Search Results (654)

Textile-reinforced concrete (TRC) sandwich panels with lightweight cores are a promising solution for sustainable and slender building envelopes. However, their structural performance depends strongly on the shear connection between the outer shells. This study investigates the flexural behavior of TRC sandwich panels with glass fiber-reinforced polymer (GFRP) rod connectors under four-point bending. Three full-scale specimens were manufactured with high-performance concrete (HPC) face layers, an expanded polystyrene (EPS) core, and 12 mm GFRP rods as shear connectors. The panels were tested up to failure, with measurements of load–deflection behavior, crack development, and interlayer slip. Additionally, a linear-elastic finite element model was developed to complement the experimental campaign, capturing the global stiffness of the system and providing complementary insight into the internal stress distribution. The experimental results revealed stable load-bearing behavior with ductile post-cracking response. A degree of composite interaction of γ = 0.33 was obtained, indicating partially composite action. Slip measurements confirmed effective shear transfer by the GFRP connectors, while no brittle failure or connector rupture was observed. The numerical analysis confirmed the elastic response observed in the tests and highlighted the key role of the GFRP connectors in coupling the TRC shells, extending the interpretation beyond experimental results. Overall, the study demonstrates the potential of TRC sandwich panels with mechanical connectors as a safe and reliable structural solution. Full article

End-of-life wind turbine blade accumulation is a growing global materials management problem and current industrial recycling routes for glass fiber-reinforced polymer composites remain limited in material recovery value. There is limited understanding on how to recover clean glass fibers while keeping thermal exposure and energy input low, and existing studies have not quantified whether very short isothermal thermal residence can still result in complete matrix removal. The hypothesis of this study is that a mild two-step thermochemical sequence can recover clean glass fibers at lower temperature and near zero isothermal dwell if pyrolysis and oxidation are separated. We used wind-blade epoxy-based GFRP in a step-batch reactor and combined TGA-based thermodynamic mapping, short pyrolysis at 425 °C, and mild oxidation at 475 °C with controlled dwell from zero to thirty minutes. We applied model-free kinetics and machine learning methods to quantify activation energy trends as a function of conversion. The thermal treatment of 425 °C for zero minutes in nitrogen, followed by 475 °C for fifteen minutes in air, resulted in mechanically sound, visually clean white fibers. These fibers retained 76% of the original tensile strength and 88% of the Young’s modulus, which indicates the potential for energy-efficient GFRP recycling. The activation energy was found to be approximately 120 to 180 kJ mol⁻¹. These findings demonstrate energy lean recycling potential for GFRP and can inform future industrial scale thermochemical designs. Full article

Fiber-reinforced plastics (FRP) have been established as spring materials for specific applications for decades. In addition to their material advantages, the associated characteristics of strength and stiffness loss due to fatigue and degradation must also be considered. For FRP springs, the stiffness loss gains importance because of functional relevance. This article focusses on the lifetime design of FRP springs from this perspective, based on the assumption that a service range develops over time and load cycles in which the spring exhibits the desired functional characteristics. This approach was investigated on FRP strip specimens subjected to torsional loading, as well as on GFRP and CFRP volute springs. The expected behaviors were confirmed, and modeling approaches for future applications were identified. Full article

This article provides a multifaceted analysis of the feasibility, purposefulness, and legitimacy of the alternative use of industrial hemp (HF) fibres processed into fabrics and mats as multilayer reinforcement in polymer structural composites, potentially replacing glass fibres (GF) in various industries, including the production of recreational vessels (yachts and motorboats) and other floating products (buoys/floats/pontoons, etc.). Based on the results of physical, mechanical, and morphological tests of new polymer structural composites HFRP vs. GFRP and a comparative analysis of their properties, a structural correlation coefficient for HFRP was determined with respect to GFRP [W_K = 1.66 (6), provided that the grammage of reinforcement of the skin/shell of the selected floating object/structure is comparable]. This article presents the possibility of meeting stringent environmental protection requirements for the future safe recycling and/or disposal of products and their post-production waste manufactured from HFRP at the end of their service life. Fire tests of these new materials have shown that it is possible to use them completely (almost 100%) in the near future, mainly through energy recovery. Full article

