Polyethylene Terephthalate Fiber-reinforced Polymer Research Articles

Experimental study on shear performance of PET FRP-strengthened RC beams without stirrups

The shear behavior of simply supported RC beams strengthened with polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) was studied in this paper. The test variables include strengthening schemes (i.e., U-wrapping and full-wrapping) and FRP reinforcement ratios. A comprehensive and meticulous investigation was conducted on the failure mode of RC beams, shear force-deflection curves, the development process of shear cracks, the evolution of FRP strain, and the interaction between FRP and concrete. The shear capacity and deformation were increased by 42.5% to 123.2% and -16.34% to 96.89% using the fully wrapped scheme, respectively. The improvement in shear capacity was 42.5% to 72.55% when the U-wrapped scheme was adopted. The PET FRP fully wrapped beams exhibited a type of ductile shear failure. The strain of PET FRP in the fully wrapped specimen exceeded 4% without fracture, ensuring the deformation capacity after the peak load. The shear deformation caused the increase in post-peak mid-span deflection. The U-wrapped specimens showed debonding failure, with the debonding strain of PET FRP being more than that of conventional FRP. Finally, six design guidelines for PET FRP shear contribution were evaluated for both U-wrapped and fully wrapped schemes.

Axial compressive behavior and design-oriented model for large-rupture-strain (LRS) FRP-confined concrete in rectangular columns

Polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) composites, which is a kind of low-carbon production and have a large rupture strain, may have prosperous application outcomes. PET FRP wrap has been explored as confining reinforcement for concrete, and the majority of investigations are limited to PET FRP-confined concrete in circular and square columns, whereas PET FRP-confined rectangular columns have barely been touched. To fill this research gap and gain a fundamental understanding of the confinement mechanism, comprehensive compressive tests on 36 columns were conducted in this study, in which the confinement thickness, cross-section aspect ratio, and specimen size were the focal points. All specimens exhibited a three-segment behavior (i.e., strain hardening-softening-hardening response). In addition, it is demonstrated that specimen size had an insignificant effect on the axial stress-strain response of small and medium columns with a height less than 400 mm, provided that their confinement levels were the same (or similar). Furthermore, the minimum effective confinement stiffness for PET FRP-confined rectangular columns to achieve sufficient confinement was 0.004, which was extracted from all available test results. A design-oriented model with improved performance was proposed and the simulated full axial stress-strain showed close agreements with the test results.

Effects of material non-linearity on the structural performance of sandwich beams made of recycled PET foam core and PET fiber composite facings: Experimental and analytical studies

This paper presents the results of experimental and analytical studies on sandwich beams subjected to three-point bending beyond their limit of proportionality. The sandwich beams were composed of polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) composite facings and recycled PET (R-PET) foam core made from post-consumer plastic bottles. The study tested three R-PET core densities (70, 80, and 100 kg/m3) and compared the results to a control group with 100 kg/m3 core density and glass FRP facings. The beam geometry and testing set-up were consistent throughout the study, with 12 beams tested in total. The results showed that all specimens exhibited non-linear load–deflection behavior, resulting in developing a non-linear analytical model using decreasing secant elastic and shear moduli under increasing loads. The proposed model was validated, and a parametric analysis was performed to evaluate its mechanical performance under different conditions, including variations in span length and the thickness of the core and facing components. Additionally, the study created a novel failure mode map to predict the failure mechanism of the sandwich panels based on core density and the PET FRP facing thickness to span length ratio, considering the non-linear behavior of both components. As a result, this study provides valuable insights into using recycled materials in construction, contributing to reducing plastic waste and mitigating environmental impact.

Compressive behavior of PET FRP-confined concrete encased CFST columns

Environmental friendly construction materials such as polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) and high-strength materials such as high-strength steel (HSS) are attracting wide attentions. In this study, a total of ten novel circular PET FRP-confined Concrete Encased Concrete-filled steel tube columns (PFCECs) with a Q690 steel tube and a PET FRP tube are tested to understand their axial compressive behavior, with the investigated variables covering the thickness of the outer PET FRP tube and the diameter ratio. The experimental results demonstrate that the load-carrying capacity of PFCECs with a given inner steel tube increase with an increase in the diameter ratio, but the ultimate axial strains and the residual axial loads do not necessarily increase with the increase of the diameter ratio. In the end, this paper compares the test results against the predictions from two existing models, and the comparisons show that the models give comparatively accurate predictions on the ultimate axial stresses/strains of the core concrete in PFCECs, but they are unable to capture complete axial stress-axial strain responses of the core concrete in PFCECs accurately.

