3D concrete printing in air and under water: a comparative study on the buildability and interlayer adhesion

3D concrete printing (3DCP) technology is still in the early stages of research in the construction industry, and the development of underwater 3D concrete printing (U3DCP) based on this technology is still in its infancy. To promote the widespread application and adoption of U3DCP, a comprehensive understanding of the performance of 3D concrete printing in air and under water is crucial. In this study, the buildability and interlayer bonding of fresh concrete in different environments were evaluated and compared. The advantages of using water buoyancy to partially counterbalance the weight of concrete and enhance buildability, and the drawbacks of weakened interlayer bonding in a water environment were highlighted. Predictive formulas for the printable height of concrete printed in air and under water considering the impact of time intervals on the characteristics of the concrete, were proposed based on the relationship between the structural build-up coefficient and the height of the printed specimens. The interfacial adhesion of concrete printed in air was higher than that printed under water. However, the interlayer adhesion over time of concrete printed in air decreased faster than that printed under water. Permeability measurements on fresh concrete confirmed that water penetration is mainly responsible for the differences observed in interface adhesion.