不同长径比聚丙烯纤维增强混凝土的力学特性

纤维长径比对混凝土力学性能影响显著，而长径比变化的实质是纤维直径和形态均发生变化，因此现有研究多是通过改变聚丙烯（PP）纤维（包含粗、细PP纤维）直径或截面形态设置长径比梯度，从而导致变量不唯一。本文对粗PP纤维（d=700 μm）和细PP纤维（d=80 μm）长径比对混凝土力学性能的影响进行了试验研究，分析了粗、细PP纤维增强混凝土的力学特性。结果表明:粗、细PP纤维增强混凝土坍落度随所掺纤维长径比增大而先降低后趋于稳定，抗压、抗弯、劈拉强度随所掺纤维长径比增大而呈现出先增大后减小的趋势，700 μm粗PP纤维最优长径比为42，80 μm细PP纤维最优长径比为200。此外，提出了宏观力学拟合计算理论用于分析粗PP纤维长径比对PP纤维增强混凝土抗弯强度的影响，以此来增强试验结果的预测性和可控性；对粗、细PP纤维在混凝土中的摩擦粘结机制进行了力学分析，掌握了影响摩擦粘结力的具体因素。 

Mechanical properties of polypropylene fiber reinforced concrete with different aspect ratios

Fiber aspect ratio has a significant effect on the mechanical properties of concrete. Because the change in aspect ratio is essentially the change in fiber diameter and morphology, the existing researches mostly change the aspect ratio gradient by changing the diameter or the cross-sectional shape of polypropylene(PP) fiber (including coarse and fine PP fiber), resulting that the variables are not unique. An experiment was carried out on the effects of the aspect ratio of coarse PP fiber (d=700 μm) and fine PP fiber (d=80 μm) on the mechanical properties of concrete. The mechanical properties of coarse and fine PP fiber reinforced concrete were analyzed. The results show that the slump of coarse and fine PP fiber concrete decreases first and then stends to be stable with the increase of the aspect ratio. The compressive strength, flexural strength and tensile strength tend to increase first and then decrease with the increasing aspect ratio. There is an optimum aspect ratio which is 42 for the 700 μm coarse PP fiber, and 200 for the 80 μm fine PP fiber. In addition, the macromechanical fitting calculation theory was proposed to analyze the influence of the aspect ratio of coarse PP fiber on the flexural strength of fiber concrete, so as to enhance the predictability and controllability of the test results. The analysis of the frictional bonding mechanism of the coarse and fine PP fibers in concrete was carried out, and the specific factors affecting the frictional bonding force were mastered.