Study On Preparation And Properties Of Aligned Steel Fiber Reinforced Cementitious Composites Using A Plate Magnetic Field

Steel fiber reinforced concrete(SFRC)has been applied in floor,ground and bridge deck projects because of its good crack resistance.During the service of actual engineering components,the stress tends to have a regular directionality,however,the steel fiber in the steel fiber concrete is distributed in random direction,and it is difficult for the steel fiber which is not consistent with the direction of tensile stress to exert its role of strengthening and toughening,resulting in the waste of steel fiber and the waste of engineering cost.Controlling the direction of steel fiber in steel fiber concrete can improve the strengthening efficiency of steel fiber and save the production cost,has the important engineering practical significance.At present,using the uniform magnetic field formed in the cavity of the electrified solenoid to control the direction of the steel fiber has obtained good experimental results.However,in practical engineering,the size of the component is generally large,and it is closely connected with the formwork and other facilities,so the steel fiber orientation cannot be implemented in the working space of the energized solenoid.Therefore,this orientation method is difficult to be applied in practical engineering.In this paper,directional steel fiber concrete(SFRC)is prepared by applying magnetic field from one side of concrete component which in the pouring vibration compaction stage with a bar magnet.This method solves the problem that the directional steel fiber by the energized solenoid which is limited by the internal space of the solenoid,and it can be used in the directional steel fiber of the large-size concrete members in the practical engineering,which is conducive to the practical application of the directional steel fiber concrete.The magnetic field device is composed of a plate magnet with a number of bar magnets in parallel,and each bar magnet is composed of a number of small magnets in series.Magnetic flux leakage exists between adjacent small magnets,forming external magnetic field with wavy magnetic field lines.The results show that the magnetic induction intensity and range of the external magnetic field formed by magnetic flux leakage are greater than that of a single bar magnet,which can drive the orientation of steel fiber in the cementitious.A number of bar magnets were formed into a plate in parallel with the poles,which can increase the size of the magnetic field and meet the requirements of the preparation of the specimen.If further increase in size,can meet the engineering requirements.According to the conventional method preparing and mixing steel fiber reinforced cementitious composites,when vibrating on the vibrating table,the flat plate magnetic field device was placed at the top of the test mould for about 60 s.The steel fibers in the mixing material that were originally randomly oriented were driven to rotate in the same direction.The analysis shows that the effective range of the magnetic field reaches more than 100 mm and the orientation effect of the steel fiber is good.The unidirectional orientation steel fiber reinforced cementitious composites prismatic specimens were prepared by using the flat magnetic field,by the three-point bending test,compared with the random random steel fiber reinforced cementitious composites prismatic specimens and the directional steel fiber reinforced cementitious composites prismatic specimens prepared by the magnetic field of the traditional energized solenoid.The results show that the flexural performance of the steel fiber reinforced cement matrix specimens prepared by the plate magnetic field is significantly better than that of the random random steel fiber reinforced cement matrix specimens;The flexural performance is closed to the steel fiber reinforced cementitious composites specimen prepared by the orienting device of the energized solenoid.