Carbon Fiber Reinforced Polymer Rods Research Articles

Shared CFRP activation anchoring method applied to NSMR strengthening of RC beams

The paper presents a novel strengthening system, which provide a shared carbon fiber reinforced polymer (CFRP) Near surface mounted reinforcement (NSMR) activation anchoring method. Nine T-section reinforced concrete (RC) beams were used in the testing scheme which contained both un-activated and activated strengthening configurations. The activated system applied a stress of 50% and 70% of the recommended ultimate capacity (2200 MPa) to a 8 mm CFRP rod. It was seen that, what seemed to be, the ultimate capacity of the CFRP rod (3300 MPa) was reached when using the activated anchoring method. A stable failure seemed to occur at this level with controlled cracking. The 50% activation provided IC-debonding as the ultimate failure mode, with an ultimate stress of approximately 3100 MPa. The shared activation method worked well, and no premature failures were experienced in the anchor system and adhesive interface between the CFRP NSMR system and the concrete substrate. A good correlation was found in the comparison of theory and test results, where following four stages were investigated: 1) initial strain of the activated NSMR CFRP bar, 2) transition zone between the un-cracked and linear elastic cracked state, 3) change from linear elastic cracked state to steel yielding and finally 4) failure.

Experimental study of Z-pin fatigue; understanding of mode I and II coupon behaviour

Insertion of carbon fibre reinforced polymer rods (Z-pins), is an effective method for the through-thickness reinforcement (TTR) of laminated composites. Whilst Z-pins are primarily used to mitigate delamination under quasi-static loading and/or impact events, the effectiveness of TTR following long-term exposure to cyclic loads still needs to be properly understood. This paper aims to fill the aforementioned knowledge gap by addressing the effect of fatigue on the Z-pins themselves, both in mode I and mode II regimes. The fatigue tests considered here are carried out on single Z-pin coupons, as well as Double-Cantilever-Beam (DCB) and End-Loaded-Split (ELS) specimens. The results indicate that, for relatively small cyclic displacements, Z-pins tolerate fatigue well, exhibiting good residual performance post-fatigue. However, increasing the amplitude of the fatigue loads damages the Z-pins and, hence, it tends to reduce the TTR residual ability to mitigate delamination under further quasi-static or impact loading.

Fatigue behavior of prefatigued reinforced concrete beams rehabilitated with near surface mounted carbon fiber reinforced polymer reinforcement

AbstractThis paper investigates the influence of cyclic preloading on the fatigue behavior of reinforced concrete (RC) beams rehabilitated with near surface mounted (NSM) carbon fiber reinforced polymer (CFRP) reinforcement. The study includes eight RC beams with dimensions of 152.4 × 152.4 × 1,521 mm. Strengthened and nonstrengthened specimens were tested under monotonic loading to obtain the flexural static capacity. Two strengthened specimens were tested as a reference under constant amplitude cyclic stress without prefatiguing. Four nonrehabilitated RC beams were prefatigued to simulate service loading conditions. Later, these RC beams were rehabilitated with NSM CFRP reinforcement and tested under the same cyclic stress range of the reference specimens. Mid‐span deflection, strain of tension steel rebars and CFRP rods, stiffness degradation, and energy dissipation were analyzed and evaluated. Experimental results show that the rehabilitated prefatigued RC beams had similar stiffness degradation and failure modes to the reference strengthened RC beams. The rehabilitated RC beams had an improvement in the fatigue responses when compared to the reference strengthened RC beams. Moreover, the postfatigue monotonic behavior of the rehabilitated RC beams showed an increase in the elastic modulus and a decrease in ductility.

