Structural Performance of Fiber-Reinforced Cementitious Composite Members Reinforced with Fiber-Reinforced Polymer Bars: A Systematic Review

Abstract

The integration of fiber-reinforced cementitious composites (FRCCs) with fiber-reinforced polymer (FRP) bars represents a significant advancement in concrete technology, aimed at enhancing the structural performance of reinforced concrete elements. The incorporation of fibers into cementitious composites markedly improves their mechanical properties, including tensile strength, ductility, compressive strength, and flexural strength, by effectively bridging cracks and optimizing load distribution. Furthermore, FRP bars extend these properties with their high tensile strength, lightweight characteristics, and exceptional corrosion resistance, rendering them ideal for applications in aggressive environments. In recent years, there has been a notable increase in interest from the engineering research community regarding this topic, primarily to solve the issues of aging and deteriorating infrastructure. Researchers have conducted extensive investigations into the structural performance of FRCC and FRP composite systems. This paper presents a systematic literature review that surveys experimental and analytical studies, findings, and emerging trends in this field. A comprehensive search on the Web of Science identified 40 relevant research articles through a rigorous selection process. Key factors of structural performance, such as bond behavior, flexural behavior, ductility performance assessments, shear and torsional performance, and durability evaluations, have been documented. This review aims to provide an in-depth understanding of the structural performance of these innovative composite materials, paving the way for future research and development in construction materials technology.

1. Introduction

Conventional reinforced concrete (RC) has historically served as a cornerstone in construction, providing essential strength and stability. Nevertheless, its intrinsic limitations have prompted the investigation of alternative materials that can more effectively address the requirements of contemporary engineering practices. A significant issue associated with traditional RC is the corrosion of the steel reinforcement. This problem can result in serious consequences, such as concrete spalling, reduction in load-bearing capacity, and, ultimately, structural failure [1,2,3,4]. Low tensile strength, susceptibility to cracking, and the brittle behavior of concrete are the other challenges of conventional RC members [5,6]. In response to these issues, researchers and engineers introduced an alternative material, fiber-reinforced cementitious composite (FRCC) reinforced with fiber-reinforced polymer (FRP) bars.

FRCC is an advanced construction material that mixes regular cement-based materials, like concrete, with various types of fibers to enhance their mechanical properties and durability. Some of the fibers used in FRCC are steel fiber (SF), synthetic fibers such as polyvinyl alcohol (PVA), polyethylene (PE), polypropylene (PP), aramid fiber (AF), and basalt fiber (BF) [7,8]. FRCCs such as engineered cementitious composites (ECCs), strain-hardening cementitious composites (SHCCs), and ductile fiber-reinforced cementitious composites (DFRCCs) have been broadly studied for their ability to undergo strain-hardening, deflection-hardening, and multiple cracking property. These properties make them well-suited for structural applications that demand improved durability and crack resistance [6,9]. As shown in Figure 1, FRCC and concrete display distinct differences in their tensile stress–strain responses. Concrete typically exhibits a brittle failure upon reaching its tensile strength. Fiber-reinforced concrete (FRC) demonstrates strain-softening behavior until it reaches its cracking resistance. In contrast, the engineered cementitious composite (ECC) displays strain-hardening behavior up to the rupture point in the post-cracking phase [10]. FRCC made with various raw materials or different material ratios exhibits different mechanical properties under compression and tension. For instance, to enhance the mix, mineral admixtures such as silica fume (SF) [11], fly ash (FA) [12], and ground granulated blast furnace slag (GBFS) [13] can be used as mineral additives or as a partial replacement for cement.

FRP bars were introduced in the construction industry in the 1980s as an alternative material to traditional steel reinforcement. Numerous studies [1,2,4,14] demonstrated the benefits of using FRP bars over conventional steel bars, particularly in their durability and reduced maintenance requirements. These bars are made from a polymer matrix reinforced with various fibers, including carbon (CFRP), glass (GFRP), aramid (AFRP), and basalt (BFRP). FRP bars combine strength, lightweight characteristics, and resistance to environmental degradation. These properties make them particularly advantageous in applications where high tensile strength, corrosion resistance, and reduced weight are critical. The mechanical performance of FRP bars, including their tensile strength, modulus of elasticity, and fatigue resistance, allows for innovative design solutions in various structural applications. As the demand for durable and efficient materials continues to grow, understanding the mechanical properties of FRP bars is essential for engineers and designers seeking to enhance the longevity and performance of modern structures. Each type of fiber offers properties that can be tailored to meet specific structural requirements.

