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The brittle behavior of concrete under axial compressive loading has been a persistent issue. This study investigates the effectiveness of a hybrid Basalt-E-glass confinement (B-CSM) in improving the compressive behavior of concrete. The B-CSM confinement demonstrates a considerable improvement in ultimate strength and strain capacity by over 250 and 500%, respectively, making it a favorable solution for enhancing the ductility of concrete structures. Specimens at 18.43 MPa unconfined strength, confined with 3-layer B-CSM, demonstrated a 258% ultimate strength enhancement. For 24.43 MPa specimens, the same confinement resulted in a 207% increase in ultimate strength. Specimens with an initial ultimate strain of 18.43 MPa, when confined with 3-layers, showed a notable 516% increase. Likewise, for 24.43 MPa specimens, the same confinement led to a significant 395% improvement in ultimate strain. The use of B-CSM confinement is also effective in terms of cost compared to synthetic fiber-reinforced polymer jackets, and its availability is widespread. Existing analytical models for fiber-reinforced polymer confinement were evaluated, and it was found that these models could not predict the ultimate strength and strain of B-CSM-confined concrete. Therefore, this study proposes a unique regression-based approach for predicting the various points of the compressive stress vs. strain curve of B-CSM confinement. These points are then used to trace the complete stress vs. strain curve, which matches closely with experimental results. This work contributes to the development of new design recommendations for B-CSM confined concrete structures, which can enhance the performance of concrete structures and potentially reduce construction costs. [ABSTRACT FROM AUTHOR]

The objective of this study is to enhance the efficiency of urban air mobility (UAM) air transportation by determining the optimal design, materials, and processes of seven different manufactured fiber-reinforced plastics (FRP), and to confirm their applicability for next-generation UAM aircraft seats. Structural designs for the aircraft seat models were carried out using carbon fiber-reinforced plastic (CFRP), glass fiber-reinforced plastic (GFRP), and GFRP chop materials, employing Autoclave, Hot-press, and vacuum-assisted resin transfer molding (VaRTM) processes, resulting in a total of seven FRP configurations. It was confirmed that CFRP seats were 50% lower weight than aluminum models, while GFRP seats showed a 30% reduction. Although Autoclave processing resulted in the highest tensile strength at 985 MPa, VaRTM processing also produced strength levels comparable to Autoclave processing. Structural integrity assessments of the seat models, utilizing the Korean aviation standards (KAS), confirmed that the designed seat models exhibited no failure or deformation under the conditions required by the technical standards. This study provides insights into the potential application of the seven types of FRP materials in the design of aircraft seats, offering weight reduction benefits and meeting the structural integrity requirements outlined by KAS. [ABSTRACT FROM AUTHOR]

Web openings in deep RC beams significantly reduce the strength and stiffness of these structural elements. To overcome this, strengthening practices have been implemented by incorporating various techniques. Several studies have reported on the application of externally bonded fiber-reinforced polymer (FRP) techniques. In contrast, research on use of steel materials, such as steel plates or bars, for strengthening is limited. Therefore, this study applied a carbon fiber–reinforced polymer (CFRP), steel plates, and steel reinforcement to investigate the importance of steel in this area of strengthening. The effects of the opening configuration, installation of the strengthening material, and thicknesses of the CFRP and steel plates were investigated. The application of CFRP, steel plates, and steel reinforcement enhanced the load-carrying capacity of the RC deep beams. Strengthening via steel reinforcement resulted in the maximum improvement among all the installation techniques, except when the CFRP and steel plate thicknesses were increased. Furthermore, maximum improvement was observed when the strengthening material was applied around the outer surface of the opening, compared with the other installation techniques. [ABSTRACT FROM AUTHOR]

This study investigates a novel retrofitting technique to prevent premature axial failure and collapse of RC walls during earthquakes, attributed to inadequate compressive strain capacity in boundary regions. The technique involves fiber-reinforced polymer (FRP) confinement using laminate and anchors. To assess its effectiveness, four full-scale RC walls retrofitted with FRP and two reference walls were tested under consistent axial loads and reversed cyclic lateral loads. The experiment examined various variables, including axial load ratio, anchor spacing, anchor cross-sectional area, confinement type, number of confinement units, and confinement zone depth. The findings revealed that FRP confinement significantly enhanced the strain capacity of concrete in the boundary regions, preventing axial failure and instead causing failure controlled by reinforcing bar fracture, resulting in up to a 100% increase in wall drift capacity. Although FRP confinement had little effect on the equivalent viscous damping ratio, it substantially extended energy dissipation by improving the drift capacity. The study suggests that in design processes, FRP confinement should maintain the stress–strain condition of the boundary regions at a prepeak condition until reinforcing bar fracture occurs, to avoid axial failure. [ABSTRACT FROM AUTHOR]

Ductility is an important structural design characteristic for ensuring that any overloaded structural member or structure shows visible warnings of an incipient or impeding failure through large deformations and/or excessive cracking. At present, there is a knowledge disparity in quantifying the flexural ductility of prestressed concrete (PC) systems, particularly with the evolution of prestressing reinforcement to incorporate nonmetallic fiber-reinforced polymer (FRP) tendons. There is a need to adopt innovative prestressing technologies and new prestressing systems to facilitate the use of partially bonded, unbonded (externally and internally), and hybrid tendons in which the prestressing reinforcement may consist of bonded–unbonded steel or bonded–unbonded FRP tendons or a combination of both. With the development of new prestressing systems incorporating FRP tendons, accurate evaluation of the ductility of these systems has become a serious concern. In an attempt to converge on a rational approach for evaluating the ductility of hybrid PC members, a review of the evolution of ductility measures proposed in the technical literature is carried out, covering conventional methods and ductility measures specified in design codes. Based on a critical assessment of these measures, it was found that the concept of net tensile strain offers, at present, a most rational approach for evaluating the ductility of prestressed concrete flexural members, which can be extended for hybrid PC members. Accordingly, a simple yet accurate design-oriented method is developed for quantifying the ductility of hybrid PC members using conventional measures such as curvature ductility ratio or, more importantly, using the net tensile strain concept. Practical Applications: In this study, different methods proposed in the technical literature for evaluating the flexural ductility of prestressed concrete (PC) members were reviewed and assessed, with particular focus on the applicability of these methods to hybrid PC members—those utilizing a combination of different prestressing systems and/or prestressing materials. Based on the results of this assessment, it is concluded that the net tensile strain concept used in design codes for designing ductile structural members can be extended easily and rationally to any type of hybrid PC systems. These include systems in which the prestressed tendons consist of a combination of bonded steel–unbonded fiber–reinforced polymer (FRP), bonded steel–unbonded steel, bonded FRP–unbonded steel, and bonded FRP–unbonded FRP. In analogy with the flexural strength and analysis approach adopted in design codes, a direct design-oriented method is developed, which would allow design engineers to effectively and efficiently estimate the nominal moment capacity of any type of hybrid PC systems, quantify their ductility by means of the curvature ductility index (or ratio), and establish their maximum reinforcement limits utilizing the net tensile strain concept. [ABSTRACT FROM AUTHOR]

The near-surface mounted glass fiber–reinforced polymer (NSM GFRP) technique may encounter problems such as peeling-off and premature failure of NSM GFRP. To tackle these issues, this study explores the effects of carbon fiber–reinforced polymer (CFRP) U-wraps on the behavior of NSM GFRP retrofitted RC beams. Six RC beams were tested. One beam served as the control beam, another was retrofitted with two NSM GFRP bars without U-wraps, and four beams were retrofitted with an identical configuration but incorporated 1–4 pairs of U-wraps at each beam end. The experimental results confirmed the efficiency of the NSM GFRP retrofitting technique. The U-wraps successfully prevented peeling-off failure and forced the GFRP bars to work until rupture. NSM GFRP retrofitting moderately extended the elastic branch of the load–deflection curve in comparison to that of the control beam, increased the yield load by 22.4% and the ultimate load by 32.2%. The U-wraps significantly extended the postyield branch, improving the yield load by 28.6%–30.2% and ultimate load by 50.9%–57.5% compared with the control beam. NSM GFRP retrofitting transitioned the high ductility (7.3) to moderate ductility (2.9). Meanwhile, NSM GFRP retrofitting with 1–4 pairs of U-wraps reduced the ductility to 4.9, 4.4, 4.0 (high ductility), and 3.4 (moderate ductility). NSM GFRP retrofitting and U-wrapping negligibly increased the elastic stiffness, whereas NSM GFRP retrofitting enhanced the postyield stiffness by 380.8%–763.6% compared with the control beam. Finally, sectional analyses were performed and accurately predicted the yield moment capacity of RC beams retrofitted with NSM FRP, which can be useful for structural engineers. [ABSTRACT FROM AUTHOR]

