Structural and environmental performance of recycled steel fiber reinforced concrete segment under the thrust force of the tunnel boring machine jacks

Abstract The present study evaluates the structural and environmental performance of recycled fibers as a low‐cost and eco‐friendly reinforcement of segmental tunnel lining. In this research, the defect effects in the support area are investigated using three types of scaled panel samples. In addition to the fiber‐only reinforced concrete, the performance of a new hybrid design is evaluated. The axial displacements, crack widths, crack lengths, and crack depths were monitored by displacement gauges and image processing. The experimental and numerical results show that the presence of defects, in addition to increasing at least five times the opening of the spalling crack, induces the appearance of new secondary cracks. Based on the results, it was observed that recycled fibers have a good ability to reduce the opening and growth of cracks. The hybrid reinforced design showed a significant performance compared to conventional reinforced segments, even in the most critical support conditions. According to several environmental parameters, the highest environmental compatibility in continuous support conditions is related to the fiber‐only reinforced concrete design; however, with presence of defects in the support area, the new hybrid reinforced design has shown the highest environmental compatibility in most environmental parameters. It was finally concluded that the fiber‐only reinforced concrete with recycled steel fibers and the new proposed hybrid reinforced concrete designs had high efficiencies in all cases in terms of structural, environmental, and economical performances. In addition to significantly reducing the crack openings in the hybrid reinforced design, the used rebars were reduced by about 40%.