Behavior of water in C-S-H

The behavior of confined and surface water in hydrophilic systems is known to differ from bulk behavior. C-S-H is a hydrophilic micro/meso-porous phase with a large surface area. Understanding how water behaves in C-S-H is crucial to elucidate phenomena associated with water sorption and dynamics, which includes mass transport properties and durability, sorption-induced volume changes, thermal properties, and viscoelastic response. Molecular simulations are a powerful tool to quantify water behavior on the atomic level. In this work, these simulations are deployed to quantify the changes in the main physical properties-namely, density, self-diffusion, viscosity, bulk modulus, thermal expansion, heat capacity, and heat of adsorption-of liquid water confined in C-S-H as a function of the pore size under osmotic equilibrium. Then, we focus on surface water and how the properties of water change as a function of the distance from the C-S-H surface. For (slit) pores smaller than about 3-5 nm, the properties of water exhibit a transition from liquid-like to a more solid-like behavior. Surface water behavior differs from bulk behavior up to the fourth adsorbed layer. The results provided are critical inputs for multiscale modeling concerning the properties of confined and bound water. Also, they provide new physical insights to revisit sorption models and understand drying processes.