The structural performance of FRCC members reinforced with FRP bars is significantly influenced by the material properties of both the composite matrix and the reinforcement bar. Due to the high tensile strength capacity of the FRP bars and the post-cracking behavior of FRCC, these members exhibit greater load-carrying capacity compared to conventional RC members. One of the main challenges of using FRP bars is their lower modulus of elasticity, resulting in higher deflection. However, the FRCC’s ability to control crack width and delay crack propagation mitigates excessive deformation. The combination of FRP bars and FRCC helps maintain structural stiffness by reducing crack-induced flexibility [15]. Despite the numerous benefits of using a combination of FRP bars and FRCC materials, their application is constrained by several technical and regulatory challenges. The building codes and design standards for FRP materials are still in development [2]. Researchers are extensively examining the combination of FRCC and FRP bars to enhance structural performance, durability, and sustainability while developing comprehensive design guidelines and innovative applications.

This paper presents a systematic review of existing articles on the structural performance of FRP-reinforced FRCC members, including their bond behavior, flexural behavior, ductility performance assessments, shear and torsional performance, and durability assessment. This review aims to provide a thorough insight into the structural performance of these advanced materials, paving the way for future research and development in the field.

2. Research Methodology

A systematic literature review is a research approach employed to collect, identify, and critically assess existing studies through a structured methodology. Various methods and techniques can be employed to conduct a systematic review [16]. This research follows the guidelines outlined by the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines and is registered on the Open Science Framework (OSF) registries. The registration link can be found here [17]. The PRISMA checklist is used to ensure transparency, completeness, and accuracy of reporting in this paper. The evaluation was conducted in five stages: (1) defining objectives; (2) choosing databases; (3) identifying keywords; (4) selecting relevant papers; and (5) extracting data.

2.1. Searching Staratagy

The “Web of Science” database was used to conduct the literature search due to its extensive coverage of peer-reviewed journals, reliable citation tracking, advanced search features, and the ability to access interdisciplinary research, which collectively facilitate a thorough and efficient review of existing literature [18]. The searching criteria were “topic”, which includes “title”, “abstract”, and “keywords”. The keywords used to formulate the filtering query were “fiber-reinforced polymer”, “fiber-reinforced plastic”, “FRP”, “FRC”, “FRCC”, “ECC”, and “SHCC”. The search link can be found here [19]. Two hundred and three articles were found in the first search, then the number of articles was refined to only peer-reviewed articles by excluding conference proceedings and pre-print articles, which reduced the number of articles to 178. Further refining was carried out to select only those related to civil engineering, material science, construction, and building technology, which reduced the number of articles to 101. Finally, the title and abstract of the articles were manually selected to assess the relevant articles that focus only on structural performance, and 40 articles were selected. Figure 2 shows the flow of the article selection methodology using the PRISMA flow chart model.

2.2. Search Result

The study reviewed 40 articles published between 1999 and 2024. Recently, researchers have shown a growing interest in using fiber-reinforced polymer bars to strengthen fiber-reinforced cementitious composites. It is shown in Figure 3 that from 1999 to 2020, studies did not exceed an average of two articles per year. In 2021 and 2022, the number of articles increased to four and five per year. However, the most significant increase was in the past two years, 2023 and 2024, when there were six and nine articles published per year.

As shown in Figure 4, the selected publications are sourced from a range of academic journals. The journal “Construction and Building Materials” (nine articles) has the highest number of publications. Three journals, “Journal of Building Engineering”, “Structures”, and “Engineering Structures” have published five articles. The “Composite structures” journal published four articles, “Journal of Composites for Construction” published two articles, and the remaining nine journals have only one published article.

3. Bond Behavior and Bond Strength

A comprehensive understanding of the bond characteristics between FRP bars and FRCC is crucial for the successful integration of this emerging technology within the construction industry. In contrast to the research focused on the bond behavior between FRCC and traditional steel reinforcement, there exists a notable lack of studies addressing the bond performance of FRCC in conjunction with FRP bars. Additionally, the different surface properties of FRP bars make their bond behavior much more complicated than steel bars. The mechanisms that lead to bond failure at the interface between FRP bars and FRCC are still under investigation, and important factors such as the type of bar, its diameter, and surface design have not been adequately studied. Furthermore, the absence of a reliable model for the bond strength between FRP bars and FRCC complicates the design and evaluation of FRCC-FRP bar systems, limiting the practical applications of both materials in engineering [20]. Several researchers conduct experimental, numerical, and analytical investigations to study these bond characteristics [20,21,22,23,24,25,26,27,28,29].

