Fiber Reinforced Polymer Bars Research Articles

Bond durability performance of sand-coated BFRP bars in high-strength fiber reinforced concrete

The ever-increasing utilization of fiber-reinforced polymer (FRP) bars has led to a surge in research regarding their bonding properties with concrete. In this study, the bond durability behavior between high-strength fiber-reinforced concrete (FRC) and sand-coated basalt FRP (BFRP) bars was examined under three different environmental conditions including immersion in seawater solution at 50 °C for 3, 6, and 9 months, immersion in the sulfuric acid solution for 3, 6, and 9 months with an ambient temperature range of 20 to 30 °C, and exposure to 270 freeze–thaw cycles. A total of 60 pull-out samples were prepared using either basalt (B) fibers or polypropylene (PP) fibers. Plain concrete pull-out samples were served as controls. Test results revealed that all exposures have degraded the bond, leading to pull-out failure in all of the specimens. Exposure to 50 °C seawater was found to cause the most significant degradation. However, the use of basalt fibers helped to mitigate the loss of bond strength in the specimens when compared to plain concrete specimens. For example, after 3, 6, and 9 months of exposure to 50 °C seawater, bond strength retentions of 73.58%, 56.04%, and 34.47% were observed for basalt FRC (BFRC) specimens, compared to 39.64%, 49.37%, and 29.61% for plain concrete specimens. On the other hand, a lower retention in bond strength of 16.28% was recorded for polypropylene FRC (PPFRC) specimens at 9 months of exposure to 50 °C seawater. The bond stress-slip relationship of the tested bars was accurately predicted using two calibrated analytical models: the Eligehausen, Popov, and Bertero (BPE) model and the Cosenza, Manfredi, and Realfonzo (CMR) model. Notably, both models showed a strong correlation with the observed bond stress-slip relationships in the experiments.

Size effect on the compressive behavior of BFRP RC circular columns: Experiments and a size-dependent stress-strain model

To investigate the size effect on compressive performance of circular concrete columns reinforced with basalt fiber-reinforced polymer (BFRP) bars and spirals, nine geometrically similar columns were fabricated and tested under concentric compression. The variables tested were cross-sectional diameters (200, 400, and 600 mm) and transverse reinforcement ratios (1.2%, 2.2%, and 3.3%). The results evidently indicated the size effect on the confined strength, corresponding strain and deterioration rate (in the post-peak branch) of concrete core confined by BFRP spirals. Specifically, with the cross-sectional diameter changing from 200 mm to 600 mm, the maximum decreases in the confined strength and corresponding strain were 14.1% and 31.9%, respectively, while the maximum increase in the deterioration rate was 318%. In addition, the size effect on confined strength could be weakened with the increase of transverse reinforcement ratio. Increasing the transverse reinforcement ratio could enhance the load-carrying capacity as well as effectively increase the confinement strength and ductility. Finally, a size-dependent stress–strain model, which considers the size effect of confined strength, corresponding strain and deterioration rate, was developed for evaluating the confined behavior of FRP RC columns.

Experimental investigation on realistic model for local bond stress-slip relationship between ribbed GFRP bars and concrete

Due to the lack of relevant research, the effect of the lateral confinement provided by stirrups and concrete cover on the bond behavior between glass fiber-reinforced polymer (GFRP) bars and concrete is ambiguous, resulting in the lack of a practical bond slip theory of GFRP bars. Therefore, it is impossible to accurately analyze the load response of GFRP-reinforced concrete (RC) structures from the stress level. In this paper, the local bond behavior of ribbed GFRP bars was systematically analyzed by the beam-end tests. The test parameters include concrete strength, stirrup spacing, and concrete cover. In addition, a bond stress-slip model considering the bonding mechanism was proposed on the basis of the beam-end tests and previous research. The results show that, the development of concrete cracks is restricted due to the existence of stirrups, and the specimens tend to fail in pull-out failure with strong confinement of stirrups. With the increase in the lateral confinement level, the failure mode of specimens transits gradually and smoothly from splitting failure to pull-out failure. Meanwhile, the peak slip of specimens with splitting failure also increases, and its maximum value does not exceed the peak slip of the corresponding specimens with pull-out failure. The confining capacity of stirrups and concrete cover was unified by a proposed parameter K. Then, a bond stress-slip model based on parameter K was established to predict the bond behavior of ribbed GFRP bars.

