Study On The Interfacial Properties Of Nano-sized Magnesium Oxide Modified Steel Fiber And Cement Matrix

Addition of steel fiber is an important way to improve the ductility of concrete and makes the failure mode of concrete change from brittle to tough.However,the interface between steel fiber and concrete is weak,and the failure of steel fiber concrete is usually due to pull-out failure of steel fiber,so the strengthening and toughening efficiency of steel fiber cannot be fully exerted in concrete.In order to improve the interfacial bond strength between steel fiber and matrix and make full use of the reinforcement efficiency of steel fiber,a new method of surface modification of steel fiber and its interfacial properties are studied in this paper.The main research contents are as follows.Firstly,two methods of steel fiber modification,precipitation-calcination and electrophoretic deposition,were studied,and electrophoretic deposition was selected as the optimal method.Using nano-sized magnesium oxide as modification medium,the influence of electrophoretic deposition voltage and electrophoretic deposition time on the quality of electrophoretic deposition was studied,and the optimized modification medium and process parameters were obtained.Then,the effectiveness of the modified method was characterized at the micro scale,and the surface morphology and microstructure of the modified steel fiber were analyzed and characterized by SEM,EDS,3D imaging with ultra-depth of field microscope and AFM.The surface morphology of the steel fibers before and after modification was observed by SEM and AFM.The surface elemental composition of the steel fibers before and after modification was detected by EDS.The surface roughness of the steel fibers was calculated by super depth of field microscope and AFM.The results show that a layer of nanoparticles is uniformly deposited on the surface of the modified steel fiber by electrophoretic deposition using M-1 under the optimized process parameters,which is significantly different from the smooth surface of the unmodified steel fiber.The AFM results show that the surface roughness S_a of modified steel fibers by electrophoresis deposition can be increased by 4.9%～76.49%.Finally,the single fiber pullout test was used to evaluate the interface of the composites,and the interface properties were evaluated using two parameters,the bond strength and pull-out energy,and the relationship between the process parameters of electrophoretic deposition modification and the interface properties was studied.The results show that the process parameters of electrophoretic deposition have significant effects on the interfacial bond strength and pull-out energy,and the influence degree on the pull-out energy is more obviously than the interfacial bond strength.Increasing electrophoretic deposition voltage and electrification time can improve the interfacial strength,and the effect of voltage on the interfacial parameters is more obvious than that of deposition time.