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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 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]

Even though many experimental studies have evidenced that fiber-reinforced polymer (FRP)-confined concrete columns under compression might exhibit a postpeak strain-softening response, followed by a hardening behavior (a stress reduction–recovery response), most existing models are only applicable to confined columns developing full hardening behavior. Additionally, their applicability is limited to a certain column cross-sectional shape (circular or noncircular). Therefore, the present study is dedicated to the establishment of a new design-oriented stress–strain model, unified for FRP-confined circular/noncircular concrete columns. For this purpose, first, a new nondimensional confinement stiffness-based index is developed, below which the column response is transformed from a full-hardening behavior (Type A) to a postpeak strain softening–hardening one (Type B). A parabolic-linear stress–strain formulation is proposed for Type A columns by developing a new expression for the calculation of the linear hardening branch's slope. For the case of Type B, a new methodology is introduced for the simulation of the stress reduction–recovery response beyond the transition zone, whose main elements are calibrated by a large test data set. The dominance degree of the noncircularity effect of the cross section on both Type A and Type B cases was assessed and reflected in the key components of the proposed stress–strain models, based on nonlinear regression analysis. With these considerations, this model could accurately simulate the impact of the noncircularity effect on the stress–strain relationship of Type A and Type B columns, whose predictive performance is validated through a comparative assessment with existing models based on large test stress–strain results. [ABSTRACT FROM AUTHOR]

To promote the application of molybdenum tailings as the fine aggregate in concrete in construction engineering and verify the feasibility of fiber-reinforced polymer (FRP) material for strengthening molybdenum tailings concrete columns, this study takes a short circular molybdenum tailings concrete column reinforced by glass FRP (GFRP) as the research object. The influences of the molybdenum tailings content (0%, 25%, 50%, 75%, and 100%), the concrete grade (C30, C40, and C50), and the layer number (0, 1, and 2) of the GFRP sheet on the axial compressive capacity of the molybdenum tailings concrete column are investigated. The experimental phenomena and failure modes of the unreinforced and GFRP-reinforced columns are analyzed. The axial compressive strengths of the unreinforced and GFRP-reinforced columns are then compared. The load–strain curve and load–displacement curve of typical molybdenum tailings concrete columns are presented. Subsequently, six classical strength models for FRP-reinforced concrete are used to calculate the axial compressive strength of the confined specimens. The results show that the best classical model has a predictive accuracy with an absolute relative deviation (ARD) of 8.5%. To provide a better prediction of the compressive strength of the GFRP-reinforced molybdenum tailings concrete column, the best classical model is further improved, and the ARD of the modified model is only 5.87%. [ABSTRACT FROM AUTHOR]

This paper presents the proposed indeterminate strut and tie (IST) method to analyze fiber-reinforced polymer (FRP)-reinforced concrete deep beams with stirrups. The solution of the IST method does not require the assumption of reinforcement yielding and is capable of reflecting the material nonlinearity of concrete. The essential features of the IST methodology for glass FRP-reinforced deep beams are discussed and then analyzed in detail. These features include modeling concrete compressive response, softening concrete compression behavior in struts, and obtaining the depth of compression nodes. For each of these features, several approaches are discussed. The proposed IST methodology is validated by comparing the analysis results with the experimental results, and recommendations for the most suitable modeling methods are proposed. [ABSTRACT FROM AUTHOR]

The hybrid fiber-reinforced polymer (FRP)–concrete–steel double-skin tubular column (DSTC) is an innovative composite member consisting of an outer FRP tube and an inner steel tube, with the space between them filled with concrete. The incorporation of ultrahigh-performance concrete (UHPC) in the DSTC yields numerous advantages over the DSTC with normal-strength concrete, particularly in terms of enhanced impact resistance. While the lateral impact behavior of UHPC DSTC has been investigated, its residual performance after lateral impact remains unexplored. To comprehend the postimpact behavior of UHPC DSTC, a series of specimens underwent lateral impact, followed by static axial compression. Additionally, intact specimens were subjected to static axial compression for comparative analysis. Subsequently, refined numerical models were developed and validated using the obtained test data. Detailed parametric studies were carried out to investigate the influences of key variables on the postimpact behavior of UHPC DSTCs. Finally, based on the ratio of residual midheight deflection to the column height, a prediction formula was proposed for the rapid damage evaluation of impacted UHPC DSTCs, and threshold values for different damage levels were suggested based on a defined damage index. [ABSTRACT FROM AUTHOR]

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Fiber-reinforced polymer confinement is considered to be effective in the retrofitting of concrete structures. The current study explores the effectiveness of one- and two-layer carbon fiber reinforced polymer (CFRP) and multiwalled carbon nanotube (MWCNT) incorporated three-layer glass fiber reinforced polymer (GFRP) confinement on concrete cylinders under aggressive exposures, such as acid, alkaline, marine, water, and elevated temperatures. At 1 wt.% MWCNT by weight of the epoxy matrix, mechanical characteristics of the laminate show a significant improvement. In the case of acid exposure, the axial load-carrying capacity of concrete specimens with single-layer CFRP confinement was equal to that of MWCNT incorporated three-layer GFRP confinement (GF3C1-AC). The axial strain of GF3C1-AC was 23% and 12% higher than one and two-layer CFRP confinement. After exposure at 400 °C, in comparison with one- and two-layer CFRP confinement, the axial strain of MWCNT incorporated three-layer GFRP confined specimens increased by 50% and 20%, respectively, which proved the efficacy of MWCNT as a heat-resistant nanofiller. The ultrasonic pulse velocity (UPV) test indicates that the confinement system protects the concrete core from sudden failure by impeding crack propagation. The test results proved that the MWCNT incorporated FRP system can be considered as a prospective substitute for CFRP systems for retrofitting applications in severe environmental conditions. [ABSTRACT FROM AUTHOR]

Predicting the shear contribution of a fiber-reinforced polymer (FRP) strengthening system in a reinforced concrete (RC) beam strengthened using the embedded through-section (ETS) method remains challenging due to the complex shear mechanisms involved. The present study proposes a new approach that analyzes the shear resistance mechanism for ETS-FRP strengthening bars by investigating their bonding behavior with concrete. First, the consistency of existing bond models and parameters for simulating the bond profile for ETS-FRP bar-to-concrete joints was studied using a simplified finite discretization method (FDM). After validation using pullout tests, the maximum bond stress, slip at peak bond stress, and slip at complete debonding were found to be consistent for all bond laws. This allows researchers and engineers to conveniently obtain suitable bond parameters for their designs. A bonding-based approach coupled with the FDM that considers various bond rules and crack compatibility for analysis of the ETS shear contribution was then developed. The proposed approach can analyze the behavior and failure progress for single ETS strengthening elements. Based on corroboration using 46 sets of beam data, the proposed method was found to more accurately predict the ETS-FRP shear contribution than current shear design models. The results of this study indicate that using the proposed method, the ETS shear resistance can be reliably estimated by applying bilinear, trapezoidal, and nonlinear bond laws considering the compatibility of nonuniform crack widths. [ABSTRACT FROM AUTHOR]

