  Cement is one of the most produced materials in the world. A major player in
greenhouse gas emissions, it is the main binding agent in concrete, to which it
provides a cohesive strength that rapidly increases during setting.
Understanding how such cohesion emerges has been a major obstacle to advances
in cement science and technology. Here, we combine computational statistical
mechanics and theory to demonstrate how cement cohesion results from the
organization of interlocked ions and water, progressively confined in
nano-slits between charged surfaces of Calcium-Silicate-Hydrates. Due to the
water/ions interlocking, dielectric screening is drastically reduced and ionic
correlations are proven significantly stronger than previously thought,
dictating the evolution of the nano-scale interactions during cement hydration.
By developing a quantitative analytical prediction of cement cohesion based on
Coulombic forces, we reconcile a novel fundamental understanding of cement
hydration with the fully atomistic description of the solid cement paste and
open new paths for science and technologies of construction materials.