Experimental Study and Discrete Analysis of Compressive Properties of Glass Fiber-Reinforced Polymer (GFRP) Bars.

Glass fiber-reinforced polymer (GFRP) has superior characteristics over traditional steel, such as lightweight, high strength, corrosion resistance and high durability. GFRP bars can be a useful alternative to steel bars in structures, specifically those in highly corrosive environments, as well as structures subjected to high compressive pressure such as bridge foundations. Digital image correlation (DIC) technology is used to analyze the strain evolution of GFRP bars under compression. It can be seen from using DIC technology that the surface strain of GFRP reinforcement is uniformly distributed and increases approximately linearly, and brittle splitting failure of GFRP bars happens due to locally occurring high strain at the failure stage. Moreover, there are limited studies on the use of distribution functions to describe the compressive strength and elastic modulus of GFRP. In this paper, Weibull distribution and gamma distribution are used to fit the compressive strength and compressive elastic modulus of GFRP bars. The average compressive strength is 667.05 MPa and follows Weibull distribution. Moreover, the average compressive elastic modulus is 47.51 GPa and follows gamma distribution. In order to verify that GFRP bars still have certain strength under compressive conditions, this paper provides a parameter reference for their large-scale application.

Bond performance of fiber reinforced polymer bars in normal- and high-strength concrete

The structural performance of reinforced concrete (RC) members depends on the bond between the reinforcing bars and surrounding concrete. Unlike steel bars, fiber-reinforced polymer (FRP) bars are manufactured with different fiber types (glass, basalt, carbon, and aramid) and have different mechanical properties and surface configurations (sand-coated, deformed, grooved, sand-coated over helical wrapping). These differences impact the bond performance between the FRP bars and concrete. This paper investigates the bond performance of new generation and different FRP bars embedded in concrete. A total of 87 pullout specimens were constructed and tested until failure. The test results are presented and discussed. The test parameters include (i) fiber type (glass or carbon), (ii) surface configuration (sand-coated, deformed, or grooved), (iii) No. 4 to No. 8 (13 to 25.4 mm diameter) bar diameters), and (iv) concrete strength (normal- or high-strength concrete: NSC or HSC). Specimens with deformed 10 M or 15 M steel bars were also fabricated as controls and tested for comparison. The embedment length and block dimensions were also considered to ensure pullout-failure mode. The test results reveal that increasing the bar diameter generally reduced the bond strength of the FRP bars, while the bar diameter had insignificant impact on the steel bars. There was a positive relationship between the concrete compressive strength and the bond strength gained. The anticipated failure modes with the high concrete strength were at the fiber resin interface due to the high confinement generated by high-strength concrete. With the lower strength, failure usually occurred at the resin–concrete interface. In addition, the test results were used to assess different analytical models for bond stress-slip relationships.

Swaged couplers for splicing GFRP reinforcing bars

Fiber-reinforced polymer (FRP) reinforcing bars are used as reinforcement in concrete structures mainly due to their non-corrosive property. FRP bars are anisotropic and use a thermoset resin as a matrix to embed the fibers. Lap splicing is the conventional method for connecting or splicing FRP bars; however, it may result in significant construction challenges due to the long development length requirements of FRP reinforcement. Mechanical splices are alternatives where lap splicing is not practical or causes congestion. The lack of an efficient mechanical splice for FRP bars is a limitation for the full deployment of the composite reinforcement in concrete construction. This paper focuses on an experimental investigation conducted on splicing No. 4 (13 mm nominal bar diameter) Glass FRP (GFRP) bars using swaged steel couplers. The investigation only addressed short-term strength and did not cover the durability performance of the coupler. Three types of swaged steel couplers, four splice lengths, and three surface deformations for GFRP bars were studied. The ultimate strength of the spliced GFRP bars, the coupler’s strength, and failure modes were determined by conducting pull-out tests. The test results showed that spliced GFRP bars could achieve up to 97% of the guaranteed tensile strength as per ASTM D7957 when a 102 mm long low-carbon steel coupler is used and a pressure less than 20 MPa is applied for swaging.

