Investigation of the surface structure and elastic properties of calcium silicate hydrates at the nanoscale.

This work is the first step towards the understanding of the structure of calcium silicate hydrate (C-S-H), the main constituent of cement paste, at the nanoscale. The first demonstration of atomic-resolution imaging of the (C-S-H) surface with an atomic force microscope (AFM) was performed. C-S-H nanoparticles (60 x 30 x 5 nm3) were partially recrystallized by Ostwald ripening after long-term equilibrium in saturated calcium hydroxide solution of different concentration, leading to C-S-H of different calcium/silicon ratio (Ca/Si). The results of atomic resolution made possible the investigation of the C-S-H cell surface parameters. The surface layer structure depended on the calcium hydroxide concentration with which it equilibrated. The change in structural properties perpendicular to the C-S-H layer was probed by modifying AFM for nanoindentation hardness measurements with a depth of indentation as low as 1 nm. The change in elastic modulus depending on the calcium/silicon ratio was evaluated and correlated in the change in structural parameters in this direction as estimated by X-ray diffraction.