Glass Fiber Reinforced Polymer Bars Research Articles

Field test of GFRP bar anti-floating anchor slurry-rock interface bonding performance

Based on fiber Bragg grating (FBG) sensing and monitoring technology, the slurry-rock interface bonding characteristics of glass fiber reinforced polymer (GFRP) anti-floating anchor and steel anti-floating anchor were investigated through the field pull-out destructive test of GFRP bars and steel anti-floating anchor. The differences in slurry-rock interface bonding properties between GFRP anti-floating anchor and steel anti-floating anchor were defined. In addition, the distribution law of shear stress and axial stress at the slurry-rock interface of the GFRP anti-floating anchor was revealed along the anchoring depth. The results showed that the axial stress at the slurry-rock interface of the GFRP anti-floating anchor is maximum at the hole opening and decreases as depth increases. The axial stress reduces to zero at the anchorage depth of about 2.4 m. The shear stress at the slurry-rock interface increases and then decreases. The slurry-rock interface bonding curve of the GFRP anti-floating anchor is approximately a straight line, while the slurry-rock interface bonding curve of the steel anti-floating anchor is a broken line with an obvious inflection point. Comparing different materials and types of anti-floating anchors indicate that the bond performance of steel anti-floating anchors is slightly higher than that of GFRP anti-floating anchors, and the bond strength of anti-floating anchors’ slurry-rock interface improves with the increase of anchor bar diameter. The synergistic effect among anchor bars, grout, and rock mass of the GFRP anti-floating anchor exceeds that of the steel anti-floating anchor. Using the finite element software ABAQUS to GFRP anti-floating anchor rod on rock interface bonding performance simulation, the simulation results was coincident with the test result.

Experimental investigation of bond and cracking behaviours in gfrp-reinforced concrete members

Although Glass Fiber-Reinforced Polymer (GFRP) reinforcing bars are becoming commonplace, their mechanical properties – low modulus of elasticity and high tensile strength – result in design of GFRP-reinforced concrete members (GFRP-RC) often being governed by deflection and crack control at the serviceability limit state. Bond performance of GFRP bars impacts the crack control provided and, due to the empirical nature of bond characterization in design, bond of GFRP remains described in relation to that of steel. To describe the bond performance of GFRP bars, a bond-dependent coefficient, kb, is adopted in design guides and standards. The bond and cracking behaviours of GFRP bars embedded in concrete – including the estimation of kb – were investigated through 80 pull-out and 12 prism tension tests. The evaluation of kb using ASTM D7913 pull-out, confirming the bond performance using a smaller number of prism tension tests, is proposed. The results showed that values of kb determined from pull-out test were about 15–20 % greater than those estimated by prism test. Nonetheless, kb values determined from both tests are similar and follow the same trends. These data obtained in this experimental programme supplemented an extant database of 137 comparable pull-out test results covering a range of GFRP bar and concrete parameters. The study concludes that ASTM D7913 pull-out tests are suitable for assessing minimum GFRP reinforcing bar bond criteria although more complex prism tests are likely required to accurately assess kb.

Effect of column dimension on the punching shear capacity of concrete slabs reinforced with GFRP bars

Traditional steel reinforcements are highly susceptible to corrosion affecting their durability and leading to structural weaknesses. The use of GFRP bars offers a corrosion-resistant alternative, potentially extending the lifespan and durability of concrete structures. With this in mind, the current research looks at the efficiency of GFRP bars towards the punching shear capacity of slabs. This study, in specific, explores the effect of column size on the punching shear capacity of glass fiber-reinforced polymer (GFRP) reinforced square concrete slabs. The research involves square concrete slabs (1500×1500 mm) reinforced with GFRP bars, which were centrally loaded until failure. Parameters like the ultimate load capacity, crack patterns, strain development in the GFRP bars and concrete, and critical punching shear area were assessed to evaluate the slabs’ behavior. The punching shear area measured at failure was notably larger than the distance specified by design codes.

