Effects of coarse aggregates size on dynamic characteristics of ultra-high performance concrete: Towards enhanced impact resistance

Coarse aggregates are recently used to address the high production costs and severe autogenous shrinkage of ultra-high performance concrete (UHPC), however, the influence of coarse aggregates size on the dynamic performances of UHPC remains poorly comprehended. Herein, the impact of coarse aggregates on the dynamic performances of UHPC is explored through a multiscale method with the focus on hydration products, micromechanical property, meso-scale fracture and macro-scale dynamic mechanical characteristics. Results show that the increasing maximum coarse aggregates size slightly enhances both the total amount and the elastic modulus of hydration products. The rise of the maximum coarse aggregate size enhances the percentage of fracture across coarse aggregates, thus, improving the impact resistance of UHPC. Regardless of the strain rates, the toughness and dynamic compressive strength enhance with the expanding maximum coarse aggregate size, while the dynamic increase factor and peak strain decrease with the rising coarser aggregates size. The damage degree of UHPC enhances with strain rate but reduces with the increasing maximum aggregate size. A conceptual enhancement mechanism of increasing maximum coarse aggregate size on the impact resistance is proposed. The present results promote the wider engineering application of UHPC containing coarse aggregates.