The dynamic impact on concrete elements is commonly encountered in civil engineering structures, e.g. store floors, street barriers, pillars, slabs, etc. The impact of a car, aircraft, fallow rock, etc. is a huge risk for structural stability. The safety of the engineering structures lies in a deep understanding of the fracture process, both on quasi-static and dynamic problems. The paper is focused on studying and deeply understanding the mechanism of crack initiation and its growth in concrete structures under dynamic conditions. It can be done only if the microstructure of the specimen is well recognized. In the numerical calculations, the discrete element method (DEM) was used [1]. DEM directly simulates the material mesostructure and thus is suitable for comprehensive studies of the mechanisms of initiation, growth and formation of localized zones, cracks and fractures at the mesoscale. In this research, the concrete 3-point bending beam was numerically investigated. The microstructure of the sample was obtained from micro-CT (the aggregate and air void shape, size and position) [2]. The 2D DEM model of concrete consists of 4 phases (aggregate and interfacial transition zones (ITZs) around them, cement matrix and voids) [3]. The novelty was, that the aggregate elements were able to fracture during calculations, which is an important issue in dynamic calculations. With a higher strain rate, the fracture is more rapid and the crack often runs thru aggregate. In contrast, in quasi-static conditions, the crack is more curved and runs mostly from ITZ to ITZ. Different piston velocities were applied (from quasi-static 0.4 mm/s up to 1250 mm/s) to study dynamic effects. The quasi-static results were directly compared to the laboratory test with a special focus on crack shape. Next, the micro and macro results for dynamic tests were discussed and compared with other research. The new DEM model, with breakable aggregates, shows its capability for dynamic calculations.