Carbon Fiber Reinforced Polymer Strain Research Articles

Enhancing bond performance of CFRP-steel epoxy-bonded interface by electrospun nanofiber veils

The epoxy-bonded interfaces between carbon fiber reinforced polymer (CFRP) and steel usually have insufficient strength and toughness, and the toughening of bonded interface is a key problem for the usage of CFRP in steel structures. In this study, electrospun nanofiber veils were first proposed to enhance the bond performance of CFRP-steel epoxy-bonded interfaces. Firstly, shear tests were conducted on neat epoxy and nano-modified single-lap aluminum-aluminum joints to determine the optimal areal density and number of layers of nanofiber veils, as well as the optimal curing processes. Then, a series of neat epoxy and nano-modified CFRP-steel double-lap joints with different bond lengths were tested to investigate the size effect of the bond behavior. The displacement and strain field evolution of the joints were captured by the digital image correlation (DIC) technique, allowing for visualization of the detailed failure process. The failure modes, load-displacement curves, CFRP strain distributions, and bond-slip relationships of the CFRP-steel joints were obtained. Both the tests on aluminum-aluminum and CFRP-steel joints show that the optimal modification strategy is incorporating 3 layers of nanofiber wels with an areal density of 4.5 g/m2, with 5 h room-temperature and 2 h 80 °C high-temperature curing. The primary failure mode of CFRP-steel joints is CFRP delamination accompanied by CFRP-adhesive interface or steel-adhesive interface debonding. The bond strengths of the modified joints with 3 layers of 1.5 g/m2 and 4.5 g/m2 nanofiber veils are increased by 7 % and 25 % compared to those of un-modified joints, respectively. The 4.5 g/m2 nanofiber veils modified bonded interface has an effective bond length of about 152 mm, with a corresponding ultimate bearing capacity of 117 kN. Different from the triangular (brittle) shape of most neat epoxy interfaces, the nano-modified interfaces have trapezoidal (ductile) bond-slip relationships, providing superior cracking resistance. Moreover, a comparison with the bond strength of SiO2 nano-particles and carbon nanotubes (CNTs) modified joints revealed that nanofiber veil modification comes to higher bond strength in most cases. The proposed electrospun nanofiber veil modification technique provides a great insight into the interfacial toughening of CFRP-steel composite structures.

Plate end debonding strength model for RC beams strengthened with FRP/SMA composites

Plate end debonding is a common failure mode for fiber reinforced polymer (FRP) strengthened beams. FRP sheets and shape memory alloy (SMA) composites can effectively slow down plate end debonding and improve beam ductility owing to the anchorage effect of SMA wires on the FRP ends. This work aims to comprehensively study the anchorage performance of FRP/SMA composite strengthened beams through both model analysis and experimental investigation. The plate end debonding strength models of existing FRP strengthened beams were initially summarized and analyzed, and an improved model was proposed to predict the debonding strength of FRP/SMA composite strengthened beams at the plate end. Moreover, the anchorage performance and flexural behavior of beams strengthened with carbon fiber reinforced polymer (CFRP) and SMA composites were studied through experiments. The failure mode of the FRP sheet strengthened beams was plate end debonding failure, while the plate end debonding failure of the CFRP/SMA composite strengthened beams occurred at the strengthening zone end, and the peeling failure was delayed owing to the anchorage effect of SMA wires on the ends of the strengthening CFRP sheets. The recovery effect of SMA wires could successfully introduce prestress into CFRP sheets. Moreover, the CFRP strain corresponding to plate end debonding increased because of the anchorage of SMA wires on the CFRP sheet in the strengthening zone. The strength and ductility of the CFRP/SMA composite strengthened beam significantly improved. The proposed model for predicting the plate end debonding strength of FRP/SMA composite strengthened beams was validated through experiments.

