385 research outputs found
Moisture behaviour and biological durability of woodâpolymer composites
In recent years wood-polymer composites appears at the European market more frequently, mainly in decking applications as an alternative for durable tropical hardwood decking. This study focuses on extruded decking products based on polypropylene (PP), polyethylene (PE) or polyvinylchloride (PVC) and wood flour. All products are commercially available on the Belgian market. Initially WPCâs were said to be resistant for biological degradation as the wood particles should be encapsulated by the polymer, but over the years several cases of fungal decay of WPC have been reported. Therefore the moisture behaviour of the different WPC decking materials was first assessed by various moistening methods to determine if the moisture content can reach levels that initiate fungal growth. Concerning this, WPC shows better results than the traditional wood composites like particle board, MDF or OSB, but clearly absorbs sufficient moisture to be critical if sorption time is long enough. Therefore, when biological durability is tested, an adequate standard, more specific for WPC products, is needed in stead of just copying the standards designed for wooden panel products. For WPC materials a moistening pre-treatment is needed prior to the proper fungal test to include moistening time as a critical factor for assessing biological durability of these materials. Furthermore placing the products in a fungal control unit that evaluates the susceptibility for airborne surface stains revealed different results and showed that fungi grew earlier and faster on weathered samples. Concluding, in spite of the different composition of the tested products, no product was significantly better or worse than the other concerning the moisture behaviour. Furthermore only a few products were to a small extent covered by moulds in the fungal control unit
Growth trends reveal the forest structure during Roman and Medieval times in Western Europe: a comparison between archaeological and actual oak ring series (Quercus robur and Quercus petraea)
At some point in time, man has influenced nearly all forests in Western Europe. Most of the original forest cover has been converted to arable land and pastures, or has been cut for the supply of firewood and construction timber. In order to secure a sustainable source of firewood, the structure of the remaining forests was often altered. Especially coppice of European oak became increasingly popular during the Roman era and the Middle Ages. Ring-width series of oak trees from Roman times and Medieval settlements were recorded. In order to extract more detailed information regarding past forest structure and management, those series were compared to growth patterns of contemporary oak. The modern oaks were selected on forests sites in Flanders (northern Belgium) with well-known structure and management. Some remarkable similarities in growth patterns were observed. These findings yield tentative assumptions regarding past forest structure and management.Les tendances de croissance rĂ©vĂšlent la structure des forĂȘts en Europe Occidentale aux Ă©poques Romaines et MĂ©diĂ©vales : comparaison entre sĂ©ries d'accroissements annuels archĂ©ologiques et contemporains (Quercus robur et Q. petraea). Au cours de lâhistoire, lâhomme a influencĂ© quasiment toutes les forĂȘts en Europe. De grandes surfaces boisĂ©es ont Ă©tĂ© transformĂ©es en champs et pĂątis ou ont Ă©tĂ© abattues pour rĂ©colter du bois de chauffage et de construction. Pour sâassurer dâune source durable de bois de chauffage, la structure des forĂȘts restantes a souvent Ă©tĂ© adaptĂ©e. Surtout les bois de taillis de chĂȘne sont devenus trĂšs populaires pendant la pĂ©riode romaine et au Moyen Ăge. Des sĂ©ries dendrochronologiques de chĂȘnes provenant dâĂ©tablissements romains et mĂ©diĂ©vaux ont Ă©tĂ© analysĂ©es. Pour obtenir plus dâinformations prĂ©cises concernant la structure et la gestion des forĂȘts antĂ©rieures, les sĂ©ries ont Ă©tĂ© comparĂ©es avec celles de chĂȘnes contemporains. Ces chĂȘnes modernes ont Ă©tĂ© sĂ©lectionnĂ©s dans des forĂȘts, avec des structures bien connues, situĂ©es en Flandres (Belgique). Quelques similaritĂ©s remarquables observĂ©es dans les modĂšles de croissance ont permis de formuler des hypothĂšses concernant la structure et lâamĂ©nagement des forĂȘts antĂ©rieures
An experimental set-up for real-time continuous moisture measurements of plywood exposed to outdoor climate
Modelling cavity ventilation behind brick veneer cladding : how reliable are the common assumptions?
