Experimental investigation of the anti-penetration mechanism of UHPC reinforced with high-strength steel bars subjected to projectile impact

Ultra-high-performance concrete reinforced with high-strength steel bars (HSSB-UHPC) is a new protective material that uses HSSB arranged in a three-dimensional cage structure as the skeleton and UHPC as the matrix. The objective of this paper is to investigate the anti-penetration mechanism of this new material. The penetration tests are performed at velocities of 548-755 m/s using projectiles with diameters of 80 mm and 125 mm, the interaction mechanism of HSSB and UHPC in the structural material is analyzed. The results show that HSSBUHPC possesses higher strength and toughness, making it an excellent anti-penetration material. After penetration, the HSSB-UHPC targets maintain good integrity, and the target failure only includes the local spalling of the concrete cover near the impact point and the formation of a cylindrical tunnel of the projectile's diameter; the penetration depth in the HSSB-UHPC is only 19.8% of that of the 40 MPa concrete and 43% of that of 168.3 MPa UHPC. The outstanding anti-penetration performance of HSSB-UHPC stems from the mutual enhancement of HSSB and UHPC: as HSSB form a compact cage structure, it imposes strong six-sided compression constraints on UHPC, produces dowel action in the motion field of shear slip, significantly restricts the forward movement of the penetrating projectile, and quickly transmits the force throughout the target, leading to improvement of the comprehensive mechanical properties, energy dissipation capacity and penetration resistance of HSSB-UHPC. The higher shear strength and higher wave impedance of HSSB-UHPC are the underlying reason for its excellent penetration resistance. The findings of this study will be of referential significance for the further study of this new material.