This study represents a significant advancement in structural health monitoring by integrating infrared thermography (IRT) with cutting-edge deep learning techniques, specifically through the use of the Mask R-CNN neural network. This approach targets the precise detection and segmentation of hidden defects within the interfacial layers of Fiber-Reinforced Polymer (FRP)-reinforced concrete structures. Employing a dual RGB and thermal camera setup, we captured and meticulously aligned image data, which were then annotated for semantic segmentation to train the deep learning model. The fusion of the RGB and thermal imaging significantly enhanced the model's capabilities, achieving an average accuracy of 96.28% across a 5-fold cross-validation. The model demonstrated robust performance, consistently identifying true negatives with an average specificity of 96.78% and maintaining high precision at 96.42% in accurately delineating damaged areas. It also showed a high recall rate of 96.91%, effectively recognizing almost all actual cases of damage, which is crucial for the maintenance of structural integrity. The balanced precision and recall culminated in an average F1-score of 96.78%, highlighting the model's effectiveness in comprehensive damage assessment. Overall, this synergistic approach of combining IRT and deep learning provides a powerful tool for the automated inspection and preservation of critical infrastructure components. [ABSTRACT FROM AUTHOR]

In an era flooded with a multitude of studies investigating the performance of concrete structures retrofitted using fiber‐reinforced polymer (FRP) materials, this review addresses the critical need for a comprehensive overview of the retrofitting of concrete members using near‐surface mounted (NSM)‐FRP composites, aiming to save time and effort while providing engineers and research community with valuable resources relevant to the field. This review focuses on the key factors influencing both the flexural and shear retrofitting processes of reinforced concrete (RC) beams, such as the percentage, type, size and geometry of NSM‐FRP reinforcement, as well as groove design, groove‐filling materials and beam depth. Moreover, the paper explores the failure modes associated with each retrofitting type, for example, debonding failures, shear/flexural failure and rupture of steel or NSM‐FRP reinforcement, to name a few. The review also delves into the bond behavior of NSM‐FRP‐bonded joints, examining factors, such as the bonded length, surface texture of NSM‐FRP reinforcement and type of bonding agent, which would affect the bond behavior and strength of the joints. The failure mechanisms associated with the bonded joints, such as interfacial bond failure, FRP rupture and splitting of the adhesive cover, are also highlighted. Finally, this compilation aims to guide engineers and researchers by offering a critical and comprehensive database for optimal designs, further development and suggesting future research directions. [ABSTRACT FROM AUTHOR]

An experimental campaign was undertaken to characterize the mechanical properties of newly proposed aluminum alloy ribs (ARs)-anchored glass fiber–reinforced polymer (GFRP) bars via tensile, short beam shear and pullout tests. The investigated variables consisted of bar surface treatments (smooth, shallow-ribbed, and deep-ribbed) and anchorage design parameters (radial extrusion and initial wall thickness). The results derived from the tensile test showed that the tensile strength of the ARs-anchored GFRP bars could be designed and optimized by adjusting the radial extrusion and initial wall thickness of the anchorage. The short beam shear test further validated that the presence of the ARs on the GFRP bar increased its interlaminar shear strength by up to 25%. The pullout test conducted on specimens with favorable anchorage design parameters based on tensile and short beam shear tests demonstrated significantly high bond strengths between 11.45 and 46.63 MPa at the bar–anchorage interface, with enhancements ranging from 60% to several times compared with that of the bar–concrete interface under different parameter combinations. The proposed ARs-anchored GFRP bars present an effective alternative to conventional GFRP bars in applications where a short anchorage length is preferred. [ABSTRACT FROM AUTHOR]

Current tunnel design provisions do not consider the shear resistance of transverse reinforcement in precast concrete tunnel lining (PCTL) segments. Such reinforcement is often designed as a minimum for shrinkage and temperature resistance. This study evaluated the behavior and shear strength of PCTL segments reinforced with glass fiber‒reinforced polymer (GFRP) bars with and without closed shear ties. A total of five full-scale rhomboidal PCTL specimens with a 1,500 × 250 mm rectangular cross section and an arched length of 2,100 mm were constructed and tested under three-point loading up to failure. The testing parameters included the configuration of the transverse reinforcement (bars versus closed ties), the spacing of closed shear ties, the longitudinal reinforcement ratio, and concrete strength. The load–deflection behavior, cracking, failure mechanisms, shear capacities, and strain in the reinforcement and concrete are discussed herein. The results indicate that all specimens experienced shear failure because of the diagonal tension failure or shear compression mode. The presence of shear stirrups enhanced the structural performance of the GFRP-reinforced PCTL segments. In addition, increasing the closed-tie ratio, longitudinal reinforcement ratio, and concrete strength increased the shear strength of the segments. A comparison between the test results and predictions made with the critical shear crack theory (CSCT) was introduced in the theoretical approach to evaluate the applicability of existing FRP design code provisions. The predictions produced according to FRP design codes can be classified between conservative and nonconservative predictions. The modified CSCT yielded predictions closest to the experimental values with an accuracy of 98%. [ABSTRACT FROM AUTHOR]

This review explores the use of Ultra-High Molecular Weight Polyethylene (UHMWPE) fiber cloth as an innovative solution for the repair and reinforcement of concrete structures. UHMWPE is a polymer formed from a very large number of repeated ethylene (C2H4) units with higher molecular weight and long-chain crystallization than normal high-density polyethylene. With its superior tensile strength, elongation, and energy absorption capabilities, UHMWPE emerges as a promising alternative to traditional reinforcement materials like glass and carbon fibers. The paper reviews existing literature on fiber-reinforced polymer (FRP) applications in concrete repair in general, highlighting the unique benefits and potential of UHMWPE fiber cloth compared to other commonly used methods of strengthening concrete structures, such as enlarging concrete sections, near-surface embedded reinforcement, and externally bonded steel plate or other FRPs. Despite the scarcity of experimental data on UHMWPE for concrete repair, this review underscores its feasibility and calls for further research to fully harness its capabilities in civil engineering applications. [ABSTRACT FROM AUTHOR]

Behavior of fiber‐reinforced polymer reinforcing bars – Experimental investigation of the stress distribution along the bond length Due to the non‐rusting properties of fiber‐reinforced polymer reinforcement (FRP), it is possible to position this reinforcement close to the surface in components without restricting its durability. In this case, the proportion of the concrete cover remains to ensure the bond. The normative minimum concrete cover is adapted to the bond behavior of reinforcing steel. As the geometry and material properties of FKB vary, their bond behavior is bar‐specific and cannot be equated with that of reinforcing steel. For this reason, the transferability of the minimum concrete cover defined for reinforcing steel to ensure the bond for FRCs must be questioned. To derive a minimum concrete cover, it is necessary to investigate the stress distribution along the bond length. The ring test was developed in the 1990s to experimentally determine the bond stress τ acting along the reinforcing bar and the radially acting internal pressure pi. This article aims at experimentally determining the stress distribution along the bond length for three different FKBs. For this purpose, the ring test is modified so that a (quasi‐)continuous measurement of the bond stress and the internal pressure along the bond length as a function of the pull‐out force is possible. As a result, the different stress distributions are compared and a minimum concrete cover to ensure the bond is derived from the internal pressure. [ABSTRACT FROM AUTHOR]

