Analysis of dynamic splitting failure characteristics of silica fume reinforced polypropylene fiber concrete based on DIC

To investigate the impact resistance of polypropylene fiber content in silica fume-reinforced polypropylene fiber concrete, a dynamic splitting experiment was conducted using the Split Hopkinson Pressure Bar (SHPB) device. The dynamic tensile strength of the specimens under varying impact pressures was examined. The evolution of strain characteristics and crack formation on the specimen surface was analyzed using Digital Image Correlation (DIC), while the fractal nature of the specimen fragments was assessed through screening. The results indicate that the stress-time history curve fluctuations in concrete with varying fiber sizes are more pronounced compared to concrete with a single fiber type. The latter half of the control group’s curve, which lacks fiber, exhibits a smooth, nearly fluctuation-free profile. The dynamic tensile strength of coarse polypropylene fiber-reinforced concrete is higher than that of fine polypropylene fiber, with increases of 7.6% and 11.3% under high impact pressure, and 7.9% and 30.8% under quasi-static conditions, respectively. As the impact progresses, the primary crack propagates from the high-strain region along the loading direction through the center of the specimen, followed by the gradual expansion or connection of secondary cracks with the main crack. The fragmentation of the specimen exhibits a degree of self-similarity. The mass ratio of fragments with particle sizes smaller than 20 mm increases, accompanied by a gradual increase in the fractal dimension. The crack opening speed of the specimen reinforced with polypropylene fibers was reduced by 45.3%, demonstrating that the polypropylene fibers significantly inhibited the macroscopic propagation of cracks.