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Wind-turbine blades pose significant disposal challenges in the wind-energy sector due to the increasing demand for wind farms. Therefore, this study researched the revaluation of Raw-Crushed Wind-Turbine Blade (RCWTB), obtained through a non-selective blade crushing process, as a partial substitute for aggregates in Self-Compacting Concrete (SCC). The aim was to determine the most adequate water/cement (w/c) ratio and amount of superplasticizing admixtures required to achieve adequate flowability and 7-day compressive strength in SCC for increasing proportions of RCWTB, through the production of more than 40 SCC mixes. The results reported that increasing RCWTB additions decreased the slump flow of SCC by 6.58% per 1% RCWTB on average, as well as the compressive strength, although a minimum value of 25 MPa was always reached. Following a multi-criteria decision-making analysis, a w/c ratio of 0.45 and a superplasticizer content of 2.8% of the cement mass were optimum to produce SCC with up to 2% RCWTB. A w/c ratio of 0.50 and an amount of superplasticizers of 4.0% and 4.6% were optimum to produce SCC with 3% and 4% RCWTB, respectively. Concrete mixes containing 5% RCWTB did not achieve self-compacting properties under any design condition. All modifications of the SCC mix design showed statistically significant effects according to an analysis of variance at a confidence level of 95%. Overall, this study confirms that the incorporation of RCWTB into SCC through a careful mix design is feasible in terms of flowability and compressive strength, opening a new research avenue for the recycling of wind-turbine blades as an SCC component. [ABSTRACT FROM AUTHOR]

This paper presents a study on the interlaminar shear strength (ILSS) retention of three types of glass fiber–reinforced polymer (GFRP) bars with different surface textures subjected to four types of conditioning environments (alkaline, alkaline, salt, acidic, and water) at two temperature levels (ambient laboratory and high temperature) for 3, 6, and 12 months. The conditioning temperature plays a critical role in reducing the strength of the bars. Scanning electron microscopy revealed the extent of damage to the fibers, resin, interface, and fracture morphologies in the cross sections. The causes of fiber cracking and lower strength upon exposure were validated by point energy-dispersive X-ray spectroscopy analyses, which detected the leaching of silicon from the fiber structure. Prediction models using multiple linear regression (MLR) and artificial neural networks (ANNs) were developed using Matrix Laboratory (MATLAB R2023b) software and compared. The coefficients of determination of the MLR and ANN prediction models were found to be 0.29 and 0.90, respectively, indicating the superiority of machine learning–based models in identifying and accounting for nonlinearities and highlighting their potential application in GFRP bars. Finally, the correlation between the transverse shear strength (TSS) and ILSS of the tested GFRP bars was identified. The ILSS of the bars was found to be approximately 0.26 times the TSS for any given conditioning scenario. [ABSTRACT FROM AUTHOR]

To evaluate the axial compressive performance of the hollow sandwich GFRP-concrete-steel double-skin tubular columns (DSTC), 15 composite column specimens were produced to study the effect of various design variables. And the study presents a rational and accurate finite element (FE) model that provides a detailed working mechanism of the DSTCs, leading to the enrichment of parametric research and the creation of an extensive database. Based upon the unified strength theory of double shear, limit equilibrium theory, and superposition theory, the study evaluates and compares the effectiveness of different bearing capacity calculation models. With each added millimeter in the thickness of the GFRP tube, the ultimate bearing capacity of the DSTC specimen increased by 23.6% and 61.8%, respectively, compared to that of the 1.5 mm thick GFRP tube sample. The lower the hollow ratio of the DSTC section, the higher its ultimate bearing capacity. Specimens with a hollow ratio of 0.3 and 0.43 showed an ultimate bearing capacity 1.4 times and 1.25 times higher, respectively, than those with a hollow ratio of 0.6. The study observes a relatively high level of precision in the results of the ultimate equilibrium theory, with an average error rate of 20%. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the two-way shear strength of precast concrete box culverts reinforced with glass fiber–reinforced polymer (GFRP) bars. The investigations included testing four full-scale specimens reinforced with GFRP bars under truck wheel load in accordance with current Canadian design codes. The load was applied to the top slab at three different distances: d (effective depth), 1.5d, and 2.5d from the tip of the haunch to the edge of the load plate. One of the specimens was placed and tested on an aggregate bedding material instead of the rigid floor of the test laboratory. Following experimental testing, a theoretical study was conducted to evaluate experimental shear strength to predicted values using different provisions of several North American and international design standards. Two-way shear failure in the top slab occurred in all tested box culverts, indicating that GFRP-reinforced concrete box culverts are critical in shear under traffic wheel loads. The behavior of the tested box culverts was significantly affected by changing the load location or testing the specimen on an aggregate bedding material. On the other hand, the available two-way shear equations conservatively predicted the two-way shear strength of the top slab of the box culverts. Moreover, the two-way shear action equation used in the Canadian standards considers only the cracking strength of concrete. Therefore, an equation has been proposed to consider the characteristics of the GFRP bars and shear span to effective depth ratio. The proposed equation accurately predicted the two-way shear strength and may be considered in future provisions. Finally, the findings demonstrated the feasibility and efficiency of using GFRP bars as internal reinforcement in concrete box culverts. [ABSTRACT FROM AUTHOR]

Glass fiber–reinforced polymer (GFRP) composites have emerged as alternative materials for building applications, and one common loading scenario for GFRP members in building structures is eccentric compression. This compression may occur due to the locations of these members in structures or shapes of their cross sections, causing compressive loads not in alignment with the centerlines of these members. Under this loading scenario, the shear stresses induced by second-order effects may lead to shear and delamination failure prior to compressive or tensile failure due to the low shear strength of GFRP composites compared with their compressive and tensile strengths. This paper presents a study on pultruded GFRP laminated plates subjected to eccentric compression loading, including experimental investigations, numerical modelings, and analytical derivations, with a focus on the effects of the slenderness of the GFRP plate and the eccentricity of the compression load on their failure mode and compressive capacity. Two types of failure mode were observed from the experiments. One was compressive/tensile failure mode, the other was shear and delamination failure mode. In a coordinate system with slenderness as the horizontal axis and eccentricity ratio as vertical axis, zones for shear failure and compressive/tensile failure were identified and a curve that delineates the two zones was developed. Furthermore, predictions of shear and delamination failures based on the results obtained from numerical and analytical studies were presented and compared with the actual failure observed from the experiments. [ABSTRACT FROM AUTHOR]

