Bonded Carbon Fiber Research Articles

Shear and flexural strengthening of reinforced concrete beams with variable compressive strength values using externally bonded carbon fiber plates

This paper presents experimental and analytical research to study the shear and flexural performance of Reinforced Concrete (RC) beams strengthened using two types of externally bonded Carbon Fiber Reinforced Polymer (CFRP) composites; including laminates and sheets. A total of 24 full-scale RC beams were tested up to failure. Concrete compressive strengths of 17, 32, and 47 MPa were used, with CFRP composites attached in six different configurations in an effort to optimize the flexural and shear load-carrying capacities of the specimens tested. Results showed that externally bonded CFRP composites considerably improved both the shear and flexural strengths of the beams. Notably speaking, the effectiveness of the CFRP composite material was inversely proportional to the concrete compressive strength. Significant improvement of the shear strength ranging from 28.9% to 29.6% was observed for beams with CFRP U-wraps compared to beams with laminate strips which ranged between 14.4% and 23.8% when the compressive strength was increased from 17 to 47 MPa. Meanwhile, those strengthened with half U-wraps had a notable improvement in their flexural strength (i.e., ultimate load carrying capacity) by a range of 22.4%–46.2%, as opposed to laminate strengthened beams that varied between 17.8% and 38.4% with increased compressive strength of the concrete mix. Finally, theoretical predictions using the ACI 440.2R-14 guidelines were compared to experimental results; however, the differences turned out to be relatively large due to the intrinsic empirical nature of the Code predicted equations.

Carbon-bonded carbon fiber composites reinforced with SiOC-based polymer derived ceramics: Microstructure and properties

Carbon-bonded carbon fiber (CBCF) composites have been used extensively for lightweight thermal insulation applications. In this work, CBCF composites reinforced with SiOC, B-modified SiOC (SiBOC) or Zr-modified SiOC (SiZrOC) ceramics were investigated. The chemical modification of SiOC precursor has significant effects on the microstructure as well as the mechanical and thermal properties of the composites. The SiBOC and SiZrOC precursor exhibit higher impregnation efficiency than the SiOC precursor. The SiBOC/CBCF composites have the highest compressive strength and best oxidation resistance, which is attributed to its preferable microstructure, where the SiBOC ceramics wrap on the fibers and provide effective protection for carbon fibers from oxygen diffusion. The strength and modulus of SiBOC/CBCF composites along z direction is 4.5 and 148 MPa, respectively. The thermal conductivity and expansion coefficient of SiBOC/CBCF composites along z direction is 0.3 W/m⋅k and 1.75 × 10−6 K−1, respectively.

Mechanical and Thermal Properties of Basalt Fibre Reinforced Polymer Lamellas for Renovation of Concrete Structures.

The level of energy consumption in renovation activities of buildings has huge advantages over the demolition of old buildings and the construction of new structures. Such renovation activities are usually associated with the simultaneous strengthening of their elements, such as externally bonded carbon fibre reinforced polymer (CFRP) lamellas or sheets on vertical and horizontal surfaces as structural reinforcements. This means the process of refurbishing a building, as well as the raw materials themselves have a significant impact on CO2 emissions and energy consumption. This research paper demonstrates possibilities of replacing state of the art, highly energy-intensive CFRP lamellas with basalt fibre reinforced plastics as energy-efficient structural reinforcements for building constructions. The mechanical and thermal properties of basalt fibre reinforced polymer (BFRP) composites with variable matrix formulations are investigated. The article considers macro- and microstructures of innovative BFRP. The investigations focus on fibre–matrix interactions with different sizing formulations and their effect on the tensile strength, strain as well as modulus of elasticity.

Influence of Laser Treatment on End Notched Flexure Bonded Joints in Carbon Fiber Reinforced Polymer: Experimental and Numerical Results.

Surface pretreatment for bonding is one of the most important steps for the manufacturing of a reliable bonded joint. In this paper, the effectiveness of an innovative pretreatment by CO2 pulsed laser for bonding Carbon Fiber Reinforced Polymer (CFRP) was investigated. End Notched Flexure (ENF) specimens were made with different densities of laser treatment, and the respective fracture toughness was obtained through the Compliance-Based Beam Method (CBBM). Furthermore, a cohesive model for simulating debonding processes was illustrated, and the cohesive parameters were obtained by an inverse method. The achieved results represent a fundamental step for the development of a numerical model useful for the determination of laser texturing as a function of the applied local stress into the bonded joint.

