## 1 Introduction
[PERSON], [PERSON], and [PERSON] [12] conducted impact tests on oil palm shell lightweight concretes reinforced by polypropylene (PP) fibers, and found that there was a strong linear relationship between the volume fraction of the PP fibers and the impact resistance. Through low-velocity impact tests, [PERSON] and [PERSON] [13] studied the responses of thin slabs of slurry-infiltrated fibrous concrete (SIFCON) with and without reinforcement, and found that binary blends of silica fume and slag improved the strength and durability characteristics significantly. [PERSON] and [PERSON] [14; 15] conducted low-velocity impact tests of high-strength concrete (HSC) and ultra-high-performance fiber-reinforced concrete (UHP-FRC) plates to study the impact resistance, and found that the UHP-FRC plates ex  
Figure 1: Crack extension of the cracked areas. (**a**) Impact crushing equipment; (**b**) Crack development of cracked core. hibited better damage control characteristics than the high-strength concrete (HSC) plates. Moreover, the crack pattern and failure mode were more dependent on the reinforcement arrangement rather than reinforcement ratio. [PERSON], [PERSON], and [PERSON] [16] conducted low-velocity impact tests on concrete slabs to study the impact resistance of reinforced concrete slabs, and found that the damage to slabs under a low-velocity impact increased with increasing impact energy. From the test results, it was found that the failure mode of a concrete slab changes with a change in the impact conditions. [PERSON] and [PERSON] [17] estimated the impact resistance of steel-fiber-reinforced concrete slabs strengthened with fiber-reinforced polymer sheets, and found that the impact resistance of the steel-fiber-reinforced concrete slabs was substantially improved by externally strengthening the fiber-reinforced polymer sheets. [PERSON] and [PERSON] [18] studied the deflection of prestressed and reinforced concrete (RC) slabs supported with different end conditions, and found that the effectiveness of prestressing on the impact resistance capacity of RC slabs could be demonstrated by comparing the deflection of RC slabs under similar impact loadings. [PERSON], [PERSON], and [PERSON] [19] studied the behavior of RC slabs subjected to impact loading under different support conditions, and finite element analyses using ANSYS Explicit STR software were also conducted to simulate the low-velocity experiments. In summary, most of the aforementioned studies primarily focused on the impact resistance characteristics of plain concrete, reinforced concrete, fiber-reinforced concrete, and fiber-reinforced concrete-based composites, and they were carried out by considering the aspects of concrete ratio, reinforcement ratio, fiber production ratio, concrete slab support types, and so on. To our best knowledge, little work has been reported that addresses the fracture mechanism of concrete slabs and the propagation mode of microcracks under the low-velocity impact of a drop hammer with different impact heads. In this study, through numerical simulation, the fracture mechanism and crack propagation mode of concrete slabs under low-velocity impact were innovatively studied under the conditions of different impact heads and different impact heights. Combined with the results of previous indoor tests, the development law of micro-cracks in concrete slabs was verified by comparison. At the same time, according to the fracture law of concrete slabs in concrete pavement during field tests, the impact device of the fracture equipment was improved and optimized, which effectively avoided the extension and penetration of longitudinal cracks and reduced the probability of the occurrence of reflective cracks in the asphalt pavement.