Research On In-situ Transport Mechanism And Randomicity Of Chloride Ions In Concrete In Marine Environment

The durability of reinforced concrete structures in marine environment is becoming more and more serious,and the corrosion of steel bars caused by chloride ion erosion is an important reason for the degradation of structural properties.It is of great significance to study the transport mechanism of chloride ion in concrete for the accurate prediction of service life of concrete structure and maintenance of concrete structure in marine environment.However,at present,many scholars have adopted the homogenization assumption,without considering the influence of the micro structure of concrete,which results in the chloride diffusion coefficient of concrete is not consistent with the theoretical value.Moreover,the distribution of aggregates and pores in concrete can’t be ignored,and it is not possible to accurately characterize the heterogeneity and randomness of chloride transport in situ.In order to study the mechanism of chloride transport in concrete,the main work of this paper is as follows:(1)The interfacial transition zone(ITZ)width in concrete was measured by electron probe technique,and the diffusion coefficient of ITZ was deduced by one-dimensional transmission test.A numerical model of concrete mesoscale scale was established,and the process of chloride ion transport in concrete was numerically simulated and the model was validated by electron probe technique.Based on the mesoscale numerical simulation,the effect of aggregate and ITZ on the chloride ion transport process was systematically studied.(2)Through the X-ray CT reconstruction technique,the three-dimensional mesoscopic numerical model of concrete is established.The numerical model can characterize the aggregate and pore structure in the concrete,and verify the accuracy of the model by electron probe technology.The effects of aggregate,porosity and ITZ on chloride ion concentration and diffusion flux field distribution were analyzed.The effects of aggregate,pore and ITZ on the concentration of chloride ion and diffusion flux were analyzed.(3)Based on the 3D model of concrete obtained by CT reconstruction,the distribution law of aggregate and pore in concrete was analyzed.The randomness rule of chloride ion transport in real concrete was analyzed by numerical simulation method.Concentration distribution histogram was used to fit and hypothesis test,and the probability density distribution function of chloride ion concentration was obtained.Finally,the influence of ITZ diffusion coefficient,aggregate shape and position on the random transmission of chloride ion was studied by comparing the different models.The research results provide the basis for analyzing the time-varying reliability of reinforced concrete members or predicting their remaining service life.