Glass Fiber Reinforced Polymer Research Articles

Nondestructive Detection of Osmotic Damage in GFRP Boat Hulls Using Active Infrared Thermography Methods

This article presents the application of infrared thermography as a nondestructive testing method (NDT) for detecting osmotic damage in glass-fiber-reinforced polymer (GFRP) and glass-reinforced polymer (GRP) boat hull structures. The aim of the conducted experiments is to explore the possibilities of applying active infrared thermography to real structures and to establish a procedure capable of filtering out anomalies caused by various thermal influences, such as thermal reflections from surrounding objects, geometry effects, and heat flow variations on the observed object. The methods used for post-processing IR signals include lock-in thermography (LT), pulse thermography (PT), pulse phase thermography (PPT), and gradient pulse phase thermography (GT). The practical application and advantages and disadvantages of infrared thermography in identifying osmotic damage in GFRP and GRP boat hulls will be illustrated through three case studies. Each case study is based on specific conditions and characteristics of different types of osmotic damage, enabling a thorough analysis of the effectiveness of the method in detecting and assessing the severity of the damage. The post-processed thermal images enable a clearer distinction between damaged and undamaged zones, improving the robustness of detection under realistic field conditions.

Durability of FRP-strengthened RC beams subjected to 110 months accelerated laboratory and field exposure

This paper presents an experimental investigation of the long-term performance of fiber reinforced polymer (FRP) composites strengthened reinforced concrete (RC) beams. The beam specimens had identical dimensions. Different FRP composites and adhesives were used, including carbon FRP (CFRP) plate bonded with Sika 30; CFRP plate bonded with Araldite 106; CFRP sheet bonded with SW-3C; and glass FRP (GFRP) bonded with Sika 330. Their performance was tested after 8, 18, 31, and 110 months of exposure to the wet-dry cyclic environment, and 48 and 110 months of exposure to the outdoor environment. Test results show that the FRP-strengthened RC beams subjected to the wet-dry cyclic environment exhibited more significant degradation compared to those subjected to the outdoor environment. In the wet-dry cyclic environment, CFRP plate/Sika 30 strengthened beams and CFRP sheet/SW-3C strengthened beams exhibited better durability performance with only 6 % and 4 % reductions in the flexural capacity after 110 months, respectively. In contrast, CFRP plate/Araldite 106 strengthened beams and GFRP sheet/Sika 330 strengthened beams exhibited larger reductions of 30 % and 31 %, respectively. Furthermore, the FRP debonding strain was reduced over time. A reduction factor is proposed for the design of FRP debonding strain based on test results to ensure long-term safety.

Enhancing the Mechanical and Fire-Resistant Properties of GFRP Composite using Boric Acid and Sodium Silicate Fillers

This study investigates the effects of Boric Acid (BA) , H3BO3, and Sodium Silicate (SS), Na2SiO3, as single fillers on the mechanical and fire-resistant properties of Glass Fiber Reinforced Polymer (GFRP) composites. Various compositions of BA and SS were incorporated into the GFRP matrix, and the resulting composites were analyzed using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermo-Gravimetric Analysis (TGA), and Differential Thermal Analysis (DTA). The results demonstrate that BA significantly enhances the amorphous structure and mechanical strength of GFRP composites, with optimal performance at 10% BA content. In contrast, SS improves thermal stability but reduces mechanical strength at higher concentrations due to agglomeration. Fire resistance testing revealed that both fillers increase the ignition time and decrease the burning rate, with BA exhibiting superior performance. These findings suggest that BA is a more effective filler for improving the mechanical and fire-resistant properties of GFRP composites, while SS can serve as a complementary additive to enhance thermal stability.

Structural Behavior of Self-Compacting Bendable Mortar Beams reinforced by GFRP Bars under Monotonic Loads