Flexural behavior and serviceability performance of SSC beams reinforced with hybrid GFRP-stainless steel bars

Using fiber-reinforced polymer (FRP) bars instead of steel bars to reinforce concrete structures has become an important method to solve the corrosion problems. FRP bars reinforced concrete (FRP-RC) beams suffer sudden failure owing to the brittleness of FRP bars. Therefore, it is suggested to add steel reinforcements in FRP-RC beams to improve the ductility. This study analyzes the flexural performance of seawater and sea sand concrete (SSC) beams reinforced with hybrid GFRP and stainless steel (SS) bars, in which GFRP bars are used as tension bars while SS bars are used as compression bars. The flexural performances of GFRP bars reinforced SSC beams and SS bars reinforced SSC beams were also studied for comparison. Based on the test results, the cracking moment, load-carrying capacity, deflection, and ductility of the SSC beams are discussed and compared with the guidance in current design codes. Results show that ACI 440.1R-15 and CSA S806-12 reasonably predict the cracking moment and bearing capacity, but both underestimate the deflection at the service load. Furthermore, the moment capacity calculation equation is proposed with good accuracy. The ratio between the reinforcement ratios of GFRP bars and SS bars is suggested to meet the ductility requirement.

Bonding Performance of Glass Fiber-Reinforced Polymer Bars under the Influence of Deformation Characteristics.

Glass fiber-reinforced polymer (GFRP) of high performance, as a relatively ideal partial or complete substitute for steel, could increase the possibility of adapting structures to changes in harsh weather environments. While GFRP is combined with concrete in the form of bars, the mechanical characteristics of GFRP cause the bonding behavior to differ significantly from that of steel-reinforced members. In this paper, a central pull-out test was applied, according to ACI440.3R-04, to analyze the influence of the deformation characteristics of GFRP bars on bonding failure. The bond-slip curves of the GFRP bars with different deformation coefficients exhibited distinct four-stage processes. Increasing the deformation coefficient of the GFRP bars is able to significantly improve the bond strength between the GFRP bars and the concrete. However, while both the deformation coefficient and concrete strength of the GFRP bars were increased, the bond failure mode of the composite member was more likely to be changed from ductile to brittle. The results show members with larger deformation coefficients and moderate concrete grades, which generally have excellent mechanical and engineering properties. By comparing with the existing bond and slip constitutive models, it was found that the proposed curve prediction model was able to well match the engineering performance of GFRP bars with different deformation coefficients. Meanwhile, due to its high practicality, a four-fold model characterizing representative stress for the bond-slip behavior was recommended in order to predict the performance of the GFRP bars.

Serviceability behavior of High Strength Concrete I-beams reinforced with Carbon Fiber Reinforced Polymer bars

Fiber Reinforced Polymer (FRP) bars are anisotropic in nature and have high tensile strength in the fiber direction. The use of High-Strength Concrete (HSC) allows for better use of the high-strength properties of FRP bars. The mechanical properties of FRP bars can yield to large crack widths and deflections. As a result, the design of concrete elements reinforced with FRP materials is often governed by the Serviceability Limit States (SLS). This study investigates the short-term serviceability behavior of FRP RC I-beams. Eight RC I-beams reinforced with carbon-FRP (CFRP) and four steel RC I-beams, for comparison purposes, were tested under two-point loading. Deformations on the concrete and crack widths and spacing are measured and analyzed. A discussion on the main aspects of the SLS of FRP RC is introduced. The service load that fulfills the serviceability requirements, at a cross-section level, ranges between 0.27 and 0.38 times the ultimate load for sections dimensioned to fail in concrete crushing. The determinant criterion is the deflection limitation

Flexural and deflection behaviour of synthetic fibre reinforced concrete beams reinforced with glass fibre reinforced polymers bars under sustained service load

