基于非球形颗粒堆积结构的非饱和水泥基复合材料反应传输性能建模

Deterioration of concrete induced by attack of aggressive species, such as gas, liquid and ions, is one of the most important factors to the durability of concrete structure. From the viewpoint of micro- or meso-scale level, cementitious composites can be regarded as granular materials based on the packing of particles with regular or irregular morphologies. And particle shape has significant influence on both microstructure and macro-properties of materials. This project plans to construct basic structural model of cementitious composites, simulate the hydration process of cement paste based on packing system of non-spherical particles, such as ellipsoids, regular polyhedrons, and superballs, etc. The influence of particle characters (including shape, size distribution and volume fraction of particle) on hydration reaction behavior of cement, microstructural evolution, and transport behavior of aggressive species in cementitious composites will be investigated. The n-point probability functions will be developed to quantify the microstructure and transport properties of cementitious composites at different stages. Based on the reality that the cementitious composites are rarely fully-saturated in use, the behavior of water adsorption and desorption behavior in unsaturated cementitious composite will be studied based on various non-spherical particle packing models. The influence of water-saturation degree and moisture distribution in pores on transport behavior of aggressive species will be comprehensively studied. The effect of the reaction between aggressive species and hardened cement paste on the microstructure of cementitious composites will be concerned. The size and spatial distribution of micro-cracks induced by various environmental actions will be quantified firstly. And the transport behavior of aggregate species in unsaturated cementitious composite with various cracking patterns will be studied. Finally, the reactive transport model of aggressive species in fractured unsaturated concrete will be developed.

气、液介质及离子的侵蚀作用是造成结构混凝土性能劣化的重要因素之一。在微细观尺度上，水泥基复合材料可以看作是由规则或不规则几何形状颗粒组成的粒子型复合材料。其中，颗粒形貌在很大程度上决定了材料的微结构特征和宏观性能。本项目拟从颗粒特征角度出发，结合椭球体、正多面体和超球等构建不同形式非球形水泥基复合材料结构模型和水泥水化模型，研究颗粒特征对水泥水化、微观结构和侵蚀介质传输性能的影响；借助多点概率函数实现对微结构的统计定量表征；鉴于实际混凝土材料很难达到完全饱和这一事实，借助多种粒子堆积模型模拟非饱和状态下材料的水分吸附脱附行为，分析饱水程度和水分分布状态对侵蚀性介质在多孔介质中传输行为的影响规律；研究侵蚀反应对微结构的影响；结合典型环境侵蚀作用下混凝土中裂纹的分布形式，研究开裂状态下材料传输性能的变化规律，建立多因素损伤累计的非饱和水泥基材料反应传输性能预测模型。

气、液侵蚀性介质的反应传输对混凝土性能的演化起着至关重要的作用。流体的传输与混凝土中缺陷（如孔、界面过渡区（ITZ）及裂纹）的含量、尺寸分布、空间布局及混凝土的饱水程度密切相关。侵蚀反应与混凝土材料的组成及侵蚀性介质的类型、浓度与环境温湿度等密切相关。为建立侵蚀性介质在水泥基复合材料的反应传输性能与材料组成、微结构及环境条件之间的量化关系，本项目从多种非球形颗粒随机堆积建模出发，用数值模拟方法研究了水泥颗粒形状对水泥浆体水化行为、微观结构和传输性能的影响，发现了硬化浆体孔隙率和相对扩散系数均随水泥颗粒球形度的增加而增大的规律。随后，本项目采用统计物理学理论、计算机模拟技术和几何概率理论研究了孔/集料/裂纹形状、尺寸及形状分布对孔网络、ITZ、裂纹网络渗流阈值的影响， 提出了一系列孔网络/ITZ/裂纹网络渗流阈值与其对应缺陷的形状、尺寸和形状分布之间定量关系的模型，开发了孔隙曲折度与孔隙的形状、体积分数、形状分布之间的量化关系模型，开发了裂纹曲折度与集料的形状、体积分数、形状分布之间的定量关系模型；结合复合材料力学模型和LBM方法研究了孔/集料/裂纹形状、尺寸及形状分布，ITZ厚度对水泥基复合材料传输性能的影响， 揭示了不同类型缺陷的形状、尺寸及形状分布对相应缺陷的渗流阈值、曲折度及复合材料传输性能的影响规律。最后，结合物理化学和地球化学的知识,建立了标准状态下磷酸钾/铵水泥的热力学数据库和包含温度影响的氯氧镁水泥的热力学数据库，采用反应热力学模拟与试验相结合的方式研究了硫酸盐、氯盐、CO2等侵蚀性介质对镁水泥浆体产物组成的影响，发现反应热力学建模有助于揭示侵蚀性介质作用下水泥基复合材料性能劣化的本质机理。本项目的研究成果为推动侵蚀性介质作用下水泥基复合材料寿命预测模型的建立提供论了坚实的理论支撑。