The objective of this study was to examine new attributes and conduct economic analyses for composite CLT (CCLT) and value-added appearance-based CLT products manufactured with varying substitution of softwood lumber with structural composite lumber (SCL) and hardwood lumber. Incentives for including such materials could be aesthetic, structural and economic.
Structural and aesthetic property assessments were carried out on prototype CLT panels. Multiple CLT panel configurations (17) were evaluated to assess the effects of including hardwood and SCL materials in the layups. Presence of hardwood in the panels’ configuration generally led to higher checking and density. Because of the higher shrinkage of hardwood, the bondline suffered from more delamination. A lower density hardwood (aspen) was included in some configurations and exhibited a greater direct compatibility with current Canadian manufacturing process. Changes to this process, such as selecting a hardwood specific adhesive may lead to improvements.
SCL’s inclusion in the panels’ layup revealed to be fairly compatible with the current CLT manufacturing process. Both LVL and LSL products performed equally well or better than the reference lumber-made CLT panel for the bondline quality, dimensional stability and visual defects development. The efficiency of the manufacturing process of the prototype CLT panels was improved when EWP was included in the layup. The lesser amount of components and the readily flat surface of SCL may have a positive impact on the economics of CLT manufacturing due to an improved efficiency.
Substitution products evaluated are characterized by a higher market price than lumber. CLT made from a combination of LSL or LVL and softwood lumber would cost about $100/m3 more to get the same return if there were no changes in the manufacturing. The burden of this cost increase would have to be offset by unique series of attributes that would add value for the customer and/or by a greater manufacturing efficiency.