Abstract
Mass Timber Construction has become a popular alternative to conventional steel and concrete in high rise buildings in Australia. Products like Glue Laminated Beams and Cross Laminated Panels introduce a more sustainable footprint. There are; however, perceived concerns with the durability and service life of these products. Such concerns are legitimate as water ingress into or wetting of the timber structure during construction and in-service are common even though proper building design and detailing dictate water exclusion at all life stages of buildings. Another way to mitigate water damage and promote durability is with preservative treatments. Fabrication practicality, preservative efficiency and economics suggest that treatment should be integrated into the manufacturing process i.e. be part of the pre-gluing processes. However, some treatments can reduce resin properties. The effects of preservative treatments on the gluability and bond strength of polyurethane (PUR) adhesives was explored to determine the potential for integration of preservative treatments in the fabrication process. Sodium Borate Anhydrous, Sodium Borate Pentahydrate, and Alkaline Copper Quaternary (ACQ) were investigated at 1% and 3% concentrations. To adhere as closely to efficient manufacturing, treatment was integrated with the planing and layup processes as follows: lamella planing, treatment application, short drying, resin application, pressure application, and >24-h curing. One untreated series of 10 samples was also fabricated. The samples were subjected to tension tests that created shear action in a purposely cut delimited bond area. Untreated timber samples exhibited the highest shear strength at 4.4 ± 2.3MPa, while the 3% concentration ACQ solution performed the worst at 0.8 ± 0.3MPa. All samples experienced brittle failure modes that originated from cohesion or adhesion failures, or both, as well as shear failure of the timber substrate. These results illustrate the potential negative effects of treatment on bond strength, concurring with previous research showing that metallic deposits affected the creation of effective adhesive bonds and that boron compounds affecting the wettability of the timber for gluing.