Shear properties and water connectivity of wet granules at high solid content concentration

The inner liquid distribution in wet granules strongly influences their mechanical properties. In this study, we examined the shear properties (internal friction angle, cohesion, storage modulus and loss modulus) of wet granules composed of graphite particles and water, and determined their inner water connectivity using X-ray refraction contrast imaging computed tomography (CT) to elucidate their correlation. At high solid content concentration (C_SC) region (C_SC = 85 wt.%), internal friction angle of wet granules was slightly lower than that of wet granules with lower C_SC, and their cohesion becomes almost zero. Furthermore, storage modulus of wet granules at C_SC = 85 wt.% was the highest among all wet granules. The X-ray CT and scanning electron microscopy (SEM) observations revealed that the water connectivity in the wet granules was in the pendular state and graphite particles fractured under shear test at C_SC = 85 wt.%. From these results, it can be concluded that lower shear cohesion at C_SC = 85 wt.% is caused by an increase in the number of isolated liquid bridges, and particle fracture results in a decrease in the internal friction angle owing to decreasing roughness of shear plane. Furthermore, the particle fracture also resulted in the higher storage modulus at C_SC = 85 wt.% in rheological measurements.