Nano-confined water and ions in cement pores

We use numerical simulations to study the behavior of water confined by planar surfaces in the presence of divalent ions. The dynamics and mobility of the water are found to be strongly dependent on confinement. At large surface separations, most of the water behaves like in bulk conditions, but in high confinement the dynamics slow down and become coupled to the ions. This in turn increases the ion ordering and thus the overall attraction between two charged surfaces when the confinement is high. From these observations, we develop an analytical prediction of the attractive strength based on the formation of correlated ion-water structures. These results reveal a new mechanism for strong electrostatic cohesion of charged particles due to the restructuring of confined water. This effect is very relevant for the case of cement, where it explains the incredible strength of the material and could be the basis for intelligent design of cements.