Moisture behavior of weathered wood surfaces during cyclic wetting : measurements and modeling

The effects of weathering on the in-service moisture behavior of wood have received only limited attention so far, with much focus being on the effect of photodegradation on the hydrophobicity of the wood surface. The objective of the present study was to examine the effect of weathering surfaces on the overall moisture behavior of wood specimens exposed to short-term cyclic spraying, with special emphasis on the surface conditions involved. Specimens cut from eight different species including hardwoods and softwoods were weathered for 8 years and continuously monitored during a single-sided cyclic spraying together with a set of axially matched controls. After each spray cycle, the duration of surface wetness was evaluated by resistance moisture sensors as well as an optical approach (colorimetric) based on time-lapse images. The moisture content in the core was monitored simultaneously by use of resistance moisture sensors. The optical method correlated well with the electrical resistance measurements and provided a simple and practical measure of the areal distribution of the surface wetness. The results showed specimens with a weathered surface to sustain a wet surface for about twice the duration of their axially matched control. A considerable, albeit smaller, effect was also observed deeper in the core. By adapting the length of the wet period on the exposed boundary, the corresponding response at the core of the Norway spruce specimens was reproduced numerically

Global survey on durability variation – on the effect of the reference species

Climate change due to anthropogenic emissions is the largest environmental challenge of ourtime. Forest-based value chains play an important role in reducing the accumulation of CO2 in the atmosphere. Maximizing the use of wood to tackle climate change requires improved understanding of the service life of timber products. This information can best be obtained from field testing and while there is an abundance of field performance data from sites all over the world, most of the data are not available in a form that can be utilised for service life models. The IRG Durability Database aims to improve the usability of existing performance data and create added value for durability research and service life prediction. The present paper takes the first steps in comparing global field test performance data from the IRG Durability Database for non-durable reference species. Data were obtained from six species above ground and ground contact field tests from 36 sites around the world. For each dataset, decay rates and service life (where applicable) were calculated. Datasets were then grouped together based on test method and species. Decay rate was faster and more uniform in ground contact than above ground. Inground contact, beech decayed most rapidly, followed by Norway spruce and Scots pines apwood. All appeared to be suitable for use as reference species, however slow-grown spruce should be avoided. There were no statistically significant correlations between ground contact decay rate and the Scheffer Climate Index (SCI). In above ground tests, differences in decay ratewere largely related to differences in moisture dynamics. Species with the greatest absorption and retention of water decayed most rapidly. Test methods that absorbed and retained the most moisture (e.g. painted L-joints) resulted in more rapid decay. Above ground decay rate and SCI were significantly correlated in two data sets that had a wide range of SCI values. Correlations were not significant when only European test sites were included. Estimating decay rate from field testing results in highly variable data. Comparing data from global test sites is made more difficult by the absence of common field testing standards

Evaluation of fractionally distilled Picea abies TMP-turpentine on wood-decaying fungi : in vitro, microcosm and field experiments

Synthetic and heavy metal antifungals are frequently used as wood preservatives. However, they exhibit relatively inert biodegradation and toxic properties when leached; this makes their replacement with environmentally degradable yet functional alternatives a key target in the wood protection industry. In this context, distilled fractions of raw thermomechanical pulp turpentine (TMP-T) from Picea abies were assessed for their wood protecting capabilities against wood-decaying fungi. Antifungal bioactivity of fractions and some of their combinations were screened on agar-plates against the brown-rot fungus Coniophora puteana. Addition of TMP-T fractions showed a significant fungal growth rate reduction, while mixtures indicated the presence of synergistic and antagonistic effects. One fraction, obtained after distilling 1 L TMP-T at 111–177 °C at 0.5 mbar, showed complete growth inhibition of Antrodia sinuosa, Serpula lacrymans, Serpula himantioides and significant inhibition of Antrodia serialis, Antrodia xantha, Gloeophyllum sepiarium, Heterobasidion parviporum at a concentration of 1000 ppm. This fraction was further examined for long- and medium-term effects on wood decay in microcosm soil-jar and field experiment, respectively. The known antifungal compounds benzisothiazolinone, 2-octyl-4-isothiazolin-3-one, 3-iodo-2-propynyl N-butylcarbamate and two commercial wood preservatives were used as reference treatments. Commercial preservatives instilled long-term efficacy against C. puteana wood decay in a soil-jar microcosm experiment, but no noticeable protection with antifungal compounds or the present treatments was found. However, a moderate effect by the TMP-T fraction from the in vitro assay was observed and the TMP-turpentine distillation residue showed a similar fungal inhibition effect to the most potent commercial treatment after 29 months in the field