Sound of a Composite Failure: An Acoustic Emission Investigation

The failure progression characteristics of adhesively bonded Carbon Fiber Reinforced Polymer (CFRP) composites are investigated using Acoustic Emission (AE) technique. Different failure progression modes such as matrix cracking, fiber breakage, delamination and through-thickness crack growth releases AE waveforms in different frequency domains. The characteristic features of these different AE waveforms are studied in Mel Scale, which is a perpetual frequency scale of average human hearing frequency. The recurring noise in the recorded waveforms has been identified more efficiently when the waveforms are analysed in Mel Scale. The recorded AE signals from the adhesively bonded CFRP under static tensile loading are stretched to match the Mel filter banks. The sampling rate of the recorded signal is adjusted from 1 MHz to 20 kHz. Following that, the Mel spectrogram and its cepstral coefficients are used for identifying the different failure modes from which the AE signals are generated. A comprehensive comparison of the AE analysis in Mel scale with conventional waveform processing techniques such as Fast Fourier Transform (FFT), Continuous Wavelet Transform (CWT), Wavelet Packet Transform (WPT) and Hilbert-Huang Transform (HHT) has been made. The advantages and further applications of Mel Scale over traditional waveform processing techniques in defining the failure modes in the composites are also discussed.

Influence of Externally Bonded CFRP on the Shear Behavior of Strengthened and Rehabilitated Reinforced Concrete T-Beams Containing Shear Stirrups

This study aims to investigate the effect of using externally bonded carbon fiber reinforced polymer (CFRP) on the strengthening and rehabilitation of reinforced concrete (RC) T-beams reinforced with steel stirrups. Three configurations of CFRP were used: 45° inclined strips, horizontal straight strips, and U-wrapped sheets. A total of 19 specimens of strengthened and preloaded RC T-beams were experimentally tested. The experimental results were compared with the theoretical values determined according to the ACI 440.2R−17 code. The results proved that all beams containing CFRP recorded higher strength than the control sample, regardless of whether the beams were tested for strengthening or rehabilitation purposes. The horizontal straight strips of the CFRP schemes recorded the highest enhancement in the shear capacity, followed by the U-wrapped sheets and inclined strips. Moreover, the ACI 440.2R−17 code overestimated the capacities of some samples.

Bond behavior of fully bonded CFRP-concrete interface with improved double shear tests

An improved double-shear pull testing method was proposed with the improvements of loading fixture, fastening, and clamping devices to discuss the bond behavior of fully bonded carbon fiber reinforced polymer (CFRP)-concrete interfaces. The improvements provided a stable CFRP-debonding process due to the anchorage effect of the peripheral fasteners . Using the improved method, double-shear experiments with fully bonded CFRP (bond width ratio β = 1) could be carried out successfully, and the bond-slip relationships of the interface on any cross-sections (lines) of the fully bonded CFRP could be obtained. All of the valid experimental data show a better linear relationship between maximum bond stress τ max and corresponding slip s 0 , and a simple bond-slip model was proposed based on Popovics's equation. • A new double shear test for fully-bonded FRP-concrete interface with the improved specimen and devices was proposed. • The failure mode of specimens can be ensured as debonding failure of FRP-concrete interface by using the testing method. • A simple bond-slip model was proposed with the experimental data based on Popovics's equation.

