Experimental investigation on the effect of accelerated ageing conditions on the pull-out capacity of compressed wood and hardwood dowel type fasteners

The widespread use of adhesives in timber construction has negative implications for the end-of-life disposal or re-use of the structural timber components. To promote the circular bioeconomy, it is preferable to substitute adhesives with more sustainable alternatives such as wood-based connectors. Today, robotic fabrication technologies facilitate the development of dowel-laminated timber (DLT) products whereby hardwood dowels are used to connect timber laminates as a substitute to adhesives. In recent years, thermo-mechanical densification of wood has resulted in significant improvements in the mechanical performance of the wood. This modified product often termed compressed wood (CW) has a shape-recovery effect which may be beneficial for the development of DLT products and timber-timber connections with improved friction fit with time. To test the hypothesis, accelerated ageing tests were carried out on CW-timber and hardwood-timber dowel type connections subjected to variable climate conditions. Finally, the capacity of the connections or friction fit was assessed using pull-out tests. Results show that the shape-recovery effect leads to the continuous expansion of the CW dowels and facilitates a friction fit with the timber substrate yielding higher pull-out loads when compared to hardwood dowels.