Flexible or bendable concrete is an Engineered Cementitious Composite (ECC) that exhibits ductile material properties, in contrast to the brittle nature of conventional concrete. The material composition of conventional concrete is modified in order to impart a flexible nature to the material. This research presents the findings of an experimental study examining the flexural response of self-compacting bendable concrete beams reinforced by Glass Fiber Reinforced Polymers (GFRP) bars under a symmetrical two-point load. The experimental work comprised the casting of eight reinforced beams. The dimensions of all beams were identical: an overall height of 150 mm, a width of 100 mm, and a total length of 1,000 mm. The beams were classified into three groups based on the type of variables adopted and the type of the strengthening method employed, the percentage of steel fibers (1%, 1.5%, and 2%), and the percentage of Polyvinyl Alcohol (PVA) (0.2%, 0.3%, and 0.4%) were also considered. The following measurements were taken: the first cracking load, midspan vertical deflections, concrete surface strains, and the ultimate load capacity. Additionally, the crack patterns were recorded and the failure mode was observed, in addition to the mechanical properties of self-mortar bendable concrete (both fresh and hardened). The results indicated that an increase in the PVA ratio from 0.2% to 0.3% and 0.4% resulted in a notable rise in the modulus of rupture and modulus of elasticity, by approximately 16% and 40%, respectively, and 0.09% and 2%, respectively. The ductility of the beams increased with the steel fiber ratio due to enhanced flexural and splitting properties, which is a positive outcome. This allows for more caution to be exercised before the beam reaches its limit of stability. Furthermore, the value of deflection at maximum load increases with the increase of steel fiber content due to the increase in load capacity.

An Artificial Neural Network Prediction Model of GFRP Residual Tensile Strength

This study uses an Artificial Neural Network (ANN) to examine the constitutive relationships of the Glass Fiber Reinforced Polymer (GFRP) residual tensile strength at elevated temperatures. The objective is to develop an effective model and establish fire performance criteria for concrete structures in fire scenarios. Multilayer networks that employ reactive error distribution approaches can determine the residual tensile strength of GFRP using six input parameters, in contrast to previous mathematical models that utilized one or two inputs while disregarding the others. Multilayered networks employing reactive error distribution technology assign weights to each variable influencing the residual tensile strength of GFRP. Temperature exerted the most significant influence at 100%, while sample dimensions had a minimal impact at 17.9%. In addition, the mathematical model closest to the proposed was the Bazli model, because the latter depends on two variables (thickness and temperature). The ANN accurately predicted the residual tensile strength of GFRP at elevated temperatures, achieving a correlation coefficient of 97.3% and a determination coefficient of 94.3%.

Performance of Steel Beams reinforced by CFRP Sheets with Fire-Retardant Coating

The objective of this study was to determine the physical, mechanical, and chemical aspects of bonding and priming Fire-Retardant Coatings (FRCs) to steel surfaces before and after fire testing. Carbon Fiber Reinforced Polymers (CFRP) have been used to strengthen steel components. Certain types of polymer systems have demonstrated high fire retardancy without additives, while others require additives to achieve optimum fire resistance. A wide range of compounds are available to enhance the fire retardant properties of these materials, characterized by their chemical nature and behavior (such as halogenated, metal complex, silicon-based, and phosphorus additives) and mode of action (either condensed or gas-phase active systems).This article provides a comprehensive overview of fire retardant additives for CFRP used in various large-scale applications, including the aerospace, automotive, railway, electronics, and civil engineering industries, as well as their fire retardant mechanisms at the microscopic, macroscopic, and nanoscale levels. In addition to fire retardant properties, this study also discusses the effects of additives on other material parameters and coatings, such as glass transition temperature, mechanical performance, and FRP processability. The primary focus is on thermoset systems, with a brief mention of thermoplastics according to the matrix compounds relevant to the FRP market size. Test results show that the direct velocity ultrasonic value varied between 3.016 and 3.618 km/s, giving an estimated compressive strength of 15.974 MPa. The standard deviation was 0.533 km/s with a relative standard deviation of 16.407%.

Implementation of multi-walled carbon nanotube incorporated GFRP as an alternative for CFRP in strengthening of concrete cylinders

