  Cohesive particles form agglomerates that are usually very porous. Their
geometry, particularly their fractal dimension, depends on the agglomeration
process (diffusion-limited or ballistic growth by adding single particles or
cluster-cluster aggregation). However, in practice, the packing structure
depends not only on the initial formation but also on the mechanical processing
of the agglomerate after it has grown. Surprisingly, the packing converges to a
statistically invariant structure under certain process conditions, independent
of the initial growth process. We consider the repeated fragmentation on a
given length scale, followed by ballistic agglomeration. Examples of
fragmentation are sieving with a given mesh size or dispersion in a turbulent
fluid. We model the agglomeration by gravitational sedimentation. The
asymptotic structure is fractal up to the fragmentation length scale, and the
fragments have a power-law size distribution. A scaling relation connects the
power law and the fractal dimension.

Soft Condensed Matter;Adaptation and Self-Organizing Systems