干湿交变下功能梯度混凝土构件界面多尺度行为及破坏机理

Based on the concept of functionally graded materials, the functionally graded concrete (FGCC) is put forward for strengthening concrete cover and extending the service life of concrete structure under wet-dry cycling condition, they use the Engineered Cementitious Composite (ECC) as the concrete surface due to its high performance. .However, failure of compound interface between the two layers in FGCC arise from the strength degradation and thermal stress evolution related to the effect of environmental factors. Once this happens, it is meaningless to perform the functionally graded design..So, serving this compound interface problem as the starting point, the proposed research is carried out by the means of interface mechanics, porous media theory and modern testing technology. Investigations of transmission characteristic and bond behavior are performed, and considering with the wet-dry cycling state and gradient structure characteristics. Our objectives are that the regularities of micro-environment, stress-strain and bond deterioration are made clear on the environmental impact-transport behavior, and numerical modelings of the FGCC are set up considering to macro- and microstructure evolution and its relationship with interfacial multiscale behavior. And then the behavior of interface on mechanical response and process of bond failure under wet-dry cycling condition are made clear. Lastly, the key design parameters of FGCC are formed to present threshold value on parameter of materials, structure and preparation process which is based mach interfacial behavior and water erosion resistance, and to evaluate its durability interface damage degree and its durability..The proposed research will provide a new method for improving durability of Yunan province hydraulic concrete structure and theoretical support for FGGC design.

基于功能梯度材料理念，利用ECC优异综合性能，对干湿交变下混凝土构件进行功能梯度设计，主动增强保护层，进而延长工程服役寿命。考虑施工条件复杂多样性，功能梯度混凝土构件(FGCC)在一定尺度仍存在界面层，环境作用下诱发界面热应力演变和粘结强度退化而先行破坏，使功能梯度化失去意义。项目以此为切入点，结合干湿交变及梯度结构特点，运用界面力学、多孔介质理论及现代化测试技术，开展FGCC传输性、粘结性能研究；弄清外部环境与传输性交互作用下界面层内微环境、应力应变及粘结退化规律；结合多尺度结构演变及其与界面多尺度行为的关系，构建FGCC数值模型，以揭示该环境下FGCC的界面力学响应特性、粘结破坏过程；最终形成FGCC的关键设计参数，反演出与抗环境水侵蚀、界面匹配的结构、材料与工艺参数的“合理域”，也可用于界面破坏程度评价及耐久性预估。研究成果丰富FGCC设计理论，也为提升云南水工结耐久性提供新方法。

现代混凝土制备技术下，混凝土早期开裂驱动力增加，脆性材料特点愈加强化，水工混凝土结构往往处于带裂缝工作。项目结合功能梯度材料理念和ECC 材料技术，对干湿条件下混凝土构件进行功能梯度设计，利用ECC 高拉伸应变能力，更好地保证构件保护层质量，在合理成本范围内实现水利工程整体耐久性提升。本项目的主要研究内容及结论如下：1） 充分利用机制砂及尾矿石粉资源，制备FGCC内层材料；采用国产PVA纤维与钢纤维混杂制备出具有明显应变硬化、多缝开裂模式特点的ECC面层材料，其极限拉伸应变在0.6%；2）揭示了功能梯度混凝土部品（FGCC）内湿度响应随面层材料参数、面层/中间层厚度比的时变规律；3）开展材料参数（扩散系数、收缩变形系数及强度等级）、结构参数（面层/中间层厚度比、几何尺寸）对FGCC界面应力的分布与时变规律及干湿循环对ECC/NC界面粘结强度的影响；在此基础上，结合FGCC氯离子传输简易模型、界面力学模型，对FGCC的进行设计，反演出具有“鲁棒性”的材料与结构参数；采用干湿循环等效模型，对FGCC界面破化程度进行预估； 根据FGCC结构体型，尤其是针对并联结构形式的功能梯度结构混凝土，提出挂网法浇筑工艺，解决了面层材料与内层材料之间的浇筑初期防止串料、硬化后期的界面融合，实现了浇筑强度的现场施工。