Nanoscale investigation of particle interactions at the origin of the cohesion of cement

The cohesion of cement grains is caused by surface forces acting between calcium silicate hydrate (C-SH) nanoparticles in interstitial electrolytic solution. The influence of pH, cations valency and concentration on the stability of the final concrete construction is investigated both through Grand Canonical Monte Carlo (GCMC) simulations and force measurement experiments. Direct measurement of the interaction between two C-S-H surfaces, performed in different aqueous solutions by AFM, show that the cement cohesion is provided by both high calcium concentration and C-S-H surface charge density. GCMC simulations in the framework of the primitive model of electrolyte solution show that calcium ions have a strong physical affinity (in opposition to specific chemical adsorption) to the negatively charged C-SH particles. The interaction between highly charged C-S-H particles in the presence of divalent calcium counterions is strongly attractive because of ion-ion correlations and a negligible entropic repulsion. These results allow one to confirm the pre-eminence of electrostatic forces in the cohesion (ion-ion correlations) of cement.
Author: A. Nonat, I. Pochard, C. Labbez, C. Plassard,, E. Lesniewska, B. Jönsson.

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