非饱和条件下氯离子侵入混凝土行为的可视化表征和多尺度模型研究

Compared with underwater saturated concrete, the unsaturated concrete of marine tidal zone, splash zone is subject to more serious damage due to the corrosion of chloride ions. In this project, according to multi-scale features of concrete microstructure and transport characteristics of corrosive media, advanced apparatuses (non-contact resistivity, nitrogen adsorption, nanoindentation and atomic force microscopy) are firstly used to investigate temporal and spatial distribution of representative elements. X-ray tomography is then applied to in-situ continuously and visually track the migration process of chloride salt solution in the unsaturated concrete. Balancing mechanism of chloride ions with enrichment, solidification and desorption is explored in the multi-level pore structure. Based on computer simulation and image processing techniques, three dimensional microstructures of low and high density C-S-H gel, cement paste, mortar and concrete are established. Four transport channels of gel pores, capillary pores, interface pores and cracks are identified with the corresponding transport coefficients determined as well. Furthermore, considering combination of humidity and concentration, the unsaturated numerical transport model of chloride ions is set up from nano-scale, micro-scale to macro-scale utilizing lattice model and finite element method. Thus, these results of project are helpful to the design and preparation of long-life concrete with transport properties.

与水下全浸区饱和混凝土相比，海洋潮汐区、浪溅区中非饱和混凝土受氯离子侵蚀破坏更为严重。本项目根据混凝土的微结构多尺度特征和侵蚀介质传输特点，采用非接触电阻率、氮气吸附、纳米压痕、原子力显微镜等现代测试技术表征各代表性单元中物相组分的时空分布；利用X射线断层扫描仪原位、连续、可视化追踪氯盐溶液在非饱和混凝土中的迁移规律，探明氯离子在多级孔隙结构富集、固化与解吸的动平衡机理；运用计算机模拟和图像处理技术分别构建低密度和高密度C-S-H 凝胶、净浆、砂浆和混凝土的三维微结构，提炼出凝胶孔、毛细孔、界面孔及裂缝四类传输通道，并确定相应氯离子传输系数；在此基础上，考虑湿度与浓度梯度耦合作用，通过格构模型和有限元算法逐尺度建立从微观→细观→宏观的氯离子传输数值模型。研究成果为基于传输性能的长寿命混凝土设计与制备奠定科学基础。

与水下全浸区饱和混凝土相比，海洋潮汐区、浪溅区中非饱和混凝土受氯离子侵蚀破坏更为严重。本项目根据混凝土的微结构多尺度特征和侵蚀介质传输特点，采用非接触电阻率、超声波、X射线断层扫描等技术表征各代表性单元中物相组分的时空分布和逾渗阈值；研究了不同水灰比、粉煤灰掺量、砂率对非饱和水泥基材料的毛细吸水、氯离子自由扩散以及稳态电迁移的传输规律；运用计算机模拟和图像处理技术分别构建低密度和高密度C-S-H 凝胶、净浆、砂浆和混凝土的三维微结构，提炼出凝胶孔、毛细孔、界面孔及裂缝四类传输通道，并确定相应氯离子传输系数；逐尺度建立从微观→细观→宏观的氯离子传输数值模型。结果表明非饱和混凝土的扩散距离与时间开根号成一次函数关系，扩散系数与饱和度变化规律符合指数函数关系；模拟结果与实验数据的对比显示两者具有较好的吻合度，尤其在低水灰比时，模拟结果的精度更高。研究成果为基于传输性能的长寿命混凝土设计与制备奠定科学基础。