Strengthening columns hold a crucial role in structural engineering and are frequently called for due to a range of factors, including heightened load requirements, structural degradation, design flaws, or the need for seismic retrofitting. Natural Fiber-Reinforced Polymers (NFRP) in concrete reinforcement has gained significant attention in recent years as a sustainable and eco-friendly alternative to strengthened reinforced concrete. NFRP jacketing presents an adaptable option, as it delivers an improved load-carrying capability as a confining effect. This paper explores the fundamental reasons behind the need for column strengthening and the advantages of employing NFRP jacketing as a preferred method. The study examined the influence of varying fiber densities and the number of fiber layers in NFRP on the mechanical properties of concrete, with a specific focus on its confined concrete compressive strength. The test specimen was a cylinder with a diameter of 150mm and a height of 300mm. NFRP, made from abaca fiber and resin, was attached around the specimen's circumference to provide a confinement effect. Axial load was applied to the test specimen. The findings indicated that introducing abaca fiber as an NFRP material increased confined concrete compressive strength by up to 37% compared to unconfined concrete. Additionally, the research offered valuable observations regarding the influence of varying the number of NFRP fiber layers on the behavior of confined concrete. Specifically, the study found that altering the number of layers, such as utilizing three layers of NFRP fibers, resulted in a measurable enhancement of approximately 15% in the stress experienced by the confined concrete specimen. Study findings suggest that natural fiber density and the number of layers play a role in enhancing concrete strength, however, their influence may not be significantly pronounced. [ABSTRACT FROM AUTHOR]

The ratio of fiber-reinforced polymer (FRP) confinement stiffness to concrete strength (confinement stiffness ratio) has been widely accepted to determine the postpeak stress‒strain behavior of FRP-confined concrete. It has been established that the effects of confinement efficiency are significantly different for normal-strength concrete (NSC) and high-strength concrete (HSC). This paper presents an experimental study of the stress‒strain behavior of carbon FRP (CFRP)-confined circular and square HSC columns. Various FRP confinement stiffnesses were designed for concretes with different strengths to achieve the same confinement stiffness ratios. The test results indicate that although the specimens had similar confinement stiffness ratios, the criterion values of the confinement stiffness ratio to distinguish the postpeak strain hardening/softening transition increased with increasing HSC strength. However, for FRP-confined NSC, it is suggested that a constant value of approximately 6.5 be used. In addition, this study also revealed that for specimens with weak confinement or nonuniform confinement (square cross sections), the change in confinement efficiency at the postpeak stage results in the recovery of the postpeak strain hardening behavior from the strain softening behavior. By incorporating the confinement efficiency parameter in the ultimate condition models for CFRP-confined HSC, the proposed model demonstrated satisfactory performance when compared with the test results. [ABSTRACT FROM AUTHOR]

Fiber-Reinforced Polymer (FRP) composites have emerged as a promising alternative to conventional steel reinforcements in concrete structures owing to their benefits of corrosion resistance, higher strength-to-weight ratio, reduced maintenance cost, extended service life, and superior durability. However, there has been limited research on non-destructive testing (NDT) methods applicable for identifying damage in FRP-reinforced concrete (FRP-RC) elements. This knowledge gap has often limited its application in the construction industry. Engineers and owners often lack confidence in utilizing this relatively new construction material due to the challenge of assessing its condition. Thus, the main objective of this study is to determine the applicability of two of the most common NDT methods: the Ground-Penetrating Radar (GPR) and Phased Array Ultrasonic (PAU) methods for the detection of damage in FRP-RC elements. Three slab specimens with variations in FRP type (glass-, carbon- and basalt-FRP, i.e., GFRP, CFRP, and BFRP, respectively), bar diameter, bar depths, and defect types were investigated to determine the limitations and detection capabilities of these two NDT methods. The results show that GPR could detect damage in GFRP bars and CFRP strands, but PAU was limited to damage detection in CFRP strands. The findings of this study show the applicability of conventional NDT methods to FRP-RC and at the same time identify the areas with a need for further research. [ABSTRACT FROM AUTHOR]

The combination use of stainless steel (SS) bars and seawater sea-sand concrete (SSC) is attractive for coastal and marine infrastructures due to the excellent corrosion resistance of SS and the eco-friendly property of SSC. Against this background, a total of 88 central pullout specimens were tested to investigate the bond behavior of SS reinforcement and SSC under different confinement levels provided by stainless steel stirrups and fiber-reinforced polymer (FRP) sheets. Several variables were designed in the present test, including the concrete type and strength, the thickness of concrete cover, rebar type, embedment length, and confinement type and level. The failure modes, bond-slip relationships, and ultimate bond strength were analyzed systematically. Test results reveal that splitting failure can be effectively prevented under sufficient confinement. The ultimate bond strength of SS bars in SSC can improve by at least 13.19% compared to counterparts in normal concrete (NC), and the enhancement of bond strength ranges from 0.49% to 37.49% with varying embedment length ratio. The confinement effects of concrete cover, stirrup, and FRP are also interpreted quantitatively by using a developed coefficient. Finally, a new bond-slip model considering dual confinement of FRP sheets and steel stirrups for SSC is developed and the proposed model performs well by comparing the theoretical predictions with the test results from this study and other relevant literature. [ABSTRACT FROM AUTHOR]

There is growing interest in utilizing natural fiber-reinforced polymer matrix composites as engineered materials for advanced applications, notably in the development of high-performance ballistic armor components. Achieving superior mechanical properties, particularly toughness, is crucial in this context. Currently, there is ongoing research into the potential of jute fiber-reinforced composites as advanced engineering materials. This study aims to present the findings of an experimental investigation on concrete beams subjected to shear, reinforced with polymer matrix composites incorporating jute fibers through jacketing. Compression bending tests were conducted and analyzed within our laboratory. The results of the experiment revealed a remarkable 69% increase in both stiffness and load capacity of the reinforced beam compared to its unreinforced counterpart. [ABSTRACT FROM AUTHOR]

A total of 66 sets of pullout specimens were prepared to investigate the bonding properties of basalt fiber-reinforced polymer reinforcement (hereinafter referred to as BFRP) with seawater sand concrete (hereinafter referred to as SSC). The volume dosages of mono-doped glass fibers and mono-doped polypropylene fibers were 0.1%, 0.2%, and 0.3%; the total volume dosage was set to be constant at 0.3%; and the doping ratios of the hybrid fibers were 1:2, 1:1, and 2:1. The effect on the bonding performance of BFRP reinforcement with SSC was studied on the condition of the diameter D of the BFRP reinforcement being 12 mm; the bond length of SSC being 3D, 5D, and 7D; and the surface characteristics of the reinforcement being sandblasted and threaded. The research showed that due to internal cracks in the matrix, salt crystals in the pores, chloride salts with high brittleness and expansion, as well as sulfate corrosion products such as "Frederick salts" in SSC, the concrete became brittle, resulting in more brittle splitting failures during the pullout test. Doped fibers can increase the ductility effect of concrete, but the bonding effect between the threaded fiber reinforcement and the SSC was not as good as that of the sandblasting group. When the bond length was 5D, the bonding effect between the BFRP reinforcement and SSC was the best, and the bonding performance of the experimental group with doped fibers was better than that of the threaded group. Finally, by combining the ascending segment of the Malvar model with the descending segment of the improved BPE model, a constitutive relationship model suitable for the bond–slip curve between BFRP reinforcement and SSC was fitted, which laid a theoretical foundation for future research on SSC. [ABSTRACT FROM AUTHOR]

