Carbon Fiber Reinforced Polymer Layers Research Articles

Static strength of CFRP-strengthened preloaded circular concrete-filled steel tube stub column columns – Part II: Theoretical and numerical analysis

Carbon fiber reinforced polymer (CFRP) has high strength and is lightweight, and it can be used to strengthen circular concrete-filled steel tubes (CFSTs). For CFSTs in service, they are usually subjected to preloading. By considering the strain lag of CFRP, a theoretical model for analyzing CFRP-strengthened preloaded CFST stub columns is presented, and corresponding equations are derived for calculating the yield strength and the ultimate strength. Using the death and birth technique of CFRP element, finite element (FE) modeling is also presented to simulate the failure process of a CFRP-strengthened preloaded CFST stub column. The reliability and the accuracy of both theoretical equations and the FE model are evaluated by comparing the predicted results with experimental results reported in Part I. Finally, the CFRP-strengthening efficiency for the yield strength and the ultimate strength is assessed through the parametric study on 48 models. The effects of CFRP layers and preloading percentage on the strength of CFRP-strengthened preloaded CFST stub columns are also discussed.

Performance of Concentrically Loaded RC Wall-like Columns Upgraded with Innovative Hybrid NSM/CFRP System

In RC (reinforced concrete) frame structures, wall-like columns are laid within the space occupied by masonry walls to maximize usable space and thus minimize the column projections into the usable area. These columns often require strengthening owing to various reasons, including increasing the number of stories, changes in building usage, and others. The use of a hybrid system comprising NSM (near-surface mounted) steel rebars combined with CFRP (carbon-fiber reinforced polymer) laminates may be considered a sound technique for strengthening such wall-like building columns. The prime aim of this study is to devise an efficient scheme using a hybrid NSM/CFRP system to strengthen existing RC wall-like columns. Six half-scale RC wall-like columns were prepared and tested under monotonic concentric axial compression. Two columns were unstrengthened to serve as control specimens (CW1 and CW2), and four specimens were strengthened using four different schemes (SW1, SW2, SW3, and SW4). As favored by architects, all strengthening schemes were designed so that the dimensions of the column cross-section were not increased. The effects of strengthening schemes on the enhancement of axial capacity, energy dissipated, and stiffness were evaluated to find the most efficient scheme. Among the four studied schemes, using vertical continuous NSM rebars in combination with the wrapping of the three CFRP layers onto the exterior column surface (in specimen SW2) was the most efficient as it enhanced the ultimate load capacity by 80%. Three-dimensional FE (finite element) analysis was also conducted to predict the response of test specimens. The test results matched well with the FE outputs, which justified the accuracy of the used constitutive models for concrete, steel rebars, and CFRP sheets.

Research on compressive behavior of CFRP-confined CFDST stub columns with square stainless steel outer tube

Carbon fiber-reinforced polymer (CFRP)-confined concrete-filled double skin tube (CFDST) stub columns with a square outer tube made of stainless steel can be characterized by their low weight, high strength, and good corrosion resistance. They have good application prospects in the field of ocean engineering. This study applied the finite element software ABAQUS to comprehensively investigate the compressive behavior of CFRP-confined CFDST stub columns with a square stainless steel outer tube and a circular inner steel tube in terms of their ultimate bearing capacity, based on previous experimental research. Through a parametric analysis and comparison, it was found that the strength and width-to-thickness ratio of the outer tube have a significant effect on improving the ultimate bearing capacity of the specimen, while the strength and diameter-to-thickness ratio of the inner tube and the number of CFRP layers have a limited effect. The development stage of the interaction stresses between the inner and outer tubes and concrete was clarified, and the location of the maximum interaction stress was determined. Finally, based on the limit equilibrium method, formulae for predicting the ultimate bearing capacity of square CFDST stub columns and CFRP-confined square CFDST stub columns were derived.

