Carbon Fiber Reinforced Polymer Concrete Research Articles

Nonlinear Finite Element Analyses of Prestressed Concrete Beams Strengthened with CFRP Laminate

Nonlinear finite-element (FE)-based quasi-static and vibration analyses of prestressed concrete beams with carbon fiber-reinforced polymer (CFRP) laminate are conducted. To establish nonlinearities in concrete and prestressing steel material properties and concrete–steel interfaces in FE modeling, numerical models of reinforced concrete (RC) and prestressed concrete (PSC) beams are developed, and their response is assessed with experimental results. The established FE model is then extended so as accurately to model CFRP laminate and the nonlinear interaction at concrete–CFRP interfaces between RC and PSC beams. Cohesive interface elements capable of showing delamination failure are introduced to model the adhesion between a concrete beam and the CFRP laminate at its soffit. Ignoring such interaction overestimates the load-carrying capacity of the beam apart from its inability to capture the delamination. The effect of the prestressing force, location and profile of prestressing tendons on the modal frequencies of unstrengthened and CFRP-strengthened beams is studied. Strengthened beams have higher fundamental frequencies, and their modal frequencies are independent of prestressing force, varying significantly with the location and profile of tendons.

Strain-hardening fiber reinforced polymer concrete with a low carbon footprint

Epoxy resin, fly ash, and silica sand were used to produce polymer concrete reinforced with glass, carbon, polyvinyl alcohol (PVA), and high strength steel micro-fibers. The effects of two resin contents: 15% and 18%, and two curing regimes: ambient and heat were assessed. Their compressive strength, permeable porosity, and uniaxial tensile stress–strain behavior were studied. The compressive strength of 15% and 18% polymer concrete were 48–62 MPa and 61–74 MPa respectively. The porosity of all types of polymer concretes was less than 1%, except 15%-PVA and 15%-glass fiber reinforced polymer concrete. Under uniaxial tensile loading, glass and carbon fiber reinforced polymer concrete portrayed a sudden brittle failure resulting from complete fiber rupture, whereas PVA and steel fiber reinforced polymer concrete demonstrated a ductile strain-hardening response. A significantly higher tensile strength was observed when the resin content was increased from 15% to 18%, particularly for glass and carbon fiber reinforced polymer concrete, whereas for PVA and steel fiber reinforced polymer concrete this improvement was small. The brittle carbon fiber reinforced polymer concrete demonstrated the highest tensile strength, whereas the ductile steel fiber reinforced polymer concrete had the highest post-crack residual strength at large strains, irrespective of the resin content. Overall, heat curing had no impact on compressive or tensile properties of any type of polymer concrete investigated.

Numerical Modeling of Response of CFRP–Concrete Interfaces Subjected to Fatigue Loading

For interfaces between externally bonded fiber-reinforced polymer (FRP) laminates and concrete, the incremental fatigue analysis for each load cycle using a finite-element (FE) model is exceptionally time-consuming. This study introduces an accurate and efficient numerical approach that accounts for the bond–slip effect under fatigue loading. A preload cycle was adopted to model the damage caused by the previous load cycles. The formulae for the upper limit of the preload and the unloading stiffness in the local bond–slip model were established. The reloading and unloading stiffnesses in the bond–slip model for an arbitrary load cycle were defined. Moreover, different bond–slip models were adopted for a numerical analysis to compare the effect of the bond–slip relations on the fatigue response of a carbon FRP (CFRP)-strengthened concrete structure. The comparisons between the numerical results and the experimental data show that the proposed approach is capable of accurately predicting the fatigue response of CFRP-strengthened structures. The debonding process of the CFRP plate from the concrete surface under fatigue loading can be predicted by the proposed model. Compared with the existing bond–slip models, the proposed model in this study is more effective in predicting the mechanical response of the CFRP-to-concrete interfaces subjected to fatigue loading.

Flexural Performance of Reinforced Concrete Beams Strengthened with Carbon Fiber-Reinforced Polymer (CFRP) under Hygrothermal Environment Considering the Influence of CFRP–Concrete Interface

As an important component, the bond behavior of carbon fiber-reinforced polymer (CFRP)–concrete interface for a reinforced concrete (RC) beam is very significant. In this study, a theoretical model was established to analyze the flexural behavior of CFRP-strengthened RC beams, and the CFRP–concrete interfacial bond–slip relationship under hygrothermal environment was unified into one model. Two failure criteria corresponding to two types of failure modes, i.e., concrete crushing and intermediate crack (IC)-induced debonding, were developed. Through the theoretical model, the flexural behavior of deflection, interfacial shear stress distribution and ultimate load of a CFRP-strengthened RC beam under hygrothermal environment were obtained and predicted. Moreover, the theoretical model was verified by test results. The results showed that the hygrothermal environment had a significant impact on the CFRP–concrete interface behavior. Compared with the control beam without hygrothermal environment pretreatment, the deflection and ultimate load of the strengthened RC beam decreased by 51.9% and 20%, respectively.

