bonding matrix adhered to the OPC concrete substrates, while small-diameter carbon fiber-reinforced polymer (CFRP) bars served as reinforcement for the bonding matrix. Single-shear tests were conducted to investigate the bond strength and failure modes between the geopolymer mortar/epoxy resin and OPC concrete substrates after 90, 180, and 360 days of exposure to a seawater environment. The interfacial degradation mechanisms were captured using scanning electron microscopy (SEM) techniques. The results showed that the interface between the geopolymer repair mortar and the OPC concrete was identified as the most vulnerable component, which dominated the failure of the geopolymer-bonded OPC concrete. SEM analysis revealed an increase in the microcrack width at this interface, resulting in a 2.86-times increase in slip between the geopolymer repair mortar and the OPC concrete after 360 days. Due to the degradation of epoxy caused by seawater exposure, the failure modes of the epoxy-bonded OPC concrete transformed from OPC concrete cracking to epoxy rapture with increasing exposure time. The bond strength of post-exposure epoxy-bonded OPC concrete was higher than that of the geopolymer–bonded OPC concrete, but the former exhibited a more brittle failure behavior.

Bond performance between ribbed BFRP bar and seawater sea-sand concrete: Influences of rib geometry

To solve the corrosion problems of steel bars in reinforced seawater sea-sand concrete (SSC) structures, fibre reinforced polymer (FRP) bars are promising alternatives. The bond between FRP bars and SSC determines the capacity and serviceability limit states of structures composed by them. The rib geometry of FRP bars is one of the most important factors influencing their bond performances with concrete. However, it has not received sufficient attentions on existing studies and standards. Therefore, this study investigated the bond performance between SSC and ribbed basalt FRP bars with different rib geometry through pull-out tests on 36 specimens. It is found that the bond strength declined with the increase of rib width and dent width, while the increase of rib height improved the bond strength. The ultimate and residual slip were strongly correlated with the rib spacing. Finally, a bond strength model that can well predict the experimental results was proposed.

Numerical Study of Shear Behavior of Geopolymer Concrete Beam Without Stirrups

Abstract The need to develop the concrete industry has increased with the increase in environmental damage resulting from building and construction operations. In the present research, the Numerical study of shear behavior of geopolymer concrete beams without stirrups by using the ANSYS program. It also includes concrete modelling to study the behavior of geopolymer concrete (GPC). The longitudinal reinforcements of beams (without stirrups) were "basalt fiber reinforced polymer bars". In order to enhance the shear behavior of the specimens, various types of fibers were added to geopolymer concrete (GPC): "steel fibers (SF), synthetic polypropylene fibers (PF), polyvinyl alcohol fibers (PVF), and carbon fibers (CF)". A numerical analysis was performed by the ANSYS version 15 program to study many parameters affecting the shear behavior of geopolymer concrete, such as longitudinal reinforcements,, and the inclusion of the opening. The results indicated that using steel fibers (SF) in geopolymer concrete increased the load failure of the tested specimens. On the other hand, using carbon fibers (CF) in the geopolymer concrete enhanced the ductility factor of these beams. The load capacity of the geopolymer concrete specimen is enhanced with longitudinal reinforcement by the CFRP bar compared to those reinforcements by BFRP bars. While the use of GFRP bars was less efficient than BFRP bars. Using FRP bars, and steel bars in strengthening geopolymer concrete beams with openings enhanced the failure load of these specimens.

Shear performance and strength of reinforced concrete non-prismatic beams with basalt fiber reinforced polymer rebars

Tapered beams, which are horizontal structural elements, possess varying moments of inertia across their length. Among these, the pier cap mode is widely employed in engineering applications. This research explores the influence of incorporating basalt fiber reinforced polymer (BFRP) bars on the shear strength of eight concrete haunched beams. While two of these beams were straight beams, the others have different inclination angles. The study aimed to examine two main factors: the angles of tapered part in the compression chord and the effect of BFRP stirrups. Results from the experiment revealed a direct correlation between increasing tapered angles and the enhancement of shear capacity in haunched beams. Consequently, a comprehensive analysis was conducted using three different codes, leading to the formulation of proposed equations derived from semi-empirical methods. The analysis demonstrated a high level of accuracy in predicting shear strength with a satisfactory safety margin.