Effect of Normal and Rubberized Concrete Properties on the Behavior of RC Columns Strengthened with EB CFRP Laminates and Welded Wire Mesh under Static Axial Loading.

The huge amounts of old and damaged tires spread worldwide has caused many complex environmental risks. The old tires have been converted to crumb rubber (CR) and tire recycled steel fiber (RSF) to facilitate their use. This study used CR to partially replace natural sand in reinforced (RC) columns. Externally bonded (EB) carbon-fiber-reinforced polymer (CFRP) laminates, welded wire mesh (WWM), and RSF were used to enhance the axial behavior of the tested columns to overcome the concrete deficiencies resulting from the inclusion of the CR instead of natural sand. Eighteen columns were prepared and tested to discuss the effects of strengthening type, CR content, RSF, and strengthening area on the axial behavior of the RC columns. Certain columns were internally reinforced with WWM, while others were externally strengthened with EB CFRP laminates. Partially or fully EB CFRP laminates were used to strengthen the columns. Moreover, one column was cast with NC and 0.2% RSF to investigate the role of RSF in confining the column. The results demonstrated a concrete strength reduction for the rubberized concrete (CRC) as the CR content increased. Conversely, the strengthened columns experienced higher load capacities than the corresponding un-strengthened ones cast with the same concrete mix. Moreover, adding 2% RSF to the NC mix could enhance the column capacity, although it decreased the concrete strength. Furthermore, using two CFRP layers increased the load capacity and ductility of the strengthened columns. The strengthened column cast with 50% CR showed the highest load efficiency (334.3% compared to the un-strengthened one).

Fatigue behavior and digital image correlation monitoring of steel plates with mixed-mode edge cracks repaired with CFRP materials

In recent years, carbon fiber reinforced polymer (CFRP) has been widely used to improve the fatigue behavior of steel structures, while most relevant studies were focused on steel components with mode I cracks. This study aims to investigate the fatigue behavior of steel plates with mixed-mode I/II edge cracks patched with CFRP sheets or plates. A total of eleven specimens were fabricated and tested. A digital image correlation (DIC) system was employed as a non-contact measurement to monitor the fatigue crack propagation. Post-processed displacement fields were used to calculate stress intensity factors (SIFs) near the crack tips. Experimental results showed that double-sided CFRP repairing could significantly improve the fatigue life of edge-cracked specimens, especially those with mode I crack rather than mixed-mode I/II crack. Corresponding finite element (FE) analyses were conducted, and good consistency was achieved with test results of crack growth trajectories and fatigue lives. Further FE analysis considered three parameters: load application angle, CFRP layer number, and initial damage level.

Experimental and analytical study on the effect of different repairing and strengthening strategies on flexural performance of corroded RC beams

This paper reports the results of a study conducted to investigate the flexural behavior of corroded reinforced concrete (RC) beams that were first repaired with different types of cover repairing materials and then strengthened with the carbon fiber-reinforced polymer (CFRP) laminates. Thirteen RC beam specimens were prepared. One specimen was used as a control beam (un-corroded, unrepaired, unstrengthened), and the reinforcing bars in twelve specimens were corroded using an accelerated corrosion setup. While five corroded specimens (two unrepaired and three repaired) were tested without strengthening using CFRP laminates, the other seven corroded specimens (two unrepaired and five repaired) were strengthened with one and two layers of CFRP laminates before testing under flexure. For the RC beams subjected to 10 and 20% corrosion of steel bars (by mass), strengthening using one layer of CFRP laminate enhanced the load-bearing capacities by 89 and 73%, respectively, while strengthening with two CFRP layers improved the load-carrying capacity by 162 and 154%, respectively. Repairing the damaged cover of the corroded RC beams using ultra-high-performance concrete (UHPC) was found to be most effective in enhancing the load-bearing capacity and stiffness, whether the corroded beams were strengthened with CFRP laminates or not. Repairing of the cover using commercial repair material also enhanced the load-carrying capacity and stiffness, with ductility more than that of UHPC. Strengthening of the corroded beams further improved the load-carrying capacity. An analytical model was developed that can predict the load-bearing capacity of the beams with a fair degree of accuracy.