Experimental investigation on the ball burnishing of carbon fiber reinforced polymer

ABSTRACTThe polymer-based materials are generally used in all industrial applications. Even if polymer bars can be machined easily, they need surface finishing treatment after the machining process. The ductile properties make coarse roughness on the surface that causes the elastic structure of polymer materials. The carbon fiber reinforced composite materials differ from polymer-based materials by high strength and stiffness. Its structure exhibits similar performances such as metallic materials. The effect of ball burnishing on the surface quality of rod workpiece was investigated in this study. To enhance the surface quality of high strength carbon fiber reinforced polymer rod workpiece, burnishing process was performed in three different parameters (force, feed rate, number of passes) and under four different mediums (dry, wet, boron oil, and mineral oil) conditions. The results of the experiments were analyzed, and optimum burnishing parameters were determined and discussed in detail. The best surface roughness value of the CFRP material used in the experiments was obtained as burnishing force: 250 N, feed rate: 0.05 mm/rev, four passes and wet medium. According to the results of variance analysis, it was found that the CFRP workpiece is the important leading factor for surface roughness with a contribution ratio of 62.47%.

Behavior of reinforced concrete beams strengthened with CFRP rod panels CRP 195

This paper investigates the behavior of reinforced concrete beams strengthened in flexure using externally bonded carbon fiber reinforced polymer (CFRP) rod panels (CRPs) fabricated using 4 mm rods spaced at 9.5 mm. The experimental program consisted of a control beam and three beams strengthened with either a continuous CRP, a spliced CRP with two half-length CRPs spliced through a 150 mm finger joint, or a spliced and end-anchored CRP. Spliced panel performed similar to the continuous one, with no debonding observed at finger joint. They resulted in a comparable strength increase relative to the non-strengthened control beam of 95 and 104%, respectively, and failed by concrete cover separation (CCS) at CRP end. When the spliced CRP was end-anchored, the increase in strength was 195% relative to the control beam, with the finger-joint still intact, and the failure mode changed to intermediate crack-induced debonding (ICID). The analytical model, developed from sectional analysis and strength models for debonding failures, is capable of predicting the load-deflection response and ultimate loads, including the two observed debonding failures. For CCS failure, two models are presented, one is based on the concrete tooth model, and the other on the shear capacity model. The ICID failure was based on limiting the CFRP strain in accordance with ACI 440.2R-17 design guide. Results showed a good correlation between analytical predictions and test data.

Experimental study on RC beams strengthened with CFRP rod panels

Externally bonded (EB) fiber reinforced polymer (FRP) laminates and fabrics have become a mainstream method for retrofitting and upgrading concrete structures. Nevertheless, when strengthening long-span members or members with limited access, labor, traffic, and equipment demands may hinder the use of continuous EB FRP. The use of carbon FRP (CFRP) rod panels is a recent application of FRP material intended to overcome the above limitations. CFRP rod panels are developed from small diameter rods and are made continuous by means of a finger joint. This study leveraged four-point bending tests to determine whether spliced CFRP rod panels can effectively serve as flexural reinforcement for concrete members. Testing included a control beam and beams strengthened with the following FRP reinforcement layouts: (1) continuous rod panel, (2) spliced panel (two half-length panels with a 150 mm finger joint), (3) spliced panel anchored at ends with CFRP fabric, (4) continuous CFRP laminate, and (5) lap-spliced CFRP laminate system. Beams bonded with either continuous or spliced rod panels failed by concrete cover separation. The beam with spliced and anchored rod panel failed by intermediate crack-induced debonding of the panel. No local debonding or other signs of distress were observed at the finger joint for the two beams strengthened by spliced rod panels. For beams bonded with continuous and lap-spliced CFRP laminates, the failure was by laminate debonding. Compared to a control specimen, the maximum load increase of the strengthened beams was as follows: 112% for the continuous rod panel; 106% for spliced rod panel; 158% for the spliced/anchored rod panel; 49% for continuous laminate; and 31.8% for lap-spliced laminate.

