Glass Fiber Reinforced Polymer Rebars Research Articles

Evaluation of the Bond-to-Concrete Properties of GFRP Rebars in Marine Environments

Increased traffic in combination with growing environmental impacts have led to the accelerated degradation of built infrastructure. In reinforced concrete structures, the corrosion of steel reinforcement is the predominant cause of deterioration. Thus, over the last years the use of glass fiber reinforced polymer (GFRP) composites as internal reinforcement bars (rebars) for concrete structures has been evaluated, and has been proved to be a viable alternative to traditional steel reinforcement mainly due to its tensile strength and non-corrosive nature. However, thus far, the GFRP rebar market is diverse and manufacturers around the world produce GFRP rebar types with different surface enhancements to improve the bond to concrete characteristics. In this study, the bond performance of three dissimilar GFRP rebar types (sand coated, helically grooved and with surface lugs) was evaluated over time in seawater environments, with a focus on the bond strength. Accordingly, specimens were exposed to seawater in circulating chambers at three different temperatures (23 °C, 40 °C and 60 °C) for multiple time periods (60 and 120 days). To evaluate the bond performance, pullout tests were conducted according to ASTM D7913. The results showed that the bond strength varied with the surface enhancement features. However, the bond strength did not vary significantly with exposure time and temperature for all three evaluated rebar types.

Field Durability Study of Vinyl-Ester–Based GFRP Rebars in Concrete Bridge Barriers

Val-Alain Bridge on Highway 20 East is the first bridge in Canada in which the concrete deck and barrier walls were fully reinforced with vinyl-ester–based glass-fiber–reinforced polymer (GFRP) bars. Built in 2004, this bridge was considered as the prototype for bridges built thereafter by the Québec Ministry of Transport (MTQ). In 2015, concrete core samples containing GFRP bars were taken from the bridge barrier wall to assess the durability of the high-performance concrete and bars. The mechanical and physicochemical properties of the concrete and GFRP bars were assessed and compared with the material properties measured during bridge construction. In addition, the durability of the GFRP bars was assessed based on the performance of the reference samples from the same production lot of the bars used in reinforcing the Val-Alain Bridge. The results reveal no significant changes in the physicochemical properties as well as microstructure of the concrete and vinyl-ester–based GFRP bars sampled from the bridge barriers after 11 years of service exposure to wet–dry cycles, freeze–thaw cycles, and deicing salts.

Mechanical properties and bond strength degradation of GFRP and steel rebars at elevated temperatures

Fiber reinforced polymer (FRP) rebars have recently been gaining popularity in the construction industry all around the world while steel rebars have been widely used so far. FRP bars, which have higher tensile strength compared to steel rebars with the same nominal diameter under normal conditions, are composed of resin matrix and fibers. In this study, mechanical and bonding properties of glass fiber reinforced polymer (GFRP) and steel rebars subjected to elevated temperature effects were investigated throughout a correlative comparison. Axial tensile tests and pull-out tests of these materials were performed subsequent to exposing them into elevated temperature effects in the range of 23–800 °C. Severe effects on the tensile properties of bare steel bars were observed after 600 °C, while this critical limit is 300 °C for bare GFRP bars. Test results show that bond strength degradation is almost linear for both type of rebars, however, 600 °C is also the critical temperature regarding the serious deterioration on concrete. Additionally, an empirical modeling approach on the bond strength degradation of rebars at elevated temperatures was proposed and it was found that comparison results have quite promising consistency based on the modeling process.

