为探究超高性能混凝土(UHPC)在不同钢纤维下的单轴拉伸力学性能,设计了10组狗骨头型试件单轴拉伸试验,研究了钢纤维长径比(37、50、64、65)、掺率(2%、3%、4%)、形状(端钩型和弧型)和成型方式(搅拌法和渗浆法)对UHPC轴拉强度、应力-应变曲线、拉伸韧性和破坏过程的影响。结果表明:端钩型钢纤维长径比增加,UHPC轴拉强度提高6.54%~9.37%,软化段残余强度比值提高5.00%~38.30%;端钩型钢纤维体积掺率从2%增至3%、4%,UHPC抗拉强度、峰值应变和软化段残余强度比值均有所提高,拉伸韧性增加;端钩型钢纤维渗浆法成型试件相比搅拌法试件,强度变化不大,但峰值应变提高53.61%~91.96%;弧型钢纤维UHPC拉应力-应变曲线具有应变硬化特性,破坏过程呈多裂缝开展;与同长径比端钩型钢纤维试件相比,弧型钢纤维UHPC峰值拉应变提高了19.41~19.96倍,软化段残余强度比值提高18.00%~70.03%,弧型钢纤维增韧效果优于端钩型钢纤维。采用硬化指数和软化段残余强度比值方法可以全面评价UHPC轴拉峰前应变硬化特征和峰后的轴拉韧性。

To explore the mechanical properties of ultra-high performance concrete (UHPC) with different steel fibers under uniaxial tension, we designed ten sets of uniaxial tensile tests on dog-bone-shaped UHPC specimens. We investigated how the aspect ratio (37, 50, 64, 65), dosage (2%, 3%, 4%), shape (end-hooked and curved), and forming methods(mixing and slurry) of steel fibers affect the tensile strength, stress-strain curves, tensile toughness, and failure process of UHPC. Results reveal that as the aspect ratio of hooked steel fiber rises, the tensile strength of UHPC increases by 6.54%-9.37%, and the residual strength ratio in the strain-softening segment grows by 5.00%-38.30%. When the volumetric dosage of end-hooked steel fiber increases from 2% to 3% and 4%, the tensile strength, peak strain, and residual strength ratio in the strain-softening segment of UHPC increase, along with an enhancement in tensile toughness. Compared with specimens formed by the mixing method, those formed by the slurry method with end-hooked steel fibers show no significant change in strength, but the peak strain increases by 53.61%-91.96%. The stress-strain curve of UHPC with curved steel fibers demonstrates strain-hardening characteristics, and its failure process involves the propagation of multiple cracks. In comparison to specimens with end-hooked steel fibers of the same aspect ratio, UHPC with curved steel fibers exhibits a 19.41-19.96-fold increase in peak tensile strain and an 18.00%-70.03% increase in the residual strength ratio in strain-softening segment. This indicates that the toughening effect of curved steel fibers is superior to that of end-hooked steel fibers. By using the hardening index and the residual strength ratio in the strain-softening segment, we can comprehensively evaluate the strain-hardening characteristics before peak axial-tensile strain and the axial-tensile toughness after peak in UHPC.