Long-term bending properties of cross-laminated timber made from Japanese larch under constant environment

Cross-laminated timber (CLT) has been used extensively in timber construction. CLT panels are typically used in roofs and floors that carry a continuous load, and it is important to examine the long-term loading capacity of CLT. However, studies that focus on the long-term loading capacity of CLT are limited. To this end, we conducted long-term out-of-plane bending tests on seven-layer CLT made from Japanese larch (Larix kaempferi) under constant environmental conditions, investigated creep performance and duration of load, and experimentally analyzed creep rupture behavior. The mean estimated relative creep after 50 years was 1.49. The sample showed a satisfactory resistance to creep as a building material. The duration of load of most of the specimens in this study was shorter than the conventional value of small clear wood specimens. Specimens had a lower duration of load capacity than solid lumber. According to the results of survival analysis, a loading level of 70% or more caused the initial failure of specimens. Creep rupture of most of the specimens occurred at less deflection than displacement at failure in the short-term loading test. Additional studies focusing on the effects of finger joints, transverse layers, and width of a specimen on creep rupture behavior are suggested.

Upgrading the fuel properties of hydrochar by co-hydrothermal carbonisation of dairy manure and Japanese larch (Larix kaempferi): product characterisation, thermal behaviour, kinetics and thermodynamic properties

This study investigated co-hydrothermal carbonisation (co-HTC) of dairy manure (DM) and wood shavings from Larix kaempferi, commonly known as the Japanese larch (JL) to enhance the fuel properties of the resulting hydrochar. The JL was mixed with the DM at 25, 50 and 75 wt.% ratios. Co-HTC was conducted at 260 °C for 20 min. The resulting hydrochars were characterised based on the physicochemical properties and the thermal behaviour. Results showed that the hydrochar solid biofuel properties improved as the ratio of JL was increased. The produced hydrochars were in the region of lignite and closed to the region of the coal with increased fixed carbon, carbon contents and lowered H/C and O/C ratios. Hydrochar with ash content of 7.2 ± 0.5% was obtained at 75 wt.% JL. In addition, the HHV of hydrochar increased remarkably to 26.4 ± 0.02 MJ/kg as the mass ratio of the JL was increased. The surface morphology of the hydrochars were altered and became distinct while the specific surface area (SSA) and the total pore volume (TPV) of the hydrochars increased at increasing the mass ratio of the JL. The surface functional groups were also altered by the co-HTC process. A decline in the combustion performance was observed after the HTC process but improved at 75 wt.% JL after the co-HTC process. The kinetic analysis also revealed that the activation energy decreased after the HTC process but increased to a higher value at 50 wt.% JL after the co-HTC process. Therefore, hydrochar production by co-HTC of DM and JL has proved to be an effective and promising solid biofuel source. Graphical abstract

Influence of adhesive and layer composition on compressive strength of mixed cross-laminated timber

Different types of wood can be used for making cross-laminated timber (CLT), which is useful as a structural material. Therefore, to assess the viability of mixed cross-laminated timbers prepared with different adhesives, their compressive strength performances were evaluated. Laminae of Japanese larch, red pine, and yellow poplar were used to manufacture eight types of mixed CLTs, which were then tested in a universal testing machine for obtaining the compressive strength. The results were then compared to those obtained from the finite element (FEM) simulation of the CLTs at proportional limit load. The compressive strength of CLTs consisting of Japanese larch laminae, with a high modulus of elasticity, tended to increase. Mixed CLT with polyurethane adhesives showed an average compressive strength that was 14% lower than that of larch CLT, while mixed CLT consisting of red pine and yellow poplar showed an average compressive strength that was 18% lower than that of the larch CLT. The CLT prepared with phenol-resorcinol-formaldehyde adhesive yielded the highest compressive strength among the three adhesives. The FEM-predicted strengths were found to be close to the actual values in all specimens. The obtained results will be useful for selecting material and adhesive for future endeavors.