Experimental study on the seismic behavior of RC columns with high axial compression ratios retrofitted by large rupture strain fiber-reinforced polymer

Fiber-reinforced polymer (FRP) composites being utilized to retrofit reinforced concrete (RC) columns has been well documented. However, the axial compression load of the FRP retrofitting RC columns was relatively limited. Aiming to analyze the applicability of FRP retrofitting RC columns with higher axial compression loads, this paper presents an experimental study on the seismic performance of RC columns retrofitted by the Polyethylene Terephthalate (PET) FRP composites. A total of twelve 1/3 scale RC columns were fabricated, including four control specimens and eight PET FRP retrofitting columns with two retrofit schemes. All the columns were tested under combined high axial compression load and cyclic lateral displacement excursions, and the maximum axial compression ratio reaches 1.1. The seismic performance of RC columns retrofitted by PET FRP was analyzed detailedly from the failure mode, shear force and deformation capacity, energy dissipation and ductility. The test results showed that PET FRP retrofitting changed the failure mode of RC columns from brittle to more ductile. The post-peak strength degradation of the columns was more rapid with the increase of axial compression ratio, but the strength degradation of the PET FRP retrofitting columns was more gradual. PET FRP retrofitting significantly improved the ductility and lateral deformation capacity of the columns even under the high axial compression ratio. PET FRP retrofitting can be applied for the RC columns with serous demand of deformation capacity due to the lighter change of shear-loading capacity and stiffness. Contrastively, the improvement of the seismic capacity of the RC columns retrofitted by the laterally wrapped scheme is higher than that of the striped wrapped scheme. Conclusions from this study provide useful references for the seismic retrofitting of RC structures.

Experimental investigation on the dynamic mechanical response of polyethylene terephthalate fiber-reinforced polymer confined pre-flawed concrete under impact loading

Polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) is expected to remarkably improve the impact resistance and bearing capacity of reinforced concrete due to its excellent mechanical characteristics of large rupture strain. The dynamic mechanical properties and damage evolution characteristics of internal pre-flawed concrete confined with the different layers of PET FRP are studied by adopting a split Hopkinson pressure bar (SHPB) apparatus at a large strain rate range of 83 s−1 to 503 s−1. It was found that damage to the specimens was strictly restricted by the PET FRP jacket, while the corresponding responses of the unconfined specimens were closely related to the strain rate. Some linear correlations can also be outlined between dynamic mechanical properties (e.g., dynamic compressive strength, toughness, and ultimate compressive strain) and strain rate, as well as the layers of PET FRP. To investigate the damage evolution characteristics further, the specimens confined with PET FRP were subjected to SHPB multiple impacts under the same launch energy level. In addition, the impact times of SHPB do affect the dynamic properties of the PET FRP-confined specimens. A linear relation holds for the ultimate compressive strain, while the effect of impact times on the strength decaying factor tends to increase and decrease at relatively low impact energies.

Behavior of unconfined and polyethylene terephthalate (PET) FRP-confined coal reject concrete under compression

Fiber-reinforced polymer (FRP) confinement has been proposed to mitigate the detrimental effects of coal rejects concrete (CRC) in the present study. Polyethylene terephthalate (PET) FRP jacket was adopted to confine CRC as a new type of novel column members, which are referred to as PET FRP-confined coal reject columns (PFCCRs). PFCCRs are often sustainable and cost-effective structural columns as the PET FRP composites are generally made from recyclable PET waste and coal rejects are industry by-products. A total of 49 columnar specimens, consisting of 21 CRC specimens and 28 PFCCR specimens were tested under uni-axial compression to understand the mechanical behavior of unconfined and PET FRP-confined CRC. The main parameters evaluated in this study were the volume replacement ratio of coal rejects and the FRP thickness. The test results indicated that the unconfined CRC specimens exhibited a significant reduction in compressive strength with the increase in replacement ratio, whereas the ultimate axial strain was enhanced. Compared with plain CRC specimens, PFCCRs had excellent deformation capacity and compressive strength with a strain hardening stress-strain response. The maximum normalized ultimate axial strain and axial stress of most of the PFCCR specimens are over 30 and 7, respectively. The stress reduction segment will occur only when the FRP confinement is insufficient. Furthermore, the test results were compared with the predictions by using existing analysis-oriented and design-oriented models for LRS FRP-confined concrete to verify their accuracy.

