A new approach to particle shape classification of granular materials

The shape of soil particles influences asphalt, concrete, and soil behavior. The image analysis and visual comparison methods are commonly employed to quantify the shape characteristics of granular materials. However, previously introduced approaches have mostly been concerned with two-dimensional aspects and cannot specify the form and sphericity for entire grains. In this study, the shape of grains with various geometries is measured using a precise three-dimensional model for each particle extracted from X-ray computed tomography (microCT) images. A new sphericity ratio is proposed based on circumscribed and inscribed spheres. Further, a new sphericity class is developed which can be used for spherical to flat and ellipsoid to elongated particles. The results of various methods have been used and compared to quantify the sphericity. According to the results, the proposed approach outperforms other classifications. Furthermore, new charts have been suggested for quantitative-qualitative particle properties according to sphericity, roundness, and roughness, which can further be used for visual comparison.