Research On Damage Similarity Theory Of Pre-stressed Concrete Specimens In Marine Atmospheric Environment

Pre-stressed concrete structures in coastal areas often have durability problems ahead of time due to long-term erosion by the sea.External environment makes them accelerate the process of failure,and repair or reconstruction cause painful economic cost.Therefore,the durability problems of pre-stressed concrete structures in the marine environment are increasingly valued by many countries.The marine atmospheric area is salt spray environment with high chloride ion concentration,and the sea gas and other external forces exacerbate the erosion of structures.It is necessary to study the damage degradation of pre-stressed concrete components in the marine atmosphere.Supported by the National Natural Science Fund Project "Research on theory and engineering application of similar marine pre-stressed concrete structure durability(51278230)",this paper explored the damage similarity between component in artificial climate simulation acceleration experiment and beam in the atmospheric area of Lianyungang dock based on the environment-time similarity theory and numerical simulation method.And concrete damage in the process of steel corrosion was also studied.The main contents were as follows:(1)The chloride diffusion coefficient calculation model was modified,considering the effects of porosity,water-cement ratio,aggregate volume fraction,erosion time,stress state and stress level on the chloride diffusion coefficient.Under the premise of satisfying concrete workability,reducing water-cement ratio and increasing aggregate volume fraction could effectively reduce the chloride ions transmission performance.The influence of pre-stress loss on the chloride diffusion coefficient was discussed by comparing calculated values of chloride diffusion coefficient with and without considering pre-stress loss.(2)The distribution of chloride diffusion coefficient in the component and the chloride ion concentration model on the concrete surface were applied to the module "The Transport of Diluted Species Interface" in COMSOL Multiphysics.Simulating the chloride ion transport process of artificial climate accelerated test components and Lianyungang port site components,the simulation results were compared with those of indoor experiment and field tests respectively.The results showed that the numerical simulation method was reliable.(3)Based on the theory of thick-walled cylinder,the ratio of annular tensile stress of the outermost edge and tensile strength of concrete was used to define the corrosion damage degree of concrete.Combining simulation results of chloride concentration on the surface of steel bar,the relationship among damage degree,corrosion current density and time was established,so as to determine the damage evolution equations of artificial climate accelerated test components and Lianyungang port site components.(4)Based on the theory of environment-time similarity,the damage similarity between artificial climate accelerated test component and dock site component was established,and the similarity constant between them was 3.19.How to use the damage similarity to predict the crack initiation time of concrete protective layer was summarized.The influence of thickness of concrete protective layer and strength grade of concrete on the corrosion damage of concrete was studied.Increasing thickness of concrete protective layer and concrete strength grade could retard the cracking time of protective layer,and increasing thickness of concrete protective layer was more effective.