Dynamic mechanical behaviors and multi-scale damage-fracture mechanisms of high-performance concrete synergistically modified with rubber particles and steel fibers under SHPB-driven impact splitting tests

• The steel fiber reinforcing effect, the rubber content weakening effect, and the rubber particle size enhancing effect shown in the impact splitting strength were revealed. • The macroscopic mechanism of complex mechanical damage and fracture of disk specimens under SHPB plate loading mode was clarified. • The mesoscopic mechanism of rubber particle size and rubber content on the synergistic energy dissipation - increasing toughness - crack resistance of steel fiber concrete under dynamic splitting was revealed. • The optimal rubber particle size and rubber content with the best dynamic and static splitting mechanical properties of RSF-C were proposed. Rubber-steel fiber concrete (RSF-C) is a new type of composite concrete material that is mixed with rubber particles and steel fibers in normal concrete (N-C). To investigate the dynamic mechanical characteristics and damage-fracture mechanism of RSF-C under impact splitting, comparative impact splitting tests were carried out on three concrete disc specimens: N-C, steel fiber concrete (SF-C), and RSF-C using the SHPB test system. The results showed that: (1) The impact splitting tensile strength showed the obvious steel fiber reinforcing effect, rubber content weakening effect (substitution ratio increases), and rubber particle size enhancing effect (particle size increases). (2) The degree of failure of the specimens increased with the increase of impact load, especially in the "triangular compression-shear fracture zone" formed at the loading ends of the N-C and SF-C specimens due to impact load, and even "semicircular bending fracture" occurred with the increase of impact load. However, the formation of the obvious "triangular compression-shear fracture zone" at the loading ends of the RSF-C specimens needs to occur under relatively larger impact load conditions. (3) Mixing steel fiber and rubber particles obviously increased the toughness of N-C, and the decrease of rubber particle size increased the crack resistance of RSF-C. However, the weak interface formed by rubber particles and cement paste also weakened the bearing capacity of the specimen, increasing the degree of damage with the increase of rubber substitution ratio. (4) For the internal structure of the N-C disc, if the material is homogeneous and continuous in all directions or the homogeneity and continuity in all directions of the edge area of the disc specimen are better than those in the central area, that is, there are more structurally weak surfaces in the central area of the disc specimen, then it is easier to meet the requirement of "the initial crack starts at the center of the disk" in the Brazilian splitting experiment. Conversely, it is more likely that "the initial cracks start from the loading ends of the disc" will occur. (5) For the internal structures of SF-C and RSF-C discs, even if there are many structurally weak surfaces in the central areas of the disc specimens, if the central areas of the disc specimens have better crack resistance due to the presence of reasonable steel fibers, then they are more likely that "the initial cracks start from the loading ends of the disc". Conversely, it is more likely that "the initial crack starts at the center of the disk".