The behavior of concrete structures subjected to shear forces involves the contribution of several shear force transfer actions, such as aggregate interlock, dowel action, concrete residual tensile along the fracture process zone, and transfer through the uncracked concrete. While the contribution and interaction between these actions dependt on the shape and kinematics of the critical shear crack, the prediction models available either do not consider all these actions or are based on linear or bilinear shapes for the critical crack. In this context, this paper presents a multiaction model in which the shear actions are considered in the equilibrium of forces and moments based on the shape and kinematics of the critical shear crack. The crack shape, represented by a quadratic Bézier curve, was obtained from an optimization process using a genetic algorithm. The results obtained from the model include the location, shape, and kinematics of the critical crack and the final shear strength and the contributions of each mechanism. The outcomes of the proposed approach were compared with experimental results reported in the literature for beams without stirrups and made with fiber-reinforced concrete (FRC) and fiber-reinforced polymer (FRP) or conventional steel bars. The experimental behavior was accurately simulated, especially for the critical shape and shear strength, which presented relative errors of around 1% and 7%, indicating good agreement. In addition, the model revealed that the residual tensile stress resulting from a discrete fiber action had the highest impact on the load-bearing capacity, following the same observations as the reference studies. The proposed model represents a promising methodology to predict the shear behavior of reinforced concrete beams with various combinations of materials. [ABSTRACT FROM AUTHOR]

In structural recycling of wind turbine blades, two options are often distinguished: reuse and repurpose. The latter was the main subject of the present research carried out by the authors in a research consortium with the leading Polish industry waste recycler. The main goal of the project was to develop, design, and demonstrate the first domestic footbridge made of decommissioned wind turbine blades, taking into account the review of existing ideas. This paper presents an experimental investigation to determine the material parameters and to evaluate the structural behavior of a decommissioned wind turbine blade to be adopted for a footbridge. Terrestrial laser scanning and comprehensive material testing were performed according to ASTM standards to determine the actual blade geometry, the stacking sequence, and the mechanical properties of the blade composite materials. The experimentally determined strengths, elastic moduli, and Poisson's ratios of the composites extracted from the shell and the spar cap along the blade were very high and definitely sufficient for the fiber-reinforced polymer bridge girders. Then, a four-point edgewise bending test was performed on an 11 m section of the blade to evaluate its structural behavior: stiffness, ultimate strength, global safety factor, and fatigue life. The full-scale model of the blade bridge girder behaved linearly elastic in the full load range up to 1,250 kN of the total load, did not reach the ultimate carrying capacity, and exhibited only small local damages (laminate cracking). The results of these tests revealed that the LM 29.1-type wind turbine blades were suitable to be reutilized as main girders for a footbridge. Using the presented research results, the first bridge in the world made of decommissioned wind turbine blades was designed and installed in the late fall of 2021 in Poland. [ABSTRACT FROM AUTHOR]

Shear strengthening of existing reinforced concrete (RC) members with externally bonded (EB) fabric-reinforced cementitious matrix (FRCM) composites represents an attractive solution with respect to alternative strengthening techniques. The EB FRCM could be side-bonded, U-wrapped, or fully wrapped around the beam cross section. Compared with analogous research on EB fiber-reinforced polymers (FRPs), limited work was performed to study the contribution of the EB FRCM to the shear strength of RC beams and was mainly focused on the U-wrapped configuration. Although various analytical models to estimate the EB FRCM shear strength contribution were proposed, their accuracy and the role of different parameters on the results obtained were not thoroughly investigated. In this paper, a state of the art on side-bonded and U-wrapped FRCM shear-strengthened RC beams is provided and discussed to highlight the knowledge gaps and identify the main parameters that control the member shear strength. The accuracy of the available analytical models for the U-wrapped configuration is assessed with respect to a database of experimental FRCM shear-strengthened RC beams collated from the literature. The results obtained point out the key features that the analytical model should have to provide accurate and reliable predictions. [ABSTRACT FROM AUTHOR]

The anisotropic behavior of fiber-reinforced polymer composites, coupled with their susceptibility to various failure modes, poses challenges for their structural health monitoring (SHM) during service life. To address this, non-destructive testing techniques have been employed, but they often suffer from drawbacks such as high costs and suboptimal resolutions. Moreover, routine inspections fail to disclose incidents or failures occurring between successive assessments. As a result, there is a growing emphasis on SHM methods that enable continuous monitoring without grounding the aircraft. Our research focuses on advancing aerospace SHM through the utilization of piezoresistive MXene fibers. MXene, characterized by its 2D nanofiber architecture and exceptional properties, offers unique advantages for strain sensing applications. We successfully fabricate piezoresistive MXene fibers using wet spinning and integrate them into carbon fiber-reinforced epoxy laminates for in-situ strain sensing. Unlike previous studies focused on high strain levels, we adjust the strain levels to be comparable to those encountered in practical aerospace applications. Our results demonstrate remarkable sensitivity of MXene fibers within low strain ranges, with a maximum sensitivity of 0.9 at 0.13% strain. Additionally, MXene fibers exhibited high reliability for repetitive tensile deformations and low-velocity impact loading scenarios. This research contributes to the development of self-sensing composites, offering enhanced capabilities for early detection of damage and defects in aerospace structures, thereby improving safety and reducing maintenance expenses. [ABSTRACT FROM AUTHOR]

This paper establishes fatigue life prediction models using the soft computing method to address insufficient parameter consideration and limited computational accuracy in predicting the fatigue life of fiber-reinforced polymer (FRP) strengthened concrete beams. Five different input forms were proposed by collecting 117 sets of fatigue test data of FRP-strengthened concrete beams from the existing literature and integrating the outcomes from Pearson correlation analysis and significance testing. Using Gene Expression Programming (GEP), the effects of various input configurations on the accuracy of model predictions were examined. The model prediction results were also evaluated using five statistical indicators. The GEP model used concrete compressive strength, the steel reinforcement stress range ratio to the yield strength, and the stiffness factor as input parameters. Subsequently, using the same input parameters, the Multi-Objective Genetic Algorithm Evolutionary Polynomial Regression (MOGA-EPR) method was then employed to develop a fatigue life prediction model. Sensitivity analyses of the GEP and MOGA-EPR models revealed that both could precisely capture the fundamental connections between fatigue life and multiple contributing variables. Compared to existing models, the proposed ones have higher prediction accuracy with a coefficient of determination reaching 0.8, significantly enhancing the accuracy of fatigue life predictions for FRP-strengthened concrete beams. [ABSTRACT FROM AUTHOR]

