Use of northern hardwoods in glued-laminated timber: a study of bondline shear strength and resistance to moisture

Abstract

The growing demand for engineered wood products in the construction sector has resulted in the diversification of the product offer. Used marginally in structural products in North America, northern hardwoods are now attracting a growing interest from industry and policy makers because of their outstanding strength as well as their high availability and distinctive appearance. Currently, there is no standard in Canada governing the use of hardwoods in the manufacturing of glued-laminated timber. As part of a larger project aiming to assemble the basic knowledge that would lead to such standard, the specific objective of this study was to assess the shear strength in dry and wet conditions of assemblies made from different hardwood species and structural adhesives. Results suggest that a mean shear strength as high as 20.5 MPa for white oak, 18.8 MPa for white ash and respectively 18.2 MPa and 17.4 MPa for yellow birch and paper birch can be obtained in dry conditions. The choice of adhesive did not affect the dry shear strength of our specimens, but differences were observed in wet conditions. Specimens bonded with melamine-formaldehyde adhesive had generally the highest wet shear strength and wood failure values. Our results also highlight the important influence of wood density on the percentage of failure that occurs in wood and, to a lesser extent, on shear strength. Further investigations on finger joint strength and full-size bending tests will allow confirming the potential for the investigated species to be used in glued-laminated timber.

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

“…Several studies showed that MUF bonded hardwood produced more than 2 times lower delamination compared to PUR bonding [30][31][32]. A recent study on white oak, white ash, yellow birch, and birch glulam specimens bonded with melamine-formaldehyde (MF) and two-component PUR (2C-PUR) showed that the loss of strength induced by the moisture and differential wood swelling caused by the vacuum-pressure cycle was considerable (50%), especially for high-density specimens bonded with 2C-PUR adhesive (around 60% reduction) [32]. Knorz et al [30] compared the bonding quality of glulam made of ash with various adhesives i.e.…”

Predicted and Experimental Bending Behaviour of Glulam Bonded by RPF Adhesive

“…Another hardwood that is increasing in its use in glued laminated timber is oak. This strong but brittle hardwood is also known for its increased content of extractive substances in the wood and specific behaviour at increased humidity [8]. Softwoods, such as poplar or alder, are also of considerable interest [9].…”

Thermal Transmittance, Dimensional Stability, and Mechanical Properties of a Three-Layer Laminated Wood Made from Fir and Meranti and Its Potential Application for Wood-Frame Windows

“…In addition, the currently growing demand for engineered wood products is largely attributable to their outstanding ecological performance. The substitution of materials having a larger ecological footprint, such as steel and concrete, by structural engineered wood products like laminated wood has proven to be effective in minimizing the environmental impacts of the building sector [1]. Furthermore, laminated wood is a material of a great aesthetic value, with various applications in the field of building components, such as doors and windows, and in the field of timber structures of big and small spans [2,3].…”