Glass Fiber Reinforced Polymer Research Articles

Behavior of GFRP reinforced concrete columns confined with inner steel spirals

AbstractThe paper investigates the behavior of glass‐fiber reinforced polymer (GFRP) reinforced concrete columns with integrated steel spirals (hybrid reinforcement). Six concrete columns were tested under eccentric axial loading, resulting in failure due to bending. Columns with outer steel longitudinal bars experienced steel yielding at peak loads, while those with GFRP outer rebars failed due to concrete crushing. The results revealed that using GFRP as outer longitudinal bars led to peak loads 3–10% lower compared to columns with steel rebars. Inner confinement by steel spirals increased the load‐carrying capacity. Additionally, columns with inner tubular steel exhibited greater strength than those with steel spirals, indicating a slightly enhanced confinement effect. A finite element model was developed to analyze structural behavior, considering both material and geometric nonlinearity. The model's accuracy was validated by comparing predictions with test results. Parametric analysis from the nonlinear FE model showed that eccentricity significantly impacted column load‐carrying capacity. Increasing inner confinement area and the number of inner longitudinal bars improved structural stiffness and load‐carrying capacity. Furthermore, a simplified theoretical method was proposed. Comparison between experimental failure loads and theoretical predictions revealed differences within 20%, indicating satisfactory reliability of the proposed method.

Experimental Investigation of High-performance Fiber-reinforced Cementitious Composite and its Effect on RC Beams by Numerical Method

In the present study, experimental investigations were initially conducted on high-performance fiber-reinforced cementitious composite (HPFRCC). A total of 9 samples were examined and subjected to a 4-point bending test. The sample lengths were standardized at 500 and 1700 mm. The variables under scrutiny included the impact of Micro Steel, Macro Steel, and polyvinyl alcohol fibers. Furthermore, the models were scrutinized under two conditions: with and without glass fiber reinforced polymer (GFRP) bars. The number of samples was 9. In the second part of the article, subsequent to verifying the experimental samples from the current study alongside a concrete beam, numerical analyses were carried out to assess the influence of HPFRCC on the behavior of RC beams. Similarly, the impact of GFRP diameter, as well as the height of HPFRCCs, on the seismic performance of RC beams, was investigated by conducting 36 numerical analyses. The analyses were carried out using nonlinear static methods, with monotonic loading. The model outputs encompass elastic stiffness, ultimate strength, relative stiffness, and energy dissipation. The experimental results showed that the use of macro steel fibers in models without GFRP rebars has better results on the flexural behavior of HPFRCC. Moreover, by reinforcing RC beams with HPFRCC, a 70% increase in energy dissipation was observed. The elastic stiffness and ultimate strength of the strengthened beam are directly proportional to the ratio of the HPFRCC's elastic flexural stiffness to that of the original beam. These results increase proportionally as this ratio rises.

Structural performance of precast concrete sandwich panels with bolt-steel plate connection subjected to axial loading

A new precast concrete sandwich panel with glass fiber-reinforced polymer connectors was proposed, utilizing bolt-steel plate connections. A compressive experiment was carried out to investigate the performance. The main damage was concrete crushing in the bolt connection region, at the panel bottom, and above the joint. The connector type, solid concrete rib, slenderness ratio, and thickness affected the failure mode and bearing capacity. The use of GFRP connectors and solid concrete ribs enhanced the ultimate bearing capacity and stiffness of the panels while reducing the lateral deflection. Higher slenderness ratios leading to reduced axial bearing capacity and increased lateral deflection. Finally, the results of the existing empirical calculation formulae were compared with experimental ones, and they were overly conservative. A new formula for predicting the bearing capacity was proposed, and the difference percentages between the proposed formula and experimental results were −0.4 %–2.8 %, which was the most accurate prediction formula.

Experimental Investigation on Pure Torsion Behavior of Concrete Beams Reinforced with Glass Fiber-Reinforced Polymer Bars

