Enhancing the blast resistance of two-stage high-performance concrete with a functionally-graded concept

In recent decades, frequent regional conflicts and terrorist attacks have exacerbated the threat of explosions to buildings. The superior mechanical properties of two-stage fiber concrete (TSFC) make it a potential choice for constructing blast-resistant protective structures. However, the blast resistance of TSFC is still not well understood and the key factors influencing its anti-blast performance remain unclear. In this study, functionally-graded TSFC is designed based on the typical damage characteristics of structures subjected to contact explosions, which synergistically combines the advantages of Ultra-High Performance Concrete (UHPC) matrix, coarse aggregates and steel fibers. Through the unique two-stage casting method, optimal distributions of fibers and aggregates is achieved according to blast resistance requirements. The blast resistance of this functionally-graded TSFC is investigated experimentally and theoretically. Results demonstrate that the functionally-graded TSFC achieves a superior resistance under contact explosion. The diameter and depth of the blast crater are reduced by 33.5 % and 53.8 %, respectively, compared to the conventional concrete with the same amounts of steel fibers and coarse aggregates. The influences of the fibers and aggregates are investigated, and the mechanism of the anti-blast performance of the functionally-graded TSFC is revealed. Furthermore, a modified formula is proposed to predict the crater depth of the functionally-graded TSFC. This study deepens the understanding of the anti-blast response of functionally-graded TSFC under contact explosion and provides more options for the innovative design of blast-resistant protective structures.