Due to its high axial bearing capacity and good ductility, the embedded steel plate composite shear wall structure has become one of the most widely used lateral force-resisting structural members in building construction. However, bending failure is prone to occur during strong earthquakes, and the single energy dissipation mechanism of the plastic hinge zone at the bottom leads to the concentration of local wall damage. To improve the embedded steel plate composite shear wall structure, the plastic hinge zone of the composite shear wall is replaced by fiber-reinforced concrete (FRC) and analyzed by ABAQUS finite element simulation analysis. Firstly, the structural model of the embedded steel plate composite shear wall structure with FRC in the plastic hinge zone is established and the accuracy of the model is verified. Secondly, the effects of steel ratio, longitudinal reinforcement ratio, and FRC strength on the bearing capacity of composite shear walls are analyzed by numerical simulation. Finally, a method for calculating the embedded steel plate composite shear wall structure with FRC in the plastic hinge zone is proposed. It is shown that the displacement and load curves and failure modes of the model are basically consistent with the experimental results, and the model has high accuracy. The axial compression ratio and FRC strength have a great influence on the bearing capacity of composite shear walls. The calculation formula of the normal section bending capacity of the embedded steel plate composite shear wall structure with FRC in the plastic hinge zone is proposed. The calculated values of the bending capacity are in good agreement with the simulated values, which can provide a reference for its engineering application. [ABSTRACT FROM AUTHOR]

The numerical modelling procedures and damage criteria of both existing and retrofitted reinforced concrete (RC) elements are crucial for reliable seismic assessment and the retrofitting of existing RC buildings. A widely used retrofitting technique involves the application of fiber-reinforced polymers (FRPs) to vulnerable RC elements, enhancing their flexural and shear capacities. However, the current version of EC8-3 does not explicitly provide guidelines for numerical modelling, nor does it offer specific information on the assessment of retrofitting elements. This study focuses on developing a concentrated plasticity modelling approach and defining the damage state criteria for retrofitted RC columns with FRPs, based on experimental data from the literature. A database comprising 99 FRP-retrofitted RC columns was compiled, and regression analysis procedures were used to calibrate the peak load rotation, ultimate rotation, and post-capping rotation capacities. The modelling approach was validated through comparison with existing formulations using OpenSees, and the results indicate its adequacy for the seismic assessment of retrofitted buildings. This research advances the seismic assessment of FRP-retrofitted RC elements by introducing a novel trilinear moment–rotation model and refined damage criteria, which provide higher predictive accuracy in comparison to existing proposals. It also addresses critical gaps in seismic assessment practices by proposing the peak load rotation as a more reliable SD limit state threshold for retrofitted columns. [ABSTRACT FROM AUTHOR]

Compared to glass fiber-reinforced polymer (GFRP) and carbon fiber-reinforced polymer (CFRP), basalt fiber-reinforced polymer (BFRP) offers distinct advantages, including the relatively lower cost and superior creep resistance. As a result, its application in the construction industry has been gaining growing attention. This paper begins by providing an overview of the fundamental background, as well as the mechanical and microscopic properties, of BFs. By exploring various application types, including one-dimensional (e.g., bars, cables), two-dimensional (e.g., grids, sheets), and three-dimensional (e.g., profiles) applications, the research progress of BFRP products in the construction industry is comprehensively summarized. Research has demonstrated the effectiveness of BFRP in a variety of structural applications, such as reinforcing existing structures (e.g., concrete or masonry) using BFRP bars, grids, or sheets, and the development of novel design concepts that integrate BFRP products with existing structural systems. Furthermore, this paper identifies unresolved challenges and proposes potential research directions, intending to promote BFRP's broader adoption as a standardized and innovative material in the construction industry. [ABSTRACT FROM AUTHOR]

With 3D printing technology, fiber-reinforced polymer composites can be printed with radical shapes and properties, resulting in varied mechanical performances. Their high strength, light weight, and corrosion resistance are already advantages that make them viable for physical civil infrastructure. It is important to understand these composites' behavior when used in concrete, as their association can impact debonding failures and overall structural performance. In this study, the flexural behavior of two designs for 3D-printed glass fiber composites is investigated in both Portland cement concrete and polymer concrete and compared to conventional fiber-reinforced polymer composites manufactured using a wet layup method. Thermogravimetric analysis, volume fraction calculations, and tensile tests were performed to characterize the properties of the fiber-reinforced polymer composites. Flexural testing was conducted by a three-point bending setup, and post-failure analysis was performed using microscopic images. Compared to concretes with no FRP reinforcement, the incorporation of 3D-printed glass-fiber-reinforced polymer composites in cementitious concrete showed a 16.8% increase in load-carrying capacity, and incorporation in polymer concrete showed a 90% increase in flexural capacity. In addition, this study also provides key insights into the capabilities of polymer concrete to penetrate layers of at least 90 microns in 3D-printed composites, providing fiber bridging capabilities and better engagement resulting in improved bond strength that is reflected in mechanical performance. The polymer material has a much lower viscosity of 8 cps compared to the 40 cps viscosity of the cement slurry. This lower viscosity results in improved penetration, increasing contact surface area, with the reinforcement consequently improving bond strength. Overall, this work demonstrates that 3D-printed fiber-reinforced polymer composites are suitable for construction and may lead to the development of advanced concrete-based reinforced composites that can be 3D-printed with tailored mechanical properties and performance. [ABSTRACT FROM AUTHOR]

This study presents a methodology for characterizing the constituent properties of composite materials by back-calculating from the laminate behavior under fatigue loading. Composite materials consist of fiber reinforcements and a polymer matrix, with the fatigue performance of the laminate governed by the interaction between these constituents. Due to the challenges in directly measuring the properties of individual fibers and the polymer matrix, a reverse-engineering approach was employed. Using the micro-mechanics of fatigue (MMFatigue), we predicted the laminate's fatigue behavior based on assumed constituent properties and compared these predictions with experimental data from fatigue tests. The properties of the fiber and polymer matrix were iteratively adjusted to minimize the differences between predictions and experimental results, enabling accurate fatigue characterization. To ensure robustness, three laminate angles—0°, 30°, and 60°—were evaluated at three temperatures: low temperature (LT: −40 °C), room temperature (RT: 25 °C), and high temperature (HT: 85 °C). The error, defined as the fatigue life difference between the prediction and the experimental results, were obtained as 2.48% at LT, 7.18% at RT, and 1.25% at HT for a laminate angle of 45°. Finally, the applicability of the multiscale-based fatigue life prediction method was demonstrated through studies on laminates with various angles under tension–compression, and compression–compression cyclic loads, as well as composite pressure vessels under cyclic loading. [ABSTRACT FROM AUTHOR]

Previous research indicates that lightweight aggregate (LWA) concrete exhibits more brittle failure under compression than conventional normal density (ND) concrete. In contrast, angle-ply fiber-reinforced polymer (FRP) filament-wound tubes filled with ND concrete show significant improvements in strength and deformability compared to hollow tubes. This study evaluates the impact of these tubes on LWA concrete to mitigate its brittle behavior. Sixteen concrete-filled FRP filament-wound tubes (CFFTs) made of ±55° filament-wound glass FRP (GFRP) were tested under axial compression. The GFRP tube's mechanical properties and fiber winding angle of ±55° allowed for a compressive strength enhancement factor ranging from two to five for the CFFTs compared to unconfined specimens. Results also revealed substantial nonlinearity and deformability in the LWA-CFFTs due to the angle-ply tube orientation. An iterative analytical model predicted the CFFT's nonlinear response, validated by experimental data. The findings demonstrate that angle-ply FRP tubes effectively enhance the bearing capacity and deformability of inherently brittle unconfined LWA concrete. [ABSTRACT FROM AUTHOR]

The destructive earthquakes in the world clearly reveal the importance of the seismic behavior of the structures. The current study proposes and numerically investigates a systematic technique for the seismic assessment and retrofit of reinforced-concrete buildings according to both material strain limit approach and Quadrants assessment method. In this study numerical analysis were made for two three-dimensional building models, namely a single-storey 30 years old existing RC building in Koyna-Warna area (Zone-IV) in India, and an earthquake-resistant designed 4-story RC building. The structural analyses were performed for two 3-D models of the selected buildings are analysed. Nonlinear static adaptive pushover analysis method was used in Seismostruct software program for two different buildings. While one of the buildings is an existing building, the other is chosen as a new building. Structural characteristics and deficiencies of the investigated single-storey existing reinforced-concrete structure necessitated seismic evaluation. The deficiencies include pitched roofs, re-entrant corners, and structural distress such as structural element cracking and cover concrete spalling, among others. The single-story RC building is retrofitted with RC jacketing and fiber-reinforced polymer sheet wrapping, while the four-storey RC building does not need to be retrofitted based on the Quadrants assessment method. Also, the significant seismic design parameters are evaluated before and after the retrofit. The results show that the material strain limit technique when combined with the Quadrants assessment method makes a more efficient technique for seismic assessment and retrofit purpose. Also, the ultimate capacity and over strength factor of the retrofitted single-storey RC existing building are found 2.04 times and 1.82 times increased in X and Y direction as compared to the building without retrofit, because of the RC jacketing and FRP sheet wrapping. [ABSTRACT FROM AUTHOR]

