Investigation of green-glued laminated timber from the Congo Basin: durability, mechanical strength and variability trends of the bondlines

The development of glulam may give complementary, added-value to an important part of the timber production in the Congo Basin. Nevertheless, the high humidity in which these timbers operate may cause problems such as cracks and severe deformations if they are not suitably bonded. Moreover, there is a lack of knowledge concerning the refined design of the bondlines of glulam assembling from the Congo Basin hardwoods. We investigated the durability, mechanical strength, and variability features of the bondlines, manufactured under higher moisture conditions. Eight hardwood species with very different properties were selected. A one-component polyurethane adhesive was used. Industrial gluing parameters were kept constant. Delamination, shear tests and analysis of bondlines thickness were carried out. Multivariate analysis and a goodness-of-fit test of the strength variability of the bondlines were performed. Optimum bondlines thicknesses were obtained. Their durability exhibited satisfactory trends up to a density of 750 kg/m3. The behaviour of the bondlines can operate in three homogeneous groups. In each of them, the variability of the shear strength can be properly modelled using a 3-parameter Weibull probability. Wood failure trends were in accordance with several international requirements. The density value of 750 kg/m3 appeared as critical for the compatibility between the shear strength, the durability and the bondlines thickness. The overall results showed the ability of several tropical timber species to be valorised in green-glulam applications. Moreover, the findings unlock new trends concerning a reliable and safe design of tropical glulam as a structural wood-based product.