The emergence of 3D printing in the concrete industry has opened up new possibilities for automated, sustainable, and rapid construction. By eliminating traditional formwork and enabling complex geometries, 3D printed concrete (3DPC) promises significant reductions in construction time, labor, and material waste. Over the past decade, research has accelerated on optimizing printable mixtures, improving buildability, and scaling up to structural applications. However, despite these advancements, 3DPC still faces challenges related to quality assurance, interlayer bonding, and long-term durability.

Given the layer-by-layer nature of 3D printing, the structural integrity of printed elements is highly sensitive to defects such as voids, weak interfaces, or uneven curing. Conventional destructive testing is not feasible for continuous monitoring during the printing process or for ensuring reliability in large-scale structures. There is a need for the development of non-destructive testing (NDT) techniques applicable to 3DPC. NDT can play a critical role across the entire lifecycle—from monitoring fresh state buildability and early-age stiffness development to detect defects during service and assessing residual performance under loading.

Guided wave methods are particularly promising because they can propagate over long distances, making them effective for detecting weak interlayer bonding and monitoring stiffness development in real time. Surface wave techniques, such as Rayleigh wave measurements, are useful for characterizing near-surface defects, monitoring curing progression, and ensuring uniformity across layers. Nonlinear ultrasonic methods offer high sensitivity to microcracks and early-stage damage that may not be detected by linear approaches, providing insight into the initiation of degradation. Diffuse ultrasonic waves, on the other hand, can probe multiple scattering regimes within complex printed geometries, offering valuable information about heterogeneity, porosity, and the presence of hidden flaws. Together, these NDT techniques provide complementary insights that can ensure the reliability and structural integrity of 3D printed concrete, supporting its transition from experimental demonstrations to full-scale, load-bearing construction.