Study of dynamic mechanical properties of lightweight ultra-high-performance concrete with varying steel fiber contents

This study presents a novel lightweight ultra-high-performance concrete (LUHPC) incorporating fly ash floating beads (FAFB) and hollow glass microspheres (HGM). The developed LUHPC achieves a compressive strength exceeding 100 MPa with a density below 1900 kg/m³. Its dynamic mechanical properties were investigated through systematic static and dynamic tests, including Split Hopkinson Pressure Bar (SHPB) experiments at strain rates ranging from 59 s⁻¹ to 211 s⁻¹ on specimens with steel fiber volume fractions varying from 0% to 2.5%. The results demonstrate a positive correlation: both dynamic compressive strength and energy dissipation capacity are significantly enhanced by higher steel fiber content and increased strain rate. Specifically, increasing the steel fiber volume fraction from 0% to 2.5% improved the energy dissipation capacity by up to 128.2%. Failure mode analysis revealed a transition from edge spalling to fragmentation with increasing strain rates, which was effectively mitigated by higher fiber content. To address the inability of existing UHPC-based models to accurately predict the dynamic increase factor (DIF) of LUHPC, a strain rate-dependent logarithmic DIF model is proposed. Based on a micro-damage element model, a dynamic constitutive model for LUHPC was established. The validity of the newly developed model was verified using experimental data. Furthermore, the relationships between the three control parameters in the constitutive model (m, F₀, and C_n) and the strain rate (ranging from 59 s⁻¹ to 211 s⁻¹) as well as the steel fiber volume fraction (ranging from 0% to 2.5%) were fitted. These findings provide crucial insights into the dynamic response of LUHPC and support its potential application in protective structures requiring materials with low weight and high impact resistance.