Fiber composite materials are key components of numerous future technologies. This results in a strongly increased demand and also in increasing amounts of waste in the upcoming years. Thus, recycling of fiber composite materials has become an intensively researched topic. At 95 wt %, glass fiber‐reinforced plastics make up the largest part. This review article will provide an overview of the state of the art of common recycling strategies and technologies, with particular focus on the advantages and challenges of glass fiber‐reinforced polymer recycling. [ABSTRACT FROM AUTHOR]

Glass fiber–reinforced polymer (GFRP) composites have been used in civil construction because of their high strength, lightweight, and corrosion resistance. However, their thermal sensitivity due to the polymer resin requires further understanding of the fire performance of these structures, because the heat from the fire could cause glass transition and decomposition of GFRP composites and degrade their mechanical properties. Fire dynamic simulations were conducted in this study to investigate heat propagation, which considered airflow aerodynamics, in typical single-story residential houses with walls and roofs in the form of GFRP web–flange sandwich structures. The temperature progressions and gradients in the GFRP wall and roof members were quantified, which allowed for the identification and further understanding of the locations and development of glass transition and decomposition in the GFRP composites during fire exposure. The effects of the building floor layouts, fire source locations, additional fire resistance gypsum plasterboard, and a fresh air supply were further discussed and clarified. [ABSTRACT FROM AUTHOR]

In response to the growing global demand for both energy and a clean environment, there has been an unprecedented rise in the utilization of renewable energy. Wind energy plays a crucial role in striving for carbon neutrality due to its eco-friendly characteristics. Despite its significance, wind energy infrastructure is susceptible to damage from various factors including wind or sea waves, rapidly changing environmental conditions, delamination, crack formation, and structural deterioration over time. This research focuses on investigating non-destructive testing (NDT) of wind turbine blades (WTBs) using approaches based on the vibration of the structures. To this end, WTBs are first made from glass fiber-reinforcement polymer (GFRP) using composite molding techniques, and then a short pulse is generated in the structure by a piezoelectric actuator made from lead zirconate titanate (PZT-5H) to generate guided waves. A numerical approach is presented based on solving the elastic time-harmonic wave equations, and a laser Doppler vibrometer (LDV) is utilized to collect the vibrational data in a remote manner, thereby facilitating the crack detection of WTBs. Subsequently, the wave propagation characteristics of intact and damaged structures are analyzed using the Hilbert–Huang transformation (HHT) and fast Fourier transformation (FFT). The results reveal noteworthy distinctions in damaged structures, where the frequency domain exhibits additional components beyond those identified by FFT, and the time domain displays irregularities in proximity to the crack region, as detected by HHT. The results suggest a feasible approach to detecting potential cracks of WTBs in a non-contact and reliable way. [ABSTRACT FROM AUTHOR]

The utilization of fiber-reinforced polymer (FRP) reinforcements in structural design is increasing due to their non-corrosive nature. However, the anisotropic features and linear elastic behavior of FRP rebars have led researchers to explore the use of hybrid combinations of FRP and steel reinforcements. Current codes and guidelines predominantly focus on the design of glass FRP (GFRP) reinforced structural elements, leaving a gap in incorporating the hybrid use of FRP-steel combinations and different types of FRP materials, such as carbon FRP (CFRP). This study conducted experimental investigations on concrete beams reinforced with GFRP, CFRP, and hybrid (GFRP-steel and CFRP-steel in combination) rebars, comparing the results with theoretical models. Ten full-scale beams were tested under monotonic loading. Test results revealed that existing codes overestimate GFRP reinforced beam displacements while underestimating CFRP reinforced beam displacements. A reduction factor is proposed for the effective moment of inertia expression given by ACI 440.11-22 to predict the deflections of CFRP reinforced and hybrid reinforced beams. The experimental data for CFRP and hybrid reinforced concrete beams align well with the predictions calculated using the proposed equations. [ABSTRACT FROM AUTHOR]

This study intended to measure the efficiency of different strengthening techniques to advance the flexural characteristics of reinforced concrete (RC) beams using glass fiber-reinforced polymer (GFRP) laminates, including externally bonded reinforcement (EBR), externally bonded reinforcement on grooves (EBROG), externally bonded reinforcement in grooves (EBRIG), and the near-surface mounted (NSM) system. A new NSM technique was also established using an anchorage rebar. Then, the effect of the NSM method with and without externally strengthening GFRP laminates was studied. Twelve RC beams (150 × 200 × 1500 mm) were manufactured and examined under a bending system. One specimen was designated as the control with no GFRP laminate. To perform the NSM method, both steel and GFRP rebars were used. In the experiments, capability, as well as the deformation and ductileness of specimens, were evaluated, and a comparison was made between the experimental consequences and existing standards. Finally, a new regression was generated to predict the final resistance of RC beams bound with various retrofitting techniques. The findings exhibited that the NSM technique, besides preserving the strengthening materials, could enhance the load-bearing capacity and ductileness of RC beams up to 42.3% more than the EBR, EBROG, and EBRIG performances. [ABSTRACT FROM AUTHOR]

A novel generation of composite sandwich beams with laminated carbon fiber)reinforced polymer skins and pultruded glass fiber-reinforced polymer core materials was examined for their flexural behavior. The strength and failure mechanisms of the composite sandwich beams in flatwise and edgewise configurations were investigated using three-point static bending tests. These sophisticated composite structures must be designed and used in a variety of sectors, and our research provides vital insights into their performance and failure patterns. In comparison to the reference specimens (FGM-1), the carbon nanotube-reinforced specimens’ bending capacity was affected and ranged from −2.5% to 7.75%. The amount of the carbon nanotube addition had a substantial impact on the beams’ application level and load-carrying capacity. Particularly, the application of 0.5 wt% additive in the outermost fiber region of the beams, such as in FGM-4, led to an increase in the bending capacity. However, the stiffness values at the maximum load were decreased by 0.3%–18.6% compared to FGM-1, with the minimum level of the decrease in FGM-4. The experimental results were compared with the theoretical calculations based on the high-order shear deformation theory, which yielded an approximation between 11.99% and 12.98% by applying the Navier’s solution. [ABSTRACT FROM AUTHOR]

