Evaluation of shear strength and durability of adhesive bond in cross-laminated timber (CLT) panels made from Nigerian Gmelina arborea timber

This study investigates the shear strength and durability of wood-adhesive bonds in Cross-Laminated Timber (CLT) panels made from Nigerian grown Gmelina arborea using one-component Polyurethane (PUR) and two-component Epoxy Resin (ER) adhesives. The block shear test and delamination test, conducted in accordance with EN 14080 (2015) and EN 16351 (2015), were employed to assess the bond quality and durability. The maximum shear strengths observed were 3.37 MPa for PUR and 2.78 MPa for ER, with respective minimum values of 2.88 MPa and 2.45 MPa. Wood failure percentage (WFP) analysis indicated that ER exhibited slightly better adhesive performance under dry conditions, while PUR demonstrated superior performance after delamination. A moderate positive correlation (r ≈ 0.579) was found between shear strength and WFP for PUR, whereas ER showed a very weak correlation (r ≈ 0.015), suggesting differing performance characteristics between the adhesives. The delamination test results showed PUR generally outperformed ER, particularly in smaller CLT-60 panels, indicating better bond durability. A strong positive correlation (r ≈ 0.984) between total delamination (Dtot) and maximum delamination (Dmax) was identified, while no significant correlation was found between delamination and WFP. The findings suggest that while PUR offers higher shear strength and better durability, ER provides more consistent adhesive performance. Panel size was also found to influence the bonding performance, with smaller panels exhibiting lower delamination percentages. Overall, PUR appears more suitable for applications requiring high durability, particularly in smaller panels, while ER might be preferable for larger panels where consistent bond quality is critical.