This paper focuses on the shear behavior of reinforced concrete (RC) beams strengthened with carbon–glass-fiber-reinforced polymer (C-GFRP) plates under different anchoring schemes. The study consisted of four reinforced specimens: specimen CS-1 with no reinforcement and three groups of reinforced specimens SR-1, SR-2 and SR-3. The studies used a four-point bending test to evaluate the reinforcement effect of mechanically anchoring C-GFRP plates. The results of the analysis of load–deflection, strain and bearing capacity indicated that a better reinforcement effect was observed with fiber-reinforced polymer. The test results suggested that the occurrence time of critical oblique cracks was delayed and the development speed of critical oblique cracks was limited by mechanically anchoring the C-GFRP plates. C-GFRP plates significantly increased the stiffness of the reinforced specimen and reflected the superiority of mechanical anchoring. The ultimate shear capacity of the mechanically anchored C-GFRP plates has been significantly improved. With a reasonable increase in the amount of C-GFRP plate, the shear resistance of the test beam became stronger. Compared with the CS-1 specimen without reinforcement, the yield load values of the reinforced specimens SR-1, SR-2 and SR-3 increased by 5.56%, 18.80% and 26.50%, respectively. The ultimate load of reinforced specimens SR-1, SR- 2 and SR-3 increased by 11.64%, 17.47% and 31.51%, respectively. The researchers deduced their theoretical calculation method from the bearing capacity of RC beams strengthened by anchoring with carbon–glass-fiber-reinforced polymer plates. The test findings were in good accord with the theoretical calculation model of bearing capacity suggested in this research. [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]

Even though several stress–strain models have been proposed for fiber-reinforced polymer (FRP)-confined concrete columns subjected to axial compressive loading, very few models can predict an axial response featuring postpeak strain-softening behavior. Furthermore, the reliability of most of these models is limited to only a certain concrete strength class (either normal-, high-, or ultrahigh-strength concrete). This study aimed to develop an analytical model for determining the axial response of FRP-confined concrete applicable to cases with different levels of confinement stiffness and concrete strength. For this purpose, this research proposed a new confinement stiffness threshold dependent on the coupled concrete strength and column dimension size effects to classify quantitatively FRP-confined concrete's behavior in two distinguished subcategories: strain-hardening behavior and postpeak strain-softening behavior. For FRP-confined concrete with strain-hardening response, a parabolic–linear stress–strain relation was developed, where a new formulation was derived for the slope of the linear second portion, calibrated by 583 test data. To simulate FRP-confined concrete with postpeak strain-softening behavior, a new methodology was proposed whose key components were calibrated by using 121 test data. With these features, the proposed model can objectively account for the integrated influence of concrete strength and confinement stiffness on stress–strain response. The predictive performance of the developed stress–strain model was evaluated by comparing the predictions of a wide range of relevant experimental test data, which confirms the model's reliability and accuracy. Compared to the other existing stress–strain models, the proposed model performed better. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP) composites offer a corrosion-resistant, lightweight, and durable alternative to traditional steel material in concrete structures. However, the lack of established inspection methods for assessing reinforced concrete elements with externally bonded FRP (EB-FRP) composites hinders industry-wide confidence in their adoption. This study addresses this gap by investigating non-destructive testing (NDT) techniques for detecting damage and defects in EB-FRP concrete elements. As such, this study first identified and categorized potential damage in EB-FRP concrete elements considering where and why they occur. The most promising NDT methods for detecting this damage were then analyzed. And lastly, experiments were carried out to assess the feasibility of the selected NDT methods for detecting these defects. The result of this study introduces infrared thermography (IR) as a proper method for identifying defects underneath the FRP system (wet lay-up). The IR was capable of highlighting defects as small as 625 mm2 (1 in.2) whether between layers (debonding) or between the substrate and FRP (delamination). It also indicates the inability of GPR to detect damage below the FRP laminates, while indicating the capability of PAU to detect concrete delamination and qualitatively identify bond damage in the FRP system. The outcome of this research can be used to provide guidance for choosing effective on-site NDT techniques, saving considerable time and cost for inspection. Importantly, this study also paves the way for further innovation in damage detection techniques addressing the current limitations. [ABSTRACT FROM AUTHOR]

The high corrosion resistance of fiber-reinforced polymers (FRPs) and related concrete structures means that they are suitable for application in the marine environment. Therefore, the replacement of steel bars with fiber-reinforced polymer (FRP) bars enhances corrosion resistance in seawater sea-sand concrete (SSC) structures. Geometric parameters significantly influence the performance of the bond between ribbed FRP bars and SSC, thereby affecting the mechanical properties of the concrete structures. In this study, the performance of the bond between ribbed (i.e., with fiber wrapping) basalt-fiber-reinforced polymer (BFRP) bars and SSC was investigated through pull-out tests that considered rib geometry and SSC strength. The results demonstrated that an increase in rib and dent widths reduced the bond stiffness, while an increase in rib height and SSC strength gradually increased the bond stiffness and strength. Additionally, the bond stiffness and bond strength were relatively low because the surface fiber bundles buffered the mechanical interlocking force between the BFRP ribs and the concrete, resulting in plastic bond failure during the loading process. Furthermore, the adhesion of the fiber bundles to the surface of the BFRP bars also influenced bond performance, with higher adhesion leading to greater bond stiffness and strength. [ABSTRACT FROM AUTHOR]

Recently, fiber-reinforced polymers (FRP) have begun to be used for steel structure reinforcement, following decades of successful utilization for the reinforcement of concrete structures. However, rehabilitation of tubular joints with a crack at the interface of mating members using FRP has rarely been investigated. A tubular KT-joint having a semi-elliptical crack subjected to axial tensile load is explored in this study. The joint was simulated using the fracture tool of ANSYS Structural, and the effect of crack size, location, and FRP reinforcement on stress intensity factor (SIF) was evaluated. The numerical simulations show that FRP reinforcement reduces the SIF, decreases the likelihood of crack growth, and may increase the fatigue life. A 4–12% reduction per millimeter thickness of unidirectional FRP was recorded. [ABSTRACT FROM AUTHOR]

The use of hollow concrete columns (HCCs) as piers and piles for bridge applications is widespread due to their higher load-carrying capacity, stiffness, and strength-to-mass ratio compared to the solid section. This study aimed to examine the behavior of HCCs reinforced with glass fiber–reinforced polymer (GFRP) bars and spirals under different loading conditions, analyze the impact of various parameters on their load-carrying capacity, and expand the research database with numerous load–moment interaction diagrams. Ten large-scale GFRP-HCCs, which had a height of 1,500 mm and inner/outer diameters of 113/305 mm, were tested under different levels of eccentricity (concentric, 8%, 16%, 33%, and 66%). A parametric study was conducted to examine the effects of the hollow ratio, longitudinal reinforcement ratio, bar compressive strength, longitudinal reinforcement type, and concrete compressive strength on HCC behavior. The study highlighted the importance of considering the compressive strength of the longitudinal GFRP bars because neglecting it underestimated the axial load and bending moment capacities of the HCCs. The results revealed that initial eccentricity had a greater impact on bending moment than second-order effects. [ABSTRACT FROM AUTHOR]

