Study On Some Aspects Of Molecular Simulation Of Silicate Minerals And Their Hvdration Products

The hydration process and microstructure development of cement have significant influence on the properties of cement-based materials. In the recent200years, experts of material got many valuable achievements through the research of this topic. However, the hydration process of cement is such complex that the hydration mechanisms couldn't be totally understood and the microstructural characteristics couldn't be obtained. Using molecular simulation as main method, some issues of cement hydration process were discussed in this paper, such as the mechanisms of the reaction of CaO and H2O, the doping modification of C3S, the microstructure of C-S-H gel, the factor which effects the hydration process etc.Besides, the validity of chosen algorithm and model were verified through the comparison of experimental data with calculated result, this new research method which has great potential value for designing the cement-based material according to engineering requirements.To understand more intricated hydration of cements clinker minerals, the interaction process of CaO, one of the most important ingredients of cement clinker, and H2O is an important implication. Calculating through first principle of quantum mechanical, we found the perfect surface of CaO(100) polarized observably compared to bulk phase, and then this surface got higher reactivity which made it adsorb H2O molecule spontaneously and form chemical bonds. At the coverage of1/4ML and1ML, the most stable adsorption site is bridge site, while the coverage is1/2ML, hole site becomes the most stable adsorption site.Kaolin was applied to cement material widely because of its outstanding adsorptivity. The water adsorptivity evolution pattern of kaolin system was studied by Monte Carlo method. When other conditions keep the same, the increasing pressure will improve the adsorption of water, while the increasing temperature will prevent adsorption. Under the admixture effects of aluminium ion, the activity of kaolin system was enhanced obviously, while the introduced positive ion to counter-balance electrovalence will change the aperture of kaolin.The reasonable model of main reactant (C3S) and product(C-S-H gel) was established based on the structure parameters which were gained through testing, then the amorphous C-S-H gel was gained through molecular dynamics simulation and Monte Carlo simulation. Based on the obtained model, the admixture effects of CuO to C3S and styrol-acrylate to C-S-H gel were investigated respectively. The introduction of CuO will lower the firing temperature of C3S clinker, but will not change the overall crystal structure only leading to slight structural change. When the content of CuO is low, it enters into the crystal lattice just through solution, which never involves any chemical reaction. When the propotion of CuO is higher than3%, solid solution will happen between CuO and C3S. In this way, new phase may form. The C-S-H gel system gained through molecular dynamics simulation and Monte Carlo simulation has short-range order and long-range disorder, which belongs to amorphous structure characteristic. The final structures under different Ca/Si ratios tend to be similar. In that situation, the coordination number of atom Si and O is4, so silicon-oxygen tetrahedron is still the basic unit, and chain structure is constructed by the bridge oxygen. The styrol-acrylate, which was admixed in C-S-H gel to modify its property, dissolved preferably and enhanced the compressibility of the original system significantly, while decreased the bulk modulus and shear modulus.Based on continuous hydration medium model, the effects of some external factors, such as the quality of cement clinker and water/cement ratio, on hydration process and microstructure development were discussed finally. Assuming the cement particles are spheres which have different radius, the complicated hydration could be equivalented to a process in which the spherical particles diffuse outward. The hydration of cement and the development of microstructure could be displayed visually through effective simulation. We could observe the microstructure distribution at different hydration period (3h,6h,3d,7d,28d) of different established models, including Portland cement, low alkali cement and highalkali cement, in which the hydration products and the distribution of pore size fitted well with the realistic process. In addition, the degree of hydration and porosity increased with the increasing water/cement ratio, while the modulus of elasticity showed downward trend. We found that the moduli of elasticity are almost the same, while the water/cement ration and porosity are obviously different in all studied systems.The research of this thesis will enhance the understanding of hydration kinetic of cement and microstructure characteristic of hydration products, meanwhile it will also extend the applied range of molecular simulation. At present, the molecular simulation has not been widely used in cement-based materials yet, so the application of the technique in this area will have great potential value in future.