The increasing application of fiber-reinforced polymer (FRP) composites necessitates the development of composite structures that exhibit high stiffness, high strength, and favorable failure behavior to endure complex loading scenarios and improve damage tolerance. Achieving these properties can be facilitated by integrating conventional FRPCs with metallic materials, which offer high ductility and superior energy absorption capabilities. However, there is a lack of effective solutions for the micro-level hybridization of high-performance filament yarns, metal filament yarns, and thermoplastic filament yarns. This study aims to investigate the hybridization of multi-material components at the micro-level using the air-texturing process. The focus is on investigating the morphological and the mechanical properties as well as the damage behavior in relation to the process parameters of the air-texturing process. The process-induced property changes were evaluated throughout the entire process, starting from the individual components, through the hybridization process, and up to the tape production. Tensile tests on multifilament yarns and tape revealed that the strength of the hybrid materials is significantly reduced due to the hybridization process inducing fiber damage. Morphological analyses using 3D scans and micrographs demonstrated that the degree of hybridization is enhanced due to the application of air pressure during the hybridization process. However, this phenomenon is also influenced by the flow movement of the PP matrix during the consolidation stage. The hybrid laminates exhibited a damage behavior that differs from the established behavior of layer-separated metal fiber hybrids, thereby supporting other failure and energy absorption mechanisms, such as fiber pull-out. [ABSTRACT FROM AUTHOR]

Highly filled thermoplastic profiles, produced by in situ pultrusion, offer excellent mechanical properties, but further processing is necessary to expand the range of their applications. Due to the thermoplastic matrix, these materials are particularly well-suited for thermal welding processes. However, the high fiber content of up to 70 vol.-% presents a significant challenge in welding, an aspect that has not yet been thoroughly investigated in the existing literature. This study focuses on the further processing of the highly-filled profiles by adapting the classic hot tool welding process with the aim of investigating the underlying welding mechanism. An IR line-emitter is used to melt the PA6 matrix of the fiber-reinforced plastic component while the second adherend (unfilled PA6) is melted with a classic heating element. Afterward, the joints are tested for tensile and bending strength. The results of these mechanical tests demonstrate that a strong bond can be formed between the adherends. The joint strength reached values of up to 39 MPa, which corresponds to a welding factor of 0.81. Optical examination of the weld seam reveals a reason for the mechanical performance. At high joining pressures, a form-fit is created between the continuous fibers in the profile and the welded-on unfilled PA6. [ABSTRACT FROM AUTHOR]

In this study, an analytical model was developed for the local bond degradation behavior between a near-surface mounted (NSM) fiber-reinforced polymer (FRP) and concrete under fatigue loading. A trilinear local bond stress–slip relationship was adopted to characterize the fundamental bond behavior at the FRP-epoxy-concrete interface at different stages of elastic, softening and debonding. A series of post-fatigue direct pull-out tests (DPTs) of NSM FRP-bonded concrete blocks was conducted to provide the local bond degradation laws for the analytical model. The bond region was discretized into finite elements to include the effect of bond degradation to different extents, and a closed-form solution was derived by virtue of appropriate boundary conditions in each fatigue cycle. The model is capable of predicting the FRP strain distribution, local bond stress distribution and relative slip development at a targeted number of fatigue cycles. The reliability of the analytical model was confirmed by experimental data, and its sensitivity to various parameters such as local bond strength, the residual bond strength ratio and Young's modulus of FRP reinforcement was also assessed in this study. [ABSTRACT FROM AUTHOR]

Lightweight concrete (LWC) is a long-standing development in the area of construction materials. LWC has become increasingly important for sustainable construction due to its reduced susceptibility to cracking. However, when exposed to extreme temperatures during fires, LWC can lose its compressive strength and ductility. This study investigates the performance of lightweight expanded clay aggregate (LECA) concrete T-beams exposed to elevated temperatures. The research also focuses on the use of an engineered cementitious composite with a basalt fiber-reinforced polymer grid (ECCBFG) as a rehabilitation method for fire-damaged T-beams. Key variables considered include the concrete cover thickness (20 and 30 mm), fire exposure duration (30 and 60 min), and thickness of the ECCBFG layer. Thermocouples were installed at various points within the beams to monitor the heat gradient across the cross-section. Fourteen concrete beam specimens were tested, including control beams, fire-damaged beams, and beams strengthened with the ECCBFG layer. Key performance parameters, such as the energy absorption, cracking load, ductility index, maximum load capacity, and corresponding displacement, were analyzed. The experimental results showed that the strengthened beams outperformed the fire-damaged beams, closely matching the performance of undamaged reference beams in most aspects, except energy absorption. The findings suggest that further research is needed to optimize certain performance indicators and address challenges in strengthening fire-damaged beams. [ABSTRACT FROM AUTHOR]

This study presents a detailed analysis of various machine learning models for predicting the interfacial bond strength of fiber-reinforced polymer (FRP) concrete, including multiple linear regression, Multigene Genetic Programming (MGGP), an ensemble of regression trees, Gaussian Process Regression (GPR), Support Vector Regression (SVR), and neural networks. The evaluation was based on their predictive accuracy. The optimal model identified was the GPR ARD Exponential model, which achieved a mean absolute error (MAE) of 1.8953 MPa and a correlation coefficient (R) of 0.9658. An analysis of this optimal model highlighted the most influential variables affecting the bond strength. Additionally, the research identified several models with lower expression complexity and reduced accuracy, which may still be applicable in practical scenarios. [ABSTRACT FROM AUTHOR]

This paper introduces cross-wound CFRP shear reinforcement of hollow HPC beams. The CFRP reinforcement was manufactured in the form of a square tubular mesh from carbon rovings oriented at ±45° from the longitudinal axis. The shear reinforcement was made in two variants from carbon yarns with linear densities of 1600 and 3700 tex. Tensile reinforcement made of BFRP bars was positioned directly around the hollow core and was used as a platform for manual winding of the shear reinforcement. The hollow beams were subjected to a three-point bending test with four configurations of the tensile BFRP reinforcement for better evaluation of the effect of the shear reinforcement under different conditions. The 1600 tex shear reinforcement increased the ultimate flexural strength by at least 89% compared to specimens without any shear reinforcement. The 3700 tex shear reinforcement yielded slightly better results in most cases but was not utilized to its full shear capacity as these specimens always failed in shear due to the delamination of the concrete matrix from the shear reinforcement. There was too much reinforcement in the beam cross-section. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP) composites are increasingly used in civil engineering for strengthening and repairing existing reinforced concrete (RC) members using externally bonded reinforcement (EBR) and near-surface mounted (NSM) methods. However, the fire performance of FRP-strengthened RC members has been an important issue that should be properly considered in the fire safety design process since FRP composites exhibit significant performance degradation at elevated temperatures. This paper aims to review studies on the fire performance of FRP-strengthened RC members based on the existing research results presented in the literature to provide a comprehensive understanding of key factors influencing the structural behavior of FRP-strengthened RC members under fire conditions. It provides an overview of FRP composite material properties, such as their mechanical and thermal behavior and bond characteristics between FRP-to-concrete interfaces at elevated temperatures. Additionally, this paper reviews experimental and numerical research conducted on FRP-strengthened RC members, examining load-carrying capacities and fire endurance ratings. Finally, this review will provide existing fire resistance design methods as well as simple design methods for temperature prediction. [ABSTRACT FROM AUTHOR]

