The addition of a fine particulate material to a Portland cement can impart an influence on the hydration of the cement with witch is blended or will act just as a simple filler. Such material may be inert or have latent hydraulic properties. This study examines the influence of the three fillers on the hydration of C3S: - zirconia, witch is insoluble in water and only fills up porosity; - limestone filler, whose effect on the hydration of C3A is well know; its interaction with C3S has yet to be detailed; - zircon, whose cristalline structure is closely related to the C3S one; zircon and C3S also possess a common ion. Zircon and limestone filler react with C3S. Limestone filler accelerate C3S dissolution and modify the nature of hydrates: carbonated silicates precipitate. Zircon consumes calcium hydroxide and changes the nature of hydrates. Zircon and limestone filler do not enhance the compactness of the granular stack but their chemical reactivity induces an increase in strength at dosages higher than 20%.