European Conference on Wood Modification 2009 Durability of Modified Wood – Laboratory vs Field Performance Gry Alfredsen 1 and Mats Westin 2 1 Norwegian Forest and Landscape Institute, NO-1432 Ås, Norway [email:gry.alfredsen@skogoglandskap.no] 2 SP Technical Research Institute of Sweden, SE-501 15 Borås, Sweden [email:mats.westin@sp.se] Keywords: AWPA E10, decay, EN 252, horizontal double layer (HDL), terrestrial microcosms (TMC), wood modification, wood plastic composites (WPC) ABSTRACT One of the main challenges for modified wood and modified wood based WPCs (Wood Plastic Composites) is to predict accurate service life time in UC3 (Use class 3, above ground) and UC4 (in soil or fresh water contact). So far, data from in-service conditions are rare, while several studies have evaluated the durability in lab or field test exposure. However, there is still a lack of studies comparing replicate modified wood products in both field and lab exposure. This study evaluates the efficacy of modified wood and modified wood based WPCs in AWPA E10, three different types of soil in lab (ENV 807), three test fields in-ground (EN 252) and two test sites close to ground (horizontal double layer test). The test material includes furfurylated, acetylated and thermally modified wood in addition to reference treated and control samples. In laboratory, both furfurylated, acetylated and thermally modified pine (212ºC) performed well. The modified wood samples performed at the same level, or better, than the reference CC and CCA preservatives in retentions for UC4 applications. In the horizontal double layer test, three years is too short time to be able to draw conclusions. However, all controls are slightly to moderately decayed in the most accelerated set-up whereas all preservative treated, furfurylated, acetylated and WPC with modified wood are sound. After 3 years of testing CCA-preserved wood performs better in-ground in field tests than in lab tests, whereas modified wood generally performs slightly poorer. Just like in the lab tests, however, acetylated wood performs equal to CCA-preserved wood in UC4. Furfurylated wood performs better than UC3 level preservative treated wood. Thermally modified wood actually performs much poorer than all preservative treated wood references. WPCs from modified wood perform well in all field tests with no visible decay. Finally, natural durability classification of the same treatment in different lab and field tests was surprisingly similar. INTRODUCTION Both modified wood and wood plastic composite (WPC) materials have had a continuous market growth over the last decade in Europe and North America, respectively. Wood modification involves the action of a chemical, biological or physical agent upon the material, resulting in a desired property enhancement during the service life of the modified wood (Hill 2006). WPC is a thermoplastic-wood-reinforced composite with more than 50% by weight of wood material (e.g. wood particles, sawdust or wood flour). Two of the main challenges for new wood based products are 1) durability in soil contact and 2) interpretation and comparison of accelerated test methods in relation to service life estimation. A range of studies have evaluated the