This paper reports the use of micro-computed tomography (CT) to measure changes in aggregate density in sediments of flocculated silica as a function of applied pressure over the course of a step-wise compression experiment. A micro-CT calibration method was developed that uses polymer-stabilized silica suspensions of varying solids concentration to permit the calculation of aggregate density and solids volume fraction directly from the micro-CT images. The results show that low-compression dewatering causes the removal of inter-aggregate water, while higher pressures are required to expel the intra-aggregate fluid. The solids volume fraction values calculated from micro-CT images were found to be in good agreement with those measured gravimetrically, by drying and weighing the samples. This work represents the first step in a description of the micro-scale mechanisms of dewatering of flocculated porous media and is part of a larger research program that studies the dewatering of difficult-to-treat mineral tailings. (C) 2019 Elsevier B.V. All rights reserved.