Glass fibre reinforced polymers (GFRP) bars have attracted increasing interest as a promising alternative for conventional steel reinforcement for its contribution towards sustainability and significantly improving the flexural performance of structural members. To mitigate the excessive deflections and crack widths exhibited by the FRP reinforced concrete members, fibre reinforced concrete (FRC) is employed which improves the toughness and cracking capacity of members. However, available research on the structural performance of FRC has focused on metallic fibres. The research presented in this paper is aimed at experimentally evaluating the influence of synthetic fibres on the time-dependent flexural behaviour of FRC beams reinforced with GFRP bars. Eight simply supported beams with varying synthetic fibre contents and GFRP bar diameters (but same reinforcement ratio) were tested under sustained service load. Creep under compression, concrete shrinkage, cracking moment, and deflection behaviour over 90 days were monitored and analyzed. Investigation revealed that the inclusion of synthetic fibres reduced the concrete deformations under creep and shrinkage by up to 22% and 26% respectively, increased the cracking capacity by 27%, increased the effective moment of inertia by 75%, and also resulted in up to 43% lower deflections. Suitability of several codes to predict the deformations and deflections under short and long-term conditions was also evaluated through comparison of the prediction models to the experimental results. Model proposed by ACI 440.1R-15 was found to predict the instantaneous deflection in beams without fibres with reasonable accuracy, however in FRC-GFRP beams, all models tend to overestimate the deflection. Presented research highlights the need for further investigation on non-metallic fibres and their contribution towards improvement of residual and flexural performance of FRC members to improve the validity of existing analytical prediction models.

Effect of Fire on Concrete Contribution to ShearResistance of GFRP RC Beams

The use of fiber-reinforced polymer (FRP) bars is becoming commonplace in various civil engineering applications due to the several advantages they offer over traditional materials. However, limited knowledge about some aspects of the behavior of FRP bars, particularly when subjected to severe fires, is hampering their widespread use. This paper presents the results of a research program to investigate the shear behavior of glass-FRP (GFRP)-reinforced beams exposed to severe fires. Three reinforced concrete (RC) beam specimens with a cross-sectional width and height of 150 mm and 300 mm, respectively, and with a total length of 1700 mm were constructed and tested under four-point bending load up to failure. The main test variables were the reinforcement ratio and the fire. The experimental results show that all beams failed as a result of diagonal tension cracking. The shear resistance and stiffness of the RC beams decreased when the beams are exposed to fire at the same reinforcement ratio. Keywords: GFRP bars, reinforced concrete beams, fire, shear capacity, crack patterns, modes of failure.

Improving corrosion resistance of BFRP bars by coating CNTs modified resin in simulated pore solution of seawater sea sand concrete

The corrosion of basalt fiber-reinforced polymer (BFRP) bars restricts their use in alkaline concrete structures. However, developing high-performance resin can improve the anti-alkaline corrosion of BFRP bars. This work investigates the alkaline resistance of BFRP bars by coating carbon nanotubes (CNTs) modified epoxy resin incorporating varying CNTs contents (0, 0.1, 0.3, and 0.5 wt%). The durability of untreated and treated BFRP bars with CNT-modified resin was evaluated using water uptake, transverse shear, and interlaminar shear tests. Scanning electron microscopy (SEM) and X-ray micro-computed tomography (micro-CT) were also used to observe the surface corrosion morphology and interior deterioration of BFRP bars, respectively, while Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were applied to analyze the resin deterioration of BFRP bars. It was found that CNTs modified resin can significantly improve the alkaline resistance of BFRP bars. After 180 d of immersion, the interlaminar shear strength (ILSS) retention of untreated BFRP bars is 31.8%, while it is 63.3, 75.0, 91.3, and 93.7% for BFRP bars treated with 0, 0.1, 0.3, and 0.5 wt% CNTs modified resin, respectively. The improvements in ILSS retention of BFRP bars treated with 0.5 wt% CNTs modified resin are 61.9% and 30.4% more than untreated and pure resin-treated BFRP bars, respectively. BFRP bars treated with 0.3 and 0.5 wt% CNTs modified resin exhibit insignificant resin hydrolysis and less porosity than untreated BFRP bars. The effective prevention of hydroxyl ions into the interior of BFRP bars and the enhancement of the anti-crack behavior of resin by CNTs are the leading causes of corrosion resistance improvement in BFRP bars. The outcomes of this study provide insights into using CNTs modified resin to improve the durability of BFRP bars in marine concrete structures.

