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.
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