The aim of this study is to examine the effect of the partial replacement of sand by Glass Fiber-Reinforced Polymer (GFRP) waste on the mechanical properties of cement mortars. Compressive and flexural tests were carried out on mortars containing 0, 3, 5, 10, and 15% (by volume) of GFRP waste. It appears that the incorporation of 3% GFRP waste did not significantly affect the mechanical strength. However, further increasing the GFRP waste content led to a reduction in the mechanical strength. The flexural strength seemed less affected than the compressive strength, since the decrease in flexural strength at a 10% replacement was only 37%, while it was 54% for the compressive strength. However, an improvement in the toughness of the mortar with an increase in the substitution rate was observed. The reference sample displayed a flexural toughness of 0.351 N·m, while the mortar incorporating 15% of GFRP exhibited a flexural toughness of 0.642 N·m. The reuse of GFRP waste in cementitious materials, therefore, constitutes an interesting recycling solution. [ABSTRACT FROM AUTHOR]

Using geopolymeric recycled aggregate concrete (GRAC) rather than conventional concrete to fill glass fiber–reinforced polymer (GFRP) tubes to produce high-performance structural members is a promising green construction technique. In this article, an experimental study investigating the impact behavior of GFRP tube-confined GRAC under axial impact loadings is presented. Moreover, split Hopkinson pressure bar (SHPB) impact tests were conducted, with several variable parameters: (1) confinement ratio (0, 6-ply, and 8-ply GFRP tubes); (2) recycled aggregate (RA) replacement ratio (0%, 50%, and 100%); and (3) strain rate (ranging from 29.4 to 263.3 s−1). In addition, the experimental results of the impact behavior of GFRP-confined GRAC were compared with those of confined ordinary portland cement (OPC) concrete. The test results showed that the confinement of the GFRP tube can remarkably improve the impact resistance of GRAC. The dynamic increase factor (DIF) of confined GRAC was higher than that of confined OPC-based concrete. Similar to OPC-based concrete, the incorporation of RA negatively influenced the impact properties of GRAC, but these influences could be alleviated by GFRP tube confinement. The compressive properties of GFRP-confined GRAC exhibited a strong strain-rate dependency, while the DIF slightly decreased with an increasing confinement ratio. Finally, a model was developed to predict the dynamic strength of GFRP-confined GRAC by reasonably considering the coupling effects of the RA replacement ratio and confinement ratio. [ABSTRACT FROM AUTHOR]

The main goal of this study is to enhance the crashworthiness performance of tubular composites to absorb more energy by optimizing the winding angle of their fibers. The crashworthiness performance of glass fiber-reinforced polymer composite pipes manufactured using the filament winding is investigated in detail. The effects of the winding angle of the fibers and thickness of the tube wall on the energy absorption were examined through quasi-static compression tests. The composite pipes were produced with 1200 tex E-glass fibers and Epikote 828 resin as the matrix material. The winding angles of ± 30°, ± 45°, ± 55°, ± 75°, and ± 90° were evaluated, and the number of the winding layers, ranged from 1 to 3, was also assessed. Quasi-static axial compressive loading was applied to 15 specimens using a hydraulic actuator. The results revealed that the one-layer specimens experienced buckling damage at low load levels, while an increase in the number of the layers led to higher load-carrying capacity and different types of damages. Furthermore, as the number of the layers increased, the load-carrying capacity and energy absorption of the specimens significantly improved. Progressive failure was observed in the specimens [± 90] for all the layers' configurations, with the specimen [± 90]3, having three layers, exhibiting the highest performance in terms of the load-carrying capacity and energy absorption. The failure modes indicated a combination of the fibers' separation, buckling, diagonal shear failure, and crushing in the upper and lower heads.

A novel generation of composite sandwich beams with laminated carbon fiber-reinforced polymer skins and pultruded glass fiber-reinforced polymer core materials was examined for their flexural behavior. The strength and failure mechanisms of the composite sandwich beams in flatwise and edgewise configurations were investigated using three-point static bending tests. These sophisticated composite structures must be designed and used in a variety of sectors, and our research provides vital insights into their performance and failure patterns. In comparison to the reference specimens (FGM-1), the carbon nanotube-reinforced specimens’ bending capacity was affected and ranged from −2.5% to 7.75%. The amount of the carbon nanotube addition had a substantial impact on the beams’ application level and load-carrying capacity. Particularly, the application of 0.5 wt% additive in the outermost fiber region of the beams, such as in FGM-4, led to an increase in the bending capacity. However, the stiffness values at the maximum load were decreased by 0.3%–18.6% compared to FGM-1, with the minimum level of the decrease in FGM-4. The experimental results were compared with the theoretical calculations based on the high-order shear deformation theory, which yielded an approximation between 11.99% and 12.98% by applying the Navier’s solution.

