非饱和普通混凝土水渗透机理分析和水渗透系数预测

Experimental measurement, random walk modeling, and effective medium theory are incorporated to study the water permeability of nonsaturated ordinary concrete. With mercury intrusion porosimetry and scanning electron microscopy, the parameters of the pore structure of cement paste are measured and the microstructure of the interfacial transition zone in concrete is characterized. A testing method is developed for the water permeability coefficient of nonsaturated cement-based samples and the water permeability coefficients of cement paste and concrete with different degrees of saturation are measured. The random walk algorithm is applied to the simulated microstructures of the interfacial transition zone and cement paste to analyze the transport mechanism of water in the interfacial transition zone and cement paste and to obtain the quantitative relationship between their relative water permeability coefficient and the water/cement ratio and the degree of saturation. Concrete is modeled as a three-phase composite material, composed of aggregates, a cement paste matrix, and interfacial transion zones. The effective medium theory for two-phase materials is extended to present an analytical method for predicting the water permeability coefficient of concrete with different degrees of saturation. Through comparison with experimental results, the validity of the analytical method is verified. The relative contributions of various key factors to the water permeability of nonsaturated concrete are quantified, the mechanism of water permeability of nonsaturated concrete is revealed, and a quantitative relationship between the water permeability coefficient and mesotructure of nonsaturated concrete is established, which provides a decision-making basis for the durability design and assessment of reinforced concrete structures.

将试验测定、随机行走模拟和有效介质理论相结合，研究非饱和普通混凝土的水渗透性。通过压汞法和扫描电镜，测定水泥石孔结构参数，表征混凝土界面微观结构。提出非饱和水泥基试样水渗透系数的测试方法，测定不同饱和度水泥石和混凝土的水渗透系数。将随机行走算法应用于重构的界面和水泥石微观结构，分析不同饱和度下水在界面和水泥石中的传输机理，获得它们相对水渗透系数与水灰比和饱和度之间的定量关系。将混凝土模拟成由骨料、水泥石基体和界面所组成的三相复合材料，通过延伸两相材料的有效介质理论提出不同饱和度混凝土水渗透系数预测的解析方法。通过与试验结果比较，验证该解析方法的有效性。量化各关键因素对非饱和混凝土水渗透性的相对贡献，揭示非饱和混凝土的水渗透机理，建立非饱和混凝土水渗透系数与细观结构之间的定量关系，为混凝土结构耐久性设计和评估提供决策依据。

混凝土已广泛应用于土木、水利、港口和核电等国家重大基础设施中，一旦由于混凝土抗渗性不足，会大大降低这些混凝土结构的使用功能和寿命，甚至在某些情况下会导致渗漏和环境污染，对人民生命安全构成严重威胁，国民经济遭受重大损失。完成了非饱和水泥浆和混凝土等温脱附试验，结合数值方法获得了非饱和水泥浆和混凝土水渗透系数和水扩散系数。发现脱水速率随着水灰比和骨料体积率的增大而增大，对于给定的饱和度，混凝土脱水速率大于水泥浆脱水速率；当混凝土饱和度小于0.4时，相对水渗透系数接近于零，当混凝土饱和度大于0.4时，相对水渗透系数随着饱和度的增大而急剧增大；水扩散系数先随着饱和度的增大而增大，当混凝土饱和度接近0.9时，水扩散系数达到峰值，并在完全饱和时骤降至零；当粉煤灰掺量为10%-30%时，掺量越高，相对水渗透系数越小，对于给定的水胶比，粉煤灰混凝土相对渗透系数比粉煤灰水泥浆相对水渗透系数高1个数量级；水胶比越大，粉煤灰掺量越低，混凝土水扩散系数越大。结合水泥水化模拟和随机行走方法，提出了非饱和水泥浆水渗透系数预测的数值方法。数值结果表明，水灰比越大，非饱和水泥浆水渗透系数越大，且随水化时间的增加其降低幅度逐渐减小。应用有效介质方法导出了水泥浆水渗透系数的解析解，发现临界毛细孔隙率与水灰比无关，而临界毛细孔径是水灰比的线性函数。将界面简化为一个附加骨料层和一个Stokes液体层，提出了混凝土水渗透系数解析预测的三相复合球模型，数值结果显示，混凝土水渗透系数随着界面厚度的增大而增大，但随着骨料体积率的增大而减小，表明骨料的稀释效应大于界面效应。通过研究揭示了非饱和水泥基材料的水渗透机理，量化了各关键因素的相对贡献，为水泥基材料的耐久性设计和评估提供决策依据。