Evaluation of 3D-Printed Concrete Properties for Tunnel Structure Rehabilitation

3D printing technology has developed as a revolutionary method for the repair of tunnel structures, meeting the escalating demands of contemporary urbanization, especially in subway systems. This study analyses the mechanical and material aspects of 3D-printed concrete, concentrating on novel alterations to boost performance. Research examined the impact of biochar as an addition on the hydration, flowability, pumpability, and mechanical qualities of 3D-printed concrete across different dosages and ages. The feasibility of ultrasonic wave velocity as a non-destructive technique for evaluating ultra-early-age mechanical characteristics of 3D-printed cement-based materials was assessed. Tests for ultrasonic wave velocity and uniaxial compressive strength were conducted on cement paste, regular mortar, and mortar improved with additives for 3D printing. The findings indicate that biochar markedly affects the shrinkage, constructability, and overall mechanical performance of 3D-printed concrete, while ultrasonic wave velocity has a robust link with early-age mechanical parameters. These findings provide a scientific basis for enhancing 3D-printed materials and techniques, hence improving their use in tunnel repair and rehabilitation.