Effects of Concrete Strength and CFRP Cloth Ratio on the Shear Performance of CFRP Cloth Strengthened RC Beams

A three-dimensional meso-scale numerical model, which considers (1) the concrete meso-structures, (2) the bond slip between concrete internal structures and steel bars, and (3) the stripping behavior of carbon fiber reinforced polymer (CFRP) cloth from the surface of the concrete component, is established to investigate the effects of concrete strength and the CFRP cloth ratio on the shear performance of reinforced concrete (RC) beams. On the basis of verifying the rationality of the shear failure model and the feasibility of the CFRP reinforcement simulation method, 30 orthogonally designed numerical models of six kinds of concrete strength and five kinds of CFRP cloth ratios were designed and established. Based on the numerical simulation results, this paper analyzes the damage evolution of the CFRP–concrete interface, the variation trend of CFRP strain along the height direction of beam, the failure mode, and the load-displacement curve. Results show the following: (1) With the increase of concrete strength grade and CFRP cloth ratio, the shear strength of RC beams strengthened with increases in CFRP cloth ratio, the influence range of concrete strength grade is 24–50%, and the influence range of the CFRP cloth ratio is 10–25%; (2) The improvement range decreases, and the improvement range of the concrete strength grade decreases, and the reduction range is about 20%; (3) Based on the simulation results, influences of concrete strength and CFRP cloth ratio on the shear strength of CFRP cloth-strengthened RC beams are quantitatively considered.

Structural behavior of CFRP-strengthened steel beams at different service temperatures: Experimental study and FE modeling

The structural performance of externally bonded carbon fiber-reinforced polymer (CFRP)-strengthened steel beams can be affected by different service temperatures. This study carried out three-point bending tests on thirteen beams, including two un-strengthened steel beams and eleven CFRP-strengthened steel beams, at temperatures ranging from −20 °C to 60 °C. CFRP plates with two different lengths (i.e., 300 mm and 600 mm) were used for the strengthening. The load–deflection curves, ultimate failure loads and the strain evolutions in CFRP plates were measured and compared. The results showed that the steel beams strengthened with 300 mm CFRP plates were failed due to plate-end debonding at all temperatures, and the debonding load decreased with the temperature increase. In contrast, the steel beams strengthened with 600 mm CFRP plates were failed due to CFRP rupture at −20 °C to 45 °C but plate-end debonding at 60 °C. A finite element (FE) model was proposed for predicting the experimental results, in which the temperature-dependent interfacial bond behavior was properly considered based on the results from the previous CFRP-to-steel double-lap shear tests. The FE model was extensively validated through the comparisons between the experimental and FE results of load–displacement curves and CFRP strain distributions at various load levels.

Experimental study on shear performance of CFRP-strengthened RC beams with geopolymer adhesive

PurposeThe effects of carbon fiber reinforced polymer (CFRP) reinforcement form, adhesive type and pre-crack width on failure mode, shear capacity, deflection response, CFRP strain response and crack patterns of strengthened specimens were investigated.Design/methodology/approachThis paper presents a geopolymer adhesive that matches the performance requirements of CFRP adhesive, which is applied to pre-cracked beams reinforced with CFRP strips. FindingsFor specimens with varying structural properties, two failure modes, the CFRP-concrete interface substrate failure and the fracture failure of CFRP, are observed. Moreover, the shear capacity, ultimate deflection and bending stiffness of the U-shaped CFRP-strengthened beams are enhanced in comparison to the complete-wrapping CFRP-strengthened beams. With an increase in pre-crack width, the increase in shear capacity of RC beams shear-strengthened with CFRP strips is less than that of non-cracked beams, resulting in a limited influence on the stiffness of CFRP-strengthened beams. The comparison of experimental results showed that the proposed finite element model (FEM) effectively evaluated the mechanical characteristics of CFRP-strengthened RC beams.Originality/valueTaking into consideration the reinforcement effect and the concept of environmental protection, the geopolymer adhesive reinforcement scheme is preferable to applying epoxy resin to the CFRP-strengthened RC beams.

Intermediate crack-induced debonding in CFRP-retrofitted notched steel beams at different service temperatures: Experimental test and finite element modeling

Carbon fiber-reinforced polymer (CFRP)-retrofitted steel beams are likely exposed to significant service temperature variations due to seasonal and daily temperature changes. However, there is lacking research on the structural performance of CFRP-retrofitted steel beams under service temperature variations. This paper presents an experimental study of fourteen beams including one intact beam, one notched beam and twelve CFRP-retrofitted notched beams tested at various service temperatures from -20°C to 80°C. The structural properties including load-deflection curves, load capacities at initial and ultimate debonding, crack mouth opening displacements at the notch and the CFRP strain measurements were examined and compared at different service temperatures. The debonding loads of CFRP-retrofitted beams were increased with the temperatures from -20°C to 60°C and decreased at 80°C. A formula was proposed to derive the local bond-slip behavior of the CFRP-to-steel interface at different temperatures from the CFRP strain measurements. The shear stiffness of the interface generally decreased with the service temperature growth, while the interfacial fracture energy first increased and then decreased. A finite element model was proposed to gain insight into the effects of interfacial thermal stress and temperature-dependent bond properties on the bond behavior and structural performance of CFRP-retrofitted beams at different service temperatures.