Li et al. [21] carried out a theoretical analysis of the debonding mechanism between FRP and ECC using a thick-walled cylinder model. The proposed model aimed to enhance the understanding of the bond behavior between the materials by examining the bond stress–slip relationship. The validity of the model is confirmed through comparison with an experimental pullout test. As shown in Figure 5, the bond stress (bond shear stress)–slip relationship was categorized into three distinct stages: an elastic stage, a softening stage, and a frictional stage. The solution to the second-order differential equation governing the bond behavior of FRP bars along the bond length was derived by incorporating the three-stage linear bond stress–slip relationship. The influence of the nonlocal parameter resulted in an increase in slip during the elastic stage and a decrease during the softening stage, while the slip remained unchanged in the frictional stage. The model’s predictions for the pullout force aligned well with the experimental data. However, it was noted that the nonlocal parameters vary across different types of FRP bars.

3.1. Influence of Bar Diameter, Modulus of Elasticity, and Surface of the Bar

Several studies show that bond performance is highly influenced by the type of FRP bar, bar diameter, and the surface treatment and configurations.

Zhao et al. [20], Wang et al. [25] and Hossain et al. [23] reported that the average bond strength decreases when the diameter of the bar increases. During pullout testing, the bond stress is not uniformly distributed along the length of the bar; instead, it exhibits a gradual decrease from the loaded end to the free end. This stress distribution contributes to the lower bond strength observed in specimens with larger diameter bars. Additionally, the shear lag phenomenon further aggravates the reduction in bond strength as bar diameter increases. The differential movement between the core and the surface fibers under tensile loading leads to a non-uniform distribution of normal stress across the cross-section of the bar. As the diameter increases, this non-uniformity becomes more pronounced. Furthermore, the Poisson effect has also been identified as a contributing factor to the reduction in bond strength [26,30]. However, Zhao et al. reported that the finite element analysis conducted for the thick-walled cylinder demonstrated that the influence of the Poisson effect on bond strength is minimal [20]. Figure 6 shows the effect of bar diameter on bond strength. However, these general trends are not observed exclusively in combination with FRCC but have also been reported in the bond behavior between conventional concrete and FRP.

Hossain et al. [23] performed a bond test using RILEM beam test method using two types of GFRP bars: low/standard modulus “LM” and high modulus “HM”. The experiment results were compared against those obtained from established code-based design equations. It is reported that the bond strength of HM bars was lower than LM bars, which was primarily attributed to the premature detachment of sand coating from the rebar core. This issue is believed to be specific to the HM bar used for their study, prompting a recommendation for further investigations using commercially available HM bars. The bond strength measured from beam tests of both LM and HM bars embedded in ECC was found to exceed the prediction made by CSA S806-12 [31], CSA S6-06 [32], ACI440.1R-15 [33], and other existing predictions. Among these, ACI440.1R-15 provided a close value of bond strength prediction compared to the other equations, with a ratio of predicted to experimental values ranging from 1.18 to 1.49. Consequently, it is suggested that modifications to these codes are warranted to enhance the accuracy of bond strength predictions for ECC.

Figure 7 shows some examples of types of rebars and surface configurations. Zhao et al. [20] developed a simplified bond-strength model based on an experimental result of a direct pullout test that considered the FRP bars’ surface geometry, such as the rib spacing and rib height. The model is validated using a proposed equation for bond strength. The maximum bond strength value from the proposed equations demonstrated a strong correlation with the experimental results. It is important to note that this model specifically pertains to ribbed reinforcing bars, where bond failure is predominantly governed by shear failure of the matrix. For reinforcing bars with different surface treatments, a more comprehensive investigation is required to accurately assess the calculation of maximum bond strength.

Kim et al. [28] conducted an experimental investigation to study the bond–slip behavior of two types of GFRP bars, helically wrapped (HW-GFRP) and sand-coated (SC-GFRP), and a steel bar in PVA-ECC. From the experimental results, it is reported that the interfacial bond strength of HW-GFRP was much higher than that of SC-GFRP and similar to the steel bar. The overall energy absorption capacity of HW-GFRP bars exceeded that of conventional steel bars. In contrast, the SC-GFRP bars showed frictional pullout failure at the interface between the resin and the fiber reinforcement, along with reduced matrix splitting, irrespective of the properties of the matrix material.

