Interface Microstructure–Based Mechanical Property Evaluation of C-S-H

The grain–grain interface of cement, which is composed of the complex needle-shaped microstructure of calcium silicate hydrate (C-S-H), is crucial in the development of the mechanical properties of cementitious composites. These C-S-H needles grow radially outward from the grain surface. This work proposes a combined experimental and modeling approach to incorporate the finer details of these needle geometries and the distribution of mechanical properties in an interface-based multiscale mechanical model for hydrating tricalcium silicate (${\mathrm{C}}_3\mathrm{S}$). At micrometer and sub-micrometer length scales ($<5\mu \mathrm{m}$), electron microscopy images revealed that the geometrical nature of these needles at the grain interface varies with days of hydration. The mechanical properties of C-S-H at the nanoscale were observed to be higher at the inner core and reduced toward the outer product. The model developed can incorporate the details of these needle microstructures and their mechanical properties at the microscale and can predict the bulk properties of hydrated ${\mathrm{C}}_3\mathrm{S}$ at higher scales.