The failure mechanism of torsional concrete beams with fiber-reinforced polymer (FRP) bars is essential for developing the design method. However, limited experimental research has been conducted on the torsion behavior of concrete beams with FRP bars. Therefore, the pure torsion test of four large-scale FRP-RC beams (2800 mm × 400 mm × 200 mm) was conducted to investigate the influence of the stirrup ratio (0, 0.49%, and 0.98%) and longitudinal reinforcement ratio (3.01%, 4.25%) on torsion behavior. The test results indicated that three typical failure patterns, including concrete cracking failure, stirrup rupturing failure, and concrete crushing failure, were observed in specimens without stirrups (stirrup ratio 0), partially over-reinforced specimens (stirrup ratio 0.49%), and over-reinforced specimens (stirrup ratio 0.98%), respectively. The tangent angle of spiral cracks at the midpoint of the long side of the cross-section was approximately 45° initially for all specimens. The torque–twist angle curves exhibited a linear and bilinear behavior for specimens without stirrups and specimens with stirrups, respectively. As the stirrup ratio increased from 0 to 0.98%, torsion capacity increased from 24.9 kN∙m to 27.8 kN∙m, increased by 12%, ultimate twist angle increased from 0.0018 rad/m to 0.0403 rad/m. As the longitudinal reinforcement ratio increased from 3.01% to 4.25%, the torsion capacity increased from 27.8 kN∙m to 28.3 kN∙m, and the ultimate twist angle decreased from 0.0403 rad/m to 0.0244 rad/m. Based on test results, the stirrup strain limit of 5200 με and spiral crack angle of 45° was suggested for torsion capacity calculation. In addition, based on the database of torsion tests, the performance of torsion capacity provisions was assessed.

Impact characteristics of S2-glass fibre/FM94-epoxy composites under high and cryogenic temperatures: Experimental and numerical investigation

The aerospace industry uses glass fibre reinforced polymer (GFRP) composites to manufacture structural and non-structural parts of an aircraft as they possess superior strength to weight ratio and exceptional corrosion resistance. Commercial aircraft operate in a very wide temperature ranges from −54 to 55 °C. Potential GFRP laminates are susceptible to impact during aircraft operation, and the temperature at impact governs the nature of damage and failure mechanisms. As a result, the current study focuses on examining how aeronautical GFRP composites behave in various temperature environments that are encountered during high- and low-altitude operations. Using S2-glass fibre/FM94-epoxy unidirectional prepreg, GFRP plates were created. Drop weight impact tests were conducted at ambient (25 °C), high (50, 75, 100 °C), and low (−25, −55 °C) temperatures, as well as at various impact energies (75, 150, 225 J). The damages were assessed visually, along with their sizes. Each testing scenario's impact parameters, including the impact load, deflection, and energy absorption, were also examined. In Abaqus/Explicit, a coupled temperature-displacement numerical model was created to predict the onset of stress and damage. According to experimental findings, GFRP plates are stiffer and show less apparent damage at cryogenic temperatures (∼15−34 % lower displacement) than they do at other temperatures. Furthermore, it was observed that the matrix softens at high temperatures, showing larger damaged area at entry but with less obvious damage and increasing energy absorption, while semi-perforation occurred under cryogenic temperatures at entry with smaller damaged area. A strong correlation is shown between the experimental and FE data, confirming the capability of FE models to predict impact damage and deflections at different temperatures in the future.

Identification of mode I fracture toughness in GFRP/Al and GFRP/Cu joints for structural batteries

Fiber metal laminates (FMLs) have been proposed as components of structural batteries, yet their elastic mismatch can lead to interface cracks, compromising structural integrity and both mechanical and electrochemical efficiency. To this end, the bonding between the metal and the composite layer is of utmost importance. In this study, the effect of various metal surface treatments on the mode I interlaminar fracture toughness of two FML configurations suitable for structural batteries — Glass Fiber Reinforced Polymer (GFRP)/aluminum laminate and GFRP/copper laminate — was examined. The surface treatments included sulfo-ferric etching, NaOH/HNO3 etching, and Sol–Gel anodizing for aluminum 2024-T3, as well as FeCl3/HCl/Glycerol treatment and Sol–Gel anodizing for copper alloy. The results were compared with untreated conditions and with the baseline GFRP/GFRP configuration. GFRP/metal coupons were designed to achieve pure mode I interlaminar fracture toughness in double cantilever beam (DCB) tests, and the designs were verified using the Virtual Crack Closure Technique (VCCT). The surface characterization of the metals was performed using contact angle tests to estimate the surface free energy, while Coherence Scanning Interferometry (CSI) was used to measure the surface roughness and topography.

