Experimental assessment of bond-line shear strength and delamination resistance in sweet chestnut glulam

Sweet chestnut ( Castanea sativa Mill.) is a locally available hardwood species with promising mechanical properties, natural durability, and potential for engineered wood products. However, its low permeability, high tannin content, and anatomical variability may affect adhesive bonding and limit its use in glued laminated timber. This study investigates the bond performance of sweet chestnut glulam manufactured with a melamine–urea–formaldehyde adhesive system. Four laminated elements were produced from conditioned chestnut boards at a wood moisture content of 12 ± 1 % , using an adhesive-to-hardener ratio of 100:30 parts by weight, an adhesive spread of 400 g/m 2 , a pressing pressure of 1.3 N/mm 2 , and assembly times of 30, 45, and 60 min. Bond performance was assessed through longitudinal shear block and delamination tests based on European standard procedures. Shear testing was limited to the 45 min condition; delamination was assessed at all three assembly times without independent replication of each condition. Longitudinal shear tests showed favourable bond-line resistance, with a mean shear strength of 11.31 N/mm 2 and a standard deviation of 1.54 N/mm 2 . Failure occurred predominantly in the wood, while complete adhesive failure was observed in only one valid test. Considering all tested glue lines, 5 of 15 specimens had an average delamination below the adopted 5% diagnostic reference level after one moisture cycle. A secondary analysis restricted to glue lines without visible pre-existing defects indicated that localized manufacturing defects contributed substantially to the observed delamination; this restricted analysis does not represent the as-manufactured performance of the elements. Under the investigated conditions, the shear results provide preliminary evidence of effective MUF bonding in sweet chestnut, but the study does not establish an effect of assembly time on bond performance.