Research On Deterioration Performance Of Prestressed Concrete Members In Chloride Corrosion Subjoining Cyclic Freeze-thaw

With good performance and energy-efficient social economy, modern prestressed concrete (PC) structures is one of the most extensive and potential structures. In the condition of long harsh corrosion, there are a series of durability problems, such as internal damage and even degradation of bearing behavior and service performance. At home and abroad, durability research on prestressed concrete structures under various erosion environment is relatively few. Combining with the National Natural Science Foundation of China, " Research on durability test and life prediction of prestressed structure under double index erosion environment"(NO:50878098), the paper has explored the influence and deteriorating law to flexural performance of PC members under freeze-thaw cycle and chloride attack, based on test analysis and theory research. the following are main achievements:(1) Durability test of prestressed concrete members under freeze-thaw cycle and chloride attack is finished. Based on orthogonal erosion test on 20 PC specimens (freeze-thaw to chloride attack, chloride attack to freeze-thaw and freeze-thaw and chloride attack at the same time), the most unfavorable condition is found out. The damage failure process of prestressed concrete member is analyzed by attenuation law of relative dynamic elastic modulus. Chloride content under different erosion conditions is measured. Then, bearing capacity deteriorating law of PC beam under freeze-thaw cycle and chloride attack is discussed by bearing capacity experiment.(2) Two-dimensional chloride ion diffusion homogeneous model in prestressed concrete considering freeze-thaw cycle and chloride attack is modeled. According to infinite spread medium, based on integrated positive and negative peak temperature difference, chloride diffusion coefficient of time dependence and the influence of temperature and humidity, two-dimensional homogeneous chloride diffusion model is deduced, under both constant boundary conditions and power function ones. The influence of water-binder ratio, stress level and age on chloride diffusion is discussed.(3) Deteriorating law of flexural performance for PC members under freeze-thaw cycle and chloride attack is simulated. With simulating the bearing capacity deteriorating law of PC beam under different corrosion conditions by finite element, the influence of corrosion condition on bearing capacity is discussed. Based on the comparison between durability test and numerical simulation, the cracking load degradation coefficient in PC beam under freeze-thaw cycle and chloride attack is fitted.(4) Reliability analysis model of PC beam with chloride attack and freeze-thaw cycle is put forward. Focusing on durability failure of prestressed marine structures and requirements on structural durability in seasonal ice regions, reliability analysis model of PC beam under chloride attack and freeze-thaw cycle is put forward by stochastic field theory, considering the influence of positive and negative peak temperature difference, chloride critical concentration and prestressing. It is discussed on the influence of discrete number on failure probability, and sensitivity analysis of chloride concentration, cover thickness and other correlated variables.(5) Durability assessment and life prediction of concrete structures (PC/RC) based on fuzzy reliability theory and Monte Carlo method. Considering uncertainty factors in durability life prediction, random distributions of various parameters are determined, taking the affecting parameters as random variables. According to the structure durability parameter calculated from actual measurement, probabilistic durability life prediction model including multi-random variables is established. Moreover, the probability distribution, statistical distribution parameters and sensibility of hypothesis parameters produced by random simulation is analyzed. The influence of hypothesis parameters variation on the prediction results is discussed.It is shown that, during the process of freeze-thaw cycle and chloride attack, prestress level plays an important role to variation of relative dynamic elastic modulus. The prestressing will offset a part of frost-heaving force, delaying crack development inside concrete, which provide reference for modification and perfection of related concrete design code.