Abstract

Natural aggregate concrete is prone to crack propagation and overall crushing under impact load, making it difficult to satisfy the service requirements for collapse resistance in building structures. In order to improve the impact resistance of concrete, this study investigated the impact of the mechanical behavior of steel–polypropylene hybrid fiber-reinforced concrete (SPFRC) using a split Hopkinson pressure bar apparatus. The effects of steel fiber content, polypropylene fiber content, and strain rate on the fractal dimension were examined, and the relationship between total energy dissipation and fractal dimension was established. The results show that the mean fragment size of the crushed specimens decreases linearly with increasing driving voltage, whereas it increases with fiber content. The fractal dimension monotonically increases with an increasing strain rate and decreases as the fiber content increases. Under a driving voltage of 1200 V and steel fiber content of 0.5%, increasing the polypropylene fiber content from 0% to 0.1% yields the largest reduction in the fractal dimension (15.00%) for specimen S0.5P0.1, exceeding the reductions from increments of 0.1%–0.25% and 0.25%–0.5%. Comparative results demonstrate that SPFRC exhibits superior impact failure resistance compared with concrete reinforced by a mono type of fiber. Exploring the correlation between fractal features and total energy dissipation can realize a more systematic and comprehensive performance assessment of concrete materials. The research results can provide quantitative theoretical support for the impact resistance evaluation and ratio optimization of SPFRC.

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