Preparationand Properties Of Aligned Steelfiber Reinforced Cement-based Composites

Studies have shown that adding steel fiber into cement-based materials improves themechanical properties of cement-based composites significantly. Fiber orientation has agreat impact on the mechanical properties of cement-based materials. From the mechanicalsense, the most effective state of the steel fiber is the fiber orientation is same or close tothe orientation of the principal tensile stress, but the steel fibers is randomly distributed inthe ordinary steel fiber reinforced cement-based composites. In order to make the steelfibers give full play to its enhancement and toughening effect, this paper presents theconcept of the aligned steel fiber reinforced cement-based composites. The aligned steelfiber reinforced cement-based composites is the composite in which the steel fibers are inthe same direction and uniformly distributed in the matrix, in order to achieve fulladvantage of the efficiency of steel fiber by certain technology.By applying a uniform magnetic field to the freshly mixed steel fibre reinforcedcement paste, all the steel fibres in the paste would have the same orientation as that ofmagnetic field. In this way, the aligned steel fibre reinforced cement paste could beprepared. The forces acted on the steel fibres and the coefficients of the movement of thefibres due to the forces were analysed. According to the movement of the fibres, theorientation of the fibres was then determined. Then, the parameters to control theorientation of steel fibres, such as magnetic induction and the action time of magnetic field,were calculated. Based on this, the preparation method of aligned steel fibre reinforcedcement paste was proposed. The experimental results showed that in the aligned steel fibrereinforced cement paste prepared according to the theoretical calculation, around90%steelfibres reached the designed orientation, and the orientation factor of the steel fibre was0.95or greater.The mechanical properties of steel fiber reinforced cement-based composite wasinvestigated with emphasis on the orientation in the perspective of micromechanics. Firstthe bridging stress model of a fiber was established by probabilistic methods, then the axialtensile strength model of aligned steel fiber reinforced cement-based composite was builded.The theoretical expression of splitting and flexural tensile strength was derived byanalyzing the relationship between the splitting and flexural tensile strength and the axialtensile strength. The softening curves of steel fiber and cement-based materials weresuperimposed according to the composite mechanics, the area under the softening curvewas the fracture energy, then the softening curve and the fracture energy of steel fibercement-based composites were obtained. The flexural and splitting tensile strength and thefracture energy of aligned steel fiber reinforced cement-based composites were tested, combined with the experiment results, the theoretical model was proved to be right. Theexperiments show that the aligned steel fiber reinforced cement-based compositesdemonstrate a significant advantage in tensile, flexural and fracture toughness than thedisordered.