Influence of Alternative Supplementary Cementitious Materials and Printing Parameters on the Mechanical Properties of 3D-Printed Mortars (2025-11)¶

Large-scale cement-based additive manufacturing, commonly known as 3D concrete printing (3DCP), exhibits greater porosity than traditional cast concrete, with pores mainly concentrated at interface regions, forming interconnected channels that negatively affect their mechanical properties. Additionally, 3DCP has a larger environmental footprint than conventional concrete due to the high cement content in printable mortars (~ 480 kg/m3). One strategy to reduce the environmental footprint is to replace cement with locally available supplementary cementitious materials (SCMs). On the other hand, printing parameters can be optimised to improve the hardened properties of 3D-printed structures. This research aims to assess the feasibility of locally sourced (zeolite and calcined clay) and recycled (mussel shell powder) SCMs in 3DCP mixes, and analyse the effects of printing parameters (filament overlap and nozzle offset) on the mechanical properties. The mechanical properties (elastic modulus, compressive strength, and splitting tensile strength) of 7 mixes were tested at different ages. Results showed that mussel shell powder delayed the binder hydration, decreasing the compressive strength of LC3LCMS and Z40MS cast (by 38.2% and 8.8%) and printed samples (by 11.2% and 13.4%) compared to their counterparts with calcium carbonate at 90 days. Z40 showed the greatest compressive strength results at all ages besides the benchmark samples with metakaolin, achieving a maximum compressive strength of 69.9 ± 1.4 MPa and 53.4 ± 4.6 MPa at 90 days for cast and printed samples, respectively. A 4 ± 1 mm filament overlap improved the mechanical properties and reduced the anisotropy.