Interface-Controlled Structural Behaviour of 3D Printed Concrete: Lessons from Masonry for Anisotropy, Print-Path Design and Standardisation.

The structural application of 3D printed concrete (3DPC) is still constrained by the difficulty of qualifying a layered, process-dependent material using standards developed mainly for cast concrete and conventional masonry. This review examines 3DPC through masonry construction to clarify how interface-controlled behaviour should be interpreted, tested and standardised. The comparison is not based on material similarity, but on the shared structural role of joints, interfaces and assemblage-level load transfer. Most previous reviews mainly discuss printability, mixture design, material development or general mechanical performance. This review instead places the printed interface at the centre of structural qualification, using masonry only as a reference for interpreting joint-controlled load transfer. The review shows that compressive strength alone is insufficient for structural qualification, since printed elements may fail through interlayer debonding, direction-dependent cracking, filament instability, reinforcement discontinuity or connection weakness. Flexural, shear, cyclic and seismic responses are particularly sensitive to interlayer quality, loading orientation and print-path geometry. Existing concrete, mortar and masonry standards remain useful references, but require 3DPC-specific reporting and testing. Accordingly, a tiered qualification route is proposed, progressing from fresh-state characterisation to interface-dominated testing and structural-scale validation.