Search Results (488)

Grouted anchors made of glass fiber-reinforced polymer (GFRP) have gained popularity in cold-region construction projects, primarily owing to their resistance to corrosion and low density. Although prior research has addressed the bond–slip characteristics of FRP-to-concrete joints, a theoretical formulation that links cumulative freeze–thaw damage of the mortar matrix to the progressive loss of bond strength at the GFRP bar–mortar interface is still lacking. This work provides a combined experimental and theoretical examination of how the bonding capacity of ribbed GFRP bars in cement mortar declines after 0, 30, 60, and 90 FTCs. Compression and splitting tension tests were carried out on mortar cubes, while pullout specimens were used to assess the interfacial bond strength. Two mortar grades commonly used in anchorage practice (M25 and M35) and two bar diameters (12 mm and 16 mm) were selected as test variables. After 90 FTCs, the maximum bond strength fell by as much as 64.1%, whereas the post-peak residual bond strength suffered an even more pronounced drop of up to 79.3%. Meanwhile, the residual-to-peak-bond-strength ratio decreased steadily with the number of FTCs, marking a shift from a mechanically interlocked interface to a friction-governed one. The higher-grade mortar (M35) experienced clearly superior resistance to freeze–thaw attack compared to M25, while the larger-diameter bars (16 mm) degraded faster. An analytical model for estimating the bond-strength degradation is proposed, where an exponential environmental factor was introduced and the decay constants were calibrated via nonlinear regression against the bond-strength retention ratios at 0, 30, 60, and 90 FTCs. The proposed models are calibrated empirical relationships that reproduce the measured degradation well within the tested parameter ranges and indicate reasonable internal stability under leave-one-group-out cross-validation. This study provides two theoretical provisions: the freeze–thaw degradation of the GFRP–mortar bond can be effectively described by a single exponential damage law whose decay constant quantifies the rate at which the interfacial capacity is exhausted, and the residual-to-peak-bond-strength ratio serves as a mechanistic indicator of the transition from mechanical interlock to friction-controlled failure. These provisions quantitatively link mortar degradation to interfacial capacity loss, thereby providing a theoretical basis for durability design of GFRP grouted anchors in cold regions. Full article

The present study evaluated the potential of waste glass fiber-reinforced polymer (wGFRP) as a soil reinforcement material for geotechnical applications. Laboratory model footing tests and large-scale direct shear tests were carried out on sandy soils prepared at three relative densities (Dr = 40%, 65%, and 85%) and reinforced with four wGFRP contents (0.5%, 0.75%, 1.0%, and 1.5%) to evaluate bearing capacity, settlement behavior, and shear strength characteristics. Environmental characterization and a performance-based economic assessment were also conducted to assess environmental compatibility and identify the optimum reinforcement content from engineering and economic perspectives. The results showed that wGFRP improved sand performance under all investigated conditions. Optimum performance was achieved at 0.75% wGFRP, where the ultimate bearing capacity increased by up to 92%, settlement decreased by up to 79.2%, and the internal friction angle increased by up to 6.2%. Environmental characterization indicated compatibility under the investigated laboratory conditions, with negligible trace-element release and no significant physicochemical, microstructural, or chemical degradation. The economically optimum reinforcement content depended on the selected engineering objective and the initial relative density. The findings indicate that wGFRP has strong potential as a sustainable, environmentally compatible, and cost-effective soil reinforcement material, offering a high-value reuse pathway in geotechnical applications. Full article

Glass fiber-reinforced polymer (GFRP) is widely used in wind power, construction, and aerospace for its superior properties. However, studies on its blown-sand erosion degradation and prediction remain limited. This study investigates the degradation and prediction of blown-sand erosion behavior in GFRP strips using a one-factor-at-a-time (OFAT) experimental design. Simulated experiments quantify the effects of factors such as erosion angle, velocity, sand flow rate, and erosion time on mechanical behavior. Results show that epoxy-layer deformation and internal fiber fracture increase with erosion angle and velocity. The tensile strength decreased by approximately 16.8% at an erosion angle of 90° when the velocity, sand flow rate, and erosion time were fixed at 26 m/s, 55 g/min, and 30 min, respectively. At an erosion velocity of 31 m/s, with the erosion angle, sand flow rate, and erosion time fixed at 90°, 55 g/min, and 30 min, respectively, the strength reduction reached 28%. Under a 45 g/min sand flow rate, the strength reduction reached 6%, while extending the erosion time to 50 min led to a decrease of 35%. Furthermore, a particle swarm optimization (PSO)-assisted, interpolation-based inverse identification model was established to back-calculate erosion parameters from measured strain fields. The mean in-sample reconstruction error was approximately 4.2%, whereas leave-one-condition-out validation yielded an overall mean error of 31.8%, with factor-specific errors ranging from 12.8% to 43.8%, indicating limited generalization to unseen conditions. This work elucidates the progression of material degradation from initial damage to severe failure and provides laboratory reference data for understanding the post-erosion residual behavior under the investigated erosion-only conditions. Full article

