Comparative Analysis of Adhesive Types on the Physical and Mechanical Performance of Glued Laminated Bamboo

In the context of the urgent need for decarbonization in the construction sector, glued laminated bamboo (GLB) has emerged as a renewable structural alternative, yet the effect of adhesive chemistry on its performance remains poorly isolated from other manufacturing variables. This study compares three adhesives, polyvinyl acetate (PVA), urea–formaldehyde (UF), and polyurethane (PUR), used to bond GLB from Phyllostachys pubescens (Moso) bamboo under identical manufacturing conditions. Physical characterization (density, moisture content, water absorption) and mechanical tests (compression, direct tension, three-point bending, and shear, parallel and perpendicular to the grain) were performed, with DIC resolving strain localization at bond lines and one-way ANOVA with Tukey’s HSD test assessing significance. PUR-bonded specimens remained intact throughout 23 days of immersion, absorbing 64.0% and 34.1% more water than PVA- and UF-bonded specimens, which delaminated after 7 and 12 days, respectively. Sensitivity to adhesive type varied systematically with loading mode: fibre-governed properties differed by at most 19% between adhesives in compression parallel to the grain, where the effect was significant only between UF and PUR (p = 0.005), whereas tension perpendicular to the grain, governed by the bond line, varied by a factor of 4.8 (p < 0.001), with PUR outperforming PVA and UF. Beyond strength, the adhesives produced distinct post-peak and failure behaviours: UF exhibited an extended, ductile yielding plateau under perpendicular compression, PUR showed a pronounced post-peak drop under compression, while under shear it produced the most gradual response and the highest absorbed energy; UF displayed abrupt, stepwise load drops under shear. In three-point bending, peak strength was fibre-governed, but the post-peak response differed: PUR showed the most abrupt load drops, whereas UF decayed more gradually. These findings guide adhesive selection in GLB according to loading mode and moisture exposure.