Meyer-Veltrup et al.: The combined effect of wetting ability and durability on outdoor performance of wood -development and verification of a new prediction approach Abstract Comprehensive approaches to predict performance of wood products are requested by international standards and the first attempts have been made in the frame of European research projects. However, there is still an imminent need for a methodology to implement the durability and moisture performance of wood in an engineering design method and performance classification system. The aim of this study was therefore to establish an approach to predict service life of wood above ground taking into account the combined effect of wetting ability and durability data. A comprehensive data set was obtained from laboratory durability tests and still ongoing field trials in Norway, Germany, and Sweden. Supplementary, four different wetting ability tests were performed with the same material. Based on a dose-response concept decay rates for specimens exposed above ground were predicted implementing various indicating factors. A model was developed and optimised taking into account the resistance of wood against soft, white and brown rot as well as relevant types of water uptake and release. Decay rates from above ground field tests at different test sites in Norway were predicted with the model. In a second step the model was validated using data from lab and field tests performed in Germany and Sweden. The model was found to be fairly reliable and it has the advantage to get implemented into existing engineering design guidelines. The approach at hand might furthermore be used for implementing wetting ability data into performance classification as requested by European standardisation bodies.

There is increasing awareness of the durability, dimensional stability, and strength properties of thermally modified timber products. Appropriate standards and test methods for industrial-scale quality control are needed. The aim of this study was to investigate the suitability of CIE L*a*b* color measurements for implementation in industrial quality control. Good linear correlation was found between a cumulated measure of L* and b* data and the heat treatment intensity for spruce (Picea abies Karst.), pine (Pinus sylvestris L.), and beech (Fagus sylvatica L.). Wood samples homogenized by milling revealed less variation in color values compared to wood surface measurements. Thus, measurements on milled wood are recommendable to obtain results with high statistical significance. Color measurements are rapid, precise, and highly reproducible. Based on the strong correlation between color data and heat-treatment intensities, color measurements could easily be implemented for quality control of thermally modified timber.

Chemically or physically modified wood materials have enhanced resistance to wood decay fungi. In contrast to treatments with traditional wood preservatives, where the resistance is caused mainly by the toxicity of the chemicals added, little is known about the mode of action of nontoxic wood modification methods. This study reviews established theories related to resistance in acetylated, furfurylated, dimethylol dihydroxyethyleneurea-treated, and thermally modified wood. The main conclusion is that only one theory provides a consistent explanation for the initial inhibition of brown rot degradation in modified wood, that is, moisture exclusion via the reduction of cell wall voids. Other proposed mechanisms, such as enzyme nonrecognition, micropore blocking, and reducing the number of free hydroxyl groups, may reduce the degradation rate when cell wall water uptake is no longer impeded.

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