Fundamental Study on Automated Interlayer Reinforcing System with Metal Fiber Insertion for 3D Concrete Printer

In recent years, 3D concrete printing (3DCP) systems have been extensively developed in the construction field as a promising new technology. In particular, additive manufacturing (AM) systems using mortar are among the most promising methods. 3DCP has great advantages such as labor work saving at labor-intensive construction sites and creating complex-shaped members with high accuracy that are difficult to create using conventional construction methods. However, printed members using AM-based 3DCP systems inevitably include discontinuous interlayers, such as cold joints of concrete structures. The presence of such defects causes strength degradation in printed structures. In addition, it is challenging to introduce reinforcing steel bars as in general RC structures for AM-based 3DCP systems. Therefore, it is necessary to overcome the defects in the interlayers using new reinforcement methods. In this study, a fundamental investigation was conducted to develop an automatic reinforcing system suitable for AM-based laminate structures by metallic fiber insertion at the interlayers. A prototype automatic metallic fiber insertion system was established. Specimens were obtained and subjected to mechanical tests to confirm the reinforcing effect of metallic fibers. In addition, the interior of the specimen was measured by X-ray CT. It was confirmed that the reinforcing effect of metallic fibers enhanced the mechanical properties of the printed specimens.