A fiber-reinforced polymer grid-reinforced engineered cementitious composite (FRPECC) is a promising strengthening composite that addresses the drawbacks of FRP and textile-reinforced mortar (TRM). The present study focused on the axial compressive behavior and constitutive models of predamaged concrete repaired with carbon FRP grid-reinforced ECC (CFRPECC). The test parameters included predamage level, grid number, and concrete strength. The test results indicated that compared with plain concrete, the peak stress (strength), strain at peak stress (peak strain), and energy dissipation capacities of CFRPECC-retrofitted predamaged concrete increased by 9%–82%, 28%–96%, and 60%–322%, respectively. The improvement increased with the number of CFRP grids and ECC thickness but decreased with concrete strength. On the other hand, the strength and elastic modulus of concrete after retrofitting degraded with an increase in the predamage level, especially when the concrete was severely damaged, while the peak strain and lateral rupture strain were barely influenced. When the predamage level increased, the enhancement of strength decreased from 41%–106% to 9%–60%. CFRPECC directly carried 11.0%–22.7% of the strength of the retrofitted concrete columns. The enhancements of strength and elastic modulus after retrofitting were mainly attributed to the confinement and axial stiffness of CFRPECC, respectively. Further, models for the strength, peak strain, and stress–strain relationship were developed for CFRPECC-retrofitted predamaged concrete. The applicability of the proposed models was verified by test results of the existing studies. [ABSTRACT FROM AUTHOR]

Green concrete made with ground granulated blast-furnace slag (GGBS) has presented itself as a sustainable alternative to traditional concrete. Similarly, the noncorroding fiber-reinforced polymer (FRP) reinforcing bars have demonstrated reliable structural performance at a competitive price. The combination of these materials substantially improves the service lifespan for reinforced concrete (RC) structures. Earlier research investigations and existing standards do not account for FRP reinforcement in the design for compressive forces. This study revisits this design approach while experimentally investigating the axial compressive behavior of slender circular GGBS-based green concrete columns reinforced with double layers of steel and glass fiber reinforced polymer (GFRP) bars and spirals. The experimental program consists of nine large-scale specimens loaded concentrically. All specimens had a diameter of 260 mm and a length of 2,500 mm, yielding a slenderness ratio of 38.5. Two control specimens were reinforced with a single steel layer having 1.2% and 2.5% longitudinal reinforcement ratios. The remaining seven specimens had an outer layer of GFRP reinforcement and an inner layer of steel reinforcement. The investigated parameters were: (1) longitudinal reinforcement ratio; (2) spiral reinforcement ratio; and (3) spiral reinforcement configuration (pitch and diameter). The experimental findings revealed that all tested columns failed in a material-type failure. However, the slenderness effects reduced the strength of the hybrid-reinforced columns compared with the control counterparts. The steel-reinforced control specimens demonstrated load-carrying capacities that agreed well with nominal capacity predictions under existing code. Conversely, the nominal capacity predictions in current codes and standards underestimated the strength of the hybrid specimens. A proposed equation from the literature that considers the compression contribution of GFRP bars was also evaluated, and a proposed correction factor was introduced to count for second-order effects. Due to the limited number of specimens in this study, future research is warranted to refine this proposed correction factor further. [ABSTRACT FROM AUTHOR]

The past two decades have witnessed rapid advances in the use of fiber-reinforced polymer (FRP) composites in different engineering fields. Advantages such as high strength-to-weight ratio, corrosion resistance, and tailority have led to immense interest in the use of FRPs in wide spectrum repair and strengthening of structures. Despite their many advantages, FRPs are highly sensitive to high temperatures, which pose a major concern for fire potential structures such as buildings. Applying proper thermal insulation can enhance the fire performance of FRP and reduce the possible fire damage to the FRP strengthened element. This study set out to experimentally investigate the effectiveness of two insulation systems, "FIRECOAT" and "REALROCK" on fire performance of CFRP and GFRP strengthened concrete specimens. Various configurations and exposure durations were considered to evaluate the effectiveness of insulating materials. To perform the experiments, cylindrical concrete specimens were fabricated and strengthened using CFRP or GFRP. After insulating the specimens, they were exposed to a standard fire curve for two different durations of 30 and 60 min. The results indicate that less than 30 min of fire, both insulation systems can provide the required protection. During long exposure duration of 60 min, only REALROCK can provide the required thermal resistance for FRP-strengthened concrete. Within the tested materials, Fire Set 60 outperformed other insulating materials. It was observed that implementing Fire Set 60 in the innermost layer of thermal insulations has crucial importance in preventing the fire induced reductions in strength of FRP-strengthened concrete elements. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP) has been used for seismic retrofitting and structural reinforcement over recent decades. Numerous researchers have created stress–strain models based on experimental data to predict the mechanical properties of FRP-confined concrete. In this study, circular and square cross-section specimens with different design concrete strength were prepared, and the compressive strength of the specimens confined with different layers of aramid FRP (AFRP) were measured in compressive tests. A constitutive model was proposed to simulate the uniaxial compressive stress–strain relationship of the AFRP-confined concrete, which was derived from the Mohr–Coulomb failure envelope theory, and the corresponding axial strain was determined from the regression analysis. The internal friction angle of the proposed constitutive model was determined for the cylindrical concrete specimens confined with one and two layers of AFRP. The compressive strength of one and two layers of AFRP-confined concrete specimens were used to obtain the parameters of the constitutive model; the absolute average error between experimental and predicted compressive strength was 7.01%. Then, the constitutive model was used to predict the strength of a three-layer AFRP-confined concrete specimen, and the absolute average error was 4.95%. The cross-sectional shape coefficient of the square concrete specimen was obtained analytically. Substituting the cross-sectional shape coefficient into the proposed constitutive model, the average absolute error of the square cross-section concrete specimen was about 3.84%. The results indicated that the proposed constitutive model can predict the compressive strength of circular and square cross-section concrete specimens confined with AFRP. [ABSTRACT FROM AUTHOR]

