CFRP Mesh Reinforced ECC-NC Under Bending And Shearing Action Interfacial Bonding Performance Analysis

With the continuous development of China’s transportation construction,facing the high demand for reinforcement and strengthening of old bridges,this paper combines Engineered Cementitious Composites(ECC)and Carbon Fiber Reinforced Polymer(CFRP).Taking advantage of the high ductility,self-healing and micro-cracking properties of ECC materials and the light weight,high strength and high durability of CFRP materials,a new highperformance composite material "CFRP mesh reinforced ECC" is proposed for strengthening to improve the long-term mechanical performance of bridges in service.In order to fully consider the bending and shear stresses of the interface under actual working conditions,10 sets of 30 CFRP mesh reinforced ECC-NC beam lap specimens were fabricated,combined with theoretical analysis,to study the strength of the matrix material(concrete and ECC),the strength of the concrete and the strength of the ECC.The theoretical analysis was carried out to study the influence of the strength level of the substrate material(concrete and ECC),bond length,bond width,interface connection method and CFRP mesh on the interface bonding performance,and to provide a theoretical basis for the interface design of CFRP mesh reinforced ECC for reinforcement.The main research contents and results of this paper are as follows:(1)CFRP mesh reinforced ECC-NC interface beam lap test was carried out,and the whole process of the test was tracked by combining Digital Image Correlation(DIC)technology: most of the specimens achieved complete peeling damage of the interface;partial peeling of the interface and fracture of the reinforcement layer occurred at the interface bond width of 100mm;the interface bond The concrete specimens were damaged in tensile shear when the length of the interface bond was 140 mm;the specimens with the full width of the interface bond and the specimens without CFRP mesh composite were damaged in the form of reinforcement fracture.The CFRP-ECC bond was maintained in most specimens,which fully demonstrated the significant improvement of the performance of the reinforcement layer by the CFRP mesh.(2)Based on the test results,we analyzed the interface bonding performance indexes such as the strain distribution law,shear stress distribution law and load-slip relationship curve of CFRP mesh reinforced ECC-NC interface,and the results showed that the interface stress and strain were mainly distributed at the loading end interface,and the interface stress and strain only increased at high loading level.The overall curve of interface load-slip relationship is characterized by the linear development stage of slip and the accelerated development stage of slip.(3)Comparing the bonding performance of CFRP mesh reinforced ECC-NC interface under different influencing factors,combined with the significance analysis of influencing factors,it is concluded that there is an effective bonding length of CFRP mesh reinforced ECCNC interface(the result of this test),and the peeling load capacity of the interface within the effective bonding length increases with the increase of the bonding length,when the bonding length exceeds the effective bonding length,the peeling load capacity of the interface When the bond length exceeds the effective bond length,the interfacial peel load capacity is no longer increased,but the interfacial ductile damage characteristics increase significantly;increasing the interfacial bond width can improve both the interfacial load capacity and the interfacial stiffness;increasing the strength grade of both concrete and ECC can improve the interfacial load capacity to different degrees;among all the influencing factors,the interfacial connection method has the most significant influence on the interfacial bond performance.(4)A prediction model of peeling load capacity of CFRP mesh-reinforced ECC-NC interface considering different influencing factors is established,which is verified to be in good agreement with the test results and has a clear physical meaning by comparison with other models.(5)Based on the comprehensive analysis of the bond-slip relationship at the CFRP mesh reinforced ECC-NC interface,the bond-slip relationship curves under different influencing factors were divided into two categories: one-stage and two-stage,and the CFRP mesh reinforced ECC-NC interface bond-slip relationship under multiple influencing factors was established based on the evaluation of different influencing factors based on the experimental results.The bond-slip relationship prediction model of CFRP mesh reinforced ECC-NC interface under multiple influencing factors was established and verified with the experimental results,which confirmed that it can describe the bond-slip behavior of CFRP mesh-reinforced ECC-NC interface under different influencing factors well.