Bond strength between ductile carbon/glass hybrid fibers-reinforced polymer bar and concrete through plate-type bond samples

The ductile carbon/glass hybrid fibers-reinforced polymer (C/G-HFRP) bar with excellent corrosion resistance is considered as an outstanding alternative to steel bar in structural concrete. The bond strength of C/G-HFRP bar to concrete plays a dominant contribution to fully realize the prominent properties of C/G-HFRP bar-reinforced concrete structures. In this work, the bond strength between ductile C/G-HFRP bar and concrete was investigated through a plate-type bond sample under direct pullout load. The effects of C/G-HFRP bar diameter, rib pitch, carbon/glass ratio, embedment length, concrete strength, cover thickness, bar type and sample type on the bond strength of C/G-HFRP bar to concrete were considered. The experiment outcomes revealed that the bond strength between C/G-HFRP bar and concrete by plate-type bond samples was 32.4 % lower than that by cube-type ones, resulting from that the influence of reaction frame on the crack propagation of concrete was eliminated during the loading procedure of plate-type bond samples. Also, the bond strength of C/G-HFRP bars to concrete increased with the tensile modulus, while the bond strength between C/G-HFRP bar and concrete was 48.5 % lower than that between steel bar and concrete. The failure mode of bond samples was controlled by the cover thickness of concrete when the compressive strength of concrete was not more than 55 MPa. Furthermore, the bond strength of sample was associated with the failure modes of test samples. The bond strength was decided by the mechanical properties of concrete when the bond sample happened splitting failure, while it was decided by the shear-resistant strength of flange ribs for C/G-HFRP bar when the failure mode of bond sample belonged to pull-out failure. Finally, the bond strength of C/G-HFRP bar to concrete was calculated by the thick-walled cylinder model.

Development of an artificial neural network based-prediction model for bond strength of FRP bars in concrete

Fiber-reinforced polymer (FRP) bars have garnered increasing attention in recent years due to their superior corrosion resistance, offering a potential solution to the significant drawback of steel corrosion in concrete. For the widespread utilization of FRP bars in concrete structures, determining the bond strength between FRP bars and concrete is a crucial topic. This study seeks to develop a prediction model to estimate the bond strength of FRP bars in concrete, utilizing an extended dataset from 1010 pull-out tests. Initially, the study evaluates the applicability of several bond strength formulas from existing codes. Subsequently, two prediction models, namely a multivariate linear regression model and an artificial neural network (ANN) model, are introduced for estimating the bond strength of FRP bars in concrete. The results indicate that the correlation between the evaluation values of existing formulas and the experimental value is very low. This is because these formulas have not yet been updated to encompass the expanded usage scopes of FRP bars with various surface processing methods and types of concrete. While the multivariate linear regression model outperforms these formulas, its accuracy is still relatively low; in contrast, the ANN demonstrates superior performance, achieving an R^2 value for both the validation and test set of more than 0.92. The findings highlight that, when considering a broader range of applications, the ANN serves as a robust tool for accurately predicting the bond strength of FRP bars in concrete, in comparison to traditional formulas and linear regression models. This assessment approach provides engineers with a convenient, high-precision tool for designs utilizing various forms of FRP bars and diverse types of concrete in practical design scenarios

Shear strength model of FRP-reinforced concrete beams without shear reinforcement

