结构型纤维对混凝土弯曲韧性和裂缝表面形态的影响

为了研究结构型聚丙烯纤维、结构型钢纤维及混杂纤维(包括结构型聚丙烯纤维和结构型钢纤维)对混凝土弯曲韧性及裂缝表面形态的影响，参照RILEM TC 162-TDF10]标准进行混凝土开口梁的三点弯曲试验。利用激光扫描仪对每个试件裂缝表面形态进行信息采集。基于裂缝表面信息，计算了四种裂缝表面粗糙程度参数(即裂缝粗糙度(R_N)、分形维数(D)、z坐标正态分布的标准差(σ_z)和裂缝曲折度(τ))，并比较分析了裂缝表面粗糙程度参数与弯曲韧性参数之间的相关性。研究表明:随着纤维掺量的增多，混凝土弯曲韧性和裂缝表面粗糙程度均随之增大。与结构型聚丙烯纤维和结构型钢纤维相比，混杂纤维在提高混凝土弯曲韧性和增大混凝土裂缝表面粗糙度方面均展现出正混杂效应。与分形维数D、z坐标正态分布标准差σ_z和裂缝曲折度τ相比，裂缝粗糙度R_N与纤维增强混凝土梁弯曲韧性参数的相关性最为显著，且存在指数函数关系。基于该函数关系，可借助纤维增强混凝土梁的弯曲试验快速估测裂缝表面的粗糙程度。 

Effects of macro fibers on crack permeability evolution of concrete under loading

In order to study the effects of macro fibers on the crack permeability evolution of concrete under loading, the splitting test was adopted to generate cracks on the concrete specimens. The crack permeability of different crack widths was measured in real time using the vacuum permeability test. The laser scanning equipment was adopted for the measurement of information and the reconstruction of the topography of crack surface. The effects of macro steel fiber, macro polypropylene fiber and hybrid fiber(including macro polypropylene fiber and macro steel fiber) on the crack permeability of concrete and the topography of crack surface were analyzed and compared. The results show that the macro fibers increase the crack surface roughness of concrete and indirectly decrease the crack permeability of concrete. With the increasing of fiber content, the crack permeability decreases. Compared to mono fiber reinforcement, the crack surface of hybrid fiber reinforced concrete is rough and the crack permeability of hybrid fiber reinforced concrete is small. With the increase of crack width, the crack permeability is closer to the value predicted by the Poiseuille flow model. Compared to modified factor ξ of Poiseuille flow model, parameter α of permeability is suitable for quantifying the effect of macro fibers on the crack permeability of concrete.