Cross-laminated timber (CLT) is an industrial building material prepared from wood and wood composite materials, in reasonable combination. As environmental concerns have become more acute, eco-friendly buildings have gradually become more favored (Sandberg, Næss, Brattebø, Andresen, & Gustavsen, 2021). In this respect, wood and wood composites stand out among many building materials due to their superior properties and environmental protection (Cao Lisha, 2020). CLT originates in Austria and Germany, and is typically made of sawn lumber planks which are layered perpendicularly and bonded together with a structural adhesive. CLT is usually used in mass panels, for purposes such as walls, floors and roofs in tall buildings. As a new kind of green building material, CLT has many distinct advantages over solid wood, such as better dimensional stability, better mechanical properties and fire resistance which make it suitable for high-rise wooden structures (Kuilen, Ceccotti, Xia, & He, 2011). Current scientific researches for CLT, has widely covered several key aspects, including the bending properties (Mayencourt & Mueller, 2019), shear properties (Ehrhart T, 2015) and other mechanical properties of CLT (Mohamadzadeh, 2015). The bonding performance (Turesson, Sharifi, Berg, & Ekevad, 2020), sound insulation performance, seismic (Sandoli A 2021) performance and the connection of CLT (Cao, Xiong, Chen, & Huynh, 2019), have also been explored to varying degrees.
To advance the industrialization of CLT, many countries have committed to the development of new native tree species for its preparation, which is beneficial not only for the production and manufacturing of CLT, but also for the development of local timber industries.. In previous studies and applications a softwood was usually used as the laminates to prepare CLT. In recent years, however, hardwood has also been experimentally applied to CLT, such as poplar (Xiaoning, 2016), and ash (Aicher, Hirsch, & Christian, 2016), as well as bamboo (Darzi, Karampour, Bailleres, Gilbert, & McGavin, 2020) and other types, and the use of these new materials has been seen to improve the mechanical properties of CLT.
In addition, many engineered wood-based composites have also been used to prepare hybrid CLT (HCLT), mix with solid wood, such as laminated veneer lumber (LVL) (Wang et al., 2017), laminated strand lumber (LSL) (Wang, Gong, & Chui, 2015) and construction-oriented strand board (COSB) (Qiao, 2020). The HCLT specimens prepared from these engineered wood products usually have good shear and bending properties. Research on the preparation of CLT from wood composite materials has expanded the material sources available for HCLT preparation and promoted the use and industrialization of HCLT. Niederwestberg et al. (Jan Niederwestberg, 2018) reported that LSL applied in the perpendicular layer of HCLT could effectively improve the shear strength. Davids et al. (Davids et al., 2017) tested the shear performance of HCLT prepared by LSL and Spruce Pine Fir (SPF). The results show that the average shear strength of HCLT prepared with SPF is 2.03 MPa, while with LSL it is 2.61 MPa, and the maximum shear strength obtained from CLT with LSL is 2.96 MPa. Meanwhile, the research results of Wang et al. (WANG Zhi-qiang, 2016) showed that the rolling shear modulus and rolling shear strength of HCLT prepared with LVL (laminated veneer lumber) were lower compared to SPF. Hence, as the perpendicular layer of HCLT, LVL only increases the overall density of HCLT, but does not improve the mechanical properties; therefore, it is not recommended to use LVL in the perpendicular layer of HCLT. Whereas, the combination of LVL in the parallel layer and SPF in the perpendicular layer can greatly improve the bending performance of HCLT. The MOE and MOR of HCLT with LVL and SPF reached 9229 MPa and 30.1 MPa, respectively. Wang’s study, which explored the mechanical properties of HCLT with LSL, reported that when LSL was placed in the parallel layer, the MOE and MOR increased by 19% and 36%, respectively, and when LSL was placed in the perpendicular layer, the MOE and MOR increased by 13% and 24%, respectively (Wang et al., 2015). Zhou et al. studied the bending properties of HCLT specimens prepared from LSL, OSL (Oriented Strand Lumber) and SPF. The results showed that LSL and OSL in any layers in HCLT can effectively improve the bending stiffness and strength of HCLT (ZHOU J, 2018).
At present, for the preparation of HCLT, most of the wood based composite materials which were used in HCLT have high density, such as LVL (600 kg/m3) (Wang et al., 2017), LSL (718 kg/m3) (Davids et al., 2017) and COSB (720 kg/m3) (Qiao, 2020). It is indisputable that the high-density materials have better mechanical properties, hence, the mechanical properties of HCLT can be improved by using wood-based composites with high density. The application of low-density wood-based composites in HCLT has not yet been sufficiently explored in current research. Studies on the mechanical properties of HCLT prepared with wood based composite materials have so far mainly focused on the major strength direction, and have not comprehensively investigated the mechanical properties of the minor strength direction, which are of particular significance when CLT is used as a plate rather than a beam.
Before a new material is introduced into HCLT, its bonding properties should first be assessed. Many scholars have raised the seriousness of this matter, especially in the event of two different materials being bonded. Therefore, many studies have been carried out on the bonding properties of various tree species, including softwood (Mingyue Li, 2021) and hardwood (Yusoh et al., 2021). For tree species which have weaker bonding properties, scholars have proposed several methods to improve the bond performance, such as surface pretreatment of materials including sanding (Knorz, Neuhaeuser, Torno, & van de Kuilen, 2015), spraying wet and adding primers (Lu, Zhou, Liao, & Hu, 2018). However, the bonding properties of wood-based composites in HCLT have not yet been investigated (Li et al., 2020). For such composites, another important factor must be considered; that is, the procuring layer formed on the surface of the plate in the process of pressing the wood-based composite.
Therefore, this study focuses on the effect of the most commonly used industrial wood-based composite OSB, used in HCLT. First, the bonding properties of OSB have been discussed. Then, OSB and larch were combined in different layups to study the interlaminar shear performance of HCLT. The overall aim of the study is to propose new materials for use in the preparation of HCLT.