Non-destructive detection of degradation in urea formaldehyde structural wood adhesive bonds by NMR relaxometry

Abstract Low-field nuclear magnetic resonance (NMR) relaxometry was examined as a non-destructive method for assessing degradation of urea-formaldehyde (UF) bondlines of laminated timber members. The study shows that UF adhesive bondlines result in distinct NMR signals between freshly bonded and harshly artificially aged bondlines (A5 treatment according to EN 302-1). Mechanical tensile shear tests showed strength reductions of up to 71%, and a correlation coefficient of $$r=0.96$$ between NMR amplitude ratios and bondline strength was found. This implies that NMR relaxometry could have the potential to detect UF adhesive degradation in laminated timber. As new non-destructive and in-situ testing method options, portable NMR devices could help determine the residual service life of structural glued timber members or support their reuse after service life.