Influences of combinational distributions of various Ca/Si ratios and defects on the mechanical properties of calcium silicate hydrates

Y. Chiang, S-W Chang
National Taiwan University,

Keywords: distribution, mechanical properties, calcium-silicate-hydrates, nanoscale


Although cement as a durable and affordable building material has been widely used in construction environments. It still remains unclear on how their microstructures and chemical compositions at the molecular level affect the mechanical properties and time-dependent behaviors. The multiscale heterogeneities in the cementitious materials hinder the scientist from comprehensively understanding the mechanisms of the macroscopic phenomenon such as creeping and shrinkage. With various hydration extent, irregular porous void and impurities like ettringite, portlandite and sulfate hydrates in the OPC (Ordinary Portland Cement), the study of the cement paste structure with accurate morphology from the molecular level to macroscale becomes challenging. In the light of determination of indentation modulus and hardness of Calcium-Silicate-Hydrate (C-S-H), the effect of random nanopores on strength and toughness performance has been recently explored. However, the defects at the nanoscale, for example, the intrinsic defective attribute of calcium silicate chains, including the mean length of chains and the calcium-to-silicon ratio (C/S), could strongly affect the mechanical properties of cement paste at the macroscale. In this study, we focus on using a molecular modeling approach to study how the combination of calcium silicate hydrates with various C/S ratio ranged from 1.5 to 1.9 would affect the mechanical properties. Molecular dynamics simulations are carried out to simulate the axial tensile tests. By analyzing atomic structures in different atomistic distributions, we reveal the relationships between the mechanical properties, including elastic modulus, toughness and ductility, and the water content and calcium-to-silicon ratio. Our results help us to bridge the atomistic structures of C-S-H with the mesoscopic material properties.