Behavior of repaired projectile bullet damaged reinforced concrete beams using CFRP sheet in conjunction with natural aggregate or recycled aggregate concrete layer

In this study, the bullet projectile performance of repaired projectile bullet damaged recycled aggregate (RA) or natural aggregate (NA) RC beams using carbon fiber reinforced polymer (CFRP) sheets in conjunction with RA or NA concrete was experimentally investigated. The experiment consists of a total of six subjected to projectile bullet loading. The effect of the type of material used in combination with the CFRP sheet was studied. According to the test findings, utilizing the CFRP sheet demonstrated a much higher load capacity than the control beams, but a decreased level of ductility. Therefore, CFRP sheet is a viable repair technique of projectile bullet damaged RA or NA RC beams. Besides, the results show that the repaired damaged RC beams with CFRP combined with the NA layer had a higher load compared to the repaired damaged RC beams with CFRP combined with the RA layer. However, CFRP in combined with RA shows a good enhancement in load capacity (115.6–117.8%). The repaired beams with CFRP and NA layer showed debonding failure while using RA with CFRP showed debonding with cover separation in repairing RA beam.

Axial compression behavior of CFRP-confined square concrete-filled double skin tube stub columns with stainless steel outer tube

Concrete-filled double skin tube (CFDST) stub columns with a stainless steel outer tube is a new kind of composite columns and potential to be widely utilized in ocean engineering owing to the excellent performance characterized by high corrosion resistance. To improve the ultimate bearing capacity and delay the local buckling of stainless steel tube, confining materials such as carbon fiber reinforced polymer (CFRP) can be adopted in these composite columns. Thus, this study conducted an experimental investigation on the axial compression behavior of CFRP-confined square CFDST stub columns with a stainless steel outer tube. The main variables were the width-to-thickness ratio of stainless tube and the number of CFRP layers. The typical failure modes, load-shortening curves, and load-strain curves of the CFDST and CFRP-confined CFDST columns were obtained. The test results indicated that the local buckling of CFDST columns can be well suppressed with CFRP wrapping, prior to CFRP rupturing. The CFRP can provide an effective confinement on the sandwich concrete and the ultimate bearing capacity enhancement increased with increasing the number of CFRP layers. Based on theoretical analysis a design model for the inner steel tube has been proposed to prevent the premature failure of the inner steel tube which can leads serious ultimate bearing capacity lose. Additionally, new methods for predicting the ultimate bearing capacity of the square CFDST and CFRP-confined CFDST are proposed based on the limit equilibrium method and twin shear unified strength theory. The predicted results are in good agreement with the experimental results and collected test data.

Modelling and evaluation of carbon fibre composite structures using high-frequency eddy current imaging

The mechanical performance of carbon fibre reinforced polymer (CFRP) composites is determined by the stacking sequence of specifically orientated ply lamina layers. In these multi-layer structures, global ply misalignment and local fibre waviness can occur during the manufacturing process, leading to reduced performance and structural failure during operation. High-frequency eddy-current testing (ECT) has previously demonstrated its capability for detecting orientation-related features, including fibre orientation and waviness. However, accurate sensor optimisation and inversion of orientation & material structure cannot be achieved without proper, validated modelling techniques to simulate CFRP features. The lack of suitable models is in part due to CFRP exhibiting highly-complex electromagnetic interactions between fibres, lamina and the ECT sensors, which are challenging to integrate. This work proposes a novel finite element modelling approach to simulate the ECT response to planar multi-layered CFRP components. The fibre tow structure of each unidirectional ply is modelled using orientation dependant 2D conductivity tensor waveforms, and virtual 2D ECT scans are simulated by shifting the waveforms within the model mesh. The results demonstrate that idealised electromagnetic characteristics of the CFRP structure can be successfully modelled compared with experimental data and that 2D ECT data of complex CFRP layers structures can be simulated with improved computational speeds, up to 5x faster compared to standard approaches. Automated data-analysis tools, including Radon transform (RT) and 2D FFT, are employed to validate the simulated 2D scan data through the characterisation of fibre orientations and simulated 2D scans used to evaluate the orientation inversion techniques. The results demonstrate that RT analysis detects fibre orientations with better accuracy, precision and consistency than equivalent 2D FFT analysis techniques. The simulation also demonstrates the reduced resistivity losses compared with isotropic materials caused by the different heterogeneous and multi-layer structures. It predicts high current densities at interfaces of plies with orthogonal orientations, resulting in an effective interface skin-depth.

