Influence of the surface roughness of grit-blasted steel on the wall friction angle of limestone powder

In this paper, the influence of the surface roughness of structural steel on wall friction with limestone powder was investigated. Different values for the surface roughness of the steel material were obtained by applying different grit blasting procedures. To measure wall friction a ring shear tester was used. The shear tests were executed using four different types of limestone powder. The analysis of the obtained data, besides the well-known influencing parameters particle size and surface roughness also the gradient angle of the surface roughness and the spread of the particle size distribution were used. The results showed an inversely proportional dependence of the wall friction angle on the wall normal stress and on the mass mean diameter of the limestone powder. In contrast, higher values for the surface roughness, the gradient angle of the surface roughness and the spread of the particle size distribution of the powder result in an increased value for the wall friction angle.