地下轨道交通循环荷载与水作用下微胶囊自修复水泥基材料的修复时效性

Active self-healing, as one of utmost important ways to improve safety and service life of concrete infrastructures, becomes the focus of increasing attention internationally. According to the characteristics of damage and cracking of underground concrete structure by traffic cyclic loading, it is proposed that the self-healing system with microencapsulation for micro-cracks should be with healing persistance, which is the ability to rehealing or preserve the properties in addition to a good performance by the early healing. The cracking and healing process were monitored online using AE, which includes using passive AE to listen to the cracking events and active AE to detect the healing events. The mechanical response of cement-based rehabilitation material with microencapsulation was studied when cyclic loads were applied based on damage mechanics, fracture mechanics and meso-mechanics. The stability affected by the underground water were discussed physically and chemically. The sustained rehealing ability and stability of this material subjected to combined cyclic load and underground water were detected, by which the mechanism of sustained reself healing were revealed. An evaluation method for the persistance was suggested on macro-, meso- and micro-levels according to AHP. The damage and healing process were numerically analyzed by introducing the "healing element", which was upscaled from the microstructure in terms of the mechanical properties, into the lattice model to estimate the healing persistance of this material. This present study can provide a scientific base for the longevity of underground concrete structures in such complicated environments, thus it is expected to be with a highlight prospect for application in practice.

自修复技术是提高混凝土结构安全性和服役寿命的重要途径之一，也是近些年混凝土研究的国际前沿热点之一。本项目根据地下结构产生的损伤开裂特点，提出对混凝土材料微裂纹的修复，微胶囊自修复技术除一般的修复效果外，还应具有修复时效性，包括持续修复能力和稳定性。提出声发射对地下环境其修复效果的连续在线监测技术：声发射被动模式研究二次损伤破坏特征，声发射主动模式监测再修复过程；结合力学试验，基于损伤力学、细观力学、断裂力学分析其修复后在循环荷载作用下的力学性能演变规律，阐明其持续修复能力。研究地下水环境对其修复力学稳定性和耐久性的影响。进一步研究其多重因素作用下的持续修复能力和稳定性，从宏微观多个层次揭示其持续修复机制。建立其修复时效性的层析分析评价模型；建立嵌入修复单元的细观格构损伤修复模型预测其修复时效性。该项目可为保证地下复杂环境下混凝土材料结构的长期性能提供科学理论指导，具有很好的应用价值与前景。

研究了微胶囊自修复水泥基材料修复过程、修复机理及修复效果：对微胶囊形貌、力学性能、稳定性等进行表征，通过研究不同外部条件对微胶囊性能的影响，确定了微胶囊制备的合成条件；基于细观力学预测了微胶囊对水泥基材料有效力学性能的影响，得到了在水泥基材料力学性能具有90%以上保证率的前提下胶囊的最大掺量范围，为试验的开展提供了理论保证；开展了制备的微胶囊在水泥基材料中的自修复行为、效果的多尺度试验研究。充分利用声发射技术对微胶囊自修复水泥基材料在荷载作用下的损伤破坏及修复过程进行了实时监测。对声发射信号进行了详细、深入的后处理，获得了大量关于材料内部破坏与修复的信息，对于揭示微胶囊自修复技术在水泥基材料中的作用机理提供了可靠的试验与理论支持；根据地下混凝土结构产生的损伤开裂特点，开展了微胶囊自修复水泥基材料的修复时效性研究，包括不同地下水环境对体系修复稳定性和耐久性的影响。研究了预损伤程度、微胶囊掺量，试件修复的腐蚀溶液对修复效果的影响。结果表明，试件修复之后其内部密实度几乎全部得到改善。由于微胶囊的制备环境为酸性（pH2-4），故在酸性环境下更容易发挥修复效果。项目已取得一定特色成果，为保证地下复杂环境下混凝土材料结构的长期服役提供了一定的科学理论指导。