3.2. Influence of Embedded Length

The bond strength reduced with an increase in embedded length. This reduction can be attributed to the calculation of bond strength based on the assumption of a uniform bond stress distribution. However, a more pronounced non-uniform distribution of bond stresses typically occurs with greater embedded lengths and the Poisson effect [23,25,30]. Wang et al. [25] reported that a greater load is needed to pull out the BFRP bar with increased embedment length. However, due to the Poisson effect, this extended embedment length results in a significant decrease in confinement and mechanical interlocking, subsequently reducing bond strength. Additionally, it has been reported that a linear relationship can effectively characterize the correlation between average bond strength and embedment length. Figure 8 illustrates the experimental findings regarding the influence of embedment length on the average bond strength of the BFRP bar.

Takasago et al. [22] studied the bond characteristics between braided AFRP and PVA FRCC and proposed a trilinear model for the bond stress–slip relationship, as shown in Figure 9. Pullout tests with varying bond lengths, fiber-volume fraction in FRCC, and cross-sectional dimensions were performed. The bond strength improved as both the amount of fiber and the size of the cross-section of FRCC increased, due to the fiber’s bridging effect along the cracks. The proposed model was checked using numerical analysis for longer bond lengths, and the results showed that the average bond stress–slip relationship matched well with the experimental results.

3.3. Influence of FRCC or ECC Characteristics

The FRCC or ECC characteristics are affected by many factors such as type of fiber, fiber-volume fraction, mix design, and curing age. The bond characteristics results of Takasago et al. [22] showed that the bond strength increased with the increase in fiber-volume fraction.

Wei et al. [27] evaluated the bond performance of GFRP bars embedded in normal-strength sea-water sea-sand ECC (SS-ECC) with PVA fibers and high-strength SS-ECC with PE fiber. A parallel test was also performed on GFRP bars in ECC made with fresh water (FR-ECC). In this study, it is reported that the influence of the saline content enhances the bold performance, and it refines the microstructures of ECC. This paper provided a more comprehensive understanding of the bond performance relationship with chemical adhesion, friction resistance, and mechanical interaction.

Table 1. The research plan and result summary of bond behavior.

Ref.	FRP Type	Fiber Type in FRCC	Study Type	Type of Test	Bond Strength (MPa)	Variables
Zhao et al. [20]	CFRP GFRP	PE	Experimental	Direct pull out	4–15	Bar diameter
Li et al. [21]	GFRP		Analytical			FRP type
	CFRP
Takasago et al. [22]	AFRP	PVA	Experimental and analytical	Direct pull out	6–9	Bond length
						Fiber-volume fraction
Hossain et al. [23]	GFRP	PVA	Experimental and analytical	RILEM beam method	9–22	Bar diameter Modulus of elasticity Embedded length
Cao et al. [24]	BFRP	PVA	Experimental and analytical	Direct pull out	10–20	Grade of ECC Surface of the bar
Wang et al. [25]	BFRP	PVA	Experimental	Direct pull out	9–15	Bar diameter Embedded length Cover thickness
Wang et al. [26]	GFRP	PVA	Experimental and analytical	Direct pull out	2–23	Grade of ECC Freeze–thaw cycle
Wei et al. [27]	GFRP	PVA PE	Experimental	Direct pull out	11–25	Fiber type Grade of ECC Testing age (curing time) Water type (fresh/sea water) Sand type (river/sea sand)
Kim et al. [28]	GFRP	PVA	Experimental	Direct pull out	17–27	Fiber-volume fraction FRP surface treatment (sand coated/helically wrapped)
Wu et al. [29]	GFRP	PVA	Experimental and analytical	Direct pull out	3–18	Grade of ECC Testing age (curing time)

provides an overview of the study design and findings reported by various researchers regarding the bond behavior between FRCC and FRP bars. The researchers employed different experimental setups to examine the bond strength. Figure 10 schematically shows the different setups used in the studies. From Table 1, it can be concluded that the bond performance of the FRP with FRCC is affected by variables such as FRP type, diameter of the bar, type of surface of the bar, modulus of elasticity of the bar, fiber type in the FRCC, fiber-volume fraction, bond length, grade of the matrix, environment, and so on.