Alkali treatment is a prevalent method to enhance the interfacial compatibility of natural fiber-reinforced polymer composites (NFRPCs). Although the influence of alkali treatment on the properties of NFRPCs has been extensively investigated, previous studies have predominantly examined individual factors in isolation, leaving the combined effects of alkali solution concentration, treatment temperature, and time relatively unexplored. In this study, an orthogonal experiment was conducted to assess the combined impacts of alkali solution (NaOH) concentration, treatment temperature, and time on the mechanical strength, thermal stability, and water absorption of bamboo fiber (BF)/polylactic acid (PLA) composites. The findings indicated that both the NaOH concentration and temperature exhibited a statistically significant effect (0.01 < p < 0.05) on the mechanical strength of BF/PLA composites, while the treatment time had no significant effect. Furthermore, all three factors had an extremely significant impact (p < 0.01) on the thermal stability of BF/PLA composites. The water absorption of BF/PLA composites was found to be significantly influenced by treatment temperature and time (p < 0.01), while no significant effect of NaOH concentration was observed. The optimal combination of alkali treatment parameters (concentration—5 wt%, temperature—25 °C, time—30 min) for BF/PLA composites was determined. Additionally, it was observed that the water absorption of alkali-treated BF/PLA composites was lower than that of untreated composites for shorter dipping times, but higher for prolonged dipping times. This work offers an important reference for the efficient application of alkali treatment to NFRPCs. [ABSTRACT FROM AUTHOR]

The first edition of ACI CODE-440.11 was published in September 2022, where some code provisions were either based on limited research or only analytically developed. Therefore, some code provisions, notably shear and development length in footings, are difficult to implement. This study, through a design example, aims at a better understanding of the implications of code provisions in ACI CODE-440.11-22 and compares them with ones in CSA S806-12, thereby highlighting a need for reconsiderations. An example of the footing originally designed with steel reinforcement was taken from the ACI Reinforced Concrete Design Handbook and redesigned with GFRP reinforcement as per ACI CODE-440.11-22 and CSA S806-12. A footing designed as per ACI CODE-440.11-22 requires a thicker concrete cross section to satisfy shear requirements; however, when designed as per CSA S806-12, the required thickness becomes closer to that of the steel-reinforced concrete (RC) footing. The development length required for a glass fiber-reinforced polymer-reinforced concrete (GFRP-RC) cross section designed as per ACI CODE-440.11-22 was 13% and 92% greater than that designed as per CSA S806-12 and ACI 318-19, respectively. Also, the reinforcement area required to meet detailing requirements is 170% higher than that for steel-RC cross section. Based on the outcomes of this study, there appears to be a need for reconsideration of some code provisions in ACI CODE-440.11-22 to make GFRP reinforcement a viable option for RC members. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP) reinforcements have been used in versatile forms in recent construction practices to enhance durability performance and, consequently, to attain longevity of concrete structures. The shear strength of FRP-reinforced concrete (FRP-RC) beams holds significant importance in structural design. However, inherent analytical uncertainty exists concerning shear in concrete members due to the distinctive material characteristics of FRP bars compared to conventional steel reinforcements, such as their low axial stiffness and bond properties. This study aims to identify the shear-resistance mechanisms developed under combined actions between concrete and FRP reinforcements. To this end, the dual-potential capacity model (DPCM) was extended to FRP-RC beam members subjected to shear and flexure, and an attempt was also made to derive a simplified method. To validate the proposed approaches, a total of 437 shear test results from RC members incorporating FRP bars were used. Findings indicate that the proposed methods can provide an acceptable level of analytical accuracy. In addition, a significant shift in the shear failure mode of FRP-RC members with no stirrups was observed from the compression zone to the cracked tension zone as the FRP reinforcement ratios increased. Conversely, when FRP stirrups were added, the shear failure mode was mostly dominated by the compression zone. [ABSTRACT FROM AUTHOR]

This paper presents the behavior of unreinforced cylindrical concrete elements confined with a hybrid system, consisting of an ultra-high-performance concrete (UHPC) jacket and basalt fiber-reinforced polymer (BFRP) grids. For exploring the feasibility of the proposed strengthening scheme, a series of tests are conducted to evaluate material properties and to obtain results related to interfacial bond, load-bearing capacity, axial responses, and failure modes. To understand the function of the individual components, a total of 57 cylinders are loaded under augmented confining conditions, including plain cores with ordinary concrete (CONT), plain cores with UHPC jackets (Type A), and plain cores with UHPC jackets plus BFRP grids (Type B). By preloading the cores at up to 60% of the control capacity (60%fc') before applying the confinement system, the repercussions of inherent damage that can take place in vertical members on site are simulated. The compressive strength of UHPC rapidly develops within 7 days, whereas its splitting strength noticeably ascends after 14 days. The adhesion between the ordinary concrete and UHPC increases over time. While the Type B specimens outperform their Type A counterparts in terms of axial capacity by more than 18%, reliance on the BFRP grids is reduced with the growth of UHPC's strength and adhesion because of the interaction between the hardened UHPC and the core concrete. The adverse effects of the preloading are noteworthy for both types, especially when exceeding a level of 30%fc'. The BFRP grid-wrapping alleviates the occurrence of a catastrophic collapse in the jacketed cylinders, resulting from a combination of the axial distress and lateral expansion of the core. Analytical models explain the load-carrying mechanism of the strengthened concrete, including confinement pressure and BFRP stress. Through parametric investigations, the significance of the constituents is clarified, and design recommendations are suggested. [ABSTRACT FROM AUTHOR]

This paper presents a new approach for damage detection in thin plates by fusing variational mode decomposition and spectral entropy (VMD-SE). In this method, after the received signal is decomposed into some intrinsic mode functions (IMFs) by variational mode decomposition (VMD), the spectral entropy ratio of the first and last IMFs is calculated for optimizing the VMD's parameters and improving its decomposition performance. Moreover, the cross-correlation coefficient between the decomposed IMFs and the reference signal is computed to separate the desired IMF, which contains more damage information. Finally, the spectral entropy of the obtained IMF is calculated as an indicator for assessing the damage's severity. The comparative analysis of the simulated signal clearly shows that only the proposed method can successfully separate the damage-related and reference signals. To verify the VMD-SE method, damage detection of two different types of damage on aluminum and composite fiber-reinforced polymer (CFRP) plates is conducted by using this new approach. The experimental results demonstrate that the parameters of VMD affect greatly its decomposition performance, and the best parameters are selected. The results also indicate that the normalized spectral entropy monotonically increases when the diameter of the through-hole or the length of the scratch increases. In addition, the correlation coefficients of the fitting lines of the plates are larger than 0.998. The experimental results of aluminum specimens demonstrate that the damage's location has an influence on the normalized spectral entropy. At last, based on the linear relationship, the severity of damage in the fourth specimen is identified. The identification results demonstrate that the relative error of the aluminum and CFRP plates is less than 7.34%, which indicates that this new algorithm by fusing VMD and spectral entropy can detect the damage size in thin plates accurately and efficiently. [ABSTRACT FROM AUTHOR]

