基于混合替代纤维的ECC材料性能设计理论及行为机制研究

Engineered Cementitious Composites (ECC) are materials featuring multiple-cracking behavior and super ductility under tension. ECC can be applied to structures that require seismic resistance and durability, in views of the fact that normal concrete is vulnerable to cracking. The application of traditional ECC is limited by its high cost due to the use of expensive Kuraray PVA fibers. This project focuses on the development of a new type of ECC prepared with inexpensive hybrid PET and domestic PVA fibers, which greatly reduces the cost of the material while still preserving its excellent mechanical properties. To achieve above, the micro-mechanical parameters of fibers, matrix and their interface are to be tailored based on ECC’s micro mechanisms and the bridging relations for each substitute-fiber will then be established. Based on the contrasting behaviors when each type of fibers bridge a crack, with a properly designed blending ratio, the domestic PVA fibers are expected to take the major bridging stress and restrict the crack opening under small deformation, while the PET fibers are expected to provide structural ductility to ensure safety under large deformation. After desirable bridging constitutive relation for hybrid fibers has been set up, the fiber dispersion in matrix will be improved with the help of image processing method on cracking patterns and rheology control. Tests such as direct tensile testing will be employed to examine the mechanical performance of designed hybrid substitute-fiber ECC and the design can then be finalized. Furthermore, a numerical model to simulate hybrid-fibers reinforced ECC’s multiple-cracking behavior will be proposed to reveal the co-bridging effect of hybrid fibers and parametric studies will also be conducted to direct the material design and optimization. This work is expected to facilitate the promotion of ECC engineering application in the future.

ECC 是一种具有超高延性和多缝开裂特征的纤维增强水泥基复合材料，其推广应用是解决混凝土开裂、提升结构耐久性和抗震性能的重要途径。采用进口PVA纤维的ECC材料价格是普通混凝土近十倍，难以大规模工程应用。本项目提出采用低成本的国产PVA和PET纤维以混杂形式代替进口纤维，制备低成本、高性能的混杂纤维ECC材料。首先，通过纤维拔出等细观试验测量、调整微观力学参数，建立替代纤维桥接本构关系。基于其不同的桥接特性，通过优化混杂比例设计，得到理想的混杂纤维桥接本构曲线，实现两种纤维在不同裂缝宽度下分别控制裂缝和吸收能量的工作机制。结合裂缝图像处理算法和流变性调节来优化混杂纤维的分散性能，并通过单轴拉伸等试验验证材料宏观力学性能，建立其优化设计方法。同时，本项目拟建立针对混杂纤维ECC的多缝开裂模型并作参数分析，深入揭示混杂纤维协同桥接的行为机理，并优化其设计方法，为ECC的大规模工程应用提供条件。

ECC是一种具有超高延性和多缝开裂特征的纤维增强水泥基复合材料，其推广应用是解决混凝土开裂、提升结构耐久性和抗震性能的重要途径。采用进口PVA纤维的ECC材料价格是普通混凝土近十倍，难以大规模工程应用。本项目提出了采用低成本的国产PVA和PET纤维以混杂形式代替进口纤维，制备低成本、高性能的混杂纤维ECC材料。首先，基于细观力学参数的实验测量，分析了水胶比、粉煤灰掺量等对细观性能影响，提出了ECC材料细观力学性能的调控方法。利用替代纤维各自的单缝本构曲线，建立了不同纤维在不同工况下作为桥接主体的混杂纤维方案设计理论。同时，基于细观力学和断裂理论，建立了混杂纤维ECC多缝开裂的数值模型，揭示多种纤维在水泥基复合材料中的协同桥接机制，为今后此类混杂纤维增强材料的设计奠定理论基础。本项目基于ECC细观力学设计替代纤维的混杂方式，并利用多尺度的理论模型进行优化和验证，成功设计出性能优异的低成本混杂替代纤维ECC材料。具有代表性的1%国产PVA+1%PET的配方较原有的进口PVA-ECC配方成本降低78.4%，较国产PVA-ECC成本降低了33%，仍能在标准养护28天时取得与两者相近的3.5MPa的拉伸强度和4%的延性，为高延性ECC材料在工程上的应用开辟了更广阔的空间。负责人以一作、通讯将相关成果发表在4篇JCR分区一区期刊上，授权/申请发明专利3项，实施新材料试验段1处，作为参与人获得教育部科技进步奖2等奖一项。