4. Flexural Behavior

The flexural behavior of structural elements provides insight into their load-carrying capacity, failure mode, ductility, and overall performance under bending loads, which are essential for safe and effective structural design. The corrosion resistance of FRP combined with the superior mechanical properties of FRCC contributes to the durability and longevity of structures, reducing maintenance costs and ensuring safety. Additionally, insights gained from studying flexural behavior can inform innovative design solutions and optimize structural systems, ultimately contributing to the development of design guidelines and standards that ensure the safe and effective use of these advanced materials in construction. Several investigations have examined the flexural behavior of FRCC members reinforced with FRP bars [22,34,35,36,37,38,39,40,41,42,43].

Yuan et al. [34] investigated ECC beams reinforced with BFRP bars through an experimental program and proposed an analytical model for the moment–curvature relationship based on the conventional strip method developed for conventional concrete by Wu et al. [44]. It is reported that the deformation capacity of BFRP-reinforced ECC beams with reduced reinforcement ratios showed an improved deformation capacity, resulting from the higher ultimate compressive strain characteristics of ECC. When comparing beams with the same size and BFRP reinforcement configurations, ECC beams exhibited significantly greater ultimate load, ultimate deformation, and energy dissipation compared to conventional concrete beams. Notably, the removal of shear stirrups from the ECC beam resulted in only a marginal decrease in load capacity and deformation when compared to a concrete beam with dense stirrups, underscoring the effectiveness of ECC in enhancing shear capacity. In a parametric study of BFRP-reinforced ECC beams, it was observed that the maximum ultimate curvature was achieved at the balanced reinforcement ratio. An increase in the compressive strength of ECC markedly improved both the ultimate moment capacity and the ultimate curvature of the beam, particularly when failure was governed by ECC crushing in the compression zone. However, the ductility, defined as the ratio of inelastic energy to total energy, remained relatively constant with variations in ECC compressive strength, irrespective of the failure mode. The moment–curvature response of the BFRP-reinforced ECC beam was predicted using a strip model, which showed a strong correlation between experimental and analytical findings.

Cai et al. [35] analyzed the flexural behavior of ECC beams reinforced with BFRP bars using a nonlinear finite element model. The simulation outcomes were validated against experimental data published by Yuan et al. [34]. Through finite element analysis, the influence of various parameters on the mechanical behavior of BFRP-reinforced ECC beams was investigated. These parameters included compressive strength (CS) values of 30, 45, 60, and 75 MPa, ultimate tensile strain (TA) levels of 0.5, 1.5, 2.5, 3.5, and 4.5%, tensile strength of ECC (TE) at 2, 4, 6, and 8 Mpa, and longitudinal reinforcement ratios (LR) of 0.2, 0.4, 0.6, 0.8, and 1%. The findings, illustrated in Figure 11, indicate that the ultimate strength of the beams increased with all parameters, except for the tensile strain of ECC when it exceeded 1.5%. Additionally, the ultimate deflection was observed to rise with increasing compressive strength and tensile strain of ECC, while the ultimate tensile stress exhibited minimal influence on the ultimate deflection of BFRP-reinforced ECC beams. Furthermore, variations in the longitudinal reinforcement ratio were found to alter the failure mode of the ECC beams. Notably, for over-reinforced beams, an increase in the longitudinal reinforcement ratio resulted in a decrease in ultimate deflection. The simulation results showed good agreement with the experimental results.

Fischer et al. [36] examined the influence of the stress–strain characteristics of FRP bars on the load–deformation behavior of FRP-reinforced ECC members subjected to reversed cyclic loading conditions. An analytical model was formulated to represent the load–deflection envelope, which was derived from the moment–curvature relationship and the sectional stiffness of the flexural members as a function of the applied load. The findings indicated that the load–deformation response of FRP-reinforced ECC is predominantly governed by flexural deformation, even at substantial drift levels, with crack initiation appearing to be largely independent of the interfacial bond properties. The inelastic deformation of ECC under compressive loads results in a reduction in flexural stiffness and ultimately leads to a gradual failure mode. However, it concurrently induces compressive strain and reduces the tensile strength of the FRP reinforcement. The analytical model demonstrated reasonable agreement with the experimental results; nevertheless, it did not account for rotational sliding, which can significantly affect the flexural stiffness and strength in certain scenarios.

Zhou et al. [37] proposed a modified model that aimed at predicting the maximum crack width in ECC beams reinforced with CFRP bars, specifically within the service limit state. The calculation methodology for this model was based on the principles of the Chinese standard GB50608 [45]. However, certain empirical equations of the critical parameters were modified to better suit different types of matrix materials. Furthermore, the average crack spacing and coefficient for the strain distribution of the FRP bars were established through regression analysis of experimental data. As a result, the applicability of this modified model is confined exclusively to ECC beams reinforced with sand-coated CFRP bars under service limit conditions.