Throughout the years, different numerical HAM-simulation tools have been developed to assess and predict the heat, air and moisture response of building components. But, though commercially available and commonly applied in building practice, still, several simplifications and shortcomings exist in the common models. Probably the most important one, is the fact that most tools neglect or strongly simplify air transport, focusing only on heat and moisture transport. Especially for the analysis of wood frame constructions, these simplified models may cause a large discrepancy between simulation results and real performance. This study aims at a comparison of the outcomes of numerical HAM -simulations for wood frame constructions with experimental data of real test cases. In particular, the focus of this paper is on cavity ventilation behind brick veneer. Therefore, a simplified version of a wood frame wall with brick veneer cladding is studied in this paper. Different common modelling assumptions are compared. Furthermore, a detailed measuring campaign has been conducted at the VLIET test building of the KU Leuven to validate the different modelling approaches. By verifying the results of the numerical simulations by the data of real test cases, the reliability of the modelling assumptions can be analysed. The results of this study clearly show that simplified assumptions on cavity ventilation in HAM-models might cause large discrepancies between simulation results and in-situ measurements
Predispositions and symptoms of Agrilus borer attack in declining oak trees
International audienceThis paper presents results of a semi-quantitative study on the role of Agrilus biguttatus F. in oak decline in Belgium. Larvae of this insect breed in living subcortical tissues of European oak. Several factors favouring attacks are discussed, among which the overall health condition and the local physical and biochemical status of the host tree. Larvae, feeding galleries, pupae, imago and D-shaped emergence-holes of A. biguttatus were observed exclusively in declining and recently dead oaks. Attacks start in the south-facing, sun-exposed parts of the subcrown stem, with a preference for thicker-barked trees or similar areas within declining trees. The feeding of early larval stages induces subcortical necrosis and longitudinal bark cracking. The more destructive tunnelling of advanced larval stages cuts functional vessels and phloem elements, which enhances the decline. In conclusion, effects on wood quality and suitable control options are discussed.PrĂ©dispositions et symptĂŽmes d'attaques d'Agrilus dans des chĂȘnes dĂ©pĂ©rissants. Nous prĂ©sentons les rĂ©sultats d'une Ă©tude semi-quantitative portant sur le rĂŽle du ColĂ©optĂšre Agrilus biguttatus F. dans le dĂ©pĂ©rissement de chĂȘnes en Belgique. Les larves de cet insecte s'attaquent au xylĂšme et au phloĂšme vivants. Plusieurs facteurs favorisant les attaques sont discutĂ©s. Parmi ces facteurs, la santĂ© gĂ©nĂ©rale et les Ă©tats physiques et biochimiques locaux de l'arbre hĂŽte semblent ĂȘtre dĂ©cisifs pour permettre sa colonisation. Des larves, des galeries sous-corticales, des nymphes, des adultes et des trous d'Ă©mergence en forme de D d'A. biguttatus ont Ă©tĂ© trouvĂ©s uniquement dans des chĂȘnes dĂ©pĂ©rissants ou morts rĂ©cemment. Les attaques commencent dans les parties ensoleillĂ©es de l'arbre situĂ©es en dessous de la couronne et exposĂ©es vers le sud, avec une prĂ©fĂ©rence pour des arbres ou des zones de l'arbre qui sont affaiblis et qui ont une Ă©corce Ă©paisse. Les larves juvĂ©niles endommagent le cambium vasculaire et provoquent ainsi une fissuration longitudinale dans l'Ă©corce. Les galeries des stades larvaires plus avancĂ©s coupent des Ă©lĂ©ments de xylĂšme et de phloĂšme fonctionnels et stimulent ainsi le dĂ©pĂ©rissement. Pour conclure, les effets sur la qualitĂ© du bois et des mesures de contrĂŽle adĂ©quates sont discutĂ©s
End-use related physical and mechanical properties of selected fast-growing poplar hybrids (Populus trichocarpa x P-deltoides)
This study focused on physical and mechanical properties of fast-growing poplar clones in relation to potential end uses with high added value. A total of 14 trees from three different clones, all P. trichocarpa x deltoides (T x D) hybrids, were felled in a poplar plantation in Lille (Belgium): six 'Beaupre', four 'Hazendans' and four 'Hoogvorst'. Growth rate was found to have no significant influence on the physical mechanical properties. Although the investigated clones are genetically closely related, important variations in physical and mechanical properties were observed. Specific features such as spatial distribution of tension wood and dimensional stability are the main quality factors. It was concluded that 'Beaupre' is suitable for a wide range of high value added applications, such as plywood or construction wood. 'Hazendans' and 'Hoogvorst' will need adapted technology in processing. Further research is needed to characterize clonally induced variation in properties and to assess adequate processing strategies for multiclonal poplar stands
Morphology and growth periodicity of plantation grown limba trees (Terminalia superba Engl. & Diels)
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