Organic calcium silicate hydrate hybrids: a new approach to cement based nanocomposites

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. Si-29 NMR data show that the organic species do not disrupt the inorganic framework of C-S-H. 2D H-1-Si-29 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.