带裂缝水泥基材料氯离子传输特性研究

论文总字数：34839字

摘 要

氯离子诱导的钢筋腐蚀是混凝土结构过早损坏的主要原因，氯离子在材料内部的传输是复杂的物理化学过程，不仅与服役环境密切相关，更取决于材料内部的微结构。水泥基材料本身是带有微观裂缝的多孔材料，而在服役的过程中受到荷载、干缩、冻融等单一因素或多因素的耦合作用，导致材料内部微裂缝进一步扩展为宏观裂缝，此时外界有害离子更易侵入材料内部，且传输过程将变得更加复杂。因此，研究带裂缝的水泥基材料氯离子传输具有重大的理论意义和应用价值，不仅能为材料的寿命预测与评估提供依据，而且为水泥基材料的耐久性设计提供理论支撑。本文通过诱导裂缝、自然浸泡的方法，对带裂缝砂浆试件进行氯离子传输试验，绘制氯离子质量百分数分布图。采用数值模拟的方法，建立适当的模型模拟氯离子在带裂缝水泥基材料中的传输性能。结合试验数据与数值软件的模拟结果，得到以下结论：随着裂缝宽度变大，饱和砂浆氯离子质量百分数增大，裂缝宽度下限值应小于50µm；上限值应大于100µm小于200µm，约为120µm。非饱和砂浆由于毛细作用力影响，氯离子质量百分数先增大后减小。裂缝宽度在100µm~200µm之间时，氯离子传输速率达到最大。

关键词：氯离子；带裂缝水泥基材料；传输机制；扩散系数；数值模拟

Transport Mechanism of Chloride Ingress into Cracked Cementitious Materials

Abstract

Chloride which leads to corrosion of rebar is the main reason to deterioration of concrete structure. Chloride transport in cementitious materials is a complex physical-chemical process, which not only is associated closely with service environment, but also depends on internal microstructure of cementitious materials. Cementitious materials that have lots of microcosmic cracks are cellular materials. Load, shrinkage, freeze thawing and other harmful factors happen to cementitious materials in the service process. Microcosmic internal cracks change into macroscopic cracks. In this situation, chloride ingress into cracked cementitious materials becomes easier, and in the same time, chloride transport becomes more complex. Therefore, studying transport mechanism of chloride ingress into cracked cementitious materials has theoretical significance and application value. This study can not only provide evidence for life forecast and evaluation of materials, but also provide theoretical foundation for durability design of cementitious materials. In this thesis, induced crack and natural immersion are implemented on mortar in order to test chloride transport mechanism of cracked cementitious material. Draw chloride content graph of cracked mortar after being immersed in sodium chloride solution for several months. With building appropriate model, simulate chloride ingress into cracked cementitious materials by means of numerical method. Analyzing the data of test and simulation, these conclusions can be obtained: When crack width gets larger, chloride mass content of saturated mortar increases. Lower limit value of crack width is less than 50µm; Upper limit value of crack width is greater than 100µm and less than 200µm, which is about 120µm. As a consequence of capillary action in dry mortar, chloride mass content increases at first and then decreases when crack width gets larger. On the condition that crack width is a certain value between 100 and 200µm, chloride transport speed reaches maximum.

KEY WORDS: chloride, cracked cementitious materials, transport mechanism, diffusion coefficient, numerical simulation.

目 录

摘要I

Abstract II

第一章 绪论1

1.1 研究背景及意义2

1.2 国内外研究现状2

1.2.1 不同裂缝特征影响研究3

1.2.2 数值模拟方法研究3

1.3 研究现状分析2

1.4 本文主要研究内容2

第二章 带裂缝水泥基材料氯离子传输机理1

2.1 完整水泥基材料氯离子传输机理2

2.1.1 饱和状态3

2.1.2 非饱和状态3

2.2 带裂缝水泥基材料传输特性2

2.2.1 传输机理3

2.2.2 裂缝宽度3

2.3 本章小结2

第三章 带裂缝水泥基材料氯离子传输试验研究1

3.1 引言2

3.2 试验2

3.2.1 试验原材料及基本性能3

3.2.2 制备试件3

3.2.2.1 完整试件3

3.2.2.2 带裂缝试件3

3.2.3 试验方法3

3.2.3.1 试样的处理与浸泡3

3.2.3.2 钻孔取粉3

3.2.3.3 氯离子含量测定3

3.3 结果与分析2

3.3.1 完整试件3

3.3.2 带裂缝试件3

3.4 本章小结2

第四章 带裂缝水泥基材料氯离子传输性能数值模拟1

4.1 引言2

4.2 基于COMSOL-Multiphysics数值模拟过程2

4.3 饱和水泥基材料氯离子传输数值模拟2

4.3.1 完整水泥基材料3

4.3.2 带裂缝水泥基材料3

4.4 裂缝宽度阈值2

4.5 本章小结2

第五章 结论与展望1

5.1 结论2

5.2 研究展望2

参考文献1

致谢1

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