Bending creep test of plywoods under long term exposure to fungal attack
Bending creep test and decay test were coupled in order to evaluate the durability of structural plywoods and preservative efficacy. Experimental blocks, 5.0 x 1.2 cm² section x 35.0 cm length, were impregnated with distilled water and inoculated with mycelial fragments of test fungus. Polyethylene bags stretched with metal frame were used as decay chambers. The chambers containing inoculated blocks and water were plugged with porous silicone plugs. Weight was hanged from the center of block. The deflection at the center of span was measured with a gauge sensor connected with a recorder. The deflection due to fungal attack appeared after 800-1200 hrs incubation. Non-treated plywoods failed by 2400 hrs. Treated plywoods containing 1 kg/m³ of TBP (Tribromophenol) did not fail even after 3800 hrs but deflected continuously. When containing 5 kg/m³ of TBP, only a slight deflection was observed. Based on the assumption that decay advanced uniformly in the parallel direction to the span but wavy like as cosine curve in the perpendicular one, creep deflections were calculated and compared with the experimental ones. It may be concluded from these results that the method is promissing for evaluating the durability of structural board materials and preservative efficacy.