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MATERIALS 55
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attracted attention among researchers, particularly the use of
renewable resources like lumber. Miguel Á. Padriñán
Cross-laminated timber (CLT) is gaining popularity as
a sustainable alternative to traditional building materials

because of its advantages, such as massive dimension, high
prefabrication potential, reduction in construction time, seismic
safety, lightweight, and ease of installation.
Conventional CLT comprises panels with three to nine
layers of wood, bonded orthogonally using structural adhesive.
Global production of CLT panels is projected to reach three
million cubic metres by 2025, with Europe contributing two
million cubic metres in 2023.
Traditionally, CLT panels have been made from softwoods For the hardwood species, rolling shear failure is often

such as spruce, pine, and fir. However, the increasing demand caused by the density variation between early and late wood,
for CLT and the decline in forest cover have driven researchers especially at the interface.
to explore the use of lower-grade plantation-grown hardwoods, The rolling shear modulus of conventional spruce CLT
such as poplar and other cultivated wood species, to meet varies from 100 to 141 N/mm2 which is reportedly lower
these needs. than that of hardwood CLT panels such as beech, maple,
Furthermore, new forest management strategies involving poplar, eucalyptus.
the cultivation of lower-grade hardwoods, such as poplar and Hardwoods are known for their superior strength and

willow, have augmented Europe’s hardwood supply. Since rigidity, which enhance the load-carrying capability of CLT
the beginning of the 21st century, numerous studies have panels by reducing the risk of rolling shear failure.
evaluated the suitability of various hardwoods for CLT panels Additionally, hardwood CLT requires 10–15 percent less
in response to changing global forest composition. material than softwood CLT to achieve comparable strength.
Rolling shear is an inherent characteristic of CLT resulting However, the primary challenge with hardwood CLT is its
from the perpendicular arrangement of subsequent layers lower bond strength and durability, as well as its tendency for
and the comparatively low shear strength and modulus increased delamination, as highlighted by various researchers.
perpendicular to the wood.
Additionally, wood has significant anisotropy, indicating that Potential Of Hybrid Or Mixed Species CLT

its properties differ across the three mutually perpendicular axes. Numerous studies have indicated the potential of hybrid or
The shear moduli in the radial-tangential (RT) plane, mixed species CLT composed of various wood species with
often referred to as the rolling shear modulus, can be up to differing densities and grades or structural composites such
ten times greater than the shear moduli in the longitudinal- as plywood, oriented strand board (OSB), laminated strand
tangential (LT) planes. lumber (LSL), and laminated veneer lumber (LVL) to enhance
Softwoods are particularly more prone to rolling shear failure material resources and achieve high-strength structural materials.
due to their elongated wood fibres, which are susceptible However, very limited studies are available on the suitability

to shearing or sliding, as well as their lower shear strength of poplar wood for homogeneous and hybrid CLT manufacturing
along the grain. with a high-density outer layer.