Glass Fiber-Reinforced Polymer Bars as Shear-Friction Reinforcement for Concrete Cold Joints

Glass Fiber-Reinforced Polymer Bars as Shear-Friction Reinforcement for Concrete Cold Joints

Pull-Out Tests for GFRP/BFRP/Steel Bars Used as Nailing for Coal-Bearing Soil Slopes in Humid Regions

Abstract Coal-bearing soil slopes are associated with a high risk of landslides when subjected to high soil water content. Steel bars have been used as soil nailing for slope stabilization; however, corrosion may occur in an aggressive environment. Glass fiber reinforced polymer (GFRP) and basalt fiber reinforced polymer (BFRP) bars have higher resistance to corrosion and could be alternatives to steel bars, but their elastic modulus and bonding strength with cement concrete are inferior to steel bars, which may result in lower reinforcement effects against landslides and hence require further investigation. In this study, the mechanical properties of different types of bars were investigated using tensile tests. The mineral composition of the soil samples was analyzed. Subsequently, pull-out tests were conducted on three types of bars (steel, GFRP, and BFRP) embedded in grouts in the soil. Up to 38 test scenarios were investigated, and the results were statistically analyzed using an analysis of variance test. The effects of several factors were studied, including the bar type, water content, soil compaction degree, and soil surcharge. The results showed that the bar type had an insignificant effect on the maximum pull-out loads, indicating the feasibility of using GFRP and BFRP bars as alternatives to steel bars for soil nailing in coal-bearing soil slopes. The reinforcement effect can be weakened by rainfall or drought events and enhanced by higher compaction energy and surcharge loads.

Strengthening of GFRP Reinforced Concrete Slabs with Openings

Using fiber-reinforced polymer (FRP) could effectively improve the strength and endurance of reinforced concrete (RC) constructions. This study evaluated the flexural behavior of one-way concrete slabs with openings reinforced with glass fiber-reinforced polymers (GFRP) bars. It strengthened using carbon fiber-reinforced polymer (CFRP) sheets around the openings. The experimental program of this study is adopted by casting and testing four one-way concrete slabs with dimensions of (150*750*2650) mm. These slabs are divided into two groups based on whether they were strengthened or un-strengthened. For each group, two different openings (either one rectangular or two square) measured 250*500 mm and 250*250 mm, respectively, were fabricated within the pure flexural zone of the specimens. The experimental results indicate that using CFRP strips increases the maximum load capacity by around 29% for the slab with one rectangular opening and 21% for the slab with two square openings compared to the un-strengthened slabs. On the other hand, the deflection at a service load is decreased by about 35% and 37% for the slabs mentioned above, respectively.

Effectiveness of FRP bar anchors for prestressed concrete members

Prestressed concrete members are widely used around the world to realize different types of structure, including bridges and skyscrapers. Steel strands are generally employed to apply a compression force into the concrete. Recently, fiber-reinforced polymer (FRP) composite bars have been considered for replacing traditional steel strands in specific applications. The main advantage of FRP bars is their resistance to corrosion. Furthermore, they may have a higher tensile strength-to-weight ratio and fatigue resistance compared to steel strands. Although using prestressed FRP bars may entail for advantages over traditional steel solutions, the anchorage system is an open issue for this technology. Indeed, the anchorage should guarantee a high level of tensile stress into the bar and, at the same time, avoid local failures.In this paper, the preliminary results of an experimental campaign comprising tensile tests of glass and carbon FRP bars with different anchors are provided and discussed. The experimental campaign was aimed at investigating the effectiveness of newly developed wedges in properly anchoring the composite bars. Tensile test results and modes of failure are discussed, shedding light on the main parameters that affect the mechanical behavior of the bars considered.

Flexural behaviour of GFRP-reinforced concrete pontoon decks under static four-point and uniform loads

Concrete pontoon decks are subject to flexural loading actions under concentrated and uniform loads caused by self-weight, live loads, and wave actions. This study investigated the structural behaviour of concrete pontoon decks reinforced with glass fiber-reinforced polymer (GFRP) bars under static four-point and uniform loading conditions. Five large-scale GFRP-reinforced concrete decks with a length of 2400 mm, width of 1500 mm, and thickness of 125 mm were tested to evaluate their moment capacity, strain behaviour, cracking propagation, and failure mechanism. The effects of the loading configurations, reinforcement arrangement, and cutout simulating the piles' location were evaluated. The edge cut-out initiated flexural-shear cracks, causing the pontoon decks to fail at an effective bending stress 10% lower than the solid decks. Decreasing the span-to-depth ratio from 5.6 to 4.0 increased the induced shear stress of a section and caused the deck to fail by shear compression. Uniform loading resulted in an even load distribution and minimized the stress concentration around the cutout. An increase in the effective depth improved all deck flexural characteristics. The equations in ACI 4401. R-15 and CSA S806–12 provided an accurate prediction for solid decks but overestimated the ultimate flexural strength of the GFRP-reinforced concrete decks with a cutout.

