Use of seawater as an accelerator in 3D printed concrete (3DPC)

Seawater (SW) is one of the viable alternatives to replace freshwater (FW) for producing concrete in regions facing extremely severe water stress. Seawater has high potential to be used as a set-on-demand accelerator among the other expensive materials being widely researched in additive manufacturing. The current study evaluated the progress of heat of hydration in 3DPC-FW and 3DPC-SW mixes using isothermal calorimetry. Furthermore, fresh and early-age properties of these mixes were studied using a flow table, manual shear vane, uniaxial unconfined compressive strength tests, and dynamic elastic modulus development. Strength development and shrinkage progress up to 28 days were evaluated. A detailed investigation reveals that an increase in compressive strength from the very first hours of hydration, a reduction in workability which could be compensated by modifying SP, and higher shrinkage were observed in SW-mixed 3DPC compared to the FW-mixed counterpart. Furthermore, the potential improvement in the speed of printing is highlighted in this study with 3DPC-SW mix demonstrating acceleration in early strength.