The current design codes for evaluating the shear strength of concrete beams reinforced with fiber-reinforced polymer (FRP) bars predominantly rely on a semi-empirical approach through test data calibration without a robust theoretical background. This approach may lead to either overestimation or underestimation, resulting in significant scattering in strength predictions. This study proposed a modified approach to enhance the existing unified shear-strength model developed for steel-reinforced concrete (RC) beams based on the compression zone failure mechanism, for predicting the shear strength of FRP-RC beams without shear reinforcement. The proposed model integrates strain and stress approaches, accounting for the distinctive characteristics associated with FRP reinforcement. Additionally, the overall shear resistance capacity of the FRP-RC beam is considered as the sum of contributions from the intact concrete of the compression zone and the aggregate interlock mechanism. The reliability of the proposed model is verified by comparing its predictions with a comprehensive database comprising 264 FRP-RC beam specimens without shear reinforcement reported by 41 research groups. Furthermore, the accuracy of the proposed model was assessed through a comparative analysis with existing evaluation methods, encompassing machine learning-based models, empirical models, theoretical models, and design codes. The results indicate that the proposed model satisfactorily predicts the shear strength of FRP-RC beams within a wide range of design parameters. In comparison with machine learning-based models, the proposed theoretical model exhibits a similar level of accuracy in terms of the mean shear strength ratio and coefficient of determination (R2) values but with less scattering, indicated by lower coefficient of variation (COV) and root mean square error (RMSE) values. In addition, the proposed model outperforms existing empirical and theoretical models, as well as current design codes, by significantly enhancing prediction accuracy, demonstrated by lower COV, RMSE, and higher R2 values. Finally, a parametric study was conducted to investigate the effects of the key parameters on the shear strength of FRP-RC beams using both the proposed model and representative existing evaluation methods.

Bond behaviour of staggered/non-staggered lap-spliced GFRP bars in concrete

This paper reports on the results of an experimental and analytical investigation into the bond behaviour of glass fibre-reinforced polymer (GFRP) splices in concrete. Eleven full-scale beam specimens in which GFRP bars were spliced within the constant-moment zone are examined. The study incorporates several key test variables, encompassing the ratio of bars lapped (33%, 50%, and 100%), surface characteristics (including sand-coated, ribbed, and wrapped bars), bar diameter (12 mm and 16 mm), and splice length (ranging from 30 to 40 times the bar diameter). The findings reveal a reduction in bond strength ranging from 12 to 24% for staggered bars when compared to their non-staggered counterparts. Furthermore, an increase in bar diameter is shown to decrease bond strength by 16%, whilst surface treatment also influences both bond strength and the pattern of cracking in the splice region. Increasing the splice length from 30 to 40 times the bar diameter enhances bar failure stress by 26%, but it also reduces the average bond strength by 9%. A new predictive equation for the design bond strength of fibre-reinforced polymer (FRP) bars is developed by utilizing a data base of 151 test results. The predicted bond strengths demonstrate greater consistency with experimental outcomes in comparison to previous models.

Design methods and recommendations for flexural concrete beams reinforced with steel-fiber composite bars

This study aims to establish a complete theoretical model for the nominal flexural strength of concrete beams reinforced with steel-fiber composite bars (SFCB-RC), and determine an optimized range for the ratio of the diameter of the steel core to the diameter of SFCBs (η). Firstly, flexural failure modes for SFCB-RC beams were determined through theoretical analysis, and two failure modes including concrete crushing (compression failure) and FRP in SFCBs rupturing (tension failure) were recommended. It was confirmed that there exists a transition region between the failure modes of tension and compression, where both modes are possible. By conducting a statistical analysis of a database including 57 SFCB-RC beams, an upper-limit reinforcement ratio was recommended for SFCB-RC beams in the transition region. Simplified equations to predict the nominal flexural strength for compression-controlled SFCB-RC beams were proposed by directly using the constitutive model of SFCBs. The flexural strength equations for tension-controlled concrete beams reinforced with fiber reinforced polymer bars (FRP-RC) were confirmed to be also suitable for SFCB-RC beams. Validation of these equations was conducted using the assembled database. Furthermore, the parametric analysis revealed an optimal range of the ratio η (0.77–0.87). This suggested range can serve as a basis for standardizing the production specifications of SFCBs.

