STUDIES OF CALCIUM SILICATE HYDRATE VIA MOLECULAR DYNAMICS SIMULATION

Abstract

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

Date of Award	2016 Aug 25
Original language	English
Supervisor	Yun-Che Wang (Supervisor)