An Anchoring Groove Technique to Enhance the Bond Behavior between Heat-Damaged Concrete and CFRP Composites

This experimental study was conducted to evaluate the effectiveness of using carbon fiber-reinforced polymer (CFRP) composites with special anchoring grooves, specifically in terms of the ability of the concrete–CFRP bond to withstand elevated temperatures. The obtained findings of this experiment clearly highlighted the effectiveness of the direction of the anchoring grooves on the behavior of the concrete–CFRP bonding area. The results also showed that high temperatures lessen the bond’s strength and the ultimate slippage. On the other hand, this study showed that increasing the length of the CFRP sheet resulted in enhancement of the bond’s strength and slippage. When exposed to temperatures above 500 °C, the structures’ residual splitting and compression strength decreased significantly, resulting in the bond’s strength reducing to 67% and the slippage to 19%, with respect to the control samples. In the non-grooved and vertically grooved beams, the CFRP–concrete bond showed a skin-peeling type of failure. It appeared, also, that the temperature and the number of anchored grooves significantly affected the bonding area of the surface; as the surface was exposed to failure in adhesion, more concrete remained attached to the CFRP composite, signifying a stronger attachment.

Dynamic compressive mechanical properties of carbon fiber-reinforced polymer concrete with different polymer-cement ratios at high strain rates

This study experimentally examined the effect of redispersible polymer emulsion powder on dynamic compressive properties of carbon fiber-reinforced polymer concrete (CFRPC). Impact experiments of CFRPC cylindrical specimens (100 mm diameter, 50 mm height) with 0.2% carbon fiber (volume ratio of carbon fiber to concrete) to 0%, 4%, 8% and 12% polymer-cement ratios (mass ratios) were done using a Φ100 mm Split Hopkinson pressure bar. The effects of emulsion powder on CFRPC were analyzed in terms of the dynamic compressive strength, deformation and toughness of the specimens. We find that at the same strain rate, the dynamic compressive strength of CFRPC initially increases and then falls with increasing polymer content. The dynamic compressive strength of the sample is highest when the polymer-cement ratio is 4%, and reaches up to 21.47–26.58%. The compressive strength and peak strain of CFRPC have obvious strain rate sensitivity. An appropriate amount of polymer can effectively improve the dynamic compression performance of CFRPC. Sample fragmentation and porosity analyses show that increasing the polymer-cement ratio reduces the number of pores in the concrete matrix, attaining a more optimal pore distribution and improved compactness.

Mechanical Properties of Carbon Fiber-Reinforced Polymer Concrete with Different Polymer-Cement Ratios.

To study the effect of redispersible polymer emulsion powder on the mechanical properties of carbon fiber-reinforced polymer concrete (CFRPC), the compressive, flexural, and splitting tests of CFRPC specimens with different polymer–cement ratios (polymer–cement mass ratios) were performed in this study. The modification effect of emulsion powder on CFRPC was analyzed from the perspectives of the strength and deformation properties of the specimens. The results show that the static properties of CFRPC increased first and then decreased with the increase of the polymer–cement ratio, in which the splitting tensile strength had the most significant increase; the flexural strength took second place and the compressive strength had a slight increase. When the polymer–cement ratio was 8%, the flexural and splitting tensile strength of the CFRPC specimens increased significantly by 36% and 61%, respectively. According to electron microscopy images, adding emulsion powder can effectively improve the structure of fiber–matrix transition zones and enhance the bond property between fibers and the matrix.

Integrity of CFRP–Concrete Interface in Sulfuric Acid

AbstractThis paper presents the interfacial behavior and deterioration mechanisms of carbon fiber–reinforced polymer (CFRP) sheets bonded to a concrete substrate subjected to sulfuric acid based on...