This experimental study investigates the effectiveness of retrofitting fiber-reinforced concrete (FRC) beams using nano-graphene oxide (GO) and carbon fiber-reinforced polymer (CFRP) sheets. The primary goal is to evaluate the combined effect of GO and CFRP sheets on the mechanical performance of FRC beams. The experimental program involved preparing and testing multiple concrete beam specimens, with some retrofitted using GO and CFRP sheets. The principal results indicate that the integration of GO significantly enhances the compressive and tensile strength of concrete. Additionally, the application of CFRP sheets markedly improves the flexural strength and ductility of the beams. The retrofitted specimens exhibited higher load-bearing capacity and greater deformation before failure compared to control specimens. The significant conclusions drawn from this study are that the combined use of GO and CFRP sheets provides a synergistic effect, improving the overall mechanical performance of FRC beams. However, failure modes such as debonding and delamination of CFRP sheets highlight the need for optimization in bonding techniques and materials. The primary research outcomes demonstrate that retrofitting FRC beams with GO and CFRP sheets is a promising approach for enhancing the structural performance. This study underscores the potential of advanced materials in structural retrofitting and provides insights for future research to address observed failure modes and further improve the retrofitting techniques. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) slabs are widely used in modern building structures due to their superior properties and ease of construction. However, their mechanical properties are limited by their punching shear strength in the connection region with the columns. Researchers have attempted to add steel reinforcement in the form of studs and randomly distributed fibers to concrete slabs to improve the punching strength. An additional strengthening method that consists of the application is a Fiber-Reinforced Polymer (FRP). However, current codes poorly calculate the punching shear strength of FRP-RC slabs. The aim of this study is to create a robust model that can accurately predict its punching shear strength, thus improving the analysis and design of composite structures with FRP-RC slabs. In this study, 189 sets of experimental data were collected and expanded using kernel density estimation (KDE), considering the small amount of data. Secondly, a punching shear strength prediction model for FRP-RC panels was constructed using XGBoost and compared with the model modeled by codes and researchers. Finally, a model explainability study was conducted using SHapley additive exPlanations (SHAP). The results show that kernel density estimation significantly improves the robustness and accuracy of XGBoost. The R-squared, standard deviation, and root mean square error of XGBoost on the training set are 0.99, 0.001, and 0.001, respectively. On the test set, the R-squared, standard deviation, and root mean square error are 0.96, 62.687, and 67.484, respectively. The effective depth of the FRP-RC slabs is the most important and proportional to the punching shear strength. This study can provide guidance for the design of FRP-RC slabs. [ABSTRACT FROM AUTHOR]

The present work sets out the evaluation of composite laminates through optimization objective functions. Genetic Algorithms (GA), as well as Simulated Annealing (SA), were performed to determine the optimal ply orientations of a fiber-reinforced polymer laminate for three given load cases: (1) in-plane loads, (2) combined moments, and (3) in-plane loads and combined moments. It searches the optimal orientation layup, which fulfills at the same time both the maximum strain criterion and the Tsai–Wu failure criterion. Construction of an objective function based on the strains and the stresses involves a minimization process to deformations and a maximization of the safety factor. For the first load case, the initial solution is [±45/0/90/±45]s, and the best solution is [(45/135)2/452]s. For the second load case, [–45/45/45/–45/0/90]s is the initial layup sequence, then, the best solution obtained is [(45/–45)2/452]s, where plies at 0° and 90° are not necessary even when axial loads are applied. For the third study case, the original layup sequence is [0/45/–45/45/0/90]s; meanwhile, the best solution calculated is [21/24/145/140/45/49]s. An interesting observation is that each pair of layers has a 5° gap. The simulations show that the qualitative results from the GA are better than the SA, but with a significantly higher computational cost. These computational tools are expected to be used as a reference guide for an optimal fiber configuration concerning the common orientations used when composite laminates are designed for a structural application. [ABSTRACT FROM AUTHOR]

The use of sustainable natural fibers as reinforcement in polylactic acid (PLA) composites offers a promising approach to developing environmentally friendly and renewable composite materials. This research article explores the impact of weave designs on various mechanical properties of fiber‐reinforced polymeric composite (FRPC) laminates. Four different weave designs, including 1/1 plain, 2/2 matt, 4/1 satin, and 3/1 twill, were developed using flax yarn obtained from the Linum usitatissimum plant. These weave designs were incorporated into composites by wrapping the flax yarn with PLA filament as the matrix, followed by compression molding. The study examines the static and dynamic mechanical properties of the subsequent flax/PLA composites, including flexural strength, Charpy strength, tensile strength, and viscoelastic characteristics like damping factor, loss, and storage modulus. The plain 1/1–reinforced composite exhibits superior tensile strength (12 MPa), tensile modulus (9800 MPa), and flexural properties (29 MPa) due to the higher number of intersection points in the weave design, while in the case of impact strength (6.7 kJ/m2), satin structure‐reinforced composite showed superior properties due to higher float length of warp yarns and lower intersection points in the weave structure. [ABSTRACT FROM AUTHOR]

The energy absorption characteristics of composites are developed for applications likely to be subjected to sudden or prolonged impacts. In lightweight applications, the possibilities of Al 6061 composites are being explored with various known materials with similar properties. Three materials of low densities but high strength was combined: hexagonal honeycomb Al 6061 core was sandwiched with polyurethane foam and embedded within two glass fiber-reinforced polymer plates. L-9 orthogonal array Taguchi DOE was adopted for the design of the experiment varying the polyurethane mixture, core height, and face sheet thickness using the three-factor method. From the output of the Taguchi DOE, twenty-seven samples were fabricated. In order to determine the force-displacement relationship for each of the test samples, a three-point bending test was performed on a universal testing machine. Energy absorption (EA) and crushing force (CF) were determined from the force and displacement values. These values were then optimized to minimize the PCF while maximizing EA. Numerical analysis performed correlated with the results from experimental samples after testing. Since energy absorption is a measure of applied force and the resulting displacement on a material, the energy absorption characteristics were discussed. [ABSTRACT FROM AUTHOR]

GFRP-concrete-steel composite columns (GCS) are formed by combining different components with excellent mechanical properties. The GCS exhibits good corrosion resistance and can serve as a pile foundation platform for offshore wind turbines. An Artificial Neural Network (ANN) is utilized to swiftly predict the loading capacity of GCS columns with various geometrical parameters. The prediction error is primarily controlled within 10%. The thickness of GFRP tubes (tG), the inner diameter of GFRP tubes (DG,i), the thickness of steel tubes (ts), the outer diameter of steel tubes (DS,o), the strength of GFRP tubes (fG), the strength of concrete (fC), and the strength of steel tubes (fS) were used as independent variables to determine the key factors affecting the loading capacity of GCS columns. The impact of the number of input variables on the final prediction accuracy is analyzed. The proportional influence of different parameters on the loading capacity of GCS column is investigated using the Garson algorithm, among which, the thickness of the GFRP tube (tG) accounts for the largest proportion, approximately 24.57%. The suitability of the artificial neural network for predicting the loading capacity of GCS columns with various geometries is revealed. The results indicate that the ANN can be utilized for high-precision compressive strength prediction, and the thickness of the GFRP tube (tG) is the most influential factor on the loading capacity of GCS columns. [ABSTRACT FROM AUTHOR]

In recent years, additive manufacturing (AM), especially large-format additive manufacturing (LFAM), has gained momentum in the manufacturing industry. While LFAM offers benefits over conventional manufacturing processes, such as minimizing material waste and providing vast geometric freedom, assessing its sustainability remains challenging due to limited data, particularly on energy consumption. Most existing data pertain to small-scale or desktop AM and are not directly applicable to LFAM. In this study, we conducted real-time measurements of electricity usage for a type of LFAM known as big area additive manufacturing (BAAM), which typically uses fiber-reinforced polymer pellets as feedstock. We collected electricity usage data from fifteen printing jobs over two months in an industrial production setting. These data fill the existing gap and can be reused to enhance the community's understanding of LFAM electricity usage, support further research, and promote sustainable development in advanced manufacturing technologies. [ABSTRACT FROM AUTHOR]

