Coarse-grained molecular dynamics study on submicron structuring of calcium silicate hydrate with enhanced tensile modulus and strength

Potential of cement-based materials for energy harvesting is encoded in their elusive mesoporous structure, and understanding the sub-micron structure of calcium silicate hydrate (C-S-H), a major binding phase of cement, is an important yet challenging task. Nanoscale C-S-H is ductile, while macroscopic performance is brittle, suggesting a gap in the transition of material properties from the nano-to the macro-scale, and a chance in finetuning the submicron (similar to 100 nm) structure to effectively deliver the atomistic properties to the bulk performance. The refined sub-micron structure of C-S-H can enhance the strength and modulus of concrete, thus providing a base material with better mechanical properties and durability. Here, two critical structural features of C-S-H, including agglomeration of globules and stacking of layers, are modeled by spherical and oblate ellipsoidal units, respectively. Coarse-grained modeling and peridynamics simulations find that the packing of ellipsoidal units is better than that of spherical units, from the perspectives of size distribution, morphology, fractality of pores and tensile properties. The analyses on the mesoporous structure shows that the ellipsoid-packing is more homogeneous than the sphere-packing model, and it yields a refined structure with enhancement in tensile modulus and strength. The submicron finetuning enhancement of C-S-H can be realized through different physical and chemical approaches, like inducing lateral growth of silicate chains by chemical additives, scaffolding materials, and conditioned hydration. This coarse-grained simulation work gives novel insights and fundamental strategies for toughening the cement matrix through delivering ductile nanoscale performance of C-S-H to macroscale cementitious materials, and provides superior performance for concrete in existing and new structures.