Novel hybrid organic–inorganic calcium silicate hydrate (C–S–H) materials have been synthesized via a sol–gel process. The materials are obtained by precipitation in alkali media of a mixture of trialkoxysilane (ethyltriethoxysilane, n-butyltrimethoxysilane or 3-aminopropyltriethoxysilane) and tetraethoxysilane diluted in CaCl₂ ethanol–water solution. XRD experiments show an increase of the basal distance of C–S–H with the content of trialkoxysilane suggesting the incorporation of organic moieties in the interlayer. ²⁹Si NMR data show that the organic species do not disrupt the inorganic framework of C–S–H. 2D ¹H–²⁹Si HETCOR NMR experiments confirm that trialkoxysilanes such as ethyl- or aminopropyl-silane are incorporated in the silicate chains of the C–S–H structure. In the case of highly hydrophobic trialkoxysilanes such as n-butyltrimethoxysilane, the results suggest that a separation occurs between silicates and trialkoxysilanes, leading to a mixture of inorganic C–S–H on one hand and 100% organosilane calcium hybrid phase on the other hand.

New covalent bonded polymer–calcium silicate hydrate (C–S–H) composites were prepared. For this purpose, two sets of hydrosoluble copolymers, both containing trialkoxysilane (T-silane) and/or methyldialkoxysilane (D-silane) functions, were synthesized. The addition of these polymers during the synthesis of C–S–H by the sol–gel method allowed us to obtain hybrid materials. The influence of different synthesis parameters, such as the silane content and the nature of the silane functions grafted to the polymer backbone, was studied. Characterisation of the composite materials by thermogravimetry and elemental analysis showed that chemical interaction of polymers and C–S–H is due only to the presence of T-silane functions. ²⁹Si CP MAS NMR analysis confirmed the existence of covalent linkages between the inorganic silicate chains of the C–S–H crystallites and the T-silane functions. The specific incorporation of these new classes of silane-modified polymers in C–S–H structure may be successfully used in the preparation of new polymer–cement composites with reinforced mechanical properties.