氯盐环境里水泥基材料孔溶液中氯离子浓缩的基础研究

Free chloride ions in the pore solution of cement-based materials are the main cause of the corrosion of steel reinforcing bars embedded in concrete. Pore solution expression is a commonly used method for determination of free chloride ion concentration in cement-based materials. Previous studies indicated that free chloride ion concentration in pore solution of cement-based materials was obviously higher than that of the chloride solution for immersion of the cement-based materials. This is called chloride ion condensation phenomenon. The proposed project intends to study the effects of various factors on the chloride ion condensation in the pore solution of cement-based materials and the changes in electrochemical properties and microstructure of cement-based materials before and after the immersion in different chloride solutions. Relationships between the chloride ion concentration in the pore solution and electrochemical properties or microstructure of cement-based materials will be established, and dynamic equations will be proposed so to clarify the mechanisms of chloride ion condensation. The results of this project will provide scientific base for measurement and explanation of chloride ion migration and binding in concrete, and for service life design and prediction of reinforced concrete structures in chloride environments.

水泥基材料孔溶液中的自由氯离子是引起钢筋混凝土中钢筋腐蚀的主要原因。常用孔溶液压滤法来测定水泥基材料中自由氯离子浓度。文献中报道压滤法得到的浸泡在氯盐溶液中水泥基材料孔溶液中自由氯离子浓度明显高于浸泡液氯离子浓度，这个现象被称为氯离子浓缩。本项目拟研究各种因素对水泥基材料孔溶液中氯离子浓缩及水泥基材料在氯盐溶液中浸泡前后电化学性能和微观结构的影响，得到不同因素对水泥基材料中氯离子浓缩的影响规律，建立孔溶液中氯离子浓缩与水泥基材料微观结构和电化学性能的关系，提出氯离子浓缩动力学过程，阐明氯离子浓缩机制。本项目的研究成果将为测试和解释混凝土中氯离子的迁移和结合及钢筋混凝土结构寿命设计和预测提供理论基础。

使用孔溶液压滤法获取水泥净浆试件的孔溶液并分析压滤液中的氯离子浓度，对试件的氯离子浓缩现象进行了系统研究,对影响水泥基材料氯离子浓聚的内部和外部因素，以及氯离子浓缩与材料微观结构和双电层特性的关系进行了讨论。得到了影响水泥基材料氯离子浓缩现象的两个主要因素，即孔结构和双电层特性。提出了基于压滤过程中微观结构的变化，以及水泥基材料内部双电层电容和Zeta电位的氯离子浓缩模型，通过相关的实验测试数据计算得到了水泥净浆试件的氯离子浓缩系数。使用实验方法将水泥基材料内部自由水与吸附水进行了定量分析，得到了不同条件下双电层内部吸附水含量的变化及其与氯离子浓缩现象之间的关系。得到了氯离子浓缩现象形成的内部机理，即氯离子在双电层范围内的聚集使固体表面处氯离子浓度相对于孔内本体溶液升高，孔溶液压滤过程中将双电层内的溶液与本体溶液一起压出试件，使得压滤溶液中的氯离子浓度相较于外部浸泡液的浓度要高.