Durability Study And Theoretial Analysis On Concrete Beams Reinforced With BFRP With Steel Bars Exposed To Marine Environments

Marine environment is a harsh and complex environment with high temperature,high humidity,high salinity,large temperature difference between day and night and strong ultraviolet radiation,which poses a huge threat to the durability of traditional reinforced concrete structures.The phenomenon of steel corrosion and concrete rust will dramatically reduce the service life of reinforced concrete structures,and seriously hinder the development and large-scale construction of marine engineering.Basalt fiber-reinforced polymer or plastics(BFRP)have the characteristics of light weight,high strength and corrosion resistance.Reinforcement bar has the advantages of large stiffness and good ductility.BFRP-reinforced concrete structure combines the excellent performance of BFRP and reinforcement bar.At the same time,it combines the structural design methods of BFRP and reinforcement bar.It provides a new idea to solve the durability problem of reinforced concrete structure in marine environment.According to the above research background,this paper adopts the structure of BFRPand steel bar mixing configuration.The short-term and long-term mechanical properties of BFRP-reinforced concrete beams are studied.The BFRPproducts include BFRP bars,SFCB and BFRPgrids.The experiments are mainly divided into three aspects: BFRP bars in artificial seawater environment,bond performance between SFCB and concrete,short-term mechanical properties of BFRP-reinforced concrete beams and durability of BFRP-reinforced concrete beams in artificial seawater environment.(1)Experiments of artificial seawater immersion corrosion and dry-wet cyclic corrosion of BFRP bars and SFCB were carried out respectively.The corrosion ages were set at 30,60 and 90 days.The bonding properties of corroded BFRP bars,SFCB and concrete were tested by unidirectional axial pull-out test.The results show that seawater immersion corrosion has a greater impact on the bond strength of BFRP bars and SFCB to concrete.The bond strength of BFRPbars to concrete is always higher than SFCB before and after corrosion.The bond strength of BFRPbars to concrete decreases with the increase of corrosion age,and the decrease is greater than SFCB.(2)Through the static load test of eight BFRP-reinforced concrete beams under four-point compression and bending,the following results can be obtained: compared with reinforced concrete beams,BFRP-reinforced concrete beams have higher bearing capacity and flexural rigidity after yielding,ductility also meets the seismic requirements,and have good comprehensive performance.When the ratio of reinforcing bars to BFRPbars as/Af is kept at 0.48,the performance of the composite beams can be optimized.At the same time,reducing the diameter of BFRP bars or increasing the BFRPmesh in the tension zone can also improve the performance of the composite beams.The mechanical properties and service performance of SFCB reinforced concrete beams are better than that of reinforced concrete beams.Reducing the diameter of SFCB can also improve the performance of SFCB reinforced concrete beams.(3)Four-point bending static load tests were carried out on reinforced concrete control beams,BFRP-reinforced concrete beams,SFCB-reinforced concrete beams,BFRP-reinforced concrete beams and BFRP-reinforced concrete beams under dry-wet cyclic corrosion in artificial seawater for 3 months and 6 months respectively.The following results can be obtained:After corrosion,the tensile steel bars and steel stirrups of the experimental beams are corroded to a certain extent,but the BFRPand SFCB have not changed significantly.The flexural stiffness of the experimental beams has been improved to varying degrees.Meanwhile,the mid-span deflection corresponding to the ultimate load has been greatly reduced.The main reason is that the long-term load coupling causes the plastic deformation of the beams,and the strength of the corroded concrete has been increased.