Influence of humidity on the binding of stone fragments via capillary bridges

Abstract

We study the humidity dependency of the adhesion (or pull-off) force between granite fragments and a silica glass plate. The particles bind to the glass plate via capillary bridges. The granite particles are produced by cracking a granite stone in a mortar and have self-affine fractal surface roughness. Theory shows that the surface roughness results in an interaction force between stone fragments and the glass plate which is independent of the size of the particles, in contrast to the linear size dependency expected for particles with smooth surfaces. We measure the adhesion force by depositing the granite particle powder, with particle sizes ranging from mm to μm (or less), on the glass plate. By turning the glass plate upside-down all particles with a gravitational force larger than the adhesion force will fall off the glass plate. By studying the size (and hence the mass) of biggest still attached particles we obtained the adhesion force, which is found to be in good agreement with the theory prediction.