Carbon fibre is the most widely utilized fibre for strengthening and retrofitting applications in the construction sector. The high cost of carbon fibre necessitates the identification of an alternative system for the retrofitting and repairing of concrete structures. In the current study, the characteristics of Glass Fibre Reinforced Polymer (GFRP), Carbon Fibre Reinforced Polymer (CFRP), and Multi-Walled Carbon Nanotube (MWCNT) incorporated GRFP are assessed with epoxy as a matrix for concrete cylinder confinement. The evaluation of one and two-layer CFRP confinement on concrete cylinders is carried out and outcomes are compared with the three-layer MWCNT incorporated GFRP confinement. A significant increase was observed in the axial compressive load-bearing capability of specimens with 1 wt percentage (wt%) MWCNT incorporated GFRP confined concrete cylinders. The axial load-carrying capability of concrete specimens with one layer of CFRP confinement was equivalent to that of specimens with 1 wt% MWCNT incorporated three-layer GFRP confinement. The axial strain of MWCNT incorporated three-layer GFRP confined specimens was 75 % more than one-layer and 12 % higher than two-layer CFRP confined specimens. According to observations, MWCNT-incorporated FRP confinement improves the energy absorption and ductility index. Ultrasonic pulse velocity test results confirmed the potency of three-layer GFRP confinement as a replacement for one and two layers of CFRP. A cost analysis is also carried out to validate the economic viability of the MWCNT-based GFRP compared to CFRP confinement.

Application of Ultrasonic Thermography in the detection of delamination in the Glass Fiber Reinforced Plastics

In the present research, the applicability of active thermography using ultrasonic excitation in detecting delamination defects has been investigated experimentally. In this regard, a Glass Fiber Reinforced Plastic (GFRP) Sample was prepared via the hand layup method. PTFE sheet pieces were considered delamination defects located inside the sample. The delamination defects were considered in the three different sizes. Moreover, three delaminations with similar sizes were placed in three different depths. The ultrasonic excitations were conducted using a Piezoelectric PZT transducer. The excitation frequency was adjusted to a constant value. The ultrasonic thermography inspections were performed with three different excitation powers. The sample was constrained in the fixed-fixed mode. The thermography inspections were carried out with three various excitation times. Results indicated that the defect of a maximum size has been detected in all inspections. Moreover, in order to enhance the detectability a trade-off of excitation power and excitation time should be selected.

Flexural behavior of steel/GFRP reinforced concrete beams having layered sections integrated with normal and rubberized concrete

Rubberized concrete (RuC) is one of the possible sustainable solutions to the problem of quickly disposing of old tires. This study introduced a new coating material (metakaolin, MK) for crumb rubber (CR) at a controlled temperature to avoid decreasing the RuC mechanical properties. Additionally, to prevent the possible reduction in the RuC strength on the RC beam behavior, the functionally graded material (FGM) approach was applied (layered beam section with RuC at 67 % of the beam section and normal concrete (NC) at the top one). The influence of RC beams on the tensile reinforcement (glass fiber-reinforced polymer (GFRP) instead of steel) was also examined. The experimental investigation comprised several concrete combinations: conventional concrete and RuC integrated uncoated and MK-coated CR replacing sand with percentages (0 %, 5 %, 15 %, and 25 %). The mechanical characteristics of concrete mixtures under compression and splitting tension tests were examined. Moreover, fourteen RC beams were experimentally loaded in flexural to investigate the impact of proposed parameters on the beam response. Following that, Finite Element (FE) modeling was carried out to examine the influence of the additional parameters on the RC beams' performance. The results demonstrate a notable improvement in the compressive strength of concrete by 17.4 % and a 25.4 % rise in split tensile strength due to the use of MK-coated CR compared to the uncoated CR. The impact of MK-created CR was more prominent in increasing the GFRP RC beam loads than the steel RC ones. In addition, using the FGM approach could eliminate the CR effect and exhibit nearly the same NC beam load.

Damage monitoring on inter-lamination of GFRP via the resistance change of the MWCNT@GF sensor

The paper aimed to investigate the performance of multi-walled carbon nanotube-coated GF (MWCNT@GF) sensors on interlayer shear damage monitoring and sensing capability of glass fiber-reinforced polymers (GFRPs) based on the resistance change under short beam shear (SBS) load. The MWCNT@GF sensor, manufactured by physical vapor deposition (PVD), was embedded into the neutral layer of laminates to form an in-situ sensing network in different directions and positions. “The MWCNT@GF sensor, manufactured by physical vapor deposition (PVD), was embedded into the neutral layer of laminates to form an in-situ sensing network.” “With the help of Keithley 2700 programmable electrometer and the 3D-digital image correlation(3D-DIC), monotonic and cyclic tests were carried out.” The monotonic test found that the off-axis sensor is more sensitive to shear failure than the on-axis sensor because of its lower shear strength. In addition, the qualitative relationship between shear damage and relative resistance was established by selecting crucial moments. In the cyclical test, the relative resistance of off-axis sensors presented a cyclic mode under cyclic load. Furthermore, the relative resistance under the first 20 cyclic loads was similar to that under monotonic loads. “Furthermore, the relative resistance under the first 20 cyclic loads was similar to that under monotonic loads, which shows that the sensor has superior sensing ability. Finally, the quantitative relation between shear damage and relative resistance was established.” “That means MWCNT@GF sensors can be used to reasonably evaluate the damage state and further evaluate the service performance, reliability and remaining life of the structure.”