Shear behavior of concrete panels reinforced with GFRP bars under cyclic diagonal tension tests

Glass Fiber Reinforced Polymer (GFRP) bars aims to improve the properties of concrete conventional reinforcement and to reduce the weaknesses of steel rebars in terms of corrosion and temperature changes. In this study, GFRP bars were evaluated as a replacement of steel bars in shear walls. Diagonal tension test under unreversed cyclic quasi-static load on Reinforced Concrete (RC) panels was used. Twenty-one concrete panels with a square section, 600 mm on each side and 100 mm thick, reinforced with distinct types and reinforcement ratios were evaluated. Two types of GFRP bars with different surface coating were used: epoxy Helical wrap (GFH), and Sand coated (GFS). For comparison purposes, RC panels with steel Welded Wire Mesh (WWM) were also assessed. The minimum vertical and horizontal reinforcement required by ACI 318 (0.25%) and half of it (0.125%) were considered. The research analyzed the hysteresis curves in terms of shear stress-strain (τ-γ) and the parameters associated with shear strength, shear strain, crack width, stiffness, and toughness. Results showed that the stiffness and toughness of panels reinforced with GFH bars is similar to that of RC panels with WWM, and the toughness of panels reinforced with GFS bars is between 25% and 38% higher than those with WWM. Different models are proposed to estimate the stiffness, toughness, and crack width of the tested panels.

Experimental investigation of concrete frames reinforced with GFRP bars under reversed cyclic loading

Fiber reinforced polymers (FRP) have been widely investigated and successfully used as internal reinforcement in new reinforced concrete (RC) members and structures such as slabs, beams, bridges, multi-storey car parks and others as means to overcome the corrosion problem of steel. The linear-elastic behaviour, brittle failure and low modulus of elasticity are some of the significant mechanical characteristics of FRP rebars which raise concerns on their capability to allow structural members to dissipate energy in seismic zones and thus limit their use in earthquake resistant RC structures (such as moment resisting frames). The behaviour of concrete frames reinforced with FRP bars is still in its early stages of research and development with only a few researchers exploring such structures under in-place cyclic loading (seismic loading). As a result, design codes do not provide guidance for RC moment frames internally reinforced with FRP. This study attempts to partially fill the gap by investigating the behaviour of glass fiber reinforced polymers (GFRP) RC frames under in-plane loading. Six 1/3 scaled RC frames were constructed and tested under reversed cyclic loading to simulate seismic loading conditions. Three were reinforced with GFRP bent bars and three (their counterparts) with conventional steel. The testing was conducted in displacement-controlled mode with the loading history according to ACI 374.1–05. Test parameters included longitudinal reinforcement ratio and arrangement in the columns and presence of links in the joints. The experimental results are presented as hysteretic curves, lateral load / drift graphs, stiffness degradation and cumulative energy dissipated with the overall indication of the feasibility of GFRP RC frames in seismic regions. All GFRP specimens successfully reached 2.75% loading drifts. The energy dissipation of GFRP specimens was lower at initial drifts compared to the steel reinforced samples, but it become greater at final drift. GFRP frames had approximately the same load bearing capacity as their counterparts and even greater in one case. Ultimate loads for G frames were reached at higher level of displacement than for S frames.

