3D Printable Eco-Efficient Mortars Under Salt Water (2025-11)¶

Concrete 3D Printing (3DP) is an emerging technology with significant potential to improve construction productivity, reduce material consumption and waste, and enable complex shapes. It is particularly promising for construction in challenging environments such as underwater infrastructure. However, traditional printable mortars are heavily dependent on Portland cement with high carbon footprint, motivating the development of low-carbon alternatives. This study aims to formulate and characterize at macroscopic scale low-carbon 3DP mortars suitable for both air and controlled submerged saline environments, with and without an Anti-Washout Agent (AWA). Mortars were designed using a blend of Portland cement, slag, and limestone filler. Fresh and hardened properties were characterized at the laboratory scale, followed by printing simple shapes in air and under salt water to evaluate printability, mechanical strength, and porosity. The results show that the developed mortars can be successfully printed in both environments. The addition of AWA increased water demand, which negatively impacted printability and mechanical strength. Mechanical tests revealed slightly higher compressive strength in 3D printed samples compared to moulded ones, with minimal anisotropy related to printing direction. Surface porosity was much higher than bulk porosity for mortars printed under salt water (88 % and 69 % increase for mortars without and with AWA). A comparable increase in surface porosity was observed in the air for mortar without AWA (68 %). However, adding AWA reduced very significantly surface porosity in comparison to the bulk for air-printed samples (15 % increase). This research demonstrates the feasibility of low-carbon 3DP mortars for underwater construction, providing valuable insights for sustainable concrete 3D printing applications.