Experimental and numerical investigation on layered UHPC beams incorporated with recycled macro fibers

The high cost of production is a major hindrance to the wider use of ultra-high performance concrete (UHPC). Recently, the authors’ group has proposed to replace expensive steel fibers in UHPC using macro fibers mechanically recycled from the solid waste of glass-fiber-reinforced polymer (GFRP). Such a concept has been justified by a series of tests, whose results indicate that the recycled macro fibers are effective in mitigating the development of cracks. However, a somewhat negative impact on UHPC strength would be generated by macro fibers. To lower the negative effect on concrete strength at the compression area and further increase the added value of macro fibers, this paper attempted to employ the layered UHPC structure, in which only the tension layer was reinforced with macro fibers. A total of 30 layered UHPC beam specimens were prepared and tested. The test variables comprised of the thickness of the bottom layer and the macro fiber volume fraction within the bottom layer. In addition, the fiber re-arrangement analysis was performed. The results revealed that, under the layer thickness of 50 mm, when the macro fiber volume fraction increased from 2 % to 6 %, the flexural toughness increased from 58.87 to 136.59 J (132.02 % enhancement). The maximum fiber efficiency was reached at the group with a fiber fraction of 2 % and a bottom layer thickness of 50 mm. Furthermore, numerical simulation was conducted to evaluate the feasibility of the tensile constitutive relation of UHPMFRC in the layered structure. The results indicated that it could not be directly used as model input in the numerical simulation of layered UHPMFRC structures when a strong fiber alignment effect was exhibited.

Flexural behavior of GFRP and steel bars reinforced lightweight ultra-high performance fiber-reinforced concrete beams with various reinforcement ratios

The synergistic operating mode of the concrete matrix and the reinforcing bar determines the dependability of a structure in complicated environments. The objective of this research has been to provide a comprehensive analysis of the flexural behavior exhibited by lightweight ultra-high performance fiber-reinforced concrete (LUHPC) beams that have been reinforced with high-strength steel bars (HRB500) and glass fiber-reinforced plastic (GFRP) bars. LUHPC was used as the matrix material with a compressive strength of 120 MPa and a density of 2050 kg/m3. This study focused on examining the impact of different reinforcement ratios (0.59 %, 1.27 %, and 1.94 %) and reinforcement types (GFRP and HRB500 bars) about the flexural performance of LUHPC beams under four-point bend loading. As demonstrated by the results of experiments, GFRP-reinforced LUHPC (G-LUHPC) beams with higher reinforcement ratios have higher peak loads, flexural stiffness, and cracking loads but lower ductility. Compared with steel-reinforced LUHPC (S-LUHPC) beams, the bending strength of G-LUHPC beams was reduced by 18.2 %, 24.2 %, and 6.7 %, the peak deflection was increased by 166.5 %, 24.8 %, and 56.9 %, and stiffness degradation and crack development were rapid. After comparing the test results with the current commonly used specifications, it was seen that the codes could better predict the cracking moments and the deflections under service loads of G-LUHPC beams. However, it was noted that both the ultimate moments and the corresponding mid-span deflections were greatly underestimated.

Experimental Investigation of the Fatigue Behavior of Fiber-Reinforced Composites under Cyclic Loading Conditions

The research presented here aims to conduct a performance assessment of fiber-reinforced composites (FRC) under cyclic loading with emphasis on Glass fiber-reinforced polymer (GFRP) & Carbon fiber-reinforced polymers (CFRP). FRCs’ use in engineering applications is occasioned by the high strength-to-weight ratios despite the poor performance under cyclic loads. In the experiments conducted CFRP was found to more than double the fatigue life for similar applied stress compared to GFRP. The study also brings out the nature of damage in each composite where GFRP is seen to be more vulnerable to matrix crack, fiber breakage, and delamination which reduce its fatigue life. On the other hand, CFRP exhibits high stiffness and high strength, which can prevent further damage to the composite structure and increase Fatigue endurance ability. These observations imply the necessity of material choice in high-stress conditions and indicate the possibility of utilizing hybrid composites to achieve a satisfactory combination of cost and service life. The following findings of the investigation of this paper will thus be useful for the improvement of FRCs in aerospace, automotive, and civil engineering where durability due to cyclic loading is crucial. Further research should be aimed at considering the influence of temperature and moisture on FRC fatigue behavior to improve the corresponding reliability at various conditions.