Rehabilitation of reinforced concrete beam: Sustainable restoration mortar with waste materials

The current application of epoxy resin in the installation of fiber sheets for concrete beam restoration presents practical challenges, limited fire resistance, and lacks environmental sustainability. Additionally, epoxy resin cannot be used on wet surfaces as it compromises adhesion and reduces durability. In this study, we propose an effective mortar formulation that incorporates waste materials such as marble powder (MP), red mud (RM), and electric arc furnace dust (EAFD) for fiber sheet installation. The performance of the developed mortar was comprehensively assessed through various experiments, evaluating compressive and tensile strengths, water absorption (WA), sulfuric acid resistance (SAR), and microstructural characteristics of the restoration mortars. Furthermore, three reinforced concrete (RC) beams were constructed and subjected to a four-point bending test. One beam was strengthened with carbon fiber-reinforced polymer (CFRP), while the other two utilized fiber-reinforced cementitious material (FRCM) with either CFRP mesh or glass fiber-reinforced polymer (GFRP) bar. The findings reveal that RC beams strengthened with CFRP mesh-restoration mortar and GFRP rebar-restoration mortar exhibit load-carrying capacities 13% and 36% higher, respectively, compared to that reinforced with CFRP sheets. This study lays the foundation for future research by demonstrating, for the first time, the superior performance of mortar-based restoration over epoxy resin, thereby opening up new possibilities for the development of concrete element restoration.

Applicability of available NDT methods for damage detection in concrete elements reinforced or strengthened with FRP

The application of Fiber Reinforced Polymer (FRP) materials in concrete structures has been rising due to their several advantages, including lightweight, high tensile strength, ease of installation, and corrosion resistance. They have been mostly implemented for strengthening and repairing existing structures in the form of an externally bonded system, i.e., sheet, jacket, near surface mounted. Furthermore, they have been recently utilized as internal reinforcement of concrete elements in the form of strands, bars, tendons, etc. Although higher durability and performance are associated with the FRP material in some aspects compared to steel, concerns remain regarding damages and defects in this material, many of which are related to their unique features. Importantly, debonding of FRP materials from a concrete surface or within a concrete element has always been an issue resulting in the premature failure of the structure. To this end, concrete elements strengthened or reinforced with FRP materials has to be inspected periodically to detect potential issues and hence prevent any premature failures. This study first determines all possible or potential damages and anomalies attributed to FRP reinforced/strengthened concrete (FRP-RSC) elements. It then investigates Non-Destructive Testing (NDT) methods that can be applicable to the inspection of FRP-RSC elements from a literature survey of past studies, applications, and research projects. Furthermore, this study evaluates the ability of two of the most commonly used NDT methods, Ground Penetrating Radar (GPR) and Phased Array Ultrasonic (PAU), in detecting FRP bars/strands embedded in concrete elements. GPR and PAU tests were performed on two slab specimens reinforced with GFRP (Glass-FRP) bars, the most commonly used FRP bar, with variations in their depth, size and configuration, and a slab specimen with different types of available FRP reinforcements. The results of this study propose the most applicable methods for detecting FRP and their damage/defects in FRP-RSC elements. This study further investigates the feasibility of two new methods for improving the detectability of embedded FRP bars. By providing the inspection community with more clarity in the application of NDT to FRP, this study offers means for verifying the performance and, therefore, help the proliferation of FRP materials in concrete structures.

Bond responses and anchorage length of GFRP bar in precast recycled aggregate concrete

Precast recycled aggregate concrete (PRAC) employs precast reject-derived recycled aggregates (PRAs) and exhibits mechanical properties on par with or superior to those of natural aggregate concrete (NAC). Nevertheless, the durability of PRAC is hampered by aged mortar. To address this issue, integrating high durability glass fiber reinforced polymer (GFRP) bars into PRAC emerges as a potential solution for constructing enduring structures. Building upon this context, the study focuses on the bond responses between PRAC and GFRP bars, an area with limited existing research. Three main tasks were conducted: Firstly, a comprehensive test program involving 108 pullout samples was conducted to investigate the key variables' effects on bond failure mode and stress-slip relationship. Subsequently, an equation was developed to determine the peak bond strength of recycled aggregate concrete (RAC) based on available test data. Additionally, reliability analyses were performed to discuss the anchorage length of GFRP bar embedded in RAC. The findings are as follows: (a) The PRAC's bond capacity initially increased then decreased with rising PRA content. At full replacement, PRAC's bond strength was 28.3% lower than NAC. However, a two stage mixing approach restored PRAC's bond capacity to NAC levels. (b) Helical wrapping of the GFRP bar consistently exhibited the highest bond capacity, with an average bond strength 51% greater than a sand coated GFRP bar and 21% higher than a GFRP bar treated with both helical wrapping and sand coating. (c) Current codes specifying the critical anchorage length for FRP bar in NAC were often unsafe for RAC. Hence, a new expression, factoring in RA content, type and RAC mixing method, was proposed to determine the suitable anchorage length.