Numerical study on the bond between CFRP rod panels (CRPs) and concrete

In this study, finite element (FE) models are developed to examine the interfacial behavior of a new retrofitting system comprised small diameter carbon fiber reinforced polymer (CFRP) rods spaced apart a distance larger than the rod diameter. The CFRP rod panel (CRP) is adhesively bonded to the concrete surface. The study explores several key parameters, including bond-slip (τ-δ) relation, effective bond length, rod diameter (D), and rod spacing-to-diameter (S/D) ratio. The models were validated against previous double-lap CRP-concrete block tests. A bilinear (τ-δ) model that provides a good correlation to the failure loads of the entire range of specimens was established. The effective bond length was found for two commonly used CRPs, and was 85 mm for one with D = 2 mm and S = 6.35 mm, and 115 mm for that with D = 4 mm and S = 9.50 mm. A parametric study using 20 FE models was carried out, considering four rod dimeters (1–4 mm) and five S/D ratios (2.2–3.18). It was found that although debonding failure consistently governs; decreasing (D) or increasing (S/D) ratio increases the ultimate strength. The effect of (S/D) ratio is more pronounced for D = 1 mm than other diameters. The study also found that debonding load of CRP is 51% higher than that of an externally bonded conventional CFRP plate of similar cross-sectional area and mechanical properties.

Finite element analysis of RC beams strengthened in flexure with CFRP rod panels

The carbon fiber reinforced polymer (CFRP) rod panel technique has recently been introduced as an efficient and economical retrofit option for concrete structures. In a previous study, an experimental testing was carried out on RC beams strengthened with several rod panel configurations (continuous, overlapped, and overlapped with fabric end-anchorage). The current study presents comprehensive FE models of the tested beams, developed to provide an in-depth examination of the rod panel and its interaction with the concrete substrate. The FE models considered different material models and presented methodologies for simulating the failure modes experienced in the tests [intermediate crack-induced debonding (ICID) and concrete cover separation (CCS)]. Various comparisons with the experiments, such as ultimate load, load mid-span deflection history, failure mode, demonstrated the validity the FE models. This study reported on vital data, such as tensile stress distribution in the rod panel, maximum interfacial shear and normal stresses at the panel-concrete interface, and location of maximum stresses. It was found that high shear stresses exist at the end of the continuous and overlapped rod panels, and high normal stresses at the edge of the rod finger joint. Wrapping the panel’s ends with fabrics resulted in reduction of end shear stresses and contributed to the prevention of CCS failure and the increase in the ultimate load. For field applications, the study recommends using the fabric wraps at the panel ends to prevent premature failures.

Carbon fiber–reinforced polymer rod panels for strengthening concrete bridges

The practice of using fiber-reinforced polymer laminates and fabric to repair and strengthen concrete structures is well established. What limits the application of fiber-reinforced polymer materials, especially in flexural strengthening, is the equipment and man power needed for continuous application when retrofits take place over waterways or multilane roadways. A carbon fiber–reinforced polymer rod panel system consisting of 1220-mm (48-in) panels made continuous through a finger joint/splice was developed to overcome these limitations. The system’s performance hinges on whether forces can be transferred from one panel to another. This study investigated the bond characteristics of carbon fiber–reinforced polymer rods, as well as the flexural behavior of concrete members strengthened with carbon fiber–reinforced polymer rod panels, to improve knowledge of the finger joint’s behavior. Bond tests were conducted using double-lap shear specimens on individual rods with both steel and concrete substrates. Further bond tests were performed on small carbon fiber–reinforced polymer rod panels on steel substrate. Flexural tests were carried out under four-point bending on small-scale reinforced concrete beams that were strengthened using continuous carbon fiber–reinforced polymer rod panels and carbon fiber–reinforced polymer rod panels spliced using a finger joint. Case studies of four field applications are presented to provide a better understanding of the system. The new carbon fiber–reinforced polymer rod panels effectively reduce labor and equipment costs for work conducted on bridges with limited access, as they enabled the performance of repair/retrofit operations by a small crew working out of a single work platform.