The glass fiber-reinforced polymer (GFRP) materials of wind turbine blades can be recovered and recycled by crushing, thereby solving one of the most perplexing problems facing the wind energy sector. This process yields selectively crushed wind turbine blade (SCWTB), a novel waste that is almost exclusively composed of GFRP composite fibers that can be revalued in terms of their use as a raw material in concrete production. In this research, the fresh and mechanical performance of concrete made with 1.5%, 3.0%, 4.5%, and 6.0% SCWTB is studied. Once incorporated into concrete mixes, SCWTB waste slightly reduced slumps due to the large specific surface area of the fibers, and the stitching effect of the fibers on mechanical behavior was generally adequate, as scanning electron microscopy demonstrated good fiber adhesion within the cementitious matrix. Thus, despite the increase in the content of water and plasticizers when adding this waste to preserve workability, the compressive strength only decreased in the long term with the addition of 6.0% SCWTB, a value of 45 MPa always being reached at 28 days; Poisson's coefficient remained constant from 3.0% SCWTB; splitting tensile strength was maintained at around 4.7 MPa up to additions of 3.0% SCWTB; and the flexural strength of mixes containing 6.0% and 1.5% SCWTB was statistically equal, with a value near 6.1 MPa. Furthermore, all mechanical properties of the concrete except for flexural strength were improved with additions of SCWTB compared to raw crushed wind turbine blade, which apart from GFRP composite fibers contains approximately spherical polymer and balsa wood particles. Flexural strength was conditioned by the proportion of fibers, their dimensions, and their strength, which were almost identical for both waste types. SCWTB would be preferable for applications in which compression stresses predominate. [ABSTRACT FROM AUTHOR]

This research advocates for the use of basalt fiber-reinforced polymer (BFRP) bars and recycled tire steel fibers to reinforce concrete beams. Six concrete beams were constructed using different volume contents of recycled tire steel fibers (0, 0.5%, 1.0%, 1.5%) and BFRP reinforcement ratios (0.48%, 0.75%, 1.08%). Mechanical properties tests were conducted to investigate the flexural characteristics and failure modes of beams utilizing the non-contact full-field strain displacement measuring technology–digital image (3D-DIC) technology. The recycled tire steel fiber (RTSF) improves flexural performance, which contributes to inhibiting crack propagation, reducing flexural deformation, and improving the first cracking and ultimate loading capacities. Under the same reinforcement ratio, in comparison to ordinary BFRP beams, the cracking load of BFRP-RTSF beams increased by 17.73%, 23.76%, and 42.94%, respectively, and the ultimate bearing capacity increased by 4.03%, 5.85%, and 13.21%, respectively. In addition, a modified calculation model of bearing capacity considering RTSF tensile strength is proposed. The predicted values of BFRP-RTSF beams match well with the experimental values. [ABSTRACT FROM AUTHOR]

This study investigates the tensile behavior of carbon-fiber-reinforced polymer (CFRP) and textile-reinforced mortar (TRM) under various design variables to enhance understanding and application in construction structures. TRM reinforced with CFRP grids is highly effective for strengthening existing structures due to its lightweight nature, durability, ease of installation, and corrosion resistance. The research aims to evaluate how design parameters such as the CFRP grid type, mortar matrix strength (influenced by the water-to-cement ratio), specimen length, and grid width affect TRM's mechanical properties. Through the direct tensile test using a universal testing machine, TRM specimens were subjected to load until failure, with data collected on stress–strain relationships, crack patterns, and strengths. Specimens included untreated CFRP grids (Groups KC, Q47, and Q85) and sand-coated CFRP grids (Specimens AQ47_7 and AQ85_7), each tested under controlled laboratory conditions. The results indicate that crack formation significantly influenced load transfer mechanisms within the specimens, with longitudinal strands bearing load as cracks propagated through the mortar matrix. The presence of sand-coated CFRP grids notably enhanced interfacial bond strength, leading to increased cracking strength and ultimate strength compared with their untreated counterparts. The findings underscore the importance of the surface treatment of CFRP grids for improving TRM performance, with implications for enhancing structural integrity and durability in practical applications. The results provide valuable insights into optimizing TRM design for better crack control and mechanical efficiency in infrastructure. [ABSTRACT FROM AUTHOR]

Natural plant fibers (NPFs) have emerged as a sustainable alternative in the manufacture of composites due to their renewability and low environmental impact. This has led to a significant increase in the use of natural plant fiber-reinforced polymers (NPFRPs) in a variety of industries. The diversity of NPF types brings a wide range of properties and functionalities to NPFRPs, which in turn highlights the urgent need to improve the properties of fiber materials in order to enhance their performance and suitability. This paper provides insight into the processing mechanisms behind NPF fiber treatments, exploring how these treatments affect the mechanical, thermal and environmental properties of NPFRPs. It also offers a critical assessment of the advantages and disadvantages of physical, chemical, biological and nanotechnological treatments. The findings of our analysis provide a basis for the development of future treatments that aim to enhance the material properties of NPFRPs, thereby increasing their competitiveness with conventional synthetic fiber-reinforced polymers. Finally, a novel thermoplastic resin composite system, Elium–NPFRP, is proposed that embodies the principles of green development. The system has been designed with the objective of capitalizing on the environmental benefits of NPFs while simultaneously addressing the challenges associated with the integration of NPFs into polymer matrices. The Elium–NPFRP composite system not only exemplifies the potential of NPFs for sustainable materials science, but is also a practical solution that can be implemented in a diverse range of applications, spanning automotive components to construction materials. This has the potential to reduce carbon footprints and promote a circular economy. [ABSTRACT FROM AUTHOR]

Natural fiber-reinforced composites are composite materials composed of natural fibers, such as plant fibers and synthetic biopolymers. These environmentally friendly composites are biodegradable, renewable, cheap, lightweight, and low-density, attracting attention as eco-friendly alternatives to synthetic fiber-reinforced composites. In this study, natural fiber-reinforced polymer foam core layered composites were produced for the automotive industry. Fabrics woven from goat wool were used as the natural fiber. Polymer foam with expanded polystyrene (EPS) and extruded polystyrene (XPS) structures was used as the core material. During production, fibers were bonded to the upper and lower layers of the core structures using resin. The hand lay-up method was used in production. After resin application, the samples were cured under a heated press for 2 h. After the production was completed, the material was cut according to the standards (10-20-30 Joule), and impact and bending tests were conducted at three different energy levels. The experiments revealed that at 10 J, the material exhibited rebound; at 20 J, it showed resistance to stabbing; and at 30 J, it experienced penetration. While EPS foam demonstrated higher impact resistance in the 10 J test, it was found that XPS foam exhibited better impact resistance and absorption capabilities in the 20 J and 30 J tests. Due to the open and semi-closed cell structure of EPS foams and the closed cell structure of XPS foams, it has been concluded that XPS foams exhibit higher impact resistance and better energy absorption properties [ABSTRACT FROM AUTHOR]

Recently, the liquid composite molding technique (LCM) has been used for producing fiber-reinforced polymer composites, since it allows the molding of complex parts, presenting good surface finishing and control of the mechanical properties of the product at the end of the process. Studies in this area have been focused on resin transfer molding (RTM), specifically on the resin rectilinear infiltration through the porous preform inserted in the closed cavity neglecting the sorption effect of the polymeric fluid by the reinforcement. Thus, the objective of this work is to predict resin radial flow in porous media (fibrous preform), including the effect of resin sorption by fibers considering a one-dimensional approach. For correct prediction of the flow behavior inside the porous media, an advanced modeling approach composed of the mass conservation equation and Darcy's law is used, and the solution of the coupled equation is obtained. Transient results of the flow front location, velocity and pressure within the mold during the resin infiltration are shown, the effects of different parameters for resin (viscosity), reinforcement (sorption term, permeability and porosity) and process (injection pressure and injection radius) are analyzed, and an in-depth discussion is performed. [ABSTRACT FROM AUTHOR]