Takasago et al. [22] conducted a four-point bending test to investigate the correlation between reinforcement strain and crack width. The assessment of crack width was performed using a predictive formula that integrated the proposed bond model along with a fiber-bridging law. The findings indicated that the number of cracks increased with an increase in fiber-volume fraction in FRCC. Furthermore, the relationship between reinforcement strain and crack width derived from the bending test was consistent with the predictions made by the formula.

Al Marahla et al. [39,46] examined how synthetic fibers affect the short- and long-term flexural performance of GFRP beams, comparing their findings with established guidelines. Their study revealed that the addition of fibers led to reductions in tensile creep, compressive creep, and shrinkage strain by 15%, 22%, and 26%, respectively. Additionally, deflection decreased by 25% to 43% depending on the fiber-volume fraction used. The experimental outcomes were assessed against prediction models for both short-term and long-term deflection as outlined in ACI 440 [33], ISIS [47], and CSA [31], which were found to be inaccurate for FRC beams. While the creep and shrinkage strain prediction models from Eurocode 2 [48] and ACI 209 [49] aligned well with the compressive strain, they tended to overestimate shrinkage strains. The authors suggested that further research and adjustments to current methodologies are necessary to make them suitable for FRC beams reinforced with FRP bars.

Behnam et al. [42] proposed a model for estimating the flexural resistance factors for FRC beams that are reinforced with GFRP bars. To assess the reliability of this model, a Monte Carlo simulation was employed for calibration. The analysis utilized data from three previously published studies, Issa et al. [50], Wang et al. [51], and Alsayed et al. [52], which were based on experimentally obtained results for FRC reinforced with GFRP bars. The target reliability index used in this assessment aligned with that of the current design code specifications. The estimated flexural resistance factors were found to range between 0.72 and 0.95.

Attia et al. [40] and Abushanab et al. [41] studied basalt FRC members reinforced with BFRP bars and reported that basalt microfibers (BMF) enhanced the flexural performance of BFRP reinforced members in terms of load carrying capacities, cracking, and ductility.

Reinforced concrete structures are designed and maintained in adverse environmental conditions, where they are subjected to cycles of drying and wetting, freeze–thaw phenomena, carbonation, and chloride ingress. These factors contribute to the corrosion of the steel reinforcement and the deterioration of the concrete matrix. Consequently, these structures may not fulfill the requirements of the ultimate limit state and the serviceability limit state when exposed to corrosive environments [53]. As discussed in the introduction, FRP-reinforced FRCC structures can resist this harsh environment. Wang et al. [38] conducted experimental and analytical investigations on the flexural behavior of FRP-reinforced ECC specimens subjected to freeze–thaw cycles. They developed formulas for the balanced reinforcement ratio, moment capacity, and stiffness of FRC-reinforced ECC specimens, based on ACI 440 [33] and GB 50608 [45]. These formulas account for the tensile capacity provided by ECC materials. The proposed model demonstrated good agreement with the experimental findings.

Despite the numerous advantages associated with FRP bars, their limited fire resistance remains a significant limitation for their utilization in the construction industry. Investigating the post-fire performance of FRP-reinforced FRCC members is crucial for assessing their serviceability and structural integrity. Jafarzadeh et al. [43] conducted both experimental and analytical investigations to evaluate the flexural behavior of FRC beams reinforced with GFRP bars following exposure to elevated temperatures of 20 °C, 250 °C, 400 °C, and 600 °C. The findings indicated that the residual flexural performance of GFRP-FRC beams is significantly influenced by the temperature of exposure. It was determined that the deflection values predicted by the equations proposed by ACI 440.1R-06 [54] and ACI 440.1R-15 [33] closely aligned with the experimental results, whereas the equations proposed by CSA S806-12 [31] and Faza et al. [55] showed very distinct values. The authors recommended further research that considers the manufacturing processes of the FRP bars, the specific exposure conditions, and the duration of exposure to heat, as well as the cooling procedures applied to the specimens.

Table 2. Summary of the research for flexural behavior.