Bond behavior of CFRP-to-steel bonded joints at different service temperatures: Experimental study and FE modeling

The bond behavior of carbon fiber-reinforced polymer (CFRP)-to-steel interface in strengthened steel structures is likely to be significantly affected by service temperature variations, mainly because of interfacial thermal stresses and the changes in the local bond-slip behavior. However, there is lack of comprehensive study on the temperature effects on the bond behavior and the debonding load of the CFRP-to-steel interface at different service temperatures. This paper presents the results from the pull-out tests on CFRP-to-steel double-lap bonded joints tested at service temperatures ranging from −20 °C to 60 °C. The test results including failure modes, debonding loads, load–displacement curves, CFRP strain distributions and interfacial shear stress and slip responses are investigated and compared. Also, a bilinear local bond-slip model is developed to describe the relationships between the shear stresses and the interfacial slips at different service temperatures. A finite element (FE) model is proposed to predict the bond behavior and the debonding loads of the bonded joints at different service temperatures and validated through the comparisons between experimental and FE results. The validated FE model is then used to further investigate the temperature effects on the CFRP strain distributions, interfacial shear stresses and the debonding loads of the bonded joints at different service temperatures. The experimental and FE results have indicated that the debonding loads of the CFRP-to-steel interface are significantly reduced at both low and high service temperatures. The elastic stiffness and the peak shear stress of the local bond-slip model are generally reduced with the service temperature increase, while the interfacial fracture energy decreases at both low and high service temperatures.

Investigation of the effect of fly ash content on the bonding performance of CFRP-concrete interface in sulfate environment

The present study focuses on the investigation of the interfacial bond behavior of carbon fiber-reinforced polymer (CFRP)-concrete under dry–wet sulfate cycles by double-sided shear testing. Besides, the effects of fly ash content on the interfacial failure characteristics, interfacial debonding bearing capacity, CFRP strain distribution, and interfacial shear stress peak were analyzed. The interfacial debonding capacity, maximum CFRP strain, and peak value of interfacial shear stress of the CFRP-concrete interface decreased with increasing erosion time under the sulfate dry–wet cycle's action, according to the sulfate dry–wet cycle test results. The sulfate resistance of the CFRP-concrete interface increased after the addition of fly ash. However, the final decrease amplitude of interfacial debonding capacity, CFRP maximum strain, and maximum interfacial shear stress all reduced as the fly ash content increased. The effective bond length of the interface gradually increased with increasing erosion time; however, the change in fly ash content had little effect on the effective bond length, and the final effective bond length of the samples with different fly ash content was the same. Moreover, the CFRP-concrete interfacial bearing capacity model under the sulfate dry–wet cycle was established by introducing sulfate's comprehensive influence coefficient and considering fly ash content's influence. In conclusion, the comparative analysis of the prediction model and test results revealed that the prediction model could well reflect the degradation law of interfacial debonding bearing capacity with sulfate attack time.

Investigation of CFRP Reinforcement Ratio on the Flexural Capacity and Failure Mode of Plain Concrete Prisms.

The utilization of carbon-fiber-reinforced polymer (CFRP) composites as strengthening materials for structural components has become quite famous over the last couple of decades. The present experimental study was carried out to examine the effect of varied widths of externally bonded CFRP on the debonding strain of CFRP and the failure mode of plain concrete beams. Twelve plain concrete prims measuring 100 mm × 100 mm × 500 mm were cast and tested under identical loading conditions. The twelve specimens include two control prisms, i.e., without CFRP strips, and the remaining ten prisms were reinforced with CFRP strips with widths of 10 mm, 20 mm, 30 mm, 40 mm, and 50 mm, respectively, i.e., two prisms in each group. Four-point loading flexural testing was carried out, and the resulting data are presented in the form of peak load vs. midpoint displacement, load vs. concrete strain, and load vs. CFRP strain. The peak load was directly recorded from the testing machine, while the midpoint deflection was recorded through the linear variable differential transducer (LVDT) installed at the midpoint. To measure the strain, two separate strain gauges were installed at the bottom of each concrete prism, i.e., one on the concrete surface and the other on the surface of the CFRP strip. The results of this study indicate that the debonding strain is a function of CFRP strip width and that the failure patterns of beams are significantly affected by the CFRP reinforcement ratio.

