Synthesis and nano-mechanical characterization of calcium-silicate-hydrate (C-S-H) made with 1.5 CaO/SiO2 mixture

In this study, calcium silicate hydrate (C-S-H) is synthesized and characterized. C-S-H slurry was made with calcium oxide (CaO) to micro-silica (SiO2) mixture ratio of 1.5 and enough deionized water. The slurry was continuously mixed for 7 days, then the excess water was removed. Two methods of drying were implemented: one method used the standard d-dry technique and the other was equilibrated to 11% relative humidity (RH). The dried powders were characterized using thermo gravimetric analysis (TGA), X-ray diffraction analysis (XRDA), and 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The stoichiometric formulas of synthetic C-S-H powders dried to d-dry and 11% RH in this study were approximated as C1.2SH0.7 and C1.2SH2.4 respectively. The powders were then compacted to create specimens with porosities similar to C-S-H in hydrated cement. The specimens underwent nanoindentation to mechanically characterize C-S-H. The experiments provide insight on the nanoscale mechanical characteristics of C-S-H.