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The objective of this work is to parametrize the early age hydration behavior of accelerated cement pastes based on the chemical properties of cement and accelerators. Eight cements, three alkali-free and one alkaline accelerators were evaluated. Isothermal calorimetry, in situ XRD and SEM imaging were performed to characterize kinetics and mechanisms of hydration and the microstructure development. The reactivity of all accelerators is directly proportional to their aluminum and sulfate concentrations and to the amount and solubility of the setting regulator contained in cement. Alite hydration is enhanced if a proper C₃A/SO₃ ratio (between 0.67 and 0.90) remains after accelerator addition and if limestone filler is employed, because undersulfated C₃A reactions are avoided. Combinations of compatible materials are recommended to enhance the performance of the matrix and to prevent an undesirable …