Experimental assessment of FRP repairing in concrete cylinders exposed high temperatures

This study presents an experimental evaluation of fiber-reinforced polymer (FRP) strengthening in concrete specimens damaged by exposure to high temperatures. For this purpose, sixty cylindrical concrete specimens were produced. Specimens exposed to temperatures of 200 °C, 400 °C, and 600 °C were strengthened using carbon and glass FRP fabrics in two or three layers. Compression tests were conducted to assess the strength of the specimens. The impact of temperature, fabric type, and the number of fabric layers on the concrete's strength was thoroughly investigated. Digital microscopy was employed to explore the formation of cracks due to temperature changes, followed by Scanning Electron Microscopy (SEM) analyses to examine the microscopic structural changes in the concrete samples. The study highlights the importance of considering changes in both strength and behavior models together when evaluating the strengthening contributions provided by FRP. The results indicate that FRP applications on fire-damaged concrete structures can provide effective strengthening up to 400 °C but may be insufficient at temperatures of 600 °C and above. Although an effective increase in strength was achieved at 600 °C, low levels of ductility were observed, which is undesirable for an engineering structure. Therefore, it has been determined that FRP-strengthening applications may not be effective in reinforced concrete (RC) structural elements exposed to temperatures of 600°C and higher.

Understanding the Effect of Drilling Parameters on Hole Quality of Fiber-Reinforced Polymer Structures.

Hole quality in composite materials is gaining interest in aerospace, automotive, and marine industries, especially for structural applications. This paper aims to investigate the quality of holes performed without a backup plate, in thin plates of glass fiber-reinforced polymer (GFRP). The samples were manufactured by two different technologies: vacuum bagging and an innovative method named vacuum mold pressing. Three experiments were designed choosing the control factors that affect the maximum cutting force, delamination factor, and surface roughness of drilled holes in composite materials based on twill fabric layers. Quality analysis of the hole features was performed by microscopy investigations. The effects of the main factors on the targets are investigated using the statistical design of experiments, considering control factors, such as support opening width, weight fraction (wf), feed per tooth, and hole area. The results showed that the feed per tooth and hole area had a more significant influence on the delamination factors and surface roughness (Sa). The best quality of the holes drilled in twill-based GFRP was achieved for a lower feed rate of 0.04 mm/tooth and used a support opening width of 55 mm.

Capacity reinstatement of reinforced concrete one-way ribbed slabs with rib-cutting shear zone openings: Hybrid fiber reinforced polymer/steel technique

This study examined the use of two configurations for capacity restoration of reinforced concrete (RC) one-way ribbed slabs containing openings in shear zones. Four specimens of half-scale comprised three ribs in addition to a top RC slab. The test plan included a control specimen without openings, one with two rib-cutting shear openings, one strengthened using a blend of carbon FRP (CFRP) composites and steel plates, and another retrofitted with a combination of glass FRP (GFRP) composites and steel plates. The two strengthening schemes were found successful at fully restoring the ultimate load of the specimens. The ultimate load of specimen strengthened using the hybrid CFRP/steel system exceeded the control slab without openings by 52%. However, in the other specimen where a mix of steel plates and GFRP sheets was used, the load capacity was only 5% less than the control specimen without openings. While the dissipated energy and stiffness were reinstated and improved for the hybrid CFRP/steel system, they were partially restored for the GFRP/steel system. Additionally, a prediction approach was developed to estimate the maximum load of the slabs. The developed approach considered potential shear and flexural modes of failure, providing close predictions of the ultimate load.

Study on the effect of multi-factor compound action on long-term tensile performance of GFRP composite pipe and life prediction analysis

In this work, the glass fiber reinforced plastic (GFRP) composite pipes used as sewerage pipes in oil and gas field environments were studied. The accelerated aging experiments were carried out under the simulated environments of three typical oil field media which including circulating air, simulated produced water and standard simulated oil. Scanning electron microscopy (SEM) was adopted to observe the microscopic morphology of the aged GFRP tubes under the three conditions. The microstructural characteristics of the aged tubes and the evolution process of internal defects were also analyzed and evaluated in combination with micro-CT technology. The attenuation pattern of the hoop tensile strength of the aged pipes was measured via the separation disk method, and the service life prediction was carried out based on the Arrhenius theory with the hoop strength as the life index. The results show that the accumulation of aging time and continuous heat input will aggravate the expansion of internal pores and cause the aggregation of small-volume defects into large-volume defects. Especially in the simulated oil environment, which has the highest sensitivity to defects. The maximum porosity reaching 1.5 % and the maximum volume of individual defects exceeding 106 μm3 after aging for 4000 h at 95 °C. The thermal aging process under the three environmental conditions had similar aging characteristics, and interfacial damage of the glass fibers was observed in all of them. The variability of hydrothermal aging is related to the hydrolytic behavior of the glass fibers, which is associated with the progressive dissolution damage of the SiO2 network in the glass fibers, as well as the breaking of silane bonds. Thus, the hydrothermal environment had the most significant effect on the hoop tensile strength decay. Ultimately, 75 % strength retention was taken as the end-of-life indicator. The predicted service life based on the Arrhenius model for the three environments of thermo-oxygen, hydrothermal and simulated oil were 23.5, 23.1 and 28.5 years at 20 °C, and 12.2, 4.9 and 10.3 years at 40 °C, respectively.

