Research On Evolution Of The CFRP-Concrete Substrate Bond Exposed To Hygrothermal Condition And Freeze-thaw Cycles

Externally bonded fiber reinforced polymer(FRP)for civil rehabilitation has become a popular technology due to the advantages of its high strength,light weight,and convenient construction.Since long-term service lives are required for civil structures under various harsh environmental conditions(e.g.,high humidity exposure,freeze-thaw cycles,tide cycles and corrosive chemical solutions),the lack of adequate long term constituent materials and bonding performance data became a major concern.The investigation on the degradation mechanisms of constituent materials and interfacial bond in the water/under the freeze-thaw cycles is the foundation for the safe,durable and economic design.In this study,the properties of FRP and the interfacial bond behavior between FRP and the concrete substrate were explored.An attempt has been made to investigate the effects of the evolution of FRPs and adhesive layer-concrete interfacial bond on the FRP-to-concrete behavior comprehensively.The main contents in this thesis are given as follows:The modeling of random fiber arrangement was investigated by ABAQUS.The effects of the volume fraction,arrangement and contact mode of carbon fibers on the moisture diffusion in the FRP were investigated.The effects of fiber in contact on the moisture diffusion is significant.The diffusivity coefficient of carbon fiber-resin was determined by the inverse analysis.The effect of the hygrothermal stress on the FRPconcrete interface was studied.It showed that the hygrothermal stress in the adhesive layer/concrete interface influenced property of FRP-to-concrete insignificantly.The effects of water immersion on properties of FRP-to-concrete constituent materials and interfacial bonding were investigated.The relationship between concrete strength,surface morphology and interfacial bonding was established.The degradaton of bonding between FRP and concrete mainly resulted from the moisture molecules.The equation between the averagenormalized interfacial moisture content and the degradation rate of interfacial bond was established.The effects of freeze-thaw cycles on the FRP-to-concrete bond evolution were investigated.The relationship of FRP-to-concrete constituent materials and interfacial bond with freeze-thaw cycles were established.The equivalent relationship between different materials and freeze-thaw regimes was established.A model used to describe the degradation of the fracture energy of the FRP-concrete bond as a function of the equivalent freeze-thaw cycles was developed.The degradation of the FRP-to-concrete can be predicted by the conditioning in the field.The debonding failure mechanisms of FRP-to-concrete were studied by the nonlinear finite element methods.FRP-to-concrete interfacial debonding models were simulated based on the concrete damage plasticity model and quasi-static analysis and the generation and development of the crack were also studied.The parametric analysis(e.g.,the thickness of the adhesive layer,the stiffness of FRP,the concrete compressive strength and the bond length)were conducted based on the FEM model verified by the experimental results.The model of FRPadhesive/concrete interface-concrete was established.The bond stress-slip relationship of adhesive layer-concrete bond was determined by inverse analysis.The model of FRP-cohesive element-concrete was simulated and then was verified by the proposed stress-slip relationship from Chapters 3 & 4.