Molecular Engineering of the Cohesionin Neat and Hybrid Cement Hydrates

Abstract

On the basis of recent molecular simulation or experimental studies, we discuss two possible strategies for improving the mechanical properties of cementitious materials by modifying the bonding scheme in the hydrates at molecular level. We focus on the calcium silicate hydrates (C-S-H). A first strategy would be based on the strengthening of the cohesion forces acting between the individual C-S-H lamellae or between their crystallites. Monte Carlo simulations in the primitive model framework and ab initio atomistic calculations suggest that the cohesion of C-S-H is mainly due to a combination of sub-nano range ionic-covalent forces and meso-range ionic correlation forces. Both types of forces may be modified, at least in theory, by changing the nature of the interstitial ions, their hydration state, or the charge density on the C-S-H lamellae. A second strategy, akin to a bio-mimetic or tissue engineering approach, would be to hybridize the hydrates by grafting organic moieties on the mineral lamellae. We show that this is easily achieved by controlled hydrolysis of mixtures of organo-silane precursors. The outcome may be a material with improved fracture energy.