Carbon Fabric Reinforced Cementitious Matrix Research Articles

Effect of anchorages on C-FRCM/concrete interfacial shear performance

In this study, single-lap shear tests were performed on 42 concrete specimens that were reinforced with Carbon Fabric Reinforced Cementitious Matrix (C-FRCM). The interfacial properties were enhanced through the use of fabric end-bending anchorage, a U-shaped hoop, and multiple U-shaped hoops. The bond performance of the C-FRCM/concrete interface was analyzed by examining the failure mode, ultimate stress, and interface slip of the specimens, considering four parameters: bond length of C-FRCM, number of fabric layers, fabric end-bending anchorage, and U-shaped hoop anchorage, as well as their respective mechanisms. The bond-slip constitutive parameters were calculated based on the trilinear cohesive material law and load-displacement simulation curves were obtained for each specimen through numerical simulation, which were in agreement with the test results, verifying the law's validity. Finally, the positive effect of anchorages on the constitutive parameters was analyzed.

Restoration of two-span RC beams with severely corroded reinforcement using C-FRCM composites

The feasibility and viability of using carbon fabric-reinforced cementitious matrix (C-FRCM) composites for restoration of continuous reinforced concrete (RC) beams with severely corroded reinforcement were examined. Five large-scale dual-span RC beams were fabricated and tested. One beam was not corroded to serve as a control. Four beams were subjected to accelerated corrosion that corresponded to a tensile steel cross-sectional loss of 40% in either the sagging or the hogging region. Such a steel cross-sectional loss would cause a comparable reduction in the yield load of bare steel reinforcing bars. Two of the corroded beams were repaired with C-FRCM composites. An analytical model was formulated and utilized to design the number of C-FRCM layers required to fully restore the original load capacity. Experimental results verified the redistribution of moments between the sagging and hogging regions due to yielding of the tensile steel at critical sections. Both sagging and hogging sections contributed to the load-bearing capacity, and hence, the reduction in the load capacity caused by corrosion in one of the critical sections was smaller than the tension steel cross-sectional loss caused by corrosion. It was possible to predict the load capacity of the tested beams with reasonable accuracy considering the residual cross-sectional area of the corroded tension steel bars while keeping their yield strength and Young’s modulus unaltered in addition to implementing other conventional assumptions adopted by international codes and guidelines. As predicted analytically and verified experimentally, rehabilitation of corroded continuous beams with appropriate number of C-FRCM composite layers fully restored their original load capacity. Research findings would assist practitioners in conducting a proper analysis of continuous RC beams with corroded reinforcement before and after repair with C-FRCM composites.

Experiments on shear behavior of reinforced concrete continuous beams strengthened by C‐FRCM

AbstractThe dual‐function retrofitting system that uses the carbon‐fabric reinforced cementitious matrix (C‐FRCM) as both the anode of impressed current cathodic protection (ICCP) system and the structural strengthening (SS) material, that is, an ICCP‐SS system, is investigated. The experimental program mainly focused on the shear behavior of C‐FRCM strengthened reinforced concrete (RC) continuous beam under the dual‐function retrofitting system. The influence of anode polarization on the shear strengthening of RC continuous beams is analyzed. Shear tests were conducted on a total of 14 corroded RC continuous beams to investigate the influence of key parameters, including anode polarization degree of prefabricated C‐FRCM plate, layer of carbon fiber mesh and side‐wrapping. The failure modes, shear capacities, and load‐deflection curves of the shear‐strengthened RC continuous beams are reported. Based on the test results, the applicability of relevant design codes was evaluated and found to provide rather conservative predictions for the shear capacity of the examined C‐FRCM strengthened RC continuous beams.

