Study On The Bond-slip Mechanism Of CFL-concrete Interface Under Hot-wet Environment

As the technique of FRP reinforced concrete structures widely used in the field of civilengineering, the durability of the strengthened structures has caused more attention in recentyears. The bond behavior of the interface plays a critical role to the reinforcing effects. Inaddition, the adhesive on the interface is very sensitive to hot-wet condition. Therefore it hasgreat significance to study the bond-slip mechanism of FRP-concrete interface under hot-wetenvironment.By taking the carbon fiber laminate (CFL, which invented by our research group) andconcrete bond face as the research object, the study here focuses on the bond-slip mechanismof CFL-concrete interface under static load and fatigue load in hot-wet condition consideringthe climate characteristic in south China. The main research contents and conclusions in thepaper are listed as follows:(1) In view of key technique ensuring the pure shear stress state on interface betweenCFL and concrete in the tests, alignment mold to pour concrete blocks, location clamp duringbonding CFL, universal load head used to pull had been developed in this article. Accidentaldebonding failure caused by eccentricity during making, installing the double-shearspecimens, and loading were avoided successfully by using the series devices, which madethe static and fatigue tests on the CFL-concrete interface were successfully carried out.(2) After pretreatment in hot-wet environment, the specimens were applied in doubleshear tests under static loads. The bond-slip mechanism of FRP-concrete interface underhot-wet environment was studied. A bond-slip model considering hot and humidity effect wasproposed based on the experimental results. Comparing the existing model, it had3characteristics such as: a) considering the aggressive effect caused by hot and humidity for thefirst time; b) the relationship between the eigenvalue in the proposed model and hot-humidityeffect were offered; c) a formula about the ductility parameters of interface and hot-wetenvironment were built in this article.(3) The bond-slip mechanism of FRP-concrete interface under hot-wet environment werepreliminarily studied through scanning electron microscope (SEM) technology from a microscopic point of view. It showed that between the raw material of CFL, resin prepreg andadhesive-concrete interface were obviously layered after pretreatment in hot-wet environment,which decreasing the bond behavior of the interface between each material.(4) The double shear fatigue test was carried out successfully to study the bond-slipmechanism of FRP-concrete interface in high temperature and humidity environment andunder fatigue load. It’s showed that bond stiffness of the interface was degraded with3stagesas cycle number increasing based on analysis on the relative slip between two concrete blocks.A secant stiffness coefficient Kfwas defined considering the features. According to the Minerlinear damage theory, a three-phase fatigue damage model was put forward to describe thefatigue damage process on the CFL-concrete interface in this paper. The proposed model hadfirstly taken into account the load level and hot-wet environment effect on the fatigue damageof the interface.(5) The bond-slip experimental curves of the CFL-concrete interface under fatigue loadin hot-wet environment were obtained through analyzing the strain data on CFL when peakload. A bond-slip model under fatigue load considering hot and humidity effect was proposedbased on the experimental results. It had3characteristics such as: a) considering theaggressive effect caused by hot and humidity for the first time, and the expression forparameter m was provided; b) the effect on bond-slip of interface by fatigue load wasdiscussed, and the impact factor was also introduced in the article; c) considering the effect ofload level, a formula describing the relationship between parameter m and load level wasproposed.