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Self-compacting concretes segregation mechanisms - Experimental study of granular interactions

Abstract : Self-compacting concretes (SCC) have a high flowability and can be placed into formwork without vibration. However, due to their high deformability, they are liable to segregate. Segregation corresponds to the loss of homogeneity between both the granular and the suspending phases. Segregation is referred to as "static segregation" when it occurs after fresh concrete has been poured into formworks, and as "dynamic segregation" when it occurs during placing. SCC must be stable to ensure the homogeneity of the mechanical strength of the final structure and its durability. SCC mix design often consists in finding a good compromise between contradictory features, i.e. high fluidity and stability. Improving the control and the complete characterisation of the rheological behaviour of fresh SCC is required to study and better understand the basic phenomena at the origin of "static" segregation. More knowledge is needed to develop new tests to estimate the segregation risk of SCC. The stability of an isolated particle immersed in a suspending phase characterised by its shear yield stress, has been studied. The initiation of segregation essentially depends on both the size and specific gravity of the coarse aggregate and on the shear yield stress of the suspending matrix. However, avoiding segregation is also a matter of granular skeleton features. A new testing apparatus has been developed to bring to display and study the interactions between coarse aggregates. This apparatus enables to measure the resisting force of a granular lattice made of spherical particles of the same diameter, immersed in a suspending phase. By comparing tests performed on both lattice and elementary particle, the interactions between particles can be quantified and taken into account in the description of segregation mechanisms. Several tests have been performed by varying the composition of the suspending phase and the lattice characteristics. Group effects are positive as far as they enhance the stability of fresh SCC. However, they depend on the solid fraction of coarse aggregates. A new stability constant can be defined to describe the segregation mechanisms. Besides, an experimental study has been carried out on concrete to illustrate the possible repercussions on SCC mix design.
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Submitted on : Monday, June 19, 2006 - 8:00:00 AM
Last modification on : Monday, June 19, 2006 - 8:00:00 AM
Long-term archiving on: : Thursday, September 30, 2010 - 7:26:33 PM

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Sandrine Bethmont. Self-compacting concretes segregation mechanisms - Experimental study of granular interactions. Engineering Sciences [physics]. Ecole des Ponts ParisTech, 2005. English. ⟨pastel-00001809⟩

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