This study investigates the interfaces of ultra-high-performance fibre-reinforced concrete (UHPFRC). The interfaces of UHPFRC-to-UHPFRC were studied using two techniques: (i) slant shear test and (ii) shear key test. Moreover, the glass fibre-reinforced polymer (GFRP) rebars were also used in the shear plane to optimise durability. Six UHPFRC push-off specimens with different GFRP reinforcement ratios and changing shear plane angles were investigated and compared to existing models and codes. The results showed that the slant shear and shear test performed better without adding the epoxy agents due to the presence of steel fibres, which provided the excellent benefit of bridging the cracks and increasing the friction resistance. Furthermore, the shear strength increased substantially with inclined shear planes, rising from 607 kN in the vertical case to 1837 kN at a 60° inclination. However, the existing equations for predicting the shear strength overpredict the shear strength with a vertical shear plane and underpredict the shear strength of the angled shear plane. The test results also confirm that steel fibres enhance shear transfer through crack bridging, while epoxy weakens the interface by limiting mechanical interlock. The linear elastic behaviour of GFRP rebars also influences the shear transfer mechanism by contributing dowel action without yielding. Full article

This study investigates the effects of different proportions of waste rubber fiber aggregates on the flexural behavior of reinforced concrete beams. Beam specimens were prepared with different proportions (5%, 10%, and 15%) of waste rubber fiber aggregates, and composite beams formed with pultruded GFRP profiles were tested under vertical load. According to the results of this study, cube compressive strength, cylinder tensile strength, and beam flexural strength decreased by 27.5%, 50%, and 47.6%, respectively, with the use of a 15% waste rubber aggregate. As a result of the four-point bending tests performed on reinforced concrete beams, the maximum load-carrying capacity of the beams decreased significantly after increasing the waste rubber aggregate ratio to 10% and 15%. However, a general improvement in the ductility of the beams was observed. One of the main results of this study is that when the waste rubber aggregate content is 5%, the best balance between strength and ductility is achieved, and the performance closest to the reference beams is obtained. The tests also revealed that the Ø10-5% specimen exhibited higher performance in terms of both load-carrying capacity and yield stiffness. On the other hand, although the 15% waste rubber aggregate ratio caused a decrease in the maximum load-carrying capacity. along with an increase in the diameter of the tensile reinforcement, this decrease was quite low. Finally, an overall decrease in energy consumption capacity was observed with increasing waste rubber aggregate content in all test beams. This can be attributed to the acceleration of shear damage in the beam and the shrinkage of the area under the load–displacement curve as the amount of waste increases. Additionally, SEM analyses were conducted in order to investigate the microstructural behavior of the rubberized concrete. This study has shown that the use of waste rubber aggregates can be environmentally and economically beneficial, especially at the 5% level. Full article

Wind turbine blades (WTBs) have always been considered one of the greatest engineering achievements. They primarily use glass fiber-reinforced polymers (GFRPs) because of their lightweight nature, impressive strength-to-weight ratio, and durability. Until now, typical disposal methods of End-of-Life (EoL) WTBs are landfill or incineration. However, such practices are neither environmentally sustainable nor compliant with current regulations. This study investigates a low-temperature solvolysis process using a poly(ethylene glycol)/NaOH system under ambient pressure for efficient decomposition of the polyester matrix, promoting the potential of chemical recycling as an alternative to landfilling and incineration by offering a viable method for recovering glass fibers from WTB waste. A parametric study evaluated the influence of reaction time (4–5.5 h) and catalyst-to-resin ratio (0.1–2.0 g NaOH per g resin) on solvolysis efficiency. Optimal conditions (200 g PEG200, 12.5 g NaOH, 10 g GFRP, 5.5 h) achieved an ~80% decomposition efficiency and fibers exhibiting minimal surface degradation. SEM and EDX analyses confirmed limited morphological damage, while excessive NaOH (>15 g) caused notable etching of the glass fibers. ICP-OES of liquid residues detected high Na (780 mg/L) and Si (139 mg/L) concentrations, verifying partial dissolution of the fiber structure under strongly alkaline conditions. After applying a commercial sizing agent (Hydrosize HP2-06), TGA confirmed ~1.2% sizing mass, and nanoindentation analysis showed the interfacial modulus and hardness of re-sized fibers improved by over 70% compared to unsized recycled fibers, approaching the performance of virgin fibers. Full article