The new American Concrete Institute (ACI) design code for glass fiber–reinforced polymer (GFRP)–reinforced concrete (RC) members specifies a single value of 1.20 for the bond-dependent coefficient (kb) of all types of GFRP bars. This value was chosen based on test data from this project, as well as a compilation of data available in the literature. This paper reports on an experimental study that assessed the kb for the new generation of GFRP bars from five different manufacturers with different surface types: deformed/ribbed, helically deformed, helically grooved, double-helical wrap/sand-coated, and sand-coated. Two bar sizes (No. 5 and No. 8)—with 15.9 and 25.4 mm nominal diameters representing the typical range of GFRP-reinforcing bars used in practice as longitudinal reinforcement in concrete members subjected to bending—were selected from each of the manufacturers. Five RC beam replicates were used to increase experimental accuracy. Therefore, a total of 60 beams, including 50 beams reinforced with GFRP bars and 10 control beams reinforced with conventional steel bars for comparison purposes, were constructed and tested to failure according to a predetermined test method. Based on the analysis, the study confirms using the bond-dependent coefficient value of 1.20 as adopted in the new ACI design code for GFRP–RC members. This value is recommended for GFRP bars complying with (or exceeding) the material specification listed in the ASTM International standard specification for solid round GFRP bars for concrete reinforcement. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymers (FRPs) have received considerable research attention because of their high strength, corrosion resistance, and low weight. However, owing to the lack of ductility in this material and the quasi-brittle behavior of concrete, FRP-reinforced concrete (FRP-RC) beams, even with flexural failure, do not fail in a ductile manner. Because the limited deformation capacity of FRP-RC beams depends on the ductility of their compression zones, the present study proposes using a precast confined concrete block (PCCB) in the compression zone to improve the ductility of the beams. A control beam and four beams with different PCCBs were cast and tested under four-point bending conditions. The control beam failed due to shear, and the PCCBs exhibited different confinements and perforations. The goal was to find an appropriate PCCB for use in the compression zone of the beams, which not only improved the ductility but also changed the failure mode of the beams from shear to flexural. Among the employed blocks, a ductile PCCB with low equivalent compressive strength increased the ductility ratio of the beam to twice that of the control beam. The beam failed in pure flexure with considerable deformation capacity and without significant stiffness reduction. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced polymer (GFRP) is widely used in engineering fields involving aerospace, energy, transportation, etc. If internal buried defects occur due to hostile environments during fabrication and practical service, the structural integrity and safety of GFRP structures would be severely undermined. Therefore, it is indispensable to carry out effective quantitative nondestructive testing (NDT) of internal defects buried within GFRP structures. Along with the development of composite materials, microwave NDT is promising in non-intrusive inspection of defects in GFRPs. In this paper, quantitative screening of the subsurface impact damage and air void in a unidirectional GFRP via microwave reflectometry was intensively investigated. The influence of the microwave polarization direction with respect to the GFRP fiber direction on the reflection coefficient was investigated by using the equivalent relative permittivity calculated with theoretical analysis. Following this, a microwave NDT system was built up for further investigation regarding the imaging and quantitative evaluation of buried defects in GFRPs. A direct-wave suppression method based on singular-value decomposition was proposed to obtain high-quality defect images. The defect in-plane area was subsequently assessed via a proposed defect-edge identification method. The simulation and experimental results revealed that (1) the testing sensitivity to buried defects was the highest when the electric-field polarization direction is parallel to the GFRP fiber direction; and (2) the averaged evaluation accuracy regarding the in-plane area of the buried defect reached approximately 90% by applying the microwave reflectometry together with the proposed processing methods. [ABSTRACT FROM AUTHOR]

Typically, archers prepare two sets of bows for competitions in case of bow breakage, but if the limbs of the bow break during a match, archers can become psychologically disadvantaged, leading to potentially fatal consequences. Archers are very sensitive to the durability and vibration of their bows. While the vibration-damping properties of Bakelite® stabilizer are excellent, its low density and somewhat lower strength and durability are disadvantages. As a solution, we used carbon fiber-reinforced plastic (CFRP) and glass fiber-reinforced plastic (GFRP) for the archery limb with stabilizer, commonly used for the limbs of the bow, to manufacture the limb. The stabilizer was reverse-engineered from the Bakelite® product and manufactured using glass fiber-reinforced plastic in the same shape as the existing product. Analyzing the vibration-damping effect and researching ways to reduce the vibration that occurs during shooting through 3D modeling and simulation, it was possible to evaluate the characteristics and the effect of reducing the limb's vibration by manufacturing archery bows and limbs using carbon fiber- and glass fiber-reinforced composites. The objective of this study was to manufacture archery bows using CFRP and GFRP, and to assess their characteristics as well as their effectiveness at reducing limb vibration. Through testing, the limb and stabilizer that were produced were determined to not fall behind the abilities of the bows currently used by athletes, and they also exhibited a noticeable reduction in vibrations. [ABSTRACT FROM AUTHOR]

This study intended to measure the efficiency of different strengthening techniques to advance the flexural characteristics of reinforced concrete (RC) beams using glass fiber-reinforced polymer (GFRP) laminates, including externally bonded reinforcement (EBR), externally bonded reinforcement on grooves (EBROG), externally bonded reinforcement in grooves (EBRIG), and the near-surface mounted (NSM) system. A new NSM technique was also established using an anchorage rebar. Then, the effect of the NSM method with and without externally strengthening GFRP laminates was studied. Twelve RC beams (150 × 200 × 1500 mm) were manufactured and examined under a bending system. One specimen was designated as the control with no GFRP laminate. To perform the NSM method, both steel and GFRP rebars were used. In the experiments, capability, as well as the deformation and ductileness of specimens, were evaluated, and a comparison was made between the experimental consequences and existing standards. Finally, a new regression was generated to predict the final resistance of RC beams bound with various retrofitting techniques. The findings exhibited that the NSM technique, besides preserving the strengthening materials, could enhance the load-bearing capacity and ductileness of RC beams up to 42.3% more than the EBR, EBROG, and EBRIG performances.

