【作者】 蔡向荣；

【导师】 徐世烺；

【作者基本信息】 大连理工大学 ， 结构工程， 2010， 博士

【摘要】 超高韧性水泥基复合材料(Ultra high toughness cementitious composites, UHTCC)是一种采用中等纤维体积掺量的乱向短纤维增强的高性能水泥基复合材料。它在拉伸和弯曲荷载作用下具有应变硬化和多缝开裂特性,拉伸应变可以达到3%以上,最大裂缝宽度可以控制在0.1mm以下。将该材料应用于混凝土结构,有望解决现代混凝土结构所面临的安全性和耐久性等问题。本文通过试验研究和理论分析,研究UHTCC的性能：(1)通过单轴拉伸试验研究UHTCC的抗拉性能,试验结果显示UHTCC在拉伸荷载作用下具有假应变硬化和多缝开裂特性,以及高延性、高韧性和高裂缝宽度控制能力。极限拉伸应变在3%以上,极限荷载时的最大裂缝宽度在0.1mm以下。而且,UHTCC试件在具有双边切口的情况下,仍然具有应变硬化和多缝开裂特性。(2)通过四点弯曲试验研究UHTCC的抗弯性能,试验结果显示UHTCC在弯曲荷载作用下具有非常显著的变形硬化特性、多缝开裂特性和高韧性性能。极限挠度高达30mm以上,如此大的变形能力足可以与铝、钢等金属材料相媲美。(3)通过单轴抗压试验研究UHTCC的抗压性能,试验结果显示UHTCC在压缩荷载作用下仍具有多缝开裂。在试件破坏过程中,这些微裂缝逐渐贯通并形成剪切斜裂缝。UHTCC的抗压强度类似于普通混凝土,抗压弹性模量约是混凝土的1／2-1／3,峰值应变约是普通混凝土的两倍,峰值荷载后的延性和韧性明显增加。(4)通过对比拉、弯性能指标建立了UHTCC拉弯对应关系,对比结果显示四点弯曲试验可以代替单轴拉伸试验,成为评价UHTCC独特力学性能的简单实用的试验方法。(5)根据抗压试验结果,参考现有的各种混凝土本构模型,分别针对结构或构件的承载能力极限状态分析和非线性分析,建立适合于描述UHTCC抗压特性的本构模型,为超高韧性水泥基复合材料在工程中的广泛应用提供必要的理论基础。(6)对比各国关于钢纤维混凝土弯曲韧性的测定与评价标准,建立了UHTCC抗压韧性评价体系,该体系通过5个抗压韧度参数从不同的角度定量的分析了UHTCC的受压韧性性能。分析结果表明UHTCC具有较高的受压韧性和塑性变形性能以及开裂后的荷载承受能力。(7)针对UHTCC的多缝开裂行为和后多缝开裂行为,在微观力学、断裂力学和数理统计的基础上,分析了UHTCC的应变硬化过程,并建立了相应的理论模型。所建立模型既可以用于复合材料的优化设计,也可以用于复合材料宏观性能的预测。更多还原

【Abstract】 Ultra high toughness cementitious composites are a kind of high performance cementitious composites reinforced with medium fiber volume fraction random short fibers. This type of composites possesses strain hardening and multiple cracking under tensile and bending load with strain capacity more than 3% and maximum crack width below 0.1mm. Using this class of composites, it is potential to solve the structural problems inherent with today’s typical concrete structures, such as security and long term durability. In this paper, the performance of UHTCC is researched by experimental studies and theoretical analysis.(1) The uniaxial tensile tests were carried out to characterize the tensile behavior of UHTCC. Test results show that UHTCC possess pseudo strain hardening and multiple cracking behaviors, as well as high ductility, toughness and crack width controlling capacity. Its tensile strain capacity is more than 3% and its maximum crack width is below 0.1mm. Moreover, the UHTCC specimens with double notches still exhibit pseudo strain hardening and multiple cracking under tensile load.(2) Four-point bending tests were carried out to characterize the flexural behavior of UHTCC. Test results show that UHTCC possess obvious deformation hardening, multiple cracking and high toughness properties under bending load. The ultimate deflection is more than 30mm which is comparable with the deformation capacity of aluminum and steel.(3) The uniaxial compression tests were carried out to characterize the compressive behavior of UHTCC. Test results show that UHTCC still possess multiple cracking behaviors. Those cracks coalesce gradually and inclined micro-cracks appear during the process of failure. The compressive strength is similar to that of ordinary concrete, and the elastic modulus is about 1/2-1/3 of that concrete, and the compressive strain at peak stress is about twice that of concrete, and the ductility and toughness have been improved obviously.(4) The relationships between tensile and flexural properties are established by the comparison of basic mechanical indexes under tensile and bending load. The comparison results show that the four-point bending test method is a simple and practical method to estimate the special mechanical performance of UHTCC substituting for the uniaxial tensile test method.(5) Based on the compression test results and referring to the existing stress-strain models of concrete, two analysis models were proposed for ultimate limit state design and non-linear analysis of UHTCC structures respectively. The study production provides necessary theoretical models for the practical engineering application of UHTCC.(6) The system for evaluating the compressive toughness properties is established by comparing different testing and evaluating standards of flexural toughness for steel fiber reinforced concrete used in various countries. Five toughness indexes are used from different points of view to quantitatively evaluate the compressive toughness of UHTCC in detail. The analysis results of all the indexes demonstrate that UHTCC possess high compressive toughness and plastic deformation capacity, and high post-crack load bearing capacity.(7) The strain hardening processes referring to multiple cracking and post multiple cracking behaviors are theoretically analyzed based on the micromechanics, fracture mechanics and mathematical statistics and the corresponding models are established. These models can be used to optimize material properties or to predict the macromechanical composite properties.更多还原