Flexural properties evaluation of homogeneous and hybrid hardwood cross-laminated timber (CLT): A comparative analysis using destructive and non-destructive methods

Several studies have demonstrated that the strength properties of hardwood cross-laminated timber (CLT) panels significantly exceed those of softwood CLT panels. In this study, the flexural properties of homogeneous and hybrid hardwood CLT were investigated using non-destructive (NDT) and destructive testing methods. Phenol-resorcinol-formaldehyde (PRF) and one-component polyurethane (1C-PUR) adhesives were used to fabricate CLT panels of homogeneous red oak, red maple, and hybrid red oak – yellow poplar panels. NDT measurements on the CLT beams were performed using transverse vibration (TV) and longitudinal stress wave timing (SWT) techniques. Using yellow poplar for the transverse layer did not significantly affect the modulus of elasticity (MOE) and modulus of rupture (MOR) of the CLT specimens but resulted in a density reduction of 9–12 %. Using PRF adhesive resulted in a higher average MOR than PUR, but the difference was significant only in the case of the red maple species. A strong linear regression was observed between the dynamic MOE (MOE d ) and the static mechanical properties, especially between the dynamic MOE measured by the longitudinal stress wave timing method (MOE d,SWT ) and MOR of the homogeneous CLT samples. Non-destructive testing methods (Transverse vibration, Longitudinal stress wave timing) allow the prediction of static mechanical properties for hybrid hardwood CLT with nearly the same level of accuracy as for homogeneous hardwood CLT. From a utilization perspective, hybrid CLT made from hardwood species can be an excellent choice when high mechanical performance is required along with moderate product density. • The mechanical properties of red oak and red maple CLT exceed those of softwood CLT. • Using yellow poplar as a transverse layer helps reduce weight while maintaining mechanical performance. • Dynamic MOE shows stronger correlations with MOR than static MOE. • NDT methods are effective for evaluating the mechanical performance of 3-layer hybrid CLT.