Improving the physical, mechanical, and creep properties of wood fiber-reinforced polymer composites is crucial for broadening their application prospect. In this research, seven types of high-density polyethylene (HDPE) composites reinforced with different mass ratios of Masson pine (Pinus massoniana Lamb.) and Chinese fir [Cunninghamia lanceolata (Lamb.) Hook.] were prepared by a two-step extrusion molding method. The mass ratios of the two fibers were 60:0, 50:10, 40:20, 30:30, 20:40, 10:50, and 0:60, respectively. The surface color, density, dimension stability, bending, tensile, impact properties, dynamic mechanical properties, and 24 h creep properties at a 10% stress level of the seven composites were investigated. Additionally, the Rule of Mixtures (ROM), the Inverse Rule of Mixtures (IROM), the Hirsch models, and the improved model were employed to simulate the mechanical properties, while the Findley index model, the two-parameter index model, and the modified ExpAssoc model were employed to simulate the creep performance of the composites. This study revealed that as the proportion of Chinese fir wood flour increased, the mechanical properties of the composites gradually improved, the storage modulus showed an increasing trend, while the loss modulus decreased, and the overall creep strain of the composites increased. Among the various models, the modified model simulated the mechanical properties of the composites the best, while the modified ExpAssoc model simulated the creep behavior most effectively. [ABSTRACT FROM AUTHOR]

This study investigates the mechanical properties of Glass Fiber-Reinforced Plastic (GFRP) pipes in the circumferential direction using the split-disk method, with a focus on understanding the influence of aggressive environmental conditions. The split-disk method was used to determine the key mechanical properties, including the hoop tensile strength and modulus, and also the Poisson's ratio, which are critical for the performance of GFRP pipes under internal pressure. The experiment was conducted under controlled laboratory conditions, and the results were analyzed to assess the effects of exposure to aggressive environments (saltwater and alkaline solutions at 20 °C and 50 °C). The correlations between the UTS, elastic modulus, and Poisson's ratio highlight how GFRP pipes degrade under environmental exposure. As the UTS decreases, so do the stiffness and lateral deformability, with the most significant reductions occurring in chemically aggressive environments at high temperatures. Exposure to an alkaline solution weakens the GFRP pipes, with the strength dropping more sharply at higher temperatures, with the UTS decreasing by 21%. Saltwater exposure reduces the elastic modulus, especially at higher temperatures, with a 14% decrease, accelerating material degradation and reducing deformation resistance. An alkaline solution further lowers the modulus, with a 21% decrease at 50 °C, showing the lowest stiffness. Air exposure, in contrast, has a less severe effect, with the pipes retaining much of their mechanical integrity. These findings collectively suggest that environmental degradation affects the overall mechanical behavior of GFRP pipes, providing valuable insights for the design and maintenance of GFRP piping systems, particularly in industries where exposure to aggressive environments is common. This study underscores the importance of considering environmental factors in the material selection and design processes to ensure the long-term reliability of GRP pipes. [ABSTRACT FROM AUTHOR]

Shear strengthening of reinforced concrete beams using near-surface mounting (NSM) method with fiber-reinforced polymer (FRP) strips is more effective because of improved bond strength, better fire resistance and high maintainability. However, the surface preparation for NSM method is a difficult process where the beam–slab corner is not accessible by the rotary blade of the groove-making equipment. Consequently, the application of NSM method becomes more difficult to apply. Therefore, in this study, the effect of reducing in NSM length on the shear strength has been investigated by reinforcing only a part of the height, not the entire web of beam, referred to as the partial-length NSM method (PLNSM). Half scaled five RC T-beams were made and tested under symmetrical four-point static loading system. All except one was strengthened in shear in which the effect of reduced NSM length was balanced by inclining the partial-length NSM strips (IPLNSM). Furthermore, to mitigate the detrimental effect of reduced lengths of NSM strips, the retrofitting was enhanced by additional externally bonded reinforcement (EBR) method using CFRP sheets. The results showed that there was no significant negative effect of reduced NSM length on the strength of the strengthened specimens, and by providing inclined NSM strips, significant improvement in the strength was observed. Additionally, the hybrid approach combining the inclined partial length NSM (IPLNSM) and EBR method showed improvement in strength and deflection capacity. Lastly, when compared with the currently available design procedures, it was found that the available formulation can predict the design strength of PLNSM and IPLNSM reinforcement, thus making them a viable option for retrofitting reinforced concrete beams. [ABSTRACT FROM AUTHOR]

This research paper focuses on the utilization of jute, and kevlar fiber, as reinforcements in vinyl epoxy based composites. Fiber-reinforced polymer (FRP) composites are widely used because they are cost-effective to produce, can be easily fabricated, and possess superior strength compared to pure polymer resins. Either synthetic fiber (SF: like glass, carbon, kevlar) or natural fiber (NF) can be used in the polymers. Due to easy accessibility, lightweight, economical cost of production and adequate properties, jute fiber is the most commonly used NF. This study involved the production of epoxy composites reinforced with kevlar and jute fibers and an experimental study was conducted to investigate the influence of stacking sequence on the mechanical properties of the composites. Composites of different stacking sequences of jute and kevlar were fabricated using the hand lay-up method. Mechanical tests like tensile, inter laminar shear, flexural, impact strengths, and hardness were carried out. Scanning electron microscopic analysis was conducted to study the failure mechanism. It was observed that KKKK (four layers of Kevlar fiber) stacking sequence showed good inter laminar shear strength and excellent strength under tension, bending, and impact loading conditions followed by KJKJ (Kevlar-jute-kevlar-jute) sequence. [ABSTRACT FROM AUTHOR]

Natural fiber-reinforced polymer composites are gaining attention for their environmental benefits, such as biodegradability and reduced carbon footprint, as well as the potential of the natural fibers to replace or partially substitute synthetic fibers in various applications. However, challenges, such as poor interfacial adhesion and moisture absorption, limit the effectiveness of natural fibers, such as pineapple nonwoven fabric (PNWF) as reinforcement materials in polymer composites. To address these challenges, this study aims to enhance the properties of PNWF through glycidyl methacrylate grafting via radiation-induced graft polymerization. A 22 factorial design was employed to assess the effects of absorbed dosage and monomer concentration on the properties of the grafted PNWF. Infrared spectroscopy and electron microscopy analyses confirmed successful grafting. The grafted PNWF exhibited improved thermal stability and mechanical properties. The resulting composites showed significant enhancements in tensile and flexural strength, specifically, with tensile strength increase ranging from 23.32 to 34.49 MPa and flexural strength from 39.14 to 54.59 MPa. Additionally, the tensile modulus ranged from 0.77 to 1.29 GPa, while the flexural modulus varied from 1.17 to 2.06 GPa. These findings highlight the potential of PNWF grafted with polyglycidyl methacrylate (PNWF-g-PGMA) as an effective reinforcement material for various applications. [ABSTRACT FROM AUTHOR]

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]

The external bonding system using CFRP composite has been extensively utilized for strengthening different structures worldwide. However, premature debonding in this strengthening technique is a critical failure that leads to the fiber not reaching its ultimate capacity. In order to enhance the capacity of the externally bonded (EB) FRP and to slow the premature debonding failure mechanism, numerous anchoring techniques have been applied to improve the bonding capacity. The externally bonded reinforcement on grooves (EBROG) technology is one of the strategies that have been recently developed to delay the debonding issue. Although extensive studies have been conducted in the literature on the EBROG method, most of these studies have been focused on the bonding characteristics of grooves in the longitudinal direction, and few studies on the effect of different designs and configurations (e.g., width, height, and spacing) in the transverse groove direction have been conducted using only CFRP fabric. In the present study, an experimental investigation was carried out to study the bond behavior of the externally bonded reinforcement on transverse grooves (EBROTG) technique on CFRP-to-concrete joints involving different parameters, including groove width, depth, spaces between grooves, and strain evolution with the corresponding bond stress–slip relationships using CFRP laminate. Twenty-four concrete prisms, divided into eight groups of three specimens, were tested using a single-lap shear test set-up. The results of testing proved that the EBROTG method furnished a proper anchor system and highly enhanced the bonding force of the tests. The increasing range of bonding strength in the specimens reinforced with the transverse grooving method ranged from 11 to 86% compared to the externally bonded reinforcement (EBR), reflecting the effect of different widths, depths, and distances between grooves. [ABSTRACT FROM AUTHOR]