| The interfacial bonding properties of the steel fiber-UHPC matrix is closely related to the overall strengthening and toughening properties of UHPC materials.In order to explore and perfect the influence of key factors on the bonding properties and improve the bonding properties between fiber and matrix,the interfacial bonding properties of steel fiber-UHPC matrix was studied by single-fiber pullout text.The main work of this paper is as follows:(1)From the perspective of steel fiber properties,the influence of different steel fiber specifications,types and embedded depths on the interfacial bonding properties of the steel fiber-UHPC matrix was studied.The micro morphology of the steel fibers surface and end morphology were observed by scanning electron microscopy(SEM)to analyze the pull-out mechanism of different types of steel fibers.The results show that:1)Increasing the diameter and embedded depths of steel fiber can improve the bonding properties;2)The hooked fibers has more significant improvement on the bonding properties;3)Two kinds of steel fibers of straight-round and hook-end has different pull-out mechanisms;4)SEM microscopic observation shows that the matrix has extrusion and scraping effect on the steel fiber in the drawing process,and the hook shape at the end of the hooked fibers has mechanical resistance effect with the matrix,which improves the bonding properties.(2)From the perspective of matrix properties,the influence of silica fume content,quartz powder content,foam reducer content and curing conditions and age on the interfacial bonding properties of the steel fiber-UHPC matrix was studied.The micro morphology of the matrix tunnel were observed by scanning electron microscopy(SEM)to analyze the change characteristics of the drawing curve of the steel fibers in different matrices.The results show that:1)silica fume has the most significant effect on the bonding properties,and the recommended dosage is 20%;2)The addition of defoamer not only does not improve the bonding properties,but also has adverse effects;3)The content of quartz powder in the range of 10%to 15%has little effect on the bonding properties.when the content is beyond this range,the bonding properties declines significantly;4)The bonding properties under steam curing is the highest,followed by hot water curing,and the lowest under standard curing.the bonding properties under 7-day steam curing is the highest,followed by 3-day and 2-day steam curing,and the lowest under 1-day steam curing.The 3-day steam curing age has been able to full play to the interfacial bonding properties of steel fiber-UHPC matrix.(3)Based on the test results of two angles of fibers and matrix,the sensitivity of different fibers and matrix to loading rate was studied,and the rate enhancement mechanism of bond performance and the failure mode of steel fibers drawing were discussed from the micro level.The results show that:1)Both straight-round and hooked fibers show significant rate sensitivity,and the straight-round steel fibers has more dependent on speed;2)The rate sensitivity of straight-round steel fibers increases gradually in five different matrix;3)The end condition of the hooked steel fibers improves its pullout resistance.However,at high pullout load rate,the increase of mechanical resistance will cause the fiber to break,thereby reducing the energy absorption capacity;4)SEM microscopic observation shows that the rate sensitivity of steel fibers pullout may be related to the different propagation modes of matrix cracks under different loading rate. |
