A mutual interaction occurs between the kinetics of the hydration of Portland cement and hydrated calcium silicate(C-S-H) formed as a result of the chemical reactions involved.The liquid phase composition that also depends on the occurring chemical reactions has a major impact on the nucleation and growth rates of C-S-H.As a consequence, the structure of the agglomerates of unordered C-S-H nanometric particles on C3S, C2S or calcite surfaces will vary from a Portland cement to another one but also in the presence of admixtures or with temperature variations.The stoichiometry of C-S-H also directly depends on the liquid phase composition.On the other hand, the induction period found during Portland cement hydration is governed by the rate of nucleation of C-S-H.Also, the percentage of hydration reached at 1 day is principally correlated to the rate and mode of growth of C-S-H and then to the permeability of water molecules and ions through the layer of C-S-H formed on cement grains.Once the parameters that enable us to tune C-S-H nucleation and growth are known, it is thus possible to master more efficiently the early hydration of Portland cement and especially reach higher percentages of reaction leading to a more efficient use of cement in the logic of sustainable development.