带裂缝混凝土硫酸根离子扩散—反应机理和试验研究

发布时间：2018-08-26 09:03

【摘要】：混凝土硫酸盐侵蚀问题是一个涉及离子化学反应,物质变化以及材料力学损伤的多物理场耦合问题,一直是混凝土耐久性的重要研究内容。地铁、隧道等地下混凝土结构在正常使用时往往存在大量的裂缝,这些裂缝将大大加速硫酸根离子的扩散,从而加速材料的劣化。因此,本文以地铁、隧道常见的带裂缝双掺混凝土为对象,建立合理的数学模型研究其性能的演化规律,进行材料的服役寿命预测,对耐久性设计具有十分重要的意义。本文通过文献研究,总结离子在裂缝内的扩散规律,并提出离子在裂缝中扩散系数的通用表达式。建立氯离子在裂缝混凝土内的简化二维扩散模型,并使用COMSOL MULTIPHYSICS商业有限元软件进行求解,并验证扩散系数通用表达式的正确性。结果表明,裂缝宽度越宽,离子浓度越大；裂缝深度越深,离子浓度越小。依据硫酸盐化力耦合机理,建立了硫酸盐影响下氯离子在裂缝混凝土中的扩散模型,并利用MATLAB进行编程求解,验证了硫酸盐化力耦合机理的正确性。依据混凝土侵蚀的化力耦合模型,建立硫酸盐混凝土二维扩散方程并使用有限差分法求解,最后进行硫酸盐侵蚀试验进行了对比验证。求解可知,离子浓度从外到内呈梯度变化,边缘最高,中心最低,离子浓度在侵蚀一定时间后保持动态平衡。
[Abstract]:Sulfate erosion of concrete is a multi-physical coupling problem involving ion chemical reaction, material change and mechanical damage of materials. It has been an important research content of concrete durability. Underground concrete structures such as subways and tunnels often have a large number of cracks in normal use. These cracks will greatly accelerate the diffusion of sulfate ions and thus accelerate the deterioration of materials. Therefore, this paper takes the common concrete with cracks in subway and tunnel as the object, establishes the reasonable mathematical model to study the evolution law of its performance and predicts the service life of the material, which is of great significance to the durability design. In this paper, the diffusion law of ions in cracks is summarized, and the general expression of diffusion coefficient of ions in cracks is put forward. A simplified two-dimensional diffusion model of chloride ions in cracked concrete is established and solved by COMSOL MULTIPHYSICS commercial finite element software. The correctness of the general expression of diffusion coefficient is verified. The results show that the wider the crack width, the greater the ion concentration, and the deeper the crack depth, the smaller the ion concentration. According to the coupling mechanism of sulphate force, the diffusion model of chloride ion in cracked concrete under the influence of sulfate is established, and the correctness of the coupling mechanism is verified by programming with MATLAB. According to the coupling model of chemical force of concrete erosion, the two-dimensional diffusion equation of sulphate concrete is established and solved by finite difference method. Finally, the sulphate erosion test is compared and verified. The solution shows that the ion concentration varies from outside to inside with the highest edge and the lowest center. The ion concentration keeps dynamic equilibrium after erosion for a certain time.
【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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