Triaxial constitutive model and meso-structural mechanism of hybrid steel fiber reinforced self-compacting concrete: Towards sustainability and resilience

• Index of area ratio toughness can quantify the fluctuating post-peak toughness. • The triaxial constitutive model considering toughness correction was developed. • The mesoscopic mechanism was revealed through X-ray CT results. Hybrid steel fiber reinforced self-compacting concrete (HSFRSCC) is suitable for applying as the concrete matrix material of precast segments, which can ensure the high local bearing capacity and avoid the initial defect. However, there were very limited studies on the triaxial constitutive model and meso -structural mechanism of HSFRSCC. In this research, the closest-packed fiber-aggregate skeleton of HSFRSCC were designed based on the modified compressible packing model (CPM). According to the uniaxial compression test, fluidity test and sustainable principle, 3 groups of optimized mix ratios with skeleton volume fraction (SVF) as variable were selected for the triaxial compression test, with confining pressures of 0, 2, …, 14 MPa. The formulas of triaxial peak stress and triaxial peak strain were established from the triaxial test results. Post-peak fracture toughness presented a fluctuating law with confining pressure, which was quantified by the novel index of area ratio fracture toughness. The comparison between HSFRSCC and ordinary concrete shown that HSFRSCC with SVF of 62 % combined the good triaxial mechanical performance and environmental compatibility. The triaxial constitutive model considering toughness correction was developed, which was proved to be applicable for HSFRSCC by three statistical indexes. Through the X-ray computed tomography test, the strengthening of steel fiber and the synergistic effect between steel fiber and aggregate were revealed and analyzed. Finally, it was found that confining pressure was the decisive factor to determine the overall fluctuating law of post-peak fracture toughness, and steel fiber and aggregate would influence the local position and value of post-peak fracture toughness.