On the arresting efficiency of CFRP-winding buckle arrestors for subsea pipelines

Carbon fiber reinforced polymer (CFRP)-winding buckle arrestor, conceived as a new type of arresting device, is capable of locally enhancing the circumferential stiffness of pipes to provide an obstacle to a propagating buckle. This type of arrestor is composed of CFRP and adhesive layers, which are wrapped around the pipe for a number of turns. In the present study, collapse experiments were conducted on four groups of small-scale pipes in a hyperbaric chamber, and the effect of CFRP layer number, arrestor length, and CFRP sheet thickness on the crossover pressure was examined. The crossover mode of relatively thinner arrestor cases was found dominated by a flattening mode, whereas the collapse mode changed into a singly symmetric U-shape mode when the arrestor became thicker. A non-linear finite element (FE) model was developed to simulate the event of the CFRP-winding arrestor crossed by the propagating buckle, where a reasonable agreement was achieved between the experiments and numerical predictions. Then, parametric analyses were numerically performed, based on which an empirical formula was proposed for the crossover pressure of CFRP-winding arrestors exhibiting the flattening mode. In addition, comparative studies with the conventional arrestor further confirmed the viability of adopting the CFRP-winding arrestor.

Mechanical performance of marine concrete filled CFRP-aluminum alloy tube columns under axial compression: Experiment and finite element analysis

This study presents the mechanical performance of marine concrete filled carbon fiber reinforced polymer (CFRP)-Aluminum alloy tube columns (CFRP-CFAT) through axial compression experiment and finite element analysis. 18 specimens were tested including 3 marine concrete filled aluminum alloy tubes (CFAT) and 15 CFRP-CFATs. The effects of the CFRP pasting position (outer and inner CFRP) and the number of CFRP layers were investigated. The typical failure pattern of specimens without inner CFRP was waist drum failure of aluminum alloy tube and concrete crushed, aluminum tube and concrete of specimens with inner CFRP were shear failure, the CFRP of all specimens was fractured. CFRP and aluminum alloy tube have fine deformation coordination performance. With the confinement of CFRP, the ultimate bearing capacity and energy absorption capacity of CFRP-CFATs were increased by up to 60.0% and 37.3%, respectively, also effectively inhibited the damage development of specimens. Moreover, a finite element model was developed, a parametric study was carried and a model for calculating the ultimate bearing capacity of CFRP-CFAT was proposed. The simulated results and calculated results were consistent with experimental results.

Numerical and analytical investigation of square timber columns confined with steel and carbon fiber reinforced polymer external jacket

