Use of thermally modified wood in building constructions

1. Use of thermally modified wood in building constructions Prof.dr. Franc Pohleven franc.pohleven@bf.uni-lj.si University of Ljubljana Biotechnical Faculty, Department of Wood Science and Technology, Rožna dolina, Cesta VIII/34 SI1000 Ljubljana, Slovenia

2. INTRODUCTION • Different wood modification process: • Thermal • Chemical • Enzimatic

4. INTRODUCTION • DIFFERENT HEATING MEDIA: nitrogen, steam, oil VACUUM – A SLOVENIAN METHOD • Exposure to high temperatures cause severe degradation of cellulose and losses in mechanical properties

5. INTRODUCTION • Temperatures from 160 °Cto 260 °C • Absence of oxygen • Process of wood modification • Chemical changes in wood cell walls • Changes of wood (=modified wood)

6. MATERIALS AND METHODS - modification SOFTWOOD or HARDWOOD

7. PROPERTIES OF THERMALLY MODIFIED WOOD • Improvement of durability and dimensional stability • Removing of resins • Improvement of resonant (acoustic) properties • Mass loss • Change of physical properties: • Colour • Reduction of strength and stiffness • Bending strength 10 % – 50 %

8. Results - change of colour

9. B S H

10. Elm wood

11. MASS LOSSES Spruce: 3 % (190 °C) –24 % (230 °C)Larch: 5 % (190 °C) –31 % (230 °C)

12. MATERIALS AND METHODS – decaytests • DECAY TESTS mini-block test (Bravery)

13. RESULTS – decaytests • DECAY – samples treated at 200 °C

14. MATERIALS AND METHODS – dimensionalstability • DIMENSIONAL STABILITY ASE – soaking/ovendrying test (3 cycles)

15. ABSORPTION OF WATER VAPOUR AT 83 % AIR HUMIDITYAND T = 25 °C 50 mm × 20 mm × 20 mm unoriented

16. Exposure at 83 % RH and 25 °C

17. RESULTS: absorption of watervapour – sprucewood

18. RESULTS: absorption of watervapour – beechwood

19. RESULTS: absorption of watervapour – oakwood

20. DIMENSIONAL STABILITY (spruce)

21. DIMENSIONAL STABILITY (beech)

22. DIMENSIONAL STABILITY (oak)

23. APPROXIMATIONOF REDUCTION OF DIMENSIONS OF MODIFIED WOOD SPECIMENS (spruce)

24. APPROXIMATIONOF REDUCTION OF DIMENSIONS OF MODIFIED WOOD SPECIMENS (beech)

25. APPROXIMATIONOF REDUCTION OF DIMENSIONS OF MODIFIED WOOD SPECIMENS (oak)

26. MATERIALS AND METHODS – MOE AND MOR • MOE, MOR static three-point bending test Zwick Z-100

27. MATERIALS AND METHODS - MOE • MOE non-destructively natural vibration analysis in clamped-free conditions

28. MATERIALS AND METHODS - MOE • MOE non-destructively inductive proximity sensor dynamic signal analyzer FFT νn

29. RESULTS – MOE and MOR • MOR AND MOE of absolute dry samples

30. Laboratory chamber for thermal wood modification

31. Industrial chamber for thermal wood modification

32. Silvaprodukt d.o.o., Ljubljana, Sovenia

41. The first product made from thermally modified wood, modified according to “our procedure”

42. CONCLUSIONS • The best characteristics of the products made of modified wood were achieved with wood, modified at temperatures between 180 °C and 210 °C • In spite of the treatment, the mechanical properties of modified wood are still appropriate for wood to be used in constructions • Wood modification process can ensure appropriate resistance for diverse ways of utilisation of wooden products, especially in in wet conditions