Hollow filament-wound glass fiber-reinforced polymer (GFRP) tubes are known for their high specific strength, corrosion resistance, and structural efficiency. The nonlinear flexural response of these structures is controlled by the interaction of material and stability mechanisms, which are not well-captured by traditional linear sectional approaches. In this paper, a nonlinear sectional analytical model is proposed to determine the flexural response and the corresponding failure modes of hollow filament-wound GFRP tubes subjected to monotonic four-point bending. The formulation combines Euler–Bernoulli beam kinematics, layered numerical integration of the annular cross-section, asymmetric nonlinear tensile and compressive constitutive relations, iterative neutral-axis equilibrium, tangent-stiffness degradation, and compression-side local shell-buckling assessment in a curvature-controlled incremental solution routine. This framework captures progressive stress redistribution, neutral-axis migration, degradation of flexural rigidity and transition from material-controlled compression failure to local shell instability. Validation was performed against experimental results for five filament-wound glass/vinylester tube configurations with nominal ±55° winding and diameter-to-thickness ratios, D/t, ranging approximately from 20 to 75. The predicted load–deflection and moment–curvature responses were in good agreement with the experimental measurements with mean errors of about 1.6% for peak load, 1.8% for ultimate bending moment and 2.4% for peak curvature. The model also reproduces the experimentally observed governing failure mechanisms over the investigated configurations. The convergence study with sectional discretization showed that 200 integration layers provide a good compromise between numerical accuracy and computational efficiency, with less than 1% variation compared to the refined 500-layer reference solution. The proposed reduced-order formulation has low computational cost in the present implementation and provides a direct physical interpretation of the evolving sectional response. Because a directly comparable finite-element runtime was not reported for the benchmark model, no quantitative FE speed-up factor is claimed. Thus, the proposed framework provides an efficient analytical tool for the nonlinear flexural evaluation of hollow filament-wound GFRP tubes in the validated geometric, loading and laminate domain. Full article

Wind turbines are among the most widely adopted renewable energy systems, yet the end-of-life management of wind turbine blades remains a major challenge. The turbine blades are primarily made of glass fiber-reinforced polymers (GFRP), which are difficult to recycle without degrading their inherent structural integrity. Instead of shredding or downcycling, this study explores a reuse strategy that preserves intact laminate from decommissioned blades and repurposes them into structural beams via glue-laminated fiber-reinforced polymers (GL-FRP) assemblies. This concept was implemented using commercial GFRP for blade-derived laminates, focusing on the structural feasibility rather than material sourcing. Adhesive joints were designed as the key enabling mechanism for structural reuse and characterized under tensile loading. Building on this, the flexural performance of GL-FRP beams was investigated in horizontal and vertical configurations, yielding an ultimate load-bearing capacity of 8 kN and 20 kN, respectively. Furthermore, stress distributions obtained from experiments, finite element (FE) simulations, and analytical frameworks were evaluated and compared. The results highlight the governing role of interlaminar stress in determining structural performance and failure of the horizontal beam. The findings provide a foundational understanding of repurposing decommissioned wind turbine blades as structural elements, offering a novel strategy for material upcycling in wind energy sector and contributing to the development of circular construction solutions. Full article

Corrosion of steel reinforcement is a major cause of deterioration in reinforced concrete (RC) structures exposed to aggressive environments. Although fiber-reinforced polymer (FRP) reinforcement provides excellent corrosion resistance, its confinement effectiveness in RC columns has not been fully understood. This study experimentally investigated the axial compressive behavior of rectangular RC short columns reinforced with steel, carbon fiber-reinforced polymer (CFRP), and glass fiber-reinforced polymer (GFRP) bars. Ten specimens with different reinforcement types and stirrup configurations were tested under monotonic axial compression to evaluate compressive strength, axial strain response, deformation behavior, failure mechanisms, and confinement performance. The results indicated that the contribution of FRP reinforcement depended on the reinforcement configuration and confinement mechanism. Specimens reinforced with CFRP longitudinal bars exhibited higher axial capacity than the steel-reinforced control specimen within the tested configurations; however, the influence of the longitudinal reinforcement ratio should also be considered. GFRP stirrups exhibited confinement behavior comparable to CFRP stirrups, whereas CFRP stirrups experienced premature fracture at bent corner regions, which reduced their confinement effectiveness and deformation capacity. Reducing stirrup spacing from 150 mm to 75 mm provided limited improvement in compressive strength because of premature stirrup failure and insufficient development of confinement effects. Existing confinement models tended to overestimate the post-peak response of FRP-reinforced columns. These preliminary findings provide experimental insights into the confinement behavior of FRP-reinforced concrete columns and contribute to the development of improved analytical models. Full article