Carbon Fiber-Reinforced Polymer Concrete Masonry Unit Bond after 20 Years of Outdoor Exposure

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Bond Behavior of Wet-Bonded Carbon Fiber-Reinforced Polymer-Concrete Interface Subjected to Moisture

The use of carbon fiber-reinforced polymer (CFRP) composite materials to strengthen concrete structures has become popular in coastal regions with high humidity levels. However, many concrete structures in these places remain wet as a result of tides and wave-splashing, so they cannot be completely dried before repair. Therefore, it is vital to investigate the effects of moisture on the initial and long-term bond behavior between CFRP and wet concrete. This research assesses the effects of moisture (i) during CFRP application and (ii) throughout the service life. Before CFRP bonding, the concrete blocks are preconditioned with a water content of 4.73% (termed “wet-bonding”). Three different epoxy resins are applied to study the bond performance of the CFRP-concrete interface when subjected to moisture (95% relative humidity). A total of 45 double-lap shear specimens were tested at the beginning of exposure and again after 1, 3, 6, and 12 months. All specimens with normal epoxy resins exhibited adhesive failure. The failure mode of specimens with hydrophobic epoxy resin changed from cohesive failure to mixed cohesive/adhesive failure and to adhesive failure according to the duration of exposure. Under moisture conditioning, the maximum shear stress (τmax) and corresponding slip (smax) of the bond-slip curve first increased and then decreased or fluctuated over time. The same tendency was seen in the ultimate strain transmitted to the CFRP sheet, the interfacial fracture energy (Gf), and the ultimate load (Pu). Analytical models of Gf and Pu for the CFRP-concrete interface under moisture conditioning are presented.

Thermomechanical Behavior of Near-Surface-Mounted Carbon Fiber-Reinforced Polymer Concrete Interface

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Fracture Properties of CFRP–Concrete Bond Subjected to Three Environmental Conditions

AbstractThis paper presents results of a series of single shear tests of carbon fiber–reinforced polymer (CFRP) bonded concrete prisms exposed to three environmental conditions, namely, temperature cycles, wet-dry cycles, and outdoor environment, in terms of shear stress-slip relationships and fracture energies. Temperature cycles and wet-dry cycles were chosen in a manner to study the sole effects of temperature cycles and wet-dry cycles. The maximum temperature of the temperature cycles was intentionally kept below the glass transition temperature of epoxy resin. In the wet-dry cycles, specimens were exposed to varying humidity while temperatures close to ambient were maintained. Also, outdoor environmental exposure was applied to address the lack of test data on natural aging of FRP-concrete bond system. All the environmental conditions were applied for extended durations (the maximum duration of 18 months). Single shear tests (pullout test) were conducted to investigate maximum normal stress developed...

Investigation of mechanical/dynamic properties of carbon fiber reinforced polymer concrete for low noise railway slab

In this paper, the mechanical/dynamic property of the carbon fiber reinforced polymer concrete (CFRPC) was investigated to reduce the vibration/noise problems on rail slab. The CFRPC was fabricated with the different weight fraction of carbon fiber and different fiber length. The oxygen plasma treatment was performed to enhance the adhesion between the carbon fiber and epoxy resin. The surface of the carbon fiber with the oxygen plasma treatment was characterized using X-ray photoelectron spectroscopy (XPS) analysis and scanning electron microscope (SEM). The flexural strength of the CFRPC was measured using 3-point bending test. Also, the frequency dependent variation of the stiffness and damping of the CFRPC were measured by impact test to characterize their ability to reduce the vibration. In this study, the CFRPC with 12mm of optimal fiber length and 2wt% of the optimal fiber content showed 25.12MPa flexural strength and 0.01954 damping value. Finally, it was found that the noise level of the railway using CFRPC sleeper was decreased by 4dB compared to that using the polymer concrete sleeper, from the impact test of the scaled model of the railway structure.

Durability of the Bond between CFRP Plates and Concrete Exposed to Harsh Environments

AbstractStrengthening and retrofitting structural members using carbon fiber reinforced polymer (CFRP) materials has gained wide acceptance in the civil engineering community because of their superior mechanical properties, light weight, corrosion resistance, and ease of use. Numerous structural reinforced concrete (RC) members have been strengthened with externally-bonded CFRP plates using epoxy adhesives that produce an increase in their load-carrying capacities. However, there are some uncertainties regarding the durability of the bond between the concrete and FRP interfaces when subjected to severe environmental exposure. Most strengthening applications are exposed to outdoor conditions and hence durability under aggressive environments must be considered. This is the subject of this investigation. Several CFRP-concrete prisms have been subjected to several sets of environmental exposure conditions and preloaded with 3 and 5 kN of sustained loading, amounting to approximately 15 and 25% of ultimate lo...

