2025 Volume 51 Issue 3 Pages 103-115
The development of utilization technologies for cross-laminated timber in the civil engineering field is being promoted as a national policy to expand its demand in Japan. In this study, post-fabrication treatment of CLT using creosote oil or copper naphthenate, which have been used for railway sleeper treatment, was investigated for use as bridge slabs. Heartwood laminae of Japanese cedar（Cryptomeria japonica）, Sakhalin fir（Abies sachalinensis）, or Japanese larch（Larix kaempferi）were used for the fabrication of 3-ply CLT specimens（90mm✕420mm✕800mm）. The wide face of each outer layer lamina was incised before fabrication to achieve uniform penetration of the preservatives. The solution uptake of copper naphthenate and creosote oil by pressure treatment was similar, with both showing greater uptake in the following order: Japanese cedar > Sakhalin fir >Japanese larch. The penetration ratios of copper naphthenate were higher than those of creosote oil, achieving nearly 100% penetration in the cross-grain area of the middle part of CLT specimens made from Japanese cedar and Sakhalin fir. In Sakhalin fir, where liquid penetration in the heartwood is difficult, and in Japanese larch, where it is extremely difficult, there was a substantial difference in the penetration levels between NCU-O and creosote oil. Although it was difficult for the preservatives to penetrate the inner layers by soaking or painting, copper naphthenate could penetrate as deeply as pressure treatment, up to 10mm from the surface of Japanese cedar CLT specimens. Additionally, it was considered that none of the treatments had a significant impact on the initial adhesive performance of CLT.