This study investigated the changes in the physical and mechanical properties of glass fiber-reinforced polymer (GFRP) rebars during and after exposure to elevated temperatures. The specimens were tested at 23 °C (ambient), 150 °C, 200 °C, 250 °C, 300 °C, and 350 °C in an electric kiln coupled to a universal testing machine, without exposure to flames. The mechanical properties evaluated were the tensile strength and modulus of elasticity. After exposure, the surface damage was examined using scanning electron microscopy (SEM), and resin loss was quantified through fiber content tests. At ambient temperature, the average tensile strength and modulus of elasticity of the rebars were 956.4 MPa and 44.7 GPa, respectively. Damage observed during heating was more severe than that observed after heating and subsequent cooling. At 350 °C, up to 37% of the tensile strength was lost during heating, whereas the maximum reduction in modulus of elasticity was 8.3%, indicating that the fibers themselves were not significantly compromised by heat. After exposure and cooling, the maximum reduction in tensile strength was less than 1% (after exposure to 150 °C), while the modulus of elasticity exhibited a 7.9% decrease (after exposure to 200 °C). The glass transition temperature was measured at 101.7 °C. SEM analysis revealed signs of resin degradation caused by heat, including superficial damage, microcracks, reduced resin cover over the fibers, and ruptured fibers. Fiber content tests after exposure demonstrated a direct correlation between reduced fiber content and the decline in mechanical properties. The behavior of GFRP rebars after heating and cooling can provide important insights for assessing structural safety in post-fire buildings, since natural cooling led to partial resin recovery and improvements in mechanical performance. Full article

As an efficient and clean renewable energy source, wind energy plays a crucial role in optimizing the energy structure and facilitating a low-carbon transition. However, onshore and offshore wind turbines in cold regions are prone to blade icing, which not only results in a decrease in power generation efficiency and an increase in blade load but also poses the risk of equipment damage. This study employed icing wind tunnel tests and numerical simulation methods to investigate the icing patterns and variations in aerodynamic performance under different blade materials, blade airfoils, and blade angles of attack. The results indicate that with the decrease in ambient temperature, the icing amount on aluminum alloy blades is significantly higher than that on glass fiber reinforced plastic (GFRP) blades; furthermore, the lower the ambient temperature, the smaller the difference in icing distribution characteristics between the two types of blades. When the blade angle of attack changes, the icing distribution characteristics on the blade surface exhibit significant variations. Under the condition of large angles of attack, the icing amount on the lower airfoil surface of the blade increases, while that on the upper airfoil surface decreases. Icing leads to a reduction in the airfoil lift coefficient and an increase in the drag coefficient, thereby causing a decline in the lift-to-drag ratio. With the extension of icing time, the aerodynamic performance of the blade continues to deteriorate. When the icing time reaches 5 min, the maximum reduction in the airfoil lift coefficient is 60.1%, the maximum increase in the drag coefficient is 40.9%, and the maximum reduction in the lift-to-drag ratio is 67.7%. In addition, the blade lift and drag coefficients undergo significant changes with the increase in the angle of attack. For airfoils with large angles of attack, a distinct phenomenon of advanced flow separation is observed after icing. This study can provide a data foundation for research on icing characteristics of wind turbine blades in cold regions and the subsequent development of anti-icing and de-icing methods. Full article

