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.

中文翻译：

---

混合钢纤维增强自密实混凝土的三轴本构模型和细观结构机制：迈向可持续性和韧性


混合钢纤维增强自密实混凝土 （HSFRSCC） 适合作为预制管片的混凝土基体材料，可以保证较高的局部承载力，避免初始缺陷。然而，关于 HSFRSCC 的三轴本构模型和中观结构机制的研究非常有限。本研究基于改进的可压缩堆积模型 （CPM） 设计了 HSFRSCC 最紧密堆积的纤维聚集体骨架。根据单轴压缩试验、流动性试验和可持续原则，选取 3 组以骨架体积分数 （SVF） 为变量的优化混合比进行三轴压缩试验，围压为 0， 2， ...， 14 MPa。根据三轴试验结果建立了三轴峰值应力和三轴峰值应变的公式。峰后断裂韧性在围压作用下呈波动规律，通过面积比断裂韧性的新指数进行量化。HSFRSCC 与普通混凝土的比较表明，SVF 为 62 % 的 HSFRSCC 结合了良好的三轴力学性能和环境兼容性。建立了考虑韧性修正的三轴本构模型，并通过三个统计指标证明该模型适用于 HSFRSCC。通过 X 射线计算机断层扫描测试，揭示和分析了钢纤维的增强以及钢纤维与骨料之间的协同效应。最后发现，围压是决定峰后断裂韧性整体波动规律的决定性因素，钢纤维和骨料会影响峰后断裂韧性的局部位置和值。