Rebar-Free 3D Printing of Transportation Infrastructure

This study investigates the fresh and hardened-state properties of printing mixtures including different dosages of steel fibers, especially at higher dosages which have not been investigated before. This study also considers the effects of other parameters such as sand-to-powder ratio and the limestone content on the properties of steel fiber reinforced printing materials, to reduce the Portland cement content which has a high carbon footprint. The obtained experimental results revealed that high-performance materials incorporating up to 2.5% steel fibers (by volume) can be successfully 3D printed. The mechanical properties of the reinforced mixtures improved significantly at high fiber dosages (2% and 2.5% vol.). By incorporating 2% and 2.5% vol. of steel fibers, the compressive strength results showed up to 109% and 50% increase in strength compared to the control mixture, at 7 days and 28 days, respectively. In addition, significant improvement in the flexural strength, tensile strength and toughness of printing materials were achieved at high dosages of steel fiber inclusion. The obtained results also reveal that the orientation and alignment degree of steel fibers in the composite is affected by different parameters such as the binder content and nozzle design. In addition, an electromechanical module was successfully designed, developed, and implemented with an existing printing system to enable a semi-automated screw insertion process in parallel with the layer deposition process. This highlights the feasibility of a fully automated layer deposition and reinforcement process for future real-life construction projects.