低模量聚酯纤维/水泥基复合材料抗冲击性能及损伤机制

研究聚酯纤维长径比、掺量对混凝土抗压强度、抗折强度、劈裂抗拉强度、断裂韧性及冲击荷载等力学性能的影响；运用复合材料理论和纤维间距理论对聚酯纤维/混凝土增韧阻裂机制进行研究，结合SEM观察微观形貌分析纤维长径比与掺量对增韧阻裂机制的影响；采用正交试验设计方法及激光扫描共聚焦显微镜(LSCM)研究冲击高度、试件厚度、长径比及掺量对纤维/混凝土抗冲击性能的影响。结果表明，长径比为300与600的聚酯纤维会降低混凝土抗压强度，低掺量长径比为150的聚酯纤维通过提高混凝土致密程度使混凝土抗压强度有所提升；在抗拉强度方面长径比为150的聚酯纤维主要以缺陷形式存在，长径比为300的聚酯纤维对改善混凝土内部拉结作用最显著，3%(与胶凝材料体积比)掺量聚酯纤维对提高混凝土抗折强度最显著；对于混凝土断裂韧性，长径比为300与600的聚酯纤维/混凝土断裂韧性提高明显，通过SEM微观形貌发现纤维拉结作用产生的微裂纹会提高混凝土耗能能力，从而提高混凝土极限荷载与破坏时中心挠度，长径比为300的聚酯纤维/混凝土抗拉强度变化规律与复合材料理论和纤维间距理论分析结果较吻合；冲击高度为影响冲击荷载大小的主要因素，纤维长径比较纤维掺量影响较大，通过LSCM三维损伤形貌分析得出长径比为150的聚酯纤维对混凝土材料损伤改善效果较显著，同等掺量下长径比为150的聚酯纤维间距较小导致混凝土局部力学性能提高，从而提高混凝土抗冲击性能。 

Impact resistance and damage mechanism of low modulus polyester fiber/cement matrix composites

The effects of length to diameter ratio and mixing amount of polyester fiber on the mechanical properties of concrete, such as compressive strength, flexural strength, splitting tensile strength, fracture toughness and impact load, were studied. The mechanism of toughening and cracking resistance of polyester fiber concrete was studied by composite material theory and fiber spacing theory. The microscopic morphology observed by SEM was used to analyze the influence of fiber length-diameter ratio and content on the mechanism of toughening and cracking resistance. Orthogonal experimental design method and laser scanning confocal microscope (LSCM) were used to study the influence of impact height, specimen thickness, aspect ratio and content on the impact resistance of fiber/concrete. The results show that the polyester fibers with ratio of length to diameter of 300 and ratio of length to diameter of 600 would reduce the compressive strength of concrete, the low content of polyester fibers with ratio of length to diameter of 150 increases the compressive strength of concrete by increasing the density of concrete. In terms of tensile strength, the polyester fibers with ratio of length to diameter of 150 mainly exist in the form of defects, the polyester fibers with ratio of length to diameter of 150 have the most significant effect on improving the concrete internal pulling, the addition of 3% (volume ratio to cementitious materials) polyester fiber is the most significant to improve the flexbility of concrete. For the fracture toughness of concrete, the fracture toughness of polyester fiber/concrete with ratio of length to diameter of 300 and 600 is significantly improved. According to the SEM microscopic morphology, it is found that the micro-cracks generated by fiber pulling action would improve the energy dissipation capacity of concrete, thus increasing the ultimate load and central deflection of concrete during failure, and the variation of tensile strength of polyester fibers with ratio of length to diameter of 300 reinforced concrete is in good agreement with the composite material theory and fiber spacing theory. Impact height is the main factor affecting the impact load, and the fiber length and diameter have greater influence than fiber content. Through LSCM analysis of three-dimensional damage morphology, it is concluded that the damage improvement effect of polyester fibers with ratio of length to diameter of 150 on concrete material is relatively significant, and at the same dosage, the small spacing of polyester fibers with ratio of length to diameter of 150 results in the improvement of local mechanical properties of concrete, thus improving the impact resistance of concrete.