Multiscale analysis of the flexural performance of FRP reinforced concrete structures

Based on existing experimental data and analysis, seven different fiber-reinforced polymer (FRP) bar models including carbon fiber-reinforced polymer (CFRP), basalt fiber-reinforced polymer (BFRP), aramid fiber-reinforced polymer (AFRP), glass fiber-reinforced polymer (GFRP), GFRP and CFRP combined (G–C), GFRP and AFRP combined (G–A), BFRP and CFRP combined (B–C), and BFRP and AFRP combined (B–A) were established. Finite element simulation analysis was conducted on seven different FRP bar combinations under static load bending tests. The flexural behavior of the specimens reinforced with different FRP bar combinations and their influencing factors were analyzed. The results showed that using AFRP as the reinforcement material for FRP composite bars in FRP reinforced concrete beams cannot effectively enhance the overall load-carrying capacity of the composite bars. The combination of CFRP with GFRP and BFRP bars significantly increases the stiffness of the FRP bar structure and improves the structural load-carrying capacity of the concrete beams.

Experimental Study on Flexural Behavior of RC Piles with Basalt Fiber-Reinforced Polymer Bars and Load Carrying Capacity Calculation

The practical application of BFRPB (Basalt Fiber-Reinforced Polymer Bars) as a support structure in foundation pit and slope engineering is relatively under-researched. The indoor tensile test presented in this paper is carried out on the bond between BFRPB and different labelled concrete. The mechanical characteristics of BFRPB, the failure characteristics, and the load-carrying capacity were analyzed. The results of this study demonstrate that the normal section stress of concrete cylindrical components with BFRP has a good linear relationship and supports the rationality of the flat section assumption. In circular reinforced concrete BFRP structures, the failure of the pile load occurs in four phases, and the cracking load is in the range of 51% to 67% of the normal yield load. The main bars increase in strain with load but become attenuated in the compression zone. The deformation of the main bars increases with the load but becomes muted in the compression zone. Based on the method of calculating the load-carrying capacity of GFRP-reinforced RC piles and the normal limit load-carrying moment obtained from in-door tests, the bending moment correction coefficient in the calculation formula for the load-carrying capacity of BFRP-reinforced RC piles was then obtained.

Comparative Performance Analysis of Small Concrete Beams Reinforced with Steel Bars and Non-Metallic Reinforcements

This research investigates the performance of small concrete beams that are reinforced with glass fiber-reinforced polymer (GFRP) bars, basalt fiber-reinforced polymer (BFRP) bars, and traditional steel bars. It addresses the limitations of traditional steel reinforcement, emphasizing the need for alternative strategies. Fiber-reinforced polymer (FRP) materials, including GFRP and BFRP, are examined for their mechanical characteristics compared to steel. The experimental program focuses on ultimate load-bearing capacity, deflection, deformation at different load levels, and failure modes. The concrete specimens, prepared according to Eurocode, consist of six small concrete beams measuring 80 × 120 × 1100 mm with varied reinforcements. The study reveals that GFRP-reinforced beams outperform BFRP and steel reinforcements in ultimate load-bearing capacity, showcasing enhanced structural performance. The GFRP-reinforced beams exhibit capacity and resilience characteristics surpassing those of both BFRP and steel, whereas the deflection observed was higher on both fiber-reinforced beams than on the steel-reinforced beams. The examination of failure modes reveals that the concrete beams that were reinforced with FRP bars showed a bending property before failure, while those reinforced with steel broke easily without bending much. This comprehensive research contributes to advancing our understanding of FRP materials’ application in concrete structures, paving the way for further optimization and overcoming limitations in reinforcement materials.