Enhanced Summer Planting Survival of Japanese Larch Container-Grown Seedlings

A previous study revealed low survival rates for Japanese larch (Larix kaempferi) summer-planted seedlings grown in Hiko-V-120 containers. This study examines nursery practices that could potentially prevent deterioration of the seedling water balance after planting to improve the survival rate of this species, which has a low drought tolerance. During summer planting, we tested (1) drought hardening or high-potassium fertilization for two months before planting, (2) antitranspirant or topping treatment at planting, and (3) the use of the JFA-150 container with a larger capacity and lower growing density than the Hiko-V-120 container. Drought hardening increased seedling drought tolerance because of the low leaf:root ratio, due to lower leaf mass production, resulting in increased survival from 74% to 93% in Hiko-V-120 containers. When JFA-150 containers were used, the leaf:root ratio was lower because of higher root mass, resulting in an increase in survival to 87%, with the highest survival of 97% when combined with drought hardening. The application of antitranspirant increased survival to over 90%, whereas topping did not, probably because of severer competition from weeds. High-potassium fertilization did not affect seedling traits or survival. For better survival of summer-planted container-grown Japanese larch seedlings, it is recommended that they be grown in containers providing sufficient cell volume and density for root growth while the seedlings are in the nursery and that irrigation be withheld for two months before planting. In addition, to obtain higher survival, an antitranspirant can be applied at planting at a cost.

A COMPARATIVE STUDY ON THE PHYSICAL AND MECHANICAL PROPERTIES OF DAHURIAN LARCH AND JAPANESE LARCH GROWN IN KOREA

To compare the wood quality of Dahurian larch and Japanese larch growing in Korea, the physical and mechanical properties were examined using the Korean standards. The proportion of heartwood was 82% and 72% in Dahurian and Japanese larch, respectively. The percentage of latewood was 42% in Dahurian larch and 35% in Japanese larch. The growth ring width of Dahurian larch was narrower than that of Japanese larch. Dahurian larch showed about 20% higher green moisture content compare to Japanese larch wood. Density and shrinkage of Dahurian larch were higher than Japanese larch. Axial compression strength, young`s modulus in compression, and shearing strength in heartwood of Dahurian larch were 11 MPa, 686 MPa, and 2.3 MPa, respectively, showing higher value than Japanese larch. The hardness was in the range of 13.8–38.7 MPa in Dahurian larch and 17.7–48.4 MPa in Japanese larch. The compression strength parallel to the grain and shearing strength in both species were significantly correlated with oven-dried density. Besides, the hardness in Dahurian larch was significantly correlated with latewood percentage and oven-dried density. In conclusion, the differences in the properties of both species were revealed and the results can be used for quality indices of both wood species.

Quantification of One-Year Gypsy Moth Defoliation Extent in Wonju, Korea, Using Landsat Satellite Images

We quantified the extent and severity of Asian gypsy moth (Lymantria dispar) defoliation in Wonju, Korea, from May to early June in 2020. Landsat images were collected covering Wonju and the surrounding area in June from 2017 to 2020. Forest damage was evaluated based on differences between the Normalized Difference Moisture Index (NDMI) from images acquired in 8 June 2020 and the prior mean NDMI estimated from images in June from 2017 to 2019. The values of NDMI ranged from −1 to 1, where values closer to 1 meant higher canopy cover. The NDMI values for 7825 ha of forests were reduced by more than 0.05 compared to the mean NDMI values for the prior 3 years (2017 to 2019). The NDMI values of 1350 ha of forests were reduced by >0.125 to 0.2, and the NDMI values for another 656 ha were reduced by more than 0.2. A field survey showed that these forests were defoliated by gypsy moth and that forests with NDMI reductions of more than 0.2 were heavily defoliated by gypsy moth. A 311 ha area of Japanese larch (Larix kaempferi) was severely damaged by gypsy moth and the proportion of larch damaged was higher than that of other tree species. This intense damage to larch suggests that gypsy moths preferentially attack Japanese larch in Wonju. Our study shows that the use of NDMI values to detect areas defoliated by gypsy moth from satellite images is effective and can be used to measure other characteristics of gypsy moth defoliation events, such as host preferences under field conditions.