This paper numerically investigated the timber confinement of columns with carbon fiber reinforced polymer (CFRP) and steel tubes under axial compression. An elastic-plastic model with linear hardening, a CFRP hashin damage, and a timber damaged anisotropic elastic-plastic model, respectively, are used to simulate the inelastic behavior of the steel tube, CFRP layers, and timber core. In addition, a comprehensive numerical study was conducted using a wide range of cross-sections, thicknesses, lengths, and the number of CFRP layers developed to varying degrees (0, 45, and 90). To confirm the accuracy of the current FEM model, numerical data is compared to the experimental model’s final strengths, behavior, and failure mechanisms. Additionally, the ultimate strengths of timber-steel and CFRP are compared to various standards and design formulas. The results reveal that columns with thicker steel tubes and more CFRP layers have an average of about 42% and 12% greater load-bearing capacity and ductility. The degree of CFRP affected the load-bearing capacity of timber columns, which increased by around 10% from 45 to 90. In comparison to specimens with equal cross-sections and thickness, shorter specimens with greater cross-sections typically have 40% higher stiffness. According to parameter studies, the AISC 360-16 American standard design approaches can be safely extended to anticipate the ultimate strength of timber-steel columns. Meanwhile, both the ACI-440 and Ilki et al. design formula predictions are the most precise, particularly at 45° with high ultimate strength.

Effect of CFRP layers on the behavior of shear-strengthened RC-beams: U-wrapping versus full wrapping

The practice of externally bonded (EB) carbon fiber-reinforced polymer (CFRP) fabrics for structural strengthening increasingly shows evidence of effectiveness for the rehabilitation of existing structures. However, debonding of fiber-reinforced polymer (FRP), particularly in shear, is still a major premature failure mode when using FRP sheets to strengthen concrete structures. This paper presents the results of an experimental investigation of the performance of full-scale reinforced concrete (RC) beams strengthened in shear using EB-FRP U-wrapping (UW) and full wrapping (FW) with different fabric thicknesses. Full wrapping is used mostly on columns with all sides accessible and does not generally apply to beams. The main objectives of this study are to optimize FRP capacity and to evaluate the effect of confinement and the effectiveness of FRP using different strengthening configurations for RC beams, such as FW and UW. The results obtained in this study reveal that fully wrapped beams exhibit enhanced CFRP contribution to shear resistance compared to U-wrapped beams. In addition, the FW configuration eliminated the CFRP debonding failure mode and resulted in an increase in concrete strain.

A novel seawater and sea sand concrete-filled CFRP-carbon steel composite tube column: Seismic behavior and finite element analysis

The seismic behavior of a novel seawater and sea sand concrete (SSC)-filled carbon fiber-reinforced polymer (CFRP)-carbon steel composite tube (SFSCT) column under combined axial compression and reversed cyclic loadings was studied in this paper. This structure makes use of seawater and sea sand resources, and CFRP was adopted to isolate the corrosion by chloride ions on the steel tube. Tests of eight composite columns were carried out. The test parameters include the axial compression ratio, the number of CFRP layers and the bonding direction. The test results revealed that all of the specimens displayed superb seismic performance with a drift ratio over 4%. The failure of the SFSCT column exhibits a typical compressive-flexural failure mode. Compared with the results of the SSC-filled steel tube columns, the hoop strain of the specimen under additional CFRP confinement is reduced by 1.6 times, and the flexural strength and drift capacity increase by 22% and 17%, respectively. A fiber model was created by finite element analysis, and parametric studies of the main design parameters were performed. The effects of the steel tube and CFRP on the seismic performance were evaluated. Using experiments and finite element analysis, the relationships among the drift capacity, axial compression ratio and confinement level were investigated. A design method for predicting the drift capacity of SFSCT columns was proposed.

Compressive behavior of CFRP-confined steel fiber-reinforced self-compacting lightweight aggregate concrete in square columns

