In modern cements, significant amounts of clinker and cementitious materials remain unreacted even after long periods. The origin of the late hydration slowdown is hence of a great importance but not well understood. In this paper, literature data on pore solution concentrations from hours until a year were analyzed by means of thermodynamic modelling. Results revealed that saturation indexes of belite decrease over the hydration time while the ones of calcium aluminosilicate glasses remain constant. Similarly, the C-S-H phase saturation indexes were found to change little over time. Additionally, they are alkali-dependent: two possible explanations for this phenomenon - reduction of capillary tension and changes to the heterogeneous nucleation rate of C-S-H - were proposed. The slowdown of the late hydration could be attributed to the slow transport of elements dissolved from the reactive surfaces to the precipitation/nucleation sites at hydration times greater than 1 day.