Shear Contribution of GFRP Reinforced Concrete Beams Mixed with Seawater, Freshwater, and Chopped Glass Fiber

The behavior and shear strength of concrete beams reinforced with longitudinal GFRP bars mixed with seawater are the subject matter of experimental research discussed in this paper. Seven beams were tested in bending to determine how much concrete contributes to shear resistance. The beams were longitudinally reinforced with glass fiber-reinforced polymer bars and were similar in size and concrete strength; however, they were not even shear-reinforced. The 3,100 mm long, 400 mm deep, and 200 mm wide beams underwent thorough testing until the failure. The test parameters included chopped fiber content (0, 0.5, 2, and 3 kg/m3), longitudinal reinforcement ratios (1.0, 1.4, and 2.0%), and mixing water type (freshwater and seawater). The test findings showed that Increasing the reinforcement ratio raised the neutral-axis depth, enabled the formation of more closely spaced cracks, and minimized the loss of flexural stiffness after cracking, according to the test results. The contribution of aggregate interlock as well as the contribution of uncracked concrete are both enhanced through increasing the area of concrete in compression. Additionally, increasing the reinforcement ratio enhances the dowel action, which reduces the tensile stresses produced in the surrounding concrete. Keywords: Seawater; Chopped Fiber; Fiber-Reinforced Polymer (FRP); Shear Strength.

Review on degradation behavior of fiber-reinforced polymer bars in marine environments

Review on degradation behavior of fiber-reinforced polymer bars in marine environments

Experimental Study and Numerical Modelling on Flexural and Shear Strengthening of RC Beam with Prestressed FRP Bars

Abstract: The most prevalent and widely used building material in the world is reinforced concrete. The primary building material for the majority of constructions, including buildings, bridges, etc., is reinforced concrete. Because of various factors, some of these buildings or portions of them are failing to perform as designed. The best solution to increase the load carrying capacity and extend the useful life of these inadequate structures is to strengthen them because replacing them would need significant investments and not be an appealing alternative. Even though the effectiveness of other techniques is widely accepted,a new effective and promising technique of strengthening civil engineering structures externally is gaining popularity, where fibre-reinforced polymer (FRP) is used. One of the most popular strengthening methods recently is the use of carbon fibre reinforced polymer (CFRP) to strengthen reinforced concrete beams. It provides a desirable way to improve the shear and flexural strengths of RC beams. The manner in which these composites are bonded to the beam has a significant impact on the behaviour of reinforced concrete beams in shear and flexure. The purpose of this study was to present a three-dimensional nonlinear finite element analysis (FEA) of a reinforced concrete beam (RC beam) reinforced by prestressed carbon fibre plate (CFRP plate). While there are many commercial programmes available for three-dimensional nonlinear FEA, each one has a unique ability to represent complex behaviour of composite materials, such as RC beams strengthened with prestressed CFRP plate and the contact interaction. Because of its reputation for accuracy in simulating the behaviour of a range of materials, including concrete, and its potent contact algorithms, the ABAQUS finite element programme was chosen for this work. Steel reinforcements were modelled as elastic- perfectly plastic materials, while concrete was studied using the concrete damage plasticity (CDP) constitutive model. The CFRP plate was modelled as an entirely elastic substance that breaks under the highest tensile strain. Concrete and steel reinforcement were considered to have a perfect connection, and the behaviour of concrete and CFRP plate was represented using a contact model. The FEA's findings were verified against experiment findings that were published in the literature. In terms of load-deflection behaviour, crack patterns, and mode of failure, the results were compared. The proposed FEA model was able to accurately simulate the behaviour of RC beams strengthened with prestressed CFRP plate based on the validation. To find out the impact of the thickness, width, and length of the CFRP plate, as well as the prestressing levels and steel grades, a parametric research was done. In particular, the strength of the RC beam for the ultimate load was shown to be increased by increasing prestressing of the CFRP plate. However, as prestressing increased, the fracture of the CFRP plate altered the mechanism of failure, preventing the ultimate load from increasing further. The use of higher grade steel improved the ability to support additional weight. Although the general load carrying capability of the CFRP plate was increased by lengthening the plate, it was discovered that strengthening RC beams by 25% of their shear span was sufficient and cost- effective. The load-deflection curve, failure modes, and crack patterns from the experiments are fairly reflected in the FE model.

