The absence of the right shoulder of the main peak in experimental measurements of Moudrakovski et al. is consistent with the latest studies of the C-S-H surface structure. Zeta potential studies of C-S-H with Ca/Si < 1.5 synthesized from SiO 2 and CaO are consistently negative , while those of C-S-H with Ca/Si > 1.5 synthesized with the drop-wise precipitation method are positive . As explained by Casar et al. , Ca 2+ adsorption is necessary to reach high Ca/Si ratios which consequently causes positive zeta potentials. Therefore, at low Ca/Si ratios negative zeta potentials are expected due to the absence of Ca 2+ adsorption sites on the surface. Since C-S-H synthesized from SiO 2 and CaO is low in Ca/Si ratios, a negligible amount surface Ca sites is expected, which is reflected by the absence of an right shoulder in the Ca NMR spectra of Moudrakovsi et al .