A study on the dynamic mechanical properties of coral concrete reinforced with polypropylene and basalt fibers

To clarify the strain-rate-dependent behavior of hybrid fiber-reinforced coral aggregate concrete, dynamic splitting tensile tests were conducted on specimens incorporating polypropylene fibers(PPF) and basalt fibers (BF) with varying lengths and volume fractions. The results demonstrate that strain rate and fiber length jointly govern the evolution of peak stress, peak strain, and dynamic increase factor (DIF). While all specimens exhibited pronounced strain-rate strengthening, fiber length primarily controlled deformation coordination at the peak stage. Specimens reinforced with 12 mm BF showed higher peak strain and stronger strain-rate sensitivity compared with 6 mm and 18 mm systems, indicating a more effective stress-transfer and crack-bridging mechanism under dynamic loading. In contrast, excessive fiber length or dosage reduced strengthening efficiency due to interfacial instability and non-uniform distribution. Hybrid fiber systems consistently outperformed single-fiber specimens in terms of dynamic tensile strength, energy dissipation capacity, and crack resistance. The findings reveal a clear coupling effect between fiber length and strain rate and identify 12 mm BF at moderate dosage as the optimal configuration for improving dynamic splitting performance. This study provides mechanistic insight into fiber-length-dependent dynamic reinforcement and offers guidance for coral concrete applications in marine structures subjected to impact and wave loading.