Clustering in engineering materials: Effects on cements materials

Trabajo presentado al CECAM Workshop on "Aging of Engineering Materials: a Computational Approach to Durability and Sustainability" celebrado en Zurich (Suiza) del 8 al 10 de Febrero de 2012.Cement has a highly complex structure when going bottom-up from nanometer to macroscopic scale. It is thus crucial to understand the nanostructure of Calcium Silicate Hydrates (CSH), composed of silica tetrahedra chains on calcium oxide layers. Furthermore, it is important to see how the silica chains affect especially the cement mechanical properties. Here, we review recent advances in modelling for cementitious materials, focusing on clustering of the silicate tetrahedra. We first apply to cement the traditionally computational and statistical physical chemistry approaches for the aggregation of atoms in clusters. The aggregation of silica tetrahedra in CSH gel is described to have certain stable lengths, in good agreement with 29Si NMR experiments. Longer chains obtained by adding silica nanoparticles increase the chain length, addition which improves cement mechanical properties and avoids the deterioration due to calcium leaching. We then investigated a widely accepted models of cement hydrates with finite silicate chains, in order to look at the cohesion forces in cement-based materials. At the nanoscale, we calculate not only the elastic properties of the CSH models, but their 29Si NMR spectra. These nanoscale elastic properties are used to get the mechanical properties of CSH gel at the mesoscale taking into account its porous structure: Longer chains seem to be linked to a stronger mesostructure of CSH gel, but their dependence is not straightforward [3]. We acknowledge the help and cooperation of I. Campillo, Y. R. de Miguel, E. Erkizia, D. Sánchez-Portal, A. Rubio, A. Porro, P.M. Echenique.Peer Reviewe