Microstructural pore changes and energy dissipation in Gosford sandstone during pre-failure loading using X-ray CT

Four X-ray CT scans at 5 μm spatial resolution using a 59 kV X-ray source were taken of a 5 mm diameter sample of Gosford sandstone under successively increasing pre-failure loads in unconfined compression. The study focussed on the evolution of microstructural pore properties following reconstruction of the radiographic projection images and segmentation into a binary representation and concatenation to form 3D datasets. Pore sizes and their distribution, orientation and surface areas were considered, as were the fractal dimensions of pore and solid spaces. The number of pores increased during early stages of loading, prior to a reduction of pore numbers at a point also corresponding to a slight stiffening of the stress–strain curve, even though volumetric compression was taking place. The pores were always well networked, with around 95% by volume being connected. Also, orientations of newly created pores tended to be near parallel to the direction of compressive loading, and therefore perpendicular to the direction of maximum tensile strains. Energy dissipation associated with the creation of new surface and the redistribution of stored energy through the newly fractured sandstone was back-calculated using the observed stress–strain response. A general increase in dissipation rate with the applied load was observed in the pre-failure region.

► 4 X-ray CT scans taken at increasing pre-failure loads in unconfined compression.
► Evolution of microstructural pore properties determined.
► Pore numbers increased during early stages of loading, then pore collapse occurred.
► New pore orientations tended to be near vertical (perpendicular to tensile strains).
► Energy dissipated by creation of surface and redistribution of stored energy.