带裂缝混凝土的非饱和传输特性试验与理论研究

Transport behavior of water/ ions is crucial to concrete durability, while that in cracked concrete with an unsaturated state is the main cause of concrete degradation in alternate wetting and drying zone. In this study, experimental and modelling methods are employed to investigate the transport properties in unsaturated or/and cracked concrete. Firstly, to characterize transport behavior in drying process of concrete, the isothermal desorption-adsorption process and law of vapor water in concrete with different degrees of saturation is investigated. Based on the balance theory of water vapor pressure, the quantitative relationship between transport coefficient and degree of saturation is established by means of proposing an equation of calculating the front profile of water in concrete. Subsequently, in order to understand transport behavior in wetting process, the temporal-spatial distribution model of water content and ion concentration is established by using imaging techniques, e.g., X-CT, NMR,water absorption and ion titration methods. The water transport height and ingress concentration of ions are in-situ and continuously tracked and observed. Afterwards, the effects of width, orientation and spatial distribution of cracks in concrete on water/ion transport behavior are explored by using centrifugation of heat-sensitive alloys and X-ray microscopy methods. The specific influence factors including capillary absorption of cracks, friction resistance from surface roughness of cracks and gravity are quantitatively analyzed. Finally, combined with the previous experimental findings, a finite element-based numerical model is employed to simulate the transport behaviour in unsaturated and cracked concrete. The above experimental and modelling research is expected to be significant for completing transport theory of concrete, providing prediction of service life and enhancing durability of concrete.

带裂缝混凝土的非饱和传输是干湿交替区混凝土耐久性破坏的主因。项目采用理论、试验与数值模拟相结合，首先研究气态水在不同饱和度混凝土中等温脱附-吸附过程和规律，基于蒸汽压平衡理论建立水蒸气传输系数与饱和度的定量关系，提出干燥锋线计算公式，实现干燥过程的定量表征。其次采用X-CT、核磁共振、吸水质量和离子滴定等方法，对液态水和离子在非饱和混凝土中传输深度和浓度进行观察和测试，建立水/离子时空分布模型，实现润湿过程的定量表征。接着采用温变合金离心法、X射线显微镜等方法，研究裂缝宽度、取向和空间分布对混凝土中水/离子传输的影响规律，分析介质在裂缝中毛细抽吸与扩散、裂缝壁摩擦阻滞和重力的影响作用。在此基础上，基于多孔介质理论，构建综合考虑裂缝和饱和度的混凝土传输模型，结合有限元模拟带裂缝混凝土非饱和传输过程和特性。研究对于完善混凝土传输理论具有重要意义，同时也为寿命预测、耐久提升提供科学支撑。

带裂缝混凝土的非饱和传输是干湿交替区混凝土耐久性破坏的主因。项目采用理论、试验 与数值模拟相结合，在以下四个方面取得重要进展和突破：.（1）以不同种类饱和盐溶液创造特定湿度环境，通过吸脱附试验获得了气态水在不同饱和度混凝土中等温脱附-吸附过程和规律，定量分析了水灰比、矿物掺合料种类与掺量对混凝土吸附-脱附性能的影响；建立了混凝土对水蒸气的吸附-脱附压力与饱和度的定量关系，提出混凝土的水分特征方程。基于蒸汽压平衡理论建立水蒸气传输系数与饱和度的定量关系，提出干燥锋线计算公式，实现混凝土干燥过程的定量表征。.（2）开发了X-CT联合Cs离子增强原位、连续监测净浆、砂浆、混凝土毛细吸水的无损测试方法，利用该方法系统研究了水灰比、矿物掺合料、砂体积掺量等因素对混凝土在非饱和状态下液体水传输的影响规律；基于重量法表征了非饱和混凝土的毛细质量吸水能力，建立了混凝土吸水系数S与饱和度θ之间的定量关系：S=a(1-θ)b；基于多孔介质水分传输理论与毛细吸水试验，构建了非饱和混凝土毛细吸水过程中水分时空分布计算模型，实现润湿过程的定量表征。.（3）采用浸泡法揭示了不同饱和度（0、0.2、0.4、0.6、0.8）混凝土分别在氯离子浸泡作用下离子随时间的传输过程和特性；阐明了水灰比、粉煤灰掺量、矿渣掺量以及混凝土饱和度对非饱和传输特征曲线中关键参数-离子结合能力、表观扩散系数、表面离子浓度的影响规律；构建了表观扩散系数D与混凝土材料参数和饱和度的定量关系。.（4）采用温变合金离心法、X射线显微镜等方法，研究毛细孔/裂缝大小、取向和空间分布对混凝土中水/离子传输的影响规律，分析介质在裂缝中毛细抽吸与扩散、裂缝壁摩擦阻滞和重力的影响作用。在此基础上，基于多孔介质理论，构建综合考虑裂缝和饱和度的混凝土传输模型，结合有限元模拟带裂缝混凝土非饱和传输过程和特性。. 研究对于完善混凝土传输理论 具有重要意义，同时也为寿命预测、耐久提升提供科学支撑。