A major challenge in today's concrete construction is to lower its carbon footprint to the least possible level. This study provides insights on a new low-CO2 alternative concrete whereby glass fiber-reinforced polymer (GFRP) materials from waste wind-turbine blades (WWTB)—termed as WWTB-GFRP—was utilized as: (ⅰ) replacement of Portland cement at 0%, 10%, 20%, and as (ⅱ) lightweight aggregate replacement for natural aggregates at 0%, 50%, and 100%. The resulting WWTB-GFRP concretes were used in concrete-filled fibre-reinforced polymer (FRP) tubes (CFFTs) whereby the latter serves as a stay-in-place formwork and external reinforcement. Pristine WWTB-GFRP materials (containing wood) and processed ones (by wood removal) were investigated. Results indicate that while both WWTB-GFRP powder and aggregates adversely affect the compression resistance (due to, respectively, the retarding effect of the powder and the slippery surface of the aggregates leading to reduced bonding with the bulk cementitious matrix), the confinement of WWTB-GFRP concrete with FRP tubes offers an innovative tool to restore the strength loss. In fact, valorizing WWTB-GFRP concrete in CFFTs allowed to increase the compressive resistance by more than 100%. Interestingly, under axial compression, FRP tube confinement shifted the stress–strain response from the conventional brittle response to a ductile one whereby the confinement affected the elastic and plastic responses differently. While FRP confinement increased in the elastic limit at higher WWTB-GFRP aggregate content, it resulted in lower slope of the plastic response at higher WWTB-GFRP aggregate content. An analytical assessment demonstrated that a WWTB-GFRP aggregate content of 55% will be optimum for enhancing both elastic and plastic responses. Building upon the ACI 440.2R-17 model for predicting the compressive response of confined concrete incorporating conventional aggregates, a modified model more sensitive to GFRP aggregates and with higher predictive ability was proposed. Research outcomes will contribute to recycling waste materials while endowing further sustainability to concrete.

Several types of fibers have enhanced the structural response of reinforced concrete-filled steel tubes (CFSTs). This article presents a state-of-the-art review of studies done on the axial compressive behavior of steel and glass fiber-reinforced CFSTs. The aim of using fibers is to improve the response of the CFSTs. This research indicates the findings of experimental programs and analytical evaluations of the effects of the fiber incorporation on the behavior of the CFSTs. The results of this research work demonstrate that steel fibers (SFs) have enough evident improving effects on the failure mode and load-carrying capacity of the CFSTs. The SFs greatly increase the ductility of the CFSTs. To enhance the compressive strength and ductility of the CFSTs, adding the SFs by 1% to the concrete mix is more effective than adding by 1.5%. The use of the SFs mixed with expansion agent considerably increases the yield and ultimate loads of the CFSTs. More glass fiber-reinforced polymer (GFRP) sheets reduce buckling and develop the compressive strength of the CFSTs. The implementation of the GFRP jackets not only enhances the load-carrying capacity of the CFSTs, but also increases their ductility. The GFRP reinforcement techniques for the CFSTs are also effective in improving their structural stiffness and energy absorption capacity. [ABSTRACT FROM AUTHOR]

This study investigates the behavior of three concrete beams reinforced with steel and GFRP bars under fire exposure. The fire tests of three beams were conducted including one control steel-reinforced concrete (RC) beam and two GFRP-RC beams. The beams were exposed to fire according to the standard fire curve ISO 834 for 3 h. The investigation parameters included the reinforcement types (i.e., steel and GFRP bars) and diameter of GFRP bars. Based on the experimental results, during fire exposure, the deflection rate of the steel-RC beam was lower than the ones reinforced with GFRP bars. The critical temperatures measured at steel and GFRP bars in the steel-RC and GFRP-RC beams were 593 °C and 300–330 °C, respectively along with the fire durations of 83 and 33–36.4 min, respectively. The different GFRP bar sizes did not affect the fire resistance process. The steel-RC beam had greater fire resistance than the GFRP-RC beams. All test specimens had a fire resistance time lower than two hours. In addition, the 2D simplified finite element method (FEM) using commercial software ANSYS was performed to predict the thermal response of the beam section. Compared with experimental results, the FE model can reasonably predict the thermal responses of the beam sections. [ABSTRACT FROM AUTHOR]

Truss‐like core sandwich panels made of glass fiber‐reinforced polymer (GFRP) composite are extensively exploited in numerous industrial and non‐industrial applications. Most of the time, these structures are exposed to extreme and heavy loads and damaged. Therefore, the mechanical properties of composite sandwich structures are important issue that should be addressed by engineers. For this purpose, the mechanical properties of a GFRP composite sandwich structures with polyurethane foam‐filled M‐shaped core are numerically and experimentally determined in this research. The sandwich panels manufactured for this study are composed of GFRP as fibers and resin epoxy as matrix material. In order to determine the bending and compressive response of the GFRP composite structures, three‐point bending and compression tests are performed using a SANTM ATM‐140 universal testing machine. A finite element method is developed to validate the precision of the experimental results. It is recognized that the finite element data are in remarkably great agreement with those obtained by experimental tests. Hence, the finite element analysis and experiment method could be utilized to predict the mechanical properties of the GFRP composite sandwich panels. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced polymer (GFRP) bars have been used in RC structures due to their high tensile strength capacity and resistance to corrosion in comparison with steel. However, international standards do not recommend their use in RC structure elements subjected to compressive loads. Currently, there is no standard method to determine the compressive characteristics of FRP bars. This article presents a new type of GFRP bars designed specially to support compressive loads: they have additional winding GFRP layers around the longitudinal fibers. An exhaustive experimental study was carried out to obtain compressive properties of the bars: compressive strength, Young’s modulus and stress-strain relation. After post-processing the experimental results of the study, this paper showed compressive strength between 50% and 60% of tensile strength, which allows employing the bars as internal reinforcement in RC structures. Their obtained Young’s modulus is the same in both tensile and compression, which enables the linear stress-strain relation to be extended to the entire range of deformations. This is most advantageous for structural analysis procedures in the linear elastic regime. Finally, based on the experimental results of failure modes, some limitations about the cross-sectional area or the slenderness were proposed for the use as internal reinforcing in RC structures, which helps the researchers in the design procedure for members reinforced with FRP bars.

