Nanolayered attributes of calcium-silicate-hydrate gels

Calcium-silicate-hydrates (C-S-H) gel, the main binding phase in cementitious materials, has a complex multiscale texture. Despite decades of intensive research, the relation between C-S-H's chemical composition and mesoscale texture remains experimentally limited to probe and theoretically elusive to comprehend. While the nanogranular texture explains a wide range of experimental observations, understanding the fundamental processes that control particles' size and shape are still obscure. This paper strives to establish a link between the chemistry of C-S-H nanolayers at the molecular level and formation of C-S-H globules at the mesoscale via the potential-of-mean-force (PMF) coarse-graining approach. We propose a new thermomechanical load-cycling scheme that effectively packs polydisperse coarse-grained nanolayers and creates representative C-S-H gel structures at various packing densities. We find that the C-S-H nanolayers percolate at similar to 10% packing fraction, significantly below the percolation of ideal hard contact oblate particles and rather close to that of overlapping ellipsoids. The agglomeration of C-S-H nanolayers leads to the formation of globular clusters with the effective thickness of similar to 5 nm, in striking agreement with small angle neutron and X-ray scattering measurements as well as nanoscale imaging observations. The study of pore structure and local packing distribution in the course of densification shows a transition from a connected pore network to isolated nanoporosity. Furthermore, the calculated mechanical properties are in excellent agreement with statistical nanoindentation experiments, positioning nanolayered morphology as a finer description of C-S-H globule models. Such high-resolution description becomes indispensable when investigating phenomena that involve internal building blocks of globules such as shrinkage and creep.