Crystallization of calcium silicate hydrates on the surface of nanomaterials

The poorly crystalline calcium silicate hydrate (C-S-H) is the primary binding phase in portland cement concrete. In this paper, the influence of adding anatase phase nano-TiO₂, nano-SiO₂, graphene oxide (GO), and multiwalled carbon nanotubes (CNT) on the crystallization and morphology of C-S-H are systematically investigated through tests. C-S-H gels were prepared using the double decomposition method, and the nanomaterial additions of nano-TiO₂, nano-SiO₂, GO, and CNT were 2 wt%, 2 wt%, 0.5 wt%, and 0.5 wt%, respectively. X-ray diffraction (XRD) results show that a more crystalline nanostructure of C-S-H is induced by the addition of nano-TiO₂ or GO. This phenomenon is further confirmed by the transmission electron microscopy (TEM) observations. The TEM observations demonstrate that C-S-H would grow on the crystal face of TiO₂ to form nanocrystalline regions with a lattice fringe spacing of 3.0 Å. When incorporated with GO, it will form a square lattice structure with a lattice constant of 3.1 Å on the surface of GO and later change to the lattice fringe structure with a spacing of 3.1 Å on the region bit away the GO surface. However, when adding nano-SiO₂ or CNT, these nanocrystalline regions are not observed. Further characterization through scanning electron microscopy (SEM) and atomic force microscopy (AFM) has been performed to investigate the effect of nanomaterials on C-S-H morphology. Different nanomaterials take a different morphology of C-S-H: sheet-shape structures for pure C-S-H, rod-shape with for C-S-H with nano-TiO₂, and granular agglomeration for C-S-H with nano-SiO₂. C-S-H with GO or CNT forms a structure of C-S-H growing on the templates.