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This study's aim was to research the ultimate loads and failure modes of single‐bolted pultruded glass‐fiber‐reinforced polymer (PGFRP) connections reinforced by glass fiber sheets (GFSs) under pin‐bearing conditions. In total, 144 specimens with various geometric parameters of GFRP bolted connections with different ratio values of the end distance of PGFRP plate to bolt diameter (e/d) and various ratio values of width of PGFRP plate to bolt diameter (w/d) were considered, and their results are here discussed (e/d = 2,3,4 and w/d = 2,3,4,5). Three types of GFSs (0°/90° GFSs, ±45°GFSs, and chopped strand mat GFSs) were molded by the vacuum‐assisted resin transfer molding (VaRTM) method and used to strengthen the connections. The results show that all three types of GFSs had good effects on the increase in the ultimate load of the connections. In addition, the strengthening effects were decreased with the increase in the e/d ratio of the connections for all types of GFSs. Moreover, theoretical equations were suggested to forecast the ultimate loads and failure modes of pin‐bearing single GFS‐strengthened PGFRP connections with high accuracy (less than 12% deviation). [ABSTRACT FROM AUTHOR]

Due to its induction heating mechanism, eddy current pulsed thermography (ECPT) has been applied to detect defects in conductive materials instead of non-conductive materials, such as glass fiber-reinforced polymer (GFRP). In order to extend the application of ECPT for nondestructive testing (NDT) of non-conductive materials, this study proposes a novel method named eddy current pulsed thermography with an inductive heating layer (ECPT-IHL). This method introduces a temporary inductive heating layer to the surface of the non-conductive materials as an auxiliary heat-generating component. Firstly, the detection mechanisms of ECPT-IHL in transmission detection mode (TDM) and reflection detection mode (RDM) are analyzed, respectively. Then, the feasibility of ECPT-IHL is verified by conducting experiments on GFRP specimens with flat-bottom back-drilled hole (FBH) defects under TDM and RDM modes. In addition, the influence of different inductive heating layers (including Q235 steel plate, 430 stainless steel foil, and flexible graphite sheet) on the defect detection effect in the two detection modes is investigated to optimize the detection performance. Finally, the detection capability of ECPT-IHL is evaluated by detecting FBH defects of different depths, and a feasible and reliable method is proposed to characterize the defect depths in TDM based on the extracted temperature difference. Notably, due to the translucence of GFRP materials, the abnormal temperature response caused by the coupling of heat radiation and heat conduction is also discussed. The results above show that ECPT-IHL successfully extends the application of traditional ECPT to non-conductive materials and is effective in detecting minor defects in GFRP laminates. [ABSTRACT FROM AUTHOR]

This study proposes using glass fiber–reinforced polymer (GFRP) as a stay-in-place structural formwork for casting bridge decks with ultrahigh-performance concrete (UHPC). The GFRP stay-in-place formworks completely replace the bottom layer of rebars, and the top steel reinforcement is also replaced by a GFRP mesh to mitigate the corrosion damage. The formworks were either a flat GFRP plate with square hollow section (SHS) stiffeners or a flat GFRP plate with new Y-shape stiffeners. Concentric static tests on five 1:2.75 scale decks were performed to investigate the effect of stiffener's configuration and the influence of the concrete strength on the performance of bridge decks. Rotational fixity support was used to simulate a real bridge deck connection of supporting girders. All specimens with the stay-in-place formwork exhibited punching shear failure. It was found that the use of Y-shape stiffeners significantly improved the load-carrying capacity of the proposed deck. Replacing normal concrete with UHPC further improved the loading capacity of the deck. The decks demonstrated excellent performance, with the load-carrying capacity 3.8–9.5 times higher than the established equivalent service load depending on the concrete strength and configuration of the GFRP stay-in-place formwork. Deflection at service load was less than span/1,600 for all the decks. Compared with normal-strength concrete (34 MPa), UHPC improved the maximum load-carrying capacity of the deck from 91.4 to 149 kN. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation and modeling of interface creep behavior of glass fiber-reinforced polymer (GRFP) tendons embedded in cemented soils. Rapid and creep pullout tests were carried out on GRFP tendons embedded in cemented soils using a specially developed pullout setup. Interface creep displacement responses for specimens with two different water–cement ratios were derived under various interface shear stress conditions. A modified Burgers model was developed to characterize the interface creep behavior by incorporating a time-dependent viscosity coefficient. This viscosity coefficient was calibrated using creep rate variation obtained experimentally. Regression fittings on a part of interface creep measurements were conducted to determine the value of the parameters of the interface creep model. Additional interface creep measurements were used to validate the applicability of the presented creep testing protocol and the effectiveness of the rheological modeling was validated. [ABSTRACT FROM AUTHOR]

This study presents the tensile properties of glass fiber-reinforced polymer (GFRP) composites under dynamic loadings. The dynamic tensile tests were performed via a high-speed servo-hydraulic testing machine with a velocity ranging from 1 m/s to 15 m/s, corresponding to a strain rate range between 4.9 s−1 and 93.7 s−1. The effects of the strain rate on the tensile strength and dynamic increase factor (DIF) were considered. The results showed that the tensile strength and DIF of GFRP increased with the strain rate. The failure pattern of GFRP was discussed via a group of high-speed camera images. The results of this research can provide useful information for future construction, e.g., protective structures under extreme impacts. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced polymer- (GFRP-) packaged optical fiber (OF) sensors are considered a promising engineering-suitable sensor for structural health monitoring. To date, some critical characteristics of the GFRP-packaged OF (GFRP-OF) sensors have not yet been thoroughly studied. This study aimed to systematically characterize the properties of the GFRP-OF sensors. Firstly, we proposed a dimension optimization method for GFRP-OF sensors by strain transfer theory, which is based on a symmetrical three-layered cylindrical model. Then, we experimentally investigated the properties of the GFRP-packaged fiber Bragg grating sensor and GFRP-packaged distributed optical fiber sensor, including their mechanical properties, strain/temperature sensing performance, fatigue resistance, and corrosion resistance. The experimental results showed that the shear bearing capacity of GFRP-OF sensors was more than 120 times larger than that of the other three coated OF sensors, indicating that GFRP dramatically enhanced the robustness of the OF sensor. The GFRP–OF sensors also feature excellent strain and temperature sensing performance with high linearity and repeatability. The results also demonstrated that the GFRP–OF sensors have good fatigue properties with absolute fluctuations of strain sensitivity coefficients throughout the fatigue cycles within 0.02 pm/με; repeatability error did not exceed 0.5%, and nonlinear errors were less than 2%. A case study presented in the last section also illustrates the effectiveness of the GFRP-OF sensor in a field application. [ABSTRACT FROM AUTHOR]