Flexural and cracking behavior of corroded RC continuous beams strengthened with energized C‐FRCM system

AbstractThis paper presents an experimental investigation into the flexural and cracking behavior of corroded reinforced concrete continuous beams with 11‐month wet–dry cycles strengthened by anodic polarized carbon‐fabric‐reinforced cementitious matrix (C‐FRCM) plates. The failure modes and flexural bearing capacities were discussed. The influences of the layer of carbon fabric mesh and complete carbon fiber‐reinforced polymer (CFRP) wrapping as end anchorage on the strengthening effectiveness were explored. The complete crack development patterns were captured by a digital image correlation system, and the results showed that the C‐FRCM system can provide satisfactory crack width control, as proved by the reduced crack spacing and the maximum crack width. The flexural capacities of the strengthened beams were effectively enhanced and the debonding failure can be eliminated through complete CFRP wrappings. Moreover, the design recommendations were proposed based on the estimation of the crack development as per related design guidelines.

Bond behavior between carbon fabric reinforced cementitious matrix (FRCM) composites with added short fibers and concrete substrates

Fabric reinforced cementitious matrix (FRCM) composites show an innovative solution for strengthening existing concrete structural elements to solve the drawbacks of organic resins in fiber-reinforced polymers (FRP) system. However, the brittle fracture of the cementitious matrix significantly reduces the efficiency of the fabric. Hence, the incorporation of short fibers into the matrix is proposed to increase the fabric efficiency. For externally bonded FRCM composites to structural element surfaces, it is a crucial issue to investigate the bond behavior at the fabric-matrix and matrix-substrate interfaces, where the effect of short fibers is non-negligible and requires further investigation. In this study, a single-lap direct shear test was used to investigate the bond behavior between carbon FRCM composites with added short fibers and concrete substrates. 36 specimens were tested and discussed by considering the effects of bond length, volume content of short fibers, type of short fibers, and bond width. The experimental results were discussed in terms of failure mode, load-slip curve, and characteristic parameters. Subsequently, the contribution of weft yarns was studied and accounted for in the developed bond-slip model, which additionally takes into account the effects of the volume content of the short fibers, the type of short fibers, and the bond width.

Influence of severe thermal preconditioning on the bond between carbon FRCM and masonry substrate: Effect of textile pre-impregnation

Fabric-reinforced cementitious matrix (FRCM) composites often include polymer-impregnated bundles to improve the exploitation of the textile mechanical properties. However, organic components may degrade when exposed to elevated temperature. In this paper, the bond behavior of a carbon FRCM applied to a masonry substrate and exposed to a thermal preconditioning up to 300 °C for 250 min is investigated. Tensile tests on the textile and flexural and compression tests on the mortar matrix, as well as single-lap direct shear tests of FRCM-masonry joints with bare and impregnated textiles, are performed. Results show that the polymeric impregnation improves the mechanical properties of the FRCM even after thermal preconditioning.

Tensile properties of carbon fabric-reinforced cementitious matrix (FRCM) at high temperatures

Despite many advantages of externally bonded FRP systems, the rapid loss of strength at high temperatures is a concern for fire scenarios. Fabric-reinforced cementitious matrix (FRCM) is deemed to perform superior at high temperatures. In this study, 84 carbon FRCM coupons were tested in tension at temperatures from 25 to 400 °C using both steady-state and transient-state test protocols. The main parameters considered in this study are the number of fabric layers and FRCM thickness, fabric orientation, target temperatures, and heating protocol. Results showed that at room temperature, the ultimate strength and cracked elastic modulus decreased by about 18% to 20% when the number of layers was increased from one to three. At 400 °C, the ultimate strength and cracked elastic modulus were reduced by up to 60 to 70% of their original values. The bidirectional FRCM specimens presented a slightly higher elastic modulus and strength than unidirectional specimens in most tests. In transient-state tests and under the same sustained load level, the failure temperature of 30 mm-thick specimens were approximately 100 °C higher than 20 mm-thick specimens. The test results showed that the carbon FRCM composites tested in this study were able to resist non-negligible tensile forces at elevated temperatures although they are significantly reduced.