Bond characteristics of CFRP strengthened concrete members bonded using Modified Engineered Cementitious Composite

This study focuses on the development of an insulating cementitious adhesive for bonding Carbon Fibre Reinforced Polymer (CFRP) fabrics to a concrete surface. The epoxy adhesive which is the generally used adhesive for CFRP shows a low thermal performance. As a potential solution, Engineered Cementitious Composite (ECC) mortar was modified as a cementitious adhesive with improved thermal insulation. The ECC adhesive was developed using locally available class F fly ash, silica sand and Polyethylene terephthalate (PET) fibres other than the generally used cement and water (PET-ECC). The selected mix proportion for PET-ECC achieved a low thermal conductivity of 0.145–0.180 W/mK which limited the heat transfer through the adhesive layer. The effective bond length of the developed PET-ECC adhesive was 125 mm and the corresponding bond strength was 224.9 MPa. The respective bond strength was further enhanced up to 570.28 MPa by sticking river sand on top of CFRP fabric using epoxy adhesive before bonding it to the concrete surface using the PET-ECC adhesive. The use of PET-ECC as the bonding agent to strengthen compression members with CFRP confinement yielded an average strength enhancement of 34%.

Adhesively bonded CFRP/Al joints: Influence of the surface pretreatment on corrosion during salt spray test

AbstractThe objective of this study was to investigate the influence of different surface pretreatments on the aging behavior of adhesively bonded carbon fiber reinforced polymers/Al joints in a standardized salt spray environment. Therefore, the bonding surfaces were acetone‐cleaned or laser‐pretreated by near‐infrared laser radiation. The pretreated surfaces were examined using optical microscopes, roughness measurements, and infiltration tests. Mechanical testing of the joints was performed in the unaged state and after five aging durations from 120 to 1440 h. The acetone‐cleaned specimens lose a maximum 20% of their initial average shear strength of 22 MPa after aging up to 1440 h. In contrast, the fracture patterns of the laser‐pretreated samples show corrosive degradation after 720 h, indicating galvanic coupling and crevice corrosion. This leads to a significant decrease in shear strength up to 50% after 1440 h of aging. Therefore, some strategies to avoid contact corrosion via the pretreatment and joining process are presented additionally.

Improvement of interface anchoring by ultrasonic vibration for adhesively bonded CFRP/Al joints

Adhesively bonded carbon fiber reinforced polymer (CFRP)/Al joints have been widely used in engineering field. However, the bonding strength still needs to be improved. In this study, ultrasonic vibration was applied during the adhesive bonding to promote the micromechanical anchoring at the interface of CFRP/Al joints. Ultrasonic vibration was exerted on the CFRP laminate to transmit the vibration to the adhesive bonding area once the joint was assembled. The strength and the strength consistency of the joints were increased by 45% and 50%, respectively. Scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) results showed that the ultrasonic vibration promoted the filling of the adhesive into the microstructures of the adherends and achieved a more compact bonding. Viscosity and contact angle of the adhesive were measured, and both of them were decreased greatly under the ultrasonic vibration, indicating that the ultrasonic vibration can increase the fluidity of the adhesive and force the wetting between the materials. Ultrasonic capillary experiment was then conducted. The adhesive in the capillary tube was prompted to rise obviously, and the meniscus was inverted with ultrasonic vibration, showing that the ultrasonic vibration produced a driving effect on filling of the adhesive in the microstructures. Therefore, the joints exhibited improved bonding strength owing to the enhanced micromechanical anchoring and physical adsorption at the bonding interface. This study is of great significance for understanding and optimization of the ultrasonic vibration strengthened adhesive bonding.

CONCRETE SLAB REINFORCED WITH GFRP AND EXTERNALY STRENGTH WITH CARBON SHEET UNDER IMPACT LOAD

When FRP bars used in concrete structures that exposed to harsh environments, their service life extended and the cost of their life cycle reduced. Recently, methods of externally bonding Carbon Fiber Reinforced Polymer (CFRP) sheets to RC slabs proposed to improve the dynamic behavior of RC slabs under impact load. In this study, the effect of the number of CFRP sheet layers (one or two) and the arrangement of CFRP sheets (covering the whole or parts of the surface) on the dynamic behavior of slabs reinforced with GFRP bar investigated. Nine specimens of (1550×1550×150) mm reinforced by GFRP bars were tested. A single control specimen was unstrings and eight specimens were strength with CFRP sheet on the tension face. A rigid steel projectile used to apply two dropping-weights of 150 kg as an impact load. The height of the drop was 5 meters. To determine punching shear capacity and critical velocity of perforation, different codes used and compared with the experimental results. The results of the experiments revealed that slab shear properties have a significant impact on their general behavior. Strength slab with carbon sheet enhances the behavior of RC slabs under impact loads and increases shear punching capacity.

