Investigation On The Bond Behaviour Between Basalt Fiber Bar And Seawater Sea-sand Concrete In Freeze-thaw Environment

As the most common building structure,reinforced concrete has serious economic damage and safety problems such as steel corrosion.The application of Fiber Reinforced Polymer reinforcement to building structures can not only effectively solve the problem of steel corrosion,but also apply seawater sea-sand concrete.Among them,whether FRP bar have good bond performance with concrete is one of the key issues in engineering applications.At present,there are sufficient studies to show that FRP bar has good bond to concrete.However,in practical engineering applications FRP reinforced concrete not only needs to have good bond properties,but also bonddurability is crucial.Freeze-thaw damage,as the second largest cause of structural damage in buildings,is only ranked after the corrosion damage of steel bars.Therefore,it is necessary to carry out research on the bond durability of FRP reinforced concrete in freeze-thaw environment.This test refers to China and American specifications.In this test,59 compression specimens,dynamic elastic modulus specimens and pull-out specimens were prepared,including 23 non-freeze-thaw specimens and 37 freeze-thaw specimens.According to the specification "Ordinary Concrete Long-term Performance and Durability Test Method",the fast freezing method is selected for antifreeze test,and the freeze-thaw cycle temperature is controlled between-18℃to 5℃,with a temperature error within 2℃.Through the physical and mechanical properties test,dynamic elastic modulus test and pull-out test,the influence of freezing and thawing cycle on the basic mechanical properties of seawater sae-sand concrete,the bond durability of BFRP reinforcement concrete,and the influence of protective layer thickness on the bond performance under freezing and thawing environment are explored.Through the above tests,the following main conclusions are drawn: 1.With the increase of the number of freeze-thaw cycles,the compressive strength,elastic modulus and dynamic elastic modulus of concrete decrease.2.With the increase of the number of freeze-thaw cycles,the strength of interfacial bonding and bonding stiffness decrease,the amount of slip increases,and the instability of bonding behavior increases.3.With the increase of the thickness of the protective layer,the bond strength increases,the amount of slip increases,and the stability of the bonding behavior increases.4.In the case of a lower protective layer,the bond stiffness increases as the thickness of the protective layer increases.Finally,the effects of freeze-thaw on the bond interface and the internal structure of concrete were studied by analysis of bond interface damage and SEM scanning electron microscopy.Based on the quadratic polynomial and Weibull models,a life prediction model with compressive strength,kinetic elastic modulus and bond strength as damage factors is established.Through the comparison of life prediction models,it is found that the interfacial bonding performance life in freeze-thaw environment is significantly lower than the life of concrete.Therefore,this thesis recommends that the interfacial bonding performance be used as one of the criteria for judging the failure of building structures in a freeze-thaw environment.