Influence Of Marine Environment On The Axial Compression Performance Of BFRP Bars Reinforced Seawater And Sea Sand Concrete Short Columns

Reinforced concrete is still the main structural form in the construction of coastal areas or islands and reefs.However,in the marine environment,reinforced concrete structures are prone to chloride ion corrosion,resulting in a significant reduction in service life.Basalt Fiber Reinforced Polymer(BFRP)bars have the advantages of environmental protection,corrosion resistance,high strength and light weight,etc.,and provide a new method to solve the problem of building durability in marine environment.On the other hand,our country has a vast sea area and abundant seawater and sea sand resources,and the mechanical properties of concrete are not greatly affected by seawater and sea sand.Therefore,in the construction of coastal areas,BFRP bars can be combined with seawater and sea sand concrete,which not only solves the problem of corrosion,but also saves the increasingly scarce river sand and freshwater resources in my country,bringing huge economic and ecological benefits.Based on this,in this paper,the axial compression performance of the uncorroded specimens was studied with BFRP bars as reinforcing bars and seawater sea sand concrete as the matrix.Then,indoor artificial seawater immersion and high temperature accelerated aging test were used to study the axial compression performance of BFRP bars reinforced seawater sea sand concrete short columns in marine environment.The specific research contents and conclusion are as follows:(1)The effects of three kinds of longitudinal reinforceme nt ratios(1.5%,2.0%,3.0%),three spiral spacings(50 mm,75 mm,100 mm)and two concrete strength grades(C30,C50)on the axial compression performance of uncorroded BFRP bars reinforced seawater and sea sand concrete short columns were studied.The test results show that the failure of BFRP bars reinforced seawater and sea sand concrete short columns starts from the buckling and fracture of the longitudinal bars,which eventually leads to the crushing of the concrete and the fracture of the spiral s;The longitudinal reinforcement ratio has little effect on the axial ductility of the specimen,but increasing the longitudinal reinforcement ratio from 1.5% to 3% increases the peak load of the specimen by 15.3% ～ 26.1%;reducing the spacing of spiral cannot increase the ultimate bearing capacity of the specimen,but it can increase the axial ductility of the specimen.By reducing the spiral spacing from 100 mm to 50 mm,the axial ductility of the specimen is improved by 26.1% ～ 121.7%;when the concrete strength grade is increased from C30 to C50,the peak load of the specimen increased by 50.9% ～ 59.5%,but the axial ductility decreased by 33.0% ～ 40.1%.(2)The axial compressive properties of BFRP bars reinforced seawater sea sand concrete short columns immersed in artificial seawater at room temperature and 55 °C for 60 days and 120 days were studied.Two kinds of concrete cover(25 mm and 35mm)and two kinds of concrete matrix alkalinity(p H=12.5 ～ 12.8 and p H=11.3 ～ 11.6)were designed for the experiment.Which is to explore the protective effect of concrete cover and concrete matrix alkalinity on the axial compression performance of the specimen.The test results show that after seawater immersion corrosion,the peak load of the specimen will increase,but the axial ductility will decrease significantly.Under the same conditions,the axial ductility of the specimen soaked at high temperature is lower than that of the specimen soaked at room temperature.Increasing the thickness of the concrete cover can protect the axial ductility of the specimen to a certain extent.The use of low alkalinity concrete matrix can effectively slow down the corrosion of the reinforcement,thereby ensuring that the specimen still has good axial compression performance under l ong-term seawater immersion.(3)Based on the existing calculation method of axial compressive bearing capacity of FRP bars reinforced concrete column and the test data of this paper,the calculation formula of axial compressive bearing capacity of BFRP bars reinforced seawater and sea sand concrete short column is discussed.This paper believes that the contribution of FRP longitudinal bars reinforcement should be considered when calculating the axial compressive bearing capacity of BFRP bars reinforcement seawater and sea sand concrete short columns.As far as the test in this paper is concerned,when the reduction factor of the compressive bearing capacity of BFRP longitudinal bars compared with the tensile bearing capacity is taken as 0.25,the calculated value of the theoretical formula of bearing capacity is consistent with the measured value,which can provide a reference for its design.