Structure and Intrinsic Mechanical Properties of Nanocrystalline Calcium Silicate Hydrate

Nanocrystalline calcium silicate hydrate (C–S–H) is the binding phase of many low-CO 2 cements. Understanding its structure–mechanical properties relationship is critical in designing sustainable concrete. For the first time, a similar basal spacing (only 0.17 Å variation) of C–S–Hs at Ca/Si ratios of 0.8–1.5 is prepared via coprecipitation. The C–S–H nanostructure is determined using X-ray absorption spectroscopy, and the intrinsic nanomechanical properties of C–S–H at various Ca/Si are measured using high-pressure X-ray diffraction. For the first time, the influence of basal spacing on the nanomechanical properties is eliminated. At similar basal spacing, the ab -planar incompressibility remains independent of Ca/Si and silicate chain length, while the c -axis incompressibility is governed by the interlayer density (i.e., interlayer Ca content). The bulk modulus of C–S–H is governed by the interlayer density—more interlayer Ca yields higher bulk modulus at comparable basal spacings. Our results show that coprecipitated C–S–Hs at higher Ca/Si have higher mechanical properties. The results have implications in designing green cement/concrete using bottom-up approaches by providing property inputs for multiscale simulation and references for validating computational methods/parameters.