Replacement of steel rebars by GFRP rebars in the concrete structures

Glass fiber reinforced polymer (GFRP) has been confirmed to be the solution as a major development in strengthened concrete technology. Synthesis of GFRP rebars by using the longitudinal glass fibers (reinforcement material) and unsaturated polyester resin with 1% MEKP (matrix material) via manual process. GFRP rebars have diameter 12.5 mm (this value is equivalent to 0.5 inch; it's most common in foundations application). GFRP surfaces are modified by the inclusion of coarse sand to increase the bond strength of rebars with concrete. Then, the mechanical characterizations of reinforced concrete with GFRP rebars are performed and compared with that of steel rebars. Preparation of concrete samples (unreinforced concrete, smooth GFRP reinforced concrete, sand coated GFRP reinforced concrete and steel reinforced concrete) with fixed ratio of ingredients (1:1.5:3) and 0.5 W/C ratio were performed at two curing ages (7 and 28) days in ambient temperature. The value of volume fraction of GFRP and steel rebars in the reinforced concrete was (5 vol. %) equally distributed with specified distances in the mold. The results show the tensile strength of GFRP rebar is 593 MPa and bend strength is 760 MPa. The compressive strength was within reasonable range of concrete is 25.67 MPa. The flexural strength of unreinforced concrete is 3 MPa and reinforced concrete with GFRP rebar, especially sand coated GFRP RC exhibit flexural strength is 13.5 MPa as a result to increase bonding with concrete and higher strain is 10.5 MPa at 28 days than that of steel reinforced concrete at the expense of flexural modulus.

A precast slab track partially reinforced with GFRP rebars

This study developed and investigated a precast slab track system partially reinforced with glass fiber reinforced polymer (GFRP) rebars in the transverse direction, which mitigated the loss of track circuit current by reducing magnetic coupling between the rails and steel reinforcements. An electric analysis was conducted and the results of the analysis verified that the GFRP rebars mitigate the reduced current strength produced by electro-magnetic induction. In the study, a threedimensional finite element method and flexural experiments were used to study the mechanical behavior of the proposed slab track.

Curvilinear GFRP bars for tunnel segments applications

Abstract The possibility of adopting glass-fiber reinforced polymer (GFRP) composite bars in tunnel segments as a substitute of the traditional steel reinforcement has been demonstrated. Nevertheless, this application requires a curvilinear shape for the reinforcement, and thus a different production process and rebar geometry. The aim of the paper is the experimental evaluation of the physical and mechanical properties of non-conventional GFRP rebars. The test procedures and obtained results are highlighted and compared with the acceptance criteria available for straight pultruded rebars. Finally, the presented outcomes show the suitability of GFRP non-conventional bars as reinforcement for precast concrete segments in tunnel applications.

Thermo‐mechanical response of concrete sandwich panels reinforced with glass fiber reinforced polymer bars

The thermo‐mechanical behavior of sandwich panels was experimentally investigated. The panels featured two external concrete layers reinforced with glass fiber reinforced polymer rebars (GFRP) and an internal expanded polystyrene insulation layer. These are typical for low load bearing and thermally insulated panels in façade claddings. To assess the suitability of the internal GFRP reinforcement, the heating condition was such that rebars in one concrete layer were exposed to temperatures higher than the glass transition temperature of the resins. Such extreme condition allowed verifying the retention of the mechanical behavior, in terms of deformability and load‐carrying capacity, with bending tests of unheated and heated panels. As main outcome, the elevated temperature produced significant modification of the insulation layer, considerable reduction of global stiffness and load‐carrying capacity, while GFRP bars were not apparently modified.

Ductile corrosion-free GFRP-stainless steel reinforced concrete elements

Corrosion of steel rebars is known to cause deterioration of concrete structures that can lead to catastrophic failures. To mitigate this problem, steel rebars can be replaced with Glass Fiber-Reinforced Polymer (GFRP) rebars. However, the lack of ductility of GFRP-reinforced elements has prevented their use in many structural applications, especially in seismic areas. Stainless Steel (SS) rebars are corrosion resistant and have adequate energy absorption and ductility. However, they are much more expensive than steel rebars. This paper proposes the combined use of SS and GFRP rebars to achieve ductile and corrosion-free elements. The first challenge for such a proposal relates to designing SS-GFRP reinforced concrete frame with adequate lateral performance in terms of initial stiffness, ductility, and strength. Design equations, which are based on a comprehensive parametric study, are developed to allow designing such a frame. A six-storey concrete frame is then designed using the proposed equations and its lateral performance is examined using pushover analysis.