This paper presents the findings of an experimental study on the structural response of glass fiber-reinforced polymer (GFRP)-concrete composite beams. The connectors were fabricated from GFRP dowels, epoxy resin-saturated E-glass roving, and/or adhesive layers. The composite beams were subjected to a four-point bending test configuration and examined for their failure modes and load-deformation characteristics. The test results showed that the developed configurations of composite beams significantly outperformed the response of the standalone GFRP I-section profile and non-composite beams. The provision of a discrete interfacial connection successfully prevented the local and lateral torsional buckling of the profile, doubled the initial stiffness, increased the load-carrying capacity by around three times, and imparted a certain degree of ductility and reserve capacity to the otherwise brittle system. The failure occurred primarily due to the shearing of the web. Other modes of failure were observed in the form of the cracking/crushing of concrete, delamination of the laminate, and buckling/crushing of the web. The epoxy-bonded composite beams displayed the highest stiffness, while those with 45° inclined dowels exhibited the highest load-carrying capacity. The results were compared against those predicted by the available analytical expressions, and required modifications are suggested. Full article

To address the challenge of detecting debonding damage in glass-fiber-reinforced polymer (GFRP) rock bolt anchorage structures, this study proposes a time reversal detection method based on piezoelectric sensing and a Convolutional Neural Network–Support Vector Machine (CNN-SVM) model. Through COMSOL 6.1 numerical simulations and laboratory experiments, the influence of debonding length, location, and quantity on the characteristics of detection signals was investigated. The results indicate that an increase in debonding length leads to a rise in the amplitude of the focused signal, a reduction in the main peak frequency, and greater energy concentration around the main peak. Specifically, the amplitude increased by 10.96% (simulations) and 54.9% (experiments) for lengths from 0 to 1200 mm, while the peak frequency decreased by 3.43% (simulations) or increased slightly (experiments). When the debonding location changes, the amplitude remains stable, while the main peak frequency increases by 4.94% in simulations and shifts to higher frequencies experimentally, and the energy exhibits an increasing trend. An increase in the number of debonding points results in decreased amplitude, elevated main peak frequency, and more severe wave packet overlap. Multi-defect configurations reduced the amplitude by 16.68% (simulations) and 3% (experiments), with peak frequency increases of up to 3.35%. Based on these characteristics, a CNN-SVM evaluation model was constructed, using the wavelet time–frequency maps of experimental signals as input and the debonding state as output. The model achieved evaluation accuracy rates of 99%, 100%, and 100% under varying debonding lengths from 10 to 100 mm, different debonding positions, and increasing numbers of debonding defects, all exceeding 95%, thereby validating the reliability and high precision of the proposed method. Full article

Based on the design concept of double-skin composite columns, this study proposes an enhanced configuration in which the inner steel tube is reinforced with fiber-reinforced polymer (FRP) stirrup-confined ultra-high-performance concrete (UHPC), leading to the development of FRP stirrup-confined UHPC–steel tube (FSCUS) hollow composite columns. Twelve glass FRP stirrup-confined UHPC–steel tube (GFSCUS) hollow composite column specimens were tested under axial compression. Analysis of load–displacement curves, and of load–strain curves of individual components, was performed. The effects of various parameters, including thickness and outer diameter of the steel tube, configuration and spacing of the GFRP stirrup, and steel fiber content of the UHPC, on the compressive behavior of the GFSCUS hollow composite columns were systematically investigated. The test results indicate that the influence of the thickness and outer diameter of the steel tube on the axial compression behavior is primarily governed by the effectiveness of the composite action between the steel tube and the confined concrete under axial compression load. The spacing and configuration of the FRP stirrup, conversely, determine the efficacy of the confinement provided to the concrete. The incorporation of steel fibers enhances both the peak load and the ductility due to their bridging effect. However, an excessive fiber content can restrict the lateral expansion of the concrete, thereby diminish the confining effect of the hoops and leading to a reduction in load-carrying capacity. Full article

