Incorporation of zinc into calcium silicate hydrates, Part I: formation of C-S-H(I) with C/S=2/3 and its isochemical counterpart gyrolite

We have investigated the incorporation of zinc into both nanocrystalline and crystalline calcium silicate hydrates with starting C/S ratios of 2/3 (0.66). Zinc was added replacing calcium in the starting mixtures [Zn/(Zn+Ca)=0–1/4; 0–10 wt.% Zn], and the resultant phases were characterised using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), differential thermal analysis–thermogravimetry (DTA–TG) and environmental scanning electron microscopy (ESEM). In both groups of samples, increasing zinc content led to gradual structural changes, until eventually a second phase was formed. Zinc was incorporated to similar limits in both sets of samples. The thermal stability of the structures increased to a certain zinc content, beyond which there was structural destabilisation. Zinc incorporation is possible up to ∼6 wt.%. Our observations strongly indicate similar zinc incorporation mechanisms in both sample series, namely incorporation of zinc into the interlayer of C-S-H(I) and the X-sheet of gyrolite for nanocrystalline and crystalline samples, respectively.