Durability of concrete-encapsulated GFRP bars subjected to seawater immersion

Glass fiber reinforce polymer (GFRP) bars have better durability than traditional steel bars, but there are few studies on their long-term performance in actual service environments especially the marine environment. To investigate the durability of GFRP bars used in cross-sea bridges, this research delves into the performance of 132 such bars, spanning diameters of 10, 12, 16, and 25 mm, in an environment that closely mimics real-world condition. The GFRP bars, encapsulated in concrete, were submerged in seawater solution, maintained at either room temperature or 60°C, for periods spanning from 0 to 183 days. Then the tensile strength and elastic modulus degradation of GFRP bars were investigated by tensile tests. Scanning electron microscope (SEM) was also used to analyze the micro-degradation mechanism of GFRP bars. In addition, this paper compares the four existing models for predicting long-term mechanical properties of GFRP bars with the experimental data, so as to determine the formulas and methods to be used in the design. The result shows that the elastic modulus of GFRP bars after 183 days of immersion in concrete pore solution was almost unchanged while the tensile strength decreased significantly. Among them, the tensile strength of 10 mm diameter GFRP bars decreased by 41.52 %, after 183 days of immersion at high temperature (60°C). The SEM method revealed that the main cause of such phenomena was the weakening of the bond between the fibers and matrix, which led to a decrease in the interface property. Finally, by fitting and comparing the relationship between the test data and the existing prediction models for the long-term mechanical properties of GFRP bars, the residual tensile strength of GFRP bars used in the actual project of Yanzhou Bridge for 100 years was predicted according to the optimal prediction model, i.e. the Serb model, and the results showed that the residual strength of GFRP bars is able to meet the current standard requirement.

Effect of BFRP ties on the axial performance of RC columns reinforced with BFRP and GFRP rebars

The adoption of fiber-reinforced polymer (FRP) bars in lieu of traditional steel reinforcement for concrete structures has gained prominence. Nevertheless, prevailing international standards have not incorporated provisions to assess the significant contribution of FRP materials to the axial capacity and deformability of compression members. This study investigates the impact of Basalt (BFRP) ties on the axial performance of full-scale concrete columns reinforced with BFRP and Glass (GFRP) rebars, alongside traditional steel longitudinal rebars. Ten columns were subjected to concentric loading, with parameters including the type of longitudinal rebars (BFRP, GFRP, and steel), spacing of BFRP ties (180 mm, 120 mm, and 60 mm), and diameter of steel rebars (16 mm and 20 mm). Varied steel rebar diameters aimed to discern the influence of axial stiffness on column behavior. Results indicate an 18 % to 26 % higher axial load capacity in steel-reinforced concrete (RC) columns compared to FRP-RC columns. Both types of FRP rebars contributed approximately 12 % to the axial capacity. Reducing BFRP tie spacing from 180 mm to 60 mm significantly increased deformability by up to 250 % in FRP-RC columns and ductility by up to 14 % in steel-RC columns. The study highlights conservative predictions in existing design equations (ACI 440.11–22 and CSA S806-12) for the axial load capacity of BFRP and GFRP RC columns, underestimating by 14 % to 20 %, as they neglect the contribution of FRP rebars. Utilizing a concrete crushing strain of 3,000 µε and 3,500 µε as the ultimate FRP compressive strain produced predictions closest to the experimental axial load capacity.

Experimental investigation on bond behaviour of the GFRP bars with normal and high strength geopolymer concrete

The study presents the experimental investigation of bond performance of normal and high-strength geopolymer concrete and Glass Fibre Reinforced Polymer (GFRP) bars. The effects of bar diameters, embedment lengths, and concrete grades on maximum pullout load and failure characteristics are investigated. When the adhesive and residual strengths of GFRP bond specimens were compared to steel specimens, the former demonstrated remarkable performance despite having differing surface properties. An energy-based equivalent bond strength approach is proposed to examine pre-peak bond performance, which demonstrating that the decreasing rate of strength is faster for higher diameter and embedment, showing a drop in bond performance. Pullout failure was noted in smaller diameter bond specimens, where the shear strength between the ribs and the GFRP bar controlled the bond strength. Concrete split failure occurs for 12 mm specimens with embedment lengths greater than 5d in both GPC40 and GPC60. Specimens with 16 mm, excluding G-16-5d-60, demonstrated concrete split failure for all embedment lengths and concrete grades; bond strength is determined by the concrete shear strength. Enhancing the concrete’s compressive strength has a beneficial impact on the bond strength as it increases ranging, from 14.57 to 32.12%. Analytical models such as mBPE and CMR were employed to derive the mathematical expression for the bond stress versus slip curve. It was found that the curves of CMR model were typically closer to experimental curves than the mBPE model.