Influences of the joint and epoxy adhesive type on the CFRP-steel interfacial behavior

The bond behavior of the interface between carbon fiber reinforced polymer (CFRP) and steel is an important factor affecting the strengthening effect. In this study, the double-shear and single-shear bonded joints were used to research the influences of test methods and epoxy adhesives on the CFRP-steel interfacial behavior. The test parameters included the joint type, adhesive type and adhesive thickness. The failure mode, ultimate load, strain on the CFRP, interfacial shear stress and bond-slip curve were compared. Test results show that the joint type affects the ultimate load, CFRP strain and interfacial shear stress but has no influence on the bond-slip relationship and failure mode. The ultimate loads of the interfaces tested by the double-shear bonded joints are higher than those of the single-shear bonded joints, and the ratio of the ultimate load is determined by the stiffness ratio between the CFRP plate and steel substrate. The adhesive type can affect the failure mode, ultimate load, shapes of the shear stress distribution and bond-slip curve. The ultimate load of the bonded joints with the adhesive A can reach two times that of the joints with the adhesive S. Compared to the specimen with the adhesive S, the specimen with the adhesive A has a lower peak shear stress but much longer stress transfer length. The bond-slip relationships are approximately bilinear and trapezoidal shape, respectively, for the specimens with the adhesives S and A.

Debonding development in cracked steel plates strengthened by CFRP laminates under fatigue loading: Experimental and boundary element method analysis

Carbon fiber reinforced polymer (CFRP) laminates can effectively enhance the fatigue life of steel structures. However, few studies have investigated the influence of crack-induced debonding in the CFRP-steel interface on the CFRP strengthening efficiency and the relationship of crack propagation and debonding development. This study experimentally and numerically – with the boundary element method (BEM) – investigated crack propagation and debonding development in CFRP-strengthened cracked steel (Q345, Q460, and Q690) plates. The fatigue test specimens were subjected to a maximum stress of 50% steel yield stress and a stress ratio of 0.1, during which real-time changes in CFRP strain distribution were recorded by digital image correlation (DIC). The CFRP strain gradient calculations showed that crack-induced debonding was crack length-dependent. The numerical fatigue life results were in good agreement with the experimental data when considering debonding and overestimated the experimental data without considering debonding, demonstrating the necessity of considering crack-induced debonding in calculation and design. Furthermore, a relationship was obtained between crack propagation and debonding development.

Mechanical properties of CFRP-strengthened prestressed concrete cylinder pipe based on multi-field coupling

Broken prestressing wires in prestressed concrete cylinder pipe (PCCP) can cause incident of pipe burst. A method was proposed to repair damaged PCCP with broken wires by externally bonding carbon fiber reinforced polymer (CFRP). A finite element model was established and calibrated against the data from a prototype-scale laboratory test. Upon calibration, a three-dimensional numerical model was built to simulate the response of PCCP pipeline with five segments. Multi-field coupling was accomplished by Mesh-based parallel Code Coupling Interface (MpCCI) to incorporate the soil–pipe interaction and the effect of hydrodynamic pressure for PCCP. The effect of externally bonded CFRP to repair PCCP with broken wires was systematically analyzed. Results show that at a certain number of broken wires, the use of CFRP for pipe repair can significantly reduce the strains for each pipe component and increase the resilience of PCCP. The improved PCCP performance was assessed on the basis of crack visibility in the concrete core, and the deformation of the steel cylinder. The CFRP strain was much less than its ultimate strain, when cracks in the concrete core became visible and the steel cylinder yielded, suggesting that failure of PCCP could be ahead of CFRP.

Numerical modeling of low strength reinforced concrete column strengthened with CFRP jacketing

Reinforced concrete column strengthened with Carbon Fiber Reinforced Polymer (CFRP) has been investigated numerically. Reinforced concrete column with low compression strength is used in this study. Concrete column is modeled by 3D solid elements with 8 nodes linear brick elements (C3D8R), whereas reinforcement bars modeled by 3D truss elements with 2 nodes first order elements (T3D2). In order to simulate concrete response in the specimen, concrete damage plasticity model with specifying damage parameters in both of compression and tension has been adopted in this paper. The specimen is subjected to uniaxial compression loading applied with displacement-controlled method. The effects of CFRP jacketing on reinforced concrete column with low compression strength are observed. The characteristic of reinforced concrete column combined with CFRP in terms of load-displacement behaviour and stress distributions are also evaluated. It is found that the numerical technique proposed in this study is quite efficient to predict the behaviour of low strength reinforced concrete column strengthened with CFRP with regard to the ultimate load, CFRP strain, and concrete strain distribution.