The disposal of glass fiber-reinforced plastic (GFRP) waste has become an urgent issue in both the engineering and environmental fields. In this study, the feasibility of reusing mechanically recycled GFRP in concrete was evaluated. Secondary screening of the recycled material was conducted to obtain different types of products, and the recycled GFRP (rGFRP) was characterized. Subsequently, the effect of rGFRP on concrete performance was evaluated using different dosages (0%, 1%, 3%, 5%) of rGFRP powder and rGFRP cluster (with different sizes and fiber contents) to replace fine aggregate in concrete preparation. The experimental results indicated that the addition of rGFRP powder has no significant impact on the mechanical properties of concrete, while the addition of a small amount of rGFRP cluster slightly improves the compressive strength and splitting tensile strength of concrete. Additionally, the short fibers in rGFRP improve the failure mode of concrete, and increased fiber content and longer fiber length demonstrate a more pronounced reinforcing effect. The challenges and potential directions for future research in the realm of reusing rGFRP in concrete are discussed at the end. A systematic process for reusing GFRP waste in concrete is proposed to address the primary challenges and provide guidance for its practical engineering application. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the compressive performance of longitudinal steel-fiber-reinforced polymer composite bars (SFCBs) in concrete cylinders confined by different type of fiber-reinforced polymer (FRP) composites. Three types of concrete cylinders reinforced with (or without) longitudinal SFCBs and different transverse FRP confinements were tested under monotonic compression. The results showed that the post-yield stiffness of SFCBs is higher when confined with high elastic modulus carbon fiber-reinforced polymer (CFRP) composite than with low elastic modulus basalt fiber-reinforced polymer (BFRP) composite. Decreasing confinement spacing did not significantly improve the compressive strength of SFCBs in concrete cylinders. The compressive failure strain of SFCBs could possibly reach 88% of its tensile peak strain in concrete cylinders confined by CFRP sheets, which is significantly higher than the value (around 50%) in previous studies. Existing design equations, which applied a strength reduction factor or a maximum compressive strain of concrete to consider the compressive contributions of SFCBs in concrete members, underestimate the load-carrying capacity of SFCB-reinforced concrete cylinders. The design equation that considers the actual compressive stress of SFCBs gives the most accurate prediction; however, its applicability and accuracy need to be verified with more experimental data. [ABSTRACT FROM AUTHOR]

In recent years, there has been a large number of studies on recycled-aggregate concrete as a potential solution to the problem of a scarcity natural resources. This study investigated the bonding performance of a new reinforcement material employed in medium and high-strength recycled aggregate concrete. The pull-out test was carried out by employing basalt fiber-reinforced polymer (BFRP) bars with different diameters (12, 14, and 20 mm) in medium and high-strength concrete with different ratios of recycled coarse aggregate replacement (0, 25, 50, 75, and 100%). Based on the concrete bond damage, the failure modes were identified, the corresponding bond mechanism was analyzed and the bond stress–slip characteristics were summarized. The effect of each parameter on the failure mode, bond strength, and the bond-slip curve between recycled-aggregate concrete and BFRP bars was evaluated. Results indicated that as the diameter of the BFRP bar increased, the failure mode was shifted, the uneven distribution of bond stress became more pronounced, and the bond strength showed a decreasing trend. Two distinct situations of medium to high-strength concrete with very different relative bond strengths at different replacement ratios were found. The relative bond strength of medium-strength concrete increased at first and then decreased with the increase of the replacement ratio of recycled coarse aggregate. A non-linear relationship between the bond strength of recycled concrete and its compressive strength was found. The two-stage model was proposed to describe the bonding behaviour more accurately between BFRP bar and medium to high-strength recycled aggregate concrete. [ABSTRACT FROM AUTHOR]

Fiber-reinforced polymer (FRP)–concrete hybrid sections, composed of FRP profiles and a concrete slab, have gathered attention in construction due to their lightweight, easy installation, and high durability. However, the low shear strength and brittle behavior of commercially available pultruded FRP profiles often leads to brittle shear failure at low load levels. To enhance the shear strength and ductility, this study proposes a novel H-shaped FRP profile that is built from two U-shaped pultruded FRP profiles and a hand lay-up sandwiched core of multi-directional fibers. Direct shear tests showed that the built-up FRP profiles failed in pseudo-ductile mode while the U-shaped pultruded FRP profiles failed in brittle mode. Built-up FRP had 1.5 times the capacity and 2.8 times the ultimate redundancy compared to pultruded FRP. Additionally, flexural tests of FRP–concrete hybrid beams revealed that the webs of the built-up FRP profiles failed in a higher shear capacity with smeared cracks. [ABSTRACT FROM AUTHOR]

Externally bonded fiber-reinforced polymers (FRPs) have been widely used for strengthening and retrofitting applications. However, their efficacy is hindered by the poor resistance of their epoxy resins to elevated temperatures and their limited compatibility with concrete substrates. To address these limitations, fabric-reinforced cementitious matrix (FRCM), also known as textile reinforced mortar (TRM), systems have emerged as an alternative solution. In this study, experimental tests were performed on concrete cylinders confined with FRCM systems that consisted of mineral mortar and poliparafenilenbenzobisoxazole fabric (PBO). The cylinders with concrete strengths of 30, 45, and 70 MPa, were confined with one or two FRCM layers, and were subjected to different target temperatures (100, 400, and 800 °C). The experimental results highlighted the confinement effect of FRCMs on the compressive strength of the tested cylinders. Cylinders exposed to 100 °C exhibited a slight increase in their compressive strength, while no specific trend was observed in the compressive strength of cylinders heated to 400 °C. Specimens heated up to 800 °C experienced a significant reduction in strength, reaching up to 82%. [ABSTRACT FROM AUTHOR]

Due to the lack of relevant research, the effect of the lateral confinement provided by stirrups and concrete cover on the bond behavior between glass fiber-reinforced polymer (GFRP) bars and concrete is ambiguous, resulting in the lack of a practical bond slip theory of GFRP bars. Therefore, it is impossible to accurately analyze the load response of GFRP-reinforced concrete (RC) structures from the stress level. In this paper, the local bond behavior of ribbed GFRP bars was systematically analyzed by the beam-end tests. The test parameters include concrete strength, stirrup spacing, and concrete cover. In addition, a bond stress-slip model considering the bonding mechanism was proposed on the basis of the beam-end tests and previous research. The results show that, the development of concrete cracks is restricted due to the existence of stirrups, and the specimens tend to fail in pull-out failure with strong confinement of stirrups. With the increase in the lateral confinement level, the failure mode of specimens transits gradually and smoothly from splitting failure to pull-out failure. Meanwhile, the peak slip of specimens with splitting failure also increases, and its maximum value does not exceed the peak slip of the corresponding specimens with pull-out failure. The confining capacity of stirrups and concrete cover was unified by a proposed parameter K. Then, a bond stress-slip model based on parameter K was established to predict the bond behavior of ribbed GFRP bars. [ABSTRACT FROM AUTHOR]

Hybrid fiber–reinforced polymer (HFRP) bars possessing high tensile ductility and excellent corrosion resistance are an attractive alternative to steel bars. However, the effect of long-term embedment of HFRP bars in concrete on the tensile ductility of bars must be investigated. This study exposes a series of ductile carbon/glass-HFRP bars to a simulated ordinary concrete environment for 3 and 6 months. The accelerated aging method was conducted at 60°C to accelerate the diffusion of moisture and hydroxyl ions into the carbon/glass-HFRP bars, which could rapidly aggravate the degradation of the HFRP bars. Moisture absorption tests, scanning electron microscopy, and Fourier-transform infrared spectroscopy were performed to reveal the degradation mechanisms of the fiber, matrix, and fiber/matrix interfaces in the exposed samples. The tensile ductility of the samples after exposure was lower than that of the samples before exposure. The tensile strength retention of the exposed samples depended on the volume fraction of carbon fibers and the total volume fraction of the fibers, which could be considered in the prediction model of tensile strength retention of the exposed carbon/glass-HFRP bars. [ABSTRACT FROM AUTHOR]