On acoustic emission for damage detection and failure prediction in fiber reinforced polymer rods using pattern recognition analysis

Fiber reinforced polymer (FRP) rods are used for pre-stressing and reinforcing in civil engineering applications. Damage in FRP rods can lead to sudden brittle failure, therefore, a reliable method that provides indicators of damage progression and potential failure in FRP rods is highly desirable. Acoustic emission (AE) signal analysis has been used for damage detection and monitoring of FRP materials. In this study, a new AE event detection algorithm, utilizing the root mean square envelope of AE signal, is applied to AE data to isolate each AE event separately, even when AE events are nearly coincident. A fuzzy c-means (FCM) clustering algorithm is used to classify these isolated AE events into 3 clusters. Scanning electron microscopy images of FRP rod cross-sections also show 3 types of damage. The hypothesis in this study is that each cluster represents a damage mechanism. The number of events in each cluster is monitored versus the percent of the ultimate load. The ratio of the number of AE events in one of the FCM clusters to the number of AE events in another FCM cluster was useful for providing an indication of when the stress levels have reached the point where the loads may cause the FRP rod to fail. The results of applying this parameter to four FRP rods show a significant slope change (factor of 10) in this ratio at around 40% and 60% of the ultimate load for glass FRP rods and carbon FRP rods, respectively. This method may prove useful in damage progression and failure prediction of the FRP rods in prefabricated structures where pre-stressed FRP is used and in field monitoring of FRP materials.

Ageing effect on the tensile behavior of pultruded CFRP rods

Pultruded rods of carbon fiber reinforced polymer (CFRP) are excellent alternative materials to steel tendons for the anchoring of deep-sea oil drilling floating platforms. However, the ageing of the rods for use as tension leg in platforms operating in harsh and unusual offshore conditions, and degradation mechanisms associated with these materials should be investigated. In this work, a systematic study was carried out aiming at evaluating how accelerated ageing affects the performance of pultruded CFRP rods, focusing on microstructure, tensile behavior, and thermal and chemical stability. CRFP rods with epoxy and with vinylester resins were evaluated. Rods were aged in hot distilled water, in hot seawater, and in UV radiation wheatherometer camera. Degradation was more severe in the vinyl-ester rods based on tensile strength and stiffness results. Deterioration of the fiber-matrix interface and consequent fiber debonding was the main failure mechanism. The vinyl-ester rods presented higher water uptake than the epoxy rods in both distilled water and seawater, and lower mechanical strength after exposed in the latter. In general, the epoxy resin CFRP rods were more resistant to the ageing processes evaluated.

Behavior of Tendons with Multiple CFRP Rods

AbstractResearch works related to the fiber-reinforced polymer (FRP) tendons have focused on the anchor system, but the anchor is not the only contribution to performance. Since civil structures require tendons consisting of multiple rods (e.g., cables, suspenders in bridges, or rock bolts in ground anchors), the characteristics of multirod tendons require targeted research. This paper presents a study on the behavior of tendons with multiple carbon FRP (CFRP) rods. Four specimens including two cable-type assemblies (TA12-9 and TA12-20) and two ground anchors (GA12-9 and GA12-20) with large-tonnage capacities were built and tested. Using strain gauges set along individual rods, the nonuniform force distribution among individual rods was observed and is discussed. The test results showed that nonuniformity is a recurring feature of a multirod tendon, with the variation in the initial length of the rods caused by installation error as its main reason. Based on the premise that tension in multiple rods obeys...

Charpy impact testing to assess the quality and durability of unidirectional CFRP rods

The most common mechanical test methods for assessing quality and durability of unidirectional fiber reinforced polymer (FRP) composites include uniaxial tension and short-beam shear (SBS) tests, which measure residual fiber-dominant and matrix-/interface-dominant strengths, respectively. Although commonly used to qualitatively evaluate fracture toughness in metals through energy absorbance, the Charpy impact test can also be used for FRP to qualitatively compare different materials or treatments. This study examines the Charpy impact test for assessing the manufacturing quality and environmental durability of unidirectional carbon FRP (CFRP) rods. The purpose is to evaluate this test for the rapid assessment of CFRP materials, compared to the more commonly used SBS test. Fractographic analysis supports the mechanical test results when correlating between test methods. Ultimately, results from the comparative impact testing demonstrated that the method induces similar failure modes as the SBS test, providing information to qualitatively compare between commercial products or conditioning effects.

