异形钢纤维对超高性能混凝土增强增韧的影响

以钢纤维掺量、类型和分布方式为变量,测试了掺异形钢纤维超高性能混凝土(UHPC)的直接拉伸性能和弯曲韧性,并采用显微镜对这种钢纤维的拔出通道和拔断截面进行了观测.结果表明:异形钢纤维对UHPC具有较好的增强增韧效果,相应试件的直接拉伸强度、断裂能及裂后承载力均大幅提高,且其掺量越大,提高幅度越显著;当异形钢纤维沿拉应力方向有序分布时,与随机分布相比,更有利于UHPC的增强增韧;相比于端钩型钢纤维,在相同掺量下,波纹型钢纤维的增强增韧效果更佳,其拔出通道更加曲折,还存在被拉直的现象,这主要是由于其与基体间存在更强的机械咬合力所致;此外,在拉拔过程中,2种异形钢纤维的断口邻近截面均出现了明显的颈缩.

Effects of Deformed Steel Fiber on Strengthening and Toughening of Ultra High Performance Concrete

By treating dosage, geometry and distribution of steel fiber as variables, the direct tensile behavior and bending toughness of ultra high performance concrete(UHPC) with the addition of deformed steel fibers were investigated. Moreover, the pull out channels and cross sections near the fractured surfaces of steel fibers were observed by means of microscope. The results show that deformed steel fibers have beneficial effects on the strengthening and toughening of UHPC, which indicates a significant improvement on the direct tensile strength, fracture energy and post cracking load bearing capacity of specimens incorporating steel fibers. Meanwhile, the improvement can be increased with the increasing dosage of steel fiber. Notably, steel fiber orientated along the direction of tensile stress provides a better performance with respect to the strengthening and toughening than the fibers randomly distributed. Furthermore, compared with hooked steel fiber, the influence of crimped steel fiber on strengthening and toughening of UHPC is more efficient and the pull out channels are more zigzag, due to the more pronounced mechanical interlocking between steel fiber and mortar matrix which further enhances the interfacial bond in between. In addition, noticeable necking phenomena appeared at cross section near the fractured surfaces of the two types of steel fiber during tensile test.