碳化作用下双掺混凝土的氯离子扩散模型及数值研究

发布时间：2018-03-17 20:27

本文选题：氯离子侵蚀　切入点：碳化氯盐耦合　出处：《南京工业大学》2015年硕士论文　论文类型：学位论文

【摘要】：钢筋混凝土是地铁工程主要的结构材料,钢筋锈蚀是导致结构过早破坏、结构失效的最主要因素。为了更好地吻合地铁工程实际服役条件,非常有必要开展碳化-氯盐双重因素同步耦合研究,从而建立更加准确的地铁隧道混凝土服役性能演化的分析理论框架,为地铁结构服役性能评估和修复提供基础理论。本文总结分析国内外混凝土氯离子传输的理论模型,采用菲克第二定律作为描述氯离子数值模型的控制方程。并通过对混凝土碳化反应机理的分析,得出碳化反应对氯离子侵蚀过程的主要影响。主要研究内容如下：(1)通过对氯离子传输机理的研究,梳理了经典传输模型及其缺陷。同时,分析已有氯离子侵蚀模型的建立过程,提出了考虑氯离子结合能力、时间依赖性、湿度及温度等多种影响因素耦合作用下的氯离子传输理论模型,列出了不同影响因素对氯离子扩散系数的影响,并给出了表达式及建议取值,并考虑工程实际修正了相关参数。通过试验数据验证了模型的可靠性。(2)开展了碳化盐雾耦合试验。主要测试各侵蚀龄期混凝土中自由氯离子和总氯离子浓度分布规律,分析氯离子结合率的变化规律,试验结果表明,自由氯离子和总氯离子含量均随着侵蚀龄期的增加而增多,但是结合氯离子的比例发生明显变化。并测出了混凝土内液相pH值变化趋势,对耦合效应的机理进行了分析。(3)通过对碳化机理的研究,建立CO2时空分布模型,得出在标准碳化条件下的C02时空分布规律。通过碳化反应过程的分析,确定碳化过程对氯离子的两大作用：化学作用和物理作用。碳化反应使混凝土的pH值降低,而使化学结合生成Friedel盐的结合氯离子得到释放。因此,碳化反应提高了自由氯离子的含量。碳化反应过程中CO2会和C-S-H凝胶以及Ca(OH)2反应生成CaCO3,这会导致混凝土中孔隙率的降低,从而在物理的角度上阻碍了氯离子向混凝土内部的扩散。(4)采用有限差分法求解本文提出的扩散-反应方程,并利用matlab编写相关程序。对提出的碳化氯盐耦合模型进行算例分析,研究随着碳化反应进行,混凝土中氯离子浓度随时间和深度的变化规律。
[Abstract]:Reinforced concrete is the main structural material in subway engineering, and the corrosion of steel bar is the main factor leading to premature destruction and structural failure. It is very necessary to carry out the research of carbonation and chloride double factor synchronous coupling so as to establish a more accurate theoretical framework for the analysis of the evolution of concrete service performance in subway tunnels. This paper summarizes and analyzes the theoretical models of chloride ion transport in concrete at home and abroad. The second law of Fick is used as the governing equation to describe the numerical model of chloride ion, and the mechanism of carbonation reaction of concrete is analyzed. The main research contents are as follows: (1) through the study of the mechanism of chloride ion transport, the classical transport model and its defects are sorted out. At the same time, the establishment process of the existing chloride ion erosion model is analyzed. A theoretical model of chloride ion transport considering the coupling of chloride binding capacity, time dependence, humidity and temperature is put forward, and the influence of different factors on chloride diffusion coefficient is listed. The expressions and suggested values are given. The reliability of the model is verified by the experimental data. The carbonized salt spray coupling test is carried out. The distribution of free chloride ion and total chloride ion in concrete of different erosion ages is mainly tested. The change of chloride binding rate was analyzed. The results showed that both free chloride ion and total chlorine ion content increased with the increase of erosion age. But the ratio of chloride ion changed obviously, and the change trend of pH value in liquid phase of concrete was measured, and the mechanism of coupling effect was analyzed. Through the study of carbonation mechanism, the spatio-temporal distribution model of CO2 was established. Through the analysis of carbonation reaction process, two major effects of carbonation process on chloride ion are determined: chemical action and physical action. Carbonation reaction reduces the pH value of concrete. Therefore, the carbonation reaction increases the content of free chloride ions. During the carbonation reaction, CO2 reacts with C-S-H gel and Ca(OH)2 to form CaCO3, which leads to the decrease of porosity in concrete. Therefore, the diffusion of chloride ions into concrete is prevented from the physical point of view. The finite difference method is used to solve the diffusion-reaction equation proposed in this paper, and the relevant program is compiled by matlab. The variation of chloride ion concentration with time and depth in concrete was studied with carbonation reaction.
【学位授予单位】：南京工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU528

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