An experimental study of granular packing structure changes under load

Abstract

A novel experimental method is developed to characterize the packing structures of granular materials. This method can be used to identify microstructural parameters for granular materials required in micromechanical modeling. Important parameters include volume fractions, particle arrangements, and contact geometry, as well as packing structure changes under applied loads. In this effort, these microstructural parameters are quantified directly from actual material samples, not from hypothetical or numerically generated structures. The method developed utilizes a high resolution X-ray computerized tomography (CT) machine to non-intrusively acquire cross sectional images of a material sample. The material sample used in this study consists of laboratory-packed, 6 mm glass beads, mixed with asphalt as a binder material. Numerical algorithms are developed to analyze these CT images to reconstruct the actual three-dimensional (3D) packing of the sample and identify the asphalt binder structure. A special loading device is designed that fits the CT machine's sample stage and can apply loads during CT scanning. Changes in the microstructural parameters under load are then studied from the reconstructed packing structure corresponding to each loading step. This paper demonstrates that the experimental technique developed is capable of accurately identifying the internal packing structure of a granular material.