In this study, the C-A-S-H composition, morphology and density are characterized for Limestone Calcined Clay Cement (LC3-50) blends containing clays with various kaolinite contents. Significant incorporation of aluminium is observed for LC3-50 blends compared with reference Portland cement (PC), and this incorporation increases with the kaolinite content of the calcined clay. No change of C-A-S-H morphology was observed by Transmission Electron Microscopy (TEM) between reference PC and LC3-50 blends, with a "fibrillar" morphology for all samples. The determination of the density of C-A-S-H measured by H-1 NMR also shows very similar results with a bulk density close to 2.0 g.cm(-3) and a solid density of around 2.8 g.cm(-3) for all systems.