NSM and hybrid techniques for retrofitting corroded RC beams using GFRP bars

This is an experimental study on the flexural performance of corroded reinforced concrete (RC) beams strengthened by three different methods using Glass Fibre Reinforced Polymer (GFRP) bars. Three methods of strengthening were used: the traditional method of replacing damaged concrete covers and installing GFRP bars, the near-surface mounted (NSM) method, and a hybrid method involving mechanical fasteners and the NSM method. In total, seventeen RC beams were constructed one of which was used as a control specimen, while the remaining sixteen were divided into four groups and were exposed to accelerated corrosion to reach a theoretical mass loss of 3.5 to 30% in tensile steels. Three groups of corroded beams were strengthened using the three methods mentioned, while the other group received no strengthening. Then, all the beams were tested under four-point loading to determine their load-deflection response, stiffness, ductility, failure mode, and strain of the GFRP bars. The results showed that the conventional strengthening method using GFRP bars was relatively efficient in restoring the load-bearing capability of corrosion-damaged beams. However, sufficient anchorage length for the GFRP bars was required to achieve high ductility. The NSM method effectively improved the load-bearing capacity of beams with low corrosion levels; however, increasing the corrosion level caused the strengthened beams to fail prematurely due to concrete cover separation. It was observed that the hybrid strengthening method improved the load-bearing capacity of corroded beams while maintaining their ductility by preventing premature failure due to concrete cover separation.

A comparative life cycle assessment of fiber-reinforced polymers as a sustainable reinforcement option in concrete beams

Environmental awareness and the need for sustainable construction inspired researchers and practitioners to explore innovative alternatives that might reduce greenhouse gas emissions and energy use related to excessive structural work. One such alternative is the utilization of Fiber-Reinforced Polymer (FRP) bars as a reinforcement in reinforced concrete members. FRP bars possess favorable characteristics like high tensile strength, lightweight and corrosion resistance compared to steel. This feature makes FRP bars a potential solution for utilizing seawater instead of fresh water in concrete mixtures, especially in areas facing a harsh climate and water shortage like the Arabian Peninsula. This paper aims to assess and evaluate the environmental impacts through life cycle assessment of glass fiber-reinforced polymer bars, carbon fiber-reinforced polymer, and steel glass fiber reinforced polymer bars compared to steel bars. Moreover, another LCA was conducted comparing steel-reinforced beams made with desalinated fresh water to GFRP/CFRP reinforced beams made with seawater for the concrete mixture. The results indicate that the GFRP bar performed better than the steel bar in 10 out of 14 categories, while the carbon fiber-reinforced polymer bar performed worse than the steel bar in 10 out of 14 categories. The SGFRP bar had a result between the steel and GFRP bar, outperforming the steel bar in 10 categories. Furthermore, the GFRP beam exhibited better environmental performance than the steel beam in 9 out of 14 categories, while the CFRP beam performed better than the steel beam in 8 categories, attributed to the reduction in reinforcement ratio due to the high tensile strength of CFRP and GFRP bars compared to steel bars. Overall, this study sheds light on the possible environmental advantages of using FRP bars in construction and highlights the importance of sustainable construction practices in minimizing environmental impacts.

