干湿循环和硫酸盐侵蚀下混凝土水分传输规律研究

发布时间：2018-08-18 09:14

【摘要】：处于海洋、酸雨等环境下的混凝土结构,遭受干湿循环、硫酸盐腐蚀等各种环境因素的侵蚀作用,混凝土的耐久性降低、服役寿命缩短。硫酸盐侵蚀是引起混凝土耐久性退化的主要因素,而干湿循环加剧混凝土硫酸盐腐蚀进程,研究硫酸盐侵蚀和干湿循环耦合作用下混凝土的耐久性问题对开展混凝土结构的长寿命设计、提高工程结构的服役安全性具有重要意义。本文针对这一问题,通过数值建模、实验测试,研究干湿循环条件下的水分传输、硫酸盐侵蚀下的离子传输与溶液结晶随侵蚀时间的变化规律。主要内容及结论如下： (1)根据混凝土中水分传输机制,运用Fick定律与Darcy定律,建立了干湿循环条件下考虑水蒸气扩散和液态水渗透机制的混凝土水分传输方程,该方程是一个非线性的偏微分方程,利用单点子域精细积分法获得了该方程在一维情况下的半解析解,并应用Matlab语言编制了相应的分析程序。 (2)设计并制作了不同水灰比的水泥砂浆试件,并按水分一维传输情况制作了厚度不同的多组切片,以开展水分在混凝土中的湿润、干燥和干湿循环等一维传输实验,以验证所建立的水分传输模型的合理性。结果表明,水分传输模型的计算值与实验测试值结果较为一致,说明本文所建立的模型可用于分析混凝土中的水分传输规律。 (3)建立了混凝土中水分传输的二维分析方程,利用单点子域精细积分法获得了该方程的半解析解,分析了混凝土棱柱体在湿润、干燥和干湿循环等各种工况下的水分传输规律。结果表明,混凝土中水分传输速率沿试件表面向内呈递减关系,且在柱截面对角线上的水分传输率较大。 (4)根据混凝土中硫酸盐溶液的对流传输过程,建立了干湿循环条件下硫酸根离子在混凝土中的传输模型,模拟了混凝土中水分蒸发后硫酸根离子浓度和硫酸盐结晶量随循环次数的变化规律。结果表明,混凝土试件表层受干湿条件影响最大,其硫酸根离子浓度随循环次数的增加而累积；干燥与湿润时间对混凝土内硫酸根离子分布的影响很大；混凝土中硫酸盐的结晶量随干湿循环次数的增加而逐渐增加。
[Abstract]:Under the environment of ocean and acid rain, the concrete structure is corroded by various environmental factors, such as dry and wet cycle, sulphate corrosion, etc., the durability of concrete is reduced and the service life is shortened. Sulfate erosion is the main factor that causes the degradation of concrete durability, while the drying and wet cycle exacerbates the process of sulphate corrosion of concrete. It is of great significance to study the durability of concrete under the coupling of sulfate erosion and dry-wet cycle to develop the long-life design of concrete structure and improve the service safety of engineering structure. In order to solve this problem, through numerical modeling and experimental test, the changes of water transport under dry and wet cycle, ion transport and solution crystallization under sulfate erosion with erosion time were studied. The main contents and conclusions are as follows: (1) according to the mechanism of water transport in concrete, using Fick's law and Darcy's law, the water transport equation of concrete considering the mechanism of water vapor diffusion and liquid water permeation is established under the condition of dry and wet circulation. The equation is a nonlinear partial differential equation. The semi-analytical solution of the equation in one-dimensional case is obtained by using the single-point domain precise integration method. The corresponding analysis program is compiled by using Matlab language. (2) cement mortar specimens with different water-cement ratio are designed and made, and multi-group slices with different thickness are made according to the one-dimensional water transport. In order to verify the rationality of the proposed water transport model, one-dimensional experiments such as wetting, drying and dry-wet circulation of moisture in concrete were carried out. The results show that the calculated values of water transport model are in good agreement with the experimental results. This model can be used to analyze the law of water transfer in concrete. (3) A two-dimensional analytical equation of water transport in concrete is established, and the semi-analytical solution of the equation is obtained by using the precise integration method of single point domain. The moisture transfer law of concrete prism under various conditions, such as wetting, drying and drying cycle, is analyzed. The results show that the water transfer rate in concrete is decreasing along the surface of the specimen, and the water transfer rate on the diagonal line of column section is larger. (4) according to the convection transport process of sulfate solution in concrete, The transport model of sulfate ion in concrete under dry and wet cycling conditions was established. The variation of sulfate ion concentration and sulfate crystallization with cycle times after water evaporation in concrete was simulated. The results show that the surface layer of concrete is most affected by dry and wet conditions, and the concentration of sulfate ion accumulates with the increase of cycle times, and the time of drying and wetting has a great effect on the distribution of sulfate ions in concrete. The crystallization of sulfate in concrete increases with the increase of dry and wet cycles.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2013
【分类号】：TU528

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