海洋环境下有害离子在混凝土结构中的非线性扩散

发布时间：2018-01-25 21:39

本文关键词： 海洋环境混凝土孔隙演化非线性扩散模型导电性能　出处：《宁波大学》2017年博士论文　论文类型：学位论文

【摘要】：影响海洋环境下有害离子在混凝土结构中非线性扩散的因素主要有三个:第一个是未水化水泥颗粒后期继续水化,混凝土中没有水化的水泥颗粒后期继续与水发生水化反应生成新的产物填充了混凝土孔隙,阻碍了有害离子的扩散;第二个是有害离子与水泥水化产物发生化学反应,有害离子通过扩散由表及里地进入到混凝土结构中,并与混凝土孔隙溶液中的水泥水化产物发生化学反应生成了新的产物,抑制了有害离子的扩散;第三个是有害离子的侵蚀损伤,随着有害离子不断地扩散,新的产物不断地增加,就会对混凝土孔隙壁产生的膨胀力作用,造成微裂缝的产生,更有利于有害离子进一步扩散,最终导致结构服役寿命达不到设计寿命而断裂损坏。本文主要研究了以上这三个因素共同作用下有害离子在混凝土结构中非线性扩散模型的建立,具体内容如下:首先,研究了在清水浸泡中混凝土没有水化的水泥颗粒继续与孔隙中的水发生水化反应导致其密度、弹性模量、抗压抗拉强度以及孔结构的演化情况。先通过试验定期测量了混凝土试样后期继续水化的质量、波速、抗压抗拉强度以及孔隙度的值,然后根据继续水化化学反应方程式、化学反应速率方程以及质量守恒定律,得到了质量、弹性模量以及孔隙度演化的理论模型,最后把试验数据与理论模型进行对比,结果表明:理论模型与试验数据非常吻合,理论模型能很好地描述混凝土后期继续水化弹性模量与孔隙度演化特性。其次,研究了在不同浓度溶液浸泡中不同配合比混凝土的密度、弹性模量以及孔结构的演化情况。首先通过试验定期测量了混凝土试样浸泡在不同浓度溶液中的质量、波速以及孔隙度的值,然后根据化学反应方程式、化学反应速率方程以及质量守恒定律,建立了氯化钠溶液中混凝土试样质量演化的理论模型,最后对氯化钠溶液中混凝土孔隙度和弹性模量演变进行了理论分析。接着,将清水中混凝土继续水化孔隙度的理论模型和侵蚀引起的损伤引入到扩散方程有效扩散系数中,用有限差分法对扩散方程进行数值求解,把扩散方程数值解与试验数据进行对比,结论如下:数值结果与试验结果非常接近,海洋环境下有害离子扩散速度取决于侵蚀损伤的发展速度,而侵蚀损伤的发展速度与侵蚀过程中的化学反应速率有关。最后,研究了在清水和不同浓度溶液浸泡中导电混凝土的波速、抗拉强度和电阻率的演化情况。首先通过试验定期测量了清水中导电混凝土的质量、波速、抗拉强度和电阻的值,然后根据实验数据确定了导电相石墨的掺量。接着为了提高导电混凝土的力学性能,通过实验确定了硅粉的掺量。最后实验测量了氯盐和硫酸盐的侵蚀下,导电混凝土的导电性能,结果表明:导电混凝土的导电性能并没有因为有害离子的侵蚀而受到影响。
[Abstract]:There are three main factors that influence the nonlinear diffusion of harmful ions in concrete structure in marine environment: the first is the continuous hydration of unhydrated cement particles. The cement particles without hydration in concrete continue to hydrate with water to form new products which fill the pores of concrete and hinder the diffusion of harmful ions. The second is the chemical reaction between the harmful ions and the hydration products of the cement. The harmful ions enter the concrete structure from the surface to the inside through the diffusion. A new product was formed by chemical reaction with the hydration product of cement in concrete pore solution, which inhibited the diffusion of harmful ions. The third is the erosion damage of harmful ions. With the diffusion of harmful ions and the increasing of new products, the expansion force of the pore wall of concrete will be produced, resulting in the production of micro-cracks. More conducive to the further diffusion of harmful ions. Finally, the service life of the structure can not reach the design life and fracture damage. This paper mainly studies the establishment of nonlinear diffusion model of harmful ions in concrete structure under the action of these three factors. The specific contents are as follows: firstly, the density and elastic modulus of cement particles without hydration in water are studied. The compressive tensile strength and the evolution of the pore structure. Firstly, the mass, wave velocity, compressive tensile strength and porosity of the concrete specimen were measured periodically. Then, according to the chemical reaction equation of continuous hydration, the chemical reaction rate equation and the law of conservation of mass, the theoretical model of the evolution of mass, elastic modulus and porosity is obtained. Finally, the experimental data are compared with the theoretical model. The results show that the theoretical model and the experimental data are in good agreement. The theoretical model can well describe the evolution characteristics of the modulus of elasticity and porosity of concrete. Secondly, the density of concrete with different mix ratio in different concentration solution is studied. The elastic modulus and the evolution of the pore structure. Firstly, the mass, wave velocity and porosity of the concrete sample immersed in different concentration solution were measured periodically through the experiment, and then according to the chemical reaction equation. A theoretical model of mass evolution of concrete samples in sodium chloride solution was established by chemical reaction rate equation and mass conservation law. Finally, the evolution of porosity and elastic modulus of concrete in sodium chloride solution is analyzed theoretically. The theoretical model of the continuous hydration porosity of concrete in clear water and the damage caused by erosion are introduced into the effective diffusion coefficient of the diffusion equation, and the diffusion equation is solved numerically by the finite difference method. The numerical solution of the diffusion equation is compared with the experimental data. The conclusion is as follows: the numerical results are very close to the experimental results, and the diffusion rate of harmful ions in marine environment depends on the development rate of erosion damage. The development rate of corrosion damage is related to the chemical reaction rate in the process of erosion. Finally, the wave velocity of conductive concrete immersed in clear water and different concentration solution is studied. The evolution of tensile strength and resistivity. First, the mass, wave velocity, tensile strength and resistance of conductive concrete in clear water were measured periodically. Then the content of conductive phase graphite is determined according to the experimental data. Then in order to improve the mechanical properties of conductive concrete, the content of silica powder is determined by experiments. Finally, the erosion of chloride and sulfate is measured experimentally. The results show that the conductivity of conductive concrete is not affected by the erosion of harmful ions.
【学位授予单位】：宁波大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TU37

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