The rapid expansion of fiber-reinforced polymers (FRPs) in wind energy, transportation, and aerospace is generating increasing amounts of accompanied waste, making effective valorization essential to a circular economy. This review compares FRP recovery technologies in terms of recovered-fiber quality, operating conditions, post-treatment, environmental impacts, and industrial applicability. Then, it also examines direct reuse, FRP remanufacturing, and reuse in cementitious composites. Quantitative synthesis indicates that high-quality recycled carbon fibers (rCFs) generally retain more than 90% of their original strength, whereas mechanically recovered glass fibers (rGFs) typically retain approximately 70–90%. The preferred pathway depends on the intrinsic value, damage state, morphology, and residual properties. Components with sufficient residual capacity should be directly reused; high-quality fibers are better suited to polymer remanufacturing; and heterogeneous or lower-grade glass-FRP (GFRP) fractions are more compatible with cementitious applications, where mechanically recycled GFRP can provide interfacial bond strengths comparable to conventional engineering macrofibers. Future research should establish quantitative links among recovered material quality, processing, interfacial behavior, and end-use performance, while adopting consistent environmental and economic assessment boundaries. A graded utilization framework is therefore required to support both large-scale and value-added reuse of FRP waste. Full article

Recycled glass fiber-reinforced polymer (GFRP) powder from decommissioned wind turbine blades offers sustainable reinforcement for wood–plastic composites (WPCs), but its efficiency is limited by poor interfacial adhesion with the polypropylene (PP) matrix caused by surface epoxy residues. In this study, GFRP/WPCs with a fixed formulation of 15 wt% GFRP, 10 wt% wood flour, and 75 wt% PP were used to compare two modification strategies: MAPP compatibilization (1–7 wt%) and H₂O₂ treatment (5–30%). MAPP modification improved the mechanical properties of GFRP/WPCs, with the optimal concentration varying by property: flexural strength reached its maximum (75.45 MPa, +24.7%) at 1 wt% MAPP, while tensile strength (+9.2%), flexural modulus (+20.7%), and impact strength (+18.9%) were maximized at 3 wt% MAPP. H₂O₂ at 10% achieved higher strength gains (tensile: +23.65%, i.e., 26.7 MPa; flexural: +27.93%, i.e., 77.4 MPa; impact: +35.29%, i.e., 16.98 kJ/m²) but moderately reduced flexural modulus. FTIR confirmed up to 71.7% epoxy removal by H₂O₂, exposing cleaner fibers. Both modifications slightly lowered thermal decomposition temperatures but increased char residues and PP crystallinity via enhanced nucleation. SEM showed that MAPP created a compatible interphase, while H₂O₂ enabled direct mechanical interlocking. Surface free energy analysis revealed that MAPP increased polar components, whereas H₂O₂ increased dispersive components. Overall, MAPP offers simpler processing and balanced properties, while H₂O₂ provides superior strength at the cost of some stiffness—providing practical guidance for tailoring recycled GFRP/WPCs for construction and sustainable applications. Full article

Glass fiber-reinforced polymer (GFRP) and carbon/glass hybrid fiber-reinforced polymer (HFRP) laminates with two vinyl ester resin systems were investigated to evaluate their early environmental response, residual mechanical performance, and damage behavior after moisture-assisted low-temperature exposure and freeze–thaw cycling (FTC). After 150 days of moisture preconditioning, the conditioned specimens were exposed to −50 °C or subjected to FTC between −50 °C and 22 °C. Tensile, compressive, flexural, in-plane shear, interlaminar shear, and compression-after-impact (CAI) tests were conducted. Fourier transform infrared spectroscopy (FTIR), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM) were used to examine chemical structure, thermomechanical response, and damage morphology. FTIR spectra showed no obvious changes in the characteristic absorption bands of the vinyl ester matrix. DMA showed condition-dependent changes in thermomechanical behavior, with the largest decrease in glass transition temperature reaching 5.5 °C after Condition 3. Tensile and in-plane shear properties were largely retained, whereas compressive, flexural, interlaminar shear, and CAI properties were more sensitive; the largest CAI strength loss was 19.1%. Hybrid stacking affected the property retention and damage tolerance of the laminates under the designed FTC condition. SEM observations identified interfacial debonding, matrix microcracking, and interlaminar crack growth as the main damage features. Full article

