Study of dynamic mechanical properties of UHPC-AAC composites based on SHPB test

Ultra-High Performance Concrete (UHPC) is widely used for repair due to its mechanical and durability properties. For example, when repairing Alkali-Activated Concrete (AAC) structures, the dynamic mechanical properties of the UHPC-AAC contact zone are essential for its impact loading resistance. This study investigated 84 UHPC-AAC composites' dynamic mechanical properties in different combinations by the Split Hopkinson Pressure Bar (SHPB) test and FEM method, which provided the dynamic stress-strain curves with varying strain rates (single AAC, single UHPC, 33%/50%/67% UHPC and composites with angular), the peak stresses, peak strains, and the energy dissipation results. The dynamic strength of the composites increases with the strain rate, and the maximum averages are 201.5 MPa and 133.4 MPa for UHPC and AAC. Based on the SHPB test data, we proposed a DIF model for predicting the dynamic strength of UHPCAAC composites. Then we verified the reasonableness of the model by correlation analysis. We also offer a coordinated performance evaluation method to complement the dynamic increase factor (DIF) model. Comparison of the dynamic stress-strain curves validates the reasonableness of the FEM and further investigates the failure and energy evolution of the contact zone during the impact process. In sum, this study provides the dynamic mechanical properties of UHPC-AAC composites and reveals their behavior under dynamic loading through SHPB tests and numerical methods. UHPC-AAC composites can effectively improve AAC's impact strength and energy dissipation capacity, and the composites have both dynamic strength and deformation properties at about 50% of UHPC without angles.