Preparation And Mechanical Properties Of Cement-based Materials Reinforced With Hybrid Steel Fiber Orientation

In practical engineering applications,most concrete structures are subjected to fixed loads over a long period of time,and the load direction remains unchanged,which can lead to deformation and cracking in specific directions.Improving the brittleness and crack susceptibility of concrete is necessary,and one effective method is to incorporate steel fiber materials.In mechanically mixed steel fiber concrete,only a portion of the steel fibers aligned with the load direction have a reinforcing effect,while the majority of the steel fibers cannot play their intended role.To improve the utilization of steel fibers,it is necessary to design steel fiber concrete with oriented reinforcement to increase the service life and performance of structures,while also reducing resource waste and costs.In this study,three-point bending tests,anti-symmetric four-point shear tests,scanning electron microscopy(SEM),and image correlation processing techniques were used to obtain information on the microstructure and strain displacement fields of the crack tip for cement-based materials reinforced with steel fibers with different orientations.The influence of the loading point position on important mechanical parameters such as toughness,normalized fracture energy,and brittleness index under the synergistic effect of mixed steel fiber orientations was deeply studied.The main research content and conclusions are as follows:(1)Preparation of hybrid steel fiber-reinforced cementitious matrix with synergistic enhancement of fiber orientation under a uniform strong magnetic field.Based on electromagnetic theory analysis and basic mechanical property experiments,the optimal control conditions for preparing hybrid steel fiber orientationenhanced cement-based composites were finally determined: 375 Gs magnetic induction intensity and 60 s magnetic field exposure time.At the same time,scanning electron microscopy was used to observe that the multi-scale steel fiber orientation-enhanced cement-based composites can more effectively prevent the generation of small cracks.It was found on this basis that the optimal steel fiber ratio of hybrid steel fiber orientationenhanced cement-based materials is different under different steel fiber contents.(2)The flexural cracking performance of hybrid steel fiber oriented reinforced cementitious composites.By utilizing image processing techniques,this study investigates the crack propagation behavior of cementitious matrix reinforced with hybrid steel fibers under three-point bending tests,with a particular focus on the effect of fiber orientation on crack opening displacement,toughness,and fracture toughness distribution.The results show that when the steel fiber content is 1.6%,and the proportion of coarse-to-fine steel fibers is 1:2,the toughness values are 1.89 times and 1.73 times higher than those of the single fiber(coarse/fine)samples,respectively,and the fracture toughness values are 1.8 times and 1.5 times higher than those of the single fiber(coarse/fine)samples,respectively.The synergistic effect of hybrid steel fibers on the cementitious matrix is thoroughly analyzed.(3)The crack propagation behavior of cementitious matrix reinforced with steel fibers oriented in a specific direction is investigated in this study.This study conducted anti-symmetric four-point bending tests on cementitious matrix reinforced with steel fibers oriented in different directions.The process of sample fracture and failure was recorded by image processing techniques,with a particular focus on analyzing the relationship between important mechanical parameters,such as loading point position,presence of unilateral notch,crack opening displacement,normalized fracture energy,and brittleness index,under the premise of steel fiber orientation enhancing the cementitious matrix.As the loading point position increased from 10 mm to 40 mm,the brittleness index of the steel fiber-cementitious matrix samples decreased by 54.44% to 332.5%,and the normalized fracture energy increased by 68.16% to 71.2%.(4)Enhanced fracture properties of I-II mixed cracks in cementitious matrix reinforced with oriented steel fibers.This passage describes a study on the fracture properties of cementitious composites reinforced with steel fibers under different fiber orientations,fiber contents,and preexisting crack distances from the center loading point.The study conducted four-point bending tests on specimens with varying parameters and recorded the fracture process using image processing techniques.The relationships between fracture performance parameters,such as pre-existing crack distance from the center loading point,steel fiber orientation,content,cementitious matrix peak load,crack angle,fracture energy,and ductility index,were analyzed.The results showed that as the pre-existing crack distance from the center loading point increased,the proportion of the ΙΙ-type component increased,and the fracture angle,peak load,fracture energy,ductility index,and strain at the crack tip of the specimens all increased correspondingly.