Segregation of sand-rubber chips mixtures subject to vertical tapping under confinement

Mixtures of rigid sand particles and soft rubber particles (rubber chips) are prepared and submitted to vertical taps in a confined cell to investigate their propensity to segregate. The mixture evolution is characterized by means of image analysis of slices obtained by a gelification technique. We show that, in case of equally sized particles, the rubber particles tend to migrate towards the bottom of the system. Yet, the segregation is not complete and is reduced when the rubber fraction is increased. Also it competes with the size induced segregation if rubber chips are larger than sand particles. A tendency to form horizontal clusters is clearly observed and increases with the number of taps. This horizontal segregation is reduced if the rubber fraction is smaller and is weakly influenced by grain size difference. Both the vertical segregation and the formation of horizontal heterogeneities are prevented by adding a small amount of water.