Durability of European oak (Quercus spp.) in ground contact – A case study on fence posts in service

Abstract

The durability of European oak (Quercus spp.) is under debate for a long time. In contrast to its classification as ‘‘durable’’ timber species according to EN 350-2 (CEN 1994), results from different comparative studies have clearly shown a lower durability, especially for in-ground exposures. To highlight this conflict more detailed, a case study on oak fence posts, which had been in service for 5, 10, 20, 30, and 60 years, was carried out. The posts were examined in terms of decay type and intensity, remaining cross section, wood moisture content, and different characteristics of the adjacent soil. The durability of the oak posts was affected by high variation. Posts prematurely failing after only five years were found as well as posts still serviceable after 60 years. Different findings of the study have the potential to increase the understanding of durability aspects in the future and might be considered for calibration and adaption of field and laboratory test methods in the future: The ground line turned out to be not the most severe exposure for posts, although it is generally assumed to be. Furthermore, no significant negative impact of remaining sapwood portions on the durability of the heartwood was found, but the important role of radial cracks for the initiation of decay became apparent. In this regard further potentially important factors for the in-ground durability are size and shape of timber components.