3D-Printed Low-Carbon UHPC Using Limestone Calcine Clay Cement (LC3)

Previous studies by the authors and others have shown that ultra-high performance concrete (UHPC) is an ideal printing material for 3D concrete printing (3DCP). However, its high carbon emissions may limit its application in 3DCP. As a solution, this study reports the development of a 3D-printed low-carbon UHPC using limestone calcined clay cement (LC3), denoted as 3DP-LC3-UHPC. The fresh and hardened properties of 3DP-LC3-UHPC were evaluated and compared with those of conventional 3D-printed UHPC using Portland cement (3DP-PC-UHPC). Conventionally mold-cast mixtures were also prepared for comparison. Fresh properties included flowability, setting time, rheological properties, extrudability, and buildability. Hardened properties included compressive strength and flexural performance in different directions. The effect of two curing regimes (heat- and ambient temperature-curing) on hardened properties was also investigated. The results showed that 3DP-LC3-UHPC possessed higher dynamic yield stress, plastic viscosity, and thixotropy recovery, and exhibited satisfactory extrudability and buildability. The 3DP-LC3-UHPC achieved compressive strengths of 130.4-169.4 MPa and flexural strengths of 26.9-30.6 MPa, depending on the testing direction. Environmental and cost assessments confirmed that 3DP-LC3-UHPC reduces carbon dioxide emissions, embodied energy, and cost by about 25%, 10%, and 9%, respectively, compared to 3DP-PC-UHPC. Overall, the findings demonstrate that 3DP-LC3-UHPC is a sustainable and cost-effective alternative to conventional 3DP-PC-UHPC.