Research Brief: Evolving the C-S-H Packing Density at the Microscale

Abstract

Cement paste is a complex multiphase material, roughly 50 percent of which, by volume, is composed of calcium-silicate-hydrates (C-S-H). The C-S-H phase, which lends the material its rigidity, appears to be a dispersion of nanometer-sized particles that densify during the course of the hydration reaction (Ioannidou et al., PNAS 2016). Because the mechanical properties, early-age internal stresses, and microstructure are critically dependent on the distribution of the high density (HD) and low density (LD) C-S-H product, research efforts are underway to better understand nanoparticle packing density at the scale of hundreds of micrometers, where a binary mixture of clinker grains and saturated pore space evolve into a porous hydrated gel. This research brief displays simulated snapshots of cement paste at varying hydration degrees and predicts the evolution of the HD and LD peaks for the distribution of the indentation modulus also observed in nanoindentation experiments.