Shear Behavior of Precast Concrete Box Culverts Reinforced with Glass Fiber-Reinforced Polymer Bars under Concentrated Load

Shear Behavior of Precast Concrete Box Culverts Reinforced with Glass Fiber-Reinforced Polymer Bars under Concentrated Load

Concrete Structures Reinforced with FRP BAR

Abstract: Fiber reinforced polymer (FRP) bars have been widely used in civil engineering used as a substitute for steel reinforcement because it has many advantages such as high strength-to-weight ratio, electromagnetic neutrality, light weight, ease of handling and no corrosion. Moreover, the productive technology becomes more and more mature and industrialized so that FRP has become one economic and competitive structure material. Based on the recent researches, this paper mainly introduces progress in the studies on concrete structures reinforced with FRP bars. These contents in this paper includes the bond performance of FRP bars in concrete, Compression Behavior, flexural behavior, and ductility of concrete structure reinforced with FRP bars in the past few years in the world .

Study on the bond properties between BFRP bars and hybrid fibers reinforced recycled concrete under freeze-thaw cycles

To study the bond properties between basalt fiber reinforced polymer (BFRP) bars and hybrid fibers which were basalt fiber (BF) and polypropylene fiber (PF) reinforced recycled concrete under freeze-thaw cycles, conducting center pull-out tests to study the effects of three factors on the bond properties: the number of freeze-thaw cycles, the volume fractions of single fiber, and the volume fractions of hybrid fibers. Based on the data obtained from the test, establishing a four-stage bond-slip constitutive relationship model. The results showed that the failure modes were pull-out failure and splitting failure. The bond strength decreased when adding the single fiber, with a maximum reduction of 13.18%, but the peak slip increased, with a maximum increase of 69.92%. When the volume fraction of BF was 0.3%, it achieved the optimal effect. The bond strength and peak slip increased when adding hybrid fibers, with maximum increases of 13.47 and 130.08%, respectively. However, excessive fiber content will reduce the increase of bond strength. The bond strength between BFRP bars and hybrid fiber-reinforced recycled aggregate concrete (HFRAC) increased when the number of freeze-thaw cycles increased but decreased when the number of freeze-thaw cycles exceeded 50. The four-stage bond-slip constitutive relationship model fitted well with the bond-slip curves. Compared with other fiber-reinforced recycled concrete specimens, this model fitted better with the curves of HFRAC specimens after freeze-thaw cycles and had the best fitting effect for the internal crack slip stage of the curves.

Bond performance of NSM FRP–concrete interfaces with epoxy under chloride‐salt conditioned environments

AbstractConcrete in coastal areas is susceptible to structural damage caused by corrosion and expansion of reinforcement. Near‐surface mounted (NSM) fiber‐reinforced polymer (FRP) bars have become effective for strengthening damaged reinforced concrete structures. The bonding performance of NSM FRP bars in concrete is a key factor limiting their application and promotion in civil engineering. In this study, the influences of the conditioned environment, such as the chloride salt concentration, immersion time, and bond length of the FRP bar, on the bonding performance were investigated experimentally. First, material properties in a conditioned environment were studied. Subsequently, the failure mode, bond stress–slip curve, and bond strength of the NSM FRP bar in concrete were investigated. Finally, the microstructure and chemical composition of the materials were revealed using scanning electron microscopy and energy‐dispersive spectroscopy (EDS) images of the materials under environmental conditions. The transfer mechanism of NSM FRP bars in concrete with epoxy was revealed. The results showed that the failure modes of the pullout specimens can be divided into epoxy splitting failure and basalt fiber‐reinforced polymer (BFRP) pulling failure. The chloride‐salt concentration was a critical factor affecting the bond properties, and the longer the bond length, the lower the bond strength. The microstructure clearly shows that the degradation of the bonding behavior at the interface of the NSM FRP bar in concrete in a conditioned environment is attributable primarily to the resin damage of the epoxy, resulting in pit corrosion. There was no significant damage to the fibers in the FRP bar, and the degradation was primarily due to resin matrix damage and interfacial debonding. The EDS results showed that the degradation of the epoxy resin and BFRP bars was caused by CO bond and SiO bond fractures, respectively.