In recent years, replacing steel bars with basalt fiber-reinforced polymer (BFRP) bars and replacing ordinary concrete with reactive powder concrete (RPC) are considered effective solutions to the corrosion problem of steel bars in ordinary reinforced concrete structures. In order to study the bonding performance between BFRP bars and RPC, a total of 27 bonding specimens were tested by pull-out test. The effects of steel fiber volume content (0%, 1.5%, 2%), protective layer thickness (25 mm, 40 mm, 55 mm, 69 mm), and bond anchorage length of bars (3 d, 4 d, 5 d; d is the diameter of the bars) on the bond performance were studied. The experimental results indicated that the BFRP bar and reactive powder (RPC) concrete interface exhibited better bonding performance, and the steel fibers mixed in RPC can play the role of crack-blocking enhancement in the specimen, which improves the shear and tensile properties of the concrete, thus improving the bond strength between BFRP bar and RPC. Three failure modes were observed in the pull-out tests: BFRP bar shear failure, splitting failure, and concrete shear failure. The bond strengths of BFRP bars and RPC with 0%, 1.5%, and 2% steel fiber content were 24.2 MPa, 32.1 MPa, and 34.5 MPa, respectively. With the increase in bond anchorage length, the ultimate bond strength tended to increase first and then decrease. There may be an optimal bonding length between BFRP bar and reactive powder concrete, and when the optimal bonding length is exceeded, the bond strength decreases with the increase in bonding length. With the increase in the protective layer thickness, the improvement in the bond strength of the BFRP bar and RPC was not very significant. [ABSTRACT FROM AUTHOR]

Glass-fiber-reinforced polymer (GFRP) bars have been widely used as a reinforcement in concrete, and glass fibers are susceptible to reacting with alkali ions in concrete pores. Thus, carbon fibers are wrapped around GFRP bars to produce carbon/glass hybrid fiber-reinforced polymer (HFRP) bars so as to promote the durability of the internal GFRP bars in concrete. This work studies the durability of the interfacial bond between GFRP bars/HFRP bars and concrete using pullout tests. The specimens are tested after immersion in distilled water for 0, 150, 255, and 544 days. The failure of the GFRP bar–concrete composite is due to damage to the GFRP bar, while the HFRP bar–concrete composite fails because of a combination of the scratching of the HFRP bar and the failure of the concrete. Both HFRP and GFRP bars are scratched as the immersion period extends. Further, the strength of the bond between the HFRP bar and concrete is lower than that of the bond between the GFRP bar and concrete, while the bond stiffness of the HFRP bar–concrete composite is higher than that of the GFRP bar–concrete composite. The bond strength of the HFRP bar–concrete and GFRP bar–concrete composites increases in the early immersion periods but decreases after 544 days of immersion in water. The retention of the bond strength of the HFRP bar–concrete composite is superior to that of the GFRP bar–concrete composite. The carbon fiber coat is proven to improve the durability of the bond between HFRP bars and concrete in water. A formula for predicting the bond strength of HFRP bar–concrete and GFRP bar–concrete composites in water is also developed. Finally, the modeling results demonstrate that the bond strength retention of the HFRP bar–concrete and GFRP bar–concrete composite is 76% and 46% after 50 years of service time, respectively. [ABSTRACT FROM AUTHOR]

Thermoset glass fiber-reinforced polymers (GFRP) have been widely used in manufacturing and construction for nearly half a century, but the large amount of waste produced by this material is difficult to dispose of. In an effort to address this issue, this research investigates the reuse of thermoset GFRP waste in normal strength concrete (NSC) and controlled low-strength materials (CLSM). The mechanical performance and workability of the resulting concrete were also evaluated. To prepare the concrete specimens, the thermoset GFRP waste was first pulverized into granular pieces, which were then mixed with cement, fly ash, and water to form cylindrical concrete specimens. The results showed that when the proportion of thermoset GFRP waste aggregate in the concrete increased, the compressive strengths of NSC and CLSM would decrease. However, when incorporating 5% GFRP waste into CLSM, the compressive strength was 7% higher than concrete without GFRP. However, the workability of CLSM could be improved to meet engineering standards by adding an appropriate amount of superplasticizer. This finding suggests that the use of various combinations of proportions in the mixture during production could allow for the production of CLSM with different compressive strength needs. In addition, the use of recycled thermoset GFRP waste as a new aggregate replacement for traditional aggregates in CLSM was found to be a more sustainable alternative to the current CLSM combinations used in the market. [ABSTRACT FROM AUTHOR]

Cracked concrete members with fiber‐reinforced polymer (FRP) reinforcement generally suffer from increased deflections compared to steel‐reinforced members due to FRP reinforcements' lower modulus of elasticity. An approach to counteract this problem can be the prestressing of the FRP reinforcement, which can significantly reduce member deflections. However, time‐dependent prestress losses occur due creep and shrinkage of the concrete and relaxation of the prestressing tendons. Within the first part of this article, mathematical approaches to determine relaxation rates from creep tests are introduced. Subsequently, short‐term and long‐term tensile tests under sustained load on glass and basalt FRP reinforcement bars are presented. Based on the experimental data and the mathematical model, relaxation rates for the investigated specimens are derived. In addition, using an approach based on logarithmic extrapolation, the relaxation rates at 1 million hours (end of service life) are calculated, and the experimentally determined residual tensile properties are evaluated. [ABSTRACT FROM AUTHOR]

The effect of using inclined fiber-reinforced polymer (FRP) U-wrap for preventing concrete cover separation (CCS) of FRP flexural strengthening in reinforced concrete (RC) beams was investigated. The beams measured 3400 mm long, 200 mm wide, and 400 mm deep and were tested under two concentrated loads. The inclined U-wraps were used to anchor the FRP flexural strengthening at its ends. The FRP materials used in both flexural strengthening and end anchorage were carbon FRP (CFRP) sheets. The inclination angle of the FRP U-wraps to the longitudinal axis of the beams was 45°. The area of FRP U-wrap was varied in terms of varying the width of U-wrap. The test results indicated that there is a minimum width of inclined FRP U-wrap required to prevent CCS and shift the failure to another mode of failure, which in this case was intermediate crack (IC) debonding. Increasing the width of inclined FRP U-wrap by 33.3% and 100% above this minimum width was found to not only prevent CCS failure but also delay the occurrence of IC debonding and increase the load-carrying capacity of the beams by 24% and 32%, respectively, higher than the calculated failure load at IC debonding. These results showed superior performance of inclined U-wraps vs. vertical U-wraps in preventing CCS and increasing the load-carrying capacity of the beams. A model for determining the minimum FRP U-wrap area required to prevent CCS including the effect of inclination angle of FRP U-wrap was proposed. The proposed model was able to accurately predict the minimum area of inclined FRP U-wrap of the test beams at which the mode of failure shifted to IC debonding. In addition, the paper presents a proposed method for calculating the load-carrying capacity of FRP-strengthened beams anchored with inclined FRP U-wrap accounting for the beneficial effect of increased capacity of the beams associated with the use of such anchors. The comparison with the experimental results indicated good agreement. [ABSTRACT FROM AUTHOR]