Experimental and numerical simulation research on the flexural performance of beams reinforced with GFRP bars and three-sides UHPC layer

This paper presents the results of the experimental investigation and numerical investigation conducted to study the flexural response of reinforced concrete beams reinforced with glass fiber reinforced polymer (GFRP) bars using three-sides ultrahigh performance concrete (UHPC) layer. The interface treatment of bubble wrap was applied in the internal surface of UHPC layer to ensure the enough interfacial bond behavior between UHPC layer and original concrete. Three tested beams, including two beams reinforced with three-sides UHPC and a reference beam, were studied through four-point bending tests and the effectiveness of flexural strengthening scheme associated with three-sides UHPC layer was evaluated. The results showed that the cracking load and ultimate load of beams reinforced with UHPC increased by 36.7%, 55.3%, and 30.0%, 42.7%, respectively, relative to the reference beam. The employment of UHPC layer could effectively control the development of surface crack width in beams. In addition, parametric studies were conducted to investigate the effects of the height of the UHPC, the thickness of the UHPC on both sides, and the longitudinal length of the three-sided UHPC layer using finite-element (FE) analysis. The results of numerical simulation were good agreement with the experimental results, indicating that the proposed finite element model could accurately predict the flexural responses of beams.

The effect of type of mechanical anchors on bond behavior of ribbed-surface GFRP bars embedded in concrete

The deficiency in the bond between concrete and fiber-reinforced polymer (FRP) bars is a major hindrance to their widespread use in concrete structures. One effective solution to this problem is to use mechanical anchors along the bar. This research investigates the effect of mechanical anchors on the bond behavior of glass fiber-reinforced polymer (GFRP) bars embedded in concrete. In the first phase, eight beam specimens were constructed and tested in flexure, in which the FRP bars contained no anchors or anchors made of polyethylene, aluminum, or steel. The increase in maximum tensile stress in the bar was 43 %, 17 %, and 12 % for specimens with steel, aluminum, and polyethylene anchors, respectively. Steel anchors were identified as the most effective option with the greatest maximum stress and greatest initial stiffness in the stress-slip curve. In the study's second phase, an additional set of 16 beam specimens was tested to investigate the effect of the number of steel anchors. The results showed that the tensile stress developed in the GFRP bar increases at a higher rate with a greater number of steel anchors. Compared to the specimen without anchors, the bar stresses increased by 20–25 % for one and 52–59 % for two steel anchors.

A NEW APPROACH TO TENSILE TESTING OF GFRP BARS

Tensile testing is a critical procedure for evaluating the mechanical properties of Glass Fiber Reinforced Polymer (GFRP) bars, which emerged as an alternative to traditional steel reinforcement in reinforced concrete structures. While significant research has led to the development of testing standards for GFRP bars, their implementation often necessitates additional specimens and specialized equipment compared to their steel counterparts. This study proposes a new method for conducting GFRP tensile tests using standard equipment designed for conventional structural steel rebar testing. By employing existing devices, our approach offers a practical and cost-effective solution for assessing the tensile properties of GFRP reinforcement. This simplified testing method aims to enhance efficiency, facilitate wider adoption of GFRP bars in reinforced concrete structures, and contribute to the advancement of sustainable construction practices.