In the past, glass fiber-reinforced polymer (GFRP)-reinforcement has been successfully applied in reinforced concrete (RC) structures where corrosion resistance, electromagnetic neutrality, or cuttability were required. Previous investigations suggest that the application of GFRP in RC structures could be advantageous in areas with seismic activity due to their high deformability and strength. However, especially the low modulus of elasticity of GFRP limited its wide application as GFRP-reinforced members usually exhibit considerably larger deformations under service loads than comparable steel-reinforced elements. To overcome the aforementioned issues, the combination of steel and GFRP reinforcement in hybrid RC sections has been investigated in the past. Based on this idea, this paper presents a novel concept for the predetermination of potential plastic hinges in RC frames using GFRP reinforcement. To analyze the efficiency of the concept, nonlinear finite element simulations were performed. The results underscore the high efficiency of hybrid steel-GFRP RC sections for predetermining potential plastic hinges on RC frames. The results also indicate that the overall seismic behavior of RC structures could be improved by means of GFRP as both the column base shear force during the seismic activity as well as the plastic deformations after the earthquake were considerably less pronounced than in the steel-reinforced reference structure. [ABSTRACT FROM AUTHOR]

Splicing glass fiber–reinforced polymer (GFRP)-concrete–steel double-skin tubular column (DSTC) is to set connection component at the joint of two or more separated GFRP tubes, and then pour concrete in the double-tube interlayer to form a continuous composite member. In this paper, the splicing DSTC composite members based on steel bar connection were designed and tested under axial compression to determine its mechanical performance. The main parameters include the connection steel ratio, the hollow ratio, and the thickness of GFRP tube. The results show that the GFRP tube presents apparent constraint effect on the concrete at about 60% of the ultimate load. The failure of splicing specimen occurred in the non-splicing section at a certain distance from the splice joint, and the stirrups at the splice joint provide effective constraint effect on the internal concrete. The proposed DSTC splicing method based on steel cage connection can satisfy the strength requirements of splice joint. Nevertheless, the increase of axial steel bar ratio cannot improve the bearing capacity of the splicing column, and the steel ratio of 2.44% is suggested for the splice joint of DSTCs under axial compression. The axial bearing capacity of splicing DSTCs significantly increases with the increase of GFRP tube thickness, but the amount of stirrups should be increased properly when a larger tube thickness is used. Two models were selected to calculate the bearing capacity of splicing members and it is found that Yu's model is more accurate in predicting splicing DSTCs. [ABSTRACT FROM AUTHOR]

The present study concentrates on optimization and the effect of machining parameters on delamination that occurs during drilling operation of pure glass fiber-reinforced polymer (GFRP) composites and added GFRP composites which were developed for resistance to erosion wear. Contribution of drilling parameters to delamination was investigated by using Taguchi method and analysis of variance (ANOVA). Relationship between machining parameters and delamination was modelled by using response surface methodology. Correlations were established between the machining parameters by quadratic regression using response surface methodology (RSM). Delamination factors in the hole entrance and exit were obtained in drilling of pure glass fiber epoxy, and SiO2- and Al2O3-added GFRP materials using the experimental plan. Delamination factors at the hole exits were found bigger than delamination factors at the hole entrances. The smallest delamination values were obtained in GFRP/epoxy composite compared to Al2O3/SiO2-added GFRP composites at the hole exit. In the investigation of machinability of composites, considering the material as a variable, it has been determined that the material has a greater effect on delamination than the cutting parameters. A new machinability index defined and the material having the best machinability of the three materials was Al2O3-added GFRP composite at the entrance. Good machinability was obtained in drilling of pure GFRP/epoxy composite at the hole exit. It has been found that the effect of feed rate on delamination is greater than the cutting speed and the cutting speed has a low effect. Optimization of the multi-objective function created for maximizing the material removal rate, minimizing the delamination, was performed, and the optimum drilling parameters were obtained. As a result of the experimental study, it was found that the amount of delamination increased although the low mechanical property-added GFRP composites with the high resistance to erosion wear in accordance with pure epoxy GFRP composites due to the lack of a strong bond between the epoxy and the fibers in Al2O3 and SiO2. It was observed that the delamination amounts of pure epoxy GFRP, Al2O3-added GFRP, and SiO2-added GFRP composites increased respectively, while the compressive and tensile strengths of these three materials decreased. [ABSTRACT FROM AUTHOR]

This study examines the punching shear and deflection performance of 16 Geopolymer concrete (GC) two-way slabs subjected to monotonic and cyclic loading by considering the reinforcement material, percentage of reinforcement, type of concrete and the concrete grade. The tested specimens indicated that the crack patterns at the failure and failure modes were almost similar regardless of the type of reinforcement or their ratio. Moreover, the slabs reinforced by fibre-reinforced polymer (FRP) bars exhibited a lower punching capacity than those strengthened by steel bars, even for similar reinforcement ratios. In addition, the results showed that upon increasing the concrete strength and reinforcement ratio, a higher punching shear capacity and lower deflections were obtained under cyclic and monotonic loading. In addition, the punching shear performance of GC slabs was found to be better than that of ordinary concrete (OC), even though both were reinforced by the basalt FRP (BFRP) bar. However, the ultimate load capacity of the slabs was reduced as a result of cyclic loading according to the capacity of the same specimen, resulting from static loading. However, the reduction is very low for slabs reinforced with FRP slabs. Further, the slabs reinforced by FRP had a better fatigue performance compared with slabs reinforced by steel bars with respect to cyclic loading. The results of the tests were also used to evaluate the accuracy of the available punching shear capacity equations. [ABSTRACT FROM AUTHOR]

