Experimental Study On The Effect Of Freeze-thaw On The Bond Behavior Of BFRP Bars

As a new building material,fiber reinforced polymer(FRP)bars have many advantages,such as high tensile strength,corrosion resistance and light weight.It is considered by many scholars that FRP bars can be used to replace or supplement steel bars to strengthen concrete structures.In order to be better applied in engineering practice,many experimental subjects related to FRP bars have been established,and the bond performance between FRP bars and concrete is one of the important research directions.Compared with CFRP,GFRP and AFRP,BFRP has the best comprehensive performance.In addition,freeze-thaw cycling will destroy the mechanical properties of concrete,which will lead to the degradation of bonding between reinforcement and concrete.In a word,it is very important to study the effect of freeze-thaw cycles on the bonding properties of BFRP bars.In this paper,freeze-thaw cyclic test,cubic compressive strength test and central pull-out test are carried out to study the bond properties of BFRP bars and concrete with different strength grades before and after freeze-thaw.The main research work and conclusions are as follows:1)Through freeze-thaw cyclic test,cubic compressive strength test and central pull-out test,the influence of concrete strength and freeze-thaw times on the bond performance of BFRP bars was explored.The study found that: Freeze-thaw has a great influence on the debonding strength,ultimate bond strength and peak slip of BFRP bars and concrete.With the increase of freeze-thaw times,the ultimate bond strength and peak slip of BFRP bars and concrete show a trend of first increasing and then decreasing,which is the same as the change trend of concrete strength with freeze-thaw times.The ultimate bond strength between BFRP bars and concrete does not increase directly with the cubic compressive strength of concrete because friction takes the largest proportion in the bond between BFRP bars and concrete.The debonding strength of BFRP bars and concrete is positively correlated with the strength of concrete.2)Based on the grey relational degree theory,this paper quantitatively analyzed the correlation degree differences between concrete strength,bond length and diameter of reinforcement on the bond properties of BFRP,GFRP,CFRP and steel bars,and the relationship between freeze-thaw times and bond properties of BFRP tendons varies with the increase of concrete strength It is found that the influence of reinforcement diameter,bond length and concrete strength on the bond performance of steel bar is different from that of FRP bars.The influence on bond performance of FRP bars is related to the types of FRP bars.The correlation degree of bond performance of GFRP bars and BFRP bars is in turn bond length,diameter of steel bar and concrete strength.The correlation degree of CFRP bars is in turn steel bar diameter,bond length and concrete strength.With the increase of concrete strength grade,the correlation degree between freeze-thaw times and degumming strength of BFRP bars decreases gradually;the correlation degree between freeze-thaw times and ultimate bonding strength of BFRP bars is greater than that between concrete strength and ultimate bonding strength of BFRP bars.