Experimental analysis of corroded RC continuous beams rehabilitated by ICCP-SS under unsymmetrical loading

In this study, a total of 14 corroded reinforced concrete (RC) continuous beams rehabilitated by a dual function system—Impressed Current Cathodic Protection-Structural Strengthening (ICCP-SS) with carbon-fabric reinforced cementitious matrix (C-FRCM), were tested under in-plane bending (resulted from unsymmetrical loading) to investigate the influences of corrosion rate, layer of carbon fabric mesh, complete wrapping as the end anchorage and loading scheme. The flexural behaviour including failure modes, load-carrying capacities, load-deflection curves and ductilities of the specimens were carefully studied. The design flexural strengths were calculated based on the current design guidelines, which were compared with the experimental results. It’s shown from the experimental data of five-point bending tests that beams strengthened with C-FRCM had higher yielding loads and ultimate loads than corroded beams without rehabilitation. However, the ductility of RC continuous beams was weakened by the C-FRCM strengthening method and its anodic polarization process, in particular for the specimens with more layers of carbon fabric meshes in prefabricated C-FRCM plates and complete wrapping as the end anchorage. Under unsymmetrical loading scheme, the delamination failure of concrete cover was observed and the application of complete wrappings was found to improve the ductility of the specimen. Comparison of the measured and predicted moment capacities showed that the current design guidelines generally underestimate the moment capacities of C-FRCM strengthened RC continuous beams, especially the specimens further strengthened by complete wrapping.

Bending behaviour of corroded RC continuous beams with C-FRCM strengthening system

This paper presents a numerical investigation into the bending behaviour of uncorroded and corroded reinforced concrete (RC) continuous beams with a strengthening system. Finite element analysis (FEA) was performed on ten RC beams considering interface performance, including five uncorroded and five corroded beams. The cracks development, bending capacities and load-displacement curves of the simulated RC beams in the loading process were validated against those from tests. Then, a parametric study including 35 RC beam models, considering the effects of carbon-fabric (CF) mesh layer, complete wrapping layer and the degree of corrosion of steel bar on their bending capacities, was conducted. Ductility and strengthening effects of specimens were discussed in the parametric study. It can be found that the carbon-fabric reinforced cementitious matrix (C-FRCM) strengthening system can improve the bending capacities of the corroded RC beams. As the layer of CF mesh increases, the ductility of the specimen decreases. The combined use of the C-FRCM plate and the complete wrapping as the end anchorage enhanced the ultimate loads of RC beams to a greater extent than those strengthened with C-FRCM plate only. The applicability of current design codes for RC beams with C-FRCM strengthening system was examined through comparisons of the bending capacity predictions of RC beams with those obtained from tests and numerical analyses. It was found that European Code (FIB Bulletin 14) provides more accurate predictions than American Specifications (ACI 549.4R-20, AC 434-0616-R1, ACI 440.2R-17) and Chinese Code (CECS 146–2003 (2007)). Therefore, design modifications based on the most accurate design rule of FIB Bulletin 14 were made. By utilizing regression analysis on the numerical results, the formula for bending capacities of the examined RC beams was proposed and showed improved accuracy.

Fabric-to-cementitious matrix bond behavior in carbon fabric reinforced cementitious matrix (FRCM) composites with added short fibers

Fabric reinforced cementitious matrix (FRCM) composites are promising composite materials with useful properties, such as non-toxicity, fire resistance, corrosion resistance, and vapor permeability. However, the brittle failure mode, fabric efficiency, and tensile strength of FRCM composites require further improvement. Accordingly, the addition of short fibers to the matrix is proposed to improve the mechanical properties of FRCM composites, which are highly influenced by the fabric-to-cementitious matrix bond behavior. The objective of this study is to investigate the fabric-to-cementitious matrix bond behavior in carbon FRCM composites with added short fibers and to propose a method to evaluate the bond parameters. In total, 75 pullout specimens were designed to investigate the effects of short fiber type, short fiber volume content, and embedded length on the fabric-to-cementitious matrix bond behavior using double-sided pullout tests. The experimental results were evaluated in terms of the peak pullout force, displacement at peak pullout force, toughness, average bond strength, and initial stiffness. A closed-form solution was presented for the pullout force-displacement relationship based on a trilinear bond-slip model that accounted for the contribution of weft yarn. Furthermore, a method for the analytical extraction of bond parameters was proposed using the main characteristics of the experimental pullout force-displacement responses.

