An approach to develop set-on-demand 3D printable limestone-calcined clay-based cementitious materials using calcium nitrate

The implementation of extrusion-based 3D concrete printing (3DCP) in large-scale constructions is currently limited by concerns regarding rheology control and the sustainability of this process. To address these issues, this study presents an approach to develop limestone-calcined clay-based cementitious (LC3) materials accelerated by Ca(NO3)2 solution in an inline static mixer-based 3DCP setup. Using this approach, a printable mixture containing only about 275 kg/m3 of Portland cement was formulated that can exhibit a good buildability performance and a 28-day compressive strength of over 30 MPa. Additionally, the effects of adding Ca(NO3)2 solution on the initial setting time, structural build-up, inline buildability, early-age hydration, and compressive strength of LC3 materials were investigated and discussed. Results show that the addition of Ca(NO3)2 solution improved the buildability and accelerated initial setting as well as the structuration due to the promoted ettringite precipitation and C-S-H nucleation. Furthermore, compressive strength at 7 and 28 days was improved through increasing the Ca(NO3)2 dosage, which can be attributed to the formation of NO3-AFm and the increase in the amount of C-S-H gels.