The natural durability of wood in different use classes - PART II
A O Rapp, U Augusta, K Brandt
The natural durability of important European wood species has been tested on 3970 speci¬mens in field trials. The wood was exposed at five test sites in Germany with different climates, at each site in European use class 4 and 3 (with and without soil contact). Within European use class 3 three different expositions were tested: vertical with sheltered end grain, vertical unsheltered and horizontal double layer (with water trap).
The test has now been running for 6 years. The results have shown that the type of exposition (use class 3 or use class 4) has a strong influence on both: the decay activity and the durability determined as the quotient of decay of tested species and Scots pine sapwood. The test site had a strong effect on decay activity and time to failure, whereas the effect on durability was lower.
Up to now it has not yet been possible to calculate the final durability classification, but so far the field tests in soil have confirmed the natural durability given in EN 350 (with the exceptions of Quercus robur and Robinia pseudoacacia, both being less durable than said in the standard). Whereas so far the above ground tests have revealed a higher durability than classified in the standard EN 350 for the tested soft¬wood species with coloured heartwood (heartwood of Larix, Pseudotsuga menziesii and Pinus sylvestris).
It became obvious that the current classi¬fication of natural durability is not valid for wood in different use classes. Future amend¬ments of the standard EN 350 seem to be reasonable. It is proposed that durability class shall be listed separately for in ground and for above ground use in the future.