To expand the use of cross-laminated timber (CLT) to exterior applications, there is a need to protect the panels from biodegrading agents such as fungi and termites. Pressure treatments are effective methods of increasing the durability of wood and wood-based products; however, studies on pressure-treated CLT are limited. In this study, preservative-treated CLT samples from prefabricated CLT panels were prepared and impregnated with Cu-based preservatives through a conventional vacuum-pressure process. The effects of panel layup (3-ply parallel, 3-ply perpendicular, and 5-ply parallel) and preservative treatment (untreated [control], copper azole-type C [CA-C], and micronized copper azole-type [MCA]) on the bonding performance were investigated. Panel layup and preservative treatment had a significant influence on the block shear strength and percentage of wood failure (WFP) of the treated panels. Overall, approximately 60 percent of the block shear specimens had a WFP of >75 percent. However, fewer than 10 percent of the delamination specimens met the ASTM D2559 (2018) limitation of 1 percent for softwood used in outdoor applications. ASTM D2559 counts shallow wood failure as delamination, which could have been a reason for the high delamination rate. The percentage of wood failure and the high rate of delamination could be due to the moisture-induced adhesion failure resulting from the pressure-treatment process. The preservative pressure-treatment of the CLT panels increased the moisture content (MC) from 12–15 percent to approximately 85 percent MC, and the severe swelling of the panels during treatment might have imposed a high stress on the bond line. However, no noticeable delamination of the panels was observed during the actual treating phase of the study. These results show the feasibility of treating prefabricated CLT panels with CA-C and MCA preservatives without compromising the bonding strength.

This study investigated the influence of wood grain angle (0, 10, 20, 30, 45, 60, 75, and 90 degrees) on acoustic emission (AE) characteristics of southern yellow pine columns subjected to compressive loading. Four AE parameters considered were counts, cumulative counts, count rate, and amplitude. The main conclusion was that AE cumulative counts versus time curves can be characterized with three distinct stages in terms of AE count rates: initiation, growth, and acceleration. The initiation stage had a constant mean count rate of 0.33 counts/s compared to the growth stage mean count rate of 19.10 counts/s, while the acceleration stage had a mean count rate of 608.40 counts/s. Within each stage, count rates increased as grain angle increased from 0 to 30 degrees, then dropped as grain angle further increased to 90 degrees. Maximum AE counts and total cumulative AE counts all increased as grain angle increased from 0 to 30 degrees and decreased as grain angle further increased to 90 degrees. Higher AE amplitudes were observed in the yield and failing stages of tested wood columns according to their stress-strain curves plotted together with their corresponding amplitude-time curves. Maximum amplitude increased as grain angle increased from 0 to 20 degrees, then had a decreasing trend as grain angle increased to 45 degrees, followed by an increasing trend as grain angle increased to 75 degrees. These differences in AE characteristics suggested that AE “signatures” in terms of AE signals do exist for timber materials when subjected to compressive loading.

Four mechanical models were proposed to derive formulas predicting the bending moment capacities of layered particleboard under simply supported center-loading. Experimental validation confirmed these models are effective tools for describing the bending moment development process, including proportional limit, yield, and ultimate points. With predicted and experimental ratios ranging from 0.88 to 1.04, Model 4 can reasonably predict the ultimate bending moment capacity of elastic–plastic and bi-modular-layered particleboard materials. Photo-elastic testing revealed neutral axis shifting toward the compressive side, resulting from the face layer’s significantly higher mean modulus of elasticity in compression than in tension. Additionally, the core material above the centerline of PB thickness contributed to tensile resistance. The proposed mechanical models require inputs such as the tensile and compressive strengths and thickness of each layer, accounting for the asymmetric strength profile and neutral axis shifting. The main conclusion was that the bending moment resistance of the particleboard depends on the combined effect of tensile and compressive strengths of all layers. A 3D plot visualized the PB’s mechanical design space, displaying feasible tensile–compressive strength combinations of particleboard layers. This enables determination of optimal strength properties for each layer. For M2 grade particleboard, the most cost-effective design occurred when the face layer reached a 5.38 MPa tensile strength, with the compressive strength ranging between 13.00 and 18.59 MPa.