Ref.	FRP Type	Fiber Type in FRCC	Study Type	Type of Test	Variables
Takasago et al. [22]	AFRP	PVA	Experimental and analytical	Bending test	Fiber-volume fraction
Yuan et al. [34]	BFRP	PVA	Experimental and analytical	Bending test	Bar diameter Reinforcement ratio Presence/absence of shear reinforcement
Cai et al. [35]	BFRP	PVA	Analytical	Bending test	ECC characteristics Reinforcement ratio
Fischer et al. [36]	AFRP	PE	Experimental and analytical	Reversed cyclic loading	Reinforcement ratio FRP surface treatment
Zhou et al. [37]	CFRP and GFRP	PVA	Experimental and analytical	Bending test	Elastic modulus of FRP bar Reinforcement ratio FRP bar type
Wang et al. [38]	BFRP	PVA	Experimental and analytical	Bending test	Environmental conditions
Al Marahla [39,46]	GFRP	PP	Experimental	Bending test	Fiber-volume fraction FRP bar diameter
Attia et al. [40]	BFRP	BF	Experimental and analytical	Bending test	Fiber-volume fraction
Abushanab et al. [41]	BFRP	BF	Numerical		Fiber-volume fraction Stirrup spacing
Bahnam et al. [42]	GFRP	PP, GF, and SF	Analytical		Fiber-volume fraction Fiber type
Jafarzadeh et al. [43]	GFRP	SF	Experimental and analytical	Bending test	Temperature Reinforcement ratio

provides a summary of the research and findings reported by various researchers regarding the flexural performance of FRCC reinforced with FRP bars. From this table, it can be concluded that the flexural performance of FRP in combination with FRCC is influenced by several factors, and efforts have been made to understand the structural response under various loading conditions and environmental factors, including the effects caused by differences in materials used for FRP and FRCC.

5. Ductility Evaluation

To assess the ductility of members reinforced with FRP bars, various methods have been developed. These methods include the energy-based approach [56] and the deformation-based approach [57]. In the energy-based approach, ductility is defined as the ability to absorb energy, represented by the ratio of total energy to elastic energy. Conversely, the deformation-based approach evaluates ductility by examining the deformability margin between the ultimate and service stages, considering both strength and deflection. Figure 12 illustrates the ductility index definition.

Jafarazdeh et al. [43] used the deformation approach to determine the ductility factor of FRC beams reinforced with GFRP bars. It is reported that all the beams have failed due to the rupture of the bar. For this reason, the effect of the fiber had no noticeable effect on the ductility factor. They also reported that specimens with a higher reinforcement ratio showed a higher deformability factor. In this regard, increasing the reinforcement ratio and using discrete fibers indicated a positive effect on the concrete-crushing mode at higher temperatures when steel fiber was used.

Liao et al. [58,59] employed a modified deformation-based method to determine the ductility indices of BFRP bars in SS-ECC beams. As illustrated in Figure 13, the study examined how the longitudinal reinforcement ratio, shear span ratio, and stirrup ratio influenced the ductility indices. The findings indicated that the ductility index decreased with an increase in the longitudinal reinforcement ratio, while it increased with higher shear span and stirrup ratios.

Wang et al. [51] employed both energy-based and deformation-based methods to assess the ductility indices of GFRP-reinforced FRC beams. They found that the energy-based approach inadequately accounts for the influence of discrete fibers in the concrete, particularly regarding the improvement in ultimate moment capacity and the corresponding increase in deflection. On the other hand, the ductility index derived from the deformation-based method effectively describes factors like load capacity and the impact of deformation on ductility.

6. Shear and Torsional Performance

Liao et al. [59,60,61] developed a modified calculation model based on ACI 440.1R-06 [54] to predict the ultimate shear capacity of SS-ECC beams reinforced with BFRP bars. The ratio of the predicted values to the experimental results was 0.97, indicating a good agreement between the model and the experimental findings. As illustrated in Figure 14, the experimental data revealed that SS-ECC beams with a low longitudinal reinforcement ratio confirmed greater shear capacity, which increased with a higher stirrup ratio or a lower shear span ratio.

Yu et al. [62] studied the torsional performance of BFRP-reinforced PE SS-ECC beams without stirrups through experiment and analysis. It is reported that the SS-ECC beams with a high fiber-volume fraction failed due to compression damage. It was found that rather than the longitudinal reinforcement ratio, the strength of SS-ECC and the height/width ratio of the beam are the critical factors to determine the ultimate torque. The effectiveness of developed FEM for prediction of torsional performance was verified and the torque–angle of twist relationship achieved a good agreement with the experimental results, as shown in Figure 15. The change in stress distribution of the cross-section was marked with three points in the typical curve. Point A represents the section subjected to pure torsional loading, where the longitudinal BFRP bars experience tensile stress. At Point B, with an increase in the angle of twist, the cross-section is subjected to shear stress. The shear stress within the SS-ECC is comparatively high, while the tensile stress in the longitudinal BFRP bars remains significantly lower than their tensile strength. At Point C, although the ultimate torque was attained, the tensile stress in the BFRP bars continued to be minimal. Nevertheless, the SS-ECC reached its maximum shear stress, leading to the failure of the SS-ECC.