Flexural bond behavior and development length of ribbed CFRP bars in UHPFRC

Ribbed carbon fiber reinforced polymer (CFRP) bars in ultra-high-performance fiber reinforced concrete (UHPFRC) are a high-efficiency combination for its sustainable substitute and high strength to weight ratio. This paper aims to investigate the bond stress and development length of ribbed CFRP bar embedded in UHPFRC using the hinged beam test. A total of 12 groups of hinged beam specimens were tested with different parameters, such as bar type (ribbed CFRP, sand coated CFRP, ribbed glass fiber reinforced polymer (GFRP), and steel bar), bonded length (4db, 10db, 20 db, and 40 db), fibers (with and without fibers in ultra-high-performance concrete (UHPC)), and presence of shear reinforcement for assessing the bonding behavior and development length of each bar. Tensile failure occurred in the steel, ribbed GFRP, and ribbed CFRP bars with bonded lengths of 10db, 20db, and 40db, respectively, and pullout failure occurred in sand coated CFRP bars regardless of bonded length. The ultimate load for the bonded length of 10 db was in order of ribbed CFRP, ribbed GFRP, steel, and sand coated CFRP bars. Compared with the bonded length, the bond stress of ribbed CFRP bars is larger than that of the ribbed GFRP and sand coated CFRP bar and these trends became more remarkable as the bonded length increased. There was no difference in the bond stress with presence of the reinforcement cage, and the bond stress increased by 20 % when the fibers were incorporated. The code-based equation for development length of ribbed CFRP bar was found to be underestimated, and ribbed CFRP, sand coated CFRP, ribbed GFRP bar of development length was proposed as 24db, 20db, and 107db.

Innovative Connection Systems for Sand-Coated and Helically Wrapped Glass Fiber–Reinforced Polymer Bars

Innovative Connection Systems for Sand-Coated and Helically Wrapped Glass Fiber–Reinforced Polymer Bars

On the Factors That Determine the Bond Behaviour of GFRP Bars to Concrete: An Experimental Investigation

It is becoming accepted that glass-fibre-reinforced polymer (GFRP) is a credible and effective replacement for steel in reinforced concrete (RC) to meet structural requirements whilst addressing durability concerns posed by steel over the long term. A better understanding of the bond behaviour between GFRP and concrete is essential for reliably and efficiently designing concrete structures with reinforced GFRP bars. This paper presents a parametric study of the bond behaviour of GFRP bars to concrete where the effects of the length, diameter, concrete strength, concrete cover thickness and rebar surface morphology of GFRP bars were investigated via a series of pull-out tests. The test results indicate that the bond strength of GFRP bars is predominantly influenced by their surface morphology, embedment length and diameter. On the other hand, the effects of concrete strength and cover thickness appear to have a limited impact on the bond strengths of GFRP rebars to concrete. It is shown that ribbed GFRP bars exhibit the highest bond energy of 89.4 Nmm and an average bond strength of 11.9 MPa. Moreover, the analysis of failure modes indicated the unique effect of GFRP surface morphology on failure mode. It is shown that 100% of ribbed GFRP failed due to concrete split, while 85% of sand-coated bars experienced failure due to bar slip. This examination of failure modes and their corresponding bond strengths provides a unique perspective on the bond behaviour between GFRP bars and concrete.

Compressive response of GFRP and BFRP bars at different temperatures and quasi-static rates

The adoption of fiber-reinforced polymer (FRP) bars in concrete structures has increased due to their superior mechanical properties and durability. However, the compressive response of FRP bars at high temperatures remains unclear. This article presents an experimental study on the behavior of glass FRP (GFRP) and basalt FRP (BFRP) bars subjected to compressive loads at different elevated temperatures and deformation rates. The study considers four different temperature conditions: ambient temperature (25 °C), 50 °C, 100 °C, and 150 °C, and two different deformation rates: 0.5 mm/min and 1000 mm/min. Digital Image Correlation (DIC) was used to accurately measure strains at high temperatures by generating a suitable speckle pattern over the specimen surface for full-field deformation measurements. The study results revealed that the modulus of elasticity and compressive strength of both GFRP and BFRP bars degraded as the temperature increased from 25 °C to 150 °C. The compressive strength reduction was higher at 150 °C compared to 100 °C, and the reduction was more significant for BFRP bars than GFRP bars. The compressive strength of GFRP bars was comparable under both strain rates for all temperature conditions. However, the elastic modulus of the bars showed a slight variation between the different load rates, especially at an elevated temperature of 150 °C. For the BFRP bars, the study found that different strain rates at ambient temperature resulted in significant deviation in the compressive strength and modulus of elasticity results. At higher temperatures, the reduction in mechanical properties was more pronounced. In summary, the study provides valuable insights into the behavior of GFRP and BFRP bars under compressive loads at elevated temperatures, which is useful for designing and assessing the performance of FRP-reinforced structures under fire conditions.