Ultrasound velocity mapping to evaluate gluing quality in CLT panels from plantation wood species

Evaluation of the glue line in CLT panels and in other wood composite products in general is of great interest. Non-destructive methods such as determination of the velocity of ultrasound waves going through the materials are commonly applied to evaluate wood products. The present work is aimed at mapping ultrasound velocity (UV) to identify problems of glue line delamination in CLT panels of 3 and 5 layers made from Gmelina arborea and Tectona grandis timber. The results showed higher UV in the 3-layered panels in both timber species, and low UV and the presence of regions of low velocity in UV isocurves of the 5-layered CLT panels, due to separation of glue line, such as un-gluing and delamination. A UV reference value for glue line free of delamination problems of 927 and 1039 m/s was set for CLT panels of G. arborea of 3 and 5 layers, respectively, and of 1073 and 946 m/s for CLT panels of T. grandis of 3 and 5 layers, respectively. Values below the UV reference suggest the presence of some anomalies or problems of delamination, such as gluing defects.