The pore solution of cement-based materials: structure and dynamics of water and ions from molecular simulations

Diffusion processes are crucial to the durability and confinement capacity of cement-based materials as well as property development. The liquid phase in cement-based materials is the pore solution, whose composition changes with age and is a function of the cement system composition. Water structure and dynamics are recognized to be affected by the presence of ions. Fundamental understanding of the physical processes underlying these changes can be critical in the elucidation of the physical origin of durability issues and in the development of new admixtures. Here, the structure and dynamics of water and ions present in pore solutions are studied using molecular dynamics simulations. Self-diffusion coefficients are computed for bulk solutions mimicking the complex composition of pore solutions. Specific ion effects on water dynamics are interpreted in terms of water reorientation time. The composition dependency of ion dynamics explains the evolution of the ionic conductivity of the pore solutions.