Out-of-plane Shear Strength of CLT with Japanese Larch or Sakhalin Fir II. Influence of accelerated deterioration treatment on shear strength and adhesive performance

The objective of this study is to investigate the effects of various environmental conditions such as dry environment, intermittent wet environment, and continuous wet environment on the out-of-plane shear strength of 5-layer 5-ply CLT with Japanese larch (Larix kaempferi) or Sakhalin fir (Abies sachalinensis). In this study, we chose five methods of the accelerated deterioration treatment regulated in the Notification 1446 of The Ministry of Construction of Japan: the boiling method with 1 cycle or 2 cycles, the vacuum and pressure method with 1 cycle or 2 cycles, and the steaming and freezing method with 6 cycles. We carried out shear tests and delamination tests after the accelerated deterioration treatment. Results from these tests were as follows: (1) the residual ratio of shear strength was about 90% in dry environment, about 80% in intermittent wet environment, and about 60% in the continuous wet environment; (2) the rate of decrease in shear strength was considerably higher than the delamination rate; (3) the wood failure near the adhesive layer and the radial check of cross layer lamina due to accelerated deterioration treatment affected the decrease in shear strength.