Compressive behavior of double-skin tubular stub columns with recycled aggregate concrete and a PET FRP jacket

This paper presents an experimental study on the compressive behavior of hybrid fiber reinforced polymer (FRP)-concrete-steel double-skin tubular stub columns (DSTSCs) with recycled aggregate concrete (RAC) and a polyethylene terephthalate (PET) FRP jacket. RAC is a green, sustainable alternative to natural aggregate concrete (NAC), while its mechanical properties are generally inferior to NAC. Polyethylene terephthalate (PET) FRP is manufactured from recycled plastics and has a large rupture strain (LRS) value of more than 7% compared to pure polyethylene FRP. In this study, a total of 20 DSTSC specimens were tested under axial compression. The main parameters studied were the RAC replacement percent (0, 50 and 100%), the FRP jacket thickness, and steel tube thicknesses (3 and 5 mm). Test results indicated that the compressive behavior of DSTSC specimens with RAC and PET FRP is similar to that of specimens with NAC and PET FRP, and both types of columns exhibit highly ductile compressive behavior. It is also observed that the compressive behavior of DSTSCs is primarily influenced by the confinement stiffness of the FRP jacket and the steel tube, and the replacement percent of RAC has marginal effect. The increase of the FRP jacket or steel tube stiffness can counterbalance the replacement percent effect of RAC on the axial compressive behavior of DSTSCs. Finally, the suitability of the existing ultimate condition models of different types of DSTSCs was investigated based on the experimental results of this study.

Durability assessment of PEN/PET FRP composites based on accelerated aging in alkaline solution/seawater with different temperatures

Large rupture strain (LRS) fiber-reinforced polymer (FRP) composites, including polyethylene naphthalate (PEN) FRP and polyethylene terephthalate (PET) FRP composites, have become increasing popular in civil construction. PET FRP and PEN FRP can be recyclable and thus they are environmentally friendly. However, the durability of LRS FRP composites under extreme environmental conditions (e.g., marine environment and high temperature) has not been understood. To this end, durability tests on 282 LRS FRP sheets after aging in alkaline/seawater solution with different temperatures (25℃, 40℃, 60℃) were conducted in this study. The microstructure of PEN FRP sheets was also analyzed using scanning electron microscope (SEM). The results show that the changes of the elastic modulus of the first linear portion and the elastic modulus of the second linear portion of PEN FRP sheets after aging in different aging temperatures are slight. For PEN FRP sheets with an aging period of 365 days in 60 °C solutions, the degradation rate of the tensile strength is around 10% for both alkaline (pH = 13.2) and seawater solutions, and the degradation rate of the tensile rupture strain is around 12.5%. Additionally, under a higher exposure temperature, there is a significant decrease in the tensile strength of LRS FRP composites. Furthermore, it shows that the durability of PEN FRP sheets was significantly affected in the alkaline environment compared to that in the seawater environment, and the alkaline resistance of PEN FRP composites is better than that of PET FRP composites.

Behavior of hybrid PET FRP confined concrete-filled high-strength steel tube columns under eccentric compression