Numerical study and seismic design of corroded circular RC columns strengthened by C-FRCM

This study aims to numerically investigate the behaviour of corroded circular reinforced concrete (RC) columns strengthened by carbon-fabric-reinforced cementitious matrix (C-FRCM) composites. Three-dimensional finite element (FE) models of the corroded circular RC columns with and without strengthening were set up and validated against previous experimental results. Based on the validated FE models, the parametric studies were carried out to investigate the effects of axial compression ratio, degree of corrosion and layer of carbon fabrics on the behaviour of corroded RC columns under cyclic loading. It shows that the lateral load resistance increased when the axial compression ratio ranged from 0.3 to 0.4, but decreased when the axial compression ratio ranged from 0.4 to 0.6; also the ductility of the corroded RC columns reduced with increasing axial compression ratio. The ultimate capacity of corroded RC columns decreased gradually with the increasing degree of corrosion. Based on the results of parametric studies, equations were developed to estimate the ultimate capacity and displacement of the corroded RC columns repaired by the C-FRCM. The proposed equations can well estimate the ultimate lateral load resisting capacity and ultimate displacement of the corroded circular RC columns strengthened by C-FRCM.

Fatigue testing of corroded RC continuous beams strengthened with polarized C-FRCM plate under ICCP-SS dual-function retrofitting system

The paper presents an experimental investigation into fatigue behaviour of corroded reinforced concrete (RC) continuous beams strengthened by carbon-fabric reinforced cementitious matrix (C-FRCM) under a typical dual-function retrofitting system. The retrofitting system adopted impressed current cathodic protection (ICCP) technique, which is an electro-chemical anti-corrosion technique for anodic polarization to reduce or prevent oxidation of metal, together with structural strengthening (SS) technique, which can effectively restore or improve the bearing capacity of the structure. In the experimental programme, a total of ten RC continuous beam specimens were tested under fatigue loading. The influence of key structural parameters on the fatigue life of the RC beams was examined, including the corrosion degree of the steel bar, fatigue load level, and charge density of C-FRCM plate. The calculation theory based on the transformed-section method for the cyclic stress amplitude of steel reinforcing bar in RC beam strengthened by C-FRCM plate was determined. On this basis, the S-N (cyclic stress amplitude versus cycles to failure) curves of the corroded RC continuous beams strengthened by polarized C-FRCM under the ICCP-SS dual-function retrofitting system were obtained by fitting the relevant fatigue data for fatigue design guidance.

Interface behaviour of carbon-fabric-reinforced cementitious matrix composites with ICCP technique

This paper studies the interface bonding performance of carbon-fabric-reinforced cementitious matrix (C-FRCM) composites with the impressed current cathodic protection (ICCP) technique. Single shear tests and pull-out tests on the C-FRCM composites are launched. Three current densities of 0, 100 and 150 mA/m2 in the ICCP technique are considered. The resistance–slip relationships for all the composites are presented. It is found that the maximum resistance of the specimens in the pull-out tests decreases significantly with the increase of current density in the ICCP technique. Moreover, numerical analyses are conducted to obtain a simplified interface bonding stress–slip relationship of the specimens in the pull-out tests.

Degradation behavior of multifunctional carbon fabric-reinforced cementitious matrix composites under anodic polarization

