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58 MATERIALS MAR/APR 2025 FDM ASIA | www.fdmasia.com

Denna Jones such as bending, knots, splitting, or fractures, were discarded
During production, lamellas with visible wood defects,

to prevent material faults from affecting the final product’s
quality. The lamellas were randomly picked based on their

visual qualities, following the guidelines provided by Jan
Brundin et al..
The outer layers were devoid of any imperfections and
had dimensions of 2000 mm × 75 mm × 20 mm (length ×
width × thickness), while the lamellas with minor permissible
amounts of defects according to the standard, were processed
for the core layer, with dimensions of 300 mm × 75 mm ×
The kiln-dried lumber exhibited a moisture content of 13 20 mm (length × width × thickness), to prepare CLT panels
percent, and was classified as Grade B. Low-density poplar, of 2000 mm × 300 mm × 60 mm.

demonstrating a moderate load-bearing capacity akin to that As such, a layup was followed as the mechanical properties
of spruce, was used for both the homogeneous CLT and the of CLT are predominantly controlled by the outer layers while
core layer of hybrid CLT panels. the core layer only serves as a link between the outer layers
The external layers of hybrid CLT panels were constructed and transfers the stress while.
from high-density maple, which exhibits exceptional mechanical Using a wooden spatula, one side of the face layers was
qualities. applied with glue at a rate of 180 g/m2 for 1C-PUR and
Additionally, homogeneous spruce CLT was made for 300 g/m2 for ME. Following the manufacturer’s instructions,

comparison. After the acquisition of the lumber, it was the ME was applied using an adhesive-to-hardener ratio of
acclimatised at 20 deg C and 65 percent relative humidity 100:100 (weight-to-weight).
before specimen preparation. The lumber’s modulus of elasticity Following glueing, each panel was assembled and pressed at
(MOE) was determined using the FAKOPP Ultrasound Timer 1 MPa pressure for 1 h at 20 deg C. The production procedure
UT-06/2013, produced by Fakopp Enterprise, Gfalva, Hungary. did not include edge glueing since it had less influence.
The mean density, moisture content and modulus of CLT panels were kept at room temperature for nearly
elasticity (MOE) values of each species have been provided. two days after pressing to completely cure adhesives. After
A single-component polyurethane adhesive (1C-PUR) trimming on both sides, CLT panels were conditioned for three
(Adhesive 2010) and a liquid melamine adhesive (Plus A011), weeks at 65 ± 5 percent RH and 20 ± 2 deg C before testing.

accompanied by a hardener (H011), provided by Akzo Nobel,
were used to fabricate the CLT panels. The objective was to Experimental Testing
evaluate the impact of the adhesive on the panels’ bending EN 16351 compliance four-point bending test was conducted
and rolling shear performance. to evaluate the bending performance, with the span length
The manufacturer and product listing assert that the being 18 times the thickness (h) of the panel (18 h), using the
ME lacks formaldehyde. The 1C-PUR is a pure solid with universal testing machine TIRA 2850 S E5, Germany (TIRA,
a viscosity between 6000 and 19,000 mPas, while a liquid Schalkau, Germany).

hardener with 65 percent solid content has a viscosity ranging Ten replicate samples, with a total of 60 specimens, were
from 1500 to 9000 mPas. examined for each adhesive and layup. The test specimens