Bonding performance of Canadian hardwoods to produce glued laminated timber

Architects and engineers have long desired the use of hardwoods in the production of glued laminated timber due to their interesting mechanical properties and a variety of textures. However, bonding hardwoods has proven challenging because of their complex anatomy and large range of densities. This study aimed to evaluate the bonding performance of four Canadian hardwoods to produce glued laminated timber, namely Quaking aspen (Populus tremuloides Michx.), American ash (Fraxinus americana L.), Large-leaf beech (Fagus grandifolia Ehrh.), and Sugar maple (Acer saccharum Marsh.). Samples were bonded with three different adhesives commonly used for softwood, i.e. 1C-polyurethane (PUr), PVAc and Emulsion Polymer Isocyanate (EPI). Tests were performed according to ASTM D905 and CSA 0122 for determining block shear strength and delamination, respectively; Additionally, the glue line profile was assessed with a micro-CT scanner using 5 mm cubic specimens. Aspen and Beech showed satisfactory performance when bonded with PUr and EPI, achieving less than 6 % total delamination and over 8.5 MPa shear strength. The absence of surface preparation with primer impaired the performance of PVAc bonded glulam. The CT-scan method was interesting for analyzing the glue line; however, in some cases, the lack of contrast between wood and adhesive was a limiting factor.