Tuning the bulk properties of bidisperse granular mixtures by small amount of fines

TL;DR

This study investigates how small amounts of fines can significantly enhance the bulk modulus of bidisperse granular mixtures, revealing an optimal size ratio and the effects of fines on dense and loose systems through discrete element simulations.

Contribution

It introduces the first detailed analysis of how minor additions of fines influence the bulk properties of bidisperse granular mixtures, identifying an optimal size ratio for maximum bulk modulus.

Findings

Adding 5% fines can boost bulk modulus by up to 20%.

Similar-sized particles have minimal impact on macroscopic properties.

An optimal size ratio exists that maximizes the bulk modulus.

Abstract

We study the bulk properties of isotropic bidisperse granular mixtures using discrete element simulations. The focus is on the influence of the size (radius) ratio of the two constituents and volume fraction on the mixture properties. We show that the effective bulk modulus of a dense granular (base) assembly can be enhanced by up to 20% by substituting as little as 5% of its volume with smaller sized particles. Particles of similar sizes barely affect the macroscopic properties of the mixture. On the other extreme, when a huge number of fine particles are included, most of them lie in the voids of the base material, acting as rattlers, leading to an overall weakening effect. In between the limits, an optimum size ratio that maximizes the bulk modulus of the mixture is found. For loose systems, the bulk modulus decreases monotonically with addition of fines regardless of the size ratio. Finally, we relate the mixture properties to the 'typical' pore size in a disordered structure as induced by the combined effect of operating volume fraction (consolidation) and size ratio.