Zhou et al. [63] proposed an empirical formula to estimate the ultimate torsional moment for FRC and ECC beams that are reinforced with GFRP bars. They analyzed the individual contributions of the concrete, PP fibers, and GFRP bars to torsional strength. The predicted outcomes showed good agreement with the experimental results.

7. Durability Performance

The study conducted by Yuan et al. [30], Hao et al. [64], and Zhou et al. [65] examined the durability of GFRP bars made from different resin types, epoxy, vinyl ester, and polyester, when subjected to sustained loads. These bars were embedded in ultra-high performance engineered cementitious composites (UHP-ECC) and immersed in an alkaline solution at an elevated temperature of 40 °C for six months. The findings indicated that GFRP bars made from polyester-based resin experienced greater degradation compared to those made from vinyl ester and epoxy resins. Furthermore, the GFRP bars embedded in UHP-ECC exhibited less degradation than bare GFRP bars, although this protective effect was less effective under sustained loading conditions. Analyses using scanning electron microscopy (SEM) and X-ray computed tomography (CT) revealed that the primary cause of degradation in the GFRP bars was matrix hydrolysis. This process negatively impacted the stress transfer efficiency between the fibers, ultimately leading to a reduction in the tensile strength of the GFRP bars.

8. Conclusions

The integration of FRP and FRCC represents a significant advancement in concrete technology, addressing the limitations of traditional RC, especially issues like steel corrosion, low tensile strength, and brittleness. A systematic overview and discussion regarding the structural performance of FRCC members reinforced with FRP bars has been presented here. Based on the findings from this review, the following conclusions can be drawn:

• The bond behavior between FRP bars and FRCC is complex and influenced by factors such as bar diameter, surface treatment, and the characteristics of the FRCC matrix.
  The bond strength decreases when the bar diameter and embedded length increase. It improves as both the amount of fiber and the size of the cross-section of FRCC increases. Further research is needed to develop reliable models for predicting bond strength and performance, as existing studies show variability in results based on different experimental setups and material properties.
• FRCC members reinforced with FRP bars exhibit superior load-carrying capacities and ductility compared to conventional RC, highlighting their potential for improved structural performance. Type of FRP, reinforcement ratio, and environmental conditions are some of the factors that highly affect the flexural and ductility performance of these members.
• The shear capacity of FRCC members reinforced with FRP bars increases with low longitudinal reinforcement ratio, higher shear reinforcement ratio, or low shear span ratio.
• It was found that the torsional resistance of FRCC members reinforced with FRP bars is more dependent on the height/width ratio than the reinforcement ratio.

In conclusion, the findings aim to inform the development of design guidelines and standards for the effective use of these innovative materials in construction, ultimately contributing to enhanced structural performance and sustainability in civil engineering applications.

9. Recommendations for Future Studies

Based on the discussion in this paper, it can be concluded that additional experimental and numerical research is necessary to fill various research gaps concerning the structural performance of FRCC elements reinforced with FRP bars. The following gaps have been identified:

• Lack of comprehensive experimental studies that cover a wide range of FRCC and FRP combinations has led to insufficient data on their performance under various loading conditions, such as dynamic, cyclic, or impact loads.
• There are inconsistencies in findings across different studies, which could arise from variations in testing methods, material properties, and environmental conditions. This validity makes it challenging to draw a definitive conclusion.
• There are fewer studies on bond behavior under different loading scenarios and environmental conditions. More research is needed to develop reliable predictive models.
• More research on the environmental impact of producing and using FRCC and FRP materials, including life cycle assessment, is needed.
• There are insufficient design guidelines or standards specifically made for the use of FRCC and FRP in structural applications, which could limit their adoption in engineering practice.

As the search for articles was restricted to peer-reviewed publications in English indexed on the Web of Science, the results of the study may not fully represent the existing literature. Future research could enhance the data by exploring publications from a range of databases for both quantitative and qualitative studies, such as Google Scholar, Scopus, and Science Direct.