Investigation of the Heat-Treatment Effect on Rock Fragmentation Characteristics Using the Dynamic Ball Compression Test

As a common physical process in mining and other rock engineering industries, rock fragmentation is mainly induced by mechanical loading. To optimize the rock fragmentation process, many methods have been proposed to pre-condition the rock material. Heat-treatment is one such rock conditioning method to facilitate rock fragmentation. It is therefore necessary to investigate the effect of heat-treatment on the characteristics of rock fragmentation. This study is concerned with the rock fragmentation in crushing, which is experimentally studied utilizing the dynamic ball compression test. The spherical specimens made of Laurentian granite (LG) are heat-treated under various temperatures (250, 450, 600 and 850 ℃). The resulting thermal damage is first examined using the X-ray Micro-computed tomography (CT) method. The spilt Hopkinson pressure bar (SHPB) system in combination with a high speed camera is then utilized to conduct the dynamic ball compression test. With the aid of the moment-trap technique in SHPB and the high speed camera, the energy dissipation in crushing is obtained at five fixed input energy levels. The results indicate that the dynamic indirect tensile strength increases with the loading rate while decreases with the increase of the treatment temperature. The failure mode of ball specimen under dynamic compression can be categorized as fragmentation and pulverization based on the particle size distribution of fragments. The influence of the treatment temperature on the crushing ratio of LG ball specimen is more significant for higher input energy. Moreover, the energy efficiency of ball specimens generally decreases with the increase of the loading rate and the treatment temperature.