Insight into elastic behavior of calcium silicate hydrated oxide (C–S–H) under pressure and composition effect

Abstract

The present work relates to the study of structural and elastic properties of Tobermorite 11Å as a function of external pressure and composition in terms of calcium to silicon ratio. Basing on the lattice dynamics method, the main aim of this work is precisely to shed light, for the first time, on the high pressure structural phase transition in Tobermorite 11Å and the possible correlation with some elastic quantities. In order to check the transferability of the potentials used we have, additionally, performed a single calculation based on the density functional theory (DFT) for a pressure of 15GPa in the case of Ca/Si=1. The variation of the unit cell parameters with pressure indicates that Tobermorite 11Å undergoes a structural instability around 15GPa along b-axis and around 20GPa along a-axis which is confirmed from our calculations of X-Rays diffraction patterns at various pressure values. We have also observed the anisotropic character of the Tobermorite structure for both cases (Ca/Si=1 and Ca/Si=0.83). Our results show that around 20GPa an important change appears in the elastic behaviour of Tobermorite. As pressure increases the calculated elastic quantities for Ca/Si=1 became closer to those evaluated for Ca/Si=0.83, which may stimulate further experimental and theoretical research on the matter.