Experimental study of static and fatigue push-out test on headed stud shear connectors in UHPC composite steel beams

Steel-concrete composite girder bridges utilize shear connectors to connect concrete deck slabs and steel girders. In current practice, the headed shear stud connector is the most used due to its reliability and ease of installation. Several studies are available on the static and fatigue behavior of welded-headed shear studs embedded in normal-strength concrete. However, relatively little is known about the static and fatigue behavior of headed shear connectors in composite beams when shear studs are embedded in ultra-high-performance concrete (UHPC). This study reports a series of pushout results carried out on headed shear connectors embedded in UHPC at pre-fatigue and post-fatigue stages. Six pushout specimens were first tested under static load to collapse. The precast normal-strength concrete slabs in the pushout specimens were reinforced with glass fiber-reinforced polymer (GFRP) bars to promote sustainable construction. This practice, commonly used in Canada, aims to eliminate the corrosion of steel bars caused by de-icing salts used during winter. The results from these tests were used to determine the applied fatigue stress range of another six identical pushout specimens, which were subjected to constant amplitude fatigue loading over 2 million cycles. Results show that the fatigue cycles applied to the specimens prior to testing them to collapse did not alter the failure mode or the crack pattern of the tested specimens. Furthermore, the studied pushout specimens considered 6 different shapes of shear pockets in which the arrangement and spacing of studs were varied. It was found that the studs in a square pocket form yielded a shear capacity of 13.9 % and 16.7 % greater than those for similar studs arranged in a single row-oriented longitudinally and transversally, respectively. The accuracy of the various design formulas specified in design codes in estimating the shear resistance of the tested specimens, as well as empirical formulas proposed to develop load-slip curves of tested specimens, is studied. It was found that the European and Japanese codes significantly underestimated the stud shear capacity, whereas the Canadian code provides a more accurate estimation.

Interlaminar toughening and self-healing mechanism for hard-and-soft layered composite laminates

This paper finds a simple and cost-effective design to create high interlaminar toughness and self-healing Euplectella Aspergillum based bio-inspired composite laminates with thermoplastic polymer poly(ethylene-co-methacrylic acid) (EMAA). Three different configuration strategies containing hard/soft structures are proposed and mode I interlaminar toughness is determined to investigate the toughening effect and self-healing behavior. The results show that configuration and fiber types have great influence on toughening and self-healing efficiency. The novel configuration can achieve an improvement of over 600% in toughness for carbon fiber reinforced plastic (CFRP) and close to 100% for healing efficiency in the case of glass fiber reinforced plastic (GFRP) laminates. All the proposed configurations eliminate unstable delamination crack propagation process observed in CFRP woven laminates. In addition, repeated self-healing behavior is studied and self-healing efficiency remains stable after three damage-healing cycles. This study reveals toughening and self-healing behaviors of different configurations and provides novel strategies for laminate design.

Flexural behaviors of GFRP-wood sandwich beams with recycled wood formwork cores

The escalating consumption of wood products has inevitably led to a rapid accumulation of waste wood, of which a large amount has been landfilled. An innovative concept has been therefore proposed to repurposes waste wood formwork as the core material of Glass Fiber Reinforced Polymer (GFRP)-wood sandwich beams. A series of four-point bending tests were conducted on these sandwich beams, with the thicknesses and orientations of strengthening GFRP layers as the main test parameters examined. The test findings indicated that the GFRP-waste wood sandwich beams failed in either buckling of compression zone or rupture of GFRP covering. In addition, the increase in the number of GFRP layer resulted in a significant increase in the both bending stiffness and flexural strength, and the beams strengthened with three-layer GFRP sheets exhibited the bending stiffness and flexural strength up to respectively 4.7 and 6.5 times greater than those without such GFRP strengthening. The analytical and numerical predictions of flexural properties of sandwich beams are in a good agreement with the test results, thereby validating the accuracy of the models employed in the present study.