Optimization of GFRP reinforcement in precast segments for metro tunnel lining

The possibility of replacing the traditional steel reinforcement with glass fiber reinforced polymer (GFRP) cages in precast concrete tunnel segmental lining has been shown by the authors in previous papers. The use of GFRP rebars as structural reinforcement in precast tunnel segments, allows several advantages in terms of structural durability or in cases of temporary lining that will have to be demolished later. Furthermore, this reinforcement type can be a suitable solution to create dielectric joints, ensuring the interruption of possible stray currents, which often lead to corrosion problems. Nevertheless, this peculiar application requires curvilinear shape of the reinforcement, and then different production process and rebar geometries. In the present work, a suggestion for the optimization of the GFRP reinforcement for tunnel segment is given. Four different GFRP cage typologies are analysed and applied as a reinforcement in full-scale tunnel segments. Both bending and point load tests are developed and the structural performances of the specimens are compared and discussed. Finally, the best solution, in terms of cost-benefit analysis is proposed.

Design of GFRP-reinforced rectangular concrete columns under eccentric axial loading

The use of glass-fibre-reinforced polymer (GFRP) reinforcement as an alternative to steel for use in reinforced concrete (RC) structures has developed significantly in recent years. With excellent corrosion resistance, a high tensile strength to weight ratio and being non-magnetic and non-conductive, GFRP is an excellent solution for projects requiring improved corrosion resistance or reduced maintenance costs. However, despite a number of recent studies illustrating the effective use of GFRP rebars as longitudinal reinforcement for concrete compression members, the current international design codes do not recommend including GFRP reinforcement in the compression member capacity calculations. A test programme was thus carried involving the construction and testing of 17 rectangular concrete columns reinforced with steel or GFRP. This paper provides full derivations of the interaction diagrams for both steel- and GFRP-reinforced concrete columns. The interaction diagrams fitted the experimental data very well for both types of RC column. It was found that the GFRP-reinforced columns did not have a ‘balance point’ on the interaction diagram, and this was clearly shown for longitudinal reinforcement ratios above 3%. It was found that excluding the strength and stiffness of GFRP reinforcement from concrete compression calculations is conservative. Theoretical capacities better represent the experimental data when the strength and stiffness of GFRP reinforcement are included. The resulting factored interaction curves were exceeded by all experimental capacities.

Tests of glass fibre reinforced polymer rectangular concrete columns subjected to concentric and eccentric axial loading

The use of Glass Fibre-Reinforced Polymer (GFRP) reinforcement as an alternative to steel for use in Reinforced Concrete (RC) structures has developed significantly in recent years. GFRP’s excellent corrosion resistance, high tensile-strength-to-weight ratio, non-magnetic, nonconductive make it an excellent solution for projects requiring improved corrosion resistance or reduced maintenance costs. Despite a number of recent studies illustrating the effective use of GFRP rebars as longitudinal reinforcement for concrete compression members, the current international design codes such as ACI 440.1R-15, CAN/CSA S806, TR55, ISO 10406-1, and fib do not recommend including GFRP reinforcement in the compression member capacity calculations. The experimental study detailed in this paper involved construction and testing of 17 rectangular concrete columns reinforced with both steel and GFRP rebars. The columns were tested to failure under various loading conditions, in order to determine the effect of load eccentricity on axial capacity. The effect of ligature spacing and confinement area on axial capacity and ductility were also examined. The most important finding is that GFRP RC columns utilising less concrete cover can achieve greater strain and deformation ductility than equivalent steel RC columns.It was shown that the load carrying capacity and ductility of GFRP reinforced columns increased when the ligature spacing was reduced from 150mm to 75mm. It was also found that, the average axial load carrying capacity of GFRP RC columns was 93.5% of their steel RC column counterparts. It was also found that, the GFRP RC columns under concentric load exhibited 3.2% average increase in the load carrying capacity with respect to the plain concrete section capacity, whereas the steel ones achieved an average enhancement of 15.8%.

Modelling bond of GFRP rebar and concrete

The structural performance of concrete structures reinforced using glass-fiber-reinforced-polymer (GFRP) rebars is sometime compromised by debonding failure. For better analyzing the GFRP bar-concrete bond behavior, this study presents two damage-based approaches for assessing the bond damage evolution. One is the secant modulus-based model and other is exponential damage model. Using the exponential damage approach, a simplified analytical model based on only one curve fitting parameter was developed to predict the bond stress-slip relationship. Then, a 3D finite element (FE) model was developed and both proposed damage-based approaches were implemented, to simulate the GFRP bond behavior. The FE model considers the nonlinear behavior of the concrete and the GFRP bar-concrete interface. The analytical and numerical predictions of the GFRP bar-concrete bond behavior are validated by comparing with the relevant results of an experimental program focused on quasi-static pullout tests. At the end, a parametric study was carried out to numerically assess the influence of some critical parameters on the bond behavior.

