Compaction dynamics of wet granular assemblies.

The extremely slow compaction dynamics of wet granular assemblies is studied experimentally. The cohesion, due to capillary bridges between neighboring grains, is tuned using different liquids having specific surface tension values. The compaction dynamics of a cohesive packing obeys an inverse logarithmic law, like most dry random packings. However, the characteristic relaxation time τ grows strongly with cohesion. A model, based on free volume kinetic equations and the presence of a capillary energy barrier, is able to reproduce quantitatively the experimental curves.