A sustainable repair method that combines impressed current cathodic protection (ICCP) and structural strengthening (SS), called ICCP-SS, has been proposed for reinforced concrete structures suffering from steel corrosion. The key component in an ICCP-SS system is a multifunctional carbon fabric-reinforced cementitious matrix (MCFRCM) composite that simultaneously functions as a tensile reinforcement and an impressed current anode. The MCFRCM composite is investigated in terms of its electrochemical performance and interfacial performance and the degradation caused by anodic polarization in alkaline solution. The results show that a relatively stable electrochemical performance can be maintained for composites polarized at a current density up to 125 mA/m2, while an exponential increase in cell voltage can be seen at higher current densities. The charge density corresponding to the occurrence of the exponential increase in cell voltage is nearly the same for all composites polarized above 125 mA/m2. Besides, the composite shows a decreased maximum pullout force and a failure mode conversion from partial rupture to complete rupture of the carbon fabric with increasing current density. The composite is degraded by the dissolution of carbon filaments due to the anodic oxidation of hydroxyl ions from the pore solution in the matrix, which results in changes in the chemical composition and morphology of the filaments. The degradation of the composite can be further correlated with the electrochemical performance and interfacial performance.

Fatigue life of C-FRCM strengthened corroded RC continuous beams under multi-intervention system

A new fatigue life prediction model for reinforced concrete (RC) beams is proposed. The model was applied to carbon-fabric reinforced cementitious matrix (C-FRCM) strengthened corroded RC beams under the impressed current cathodic protection (ICCP) and structural strengthening (SS) multi-intervention system. The stress development of steel bar in the fatigue process was captured by employing the fracture mechanics and finite element (FE) analysis. The concept of equivalent initial flaw size (EIFS) was also introduced to account for the actual initial micro crack size of steel bar. The feasibility of the model was validated through comparisons of the numerical deflection, the strain of steel bar and fatigue life of RC beams against the test results. The validated model was then used to examine the effects of key parameters including load level, corrosion degree of steel bar and polarization degree of C-FRCM. Furthermore, the results of the parametric study were used to fit S-N curve and analyse the reliability. The high accuracy of the model was shown to be suitable for the fatigue life prediction of ICCP-SS system in long-term service. It was also found that the fatigue life of the corroded RC beams was greatly improved through strengthening with C-FRCM.

Optimization and design of carbon fabric‐reinforced cementitious matrix composites

AbstractInterest in carbon fabric‐reinforced cementitious matrix (C‐FRCM) composites as structural strengthening materials for reinforced concrete structures has recently increased. In such applications, the mechanical properties of C‐FRCM composites are the key to unlocking the corresponding strengthening effects. Therefore, this study explores different optimization approaches to improve the loading behaviors of C‐FRCM composites, such as different carbon fabric contents in the cementitious matrix and different surface treatments of the carbon fiber meshes. Then, a series of tensile tests are carried out to evaluate the performance of the modified C‐FRCM composites. Furthermore, experimental results of other FRCM composites are collected from the literature to create a larger data pool for analysis. Finally, two existing constitutive models for FRCM composites — the Aveston‐Cooper‐Kelly (ACK) model and the AC434 model — are compared against these experimental data.

Experimental study on hysteretic behavior for corroded circular RC columns retrofitted by ICCP-SS

An experimental study on nine circular reinforced concrete (RC) columns is presented in this paper, wherein one column specimen was adopted as the reference group, the other eight specimens were subjected to accelerated corrosion. After the accelerated corrosion for 180 days, two of the corroded columns were protected by impressed current cathodic protection (ICCP), while the other six corroded columns were further repaired by structural strengthening (SS). A combination of ICCP and SS, namely ICCP-SS, is adopted in this study, which adopts the carbon-fabric reinforced cementitious matrix (C-FRCM) as anode and strengthening material. Finally, specimens were cyclically loaded in a horizontal direction under different axial loads. The results indicated load-carrying and energy dissipation capacities of specimens were deteriorated due to corrosion. This phenomenon is severer under higher axial load. The dual function of ICCP-SS technique does not only improve load-carrying and energy dissipation capacities of RC columns, but also reduce the on-going corrosion of steel re-bars. These benefits can be attributed to the confinement effect to the column base provided by the C-FRCM composites and the ICCP effect using carbon fabric mesh in the C-FRCM composites as anode.