An Experimental Evaluation of Mechanical Properties of Hybrid Reinforcements

This paper presents the mechanical properties of unidirectional hybrid reinforcements formed from continuous fibres impregnated with a fibre binding material which are used for reinforcing the concrete. Recently FRP (Fibre Reinforced Polymer) manufacturers and suppliers have been increased all over the world because of the superior performance of FRP products in the construction industry. Its non-corrosive nature has turned the attention of many researchers to make several studies on different type of FRP products. Through a vast research, several standards also have been formulated. In this regard a new combination of FRP materials is tried in this paper and its properties have been derived. Carbon fibre and glass fibres fuse in this study to form a new hybrid rebar. The design properties such as tensile strength, tensile modulus, and compressive strength have been studied as per ASTM standards and it has been identified that the Hybrid rebar show a superior performance in comparison with GFRP (Glass FRP) and Steel rebars. This extraordinary performance of hybrid composite material increases the extensive engineering applications such as transport industry, aeronautics, naval, automotive industries.

Experimental evaluation of bonded overlay and NSM GFRP bar strengthening on flexural behavior of precast prestressed hollow core slabs

A hollow core slab is a precast prestressed concrete member with longitudinal cores that reduce its self-weight. Strengthening of prestressed hollow core slabs is required for several reasons to maintain their structural integrity. The main focus of this research is to understand the flexural behavior of hollow core slabs and failure modes with hybrid strengthening techniques including bonded overlay and near surface mounted (NSM) glass fiber reinforced polymer (GFRP) bars. The test variables include different strengthening techniques such as (i) bonded overlay with and without shear keys, (ii) NSM GFRP rebar and (iii) hybrid strengthening combination which includes a thin bonded overlay in the compression region and NSM GFRP bars in the tension region. A total of seven full scale slabs were cast, strengthened and tested until failure. Test results show that bonded overlay increases the flexural strength by 89% without much compromise on the ductility when compared to control slab, whereas NSM GFRP bar strengthening increases the strength by about 100% but with reduced ductility. Hybrid strengthening led to a highest increase in the ultimate strength (about 200%) and ductility when compared to only NSM and only bonded overlay strengthening.

Improved bond behavior between GFRP rebar and concrete using calcium sulfoaluminate

Glass Fiber Reinforced Polymer (GFRP) rebars have great potential for applications in concrete structures under corrosive environment. The bond behavior between GFRP rebar and concrete needs to be understood for such applications. This paper presents a new method for improving the bond behavior using Calcium Sulfoaluminate (CSA). CSA has an expansive effect when added to the concrete mixture. It is proposed to embed the GFRP rebar in the fresh expansive concrete which is encased by the surrounding hardened concrete. When the fresh expansive concrete gradually becomes hardened, the expansion is restrained by the surrounding concrete, resulting in confining pressure on the GFRP rebar. To validate the proposed method, experimental pull-out tests were conducted to quantify the improved bond behavior between GFRP rebar and concrete. Steel rebar pull-out test was also carried out for comparison purpose. The experimental results were reported including failure modes, ultimate pull-out capacities and bond-slip responses. It was found that the bond behavior between GFRP rebar and surrounding concrete was greatly improved using the proposed method.

Remarks on bond of GFRP rebars and concrete

Abstract The paper presents and extensive investigation on the bond behaviour between GFRP (glass fibre reinforced polymer) rebars and concrete. Pull-out tests were performed on helically wrapped and sand coated GFRP rebars with a wide range of diameters. Nonlinear finite element simulations of the tests allowed determining the effective distribution of the bond stress in the development length and the debonding propagation. An analytical model was developed to have an accurate prediction of the stress distribution at the interface and results were assessed with the numerical ones. Finally, the outcomes were compared with the design equations for the development length of FRP bars suggested in some design codes to assess their reliability.