Self-compacting lightweight aggregate concrete (SLC) is greatly limited in the application of tensile and high-shear structures due to its obvious brittleness and low elastic modulus. Therefore, carbon fiber-reinforced polymer (CFRP)-confined steel fiber-reinforced self-compacting lightweight aggregate concrete (SFSLC) square columns were proposed, and axial compression tests were conducted in this paper. The effects of the steel fiber content, CFRP layers, and compressive strength grade of core concrete on the mechanical properties of SLC square columns were studied. According to the experimental phenomena and stress–strain curves, the synergistic effect of steel fiber and CFRP can obviously improve the failure mode and mechanical properties after peak stress. In contrast, the synergistic effect of the steel fiber and CFRP would be weakened by increasing the compressive strength grade of the core concrete. With the increase in steel fiber content, the deformability of the core concrete was improved, which increased the lateral confinement effect of the CFRP. When the number of CFRP layers was small, the mechanical properties of the specimens were significantly improved by adding a small number of steel fibers. With the increase in the number of CFRP layers, the reflection of internal defects caused by excessive steel fibers could be decreased. Based on the experimental study, the influence of variables on the confinement effect was analyzed, and the influence coefficient λ of steel fiber on the deformation of the specimen was introduced to establish the stress–strain curve models of CFRP-confined SFSLC square columns. Compared with the experimental curve, the model has higher prediction accuracy.

Structural Behaviour of Polystyrene Foam Lightweight Concrete Beams Strengthened with FRP Laminates

Lightweight concrete (LWC) is one of the most important building materials nowadays. Many research studies were focused on LWC produced using lightweight aggregates. However, limited work was cited for LWC produced using polystyrene beads. In this study, LWC beams strengthened with carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP) were experimentally tested to investigate the improvement in their flexural and shear behaviours. LWC in this investigation was achieved by partial replacement of normal aggregate by polystyrene beads and resulted in approximately 30% less weight compared to Normal weight concrete. Fourteen Reinforced Concrete (RC) LWC beams of 100 mm by 300 mm cross section having an overall length of 3250 mm were tested under four-point bending. These beams were designed, detailed, and tested to obtain flexural and shear mode of failure. These beams were divided into two groups based on the intended failure mode. In each group, six beams were strengthened using CFRP and GFRP laminates, while the remaining one beam was used as control. The tested parameters were the type of FRP, the width of the laminates used in shear strengthening, and the number of layers used in flexural strengthening. It was found that strengthening of LWC beams using CFRP and GFRP layers resulted in increasing the loading capacity and decreasing deflection as compared to control. The strengthening with CFRP and GFRP is also suitable in reducing the crack width and crack propagation which is more significant in LWC beams. The experimental results were also compared with the expressions in codes for forecasting the strength of LWC beams and it was that these expressions are compatible with the experimental results.

Numerical study of surface fatigue crack growth in steel plates repaired with CFRP

This paper presents a numerical study of the fatigue behaviour of carbon fibre-reinforced polymer (CFRP) repaired steel plates with a surface crack under uniaxial cyclic tension. A simulation programme for surface fatigue crack propagation has been developed by means of Abaqus-Python scripting. Validation of models was first performed analytically and experimentally, through evaluation of the stress intensity factor (SIF) and fatigue life of unrepaired specimens, respectively. The developed programme was then used to simulate the fatigue behaviour of surface cracked specimens repaired with CFRP sheets. Different aspect ratios of surface cracks, numbers of CFRP layers, CFRP sheet widths and types and CFRP repair schemes (i.e. single- and double-sided reinforcement) were considered, to assess their influence on the CFRP repair efficiency. The results showed that applying CFRP sheets could effectively reduce the SIF of the surface cracks, thereby prolonging the fatigue life of the steel plates. Further, the repair performance improved with more and wider CFRP sheets and higher equivalent modulus but remained almost unchanged for different crack aspect ratios, while the single-sided CFRP repair outperformed the double-sided repair in efficiency. The present study is of instructive value for application of CFRP materials to the repair of surface cracked metallic structures.

