Miljøeffekter ved bruk av tre. Sammenstilling av kunnskap om tre og treprodukter

- Hvis man tar utgangspunkt i den energien som tømmeret representerer, går mindre enn 3 % av denne med til å fremskaffe dette tømmeret til industrien. Om lag halvparten av energiforbruket fra skogetablering til industritomt er knyttet til tømmertransport. - I livssyklusfasene til boliger og kontorbygg er det bruksfasen som utgjør det største energiforbruket, ca. 85-93%. - Drivhusgassbalanse og energi som går til gjenvinning, vil i stor grad avhenge av hvordan tre behandles etter riving og eventuell substitusjon av fossilt brensel. For trekonstruksjoner er den energien som frigjøres ved forbrenning av rivingsvirke, minst like stor som den energien som kreves til fremstilling av trekonstruksjonene. - I 95 % av de gjennomgåtte studiene i denne undersøkelsen der tre ble sammenlignet med alternative materialer, har man kommet til at tre var like bra (35 %) eller bedre (60 %). - Gode levetidsdata for tre og trekomponenter er helt avgjørende for gode LCA analyser. Økt levetid på bygningsdeler i tre vil kunne bidra til økt karbonbinding. Det er derfor av stor betydning å finne nye trebeskyttelsessystemer som bidrar til økt levetid. - Nyere undersøkelser peker i retning av at den største samlede reduksjonen i CO2-utslipp til atmosfæren oppnås ved å drive et intensivt skogbruk. Dette er basert på forutsetninger om at biomassen fra skogen benyttes til å substituere mer energikrevende produkter, samt til substitusjon av fossilt brensel. I praksis vil et intensivt skogbruk kunne komme i konflikt med en del av kravene som er satt til et bærekraftig skogbruk.publishedVersio

Prirodna trajnost drva izloženoga iznad zemlje – pregled istraživanja

Besides its inherent resistance against degrading organisms, the durability of timber is influenced by design details and climatic conditions, making it difficult to treat wood durability as an absolute value. Durability classification is, therefore, based on comparing performance indicators between the timber in question and a reference timber. These relative values are grouped and related to durability classes, which can refer to a high range of service-lives. The insufficient comparability of such durability records has turned out to be a key challenge for service-life prediction. This paper reviewed literature data, based on service-life measures, not masked by a durability classification. It focused on natural durability of timber tested in the field above-ground. Additionally, results from ongoing aboveground durability studies in Europe and Australia are presented and have been used for further analysis. In total, 163 durability recordings from 31 different test sites worldwide based on ten different test methods have been considered for calculation of resistance factors. The datasets were heterogeneous in quality and quantity; the resulting resistance factors suffered from high variation. In conclusion, an open platform for scientific exchange is needed to increase the amount of available service-life related data.Osim otpornosti drva prema štetnim organizmima, na prirodnu trajnost drva utječe i dizajn detalja na proizvodima od drva te klimatski uvjeti, pa je teško razmatrati svojstvo trajnosti drva kao apsolutnu vrijednost. Stoga je klasifikacija trajnosti drva utemeljena na usporedbi pokazatelja izgleda drva, čija se trajnost određuje prema izgledu referentne drvne građe. Te su relativne vrijednosti grupirane i povezane s klasama trajnosti, što se može odnositi na veliki raspon životnog vijeka drvnih proizvoda. Nedovoljna usporedivost takvih zapisa trajnosti pokazala se kao ključni izazov za predviđanje životnog vijeka drvnih proizvoda. U radu se daje pregled literaturnih podataka utemeljenih na životnom vijeku drvnih proizvoda koji nisu maskirani klasifikacijom trajnosti. Naglasak je na prirodnoj trajnosti drva ispitanoj pri izloženosti drva iznad zemlje. Osim toga, prezentirani su rezultati aktualnih istraživanja prirodne trajnosti drva iznad zemlje u Europi i Australiji te su iskorišteni za daljnju analizu. U obzir za izračun faktora otpornosti uzeta su ukupno 163 podatka o trajnosti drva dobivena s 31 različitoga ispitnog mjesta u svijetu na temelju deset različitih metoda ispitivanja uzeti. Skupovi podataka su heterogeni s obzirom na kvalitetu i količinu, što je rezultiralo velikom varijacijom čimbenika otpornosti. Zaključno, potrebna je otvorena platforma za znanstvene razmjene kako bi se povećala količina dostupnih podataka o životnom vijeku proizvoda

Modelling the Material Resistance of Wood—Part 3: Relative Resistance in above- and in-Ground Situations—Results of a Global Survey

Durability-based designs with timber require reliable information about the wood properties and how they affect its performance under variable exposure conditions. This study aimed at utilizing a material resistance model (Part 2 of this publication) based on a dose–response approach for predicting the relative decay rates in above-ground situations. Laboratory and field test data were, for the first time, surveyed globally and used to determine material-specific resistance dose values, which were correlated to decay rates. In addition, laboratory indicators were used to adapt the material resistance model to in-ground exposure. The relationship between decay rates in- and above-ground, the predictive power of laboratory indicators to predict such decay rates, and a method for implementing both in a service life prediction tool, were established based on 195 hardwoods, 29 softwoods, 19 modified timbers, and 41 preservative-treated timbers

Modeling the material resistance of wood—part 2:Validation and optimization of the meyer-veltrup model

Service life planning with timber requires reliable models for quantifying the effects of exposure-related parameters and the material-inherent resistance of wood against biotic agents. The Meyer-Veltrup model was the first attempt to account for inherent protective properties and the wetting ability of wood to quantify resistance of wood in a quantitative manner. Based on test data on brown, white, and soft rot as well as moisture dynamics, the decay rates of different untreated wood species were predicted relative to the reference species of Norway spruce (Picea abies). The present study aimed to validate and optimize the resistance model for a wider range of wood species including very durable species, thermally and chemically modified wood, and preservative treated wood. The general model structure was shown to also be suitable for highly durable materials, but previously defined maximum thresholds had to be adjusted (i.e., maximum values of factors accounting for wetting ability and inherent protective properties) to 18 instead of 5 compared to Norway spruce. As expected, both the enlarged span in durability and the use of numerous and partly very divergent data sources (i.e., test methods, test locations, and types of data presentation) led to a decrease in the predictive power of the model compared to the original. In addition to the need to enlarge the database quantity and improve its quality, in particular for treated wood, it might be advantageous to use separate models for untreated and treated wood as long as the effect of additional impact variables (e.g., treatment quality) can be accounted for. Nevertheless, the adapted Meyer-Veltrup model will serve as an instrument to quantify material resistance for a wide range of wood-based materials as an input for comprehensive service life prediction software

Effect of kerfing on crack formation in Scots pine log house timber

In Norway log buildings are normally produced from logs canted on two sides. The canted faces are prone to crack formation during drying. This can cause some disadvantages, e.g. the cracks can trap water from rainfall, because the canted faces form the wall surfaces in the log buildings.publishedVersio

Furukjerneved - et naturlig holdbart materiale

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Furukjerneved - et naturlig holdbart materiale

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Gran som ubehandlet utvendig kledning

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Effect of kerfing on crack formation in Scots pine log house timber

In Norway log buildings are normally produced from logs canted on two sides. The canted faces are prone to crack formation during drying. This can cause some disadvantages, e.g. the cracks can trap water from rainfall, because the canted faces form the wall surfaces in the log buildings