Research On The Durability Of Concrete Column With Hybrid Reinforcement Of BFRP Bars And Steel Bars In Marine Environment

In the marine environment,traditional concrete structures are facing the severe security risks of steel corrosion and reduction of service life.fiber-reinforced polymer(FRP)materials have the advantages of high strength-to-weight ratio,corrosion and fatigue-resistance,which can improve the service life of concrete structure under the marine environment.By using BFRP bars and steel bars as reinforcement materials at the same time,a hybrid reinforcement member with FRP bars and steel bars can be formed,which can combine the advantages of BFRP bars and steel bars.It is expected to solve the durability problem of traditional concrete structures in the marine environment.However,the steel bar has the risk of corrosion in the marine environment,and the BFRP bar has the disadvantage of poor rigidity and ductility.Therefore,ensuring the simultaneous improvement of durability and structure is the key to studying the FRP bar-steel bar hybrid reinforcement member.In view of the above problems,this paper studies the mechanical properties and durability of BFRP bar-steel bar hybrid reinforced concrete columns.The research contents are as follows:(1)Experimental studies were performed on the durability of BFRP bars and Steel-FRP Composite Bars(hereinafter referred to as SFCB)in three corrosive environments at 55 ° C.The corrosive environment includes: wet-dry cycle of seawater solution,concrete wrapped +wet-dry cycle of seawater,salt and alkali mixed solution,and the corrosion age period is set as 40 days,80 days,and 120 days.The results show that in three corrosive environments,the strength retention rate of BFRP bars is higher than that of SFCB.For each test specimen,the descending order of the corrosive environment by the tensile strength degradation is:seawater dry< wet cycle Wrap <Salt-alkali solution immersion;Under various corrosive environments,the yield strength of SFCB tendons also remains basically stable.(2)Experiments were performed on BFRP bar-steel bar hybrid reinforced concrete columns with different reinforcement forms,and the bearing capacity,deflection,and maximum crack width were recorded.The results show that for BFRP bar-steel bar hybrid reinforced concrete columns,the ultimate bearing capacity under big eccentric compression will increase with the replacement rate of BFRP bars(equivalent stiffness replacement),but the improvement is limited;the utilities of smaller-diameter BFRP bars can reduce the maximum crack width.Compared with the RC columns,SFCB reinforced concrete column can maintain better bearing capacity and crack control ability.(3)The test of 4 kinds of concrete columns with different reinforcements under the 55 °C seawater dry-wet cycle was carried out.The age of corrosion is 3 months and 6 months.Reinforcement forms include RC column as control group,BFRP bar-steel bar hybrid reinforced concrete columns,BFRP grid-BFRP bar-steel bar hybrid reinforced concrete columns and SFCB reinforced concrete column.The results show that after corrosion,the flexural rigidity of each specimen increases,and the maximum crack width decreases.Compared with the above reinforcement forms,SFCB reinforced concrete column shows better durability.