Abstract: In this paper, a directional method of steel fiber in high performance concrete was designed by using magnet. The working performance of concrete was adjusted by changing the amount of water reducing agent. The relationship between the directional effect of steel fiber and the rheological properties and mechanical properties of concrete was studied. The results show that with the increase of mass fraction of polycarboxylate superplasticizer, the yield stress and plastic viscosity of concrete decrease gradually, and the fluidity increases. When the mass fraction of water reducer is greater than 2.5%, the yield stress and fluidity gradually tend to be stable, but the plastic viscosity still maintains a decreasing trend. The lower the yield stress and plastic viscosity is, the better the fiber orientation effect is. The directional coefficient of unoriented steel fiber is 0.479~0.526, while the directional coefficient of steel fiber under magnetic field is 0.815~0.912. The flexural strength of concrete with oriented steel fiber increases by 24.0%~43.3%, and the toughness index I₂₀ increases by 38.4%~69.9%. In addition, the magnetic field has no obvious effect on the dispersion of steel fiber, and there is no significant difference in compressive strength between oriented specimen and unoriented specimen.

Key words: high performance concrete, steel fiber, orientation, rheological property, mechanical property