Cement Hydration Simulation Based Prediction Of The Water Permeability Of Cement Paste

The water permeability of concrete is a key index for the durability assessment and design of reinforced concrete structure and it depends on the characteristics of the mesoscopic structure of concrete. The microstructure of cement paste is reproduced in this thesis. The theory of permeability is combined to predict the water permeability of concrete. The following three aspects are mainly studied.According to the principles of hydration kinetics, the whole process of cement hydration is simulated. The validity of the simulation method is preliminarily verified by comparing the simulated degree of hydration with experimental data in the literature. The effects of the water/cement ratio, the minimum cement diameter, maximum cement diameter, and temperature on the degree of hydration are evaluated in a quantitative manner.Based on the simulated microstructure of cement paste, the structural characteristics of capillary pores in cement paste are analyzed. A computer simulation method of the porosity and the specific surface area is proposed. The effects of the water/cement ratio, the minimum cement diameter, the maximum cement diameter, and temperature on the porosity and the specific surface area are evaluated quantitatively. The results showed that the porosity decreases with the decrease of the water/cement ratio, the minimum cement diameter, and the maximum cement diameter but increases with decreasing the temperature. At the age of 28 days, the specific surface area decreases with the decrease of the water/cement ratio but increases with decreasing the minimum cement diameter, the maximum cement diameter, and the temperature. In addition, a computer simulation method of the size distribution of capillary pores is also proposed. The effects of the water/cement ratio and the maximum cement diameter on the size distribution of capillary pores are discussed.According to the principles of permeability in porous materials, a isotropic permeability model of cement paste is established, and the modified Kozeny-Carman equation is discussed. It is found that the modified equation is only valid when the porosity is larger than the critical value. The solution process of the general effective medium theory is modified. The water permeability of cement paste with a porosity smaller than the critical value is discussed. The validity of the method is preliminarily verified by comparing the numerical results with those given by the lattice Boltzmann model. The results show that, during the cement hydration process, the water permeability decreases with a decrease in porosity. When the porosity is smaller than the critical value, the water permeability reduces dramatically. For a given water/cement ratio, the water permeability decreases with the increase of the degree of hydration. For a given degree of hydration, the water permeability decreases with decreasing the water/cement ratio, the minimum cement diameter, and the maximum cement diameter.