超高性能混凝土流变特性及其对纤维分散性的影响

摘要

优异的分散性能是纤维充分发挥增强增韧作用的关键.为了明确高掺量钢纤维在超高性能混凝土(UHPC)中的分散特征并提高纤维的分散性,采用抗压强度、抗弯强度等力学性能试验、混凝土流变仪以及图像分析技术,分别研究了降粘掺合料、钢纤维掺量对UHPC力学性能、流变性能以及纤维分散性能的影响.结果表明:降粘掺合料对UHPC力学性能无明显提升作用,但可显著降低UHPC基体的屈服应力和塑性粘度,同时可降低钢纤维导致的屈服应力和塑性粘度增加幅度;随着纤维掺量的增加,纤维轴向取向系数和有效利用率降低,而降粘掺合料可提高纤维轴向取向系数和有效利用率;UHPC基体的流变性能、纤维分散性能以及力学性能三者密切相关,基体流变参数越小,纤维轴向取向系数越高、纤维有效利用率越高,则UHPC力学性能越好.%High dispersion is the key to achieve optimum benefits from the fibers for UHPC.In order to understand and improve the fiber dispersion in ultra high performance concrete (UHPC) with high content of steel fiber (SF),this work employed concrete rheometer,image analysis technology and mechanical properties tests such as compressive strength,flexural strength,to investigate the effects of viscosity-reducing admixture and SF content on UHPC's mechanical properties,rheological properties and fiber dispersion.Results showed that viscosity-reducing admixture could significantly reduce the UHPC matrix's yield stress and plastic viscosity,and alleviate the increases of yield stress and plastic viscosity induced by SF addition.Both axial orientation factor and fiber efficiency would decrease by increasing SF content,but increase with the dosage of viscosity-reducing admixture.Our work suggests that the rheological properties,fiber distribution and mechanical properties of UHPC are highly correlated:lower rheological parameters can lead to higher axial orientation factor and higher fiber efficiency,and consequently,higher mechanical properties of the SF-contained UHPC.