Calcium-Silicate-Hydrate (C-S-H) has been studied extensively over the last few decades to gain understanding toward the underlying mechanism of different stages during cement hydration. The variable stoichiometry and nanocrystallinity of C-S-H makes it difficult to characterize experimentally. The second most abundant hydration product of cement is portlandite which has a simpler crystalline structure in comparison to C-S-H and has been used as a training/building system for future simulation of C-S-H bulk and surfaces. In this PhD project we are interested in a better fundamental understanding of the interaction of sulfate and secondary ions (Aluminium, Magnesium,...) with cementitious materials (e.g. portlandite and C-S-H). It has been shown that sulfate considerably affects the morphology of growing portlandite and C-S-H which will affect the physical properties of cement and concrete. A better fundamental understanding of this adsorption or incorporation into bulk structures will improve our understanding of the growth of C-S-H in the presence of such ions. In this project, utilizing molecular dynamics and metadynamics, we will systematically investigate the interaction of ions found in cement pore solutions with portlandite and C-S-H. For this purpose, we will use the Brick model recently developed in our group by Mohamed et al. (1) to create model structures for the C-S-H. We also have started to develop a new force field (ERICA FF1) which constitute different atom types needed for these simulations which are not included in previous cement force fields (Cement FF1 (2) and Cement FF2 (3)â   .