Scholarly record
NON-DESTRUCTIVE EVALUATION OF STRUCTURAL ANISOTROPY IN 3D-PRINTED MORTAR USING MULTI-FEATURE IMPACT-ECHO ANALYSIS
Abstract
Extrusion-based three-dimensional concrete printing (3DCP) produces a periodic layer structure that renders the printed material inherently anisotropic. Quantifying this anisotropy non-destructively is essential for in-situ quality assurance. In this study, impact-echo (IE) signals were acquired on 52 laboratory-produced 3D-printed mortar prisms in two layer orientations: K (layers perpendicular to the test surface) and R (layers parallel to the test surface). Three IE wave types per specimen - longitudinal (FL), flexural (FF), and torsional (FT) - were recorded, and 36 signal features were extracted, covering amplitude, spectral, decay, and onset descriptors. Unsupervised principal component analysis (PCA) yielded a biplot in which K and R specimens occupy partially separated regions along PC1 (21.7% explained variance). Non-parametric Mann-Whitney U tests with Benjamini-Hochberg FDR correction (alpha = 0.05) identified five statistically significant features: the dominant frequency of the FF wave (fdom,FF, r = +0.78, p-adj less than 0.001) and FL wave (fdom,FL, r = +0.59, p-adj = 0.005) ranked highest, with R specimens resonating approximately 12% higher than K specimens. Supplementary discriminators included the FL-wave crest factor (r = +0.56), FT-wave SNR (r = -0.54), and FL-wave RMS amplitude (r = -0.44). A sensitivity analysis excluding twelve paired specimens confirmed the two dominant-frequency features as robust.
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