An Automated Pin Insertion Method for 3DCP and Its Reinforcement Effects on Beam Specimens

In recent years, 3D concrete printing (3DCP) for construction has been actively developing. 3DCP is expected to significantly reduce the labor intensity of conventional on-site work and possess the capability to create free-form shapes of high precision without molds. This characteristic can contribute to a reduction in environmental impact by reducing the use of molds and excess waste materials. However, the additive manufacturing method inevitably introduces interlayer de-fects, weakening the structural integrity. Reinforcement against brittle failure is crucial in countries prone to earthquakes like Japan. Unlike traditional reinforced concrete structures with steel bars, 3DCP encounters difficulties in reinforcing, and the reinforcement methods have not yet been firmly established. For exam-ple, there is a method to place the rebar in advance, build the perimeter with 3DCP, and then pour concrete inside, but it does not take advantage of the un-manned work of 3DCP. Therefore, the authors proposed an automatic system in which reinforcement pins are synchronously inserted from the printer head as a part of the printing process. This reinforcement method combines labor force saving and flexible configuration. In this study, a device was developed to auto-matically insert cylindrical steel pins perpendicularly to penetrate the mortar lam-ination surface. Using the proposed method, H-shaped beam specimens with a length of 900 mm were fabricated, and four-point bending tests were conducted to evaluate the effect of reinforcement by insertion pins. The results demonstrated the capability of producing large-sized beam specimens through the automated pin insertion method in 3DCP. Moreover, it was confirmed the reinforcement pins could significantly enhance flexural toughness, with improvements of ap-proximately 3.8 times compared to specimens without reinforcement.