Shear strength of hybrid GFRP-steel reinforced concrete corbels without vertical stirrups: Experimental research and prediction models

This paper investigates the behavior and predicts the shear strength of concrete corbels reinforced with hybrid glass fiber reinforced polymer (GFRP)/steel reinforcement bars. For this purpose, the study consists of two main parts: the first part was an experimental study carried out on eight hybrid reinforced concrete corbels and four GFRP reinforced concrete corbels with a shear span to depth ratio (a/d) of 0.7 and 1.0; in the second part, a nonlinear finite element model (NFEM) was developed and validated against experimental results. Comprehensive parametric studies based on the validated NFEM were conducted to assess the impact of main parameters on the shear capacity. As a result, an empirical formula predicting the shear capacity of hybrid RC corbels was proposed. Furthermore, a softened strut-and-tie model (SSTM) was further developed to predict the shear capacity of hybrid RC corbels. The test results indicate that increasing the steel reinforcement ratio significantly enhances the shear strength. The width of the inclined crack band narrows as a portion of GFRP reinforcement is replaced with steel reinforcement. The NFEM shows good agreement with test results in terms of load-deflection curve, strain of rebar and failure modes. The proposed empirical formula and extended SSTM accurately predict the shear capacity of hybrid RC corbels compared to test results and numerical simulations.

Nonlinear dynamic study of FG-GFRC-NPR structures

The functionally graded glass fibre-reinforced polymer composite(FG-GFRC) is one of the contemporary sophisticated materials that may be employed for a variety of technical purposes. The shock absorption capacity of FG-GFRP laminates can be improved by incorporating auxetic property (i.e., negative Poisson's ratio NPR) in the structures, which can be attained by a particular stacking sequence of glass fibres (GF) and a different percentage of GF distribution along the thickness direction within the FG-GFRP structure. The nonlinear dynamic behaviour of such structures must be investigated. The clamped-clamped FG-GFRP-NPR structure is stimulated under a uniform transverse load distribution in the current work. Based on the higher-order shear deformation theory (SDT), the displacement field and nonlinear stress–strain relationship are derived. The nonlinear differential equation with cubic non-linear components were derived using Hamilton’s principle and transformed using Galerkin’s technique and obtained governing equation of motion. MATLAB has been used to conduct all numerical simulations. A time series, a phase picture and a Poincare diagram (PCM) were generated to characterize the vibration behavior of such auxetic structures.

Towards fiber-reinforced front-sheets for lightweight PV modules in VIPV

Novel approaches in the field of photovoltaics, such as building or vehicle integration require investigations of lightweight PV module concepts [1]. This research proposes and evaluates a lightweight PV module concept using glass fiber-reinforced polymers (GFRP) based on epoxy composites within the module stack. The usage of GFRP as front material as proposed in this work, reduces weight by 44–74 % compared to conventional glass-back sheet modules. We show results that with the proposed module stack hail impact resistant module can be built with small and large size avoiding any cell cracks after impact. Additionally, modules with GFRP front layer withstand thermal cycling tests with low power losses ranging from −0.9 % to −1.1 % at Pmpp depending on the individual GFRP layer. We also show results of cut susceptibility tests with an increased performance compared to modules with a polymeric front layer. Development topics remain as shown by damp-heat and UV irradiation testing, were an optimization of the module stack still needs to be performed.

Defect Detection of GFRP Composites through Long Pulse Thermography Using an Uncooled Microbolometer Infrared Camera.

