In-ground durability of wood-based products – Comparative assessment of graveyard field tests and terrestrial microcosms
A Soetbeer, L Meyer, C Brischke, P Larsson-Brelid, J Jermer
Traditionally wood durability and the effectiveness of wood preservatives are determined in so-called graveyard tests (according to EN 252 or AWPA E7). For laboratory testing, terrestrial microcosms (TMC) can serve as an alternative. Both tests have been applied for different types of wood-based materials, preservative treated, modified and unmodified wood. However, the usability of laboratory results for predicting the performance of wood products under field conditions has been discussed controversially for a long time.
With the purpose of profounder understanding, a comprehensive test was set up to compare re-sults from different laboratory and field tests considering the full range of wood based products. In total 34 materials (11 native softwoods, 5 native hardwoods, furfurylated, acetylated and thermally modified timber as well as different preservative treated timbers) have been exposed in ground at the test sites Borås, Sweden, and Hannover, Germany. Furthermore lab tests with TMCs have been conducted. Therefore an active compost soil producing high soft rot decay was used as well as the field soil from the two test sites to allow direct comparison.
The mass loss obtained in the TMCs differed drastically whereby compost soil showed the high-est decay activity. Generally, the obtained mass loss was lower in the Borås soil compared to the soil from Hannover. However, this was not confirmed by the decay progress observed in the Bo-rås field, which was approximately equal to the activity in the Hannover field. Furthermore, some materials suffered from brown rot decay in the field which was absent in the TMCs, where moisture conditions were unfavourable for brown rot fungi.
Different indicators and statistical measures were assessed with respect to their potential for pre-dicting the outdoor performance of the various wood-based materials. In spite of a general com-pliance between lab and preliminary field test results, a remarkable number of discrepancies pointed on the need for field tests representing all relevant types of decay.