水泥基孔隙材料多场多离子迁移过程研究

发布时间：2018-03-13 23:08

本文选题：水泥基孔隙材料　切入点：多场多离子传输　出处：《清华大学》2015年博士论文　论文类型：学位论文

【摘要】：水泥基材料在服役条件下受多种环境作用,孔隙与环境间的物质迁移决定材料长期性能的演变规律。全面描述水泥基材料中多种离子在多场条件下的迁移过程对准确预测材料与结构的耐久性和使用寿命有重大意义。本文研究目的是建立多场多离子迁移理论模型,准确预测水泥基材料与结构的长期耐久性。本文首先研究了多场多离子迁移过程理论,讨论了发生在水泥基孔隙材料中的多场环境、固液平衡和气液平衡等基本条件。水泥基材料中的多场环境涉及浓度场、电场、温度场和湿度场。本文考虑了外加电场和多离子迁移过程产生的局部电场;考虑了固相溶解平衡和离子吸附平衡,采用固溶体理论描述了CH和C-S-H的溶解平衡;利用化学势和力学平衡关系建立了水蒸气与孔隙水、孔隙气相与液相的平衡条件。本文然后在多场多离子迁移理论基础上,建立了全面考虑热量、湿度、多离子耦合传输的多场多离子(THI)数值模型,并考虑了放射性核素离子的迁移过程及其衰变过程。本文通过水蒸气等温吸附实验、放射性核素吸附实验以及核素溶液浸泡试验,研究了水泥基材料的吸附性质。采用文献数据分别从溶蚀、氯离子迁移以及核素迁移过程验证了THI模型的适用性。基于模型研究了胶凝体系和环境条件对水泥基材料孔隙中的物质传输过程的影响规律。研究表明:(1)普通硅酸盐水泥复合矿物掺合料后抗溶蚀性能下降,但离子扩散系数减小,对放射性核素的阻滞作用增大;(2)环境pH值的升高会有效抑制溶蚀作用和降低核素逸出量;(3)环境溶液的盐浓度会影响材料内部局部电场分布以及核素迁移过程。本文最后使用THI模型分别完成了对海底沉管隧道120年寿命期内的耐久性评估和混凝土高整体容器(HIC)300年寿命期间的安全性评估。沉管隧道耐久性评估表明:溶蚀过程对材料耐久性影响不大,温度对离子迁移过程的影响远大于海水压力的影响,120年期间沉管隧道中钢筋不会发生锈蚀。HIC安全性评估表明:溶蚀过程会明显增大放射性核素的累积逸出量,辐解升温和压力积聚都会增大放射性核素逸出量,但温度影响明显大于压力影响,容器壁厚增大对核素的阻抑效果明显。
[Abstract]:Cement based materials are subjected to a variety of environmental effects under service conditions, Material migration between pores and environment determines the evolution of long-term properties of materials. A comprehensive description of the migration process of multiple ions in cement-based materials under multi-field conditions can accurately predict the durability and service life of materials and structures. The purpose of this paper is to establish a multi-field and multi-ion transport model. The long-term durability of cement-based materials and structures is accurately predicted. In this paper, the theory of multi-field multi-ion migration is studied, and the multi-field environment occurring in cement-based porous materials is discussed. The basic conditions of solid-liquid equilibrium and gas-liquid equilibrium are as follows: the multi-field environment in cement-based materials involves concentration field, electric field, temperature field and humidity field. In this paper, the local electric field produced by the external electric field and the multi-ion migration process is considered. The solid solution equilibrium and ion adsorption equilibrium were considered, the dissolution equilibrium of Ch and C-S-H was described by solid solution theory, and the relationship between water vapor and pore water was established by chemical potential and mechanical equilibrium. The equilibrium condition of pore vapor phase and liquid phase. Based on the theory of multi-field and multi-ion migration, a numerical model of multi-field and multi-ion THIs with heat, humidity and multi-ion coupling transport is established in this paper. The migration process and decay process of radionuclide ions are also considered. In this paper, the isothermal adsorption of water vapor, the adsorption of radionuclides and the immersion of radionuclides in solution are studied. The adsorption properties of cement-based materials were studied. The applicability of THI model was verified by chloride ion migration and nuclide migration process. Based on the model, the effects of gelation system and environmental conditions on the mass transport process in the pores of cement-based materials were studied. The corrosion resistance of acid-salt cement compound mineral admixture was decreased, But the ion diffusion coefficient decreased, The inhibition effect on radionuclides is increased. The increase of environmental pH value can effectively inhibit the dissolution and decrease the amount of radionuclide escape. The salt concentration in the solution will affect the local electric field distribution and the radionuclide migration process. In the end, THI model is used to evaluate the durability of submerged tunnel during 120 years of life and the safety of concrete high integrated container during 300 years. The evaluation of durability of immersed tunnel shows that the corrosion process is the process of corrosion. It has little effect on the durability of materials. The effect of temperature on the ion transport process is much greater than that on seawater pressure. During 120 years, the corrosion of steel bars will not occur in the tunnel. HIC safety evaluation shows that the cumulative emission of radionuclides can be significantly increased by the dissolution process. Both radiolysis and pressure accumulation can increase radionuclide emission, but the effect of temperature is greater than that of pressure, and the inhibition effect of vessel wall thickness on radionuclide is obvious.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TU528

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