Fiber-reinforced polymer (FRP) wraps as external confining device have been employed to enhance the performance of concrete-filled steel tube (CFST) columns, and the axial compressive behavior of FRP-confined CFST columns have been intensively investigated. Although FRP confinement could enhance the mechanical performance of CFST columns with a high-strength steel (HSS) tube, they are prone to buckling failure, especially under eccentric compression. The purpose of this study is to experimentally investigate the mechanical performance of polyethylene terephthalate (PET) FRP-confined CFST columns (PFCCFSTs) under eccentric compression. A total of eight circular PFCCFSTs were tested for investigating the effects of a range critical parameters (i.e., column slenderness ratio, eccentricity-to-diameter ratio, and thickness of the PET FRP jacket) on the eccentric compressive behavior of PFCCFSTs. The test results show that the typical load-strain curve of PFCCFSTs generally consists of an initial linear ascending segment, followed by a transition segment and a descending segment. It is demonstrated that the load deterioration of PFCCFSTs is more sensitive to the increase of eccentricity-to-diameter ratio than the slenderness ratio, while the PET FRP thickness has little influence on the load bearing capacity of PFCCFSTs. The predictions from a theoretical model are compared with experimental results, and demonstrate that the model underestimates the ultimate lateral deflections due to the ignorance of the strain gradient effect in eccentrically loaded columns.

Behavior of FRP-confined FRP spiral reinforced concrete square columns (FCFRCs) under axial compression

Fiber-reinforced polymer (FRP) confinement has been demonstrated to be efficient in enhancing the deformation and strength capacities of concrete, while Polyethylene terephthalate (PET) FRP-confined concrete easily exhibits a strain-softening stress-strain behavior, especially for PET FRP-confined concrete in square columns. In this study, novel PET FRP-confined FRP spiral reinforced concrete square columns (FCFRSCs) are proposed. Capitalizing the benefits of internal FRP spiral reinforcement, the strain-softening behavior of PET FRP-confined concrete is expected to be alleviated, leading to excellent mechanical performance of the proposed square columns. The axial compressive behavior of FCFRSCs, as well as square concrete-filled PET FRP tube columns (CFFTs) and FRP reinforced concrete columns (FRCs) as reference columns, were investigated via experimentation. The experimental results show that the strain softening behavior of confined concrete in FCFRSCs has been substantially enhanced with the internal FRP reinforcement, confirming the viability of the system. The strain softening behavior of FRP-confined concrete after the first peak is prevented and a hardening behavior is achieved for concrete in FCFRSCs, especially when the GFRP spiral pitch is 30 mm.

Behavior of FRP Ring-Confined CFST columns under axial compression

Although concrete-filled steel tube (CFST) columns have been widely accepted in applications, they suffer deterioration due to various reasons. On the other hand, the concrete and the steel in CFST columns subjected to compression are not perfectly bonded at the initial loading stage. To this end, fiber-reinforced polymer (FRP) rings are proposed to strengthen the CFST columns in the present study. By strengthening CFST columns with FRP rings, it is expected that their nominal yield strength is increased and the strengthened CFSTs exhibit a monotonic ascending load–strain behavior under compression. An experimental study on axial compressive behavior of FRP ring-confined CFST (FRCCFST) columns is carried out and the effects of the FRP type, the FRP ring thickness (0, 2, 3, 4 layers) and the FRP ring clear spacing (40, 80, 120 mm) on the axial compressive behavior of FRCCFST columns are investigated in this study. The experimental results show that FRP rings substantially enhance the ultimate load capacity and slightly enhance the yield strength of CFST columns. The ultimate axial strain of polyethylene terephthalate (PET) FRP ring-confined specimens is much better than that of CFRP ring-confined specimens due to the large ultimate tensile strain of PET FRP. The ultimate stress and strain of concrete in CFST specimens are obtained and compared with those provided by existing stress–strain models to examine their accuracy and capability.

PET FRP-concrete-high strength steel hybrid solid columns with strain-hardening and ductile performance: Cyclic axial compressive behavior

This paper presents the results of an experimental program on the behavior of fiber-reinforced polymer (FRP)-concrete-high strength steel solid columns (FCSSCs), with an outer polyethylene terephthalate (PET) FRP tube and an inner circular high-strength steel (HSS) tube, under cyclic axial compression. A PET FRP tube has a much larger rupture strain and a larger FRP hoop strain efficiency, leading to an excellent ductility of PET FRP-confined concrete. The HSS tube, which has a good deformation compatibility with the PET FRP-confined concrete in FCSSCs, provides a much larger longitudinal load carrying capacity and a larger confinement to the core concrete compared with a normal strength steel tube. The experimental results demonstrated that the axial load carrying capacity of an FCSSC is much larger than the summation of the axial load resistance of the hollow steel tube and that of the concrete-filled FRP tube; the buckling of the HSS tube is also prevented so that its post-yield material strength is effectively utilized. It is found that cyclic load-strain envelope curves lie closely to the corresponding monotonic load-strain curves, and repeated loading cycles increase the plastic strain while decrease the reloading new stress. The existing stress-strain model fails to provide an accurate prediction on the cyclic axial behavior of concrete under combined PET FRP-steel confinement.