Tensile Performance, Lap-Splice Length and Behavior of Concretes Confined by Prefabricated C-FRCM System

Results of an experimental study aimed to evaluate tensile performance, lap-splice length of carbon fabric-reinforced cementitious matrix system (C-FRCM), and performance of concretes confined by C-FRCM are presented. Green high-strength mortar was used in this study which actively utilized recycled fine aggregate and fine waste glass powder to partially substitute cementitious binder. Test plans were developed in due consideration of prefabricated C-FRCM for strengthening concrete columns: 14 tensile tests, 12 lap-splice tests, and 6 uniaxial compression tests of plain concrete specimens confined by C-FRCM were performed. Test variable for the tensile test was number of fabric layers (one or two layers). Nominal strength of the C-FRCM with two fabric layers was 11.0 MPa while it was 7.4 MPa with one fabric layer in tension. Full strength of the carbon fabric was developed in all tensile tests while the C-FRCM with two fabric layers (with axial fiber amount = 0.59% by vol.) showed pseudo-ductile behavior. From the lap-splice tests in direct tension, an increased lap-splice length was required for the double fabrics over that for the single fabrics. The required splice length was about 170 mm for the single fabrics and it was about 310 mm for the double fabrics. Plain concrete cylinders and prismatic specimens were laterally confined by C-FRCM and subjected to uniaxial compression. All test results showed strain-softening behavior. Compressive strength increased by 10–41% while ductility also increased by 6–45% indicating applicability of the prefabricated type C-FRCM in the future.

Study on the Corroded Hollow Section RC Columns Strengthened by ICCP-SS System

In this paper, the behavior of corroded hollow section RC (reinforced concrete) columns strengthened by an Impressed Current Cathodic Protection and Structural Strengthening (ICCP-SS) system was investigated. The Carbon Fabric-Reinforced Cementitious Matrix (C-FRCM) composite serves dual functions in the intervention method. The axial compression behavior of strengthened columns was firstly investigated through axial compression tests. The influence of corrosion ratio and C-FRCM strengthening on the test results, such as failure mode, load–displacement curve, ultimate load, and ultimate strain, were analyzed. Test results showed that the ultimate load of the corroded specimens could be enhanced significantly by C-FRCM, and the ductility of the strengthened specimens was larger than the specimens without strengthening, especially for the specimens with higher corrosion ratios. Secondly, the effects of the ICCP-SS system on the migration and distribution laws of chloride ions (Cl−) in hollow section RC columns were analyzed by the potentiometric titration method. The main parameters include charging time, current density, and salt addition. Results showed that the rebar would have a certain blocking effect on the migration of Cl−, which resulted in that the content of Cl− in the inner side of the rebar was always larger than that of the outer side; and research results also showed that the increase of impressed current density and charge time would reduce the Cl− content on both sides of the rebar, while the impressed current would cause the Cl− near the rebars to constantly move toward the vicinity of CFRP.

Fatigue behavior of corroded reinforced concrete continuous beams with multi-intervention system

The corrosion of steel rebars in reinforced concrete (RC) structures will lead to the deterioration of fatigue performance and fatigue life. For the sake of resolving the corrosion problems of RC structures, the Impressed Current Cathodic Protection (ICCP) and Structural Strengthening (SS) techniques are often applied to repair the corroded RC structures. In this study, the ICCP-SS techniques are combined to retrofit the deteriorated RC continuous beams by using the carbon-fabric reinforced cementitious matrix (C-FRCM), and the C-FRCM composites comprised of carbon fabric mesh and inorganic cementitious matrix will served as anodic material for ICCP and the structural strengthening material in the ICCP-SS multi-intervention system. By analyzing the test results of fatigue life, failure mode, cracks in concrete, mid-span deflection, tensile strain of steel rebars and internal force redistributions of the test beams under fatigue load, the influence of reinforcement corrosion and the ICCP-SS retrofitting method on the fatigue performance of RC continuous beams were discussed. The test results showed that the strengthening effect of C-FRCM composites can reduce the generation of cracks in concrete and improve the flexural rigidity as well as fatigue life of the continuous beams effectively, however, the improving effect will decrease for the specimens with higher circulated charge density along with a higher polarization effect of C-FRCM composites.