This paper reports on a series of four-point bending experiments to investigate the shear capacity of reinforced concrete (RC) beams strengthened with externally bonded basalt fiber–reinforced polymer (BFRP) sheets. The experimental results show that BFRP sheets can significantly increase RC beams' shear capacity and ductility. To analyze the fracture and mechanical behaviors of BFRP sheet–strengthened RC beams, a three-dimensional (3D) finite-element model (FEM) based on the application of cohesive elements was developed. Mixed-mode constitutive models of the BFRP–concrete interface, the concrete potential fracture surface, and the reinforcement–concrete interface were proposed. The proposed constitutive models were able to characterize the interface's normal separation, tangential slip, and friction. A comparison of the simulation and experimental results indicates that the proposed numerical model can appropriately simulate the mechanical response, crack propagation, and crack distribution of BFRP sheet–strengthened RC beams. Finally, based on the proposed 3D FEM, a series of numerical tests were conducted to investigate the influence of key parameters (i.e., sheet elastic modulus, sheet bonding area, and sheet bonding angle) on the shear capacity of BFRP sheet–strengthened RC beams. [ABSTRACT FROM AUTHOR]

Using large rupture strain (LRS) fiber-reinforced polymer (FRP) composites as confining material has become increasingly prominent in structural repair or retrofitting, owing to their advantageous high deformation capacity. Economic and rational usage of LRS FRP relies on displacement-based design, which requires calculation of the ultimate deformation of a member. However, prediction of the ultimate strain of LRS FRP–confined concrete is more complex and can be more inaccurate than prediction of strength, especially for structural elements under large deformation or severe damage conditions. This study proposes a unified ultimate strain model for LRS FRP–confined concrete based on an energy balance method. A unified expression form is derived using this method, providing an ultimate strain model with no restrictions on column cross section, in terms of circular, square, or oblong columns. The proposed ultimate strain model has a wider application and a better performance than other models. Furthermore, according to this paper's updated database, the characteristic points on the whole stress–strain curve can also be accurately determined. Using the new ultimate strain model for LRS FRP–confined concrete and its characteristic points, the whole entire stress–strain curve of LRS FRP–confined concrete is accurately derived. [ABSTRACT FROM AUTHOR]

This paper has developed a semi-empirical model to evaluate the dry shrinkage strain and creep coefficient of concrete with graphene oxide nanosheets (GONs). The effect of adding GON on the dry shrinkage strain and creep coefficient is fully investigated. Also, the dependency of the dry shrinkage strain on the age when drying begins is carefully examined. Afterward, the results are compared with the results of available models which predict dry shrinkage strain and creep coefficient of common concrete and GON reinforced concrete. It is found that the developed model in this paper can fully predict the dry shrinkage stain and creep coefficient of concrete with GON. The predictions from the model are consistent with the most cited experimental measurements of dry shrinkage strain and creep coefficient of concrete containing GON. The outcomes of this investigation can pave the way to fabricate a sustainable concrete structure and achieve high-performance concrete. [ABSTRACT FROM AUTHOR]

The accurate prediction of reference points on the axial stress–axial strain relationship of fiber-reinforced polymer (FRP)-confined concrete is vital to pre-design structures made with this system. This study uses an artificial neural network (ANN) for predicting hoop rupture strain (εh,rup) and transition zone, namely transition strain (εc1) and stress (f'c1), on axial stress–strain curves of FRP-confined concrete. These are key parameters for estimating a transition zone of stress–strain curves. In this study, accompanied with these parameters, ultimate condition parameters, including compressive strength and ultimate axial strain, were predicted using a comprehensive database. Various combinations of input data and ANN parameters were used to increase the accuracy of the predictions. A sensitivity analysis and a model validation assessment were performed to evaluate the predictability of the developed models. At the end, a comparison between the proposed models in this study and existing ANN and design-oriented models was presented. It is shown that the accuracy of the developed ANN models in this study is higher or comparable to that of existing ANN models. Additionally, the developed models in this study to predict f'c1 and εc1 exhibit a higher accuracy compared to existing design-oriented models. These results indicate that the proposed ANN models capture the lateral confinement effect on ultimate and transition zones of FRP-confined concrete with a more robust performance compared to existing models. [ABSTRACT FROM AUTHOR]

• Confinement stiffness of BTRM jackets relies on the mortar strength. • High-strength mortar slightly reduces hoop rupture strain of BTRM jackets. • A refined model more accurately captures the behavior of confined concrete. Numerous studies have investigated the behavior of textile reinforced mortar (TRM)-confined concrete, yielding various stress-strain models predominantly derived from fiber-reinforced polymer (FRP)-confined concrete. Yet, these models frequently overlook the intricate constitutive behavior of TRM materials and inadequately capture how TRM delivers its confinement effects. This often leads to inaccurate representation of the true characteristics of the confinement system, particularly the crucial role of mortar. This paper focuses on the impact of variations in textile layers and mortar matrix strength on the stress-strain behavior of basalt TRM (BTRM)-confined concrete, aiming to enhance our understanding of the confinement mechanism. Additionally, the study critically evaluates the key components of an existing analysis-oriented stress-strain model for FRP-confined concrete and introduces a refined version that more precisely depicts the behavior of confined concrete. This refined model integrates an identified confinement mechanism to provide accurate predictions of BTRM-confined concrete behavior. Our results reveal that low-grade mortar significantly decreases the actual confinement stiffness of BTRM jackets, inducing a steeper decline in the stress-strain curve, while high-strength mortar slightly diminishes the hoop rupture strain. To address the challenges of quantifying the complex confinement effect-compounded by the variable stress state and constitutive behavior of TRM-a novel coefficient, termed km, is introduced to gauge the influence of mortar strength on the confinement stiffness within the confining pressure equation. Predictive outcomes, including stress-strain and axial-to-lateral strain curves, show close alignment with experimental data, particularly in the slope at the plateau stage. This research significantly advances the quantitative understanding of TRM confinement effects and proposes the potential for designing more ductile structures using these materials, which could lead to enhanced resilience against seismic events and other structural challenges. [ABSTRACT FROM AUTHOR]

This article proposes a new constitutive model for the cyclic behavior of rubberized concrete confined with fiber‐reinforced polymer (FRP) sheets. The model is calibrated with experimental results from 18 confined rubberized concrete (CRuC) cylinders tested in cyclic compression. The cylinders had 60% total aggregate volume replacement with recycled tyre rubber. Parameters investigated include the type of confining material (Carbon or Aramid FRP) and number of layers (two, three, or four). The results indicate that using FRP confinement leads to a strong (up to 100 MPa) and highly deformable (axial strains up to 7%) rubberized concrete that can be used in structural applications. The proposed constitutive model predicts accurately the material response under cyclic loading and can thus be used for design/analysis of highly deformable components made of FRP CRuC. This article contributes toward the development of advanced constitutive models for FRP CRuC, thus promoting the wider use of recycled materials in construction industry. [ABSTRACT FROM AUTHOR]