Revealing the nanoscale mechanism of water states in the interparticle cohesion of calcium silicate hydrate

Calcium silicate hydrate (C-S-H) is the primary binding phase governing cohesion of cementitious composites, with mechanical strength, shrinkage, and creep closely linked to water state. Yet, the sub-micron structure and water state transitions remain elusive, a critical bridge controlling material behavior, hindering molecular-level understanding of how water impacts cohesion. An upscaling algorithm is developed to overcome barriers in constructing sub-micron C-S-H, enabling quantification of interlayer water, adsorbed water, and free water, revealing the impact of water state on mechanical and creep behavior. Molecular dynamics simulations show that C-S-H exhibits optimal performance when particles are closely packed. Monolayer adsorbed water forms bridging hydrogen bonds, preserving structural integrity but reducing interparticle cohesion. Free water acts as a lubricant, increasing non-affine displacement and shifting tensile fracture from transgranular to intergranular. This study advances understanding of the nanoscale mechanism of water on interparticle cohesion, providing a foundation for developing robust and durable cementitious composites.