A novel method of density determination for waterlogged woods: Comparison with a known classical technique (2012)

In the course of research for conservation treatments of the waterlogged woods archaeological artefacts, characterisation of degree of woods decay seemed to be a major step in choosing of feeler concentrations for structural consolidation. For purpose, the Maximum Water Content (MWC) and density were the common parameters used for determining degree of the waterlogged woods degradation. As for fresh wood, assessment to the real density of waterlogged woods ( GR R ) was fastidious. Then, the conditional density ( GC R ) of wood was always determined on basis of Smith relation. The latter was subjected to an established hypothesis that stipulates a constant value for density of wood dry-matter of about 1.5. The actual paper proposes a novel method for determination of waterlogged wood conditional density. It’s fundamentally based on Archimede principle, as those kinds of woods were completely watering submersible. The obtained results have been compared with those from application of the modified Smith formula. A good correlation was reached between the two methods. It immediately followed that assumption of constant density of fresh wood dry-matter (value 1.5), drove to a good approximation in usage of Smith formula. However, this approximation did not still hold for slightly degraded woods as shown by compared results of these two methods. The main advantage of the proposed method linked with its practical measurements in real conditions and the fact that no assumption for the wood cell wall density was necessary. Key words : Wood, waterlogged, conditional density, maximum water content. Dans les recherches relatives aux traitements dedies a la conservation des objets archeologiques en bois gorges d'eau, la caracterisation du degre de degradation du bois constitue une importante etape dans le choix des concentrations du materiau d'impregnation - consolidation. La teneur maximale en eau et la densite sont couramment utilisees pour evaluer l’etat de degradation du bois. L'acces a la densite reelle d’un bois gorge d'eau (RGR) est ardu. La densite conditionnelle (RGC), determinee a partir de la relation de Smith modifiee, a donc ete admise quand bien meme elle reste sujette a l'hypothese de la constance de densite de la matiere seche du bois. Le present article propose une nouvelle methode de determination de la densite des bois gorges d'eau. Elle est  fondamentalement basee sur le principe d'Archimede et tien  pratiquement au fait que ces types de bois sont completement submersibles dans l’eau. Les resultats obtenus, compares a ceux determines par la formule classique de Smith, ont montre une bonne correlation entre les deux methodes. Il s’en suit immediatement que, l’hypothese sur la densite de matiere seche du bois frais (1,5) est bien confirmee. Toutefois, l’approximation ainsi faite ne tient plus pour les bois peu degrades. Les avantages de la nouvelle methode sont  essentiellement lies au fait qu’elle s’appuie sur des mesures pratiques en conditions reelles et qu’aucune hypothese, sur la valeur de la densite de la substance de la paroi cellulaire, ne soit necessaire pour son application. Mots cles : Bois, gorge d'eau, densite conditionnelle, teneur maximale en eau.