Rheology of cohesive granular material with tuneable cohesive strength

We report the findings of an experimental investigation on the flow of cohesive granular materials in a partially filled rotating drum. The inter-particle cohesive force is varied by adding different amounts of glycerol to dry glass beads. In the rotating drum we measure the avalanche angle as a function of liquid content and find a non-monotonic trend. The avalanche angle initially increases with the addition of glycerol, reaches a maximum value and then decreases with further increase in the glycerol content. Another interesting feature observed in our experiments is the formation of agglomerates, which continuously form and break during flow. These agglomerates form if the liquid content exceeds a critical value, and seem to play a key role in the intermittent behavious of the surface dynamics of the avalanches, including the nonmonotonicity in the angle of repose.