Influence of Environmental Exposures on the Mechanical Performance and Durability of 3D-Printed Cementitious and Alkali-Activated Composites.

This study evaluates the mechanical performance, anisotropy, and spatial variability of 3D-printed cementitious and alkali-activated composites under laboratory, atmospheric, and freeze-thaw conditions. Alkali-activated composites exhibited substantially higher shrinkage than cement-based mixtures, reflecting differences in their reaction mechanisms and pore structure development. Compressive strength was measured in two orthogonal directions representing perpendicular (⟂) and parallel (∥) behaviour. Non-activated mixtures exhibited compressive strength of 11-12 MPa, whereas alkali-activated composites reached 19-20 MPa in the reference condition. Atmospheric exposure increased compressive strength by 10-22%, while freeze-thaw cycles did not significantly affect perpendicular strength. Flexural strength of non-activated mixtures remained low (3.7-5.3 MPa), whereas activated composites showed higher values in the reference state (8.8-15.0 MPa) but decreased after atmospheric exposure to 5.3-5.8 MPa. The degree of anisotropy increased significantly for alkali-activated mixtures (from 0.09 to 0.24) while remaining relatively stable for non-activated materials (0.04-0.11). Glass fibres showed no significant degradation after environmental and freeze-thaw exposure, while merino wool fibres exhibited only minor surface irregularities, confirming the potential of both fibre types for use in sustainable lightweight 3D-printed cementitious and alkali-activated composites.