Comb-like copolymers as polycarboxylate ether (PCE) are added to concrete to make it more fluid and facilitate its placement.The evolution of the workability at early age is conditioned by cement hydration and more precisely by those of aluminate phases.At the same time, the cement hydration is modified by the presence of superplasticizers which have secondary effects (retardation, impact on hydrates morphology) depending on the superplasticizer structure.But the structure is not the only important parameter and the addition time (direct or delayed) can also have a great impact.Our goal was to show how the first minutes of the hydration (started with or without PCE) can condition the rheology during the first 2 hours by a study on the addition time.We defined a model reactive system based on Tricalcium Aluminate/Calcium sulfate/Calcite to mimic a fresh cement paste.