Influence of limestone calcined clay cement on properties of 3D printed concrete for sustainable construction

The research on emerging digital construction techniques, particularly the 3D concrete printing of cement-based materials, is imperative owing to the several economic, environmental, and societal benefits it offers over conventional cast-in-place concrete. In this study, limestone calcined clay cement (LC3) was utilised for 3D printed concrete (3DPC) production towards sustainable composite infrastructure by replacing up to 50% of ordinary Portland cement (OPC) with limestone and calcined clay (LC2). The fresh, rheological, and hardened mechanical properties of fibrereinforced 3DPC were investigated. Six different 3DPC mixes were made for these purposes: the control (no LC2), four mixes with 1.0, 0.91, 0.8, and 0.6% superplasticiser (SP) dosages, and the last mix without micro-synthetic polypropylene fibre. Findings revealed that achieving a slump of less than 10 mm and a slump flow between 140 and 160 mm as required by relevant standards (ASTM C1437 & C230/C230 M) is crucial in obtaining an extrudable 3D concrete mixture. A finite flow value and satisfactory rheological properties are achieved in mixes C (with 0.6 SP), D (0.8 SP), and Dadj (0.91 SP) to produce a feasible 3D printable cement-based concrete mixture. Test results validated the promise of LC2 as a partial replacement for OPC in digital concrete depending on the testing orientations of the printed samples. Buildability performance using a gantry-type 3D printer was conducted and the significant orthotropic phenomenon was indicated in the compressive properties of printed samples. The presence of fibres toughened the cylindrical strength perpendicular to the layer-interface-plane and enhanced the bearing load in tension and flexure, thereby making the direction 1 (D1) interfacial flexural/tensile bearing capacity comparable to cast-in-situ 3DPC samples.