Static And Dynamic Toughness Of Green Ultra-high Performance Steel Fiber Reinforced Concrete

Ultra-high performance concrete is a new cement-based material with high strength,high toughness and excellent durability.However,the traditional UHPC usually uses a large amount of cement and silica fume as the cementitious material,with high-strength fine aggregate and steel fiber as the reinforcing phase,and adopts special processes,resulting in high cost,high energy consumption and low productivity,which restricts the extensive application of UHPC in engineering practice.In view of the above problems,this paper studied the feasibility of UHPC prepared by waste CRT funnel glass,and studied systematically the effect and mechanism of silane coupling agent modified steel fiber on the static and dynamic toughness of UHPC,aiming to develop low energy consumption and ecological green UHPC material with good working performance,mechanical properties and static and dynamic toughness.The main research and conclusion are as follows:The UHPC was prepared by replacing the river sand with waste CRT funnel glass,to study the basic properties of green UHPC.The flow properties,physical properties,mechanical strength and bending toughness of CRT funnel glass UHPC were tested respectively,and the intrinsic relationship between microstructure evolution and macroscopic properties was analyzed.The results show that with the increase of the replacement rate of waste CRT funnel glass,the fluidity,harden density and lead ion leaching concentration of UHPC gradually increase,the mechanical strength and flexural toughness decrease gradually.XRD and BSEM analysis showed that CRT funnel glass would inhibit cement hydration and weaken the interface transition zone,resulting in a decrease in UHPC strength.When the replacement rate is 25%,the overall performance is the best.The steel fiber was modified by silane coupling agent,to study the flexural behavior of the modified and deformed steel fiber UHPC.Based on the three-point bending test,the evaluation indexes of initial crack strength and corresponding deflection,peak strength and corresponding deflection,flexural toughness and toughness index were established.The effect of various steel fibers on UHPC bending toughness was analyzed,and the working mechanism of silane coupling agent modification is revealed.The results show that with the increase of the modified concentration,the flexural strength and flexural toughness of UHPC increase gradually,the compressive strength and toughness index increase firstly and then decrease,and reach the maximum when the concentration is 1%.The modification of silane coupling agent increased the friction of fiber interface,andthe bond between the matrix and steel fibers was strengthened by chemical bonding and physical adsorption,which improved the interfacial bonding performance and thus played a role of strengthening and toughening.The dynamic impact compression test of UHPC was carried out with split Hopkinson pressure bar,to study the effect on impact resistance of modified and deformed steel fiber UHPC.The effects of various steel fibers on the dynamic compressive strength,peak strain,impact toughness and failure morphology of UHPC were analyzed,and the impact failure process of UHPC materials under various impact velocities was reproduced by numerical simulation.The results show that UHPC materials have obvious strain rate effects.Under the same strain rate,the modified steel fiber UHPC has better impact resistance,and its failure mode is that there is no visible damage at lower strain rate,and cracked but not separated at medium strain rate,and broken but not crushed at higher strain rate.The simulation analysis shows that the impact failure process can be divided into two stages with crack propagation and crushing failure.