Atomic-Level and Surface Structure of Calcium Silicate Hydrate Nanofoils

Deciphering the calcium silicate hydrate (C-S-H) surface
is crucial
for unraveling the mechanisms of cement hydration and property development.
Experimental observations of C-S-H in cement systems suggest a surface
termination which is fundamentally different from the silicate-terminated
surface assumed in many atomistic level studies. Here, a new multiparameter
approach to describing the (001) basal C-S-H surface is developed,
which considers how the surface termination affects the overall properties
(Ca/Si ratio, mean chain length, relative concentration of silanol
and hydroxide groups). Contrary to current beliefs, it is concluded
that the (001) C-S-H surface is dominantly calcium terminated. Finally,
an adsorption mechanism for calcium and hydroxide ions is proposed,
which is in agreement with the surface charge densities observed in
previous studies.