Development of data-driven prediction model for CFRP-steel bond strength by implementing ensemble learning algorithms

Bonding carbon fiber reinforced polymer (CFRP) laminates has been broadly utilized in steel structure rehabilitation. As for the final strengthened capacity, the bond strength between CFRP and steel usually plays a dominant role instead of the CFRP’s mechanical property. However, the bond behavior of the CFRP-steel (CS) interface is very complicated with various failure modes and consequently the bond strength is hard to estimate leading to the CFRP strengthened steel structure insecure. Under this circumstance, in order to accurately predict the bond strength of CS, efficient data-driven models were developed through implementing ensemble learning (EL) algorithms named by “gradient boosting decision tree (GBDT)” and “random forest (RF)” as two representative ones on a collected CS single-shear test database. These models’ performances on bond strength prediction were compared and also three representative machine learning algorithms “artificial neural network (ANN)”, “support vector machine (SVM)” and “classification and regression tree (CART)” are utilized for validating the necessity. The comparison results indicate that the model generated by the GBDT algorithm attains the best accuracy for CS interfacial bond strength prediction (R2 = 0.98) among the ensemble and machine learning algorithms. Through model explaning analysis, the mechanism behind the GBDT based prediction model was also carefully verified. After these tests and analyses, the GBDT based model was proved to have the potential to facilitate the design and evaluation of CFRP strengthened steel structures.

The role of broken fibres on crack migration into 0° surface plies in adhesively bonded carbon fibre composite joints

Crack migration into the composite in adhesively bonded joints can cause a major degradation of strength. This usually occurs via cracks in the surface plies, but this paper demonstrates that crack migration can occur in joints even with 0° surface plies. The role of surface treatment is investigated by comparing grit blasted and plasma surface treatment before the secondary bonding process. Unidirectional Double Cantilever Beam specimens and quasi-isotropic Double Lap Joints with surface 0° plies were tested. It was found that with grit blasted specimens, crack migration occurred due to broken fibres present on the composite surface. Plasma treated specimens with no broken fibres on the surface failed in the adhesive with substantial increases in the Mode I fracture toughness and the strength of the double lap joints.

Shear strengthening of RC beams using NSM CFRP bonded using cement-based adhesive

The shear strength of existing Reinforced concrete (RC) members can be improved by bonding Carbon fibre reinforced polymers (CFRPs) as Near-surface mounted (NSM) or Externally bonded reinforcement (EBR). CFRPs are typically bonded to RC members using epoxy resins which have low glass transition temperatures resulting in poor fire performance. In an effort to improve the fire performance of CFRP strengthened members, researchers have developed Cement-based adhesives (CBAs) and verified their efficacy using NSM CFRP-to-concrete joint tests, however no applications have been conducted on full-scale RC beams strengthened in shear using NSM CFRP and CBA. This study attempts to fill this gap and involves testing fourteen RC beams strengthened in shear using NSM CFRP textile bonded using CBA. The experimental results showed that CFRP textile bonded using CBA in NSM configurations significantly improved the shear capacity of the RC members. Further, comparisons were made between CBA and epoxy resins as bonding agents and it was found that CBA achieved comparable results to epoxy when used in the configuration explored. The results of NSM-CFRP strengthened beams with CBA showed shear strength improvements of 97% and 70% using CFRP textile and laminate, respectively. Therefore, the use of CBA in the NSM CFRP strengthening techniques is considered a good substitute for epoxy resins for bonding CFRP to concrete members.

