Calcium-Silicate-Hydrate (or C-S-H), the major binding phase in cement pastes and concretes, is a porous hydrated material that can be conceptualized as an assembly of nanoparticles of~5 nm mean diameter.Interaction forces between these nanoparticles are at the origin of C-S-H chemical, physical, and mechanical properties at the meso-and macroscales.These particle interactions and resulting properties may be affected significantly by nanoparticle density and by environmental conditions such as temperature, relative humidity, or concentration of chemical soecies in the bulk solution.