Bonding quality of cross-laminated timber: Evaluation of test methods on Eucalyptus grandis panels

The objectives of this study were (1) to analyse different testing methods for evaluating face-bonding quality of cross-laminated timber from Eucalyptus grandis timber bonded with a one component polyurethane adhesive and (2) to evaluate the effect of different processing variables on the face-bonding quality of cross-laminated panels. A 3 × 2 factorial design was used to test the effect of clamping pressure, wood density, and presence of stress relief grooves on the bonding quality. Two existing test methods from the EN 16351 standard and two recently developed test methods were used in the evaluation. Among them a combined delamination and shear test, seems to have potential to determine bond quality of cross-laminated timber panels since it evaluates both the durability and shear strength of a joint while minimising the effect of rolling shear. Complex failure behaviour in the different tests and various interactions between the factors evaluated (density, grooves, pressure) make it difficult to reach firm conclusions on the effect of each factor. In general though, the presence of grooves had a negative effect, both increasing the delamination and decreasing the shear strength (whatever the pressure and density used during processing). High clamping pressure was preferable, particularly when high density material was used. Wood density had a positive effect on shear strength when determined on dry specimens, and a negative effect on delamination. Results indicated that the production of Eucalyptus grandis cross-laminated timber could be possible and that face-bonding quality suitable for structural use could be achieved when using a clamping pressure of 0.7 MPa and with no stress relief grooves present.