To develop optimum engineered steel fibers as reinforcement for ultra-high-performance concrete (UHPC), three different types of steel fibers having various geometries, such as circular straight (C), non-twisted triangular (T0), and singly twisted triangular (T1), were considered. The surface of the steel fibers was also modified using an electrolyte solution comprising ethylenediaminetetraacetic acid (EDTA). The surface morphology was quantitatively evaluated, and the pullout and tensile behaviors of UHPC with the steel fibers were examined. The roughness of the fiber surface increased with the duration of immersion in EDTA electrolyte solution up to 9 h, and the roughness parameter increased by approximately 10 times. The C fiber absorbed the highest pullout energy (632.1 mJ), followed by the T0 and T1 fibers, whereas the T1 fiber most effectively increased the tensile strength and specific energy of UHPC, followed by the C or T0 fiber. The surface treatment efficiently enhanced both the pullout and tensile performance of UHPC with the C and T0 fibers owing to the increased surface roughness, whereas it deteriorated the tensile performance of UHPC with the T1 fibers. Steel fiber types that produced severe matrix spalling at the inclined condition or those that were ruptured in UHPC had a higher possibility of inferior tensile performance than those with minor matrix spalling and nonrupture. As an optimal reinforcement strategy of UHPC, 6-h treatment of C and T0 fibers or the pristine T1 fiber was recommended, which helped to achieve tensile strengths of 17.5–20.4 MPa and specific energies of 106.7–113.0 kJ/m³.

为了开发最佳的工程钢纤维作为超高性能混凝土（UHPC）的增强材料，应使用三种不同类型的具有不同几何形状的钢纤维，例如圆形直（C），非加捻三角形（T0）和单加捻三角形（ T1）。还使用包含乙二胺四乙酸（EDTA）的电解质溶液对钢纤维的表面进行了改性。定量评价表面形态，并检查UHPC与钢纤维的拉伸和拉伸行为。纤维表面的粗糙度随着在EDTA电解质溶液中浸泡9个小时而增加，并且粗糙度参数增加了大约10倍。C纤维吸收了最高的拔出能量（632.1 mJ），其次是T0和T1纤维，T1纤维最有效地提高了UHPC的拉伸强度和比能，其次是C或T0纤维。由于增加了表面粗糙度，表面处理有效地增强了C和T0纤维对UHPC的拉伸性能和拉伸性能，而对T1纤维对UHPC的拉伸性能却产生了不利的影响。与在较小的基体剥落和不破裂的情况下相比，在倾斜条件下产生严重基体剥落的钢纤维类型或在UHPC中破裂的钢纤维具有较高的抗拉性能。作为UHPC的最佳增强策略，建议对C和T0纤维或原始T1纤维进行6小时处理，这有助于获得17.5–20.4 MPa的拉伸强度和106.7–113.0 kJ / m的比能 由于增加了表面粗糙度，表面处理有效地提高了C和T0纤维对UHPC的拉伸性能和拉伸性能，而对T1纤维对UHPC的拉伸性能却产生了不利影响。与在较小的基体剥落和不破裂的情况下相比，在倾斜条件下产生严重基体剥落的钢纤维类型或在UHPC中破裂的钢纤维具有较高的抗拉性能。作为UHPC的最佳增强策略，建议对C和T0纤维或原始T1纤维进行6小时处理，这有助于获得17.5–20.4 MPa的拉伸强度和106.7–113.0 kJ / m的比能 由于增加了表面粗糙度，表面处理有效地增强了C和T0纤维对UHPC的拉伸性能和拉伸性能，而对T1纤维对UHPC的拉伸性能却产生了不利的影响。与在较小的基体剥落和不破裂的情况下相比，在倾斜条件下产生严重基体剥落的钢纤维类型或在UHPC中破裂的钢纤维具有较高的抗拉性能。作为UHPC的最佳增强策略，建议对C和T0纤维或原始T1纤维进行6小时处理，这有助于获得17.5–20.4 MPa的拉伸强度和106.7–113.0 kJ / m的比能 T1纤维会降低UHPC的拉伸性能。与在较小的基体剥落和不破裂的情况下相比，在倾斜条件下产生严重基体剥落的钢纤维类型或在UHPC中破裂的钢纤维具有较高的抗拉性能。作为UHPC的最佳增强策略，建议对C和T0纤维或原始T1纤维进行6小时处理，这有助于获得17.5–20.4 MPa的拉伸强度和106.7–113.0 kJ / m的比能 T1纤维会降低UHPC的拉伸性能。与在较小的基体剥落和不破裂的情况下相比，在倾斜条件下产生严重基体剥落的钢纤维类型或在UHPC中破裂的钢纤维具有较高的抗拉性能。作为UHPC的最佳增强策略，建议对C和T0纤维或原始T1纤维进行6小时处理，这有助于获得17.5–20.4 MPa的拉伸强度和106.7–113.0 kJ / m的比能³。