Dynamic Behavior of PET FRP and Its Preliminary Application in Impact Strengthening of Concrete Columns

Polyethylene terephthalate (PET) fiber has attracted significant attention for reinforced concrete (RC) structure rehabilitation due to its large rupture strain (LRS; more than 7%) characteristic and recyclability from waste plastic bottles. This study presents a dynamic tensile test of PET fiber bundles performed using a drop-weight impact system. Results showed that the tensile strength and the elastic modulus of the PET fiber bundles increased, whereas the failure strain and the toughness decreased with the increasing strain rate from 1/600 to 160 s−1. In addition, the performance of concrete confined with the PET fiber-reinforced polymer (FRP) under impact loading was investigated based on a 75 mm-diameter split Hopkinson pressure bar (SHPB) device and a drop-weight apparatus. For the SHPB test, owing to the large rupture strain property of PET FRP, the PET FRP-confined concrete exhibited significantly better performance under impact loading compared to its counterpart confined with carbon FRPs (CFRPs). During the drop-weight test, the confinement of the PET FRP composites to the concrete columns as external jackets not only improved the peak impact force, but also prolonged the impact process.

Shear strengthening of corroded reinforced concrete columns using pet fiber based composties

Polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) composites are characterized by a large rupture strain (LRS) (usually larger than 5%) but a low elastic modulus compared to conventional FRP materials made of carbon, glass, and aramid fibers. Previous studies have proved that the use of PET FRP sheets as jacketing materials for plain concrete or reinforced concrete (RC) columns could efficiently enhance their ductility. This paper presents a combined experimental and analytical study on the shear strengthening of corroded RC columns with stirrups having different levels of corrosion before strengthening. The shear resistance contributions from the substrate column and PET FRP sheets at various volume ratios were carefully examined and their interaction mechanisms were discussed. Design equations following a conventional truss analogy were then proposed to predict the shear strength of PET FRP-wrapped columns considering the effect of stirrup corrosion, and the predictions were verified against the test results.

Compressive Behavior of PET FRP–Confined Circular, Square, and Rectangular Concrete Columns

AbstractThis paper presents the results of an experimental study on the compressive behavior of circular and noncircular concrete columns confined by polyethylene terephthalate (PET) fiber-reinforced polymer (FRP). The main objective of this study is to observe the compressive behavior of PET FRP–confined noncircular concrete columns, in which the cross-sectional geometry significantly influences the effectiveness of FRP confinement. For this purpose, 54 specimens were tested under monotonic axial compression. The parameters considered were the cross-sectional shape (i.e., circular, square, and rectangular), the corner radius in case of square and rectangular specimens, and the number of FRP layers. The results of this study showed that, unlike the bilinear stress-strain response of square and rectangular concrete columns confined by other FRP materials, PET FRP–confined square and rectangular concrete columns exhibit a distinct trilinear relationship. Owing to the large rupture strain (LRS) characteristi...

Experimental Study on Shear Behavior of Reinforced-Concrete Members Fully Wrapped with Large Rupture-Strain FRP Composites

AbstractThis paper presents an experimental study on the shear behavior of RC members fully wrapped with polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) composites, which are a new type of FRP material characterized by a much larger rupture strain (LRS) compared with conventional FRPs (i.e., made of carbon, glass, and aramid fibers). A total of 10 PET fully-wrapped RC beams, which were designed to fail in shear and with different shear-span to effective-depth ratios, transverse reinforcement ratios and shear strengthening ratios, were tested under 4-point bending loads. The overall load-deflection responses and the shear deformation of the beams as well as the strain development of the transverse steel reinforcement and the FRP jackets were carefully observed. Based upon the extensive strain measurements, the shear contributions by concrete, FRPs, and transverse reinforcement are differentiated. It was found that the use of PET FRP composites as the jacket material of RC members could shif...