Assessment of bonding durability of CLT and glulam made from oak and mixed poplar-oak according to bonding pressure and glue type

Abstract

The objective of this study is to evaluate the influence of manufacturing parameters on the bonding quality of CLT and glulam made from oak and mixing poplar and oak species. Studied bonding parameters were bonding pressure and glue type. To test the bonding durability, the specimens were subjected to a vacuum pressure cycle followed by drying to the initial weight. The bonding quality was then measured from delamination, residual shear strength, and wood failure percentage (WFP). Bonding pressure and type of glue appeared to have a significant influence on the bonding quality of CLT or glulam, with also significant interactions with the kind of species bonded. If a 0.8 N/mm² bonding pressure seemed to provide better results, vacuum-pressed (0.085 N/mm² bonding pressure) mixed poplar-oak CLT or glulam glued with PUR were very close to reaching the requirements of the standards. Generally, CLT or glulam entirely made from oak delaminated more than the mixed specimens. However, their residual shear strength can be comparable or even superior to what was obtained with mixed poplar-oak specimens. As a result, residual shear strength after delamination test may be interesting to consider as an additional criterion to assess glue line integrity of hardwood CLT or glulam products.