Effects of material properties on segregation of binary and ternary powder mixtures in a small scale cylindrical silo

The segregation of binary and ternary particulate mixtures at filling and at discharge of a 0.4 m³ cylindrical silo has been investigated experimentally. Raw materials used in commercial construction products are utilized and include bulk solids with different particle size, solid density and shape. Mixtures with varying mass fractions, particle size ratio or size distribution, particle solid density ratio and flow properties (free-flowing to cohesive) are prepared. Discharge flow patterns are determined either visually or by using tracer particles. This work gives qualitative information on the influence of material properties on the embedding, (impact) fluidization and air-current segregation mechanisms, which are relevant for the handling of commercial dry mineral-based construction materials in silos of industrial scale. The results show that material properties have a significant effect on the distribution of the powder mixture at silo filling, while the material distribution at filling and the discharge flow pattern determine the composition at emptying. At filling, mixture composition (component mass fractions) determines the segregation pattern, that is, whether fines are accumulated in the center or at the silo walls. For the latter, segregation is aggravated by increasing the particle size ratio between coarse and fine component for a binary mixture or size distribution for a ternary mixture, or by reducing the particle solid density ratio between fine and coarse component significantly below unity.