Study On Fatigue Bond Behaviour Between Basalt Fibre-reinforced Polymer Bars And Recycled Aggregate Concrete

The corrosion of steel bar will bring three aspects of damage to the reinforced concrete structure,such as the reduction of bearing capacity,stiffness and ductility.As the reinforced concrete structure is widely used in modern architecture,the corrosion problem of reinforcement can not be ignored.Applying FRP bars to concrete structures instead of steel bars is expected to completely solve the corrosion problem of steel bars.However,the bonding property is the key to the practical application of FRP bars in engineering.The existing research on the static bond performance of FRP reinforced concrete has achieved more fruitful results,but few literatures have studied the bond performance of FRP reinforced concrete under fatigue loads.In fact,roads,bridges,subways and other structures in their service provide,not only bear the action of static load,but also the action of fatigue load.Therefore,it is necessary to study the bonding fatigue properties of FRP bars to concrete.In this test,two sizes of 150mm×150mm×150mm and200mm×200mm×200mm were prepared according to the requirements of concrete protective layer of Pull-out specimens according to the specifications of China,the United States,Japan,Canada and other countries.A total of 53 BFRP bar concrete Pull-out specimens were prepared in this test.Through static loading test and fatigue loading test,the bonding fatigue properties of BFRP bars to concrete were studied.In this thesis,the bond behavior between BFRP bars and concrete under fatigue loading is studied by pull-out test,the bond interface damage and bond slip behavior of specimens under fatigue loading are summarized,and the bond fatigue mechanism between BFRP bars and concrete under fatigue loading is deduced.In addition,the effects of surface shape,diameter of BFRP bars,concrete type,fatigue stress level and fatigue cycles on the bond fatigue performance were analyzed by studying the bond stiffness and maximum slip at fatigue stage as well as the bond stiffness,bond strength and residual bond strength at static pull-out stage.It is found that the surface shape of BFRP bars plays a key role in the bonding mechanism.Different surface shapes will lead to different bonding mechanisms.The effect of fatigue loads can also affect the bonding mechanism.It is also found that the fatigue loads has a great effect on the bond performance between BFRP bars and concrete.Fatigue loads can reduce defects and improve the bond stiffness obviously.For the specimen whose surface form is pure deformed and sand-coated fibre-wrapped,the fatigue loads will lead to the obvious improvement of bond strength.At the same time,the fatigue load will also aggravate the damage of the bond interface.Finally,the bond stress-slip constitutive model of BFRP bars and recycled concrete under fatigue load is proposed.The model is divided into two parts: fatigue loading stage and static pull-out stage.In this thesis,the bond stiffness formula and the maximum slip formula of recycled concrete specimens with BFRP bars during fatigue loading stage are proposed,and the constitutive model of bond stress-slip relationship during fatigue loading stage is established by using these two formulas.Then,based on the existing model of FRP reinforced concrete under static loading,a constitutive model of bond stress-slip relationship between BFRP reinforced concrete and recycled concrete specimens during the static pull-out stage is proposed.It has been proved that the model curve and the test curve have a good fitting effect.