Experimental study on the bond behavior of the CFRP-steel interface under rapid loading

In this paper, a series of the carbon fiber reinforced polymer (CFRP)-steel single-shear specimens was manufactured to investigate the effects of the adhesive types and loading rates on the bond behavior of CFRP-steel interfaces. The main properties of the bonded joints were examined under loading rates of 0.01 mm/s, 10 mm/s and 100 mm/s, including the failure mode, the ultimate load, the load-slip curve, the CFRP strain distribution and the bond-slip relationship. The experimental results showed that the main mechanical properties of CFRP plate and adhesives increased with increases in the loading rate. The ultimate load of the CFRP-steel joint with adhesive sikadur-30 (CN) increased with increasing loading rate, while the ultimate load of the interface with adhesive sikadur-30 substantially decreased as the loading rate increases from 0.01 mm/s to 10 mm/s. Finally, the bilinear bond-slip parameter model was proposed by analyzing the influence of loading rate on key parameters.

Impact of anchored holes technique on behavior of reinforced concrete beams strengthened with different CFRP sheet lengths and widths

The premature de-bonding failure, of the carbon fiber reinforced polymer (CFRP) composites, is among the most important problems that hinder external strengthening utilizing CFRP sheet. Although it is recommended to use the end anchorage systems to address this important issue, it is needed to further explore the impact of those systems on enhancing the flexural performance of strengthened reinforced concrete (RC) beams. Therefore, most interest is focused on the feasibility of using the anchored holes to improve the behavior of RC beams. The proposed anchored technique includes the preparation of the bonding surface of each concrete beam. Later, the anchoring holes have been drilled using a rotary drill at the end of the bonded area. Seventy four RC beams were used to conduct the experimental program. Seventy two of those samples were externally strengthened by a CFRP sheet. The investigated parameters, in this study, were: the length of CFRP sheets, the width of CFRP sheet, and number of anchored holes. The performance characteristic of each tested beam was evaluated in terms of load versus each of: the mid-span deflection curve, failure mode, ultimate load capacity, ultimate deflection, displacement ductility index, stiffness, energy absorption, energy absorption ductility index, performance factor, and CFRP strain. The study results showed a significant improvement in the majority of the investigated parameters. The results, also, showed that the behavior of the tested beams was more effective when using anchored holes combined with CFRP strengthened beams. This improvement is due to the efficient anchored holes in providing external cracks arresting mechanism after steel reinforcement yielding and cracking and even after reaching the ultimate load capacity. Finally, the efficiency of the adopted end anchored holes system in enhancing ductility in flexural-strengthened RC beams is explored in detail.

Hybrid CFRP-steel for enhancing the flexural behavior of reinforced concrete beams

Hybrid use of Carbon fiber reinforced polymer (CFRP) composites with conventional construction materials offers an ample opportunity to develop economical and high-performance structures. However, anchoring and debonding problems remains a challenge for the accomplishment of this technique. In this study, a novel application was implemented in which the CFRP sheet was integrated as internal flexural reinforcement for RC beams. The target was to evaluate the contribution of the CFRP sheet to the flexural performance and thus assess the efficiency of using the CFRP sheet as primary or supplemental flexural longitudinal steel reinforcement. CFRP sheet can be cut without difficulty to any width/length and then attaching them to the main steel bars without using epoxy. Similar to the longitudinal steel reinforcement, the CFRP strips work integrally with steel reinforcement as the concrete confines them. The investigated parameters are the number of CFRP layers, CFRP sheet length, strengthening type (internal or external strengthening). Therefore, the feasibility of internal strengthening for improving the behavior of RC beams is of vital interest. The performance of each beam was evaluated in terms of failure mode, load versus mid-span deflection curve, ultimate deflection, ultimate load capacity, stiffness, displacement ductility index, energy absorption, energy absorption ductility index, performance factor, and CFRP strain. The results show a significant improvement in the majority of the investigated parameters and show the effectiveness of internal strengthening. The internal strengthening provided external cracks arresting mechanism and even after reaching the ultimate load capacity.

