The use of shank-containing screws to provide the adhesion pressure needed during CLT manufacturing using young Eucalyptus wood

Abstract

In the last two decades, wood has regained relevance in the construction industry of Europe, mainly driven by the adoption of cross laminated timber (CLT). This trend has reached other regions, but specially in developing countries this demand is facing a bottleneck: the high costs of the equipment for CLT manufacturing and the skilled labour to operate it. This study has the objective to test CLT samples manufactured with a novel and simple method using shank containing screws to generate pressure for the adhesion of layers. Three screw densities were used (30, 50 and 100 screws m⁻²) and compared to control samples (manufactured in a press under 0.5 MPa). Screws generated an average load of 0.85 kN and the interaction of wood and thread seemed more important than the interaction of wood with the head. All treatments met the shear strength on the glue line requirements from standards, with equivalent average values, approximately 3 MPa. Only the control treatment met the technical standard requirements for total and maximum delamination (10 and 40%) or minimum and average wood failure (50 and 70%). The 50 screws m⁻² treatment was close to meeting one of the delamination requirements, 40% maximum delamination. Although not fulfilling all the requirements, the CLT standard considers the use for high-rise buildings and the proposed method could be adopted for less demanding applications, such as single and double storey residences. Changes can be made on the manufacturing parameters to decrease the delamination, starting from the adhesive used and the screw geometry. With more research, the new method described can unlock the adoption of CLT in less developed regions that will be beneficial for the local economy since the forest and timber industry can generate many jobs and promote the adoption of wood buildings.