Ref.: MceCge04-001
Apresentador: João Manuel M Cordeiro
Autores (Instituição): Cordeiro, J.M.(Universidade Estadual Paulista); Claverie, J.(Institut National des Sciences Appliquees); Bernard, F.(Institut National des Sciences Appliquees); Kamali-Bernard, S.(Institut National des Sciences Appliquees);
Resumo:
Tricalcium silicate (C3S) hydration is a highly relevant topic toward a better understanding of ordinary Portland cement. Molecular Dynamics (MD) simulations can provide relevant information about water behaviour at interface with mineral surfaces.
For the first time, the influence of C3S protonation on water structure and dynamics is assessed by simulating the Ca-rich (040) surface in contact with water. The recently extended INTERFACE force field for C3S, including parameters for hydroxyl and silanol groups, was used to perform classical MD calculations.
The water layered structure arising from strong hydrogen bonding with the mineral surface decays with increasing hydration of the first atomic layer. We found that the presence of hydroxyl and silanol groups, as well as desorption of calcium cations strongly influence the structural and dynamical properties of water. The layered structure of water, observed at the interface with the surface, decays from the hydration of oxides and is strongly affected by the protonation of silicates SiO44- to HSiO43-. We thus showed that the structural behaviour of water is based on the strength of the hydrogen bonds created between the first water layer and the ionic species of the mineral surface. When those hydrogen bonds are stable, the existing network remains well defined and structured.
The protonation of oxides and oxygen atoms of silicate leads to changes in charge distribution and weakens hydrogen bonds between the surface and the first water layer. This behaviour is reflected in the orientation probability distribution water molecules of the first layer. A preferential orientation of water molecules on the dry C3S exists because of the three bonding types observed (namely Oi-Ow-Oi, Os-Ow-Os and Oi-Ow-Os), whereas H2O molecules gain rotational motion when hydration occurs, with uniform orientation probability distribution. In the range of 4 Å to 16 Å from the interface, their translational motion decreases with the degree of hydration because of the perturbation introduced by the solvated ionic species. The study of dynamical properties such as diffusion and life-time hydrogen bonds adds new insights into the interfacial behaviour related to hydration reactions. The present simulations treat the protonation steps incrementally, and allowed to describe the behaviour of water at several degree of hydration of the first atomic layer.