Experimental study on dynamic mechanical properties of mortar-sandstone composite under impact load

Mortar-rock composite structures are very common in underground engineering. Their mechanical behaviour and failure modes are much more complicated than those of pure mortar or rock structures. Understanding the energy and damage evolution of composite structures under impact loads is important for the stability of en-gineering structures. In this paper, dynamic compression tests of different grades of mortar-sandstone composite specimens were carried out by using the Hopkinson pressure bar system and a high-speed photography system to investigate the effects of impact velocities and mortar strength on the mechanical properties, energy dissipation and failure modes of the composite specimens. The results showed that the dynamic peak stress, energy con-sumption characteristics, impact toughness index and fragmentation blocks of the mortar-sandstone composite were obviously affected by strain rate. The mortar-sandstone composites had a progressive failure mechanism, and the strengths of the end and the junction of the mortar specimens were less than those of other regions. Cracks formed in the composite specimens mainly from both ends of the mortar, and the specimens were dominated by splitting failure. Increasing the mortar strength grade improved the dynamic compressive strength and the elastic energy storage of the samples, resulting in larger bearing capacity and less damage. With increasing impact velocity, the degree of fragmentation of the composite specimens increased, the average fragmentation blocks decreased, and the mortar specimens were damaged more severely than the sandstone. The mortar specimens finally broke into powder debris, while the sandstone finally broke into fragments.