| Summary: | 碩士 === 國立成功大學 === 土木工程學系 === 104 === In this thesis, the molecular dynamics (MD) simulations techniques were adopted to study the atomic structures and physical/mechanical properties of C-S-H for its thermal expansion coefficient, bulk modulus, indentation modulus and hardness at various temperatures and pressures. The interatomic potential is of the CLAYFF type, consisting repulsive and attractive energy terms for short-distance interactions, as well as the Coulomb electrostatic energy
terms for long-distance interactions. The chemical composition of the C-S-H model is (CaO)1:65(SiO2)(H2O)1:75, and its density is about 2.56 g/cm3. It is composed by silicate layers with calcium ions, labeled as Cas, nearby. Between the calcium-silicate layers, there are water molecules and calcium ions, labeled as Caw. From our atomic structural analysis, at the ambient environment, the radial distribution function, Qn and structural factor are consistent with literature data. The nuclear magnetic resonant spectrum of the C-S-H shows the ratio of Q0:Q1:Q2 equal to 1:2:7. However, at high temperature (800 C), Q2 is largely reduced, and Q0 and Q1 silicate morphology dominates. As for the physical properties, our calculated data with the NPT ensemble are consistent with literature data with noticeable differences at the ambient environment. The differences may be due to thermal fluctuation noises. It is found that in some temperature and pressure regime, the thermal expansion coefficient of C-S-H may be negative.
The indentation load-displacement curves may exhibit jumps, indicating slips may occur in the C-S-H layer structures during loading. Our calculated the un-relaxed hardness values of C-S-H
are in the range of 4.63 GPa to 13.93 GPa. In ambient, its bulk modulus is about 49 GPa. As temperature increases, hardness and indentation modulus decease, as well as the layered structures are smeared.
|
|---|
