Rotations in shear bands and polydisperse packings

High resistance concrete or hard ceramics needs extremely dense granular packings which can only be realised when the size distribution of grains follows a powerlaw. We discuss the perfectly dense limit, namely Apollonian packings in three dimensions and show in particular the existence of space filling bearings rotating without slip and without torsion. When a dense packing like tectonic gouge is deformed, it glides internally on shear bands. The existence of rotations in shearbands is evidenced by molecular dynamics simulations of disks. (C) 2004 Elsevier B.V. All rights reserved.