The detection of impact and depth defects in Glass Fiber Reinforced Polymer (GFRP) composites has been extensively studied to develop effective, reliable, and cost-efficient assessment methods through various Non-Destructive Testing (NDT) techniques. Challenges in detecting these defects arise from varying responses based on the geometrical shape, thickness, and defect types. Long Pulse Thermography (LPT), utilizing an uncooled microbolometer and a low-resolution infrared (IR) camera, presents a promising solution for detecting both depth and impact defects in GFRP materials with a single setup and minimal tools at an economical cost. Despite its potential, the application of LPT has been limited due to susceptibility to noise from environmental radiation and reflections, leading to blurry images. This study focuses on optimizing LPT parameters to achieve accurate defect detection. Specifically, we investigated 11 flat-bottom hole (FBH) depth defects and impact defects ranging from 8 J to 15 J in GFRP materials. The key parameters examined include the environmental temperature, background reflection, background color reflection, and surface emissivity. Additionally, we employed image processing techniques to classify composite defects and automatically highlight defective areas. The Tanimoto Criterion (TC) was used to evaluate the accuracy of LPT both for raw images and post-processed images. The results demonstrate that through parameter optimization, the depth defects in GFRP materials were successfully detected. The TC success rate reached 0.91 for detecting FBH depth defects in raw images, which improved significantly after post-processing using Canny edge detection and Hough circle detection algorithms. This study underscores the potential of optimized LPT as a cost-effective and reliable method for detecting defects in GFRP composites.

Investigation of thermolabile particles for debonding on demand in fiber reinforced composites

Glass fiber reinforced plastics (GFRP) are essential for lightweight design and are manufactured in high quantities. Since there is no suitable method for recycling, the GFRP are mostly grinded and used as filler at end of life. In this work, the well-known principle of debonding on demand is considered to enable feasible and value-retaining separation of glass fibers from the polymeric matrix. To this end, gas-releasing thermo-responsive substances (TRS) like carboxylic or amino acids are introduced to the composite to investigate their potential for causing delamination after heating. To promote sufficient fiber/matrix adhesion, the TRS are encapsulated with silica or immobilized on magnetite particles. Furthermore, the immobilization synthesis is scaled up by using a custom-made continuous flow reactor. Finally, a new sizing mixed for glass fiber spinning, containing the particles, is formulated. The experiments reveal that a maximum of 0.5 wt.% particles can be used in the sizing to coat the fibers. Although all tested samples show a significant organic functionalization, the particles functionalized with TRS do not trigger sufficient delamination at the current state of development.

Stress-strain modelling of circular concrete-filled FRP–steel composite tube columns under axial compression load

Concrete filled-circular steel tube (CFCST) columns, when externally confined with carbon or glass fiber-reinforced polymers (FRP) sheets and subjected to axial load, exhibit improved strength and ductility compared to unconfined cases. The mechanical properties of the confinement materials are crucial in determining the stress-strain relationship of the confined concrete. This study presents an in-depth analysis of the stress-strain behavior of FRP-confined CFST columns, based on data from 252 specimens. It examines a range of factors, including various infill concrete grades from 14.15 to 140.39 MPa, two types of carbon steel outer tubes with yield strengths (fy) from 226 to 466.5 MPa, and two types of FRP (CFRP and GFRP) with tensile strengths from 1260 to 4900 MPa. The complete axial stress-strain curve is divided into four phases according to a mathematical expression by Wu and Wei (2015): the elastic phase, nonlinear transition phase, linear softening phase, and residual phase. New formulas for ultimate stress, based on confinement stress, were proposed by Hassanin et al. (2023), while the ultimate strain was calculated using the classical formula by Richart et al. Peak stress and strain were determined through statistical linear regression analysis using SPSS software, based on 252 experimental data points and involved using a combined factor of steel contribution (Elsfco) and FRP contribution (Elffco). Eight specimens were specifically used to validate the models through Finite Element Method (FEM) simulations. The accuracy of the predicted analysis results was also assessed by comparing them to existing models. The evaluation showed that the models successfully simulated the complete stress-strain curve of FRP-wrapped CFST columns under axial load, producing satisfactory results. These four models provide reliable results for calculating ultimate stress, ultimate strain, peak stress, peak strain, and the complete stress-strain behavior of these columns.