Forming process and damping properties of carbon fiber-reinforced polymer concrete

Carbon fiber-reinforced polymer concrete has good damping property that can be used to produce machine tool beds, spindle boxes, and some other basic mechanical components in order to better satisfy the requirement of high-speed and high-precision machining accuracy. In order to get the influence of different components, the damping model is built on the basis of energy dissipation theory and the damping loss factor is defined as a new parameter to characterize the damping property. Typical samples are prepared and single factor experiments of fiber length, fiber dosage, coal ash’s usage, and different surface treatment of carbon fibers are used to validate the aforementioned assumptions. Research results show that the coal ash used in carbon fiber-reinforced polymer concrete plays an important role in enhancing damping. A weak interface bonding condition can get a better damping performance than a strong one. The best damping performance is consistent with reasonable fiber length and its dosage.

Forming Process and Mechanical Properties of Fiber Reinforced Polymer Concrete for Elementary Machine Parts

For the good vibration alleviating properties, polymer concrete (PC) has attracted much attention in the field of elementary machine components. In order to get more excellent mechanical properties, the forming process and mechanical properties of PC were concerned. In this research, glass fiber and carbon fiber were applied to improve the mechanical properties of PC. A series of PC and fiber reinforced polymer conctete (FRPC) specimens were prepared basing on the orthogonal tables for property test. Compression strength test was carried out. It is obvious that FRPC is better than PC as far as compression strength is concerned, and carbon fiber reinforced polymer concrete (CFRPC) is better than glass fiber reinforced polymer concrete (GFRPC). Trend curves about the relationship between fiber length and compression strength, as well as that between fiber dosage and compression strength were drawn. Relationship between the considered factors and compression strength is analyzed basing on the experiment results and the trend curves. Strengthening fibers would bear most of the internal stress when the specimen is faced to outer loads. Thus, FRPC has much better properties than PC. Mechanical properties of CFRPC are relatively better than that of GFRPC, for the strength of carbon fiber is better than that of glass fiber. It could be concluded that glass fiber is the proper strengthening fiber for PC considering both technical and economical factors.

Forming process and mechanical properties of fibers-reinforced polymer concrete

For good vibration alleviating properties, polymer concrete has attracted much attention in the field of elementary machine components. In this article, glass fiber and carbon fiber were applied to improve the mechanical properties of polymer concrete. Seen from the experimental results, as far as compression strength is concerned, fiber-reinforced polymer concrete is better than polymer concrete, and carbon fiber-reinforced polymer concrete is better than glass fiber reinforced polymer concrete. However, considering both technical and economical factors, it could be concluded that glass fiber is the proper strengthening fiber for polymer concrete.

A Study on Carbon Fiber Influence to Rebar Corrosion in Concrete

Rebar corrosion test of Carbon Fiber Reinforced Polymer (CFRP) concrete was did. Carbon fiber in concrete improved the compression strength of the concrete, but width and number of concrete cracks was not reduced, carbon fiber has not obvious act for improving concrete corrosion crack behavior. CFRP concrete Corrosion potential was a little high than common concrete, carbon fiber has not obvious act for improving concrete behavior in protecting steel beyond corrosion. The porosity of the carbon fiber reinforced polymer concrete was twice of the common concrete, carbon fiber added to concrete lead to increase porosity and maybe decrease concrete behavior in protecting the embedded steel in corrosion.

Numerical Investigation of Creep Effects on FRP-Strengthened RC Beams

Numerical analysis using a finite-element model was performed to simulate and investigate the long-term behavior of two RC beams with similar steel reinforcement, cast from the same batch of concrete. One beam was a plain RC beam and the other beam was strengthened using carbon fiber-reinforced polymer (FRP) strips. The deflections of both beams have been monitored for 5 years after loading. The finite-element model included both creep of concrete and viscoelasticity of the epoxy adhesive at the concrete-carbon FRP (CFRP) interface. The results of the finite-element analysis are compared to experimental observations of the two beams. The finite-element analysis was found to be able to simulate the long-term behavior of the CFRP-strengthened beam and help us understand the complex changes in the stress state that occur over time.

Shear Friction Capacity of Concrete with External Carbon FRP Strips

Carbon Fiber Reinforced Polymer (CFRP) composite strips were used to strengthen concrete externally at a known failure plane to resist shear friction. The uncracked push-off specimens were externally reinforced with CFRP composites using a reinforcement ratio ranging from 0.3 to 1.2%. The shear friction capacity of plain concrete without steel reinforcement was increased 1.32–3.25 times, and was found to be a function of the shear-to-normal stress ratio. The shear friction strength ranged from 0.17fc′ to 0.27fc′ for the reinforcement ratios studied. Tests with various wrapping schemes showed no evidence that additional shear friction capacity could be developed for a four-sided scheme compared to a two-sided scheme. The shear friction strength of the initially uncracked connections was found using experimental results, which combine the shear friction contribution of concrete and that of concrete–CFRP interaction, similar to current practice for internal steel reinforcement.