This study investigates the degradation behavior of decommissioned wind turbine blade composites in organic fluid systems, with particular focus on the subcritical acetic acid route. Supercritical acetone and supercritical n-butanol were used as screening media, while retired-blade glass fiber-reinforced polymer (GFRP) composites and laboratory-prepared glass fiber/epoxy composites were used to compare resin removal and fiber recovery behavior. The screening results showed that supercritical acetone and supercritical n-butanol caused partial matrix degradation but left visible organic residues on recovered fibers, whereas subcritical acetic acid produced cleaner fiber surfaces under lower-pressure conditions. The effects of temperature and reaction time were then analyzed in the subcritical acetic acid system. At 280 °C for 60 min, the epoxy resin degradation rate reached 99.81%, and the recovered glass fibers retained 96.49% of their tensile strength. Gas chromatography–mass spectrometry (GC–MS) analysis indicated that the liquid products mainly contained phenols, esters, and other oxygenated organics, with bisphenol A derivatives as representative components. These products suggest a coupled degradation process involving epoxy network swelling, bond cleavage, fragment release, and secondary acetylation in acetic acid. The boiling-point difference between acetic acid and the main degradation products, together with the product distribution obtained after recovered-acid addition, indicates the potential of acetic acid reuse. These findings support subcritical acetic acid as a promising medium for resin removal and glass-fiber recovery from decommissioned wind turbine blade composites. Full article

This study investigates the shear behavior and failure mechanisms of innovative hybrid structural beams fabricated by filling pultruded glass fiber-reinforced polymer (GFRP) box sections with waste rubber-reinforced concrete (RuC). Environmentally friendly concrete was produced by replacing natural aggregate with recycled tire-rubber fibers at proportions of 0%, 5%, 10%, and 15%. Twelve hybrid beam specimens were tested to evaluate the synergistic effects of rubber content and stirrup spacings of 16, 20, and 27 cm on shear capacity, ductility, and crack propagation. The experimental results revealed that the reference specimen (S16-0%) exhibited the maximum shear capacity of 154.41 kN and a brittle failure mode, while an increase in rubber content to 15%, combined with wider stirrup spacing, significantly reduced this capacity to a minimum of 96.89 kN (S27-15%). However, the 5% rubber replacement ratio achieved an optimal performance balance by preserving sufficient load-carrying capacity while enhancing flexural deformation and ductility, particularly in specimens with 16 cm stirrup spacing. Damage analysis demonstrated that longitudinal splitting cracks initiated in the mid-span tension zone at the bottom of the pultruded profiles, with final localized damage concentrated at the geometric corners of the box section. Crucially, the outer pultruded GFRP profiles provided substantial structural confinement, effectively mitigating the strength loss associated with high rubber incorporation and controlling the progression of sudden brittle failure. These findings highlight that combining pultruded GFRP profiles and optimized RuC offers a structurally viable and sustainable solution for modern infrastructure applications. Full article

Glass fiber-reinforced polymer (GFRP) is increasingly used in civil engineering because of its high strength-to-weight ratio, corrosion resistance, durability, and low maintenance requirements. However, its inherently brittle behavior and limited ductility restrict its application in seismic regions due to poor energy dissipation capacity. To address this limitation, this study proposes a novel hybrid system comprising pultruded GFRP profiles and a replaceable steel link with ductile pipe sections. The pipe element confines inelastic deformation to the steel components while keeping the GFRP members elastic. Numerical results demonstrate stable hysteretic behavior with no significant degradation in strength or stiffness, confirming the effectiveness of the proposed system. Also, increasing the ratio of the pipe thickness to the flange thickness of the steel link (β) ensures suitable performance provided that plastic hinge formation remains confined to the ductile pipe element and replaceable steel link. Adding the pipe element to the I-shaped steel link increases web stress when β ≤ 1.0 (leading to web yielding), while stresses in the flange, GFRP beam, and GFRP columns are reduced by 46–51%, 17–60%, and 15–40%, respectively. However, for β > 1.0, stresses in GFRP components are not reduced but slightly increase by 1–9% (negligible), making β > 1.0 not recommended. Also, by changing the $\beta =0.50$ to $0.75$, $1.00$, $1.25$, and $1.50$, the flexural capacity, stiffness, and energy dissipation are enhanced by 1.51 times to 2.46 times, 1.18 times to 1.38 times, and 1.35 times to 1.68 times, respectively. Finally, the necessary design equations for the proposed system are presented. Full article