Reinforced Concrete Beams Strengthened with NSM CFRP Rods in Shear

This experimental research aims to investigate the possibility of using Carbon Fiber-Reinforced Polymer (CFRP) rods to strengthen in shear concrete structural members with the Near Surface Mounted reinforcement (NSM) technique. Seven reinforced concrete beams were tested in flexure with or without traditional shear reinforcement. Carbon-epoxy pultruded FRP (CFRP) rods with 6 mm in diameter were used. The possibility of using a mortar as filling material with surface pre-conditioned CFRP rod is investigated and compared to resin performance. Results show that NSM technique is very efficient to strengthen reinforced concrete beam in shear. Using the resin instead of mortar as the filling material still increases the efficiency of the shear strengthening but the gain is only moderate. The experimental results are compared with existing analytical models.

Fatigue Bond Characteristics and Degradation of Near-Surface Mounted CFRP Rods and Strips in Concrete

AbstractThis study investigates the bond characteristics and degradation under fatigue loading of near-surface mounted (NSM) carbon-fiber-reinforced polymer (CFRP) rods and strips embedded in concrete. Thirty-six concrete block specimens (350×300×150 mm) were tested under single shear. Sinusoidal waveform fatigue loading with a range of 10–50% of the corresponding static bond strength was applied with the number of cycles varying from 0 to 10,000, which was then followed by static pullout test to determine the local bond-slip relationship between the NSM reinforcement and concrete. Two separate sets of specimens were also subjected to the same fatigue loading up to failure to obtain the corresponding fatigue life. It was found that specimens strengthened with NSM rods mostly failed due to the breakage of concrete and epoxy, while those with NSM strips all failed due to slippage of NSM reinforcements at a lower pullout strength after the fatigue cycles. For both types of reinforcement, as the number of fa...

A FEM-based model to study the behaviour of corroded RC beams shear-repaired by NSM CFRP rods technique

This paper presents the main features of a finite element FE numerical model developed using the computer code FEMIX to predict the contribution of near-surface mounted (NSM) carbon-fibre-reinforced polymer (CFRP) rods to the shear repair of corroded reinforced concrete RC beams. In the RC beams repaired in shear with the NSM technique, the CFRP rods are placed inside grooves pre-cut into the concrete cover of the RC beam’s lateral faces and are bonded to the concrete with high performance epoxy adhesive. Experimental and 3D numerical modelling results are presented here in terms of load–deflection curves and failure modes for 4 short corroded beams: two corroded beams (A1CL3-B and A1CL3-SB) and two control beams (A1T-B and A1T-SB), the beams noted B were repaired in bending only with NSM CFRP rods while those noted SB were repaired in both bending and shear with the NSM technique. The corrosion of the tensile steel bars and its effect on the shear capacity of the RC beams is discussed. Results show that the FE model is able to capture the main aspects of the experimental load–deflection curves of the RC beams. They also present the experimental failure modes and FE numerical modelling crack patterns, both of which gave similar results for non-shear repaired beams, which showed a diagonal tension mode of failure, and for shear-repaired beams, which failed due to a large flexural crack in the middle of the beams, along with the concrete crushing. Three-dimensional crack patterns were produced for shear-repaired beams in order to investigate the splitting cracks occurring at the middle of the beams and near the support.

Behaviour of corroded reinforced concrete beams repaired with NSM CFRP rods, experimental and finite element study

Abstract The near surface mounted reinforcement (NSM) technique is one of the promising techniques used nowadays to strengthen reinforced concrete RC structures. In the NSM technique, the Carbon Fibre Reinforced Polymer (CFRP) rods are placed inside pre-cut grooves and are bonded to the concrete with epoxy adhesive. This paper investigates corroded RC beams repaired with NSM CFRP rods and studies the failure mode of the repaired beam according to experimental and numerical modelling results. Experimental results and numerical modelling results of a 2D finite element (FE) model using the FEMIX computer code were obtained on five, 3-m-long beams: three corroded RC beams that had been exposed to natural corrosion for 25 years and two control beams with no corrosion. Two beams, one corroded and one control (A1CL3-R and A1T-R) were each repaired in bending with one 6-mm-diameter NSM CFRP rod and were then tested in three-point bending up to failure. The corrosion of the tensile steel bars and steel stirrups was studied. Ultimate capacity, yielding capacity and failure modes are also discussed. The experimental results showed that the NSM technique increased the overall capacity (ultimate load capacity and yielding capacity) of control and corroded beams despite a non-classical mode of failure with separation of the concrete cover occurring in the corroded beam due to damage induced by corrosion. The FE numerical modelling results from FEMIX were compatible with the experimental ones except for the repaired corroded beam A1CL3-R, for which a three-dimensional model using the commercial software ABAQUS was required. Finally some comparisons were made between the experimental and FE numerical modelling results obtained using ABAQUS in order to study the specific mode of failure of the corroded beam, which occurred by the separation of concrete cover.

