Mesoscopic And Stochastic Study On Multi-factor Coupled Concrete Erosion

The problem of concrete durability is a global problem, and the harmfulness of concrete deterioration has reached a common understanding in the world. Many domestic and foreign scholars have studied such problems as chloride ion erosion and carbonization in concrete. However, the durability of concrete is a system engineering composed of the material, structure, natural environment and service environment, and the single factor research cannot fundamentally solve this problem. Up to now, a multi-factor coupled numerical model that can systematically reflect the durability of concrete structure has not been established. Emphasis in this paper was focused on such degradation factors as chloride ion transport, concrete carbonation, water transport, load effects and the coupling relationship between them, and a multi-factor erosion coupled numerical model was proposed. Based on the gradation theory and Carlo Monte method, the mesoscopic stochastic concrete model was presented. Finally, the multi-factor erosion coupled numerical model was combined with the mesoscale stochastic concrete model, thus a multi-factor erosion coupled stochastic mesoscale model of concrete was established. Furthermore, the solution, verification and discussion of the multi-factor model were carried on at different scales from macro to mesoscale. It is believed that the research will have some significance in promoting the study of the durability of concrete in both theoretical research and practical application. The main research contents are as follows:(1)A comprehensive multi-factor correction numerical model of chloride transport in saturated water was performed, and the transport behavior of chloride ions in saturated concrete was studied. The general range of parameters in the model were given, and the sensitivity of each parameter was analyzed. And the calculation results of the modified model were compared with the measured data.(2)The convection-diffusion control equation of chloride ion transport in drying-wetting alternant environment was set up, and the model test, model validation and model parameter analysis were carried out. The temporal and spatial variation of chloride ion concentration in drying-wetting alternant environment was summarized.(3)A more comprehensive model of the coupling of carbonation, water transfer and chloride ion transport in concrete was built for the first time. The hydration process and carbonization process were parameterized, the numerical model of hydration process and the carbonization process were established, and then the numerical model of carbonation was established by the combination of the two. Based on the coupling relationship between concrete carbonation and chloride ion transport, the coupling model of carbonation and chloride ion transfer was established. Based on the relationship between chloride ion transport and water transport, a coupled model of chloride transport and water transport was established. Finally, these models were integrated to establish a coupling model of carbonation, water transfer, and chloride ion transport.(4)For the first time, a model of the coupling of carbonation, moisture transport, chloride transfer and loading effects was set up, and was solved, verified and discussed. The relationships between porosity and strain, strain and load were established, and the relationships between porosity and chloride diffusion coefficient, moisture diffusion coefficient and CO2 diffusion coefficient were established. In accordance with these coupling relationships, loading effects-chloride transfer coupling model, loading effects-carbonation coupling model, and loading effects-water migration coupling model were set up respectively, and then, the carbonation-moisture transfer-chloride ion transfer-loading effects coupling numerical model was established, and was verified and discussed.(5)The random characteristic of concrete was studied, and the mesoscopic stochastic concrete model was established. A two dimensional circular aggregate model was built, and the aggregate model of circular and elliptical random mixture was proposed for the first time, thus the shape of aggregate is more in line with the requirements of randomness and the practice. The 2D polygon aggregate model was established, and the influence of sharp angle was took in to account for the first time, which makes the model more consistent with the actual aggregate shape. Compared with the model of aggregate by other scholars, this model took into account not only the aggregate gradation and shape, but also the random distribution of particle size, and the equivalent particle size method was abandoned, thus the random aggregate model is more close to the actual. The software fig2 dxf 2016 was developed to convert random aggregate model built based the MATLAB platform to a common DXF interface format, making the aggregate model can be opened and edited by CAD and most of the finite element softwares.(6)For the first time, a multi-factor erosion coupling mesoscopic stochastic model of concrete was built. By means of a large number of numerical experiments of mesoscopic stochastic concrete specimens, the random characteristics of the carbonation depth and the concentration distribution of the erosion medium were analyzed, and the corresponding stochastic model were proposed.