混凝土微观力学性能表征及冻融循环影响

发布时间：2018-06-11 11:25

本文选题：纳米压痕 + 扫描电镜　；参考：《上海交通大学》2015年硕士论文

【摘要】：由于全球气候恶化,各种工程结构在极端天气下的耐久性逐渐成为关注的焦点,其中大部分大型工程结构是由混凝土构成的,因此研究混凝土的耐久性,特别是冻融循环下的耐久性就具有重要的现实意义。混凝土作为一种多相复合材料,其微观力学性能决定了宏观的耐久性。本文从实验力学的角度对混凝土的微观力学性能进行研究,具有重要的现实和科学指导意义。首先,本文利用先进的表征手段——纳米压痕表征了混凝土材料各组分的微观力学性能,主要包括压痕模量、硬度和蠕变率三个物理参量。由于混凝土的复杂性,研究采用了统计学的方法来分析、处理试验数据。研究结果发现,混凝土浆体和骨料在压痕模量和硬度方面差别很大,这种差别为定量确定界面过渡区提供了依据。压痕模量和硬度的相关系数为0.75,并且都不满足正态分布,因此,在研究冻融循环影响时,需要采用非参数统计方法,并且着重研究一个物理参量随冻融变化情况就可以了。接触蠕变的研究揭示了混凝土的蠕变行为主要来自于浆体。混凝土基本微观力学性能的研究为研究冻融循环奠定了基础。用扫描电镜和纳米压痕对不同冻融循环的混凝土样品进行研究时,采用了概率核密度估计的方法。结果显示,混凝土受冻融循环影响下的力学行为也具有多尺度性。500nm尺度下,浆体继续水化导致高密度水凝胶进一步形成;10um尺度下,微裂纹进一步扩展导致宏观断裂能量降低。从混凝土的多尺度力学行为研究可以得出如下结论,多尺度材料的力学行为具有多尺度性,需要从不同的尺度来进行研究。本研究利用纳米压痕深入探究了混凝土的微观性能以及冻融循环导致的材料性能的变化。
[Abstract]:Due to the deterioration of global climate, the durability of various engineering structures in extreme weather has gradually become the focus of attention, most of which are composed of concrete, so the durability of concrete is studied. Especially the durability of freeze-thaw cycle has important practical significance. As a kind of multiphase composite material, the microscopic mechanical properties of concrete determine the macroscopic durability. In this paper, the microscopic mechanical properties of concrete are studied from the point of view of experimental mechanics, which has important practical and scientific guiding significance. Firstly, the micromechanical properties of each component of concrete are characterized by nano-indentation, which includes three physical parameters: indentation modulus, hardness and creep rate. Because of the complexity of concrete, the statistical method is used to analyze and process the test data. The results show that there are great differences in indentation modulus and hardness between concrete paste and aggregate, which provides a basis for quantitative determination of interfacial transition zone. The correlation coefficient of indentation modulus and hardness is 0.75, and neither of them satisfies the normal distribution. Therefore, in studying the effect of freeze-thaw cycle, it is necessary to adopt a non-parametric statistical method, and focus on the study of a physical parameter changing with freezing and thawing. The study of contact creep reveals that the creep behavior of concrete mainly comes from slurry. The study of the basic micromechanical properties of concrete lays a foundation for the study of freeze-thaw cycle. The probabilistic kernel density estimation method is used in the study of concrete samples with different freeze-thaw cycles by SEM and nano-indentation. The results show that the mechanical behavior of concrete under the influence of freeze-thaw cycle also has the multi-scale of .500nm, and the further hydration of the slurry leads to the formation of high density hydrogel at the scale of 10um, and the further propagation of microcracks leads to the decrease of macroscopic fracture energy. The following conclusions can be drawn from the study of multi-scale mechanical behavior of concrete: the mechanical behavior of multi-scale materials is multi-scale, which needs to be studied from different scales. In this study, nano-indentation was used to investigate the microcosmic properties of concrete and the changes of material properties caused by freeze-thaw cycles.
【学位授予单位】：上海交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU528

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