| With the implementation of the maritime power strategy,ocean and port buildings and structures will become new construction hot spots.The use of traditional reinforced concrete structures in marine engineering not only increases the construction period and cost,but also intensifies the consumption of natural gravel resources and freshwater resources.Basalt fiber reinforced polymer(BFRP)bars are used to seawater and sea sand concrete(SWSSC)to construct marine engineering structures,which can fundamentally avoid the corrosion of steel bars and solve the problem of scarcity of freshwater and river sand resources.But under strong alkali environment such as the internal environment of SWSSC,the basalt fiber will be etched and the resin-fiber interface bond will deteriorate,resulting in severe degradation of the longterm performance of the BFRP bar.It caused the durability problem of BFRP bars to reinforce the concrete structure of SWSSC.At present,most of the research on the durability of BFRP bars are to directly immerse the BFRP bars in alkaline solution to simulate its internal environment in concrete under the laboratory accelerated aging test.This method is difficult to reflect the dynamic changes of the internal alkalinity of real SWSSC.In addition,due to the long time-consuming and high cost of the durability test,so far at home and abroad,there is a lack of reports on the long-term performance of BFRP bars in actual marine environments.In view of the shortcomings of current research,this paper studied the long-term mechanical property degradation of BFRP bars in SWSSC under accelerated aging conditions in the laboratory and actual marine environments,and the long-term performance of BFRP bars in SWSSC under marine service environment is discussed.By using different solution environment(alkaline solution,artificial seawater and distilled water),temperature(room temperature,40°C and 60°C)and SWSSC wrapped thickness as variables,through the implementation of accelerated aging tests at different time scales,to clarify the degeneration rule of macroscopic mechanical properties(tensile strength,tensile modulus,interlaminar shear strength and transverse shear strength)of BFRP bars in SWSSC.Combined with microscopic testing techniques(SEM,FTIR and DMTA),the degradation mechanism of BFRP bars in SWSSC under the marine environment is explained.On this basis,the Arrhenius formula is used to establish the service life prediction model of BFRP bars,and combined with the exposure test data in a typical subtropical marine environment(Zhanjiang Port Exposure Test Station).The equivalent relationship between laboratory acceleration and actual service environment is proposed.The main research contents and conclusions are as follows:(1)Long-term mechanical performance tests of BFRP bars in SWSSC under accelerated aging conditions are carried out in the laboratory,to analyzed the tensile property degradation rules of BFRP bars in SWSSC under different solution environments,temperatures and SWSSC wrapped thickness.The results show that after immersing for one and a half years in the laboratory under accelerated aging conditions,the degradation rate of BFRP bare bars in alkaline solution environment is much faster than that in seawater and distilled water.Immersing in distilled water at room temperature after 540 days,the tensile strength retention rates of BFRP bare bars,SWSSC10 and SWSSC20 specimens were 79.1%、61.5% and 38.8% respectively.Concrete pore fluid is the main factors that cause long-term performance degradation of BFRP bars in SWSSC.With the increase of SWSSC wrapped thickness,the deterioration degree of BFRP bars is more serious.(2)Research on the degradation of interlayer properties of BFRP bars in SWWSC under the laboratory accelerated aging test.The results show that the degradation rate of interlaminar shear strength of BFRP bars wrapped in SWSSC is much higher than the transverse shear strength,which indicates that the degradation of the mechanical properties of BFRP bars wrapped in SWSSC is due to the poor adhesion of fiber resin interface and the fibers in a corrosive environment.FTIR results show that basalt fibers are more significantly corroded than resin during the aging process.(3)The BFRP bar-SWSSC interface derivates white gelled substance after immersing in high temperature environment.FTIR is used to analyze the cause of the white gelled substance.The results of the study indicate that the substance is probably an alkali silicic acid gel formed by alkali aggregate reaction of basalt fiber in the internal environment of high temperature and humid SWSSC.(4)Carry out the long-term performance test of BFRP bars in seawater and sea sand concrete under actual marine environment,and compare the test results under laboratory accelerated aging test.The results show that the degradation rate of tensile strength,interlaminar shear strength and transverse shear strength of BFRP bars exposed to the marine environment is lower than the accelerated laboratory aging test.The p H value of the solution is high due to the precipitation of alkaline substances in seawater and sea sand concrete in the laboratory immersion environment,which causes continuous erosion of the fiber-interface adhesion performance and the resin matrix.(5)Arrhenius formula is used to make long-term predictions on SWSSC10 and SWSSC20 specimens,and the prediction results are compared with the test results in the actual marine environment.The equivalent relationship between laboratory acceleration and actual service conditions is proposed.The results show that the equivalent time relationship of SWSSC10 and SWSSC20 specimens between the accelerated laboratory aging and the actual service environment are 1.79 and 1.69,respectively.(6)The long-term life of BFRP bars in ordinary concrete and seawater sea sand concrete are predicted.The results show that when the thickness of the concrete is thin,the long-term life of BFRP bars in seawater sea sand concrete is higher than that of ordinary concrete,which is due to the change in alkali environment in seawater sea sand concrete after hydration reaction.However,with the increase of the thickness of the concrete,the long-term life of BFRP bars in seawater and sea sand concrete is lower than that of ordinary concrete,because the greater the thickness of the package,the more salt and alkali substances it contains,resulting in continuous exposure of the BFRP bars in high concentration salt and alkali environment. |
