Study On Interfacial Bonding Properties Of BFRP Concrete Under Freeze-thaw

Basalt fiber reinforced composites have many advantages,mainly including light weight,high strength,high temperature resistance and corrosion resistance.They can be seen in many fields such as bridges,housing construction,aerospace and so on.Freeze-thaw cycle is one of the biggest threats to the structure of seasonal freezing areas.The structure strengthened with FRP may be in the harsh environment of freezing and thawing,which may reduce the bonding performance and durability of the interface,and even cause potential safety hazards.It is very necessary to study the interfacial bonding properties under freeze-thaw.The main research contents and conclusions of this paper are as follows:(1)Through the tensile test of basalt fiber cloth and epoxy resin under the action of freeze-thaw,the changes of tensile strength,elastic modulus and elongation of the specimen are explored through the measured data.The test shows that the freeze-thaw cycle has almost no obvious effect on the mechanical properties of basalt fiber cloth.The ultimate load,tensile strength and elongation of epoxy resin specimens decreased with the freeze-thaw cycle,and the freeze-thaw effect would have an adverse effect on the epoxy resin.(2)Through the compression test of concrete,the change of mechanical properties of concrete cube after freezing and thawing is explored.The test shows that the compressive strength and surface tensile strength of concrete test blocks decrease significantly after freezing and thawing.The quality of concrete test block increases instead of decreasing.(3)Through the double shear test under the action of freeze-thaw,the bonding performance of the interface is explored by controlling the freeze-thaw times,bonding length,adhesive layer thickness and concrete strength grade.Observe the failure law,stress-strain distribution,slip amount and the change trend of the maximum failure load of the bonding surface.The results show that the interface is peeling failure,and the interface tends to invade the adhesive layer after freeze-thaw.The change of bond length,adhesive layer thickness,concrete strength grade and freeze-thaw times will affect the ultimate bearing capacity.The softening load of the specimen after freeze-thaw is about 65%,while the softening load of the specimen without freeze-thaw is about 70%.The freezing-thaw action reduces the softening load of the specimen,and will reduce the ultimate strain value and the ultimate slip value of the interface.(4)Through the interface double shear test under the condition of freeze-thaw followed by paste,the changes of stress-strain law,slip value,ultimate bearing capacity,shear stress and interface fracture energy of the specimen under the sequence of freeze-thaw were studied.The test results show that the ultimate bearing capacity,ultimate strain,end slip,shear stress and interfacial fracture energy of the specimens pasted after freeze-thaw are slightly higher than those pasted before freeze-thaw.After the freeze-thaw cycle,the effective bonding length of the interface will decrease.With the increase of concrete strength grade,adhesive layer thickness and bond length,the interfacial fracture energy will increase,but the increase of freeze-thaw times will lead to the decrease of interfacial fracture energy.The bond slip constitutive model is established through the measured data,and compared with the existing classical models of parabolic model,hyperbolic model and bilinear model.It is found that it is the closest to popovics model,and the fitting model formula is obtained.