Flexural behavior of ultra-high-performance fiber-reinforced concrete beams reinforced with GFRP and steel rebars

This study describes the flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams reinforced with glass fiber-reinforced polymer (GFRP) rebars and hybrid reinforcements (steel+GFRP rebars). Three GFRP bar-reinforced beams and four hybrid reinforced beams with different reinforcement ratios were fabricated and tested. Owing to the strain-hardening characteristics of UHPFRC, all test beams exhibited very stiff load–deflection behavior after the formation of cracks and satisfied the service crack width criteria of CAN/CSA S806. In addition, deformability factors higher than the lower limit of CAN/CSA-S6 were obtained for all test beams. The increase in the reinforcement ratio of GFRP rebars resulted in the improvement of their flexural performances, including post-cracking stiffness, load carrying capacity, and ductility (or deformability). The use of hybrid reinforcements by replacing a part of a GFRP rebar with a steel rebar contributed to a higher post-cracking stiffness before steel yielding, but led to lower deformability. Based on a sectional analysis, both AFGC/SETRA and JSCE recommendations were appropriate for predicting the moment–curvature response of UHPFRC beams with GFRP rebars and hybrid reinforcements: the average ratios of the maximum moments obtained from experiments and numerical analyses were found to be 1.12 and 0.94, respectively.

Modeling of Bond of Sand-Coated Deformed Glass Fibre-Reinforced Polymer Rebars in Concrete

In this paper, 30 beam tests, 48 Losberg pullout tests and 6 standard pullout tests were conducted to investigate bond-slip response of sand-coated deformed glass fibre-reinforced polymer (GFRP) rebars in concrete. The specimen parameters varied were concrete strength, embedment length, bar diameter and test method. Two failure modes including pullout failure and splitting failure were observed. The experimental bond stress-slip (τ-s) curves of sand-coated deformed GFRP rebars in concrete in pullout failure included a micro-slippage branch, a slippage branch, a descending branch and a residual branch, while the τ-s curves in splitting failure included a micro-slippage branch and a slippage branch. Based on the tests, a new bond-slip constitutive model for sand-coated deformed GFRP rebars in concrete was presented. Compared with other available models, the model proposed in this paper can provide more reliable simulations of the test results.

Numerical simulation on structural behavior of UHPFRC beams with steel and GFRP bars

This study simulates the flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams reinforced with steel and glass fiber-reinforced polymer (GFRP) rebars. For this, micromechanics-based modeling was first carried out on the basis of single fiber pullout models considering inclination angle. Two different tension-softening curves (TSCs) with the assumptions of 2-dimensional (2-D) and 3-dimensional (3-D) random fiber orientations were obtained from the micromechanics-based modeling, and linear elastic compressive and tensile models before the occurrence of cracks were obtained from the mechanical tests and rule of mixture. Finite element analysis incorporating smeared crack model was used due to the multiple cracking behaviors of structural UHPFRC beams, and the characteristic length of two times the element width (or two times the average crack spacing at the peak load) was suggested as a result of parametric study. Analytical results showed that the assumption of 2-D random fiber orientation is appropriate to a non-reinforced UHPFRC beam, whereas the assumption of 3-D random fiber orientation is suitable for UHPFRC beams reinforced with steel and GFRP rebars due to disorder of fiber alignment from the internal reinforcements. The micromechanics-based finite element analysis also well predicted the serviceability deflections of UHPFRC beams with GFRP rebars and hybrid reinforcements.

Investigation of bond in concrete of GFRP and steel hybrid rebar

Fiber reinforced polymer (FRP) rebar is a great alternative to the conventional steel reinforcing bar because of its corrosion-free characteristics and high strength. This study introduces a newly developed hybrid FRP rebar which is composed of a conventional steel rebar inside and glass fiber reinforced polymer (GFRP) on the outer surface. The developed hybrid rebar takes advantage of overcoming the low elastic modulus from their composite action and durability as the outer GFRP surface resists corrosion. In addition, this hybrid GFRP rebar is also cost-effective. This study investigated the bonding characteristics between the newly developed hybrid FRP rebar and concrete. A direct pull-out test was conducted following the KS F 2441 testing method. In the test result, the bond strength and slip relationship were investigated for test variables. The rebar outer diameter was 16 mm, and inside steel rebar diameters were 10 and 13 mm with varying thickness of GFRP.