The use of Glass Fiber-Reinforced Polymer (GFRP) bars to reinforce concrete beams can provide high resistance to corrosion, high performance, high sustainability, and reasonable strength but with low ductility. This study focused on the structural behavior and indirect evaluation of the ductility index of hollow and solid beam specimens reinforced with GFRP bars, steel bars, or both (hybrid). Eight simply supported beam specimens with dimensions of 1200 mm (length), 150 mm (height), and 100 mm (width) were made using self-compacted concrete (SCC) and tested using two-point repeated loading. The tests results showed that the ultimate load capacity of the tested solid and hollow beams reinforced with GFRP bars were 78% and 67% higher than that of the corresponding solid and hollow beam specimens with steel-bar reinforcement. The measured energy absorption is “instantaneous” energy absorption because the residual stress disappears after the load is removed at the end of the test and any cracks will close due to the semi-linear response of the beam specimens reinforced with GFRP bars. Regarding the solid beam specimens, those containing GFRP bars showed an increase in energy absorption of 64–127% compared with the corresponding reference beams. The hollow beam specimens containing GFRP bars showed an increase in energy absorption of 21–68% compared with the corresponding reference beam containing three steel bars. Full article

Crack detection in composite structures remains a central challenge in structural health monitoring, particularly when sensing must rely on a small number of embedded multiplexed fiber Bragg gratings (FBGs). Here, we present a physics-guided convolutional neural network (CNN) framework for crack-associated event detection from multiplexed FBG interrogator signals acquired during the three-point bending of glass-fiber-reinforced polymer (GFRP) beams. The dataset was constructed from raw interrogator recordings and synchronized force–displacement metadata while preserving the cracked and non-cracked loading stages present in the experiments. Each candidate response was encoded by 13 synchronized optical, loading, and mechanics-guided descriptors, including Euler–Bernoulli expected strain and residual terms, where the residual denotes the difference between the measured response and the elastic response predicted by beam theory. A compact one-dimensional CNN operating on 30-response sequences was evaluated on 64 experimental runs under strict leave-one-run-out validation. At the selected operating point, the model reached window-level precision of 0.900, recall of 0.910, F1 score of 0.905, and balanced accuracy of 0.942, while the corresponding run-level decision reached a precision of 0.833, a recall of 1.000, an F1 score of 0.909, and a balanced accuracy of 0.969. Bootstrap resampling over runs yielded 95% confidence intervals of 0.787–0.978 for window-level F1 and 0.769–1.000 for run-level F1. To probe generalization beyond the initial fabrication batch, the final frozen pipeline was also tested once on seven later-batch runs from two newly manufactured specimens, where it reached a window-level precision of 0.908, a recall of 1.000, an F1 score of 0.952, a balanced accuracy of 0.969, an ROC-AUC of 0.979, a PR-AUC of 0.955, and perfect run-level classification. These results show that a compact sequence CNN, enriched with mechanics-guided strain interpretation, can extract robust crack-event signatures from multiplexed FBG measurements while preserving a simple and reproducible modeling pipeline. Full article

This study investigates the flexural behavior, load-carrying capacity, and crack propagation of concrete beams reinforced with hybrid glass-fiber-reinforced polymer (GFRP) and steel bars. To evaluate the structural performance, concrete beam specimens with cross-sectional dimensions of 150 mm × 300 mm and a total length of 2050 mm were fabricated using a design concrete compressive strength of 35 MPa and tested under flexural loading. Each tested specimen featured a distinct hybrid reinforcement configuration to investigate the influence of bar arrangement on the mechanical behavior. Flexural cracks were systematically monitored using a crack-width comparator gauge at specific loading stages, accounting for key milestones such as ultimate load capacity and sudden load drops. The experimental findings were complemented by an analytical model to validate the performance parameters and predict the ultimate capacity. The results demonstrate that the specific configuration and arrangement of hybrid reinforcement significantly influence the post-cracking stiffness and crack growth. Specifically, the hybrid configuration effectively balances the ductile response of steel with the brittle behavior of GFRP, achieving significant control over serviceability crack widths and an enhanced ultimate load-carrying capacity. Experimental results indicated that for elements exhibiting identical axial stiffness, the reinforcement layering configuration provided a 66% improvement in the deformability factor alongside a 10% enhancement in the load-carrying capacity. It is recommended that the steel tension reinforcement be positioned in the inner layer at a spacing of about two times the GFRP bar diameter to mitigate corrosion risks. Additionally, it was established that the theoretical load capacity accounted for 70% to 86% of the experimental load capacity. Full article