Experimental investigation on in-plane shear behavior of E-glass fiber/epoxy laminated composites under different strain rates

Glass fiber reinforced polymer (GFRP) has been widely applied in buildings and bridges owing to its excellent material properties. The GFRP as a bearing load component in structures may be damaged, with an increasing threat from accidental impact. To understand the dynamic in-plane shear properties of GFRP is essential, which is a basis to design and evaluate structures. In this study, the ±45° specimens of GFRP laminated were tested to investigate the in-plane shear properties with the strain rate from quasi-static to 106 s−1. The dynamic test was conducted by INSSTRON VHS and the stretch process was record by high-speed camera. The Digital Image Correlation (DIC) method was used to obtain strains of the specimens. And the field-emission scanning electron microscopy (SEM) technique was used to observe the fracture surface of the specimen. The results indicated that the failure mode, shear strength, failure strain, failure strain, absorbed energy and shear modules possessed strain rate effects. Furthermore, the empirical equations were proposed, which can be used to predict the dynamic increase factor at different loading rate.

Axially loaded rectangular FRP-concrete-steel hybrid multi-tube concrete stub columns: Performance, confinement mechanism, and design-oriented model

This paper presents an experimental investigation of rectangular glass fiber-reinforced polymer (FRP)-concrete-steel hybrid multi-tube concrete columns (MTCCs) subjected to monotonic axial compression to explore their mechanical behavior and confinement mechanism. Sixteen rectangular MTCCs and eight concrete-filled FRP tube columns (CFFTs) were tested. Four experimental variables, namely aspect ratio, FRP thickness, steel volume ratio, and steel tube configuration, were taken into consideration. The experimental results demonstrated that rectangular MTCCs’ load-bearing capacity and deformability diminished with increasing aspect ratio, as it reduced the effective confinement area of FRP tube to concrete. Additionally, the confined concrete’s compressive strength and axial deformability of rectangular MTCC (with a 6.4% steel volume ratio) enhanced by 21.5% and 32.9%, respectively, compared to the corresponding CFFT. This demonstrated the effectiveness of additional steel confinement. Furthermore, the confinement mechanism of rectangular MTCCs was clarified based on the full-range compressive behavior and dilation property of confined concrete. It included unconfined stage, transition stage, and hardening stage. Finally, a stiffness-based design-oriented model for rectangular MTCCs was established with favorable accuracy.

Predicting long-term tensile degradation of GFRP rebars embedded in concrete with a reconsidered environmental reduction factor [formula omitted]

Glass fiber reinforced polymer (GFRP) has been considered as an advanced material to replace conventional steel reinforcements in concrete structures to address the corrosion issue. The degradation of GFRP rebars, which may threaten both the durability and safety of infrastructures, is a major concern. To predict the 100-year strength retention of GFRP under various temperature and relative humidity conditions, the environmental reduction factor (CE) is applied in engineering. The conventional CE based on the assumption of logarithmic degradation model is commonly utilized during the degradation phase spanning from a few years to decades; however, it is not applicable to the initial and perpetual degradation phases. To address this issue, a novel environmental reduction factor (CE′) based on the exponential degradation model considering temperature and relative humidity is proposed in this study. Both CE and CE′ are mathematically deduced from empirical degradation data and then evaluated in a case study involving GFRP-concrete samples soaked in water at 23, 40 or 60 °C for up to 12 months within the authors’ dataset. Experimental results show that the GFRP tensile strength degradation is closer to the exponential model, reaching a plateau (47.4%) after 12-month exposure to 60 °C water. Moreover, the tensile strength retention of GFRP rebars in Vancouver (10 °C), Shanghai (16 °C) and Houston (22 °C) is predicted considering various scenarios of relative humidities (0–90%). Further research indicates that CE′ (0.65–0.78) exhibits a smaller value compared to CE (0.81) at a temperature of 22 °C and a relative humidity of 90% following a 100-year exposure period, thereby providing engineers with a more conservative design approach for GFRP in real-world scenarios. Nevertheless, this exponential degradation model requires a thorough consideration of severe degradation state during the extended aging period, which may not be applicable to GFRP structures exhibiting exceptional durability.

Experimental Study on Axial Compression Behavior of Molybdenum Tailings Concrete Column Confined by GFRP

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%.