Research Of Damage Mechanism Of Cement Concrete Pavement Under Freezing Environment Based On Fem Numerical Simulation

Ice freezing disaster is a nature disaster that is very common in the south and southwest region of China. Ice freezing disaster caused great damage to the transportation infrastructure, influenced the local people's produce and life severely.The process of ice's damage to the cement concrete pavement is firstly the saturated pores in the pavemnet freeze when the temperature reaches the freezing temperature, the form of ice makes the pores tensed, then the mirco-cracks appear in inner pavemnet. Then the mirco-cracks expand to invisable, large cracks due to the continuous stress. At last the pavement is destroyed for it losts its capacity of loading. As we know, concrete as a brittle material, its tensile strength is far beyond compressive strength, so the tensile stress is a fatal factor to the destroy of concrete. The pore tensile stress in the inner pavement can be divded into 3 categories: 1.In the closed-pores with the pores saturated, the water in the pores becomes ice, due to the difference between the density of water and ice, the volume of ice is greater then water, this makes the pores expand, produce tensile stress to the pavement. 2.In the opend-pores,the process of water becomes ice expels the free water to the smaller, unfrozen pores, this process produces precolation pressure. 3.In the same pore, the differential pressure between ice and water due to the effect of capillary pore interfacial tesion. It is generally believed that the second and third stress are main stress that destroy the pavement subjeced to the frozen condition. This thesis's research is based on the hypothesis that the ice's damage to pavement is precolation pressure.At the same time, during the process of temperature changing, the inner pavement's temperature field will changed notable for the existence of the ice in the pore. This will produce temperature stress to the pavement.The main contents of this thesis are listed as follows:1.Introduce the mirco-structure of the main material-concrete, which forms the cement concrete pavement, and the forming and expanding process of the ice in the poers, the pressure during the process of ice forming.2.Creating a nano-scale pavement micro-modle, then arrange a pore in the model. Using the FEM software-Ansys, based on the basic principle of heat transfer, simulating and analysing the influence of inner pavement's temperature field while the pore diameters and water-ice content are different. Deducing the function relationship between the pore diameters, water-ice content and the temperature difference. The conclusion of this analyse is that due to the existence of pore and ice crystal, the uniform temperature field disturbed notably. From the analysis also discovers the temperature stress loaded on the pore is a process of firstly decreases, then increases.3.Based on the stress field, pore media precolation field and temperature field of multi-physics coupling theory, using software Comsol to1 simulate the process of ice forming in the inner pavement.Accroding to different cooling rate, porosity, permeability coefficient and pores accumulation distrubution functions,design 4 suites models. Every suite contains 4 models used for comparing. Calculating the stress and starain due to ice. Getting some reference points's curves of stress and starain to temperature. Preliminary obtain the damage mechanism of ice to the rigid pavement.