Seismic behavior of RC columns strengthened with near-surface-mounted aluminum alloy bars and CFRP wraps

This paper proposed a near-surface-mounted (NSM) strengthening technique by using aluminum alloy (AA) bars and carbon fiber-reinforced polymer (CFRP) wraps to improve the seismic behavior of square reinforced concrete (RC) columns. Eight strengthened concrete columns with square cross sections of 250 mm × 250 mm and 1600 mm shear span were tested under axial compression and reversal cyclic loading to investigate the effects of NSM reinforcement ratios (0.36–1.29%), layers of CFRP wraps (0 and 3), and axial compression ratios (0.1 and 0.4) on the seismic behavior. The failure mode, hysteretic response, load-bearing capacity, ductility, stiffness degradation, and energy dissipation capacity of those column specimens were analyzed. Results indicated that the lateral load-bearing capacity, stiffness, and cumulative energy dissipation capacity increased with the increase of the NSM reinforcement ratio. The CFRP wraps in the NSM technique can provide hoop confinement to avoid the buckling failure of NSM AA bars, and improve the seismic behavior by mitigating spalling of concrete. When increasing the axial compression ratio from 0.1 to 0.4, the lateral load-bearing capacity and cumulative energy dissipation capacity increased significantly, while the stiffness degradation became obvious. In addition, three-dimensional (3D) finite element (FE) models were developed and verified by comparisons in the deformation and lateral loads at characteristic points, as well as the strain distribution along NSM AA bars. The verified FE models can be used to analyze the damage of concrete and the stress distribution at the interface between epoxy and concrete.

Experiment and theoretical analysis of carbon fiber reinforced polymer strengthened square steel tube under eccentric load

Carbon fiber reinforced polymer (CFRP) has many advantages, such as light weight, high strength, and excellent corrosion resistance. In this paper, the experimental research of the square steel tube reinforced by carbon fiber reinforced polymer was performed, and its ultimate bearing capacity formula was derived. The tests were based on the previous results of our research group. Six sets of the test are performed by altering two-layer-CFRP and the eccentricity. The test results demonstrated that CFRP improved the ultimate bearing capacity of square steel tubes. As the number of layers of CFRP increased, the growth rate of bearing capacity gradually declined, and reinforcement of CFRP on specimens of large eccentricity was significantly effective than that of small eccentricity one. After longitudinal CFRP was stuck, a circumferential layer of CFRP in the middle of the square steel tube can improve the reinforcement effect. This paper referred to the existing codes and took the idea of area substitution to derive the ultimate bearing capacity formula of the steel tube reinforced by CFRP. The calculated values of the formula were compared with those of the experiment, and the difference is within the range, which proves the rationality of the derived formula.

Experimental study on performance of CFRP-strengthened RC beams with geopolymer and epoxy

PurposeIn this paper, to obtain shear and bending performance of carbon fiber-reinforced polymer (CFRP)-strengthened beams bonded by geopolymers, the effects of impregnated adhesive types, strengthened scheme, CFRP layer and pre-cracked width are investigated, and the performance of CFRP-strengthened beams is validated by the establishment of Finite Element Models (FEMs).Design/methodology/approachIn this paper, static loading test and finite element analysis of epoxy-CFRP-strengthened (ECS) and geopolymer-CFRP-strengthened (GCS) were carried out, and the bearing capacity and stiffness were compared, the results show that GCS reinforced concrete (RC) beam is feasible and effective.FindingsThe bearing capacity, crack distribution and development, load–deflection curves of GCS RC beams with different pre-crack widths were investigated. The reinforcement effect of geopolymer achieves the same as epoxy, effectively improving the ultimate bearing capacity of the beam, with a maximum increase rate of 28.9%. The failure mode of CFRP is broken in the yield failure stage of GCS RC beam with reasonable strengthening form, and the utilization rate of CFRP is improved. CFRP-strengthened layers, pre-cracked widths significantly affect the mechanical properties, and deformation properties of the strengthened beams.Originality/valueCompared with ECS RC beams, the bearing capacity and stiffness of GCS RC beams are similar to or even better, indicating that GCS RC beam is feasible and effective. It is a new method for CFRP-strengthened beams, which not only conforms to the concept of national ecological civilization construction, but also provides an economical, environmentally friendly and excellent performance solution for structural reinforcement.