Spray-based 3D concrete printing for complex reinforced concrete components

The construction industry is under increasing pressure to automate, particularly in Japan, where demographic changes are shrinking the pool of skilled workers. Against this backdrop, the Shimizu Corporation has introduced a spray-based 3D printing system for concrete aimed at manufacturing large, curved, and reinforced components. This approach deliberately differs from established extrusion-based methods that deposit concrete layer by layer and encounter technical limitations when integrating reinforcing steel.

At the core of the system is a gantry robot with nine degrees of freedom, combining a seven-axis articulated arm with a two-axis XY positioning unit. This configuration enables coverage of a build volume measuring six meters in depth, four meters in width, and three meters in height. The spray process allows concrete to be applied from variable angles and distances, making it possible to fully encase even complex reinforcement cages. Motion planning is not carried out purely empirically but is supported by a material spray simulation.

This simulation was developed jointly with the Computational Engineering and Robotics Lab at Carnegie Mellon University, led by Professor Kenji Shimada. The model developed at the Computational Engineering and Robotics Lab makes it possible to optimize nozzle paths, spray distance, angles, speed, and material feed rate in advance. The goal is to reduce material accumulation and defects while improving the dimensional accuracy of the components.

In initial demonstrations, a twisted, curved wall with cantilevered upper and lower sections was produced. The approximately 2.5-meter-high component was completed within four hours and served as a proof of feasibility for complex geometries. Looking ahead, Shimizu sees spray-based 3D printing as a way to reduce personnel requirements on construction sites while simultaneously expanding design freedom in reinforced concrete construction. Further development work is intended to increase the level of automation and prepare the technology for use under real construction site conditions.