Abstract : The High Performance Concrete, from high to low plastic consistency, develops high long term mechanical resistances. Nevertheless, it presents the disadvantage of a very hard filling in dense steel reinforcements rebars like in the Millau's viaduct piles, which constitute a framework of barriers for the concrete casting by vibration. To guarantee a total filling in the framework, the self compacting concretes are the issue and are adopted respecting mechanical performances and durability maintains. The characterisation of the rheological properties as fluidity and filling ability at the concrete scale gives the physical basis to explain the phenomena implicated in the transition between a concrete of ordinary rheology to a concrete of very high fluidity and gives a better understanding of the mix design variations, as for the granular volume fraction and the gravel to sand ratio, and their consequences. The stability and thixotropy of the suspending fluid where cement, fine sands, diverse fillers and superplasticizers coexist play an important role on the fluidity and stability of the concrete. Nevertheless, shrinkage measurements under drying conditions underline the granular volume fraction incidence on very high drying shrinkage that leads to early cracking. Thus, the replacement of the cement by mineral fillers less reactive has been undertaken. Then, thermal analyses identify the microstructural physico-chemical developments that explain the mechanical resistances maintain, even after the modifications of the mix design.