Corrosion continues to be a major challenge affecting the service life, safety and durability of steel-reinforced concrete (RC) structures. The deterioration of steel not only reduces structural capacity but also increases long-term maintenance costs. To address this limitation, glass fiber-reinforced polymer (GFRP) is being investigated as an alternative to conventional steel reinforcement, particularly in aggressive environments. This work examines the behavior of composite columns reinforced with GFRP bars with steel stirrups. Sixteen square columns of 150 × 150 × 850 mm dimensions, cast with M30 grade concrete, were reinforced using either GFRP or steel, while varying stirrup spacing and bar diameters. Experimental observations showed that GFRP reinforcement contributed about 10–12% of the ultimate capacity of the columns. A marked enhancement in load carrying capacity of GFRP-RC columns was obtained with closer stirrup spacing. The axial strength of GFRP-reinforced columns was comparable to steel-reinforced ones with the same main reinforcement ratio. Ductility increased by 12% when stirrup spacing was reduced. The difference between analytical and experimental values ranged between 12% and 15%, whereas experimental and numerical results differed by 10–12%. Based on these results, a modification factor derived from IS 456:2000 is proposed for predicting the capacity of ‘GFRP-reinforced’ columns. The outcomes clearly highlight the potential of GFRP reinforcement as a durable, sustainable and practical substitute for conventional steel reinforcement. Full article

The present study investigated the tensile behavior, failure mechanisms and deformation characteristics of glass fiber-reinforced polymer (GFRP) composites with symmetric [0°/90°/90°/0°] and asymmetric [0°/90°/0°/90°] stacking sequences across a temperature range of 30–150 °C. Tensile testing revealed superior mechanical performance in the symmetric lay-up, with higher tensile strength and failure strain sustained across elevated temperatures. Failure mode analysis revealed a transition from ductile failure to brittle failure with increasing temperature, which was more pronounced in the asymmetric lay-up, along with increased delamination and reduced fiber pull-out. Failure surface examination supported these findings, revealing better interfacial bonding and matrix integrity in the symmetric lay-up. Deformation analysis further confirmed a more homogeneous distribution of strain and longer failure time in symmetric laminates. Across all the metrics, including toughness, energy absorption, and strain uniformity, the symmetric configuration outperformed the asymmetric counterpart, underscoring the critical role of balanced stacking in enhancing the thermal durability. The observed temperature-induced degradation and its impact on mechanical and failure behavior emphasize the need for temperature-sensitive design strategies in GFRP-based structures. Full article

The current study aims to investigate the effect of using hybrid bars on the bending characteristics of hybrid fiber-reinforced concrete (FRC) beams. For this purpose, a series of flexural tests on FRC beams were conducted. Four FRC beams were fabricated, each with a section of 120 mm × 185 mm and an overall length of 1.5 m. The FRC beams’ tension reinforcement consisted of a hybrid configuration of steel and glass fiber-reinforced polymer (GFRP) rebars. The concrete mix included a hybrid fiber content of 1% by volume, with 0.75% for hooked-end steel fibers (SF) and 0.25% polypropylene fibers (PP). The simply supported FRC beams were tested under the action of two-point loads. The results demonstrated that the inclusion of hybrid fibers substantially improved the crack widening and propagation in FRC beams compared to normal concrete (NC) beams. The maximum load capabilities of the FRC beams surpassed those of the NC beams up to 13.2%. The GFRP bars further enhanced the beams’ load-carrying capacity with an observed increase of up to 42.5%, when compared to the steel-reinforced FRC beam (BFRC-3S). Additionally, hybrid reinforcement improved ductility, with increases of 39.1% and 167.1% when one or two GFRP bars were replaced by steel, respectively. Full article