Research On The Corrosion And Freeze-thaw Coupling Damage Of The Critical Muti-phases Region In Reinforced Concrete Components

Reinforced concrete structure is the most widely used structure type at present.The "soft" load in the service process of the structure will lead to the deterioration of the material durability,and then shorten the service life of the structure.Facing the cold region of reinforced concrete structures,this paper adopts theoretical analysis,numerical simulation and experiment with the combination of means,in view of the typical solid liquid gas three phase zone,under the coupled action of corrosion and freeze-thaw durability degradation research,in order for safety assessment of reinforced concrete structure,maintenance,and provide a scientific basis for whole life design.The main content of this paper is as follows:Firstly,the water transport model of reinforced concrete member in solid-liquid gas three-phase zone is established,and the influence of main factors on the capillary water absorption in three-phase zone is analyzed.According to the conservation of mass and darcy’s law has established the concrete capillary water absorption phase control equation when Richard equation,using the zhou’s model in the literature in as boundary conditions,through the experiment fitting to get the suitable parameter calculation,finally got to describe concrete to become saturated by unsaturated porous media evolution process,the mathematical model and numerical calculation method of the two-dimensional mathematical model is established.The corresponding relationship between concrete moisture content and resistivity is established,and the results of numerical calculation are verified by experiments.In addition,the influences of water-cement ratio,initial water content and geometric configuration on the capillary water absorption of concrete specimens are further analyzed.Secondly,a particle transport model of reinforced concrete erosion in the solid-liquid gas three-phase zone was established to characterize the electrochemical characteristics of corrosion in the three-phase zone qualitatively and quantitatively.The governing equations of erosion particle transport in the three-phase zone of concrete slabs were established by using Nannst-Plank equation,mass conservation equation and charge conservation equation.The corresponding boundary conditions were obtained according to the polarization curves of specimens in the three-phase zone under the same conditions.Then the mathematical model and numerical calculation method of erosion particle transport in the three-phase zone of reinforced concrete were established.The half potential and local current densities of concrete slabs at different ages are compared and analyzed to verify the accuracy of the numerical results.In addition,electrochemical impedance spectroscopy and step excitation method were used to quantitatively characterize the corrosion electrochemical characteristics of reinforced concrete in three-phase zone.Finally,the deterioration mechanism of reinforced concrete in the three-phase zone under the coupling of freeze-thaw and corrosion is studied.The qualitative and quantitative deterioration characteristics of reinforced concrete specimens under freeze-thaw cycles were obtained by appearance inspection and mass loss rate statistics.The corrosion electrochemical characteristics of reinforced concrete specimens in three-phase zone under different freeze-thaw cycles were characterized by electrochemical impedance spectroscopy,step excitation and polarization curves,and the results were compared with those at room temperature.The passivating film,resistance of concrete and pore solution,corrosion current density and solute diffusion evolution law of reinforced concrete in the early,middle and failure period of freeze-thaw corrosion were mastered,and the corrosion freeze-thaw coupling damage mechanism of reinforced concrete in three-phase zone was revealed.