Comparison of the dynamic characteristics of GFRP, CFRP, and hybrid composites subjected to repeated low‐velocity impact

AbstractThe current study used the vacuum‐assisted hand lay‐up method (VAHLM) to manufacture glass fiber‐reinforced polymer (GFRP), carbon fiber‐reinforced polymer (CFRP), and glass/carbon fiber‐reinforced hybrid composites to examine the influences of fiber materials and hybridization on the repeated low‐velocity impact (LVI) responses. In this regard, the manufactured composites were exposed to repeated LVI loading at 3 m/s under 25.2 J impact energy, and thus dynamic characteristics such as total impulse, contact/bending stiffness, interaction time, peak force/displacement, and absorbed‐rebounded energies depending on the impact number were acquired. LVI tests were continued until penetration was observed in the composites, at which point the penetration threshold numbers for each composite type were acquired. Furthermore, the macro‐scale damage analyses depending on the impact number were gradually examined, and the impacts of hybridization and fiber material on the damage mechanisms were determined. The study found that GFRP, hybrid and CFRP composites had the highest impact resistance, respectively, and that glass fiber‐reinforcement is well‐suited for applications that require higher impact resistance. When the average penetration threshold numbers for the composites were examined, it was observed that GFRP composites had approximately five times higher penetration threshold numbers than CFRP composites and that hybrid specimens exhibited similar properties to CFRP composites in terms of impact resistance. This scenario was linked to the various deformation capabilities of glass and carbon fibers, and it was concluded that the high‐deformation capability of the fibers improved the penetration threshold numbers.Highlights Effects of hybridization and fiber material on LVI responses were examined. Fiber material has a significant influence on impact resistance. Penetration threshold number can be associated with the fibers' strain capability. The adhesion factor plays an active role in the damage of hybrid specimens.

Research on Acid Aging and Damage Pattern Recognition of Glass Fiber-Reinforced Plastic Oil and Gas Gathering Pipelines Based on Acoustic Emission.

Pipelines extend thousands of kilometers to transport and distribute oil and gas. Given the challenges often faced with corrosion, fatigue, and other issues in steel pipes, the demand for glass fiber-reinforced plastic (GFRP) pipes is increasing in oil and gas gathering and transmission systems. However, the medium that is transported through these pipelines contains multiple acid gases such as CO2 and H2S, as well as ions including Cl-, Ca2+, Mg2+, SO42-, CO32-, and HCO3-. These substances can cause a series of problems, such as aging, debonding, delamination, and fracture. In this study, a series of aging damage experiments were conducted on V-shaped defect GFRP pipes with depths of 2 mm and 5 mm. The aging and failure of GFRP were studied under the combined effects of external force and acidic solution using acoustic emission (AE) techniques. It was found that the acidic aging solution promoted matrix damage, fiber/matrix desorption, and delamination damage in GFRP pipes over a short period. However, the overall aging effect was relatively weak. Based on the experimental data, the SSA-LSSVM algorithm was proposed and applied to the damage pattern recognition of GFRP. An average recognition rate of up to 90% was achieved, indicating that this method is highly suitable for analyzing AE signals related to GFRP damage.

Bearing Capacity of Hybrid (Steel and GFRP) Reinforced Columns under Eccentric Loading: Theory and Experiment

In order to reveal the mechanical behavior of short concrete columns reinforced with hybrid steel and glass FRP bars, 10 specimens were designed for eccentric compression tests. The effect of eccentricity and load–displacement/strain of the specimens was studied. Test results indicate that the damage process and failure mode of these hybrid RC columns was similar to those in the conventional steel-reinforced concrete columns. The mode of failure for all specimens is characterized as large eccentricity compression failure, and the ultimate bearing capacity of the columns decreases with the increase in eccentricity. However, the impact of the varying axial stiffness ratio between GFRP and steel bars on the bearing capacity can be considered negligible. In addition, based on theoretical analysis, two boundary states for distinguishing failure mode and the formulae for calculating ultimate bearing capacity in different failure modes of eccentrically loaded hybrid RC columns are proposed. The computed results agree well with test results.

Development of Sustainable and Innovative Manhole Covers in Fibre-Reinforced Concrete and GFRP Grating

In several countries, manhole covers made of steel are being stolen, with significant economic losses for private and public entities, and even causing accidents. In this work, a new manhole cover is developed using fibre-reinforced cementitious (FRC) materials and glass fibre-reinforced polymer (GFRP) gratings. Since the GFRP gratings are immune to corrosion, and FRC is a relatively low-cost material, manhole covers in FRC reinforced with GFRP gratings are durable and not so appealing to be stolen as those made from steel. An experimental program with manhole cover specimens made with two types of FRC and two types of GFRP gratings was executed by investigating the strength, stiffness and post-cracking tensile capacity of the FRCs and the stiffness and flexural capacity of the two GFRP gratings. It was demonstrated that the developed manhole cover concept can be of class A15 up to D400 according to the recommendations of BS EN 124:1994.