Research On Fatigue Performance Of BFRP Bars In Seawater And Sea Sand Concrete Environment

In recent years,with the continuous development of national infrastructure and marine platforms,coastal cities have started to expand on a large scale,and thus new concrete structure projects such as cross-sea/sea defense are also increasing year by year.However,the high content of chloride ion(Cl~-)in seawater and sea sand has a significant effect on the corrosion and deterioration of steel reinforcement,which greatly limits the application of steel reinforced seawater and sea sand concrete structures.Therefore,fiber reinforced polymer bar(FRP bar),which is characterized by its light weight,high strength,excellent fatigue and corrosion resistance,is considered to be used in conjunction with seawater and sea sand concrete to avoid the corrosion and deterioration of steel reinforcement in these new concrete structures.There have been many different types of FRP bars used in civil engineering structures,but the studies on fatigue performance of basalt FRP(BFRP)bars are only limited to conventional concrete(alkaline)and seawater(salt water)environments.To data,the studies on the fatigue performance of BFRP bars in seawater and sea sand concrete(high salt and alkaline)environments have not been reported.Therefore,this study investigates the fatigue performance of BFRP bars in seawater and sea sand concrete environment.In this study,fatigue tests were carried out on BFRP bars before and after ageing in seawater and sea sand environment.In addition,scanning electron microscope(SEM)was used to analyze the microstructure of BFRP bars in different aging conditions.Further,Arrhenius equation was used to predict the fatigue life of BFRP bars at different ageing times and temperatures.The results show that:the fatigue damage of the unaged BFRP bars is caused by the continuous expansion of the transverse cracking of the matrix and is strongly related to the deboning of the fiber-matrix interface;the applied stress range has a great influence on the fatigue life of BFRP bars,while the stress level has relatively slight influence on the fatigue life;the fatigue cycling and corrosion conditions have almost no effect on the modulus of elasticity of the BFRP tendons;the simulated seawater and sea sand concrete pore solution can penetrate into BFRP bars,which causes hydrolysis between of the matrix,resulting in localized deboning of fiber-matrix interface under fatigue loading,and high temperatures can accelerate this hydrolysis reaction,finally causing degradation of fatigue performance of BFRP bars in seawater and sea sand concrete environments;through Arrhenius equation,after 100 years of aging of BFRP bars in the seawater and sea sand concrete environment,the predicted values of the fatigue strength of BFRP tendons are 0.21 f_u,0.26 f_u and 0.30 f_u in the areas of 20°N latitude,40°N latitude and 60°N latitude,respectively.In a word,the results in this study may provide a certain experimental basis and theoretical guidance for the fatigue design of BFRP bars in seawater and sea sand concrete environments.