Field Performance of Glued Laminated Timber (Glulam) Manufactured from Thin Treated Lamina

Abstract

Glued Laminated Timber, commonly referred to as Glulam, is an important structural wood product, suitable for use in exterior applications provided it is protected against decay by building design, natural durability, or treatment. Bonding treated lamina made from refractory species is challenging because resurfacing after treatment can remove much of the treated zone and create a waste disposal challenge. It was hypothesized that use of roll-pressing rather than resurfacing could address this. When an adhesive modifier was used to prevent the adverse effects of wood preservatives on adhesive bonding, treated lamina that were replaned before gluing had similar shear strength to untreated planed lamina. However, the treated lamina that were roll-pressed before gluing had lower shear strength than the replaned lamina. The consequence of this weakening was evident in an above-ground field test where delamination was observed in several test units after 12 years of exposure. Decay resistance was evaluated in above-ground, ground contact, and ground proximity tests. The decay resistance of treated glulam was high with only low levels of decay reported in all tests, while untreated controls showed advanced decay or failure. Yellow cedar glulam, included as a reference in the ground proximity test, showed moderate decay after 10 years of exposure.