Resistance of heat treated Ash wood under steam pressure: rot fungi, soil micro-organisms and termites

IRG/WP 16-40724

K Candelier, S Hannouz, M-F Thévenon, D Guibal, P Gérardin, M Pétrissans, R Collet

Thermal modification processes have been developed to increase the biological durability and dimensional stability of wood. The aim of this paper was to study the influence of ThermoWood® treatment intensity on wood decay resistance improvement against soil-inhabiting micro-organisms, brown/white rots and termite’s exposures. All of the tests were carried out in the laboratory with two different complementary research materials. The main research material consisted of Ash (Fraxinus excelsior L.) wood thermally modified at temperatures of 170ºC, 200ºC, 215ºC and 230ºC. The reference materials were untreated Ash, Beech and Pine woods, for each biological test. An agar block test was used to determine the resistance to two brown-rot and two white-rot fungus according to CEN/TS 15083-1 (2005) directives. Durability against soil-inhabiting micro-organisms was determined relating to the CEN/TS 15083-2 (2005) directives, by measuring the Weight Loss, modulus of elasticity (MOE) and Modulus of rupture (MOR) after incubation periods of 24, 32 and 90 weeks. Finally, Reticulitermes santonensis specie was used for the termite’s exposure non choice screening test with a size sample adjustment according to EN 117 (2005) standard directives. Thermal modification increased the biological durability of all samples. However, high thermal modification temperature over 215°C, representing by a wood mass loss (ML %) due to thermal degradation of 20%, was needed to reach resistance against decay comparable with the durability classes of ‘‘durable’’ or ‘‘very durable’’ in the soil bed test. The brown-rot and white-rot tests gave slightly better durability classes than the soil bed test. Whatever heat treatment conditions, thermally modified ash wood was not efficient against termite’s attacks.


Keywords: ash wood, biological durability, brown/white rots, soil bed test, termites, thermal modification

Conference: 16-05-15/19 Lisbon, Portugal


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