Influence Of Hybrid Fibers On Mechanical Properties And Strengthening And Toughening Of UHPC

Ultra High Performance Concrete（UHPC）is a new type of concrete material with clear performance indicators.Brittleness is one of the inherent defects of concrete materials.The addition of steel fibers can significantly improve its fracture strength,toughness and energy absorption capacity,and transform the original brittle failure of the matrix into plastic failure,which is of great significance to UHPC.However,studies have shown that when 1.0% steel fiber material is incorporated into the matrix,the cost exceeds the cost of the matrix itself.It can be seen that the steel fiber material is still too expensive,so the high material cost has become an important factor limiting the widespread use of steel fiber reinforced UHPC.In order to make full use of the value of steel fibers,without sacrificing the excellent properties of UHPC,and to reduce the volume content of steel fibers,a more practical approach is to incorporate some relatively inexpensive synthetic fibers into the UHPC matrix.According to the research of many scholars,synthetic fibers are not only cheaper than steel fibers in price,but also have various properties that are not inferior to steel fibers.Mixing them with steel fibers can reduce costs while reducing costs.Greatly improve the performance of UHPC matrix.At present,some of the more common synthetic fibers are polyethylene fiber（PE）,polypropylene fiber（PP）,polyvinyl alcohol fiber（PVA）,etc.In this paper,steel fiber and PE fiber are selected to be mixed,and the total volume content of 2% is prepared.Hybrid fiber UHPC.Through the fluidity test,compressive,flexural,splitting tensile strength test and flexural toughness test,the effects of single fiber blending and fiber blending on the flow properties and mechanical properties of UHPC were studied.The main research contents are as follows:（1）Under the water-to-binder ratio of 0.2,in terms of single-doped steel fibers,the influence of end-hook steel fibers（HF）on the fluidity is stronger than that of corrugated steel fibers（CF）and straight steel fibers（SF）,and end-hook steel fibers（HF）The steel fiber has the best effect on improving the strength and toughness of UHPC;for single-doped PE fiber,the fluidity is the worst when mixed with 18 mm PE fiber,but 18 mm PE fiber improves the flexural strength,splitting tensile strength and bending toughness of UHPC.Best results.（2）When the total volume content of 2% is constant,when 0.5% of end hook steel fiber（HF）and 1.5% of 18 mm PE fiber are mixed,the UHPC fluidity value is reduced to the lowest,only 115 mm,which is lower than that of plain UHPC.53.1%;when 1.5% of end-hook steel fiber（HF）was mixed with 0.5% of PE fiber,the compressive strength of UHPC reached the maximum value in the mixed group;when 1.0% of end-hook steel fiber（HF）and 0.5% of PE fiber were mixed with When 1.0% PE fiber is mixed,the improvement effect of UHPC flexural strength and split tensile strength is the best.（3）The effect of mixing steel fiber and PE fiber on the initial crack strength and initial crack deflection of UHPC is not obvious,but it has a significant effect on the peak strength and peak deflection,and 1.0% PE fiber and 1.0% end hook steel fiber（HF）mixed,the improvement effect on the bending toughness of UHPC is the best.In general,the hybrid of steel fiber and PE fiber has a good "positive synergistic effect",and the effect of hybrid fiber on the strength and toughness of UHPC is better than that of single-doped steel fiber and single-doped PE fiber.