Crack propagation and debonding development of CFRP laminate strengthened high-strength steel plates under fatigue loadings

Carbon fiber reinforced polymer (CFRP) has been used to strengthen steel structures to enhance fatigue life. A crack growth induced debonding region in the adhesive-steel interface has been observed in failure modes. However, limited studies focus on its gradual development with fatigue loadings, especially for CFRP laminate strengthened cracked high strength steel plates. The purpose of this paper is to obtain the corresponding relationship of crack propagation and debonding development. Thus fatigue tests with measuring real-time change of CFRP strain distribution by Digital Image Correlation (DIC) system were conducted for Q345, Q460, Q690 steel under fatigue loading at the same stress level 50% but difference stress ranges. Although debonding at the adhesive-steel interface is invisible, through calculation of strain gradient, it is found that as the increase of crack length, the debonding region around the crack tip occurs and gradually becomes larger. Furthermore, the shape of debonding region is always similar to an ellipse from the beginning of loading to failure.

Influence of hygrothermal ageing on the mechanical properties of CFRP-concrete joints and of their components

Externally bonded (EB) fiber reinforced polymer (FRP) composites have been effectively employed to strengthen existing reinforced concrete (RC) structures. However, relatively limited information is available regarding the long-term behavior of FRP-concrete joints. In this paper, different experimental tests are employed to investigate the effect of hygrothermal ageing on the bond behavior of a carbon FRP composite applied to a concrete substrate and on the mechanical properties of the epoxy resin and FRP composite considered. The experimental campaign includes tensile tests of epoxy resin, carbon FRP (CFRP) coupon, pull-off tests of the CFRP bonded to the concrete substrate, and single-lap direct-shear tests of CFRP-concrete joints. Specimens were conditioned in warm water (38 ± 2 °C) for 500, 1000, and 1500 h to accelerate the possible degradation induced by a simulated high-moisture exposure environment. The parameters studied were the tensile properties of epoxy resin and CFRP coupons and the fracture energy of the CFRP-concrete interface, which was computed from the CFRP strain measured in the single-lap direct-shear tests using the digital image correlation (DIC) method. Results indicate that both the mechanical properties of the epoxy resin and the CFRP-concrete interface fracture energy were slightly affected by the exposure conditions.

Experimental study on the bond behavior between CFRP plates and steel substrates under fatigue loading

This paper reports an experimental study on the fatigue behavior of bonded interfaces between carbon fiber reinforced polymer (CFRP) plates and steel plates. A total of 20 single-shear bonded joints were tested under monotonic and fatigue loading. The digital image correlation (DIC) method was employed. The effects of the load ratio, adhesive thickness and adhesive type on the fatigue life were investigated. The failure mode, fatigue life, relative slip, load-slip curve, CFRP strain and interfacial shear stress are presented. The results indicated that the cohesive failure was the dominated failure mode for all specimens. With the increase of the loading cycles, the debond initiated firstly at the loaded end and then propagated gradually toward the free end, which was obviously reflected by CFRP strain and shear stress distributions. The hysteresis was observed in the load-slip curve, indicating the energy dissipation occurred in the interfaces. The fatigue life decreased dramatically with the increase of the load ratio. When the load ratio was the same, the fatigue life decreased with an increasing adhesive thickness, and the fatigue life of the specimen with Sikadur-30 was longer than that with Araldite-2015. However, when the load range was similar, the fatigue life increased with an increase in the adhesive thickness, and the fatigue life of the specimen with Araldite-2015 was longer than that with Sikadur-30. The distribution shapes of the shear stress for two types of the specimens were approximately trapezoidal and triangular under monotonic and fatigue loading.

Interfacial bond-slip degradation relationship between CFRP plate and steel plate under freeze-thaw cycles

The bond-slip degradation relationship of a carbon fiber reinforced polymer (CFRP)-steel bonded interface is crucial for predicting the long-term behavior of CFRP-strengthened steel structure under a freeze-thaw (F-T) environment. A total of 16 single-shear bonded joints were tested to investigate the effect of the bond length and the F-T cycles on the CFRP-steel bonded interfaces. The strains on the CFRP surface and the relative slips between the CFRP plate and steel plate were measured by using three-dimensional digital image correlation (3D-DIC) technology. The main properties of the bonded joints were examined, including the failure mode, the ultimate load, the load-slip curve, the CFRP strain distribution and the bond-slip relationship. The degradation models for the bond-slip parameters were formulated by introducing the damage factors, and the interfacial bond-slip degradation relationships were subsequently developed. Finally, the proposed degradation relationship was validated through comparison with the experimental bond-slip relationships and the predicted relationships under different F-T cycles.