Résumé
This paper presents the first part of an investigation on the natural durability of mixed plywood made of durable and non durable plies from the following selected timbers: Cedrus atlantica, Cupressus sempervirens, Castanea sativa, Populus sp. I 214 and Fagus sylvatica. In order to carry out this study, the natural durability of the massive wood used to manufacture the plywood panels was assessed towards wood both white and brown rots (Coriolus versicolor and Coniophora puteana respectively) according to the guidance of the EN 350-1 standard. The sampling was done by taking into account the axial and radial position of the wood samples (sapwood, inner heartwood, outer heartwood) into the log, and sapwood was separated from heartwood when possible. Moreover, the ultrasound velocity was evaluated on these wood samples before and after fungal degradation. On the other hand, the density and the longitudinal modulus of elasticity of the timbers used were measured. In terms of natural durability, the results obtained showed that some differences were noticed between the sapwoods tested, but all of them were considered as non durable. Poplar and beech were shown non durable, on the contrary of chestnut, cypress and cedar heartwood that were very durable. A significant decrease of ultrasound velocity was shown when the decay and the mass loss were considerable. It appeared also the response of the ultrasound velocity was different from brown and white rot decay. Nevertheless, ultrasound velocity measurement was an efficient non-destructive method to evaluate biological decay. The natural durability, as well as the physical and mechanical properties evaluated on massive wood are of interest in order to .predict the properties of the plywood that will be manufactured from these studied timbers. These results could be helpful to determine the influence of percentage and pattern of the different plies within the plywood panel, ply thickness and glue lines on the natural durability of plywood. (Résumé d'auteur)