Dynamic Characteristics and Impact Resistance of Recycled Concrete under Shock Loading

Recycled aggregate concrete is a sustainable construction material, but its weak interfacial transition zone and high defect sensitivity often lead to insufficient toughness and performance degradation under impact loading. To improve the dynamic resistance of recycled aggregate concrete, this study proposes a multi-objective mix optimization method combining the Non-dominated Sorting Genetic Algorithm II and the Entropy Weight-Technique for Order Preference by Similarity to Ideal Solution. Silica fume and multidimensional polypropylene fibers are introduced to enhance the interfacial compactness and crack-bridging capacity of recycled aggregate concrete. The optimized mix proportion is evaluated using split Hopkinson pressure bar tests, strain monitoring, ultrasonic testing, and crack width measurement. The results show that the optimal silica fume and multidimensional polypropylene fiber contents are 1.39 % and 0.97 %, respectively. Compared with plain concrete, the composite-enhanced recycled aggregate concrete exhibits significantly improved dynamic strength, ductility, and energy dissipation capacity. The peak stresses of grade C30, C40, and C50 recycled aggregate concrete reach 51.9, 76.5, and 109.2 MPa, respectively, representing an increase of more than 60 %. The crack width is reduced by approximately 50 %, and the energy dissipation ratio reaches 0.30. These findings indicate that the silica fume and multidimensional polypropylene fiber synergistic reinforcement strategy effectively improves the impact resistance and structural stability of recycled aggregate concrete, providing a feasible material design approach for tunnel linings, blast-resistant structures, and other impact-prone engineering applications.