Numerous fibers combinations are used in the construction industry for improving the fracture resistance of hybrid fiber-reinforced concrete (HyFRC). In this paper, the effects of fiber combination on the mechanical properties of FRC are studied. For this purpose, different volume percentages of the added fibers with different compositions are used to investigate their influences on the fracture toughness and tensile strength of the concrete. Different fiber compositions including the steel, carbon and polypropylene of different volume ratios can be added to the concrete specimens for measuring their tensile strength and critical stress intensity factor of the samples containing preexisting cracks. Therefore, some concrete specimens are prepared by adding 1% carbon fibers and different ratios of steel and polypropylene fibers. The direct tensile testing machine and the indirect Brazilian tensile test apparatus are used to measure the tensile strength of the HyFRC specimens in the laboratory. Some specimens are also used to measure the fracture toughness (Mode I) of the HyFRC by using the novel compression-to-tensile load converting device implemented in the universal tensile testing machine. The novelty of this paper is to render a new approach for the measurement of tensile strength and fracture toughness of hybridized fiber-reinforced concrete (HyFRC) by adding different kinds of fibers. These experimental results show that by changing the ratios of the carbon, steel and polyethylene fibers the tensile strength and fracture toughness of HyFRC specimens change accordingly.

许多纤维组合用于建筑行业，以提高混合纤维增强混凝土 (HyFRC) 的抗断裂性。本文研究了纤维组合对FRC力学性能的影响。为此，使用不同体积百分比的添加不同成分的纤维来研究它们对混凝土断裂韧性和抗拉强度的影响。可将不同体积比的钢、碳和聚丙烯等不同纤维成分加入混凝土试件中，以测量含有预先存在裂缝的试件的抗拉强度和临界应力强度因子。因此，一些混凝土试件是通过添加1%的碳纤维和不同比例的钢和聚丙烯纤维来制备的。实验室采用直接拉力试验机和间接巴西拉力试验仪测量HyFRC试样的抗拉强度。通过使用在万能拉伸试验机中实施的新型压缩到拉伸载荷转换装置，一些试样还用于测量 HyFRC 的断裂韧性（模式 I）。本文的新颖之处在于通过添加不同种类的纤维，为测量混合纤维增强混凝土 (HyFRC) 的拉伸强度和断裂韧性提供了一种新方法。这些实验结果表明，通过改变碳纤维、钢纤维和聚乙烯纤维的比例，HyFRC 试样的拉伸强度和断裂韧性会相应地发生变化。