混凝土中氯离子双时变扩散过程解析与混凝土结构耐久性定量设计

发布时间：2018-03-29 22:37

本文选题：混凝土结构　切入点：氯离子　出处：《广西大学》2017年硕士论文

【摘要】：在氯化物环境中,氯离子通过扩散作用侵入混凝土内部造成的钢筋锈蚀和混凝土保护层开裂剥落等耐久性退化现象,是导致钢筋混凝土结构难以满足预定设计使用年限的重要原因之一。因此,准确分析混凝土中氯离子的扩散过程,并建立相应的解析模型,是氯化物环境下混凝土结构耐久性分析与设计的重要前提。分析表明,氯离子扩散系数和混凝土表面氯离子浓度的时变性对氯离子的扩散过程具有重要影响。同时,混凝土结构的几何外形也会影响混凝土中氯离子的扩散过程和积聚规律。然而,现有的氯离子扩散解析模型无法综合考虑氯离子扩散系数和混凝土表面氯离子浓度的时变性以及混凝土结构几何外形等因素的影响,导致难以合理描述混凝土中氯离子的扩散过程,计算精度和适用性有限。鉴于此,本文综合考虑氯离子扩散系数和混凝土表面氯离子浓度的时变性及混凝土结构几何外形对氯离子扩散过程的影响,分别建立了矩形和圆形截面混凝土中氯离子双时变扩散的解析模型,在此基础上提出了混凝土结构的耐久性定量设计方法。主要研究内容包括:(1)综合考虑氯离子扩散系数和混凝土表面氯离子浓度的时变性,基于三维正交直角坐标系下的Fick第二定律扩散方程,结合变量代换法和杜哈梅尔定理,建立了矩形截面混凝土中氯离子双时变扩散的解析模型,从而克服了现有解析模型无法综合考虑氯离子扩散系数和混凝土表面氯离子浓度的时变性以及氯离子扩散维数等因素影响所存在的缺陷。通过与数值分析结果和现场实测数据的对比分析,验证了该解析模型的有效性和适用性。分析结果表明:氯离子扩散系数和混凝土表面氯离子浓度的时变性对混凝土中氯离子浓度的分布规律具有显著影响;所建立的双时变解析模型不限定混凝土表面氯离子浓度的时变函数形式,具有适用性强、计算精度高等优点。(2)基于三维柱坐标系下的Fick第二定律扩散模型,综合考虑氯离子扩散系数和混凝土表面氯离子浓度的时变性,结合变量代换、杜哈梅尔定理和变量分离法,建立了圆形截面混凝土中氯离子的二维和三维双时变扩散解析模型,并通过与数值分析结果进行对比,验证了该解析模型的有效性。分析结果表明,该解析模型不限定混凝土表面氯离子浓度的时变函数形式,计算精度较高,适用性较强,为圆形截面混凝土中氯离子的二维和三维扩散过程分析提供了有效途径。(3)基于所建立的混凝土中氯离子双时变扩散的解析模型,结合氯离子扩散场补偿长度理论和混凝土结构的耐久性控制区模型,确定了混凝土结构耐久性设计参数与设计使用年限、钢筋脱钝的临界氯离子浓度、混凝土表面氯离子浓度、混凝土保护层厚度等参数之间的量化关系,提出了海洋氯化物环境下混凝土结构的耐久性定量设计方法。通过与传统的耐久性设计方法对比,验证了该方法的有效性和适用性,从而解决了传统耐久性设计方法缺乏定量的耐久性设计模型,无法定量计算确定耐久性设计参数所存在的缺陷。
[Abstract]:In chloride environment, chloride ion diffusion through the invading of concrete caused by reinforcement corrosion and concrete protective layer cracking and durability degradation phenomenon, is the result of reinforced concrete structure is one of the important reasons is difficult to meet the predetermined design life. Therefore, accurate analysis of the chloride ion diffusion in concrete, and to establish the corresponding analytical model that is an important prerequisite for the design and analysis of durability of concrete structures in chloride environment. Analysis shows that the diffusion process plays an important role in degeneration of chloride ion diffusion coefficient and the concrete surface chloride ion concentration of chloride ion. At the same time, the geometry of the concrete structure will affect the diffusion process and the accumulation of chloride ions in concrete yet. Not, considering the chloride diffusion coefficient and the surface chloride ion concentration of concrete chloride ion diffusion model of the existing time Effect of modified concrete structure and geometry and other factors, make it difficult to describe the diffusion process of chloride ion in concrete, the calculation accuracy and applicability is limited. In view of this, considering the effect of chloride ion diffusion coefficient and the concrete surface chloride ion concentration and time dependence of geometric shape on concrete chloride ion diffusion process, analysis model of concrete rectangular and circular cross section of chlorine ion in dual time-varying diffusion are established, based on the proposed quantitative durability design method of concrete structure. The main research contents include: (1) considering the chloride ion diffusion coefficient and the concrete surface chloride concentration change with time and the Fick's second law of 3D orthogonal cartesian coordinates. The diffusion equation based on the combination of variable substitution and the Duhamel theorem, the rectangular section of chloride ions in concrete double variable diffusion solution to establish In order to overcome the existing analysis model, analytical model not considering the defects of degeneration and chloride ion diffusion dimension of chloride ion diffusion coefficient and the surface chloride concentration of concrete. By analyzing and comparing the results with measured data and numerical analysis, verify the validity and applicability of the model analysis. The results showed that there are significant effect on the distribution of time variation and chloride diffusion coefficient of concrete surface chloride ion concentration of chloride ion concentration in concrete; the double variable analytical model is not limited to the concrete surface chloride concentration of the time-varying function form, has strong applicability and accuracy. (2) diffusion model based on Fick's second dimensional cylindrical coordinates, considering the chloride ion diffusion coefficient and the concrete surface chloride concentration change with time and with variable substitution, Duhamel theorem and variable separation method, a two-dimensional chloride ion in concrete circular section and three-dimensional double time-varying diffusion analytical model is established, and the results were compared with numerical analysis, to verify the validity of the analytical model. The analysis results show that the analytical model does not limit the concrete surface chloride ion concentration variation function, high accuracy, strong applicability, provides an effective way for the two dimensional analysis of chloride ion in concrete circular section and three-dimensional diffusion process. (3) developed analytical model of chloride ions in concrete double diffusion based on the combination of chloride ion diffusion field length compensation theory and the durability of concrete structure control model sure, the concrete structure durability design parameters and design life, critical chloride concentration of rebar depassivation, surface chloride ion concentration of concrete, thickness of concrete protective layer The quantitative relationship between the parameters of the proposed marine chloride environment the durability of concrete structure in quantitative design method. By comparing with the traditional method of durability design, verify the validity and applicability of the method, so as to solve the traditional method for durability design lack of durability design model of quantitative and quantitative calculation to determine the defects the durability design parameters exist.

【学位授予单位】：广西大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU528

【参考文献】