Experimental study on compressive behavior and failure characteristics of imitation steel fiber concrete under uniaxial load

The concrete columns suffer from spalling and flaking in the room and pillar mining method, which affects service performance. The energy absorption and deformation failure laws of fiber concrete structures under compression load need further study. In this study, four types of imitation steel fiber concrete specimens were prepared, and uniaxial compression experiments were carried out. Simultaneous photographic and acoustic emission monitoring was conducted to investigate the compression energy absorption, crack evolution, fracture surface fractal and RA/AF value characteristics of fiber concrete. The results obtained in the present work are as follows. Imitation steel fiber concrete showed the best compressive and energy absorption performance with a 0.4-0.6% fiber/mortar mass ratio. A higher dosage of fibers prolonged the yield time but also led to earlier macroscopic cracking. The bond between imitation steel fiber and matrix can disperse the stress, which significantly improved the toughness of concrete. For every 0.2% increase in fiber content, the pre-peak toughness index CTI and post-peak damage absorption energy FCEC increased by about 10% and 50%, respectively. Both plain concrete and fiber concrete specimens developed macroscopic cracks under local tensile stresses. The proportion of shear fracture in plain concrete reached 80.1% and dominated during the secondary crack development. The proportion of tension and shear fracture in fiber concrete was less disparate and showed a mixed pattern with synergistic action. The proportion of shear fractures gradually increased with the increase in fiber content. The calculated results of the RA/AF method corresponded well with the crack morphology. With the increase in fiber content, the bridging effect of fiber became more obvious, and the ability of specimens to resist cracking improved significantly. The fractal characteristics of the fracture surface of each specimen were investigated. The plain concrete specimens had a relatively complete surface when destroyed, and their fractal dimension was only 1.62, the lowest among all the specimens. The surface of fiber concrete was more fragmented, and their fractal dimension was higher, with the fractal dimension D increasing by 0.2-0.4 for each 0.2% increase in fiber content. This study can provide a reference for the fiber concrete pillar designs.