A critical view on early indicators for above ground field performance of wood

IRG/WP 13-20509

C Brischke, L Meyer, G Alfredsen, P-O Flæte, L Francis, M Hansson, P Larsson Brelid, J Jermer

Above ground field tests are quite often a balancing act between the provision of realistic test conditions, reliable statistics, and acceptable long test durations. Within this study we therefore reviewed 543 data sets from above ground field tests performed at 36 different test sites in 8 countries in Australia and Europe. The main objective was to investigate possible correlations between early stages of decay and the actual service life of the specimens. Therefore native soft- and hardwoods were considered as well as modified and preservative treated timber. It was shown that the average service life of test specimens can be predicted by using the median time till failure. By this the overall test duration can be significantly reduced. The use of ‘earlier’ predictors turned out to be problematic due to high variation of field test results, which are mainly related to the wide range of moisture regimes within above ground exposure. For in ground situations, rating 4, ‘failure’, is probably a relevant level for end of service, but in particular above ground exposures the decay acceptance level might be lower e.g. in decking. Therefore lower thresholds might be considerable and will allow for further time saving when testing wood above ground, but still providing realistic exposure conditions.

Keywords: decay type, horizontal double layer, L-joint, lap-joint, service life, statistical re-analysis, test site

Conference: 13-06-16/20 Stockholm, Sweden

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