Bond performance of CFRP bars embedded in UHPFRC incorporating orientation and content of steel fibers

The bond behavior of carbon fiber-reinforced polymer (CFRP) bars embedded in ultra-high-performance fiber-reinforced concrete (UHPFRC) is a pivotal factor affecting the performance of CFRP bar-reinforced UHPFRC structures. The present investigation delves into the bond performance of CFRP bars in UHPFRC by conducting tests on thirty-six pullout specimens. In these tests, the effects of steel fiber orientation, steel fiber content, and CFRP bar diameter were considered. The results revealed that specimens with 12 mm-diameter CFRP bars primarily failed in a splitting-pullout mode, whereas those with 10 mm- and 8 mm-diameter CFRP bars exhibited pullout failure. It was observed that specimens containing 45° oriented steel fibers have the maximum bond strength (∼35.30 MPa), as the cracks within UHPFRC were more effectively constrained. The bond strength was found to increase with an increase in steel fiber content, attributed to the improved cracking resistance of UHPFRC. The average bond strengths of specimens with fiber contents of 2% and 2.5% are respectively increased by 10.66% and 14.52% compared to those with a fiber content of 1.5%. The bond strength increases with the increase in CFRP bar diameter, owing to the greater rib height and rib height-to-inner diameter ratio of larger-diameter CFRP bars. Finally, a theoretical model was developed to predict the bond strength, with an average ratio of predicted results to experimental results of 0.93 and a standard deviation of 0.176.

Investigating the Flexural Performance of Basalt Fiber Reinforced Polymer (BFRP) Bars at Elevated Temperatures

The FRP-reinforced concrete constructions may be subjected to elevated temperatures, which may compromise the structural integrity of the bars and, finally, the whole structure. As a result, the thermal stability of the FRP bars needs to be properly examined before they can be completely used in the construction field. Flexural strength testing has been utilized as a standard approach for determining the uniaxial tensile strength of brittle materials since it is less costly and easier to perform than the direct tension test. While the findings achieved were not absolute tensile data, they can offer a prediction of the relative tensile strength of the FRP bars. The flexural behavior of basalt fiber-reinforced polymer (BFRP) bars with different nominal diameters (8.0 mm, 10.0 mm, 12.0 mm, and 14.0 mm) exposed to increased temperatures (up to 150 °C) was examined in this research. According to the findings, when the temperature rises, the stiffness and flexural strength of the BFRP bars reduce. As the temperature approached the glass transition temperature (Tg) of the bars, a significant decrease in stiffness and strength was noted. These outcomes were also seen in other studies' pure tension tests of FRP bars. At higher temperatures, bigger nominal diameter bars are superior to smaller nominal diameter bars in terms of flexural strength decaying resistance. Although a comparable flexural stiffness degradation was noted as temperature increased.

Durability of bond between carbon/glass hybrid fiber-reinforced polymer (HFRP) bar and concrete in water

Glass-fiber-reinforced polymer (GFRP) bars have been widely used as a reinforcement in concrete, and glass fibers are susceptible to reacting with alkali ions in concrete pores. Thus, carbon fibers are wrapped around GFRP bars to produce carbon/glass hybrid fiber-reinforced polymer (HFRP) bars so as to promote the durability of the internal GFRP bars in concrete. This work studies the durability of the interfacial bond between GFRP bars/HFRP bars and concrete using pullout tests. The specimens are tested after immersion in distilled water for 0, 150, 255, and 544 days. The failure of the GFRP bar–concrete composite is due to damage to the GFRP bar, while the HFRP bar–concrete composite fails because of a combination of the scratching of the HFRP bar and the failure of the concrete. Both HFRP and GFRP bars are scratched as the immersion period extends. Further, the strength of the bond between the HFRP bar and concrete is lower than that of the bond between the GFRP bar and concrete, while the bond stiffness of the HFRP bar–concrete composite is higher than that of the GFRP bar–concrete composite. The bond strength of the HFRP bar–concrete and GFRP bar–concrete composites increases in the early immersion periods but decreases after 544 days of immersion in water. The retention of the bond strength of the HFRP bar–concrete composite is superior to that of the GFRP bar–concrete composite. The carbon fiber coat is proven to improve the durability of the bond between HFRP bars and concrete in water. A formula for predicting the bond strength of HFRP bar–concrete and GFRP bar–concrete composites in water is also developed. Finally, the modeling results demonstrate that the bond strength retention of the HFRP bar–concrete and GFRP bar–concrete composite is 76% and 46% after 50 years of service time, respectively.