Standardised quantification of structural efficiency of hybrid reinforcement systems for developing concrete composites

Various types of materials and technologies have been developed either for reinforcing or strengthening concrete structures. However, there is no uniform methodology to quantify and compare the mechanical characteristics of different reinforcement systems. Residual stiffness of flexural elements is the suggested measure of the reinforcement’s structural effectiveness, involving concrete into composite action. This manuscript proposes a new testing layout designed to form multiple cracks in a small laboratory specimen and a simplified analytical approach to quantifying the flexural stiffness of the standardised test samples. The achieved analytical solution to the stiffness problem requires neither iterative calculations nor the loading history description. That makes it acceptable for quantifying and comparing the residual stiffness of elements with various combinations of reinforcement materials. The proposed analysis procedure also enables determining the mechanical performance decay under repeated and long-term loading conditions without a loss of the calculation adequacy. Flexural tests illustrate the application of the proposed technique—the 38 specimens were mechanically loaded until failure. Several composite reinforcement schemes, including steel and glass fibre reinforced polymer (GFRP) bars, externally bonded carbon fibre (CF) sheets, and near-surface mounted (NSM) carbon fibre reinforced polymer (CFRP) strips in various combinations, are considered. The analysis reveals an exceptional efficiency of hybrid reinforcement systems, combining steel and CFRP components.

Influence of concrete compressive strength on the debonding failure of externally bonded carbon fiber reinforced polymers

Influence of concrete compressive strength on the debonding failure of externally bonded carbon fiber reinforced polymers

Cyclic Loading Behaviour of Externally Bonded CFRP Reinforced Concrete Beam-Column Joint

Cyclic loading behaviour of RC beam-column joints strengthened with externally bonded Carbon Fiber Reinforced Plastic (CFRP) was analysed through Abaqus CAE software. Effect of the number of CFRP layers and the strengthening technique on failure modes, hysteretic curves, skeleton curves, ductility, and energy dissipation capacity were studied. The results show that the strengthening of RC beam-column joints by externally bonded CFRP can effectively improve the cyclic loading behaviour. Strengthening the joint by fiber bands enhances ductility and energy absorption capacity. The increase in the number of CFRP layers leads to enhance energy absorption capacity significantly as compared to ductility.

Shear Strengthening of Reinforced Concrete T-Beams with Anchored CFRP Laminates

Abstract Strengthening of existing reinforced concrete (RC) structures by externally bonding carbon fiber–reinforced polymers (CFRP) applied to the concrete substrate has proven to be effective in ...

Interlaminar Strength Analysis of Bonded Carbon Fiber Rods

Interlaminar failure of bonded composite structures is quite often. Nowadays there is a lot of lightweight high reliability carbon or glass fiber (CFRP or GFRP) reinforced polymer composite constructions with bonded carbon or glass fiber rods. In order to better understand the delamination processes of the rods, analytical equations were analyzed. Later, mode I interlaminar failure experiments with CFRP rods 3x3 mm were performed and fracture toughness GIC = 135 J/m2 was found. According to the analytic equations, experiment and values, given literature, finite element model (FEM) of the bonded carbon fiber rods was created in software LS-Dyna. Most of the differences between experimental and simulated force-displacement curves are not higher than 6 % what validates the FEM of the bonded CFRP rods. Also, additional methods, such as peridynamics of the bond area of the rods were analyzed. Offered finite element approach of the bonded CFRP rods is very useful for FEM creation to design and evaluate high reliability CFRP or GFRP constructions.

Stress Intensity Factor Assessment for the Reinforcement of Cracked Steel Plates Using Prestressed or Non-Prestressed Adhesively Bonded CFRP.

The use of adhesively bonded carbon fiber reinforced polymer (CFRP) materials to reinforce cracked steel elements has gained widespread acceptance in order to extend the lifespan of metallic structures. This allows an important reduction of the stress intensity factor (SIF) at the crack tip and thus a significant increase of the fatigue life. This paper deals with the assessment of the SIF for repaired cracked steel plates, using semi-empirical analysis and finite element analysis. Metallic plates with only one crack originating from a center hole were investigated. Virtual crack closure technique (VCCT) was used to define and evaluate the stress intensity factor at crack tip. The obtained modeling results are compared with experimental investigations led by the authors for different reinforcement configurations including symmetrical and non-symmetrical reinforcement, normal modulus and ultra-high-modulus CFRP plates, and pre-stressed CFRP plates. Results show that finite element model (FEM) analysis can obviously simulate the fatigue performance of the CFRP bonded steel plates with different reinforcement configurations. Moreover, a parametric analysis of the influence of the pre-stressing level was also conducted. The results show that an increase of the pre-stressing level results in an increase of the fatigue life of the element.