Breaking barriers in underwater construction: A two-stage 3D printing system with on-demand material adaptation

Underwater concreting remains one of the most challenging construction activities, which has resulted in the development of complex material formulations to minimize washout. The automation and customization offered by 3D concrete printing (3DCP) presents a promising pathway for advancing underwater construction but adds additionally complexity to material formulations. In this study, we highlight the capabilities of a two-stage 3DCP system that can inject an admixture at the nozzle with real-time dosage control (an in-built feature of the most two-stage systems). By printing samples with varying overhang angles in both air and underwater, we demonstrate the ability of the two-stage system to overcome major obstacles in underwater construction. In addition to providing real-time modification of extruded material properties, this approach eliminates the need for addition of anti-washout admixtures prior to pumping, which often comprise flowability and strength. While experiments were conducted in static water environments, the system's in-built real-time control mechanism suggests potential adaptability to fluctuating underwater conditions, warranting further investigation. Our findings offer a scalable, responsive framework for 3D printing that could transform the future of marine and offshore construction.