*Article* **Research on the Mechanical Performance of Carbon Nanofiber Reinforced Concrete under Impact Load Based on Fractal Theory**

**Wei Xia 1,\*, Jinyu Xu 1,2 and Liangxue Nie <sup>1</sup>**


**Abstract:** The research is focused on the dynamic compressive strength, impact toughness and the distribution law of fragmentation size for the plain concrete and the carbon nanofiber reinforced concrete with four fiber volume contents (0.1%, 0.2%, 0.3% and 0.5%) under impact load by using the *Φ*100 mm split-Hopkinson pressure bar. Based on the fractal theory and considering the micropore structure characteristics of the specimen, the impact of the strain rate and the dosage of carbon nanofibers on the dynamic mechanical performance of concrete is analyzed. According to the results, both the dynamic compressive strength and the impact toughness increase continuously with the improvement of the strain rate level at the same dosage of fiber, showing strong strain rate strengthening effect; at the same strain rate level, the impact toughness increases gradually with the increase in the fiber dosage, while the dynamic compressive strength tends to increase at first and then decrease; the distribution of the fragmentation size of concrete is a fractal in statistical sense, in general, the higher the strain rate level, the higher the number of fragments, the lower the size, and the larger the fractal dimension; the optimal dosage of carbon nanofibers to improve the dynamic compressive strength of concrete is 0.3%, and the pore structure characteristics of carbon nanofiber reinforced concrete exhibit obvious fractal features.

**Keywords:** carbon nanofiber reinforced concrete; impact load; dynamic compressive strength; pore structure characteristics; fractal dimension