Several types of fibers have enhanced the structural response of reinforced concrete-filled steel tubes (CFSTs). This article presents a state-of-the-art review of studies done on the axial compressive behavior of steel and glass fiber-reinforced CFSTs. The aim of using fibers is to improve the response of the CFSTs. This research indicates the findings of experimental programs and analytical evaluations of the effects of the fiber incorporation on the behavior of the CFSTs. The results of this research work demonstrate that steel fibers (SFs) have enough evident improving effects on the failure mode and load-carrying capacity of the CFSTs. The SFs greatly increase the ductility of the CFSTs. To enhance the compressive strength and ductility of the CFSTs, adding the SFs by 1% to the concrete mix is more effective than adding by 1.5%. The use of the SFs mixed with expansion agent considerably increases the yield and ultimate loads of the CFSTs. More glass fiber-reinforced polymer (GFRP) sheets reduce buckling and develop the compressive strength of the CFSTs. The implementation of the GFRP jackets not only enhances the load-carrying capacity of the CFSTs, but also increases their ductility. The GFRP reinforcement techniques for the CFSTs are also effective in improving their structural stiffness and energy absorption capacity.

This study investigates the behavior of three concrete beams reinforced with steel and GFRP bars under fire exposure. The fire tests of three beams were conducted including one control steel-reinforced concrete (RC) beam and two GFRP-RC beams. The beams were exposed to fire according to the standard fire curve ISO 834 for 3 h. The investigation parameters included the reinforcement types (i.e., steel and GFRP bars) and diameter of GFRP bars. Based on the experimental results, during fire exposure, the deflection rate of the steel-RC beam was lower than the ones reinforced with GFRP bars. The critical temperatures measured at steel and GFRP bars in the steel-RC and GFRP-RC beams were 593 °C and 300–330 °C, respectively along with the fire durations of 83 and 33–36.4 min, respectively. The different GFRP bar sizes did not affect the fire resistance process. The steel-RC beam had greater fire resistance than the GFRP-RC beams. All test specimens had a fire resistance time lower than two hours. In addition, the 2D simplified finite element method (FEM) using commercial software ANSYS was performed to predict the thermal response of the beam section. Compared with experimental results, the FE model can reasonably predict the thermal responses of the beam sections.

A total of nine specimens were constructed and tested under cyclic loads to investigate the differences in seismic behavior between glass fiber-reinforced polymer (GFRP)-reinforced concrete (RC) joints and RC beam-to-column joints. The experimental parameters included stirrup ratios, axial pressure ratios and concrete strength of the beam-to-column joints. The cyclic loading test results showed that the GFRP-RC beam-to-column joints can withstand significantly high lateral deformations without exhibiting brittle failure. Moreover, the RC beam-to-column joint exhibited significantly higher energy dissipation and residual displacement than the GFRP-RC beam-to-column joint by 50% and 60%, respectively. Finally, a shear capacity calculation method for the core zone of this kind of joint was proposed, which agreed well with the experimental results.

Concrete-filled glass fiber-reinforced polymer (GFRP) tube (CFFT) columns benefit from significant concrete confinement effects that enhance its structural performance compared to conventional internally reinforced concrete members. CFFTs are currently utilized mostly for exterior applications, as the uncertainty of their performance in fire situations has slowed their adaptation in buildings. To address this uncertainty, a series of ambient temperature and fire tests were conducted on CFFT columns with slenderness ratios (KL/r) ranging from 6.9 to 62.4, using GFRP tubes of 113 mm outer diameter and 3.8 mm wall thickness. The strength increase provided by the GFRP tubes as compared to plain concrete columns was reduced from the initial 214% increase at a KL/r of 6.9 to 104% at a KL/r of 62.4. The fire tests revealed that unprotected CFFT columns with KL/r = 57.4 were able to sustain the applied design service loads (44% of ultimate capacity) for up to 108 min in a standard fire. However, it was determined that the unprotected GFRP tubes lost their structural integrity after approximately 10 min of fire exposure, when the temperature on the inside of the tube reached 350°C, thereby only providing thermal protection to the concrete core after the 10-min mark. The unique outcomes of this new study indicate that CFFT columns can be a viable design option in fire situations. [ABSTRACT FROM AUTHOR]

This study aims at assessing the long-term bond behavior of headed-end glass fiber-reinforced polymer (GFRP) bars to basalt fiber-reinforced cementitious composite (BFRCC) exposed to 300 consecutive freezing-and-thawing cycles, followed by 75 cycles of wetting and drying, mimicking successive winter and summer seasons. A total of 85 pullout specimens reinforced with recently developed basalt fiber pellets and steel fibers were tested. The durability of the specimens was quantified in terms of visual analysis, residual compressive strength, relative dynamic modulus of elasticity, as well as the residual pullout capacity. The addition of fibers was capable of retaining approximately 90% of the pullout capacity for specimens exposed to harsh conditions owing to the restriction of cracks in the fiber-reinforced cementitious composites. Therefore, the results confirmed the suitability of steel-free reinforcement systems for long-term application under severe freezingand- thawing and wetting-and-drying environments. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced polymer (GFRP) ship structures are generally fabricated by hand lay-up; thus, the environmental factors and worker proficiency influence the fabrication process and presence of error in the non-destructive evaluation results. In this study, the ultrasonic testing of GFRP hull plate prototypes was conducted to investigate the statistical significance of the influences of the design parameters, e.g., the glass fiber weight fraction (Gc) and thickness variations, on the measurement error. The GFRP hull plate prototypes were fitted with E-glass fiber chopped strand mats (40 wt % content) with different thicknesses (7.72 mm, 14.63 mm, and 18.24 mm). The errors in the thickness measurements were investigated by conducting pulse-echo ultrasonic A-scan. The thickness variation resulted in increased error. Furthermore, hull plate burn-off tests were conducted to investigate the fabrication qualities. Defects such as voids did not have a significant influence on the results. The statistical analysis of the measurement errors confirmed that the thickness variations resulted in a strong ultrasonic interference between the hull plates, although the hull plates had similar specific gravity values. Therefore, the ultrasonic interference of the layer group interface should be considered to decrease the GFRP hull NDE errors with respect to an increase in the thickness and Gc. [ABSTRACT FROM AUTHOR]