非饱和损伤水泥基材料的物质传输性质研究

Mass transport process in cement-based materials is the basis of durability issue. Meanwhile, transport properties also reflect materials' capacity of resisting external media intrusion. The durability of cement-based material is mostly determined by its transport properties of deleterious agents. In real services concrete structure are always under humid environment, and cracks unavoidably exist due to the combination of mechanical load and environmental actions. So transport properties of unsaturated damaged cement-based materials is of significant importance for long-term performance of concrete structure. .In this proposal, transport properties will be quantified by both gas permeability and electrical conductivity. Firstly, the influence of pore structure characteristics on transport properties will be analyzed. Then, experimental simulation will be employed to measure the evolvement of damage under long-term load action, and the relationship between damage and transport properties after long-term loading action will be discussed. After that, the transport properties of damaged cement-based materials at different water saturation will also be measured. Finally, based on the experimental study on the fractal characteristic of pore and crack structures, the relation between microstructure, saturation degree and transport properties will be founded. A mathematical model of transport properties of unsaturated damaged cement-based materials will be established by employing effective medium theory and percolation theory, and the model will be validated by macroscopic experimental results. The perspective of this research program is that the results can be used for design, assessment and prediction of structure durability under different real service condition.

水泥基材料内部物质传输过程是耐久性研究的基础问题，同时，物质传输性质也是反映材料内部微结构对外部介质侵入的抵抗能力。混凝土结构在荷载、环境等因素作用下会出现裂纹，且几乎都处于非饱和状态。因此，研究非饱和状态下损伤水泥基材料的物质传输性质对评价材料耐久性优劣、提高结构使用性能等具有重要意义。课题选用气体渗透率和电导率作为耐久性指标进行研究。首先通过试验分析孔隙结构对材料传输性质的影响；研究实际服役水泥基材料在长期荷载作用下损伤的演化规律，探讨开裂状态与传输性质之间的关系；研究损伤水泥基材料在不同饱水度下传输性质的变化规律。结合试验获得的孔隙、裂纹结构的分形描述和统计特征，应用有效介质理论和逾渗理论研究孔隙、裂纹结构及饱水度与传输性质的理论关系，最终建立非饱和损伤水泥基材料传输性质的数学模型，并利用试验结果进行对比验证，为实际工程中水泥基材料的耐久性设计、评估及寿命预测提供科学依据与理论支持。

水泥基材料内部物质传输过程是耐久性研究的基础问题，同时，物质传输性质也是反映材料内部微结构对外部介质侵入的抵抗能力。水泥基材料耐久性的优劣取决于侵蚀性介质向材料内部传输速度的快慢。混凝土结构在荷载、环境等因素作用下会出现裂纹，且几乎都处于非饱和状态。因此，研究非饱和状态下损伤水泥基材料的物质传输性质对评价材料耐久性优劣、提高结构使用性能等具有重要意义。.课题利用孔隙率、比表面积、孔隙尺寸分布、特征孔径等物理参数表征水泥基材料的孔隙结构，分析不同的孔隙结构参数对物质传输性质的影响；研究长期荷载作用下水泥基材料的开裂损伤演化规律，分析不同程度的裂纹损伤对传输性质的影响；依据气体在非饱和水泥基材料内的渗透传输过程，进一步建立气体渗透性与饱水度的关系。理论研究方面，采用分形理论描述材料微观结构的分形描述和统计分析；将损伤水泥基材料看作是由孔隙、裂纹介质组成的多孔材料，利用有效介质理论、逾渗理论的研究思路和分析方法，结合测定的裂纹网络的几何形貌特征，建立考虑孔隙、裂纹连通特征的有效介质理论模型和逾渗模型，预测损伤水泥基材料的物质传输性质，为定量研究实际服役混凝土材料的耐久性提供科学依据，并为研究不同服役环境下侵蚀介质的具体传输过程提供研究基础与理论支持。