Spray-based 3D printed tunnel slag concrete: Evaluation for printability and mechanical performance

A spray-based 3D (S-3D) printed tunnel slag concrete material is developed in this paper. The effects of tunnel slag as fine aggregate, with replacement rates of 0 %, 60 %, 80 %, 100 %, and 120 %, on the workability, printability, and mechanical properties of the S-3D printed concrete are systematically investigated. The hydration process of the printed concrete is further analyzed by SEM, XRD, and X-CT. The test results demonstrate that the fine particles and stone powder in the tunnel slag, along with its rough texture, significantly optimize the rheological property of the concrete. The concrete with 100 % tunnel slag exhibits optimal thixotropy, printing accuracy, and buildability, along with enhanced mechanical properties. The compressive, flexural, and interlayer splitting strengths of the S-3D printed concrete with 100 % tunnel slag at 28 d increased by 8.84 %, 7.69 %, and 8.72 %, respectively, compared to the printed concrete without tunnel slag, achieving maximum strengths of 77.6 MPa, 14.0 MPa, and 2.12 MPa. The rough surface of the tunnel slag also facilitates stronger interface bonding with the cementitious materials. Additionally, combined with the effect of S-3D printing process, the S-3D printed concrete with 100 % tunnel slag shows a minimum porosity, decreased by 41.30 % compared to the printed concrete without tunnel slag. A tunnel lining structure model is successfully printed using the optimal 100 % tunnel slag concrete, demonstrating a novel approach to the resource utilization of tunnel slag and its application in intelligent lining construction.