Experimental Study On Bonding Performance Of FRP Bars-Recycled Aggregate Concrete

The large-scale exploitation of natural aggregates and the stacking and landfill of construction waste have caused great damage and pollution to the natural environment.The corrosion of steel bars in concrete structures has greatly reduced the service life of structures.In order to achieve green and sustainable development,Fiber Reinforce Plastic Bars(FRP bars)-recycled aggregate concrete(RAC)structures have emerged.The combination of FRP bars and RAC can not only alleviate the damage to the environment caused by the exploitation of natural aggregates,but also solve the corrosion problem of steel bars in concrete structures.However,whether FRP bars-RAC can replace the original reinforced concrete structures in buildings depends mainly on the bonding performance of FRP bars-RAC.Therefore,it is of great significance to carry out experimental and theoretical research on the bonding performance of FRP bars-RAC for the popularization and application of FRP bars-RAC structure.In this paper,through the combination of experiment and theory,the mechanical properties of RAC foundation and the influencing factors of FRP bars-RAC bonding performance are studied comprehensively.The specific research contents are as follows :(1)Study on mechanical properties of RAC foundation.The effects of recycled aggregate replacement rate(0 %,25 %,50 % and 100 % for each strength)on the compressive and tensile strength of RAC were analyzed by axial compression and splitting tests.The test results show that for the same strength grade of concrete,when the replacement rate of recycled coarse aggregate is low,the compressive and splitting tensile strength of RAC decrease slightly.When the recycled coarse aggregate is fully used,the strength of RAC will decrease significantly,and the decrease of splitting tensile strength is higher than that of compressive strength.With the increase of RAC strength grade,the influence of recycled coarse aggregate replacement rate on the strength of RAC is more significant.(2)Study on bonding properties of FRP bars-RAC.Through a large number of pull-out tests of FRP bars-RAC,the effects of recycled aggregate replacement rate(0 %,25 %,50 %and 100 %),FRP bars diameter(8,10 and 12 mm)and RAC cover thickness(20,30,40 and70 mm)on the failure mode and bond strength of FRP bars-RAC were studied.The test results show that the incorporation of recycled aggregate reduces the ductility of concrete.With the increase of recycled aggregate replacement rate,the bond strength of FRP bars-RAC and the ultimate slip of FRP bars decrease gradually.At the same time,with the increase of FRP bars diameter and anchorage length,the bond strength between FRP bars and RAC decreases gradually.However,the bond strength between FRP bars and RAC can be improved by increasing the strength of RAC and the thickness of protective layer.According to the theory of thick-walled cylinder,through the analysis of experimental data,the bond strength model of FRP bars-RAC was established with the diameter of FRP bars,rib inclination angle,rib spacing,strength of RAC and thickness of protective layer as variables.The calculated values of the model are in good agreement with the measured values,and the ratio of the calculated values to the experimental values is between 0.66-1.(3)Study on bond-slip constitutive model of FRP bars-RAC.Through the comparative analysis of the bond-slip curve of FRP bars-RAC,the existing bond-slip constitutive model of FRP bars(steel bars)-RAC is used to fit the bond-slip curve obtained from the test.Through the analysis of the bond-slip curve obtained from the existing model,a bond-slip constitutive model suitable for FRP bars-RAC is established.The predicted curve of the model is in good agreement with the experimental curve,both of which are above 0.99.