Repair of reinforced concrete deep beams using post-tensioned CFRP rods

Abstract A repair method for reinforced concrete deep beams with external unbonded post-tensioned carbon fiber reinforced polymer (CFRP) rods is presented. Reinforced concrete deep beams in this research were pre-damaged to simulate reinforced concrete girder webs with diagonal cracks. Experimental data and analytical methods for predicting the ultimate capacity of reinforced concrete deep beams which include the effect of externally post-tensioned CFRP rods are examined. The ultimate load capacity of the repaired beams was increased compared to the nominal capacity of the control beam while the deflection capacity remained the same. Strut-and-tie models of the control and repaired reinforced concrete deep beams predicted the ultimate load capacity with reasonable accuracy. The strut-and-tie models were optimized to reduce the ratio of experimental to analytical ultimate load capacity.

Behaviour of corroded shear-critical reinforced concrete beams repaired with NSM CFRP rods

This paper discusses the results of an experimental program designed to investigate the effect of repairing the RC corroded shear-critical deep beams with near surface mounted (NSM) carbon fibre-reinforced polymer (CFRP) rods. A 28-year-old RC beam corroded by exposure to a chloride environment was cut into two small short-shear-span beams, along with a control beam of the same characteristics (age, length and cross-section). One RC corroded deep beam was repaired in bending and the other one was repaired in both bending and shear with NSM CFRP rods. Force–displacement curves were plotted for the corroded and control beams. After the beams had been tested up to failure, the loss of mass was measured and plotted for both the longitudinal and transverse reinforcement. The slip of tensile reinforcement at the end of the beams was also measured during the tests.Experimental results show that both corroded and control deep beams repaired only in bending failed due to shear mode of failure (diagonal tension failure), while corroded and control beams repaired in both bending and shear failed due to concrete crushing. The test results also showed that the corrosion of both longitudinal and transversal reinforcement hardly modified the mechanical response of deep beams.

CFRP Shear Strengthening of Reinforced-Concrete T-Beams with Corroded Shear Links

This paper investigates the structural behavior of uncorroded as well as corroded RC T-beams strengthened in shear with either externally bonded (EB) carbon fiber–reinforced polymer (CFRP) sheets or embedded CFRP rods. Nine tests were carried out on RC T-beams having an effective depth of 295 mm and a shear span to effective depth ratio of 3.05. The investigated parameters are the shear link corrosion level (uncorroded, 7% corroded, or 12% corroded) and type of CFRP strengthening system (EB CFRP sheets or embedded CFRP rods). The unstrengthened beams with shear link corrosion levels of 7 and 12% had shear strengths that were 11 and 14%, respectively, less than the shear strength of the uncorroded unstrengthened beam. Both the embedded CFRP rods and EB CFRP sheets were effective in enhancing the shear strength of tested beams but the effectiveness of both strengthening systems decreased with increasing shear link corrosion level. The shear strength enhancement provided by the embedded CFRP rods and EB CFRP sheets decreased from 19 and 15%, respectively, to 12 and 11%, respectively, with an increase in shear link corrosion level from 7 to 12%. Corrosion of the shear links did not have a significant effect on the beam stiffness. Premature debonding limited the effectiveness of the EB CFRP sheets whereas the embedded CFRP rods did not exhibit signs of debonding and therefore showed higher effectiveness.