微细钢纤维/PVA纤维混杂超高韧性水泥基复合材料研究

Ultra High Toughness Cementitious Composite (UHTCC) is a kind of high-performance cementitious composite. Its significant strain hardening properties and excellent energy dissipation capability make it considered as a potentially ideal material for high rise buildings，bridge engineering and protection engineering for structural safety promotion, but its relatively low compressive strength hinders this potential come true. The design theory of this type of materials doesn't advice high compressive strength which usually leads to significantly decreased strain hardening properties. To solve this problem, fiber hybridization technology is used to develop new type UHTCC which possess high compressive strength and high ductility at the same time. PVA fiber is chosen for control crack width and guarantee ductility, and hooked end micro steel fiber is used for achieving high tensile strength and reducing the unfavorable effect caused by compressive strength increase. In the project, optimization of matrix proportion, optimization of mixing processes and fibers hybridization proportion, single fiber pull-out properties, uniaxial tensile properties, uniaxial compressive properties, development of hybrid UHTCC design theory etc. will be systematically studied. The resulting hybrid UHTCC, which possesses compressive strength grade no less than C60 and 3-dimensional ultimate tensile strain no less than 1%-2%, will make the aforementioned potential come true. The discovery of single fiber pull-out properties, fiber hybridization effect and the mechanism of rate dependence of the mechanical properties of hybrid UHTCC will provide scientific basis for further modification of fibers and UHTCC composites. The proposed 3-dimensional constitutive models will provide design reference for structural design and analysis.

超高韧性水泥基复合材料（简称UHTCC）因具有显著应变硬化特性和卓越耗能能力，有潜力成为应用于高层、桥梁和防护工程以显著提高结构安全性的理想材料。但这类结构普遍对混凝土有高强度要求，极大限制了目前普遍处于中低强度的UHTCC在此类工程中的应用。UHTCC高强度化是必然趋势，随之可能导致应变硬化特性显著降低。为解决这一矛盾，本项目拟采用微细钢纤维/PVA纤维混杂技术，开展基体优化、搅拌工艺优化、单丝纤维拉拔特性、混杂UHTCC 设计模型、轴拉、轴压特性等一系列研究工作，开发出强度等级不低于C60，准三维极限拉应变不低于1%-2%的新型UHTCC。本项目揭示的单丝纤维拉拔特性、纤维混杂效应以及UHTCC力学特性应变率效应发生机理都将为进一步纤维改性和UHTCC性能优化提供必要的科学依据，基于三维尺度UHTCC本构模型的提出将为其在高层结构等结构中的应用提供必要设计参考依据。

超高韧性水泥基复合材料具有显著的应变硬化性能和优异的裂缝无害化分散能力，同时还具有良好的耐久性和抗疲劳性能，该类材料在结构抗震、桥梁结构和防护工程等领域有着广泛的应用前景。用于结构时，这些工程往往对材料抗压强度有较高的要求（通常C50是很多工程的一个门槛），传统的UHTCC仅有20~40MPa左右，难以满足要求。追求UHTCC高的抗压强度往往会导致应变硬化性能的显著降低，单纯使用PVA纤维很难实现两者的统一，将PVA纤维和钢纤维混杂使用是一个潜在可行的技术路线。本项目开发了一套新型单根纤维拔出实验试样模具及成型方法，该方法的实施有望解决现有方法依赖纤维厂家的配合、依赖高精度切割机及熟练操作人员、对纤维无切割、测试时试样可以获得较为一致的边界条件，这些改进保证了今后的单根微细纤维拉拔试验使用商用短切纤维即可进行，试验过程更趋于合理，实验结果将更加可靠，未来可为纤维/基体界面性能表征提供更有利的试验方法，未来可以为相关力学模型的简历提供更可靠的科学依据；本项目遗憾未能利用PVA纤维和钢纤维混杂实现三维尺寸下极限拉应变达到1%~2%的C60UHTCC，但幸运的是，采用对基体改性的方式，实现了UHTCC抗压强度和应变硬化性能的同步提升，研究得到抗压强度50MPa的UHTCC材料，其极限拉应变利用三维尺寸试件测试可达到4%以上，可为一些结构工程的建设提供性能更加优异的UHTCC材料；；此外，本项目对钢纤维外形进行了优化，用其制备的新型高受压韧性混凝土抗压强度可达到170MPa以上，极限压应变可达到5%以上，该材料预计未来在防护工程和结构抗震等领域都有着广阔的应用前景。