Distribution of local void ratio in porous media systems from 3D X-ray microtomography images

We present in this paper a methodology to calculate the distribution of local void ratio in porous media systems from high-resolution three-dimensional images. We introduce an algorithm to calculate the distribution of local void ratio from 3D images based on distance and watershed transforms. The watershed transform is used to segment touched or overlapped particles in an efficient way and the distance transform is used to calculate the boundaries of local void regions. The algorithm is validated using computer simulated 3D images of regular packing, irregular (non-spherical particles) packing, and random uniform spherical packing. Results show that the algorithm is robust, accurate and can be used to calculate local void ratio distribution of 3D systems regardless of irregularity in shapes, sizes, or arrangement of particles. X-ray microtomography images of different glass bead systems are used to calculate distributions of local void ratio. Parameters of distributions are function of porosity and particle-size distribution. The maximum local void ratio in each system is less than 3.0 and the minimum is greater than 0.2.