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Use of thermally modified wood in building constructions. Prof.dr. Franc Pohleven [email protected] - lj.si University of Ljubljana Biotechnical Faculty, Department of Wood Science and Technology, Ro ž na dolina , Cesta VIII/34 SI1000 Ljubljana, Slovenia. INTRODUCTION.

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Use of thermally modified wood in building constructions

Use of thermally modified wood in building constructions

Prof.dr. Franc Pohleven

[email protected]

University of Ljubljana

Biotechnical Faculty,

Department of Wood Science and Technology,

Rožna dolina, Cesta VIII/34

SI1000 Ljubljana, Slovenia


Introduction
INTRODUCTION

  • Different wood modification process:

  • Thermal

  • Chemical

  • Enzimatic


Introduction1
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


Introduction2
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)


Materials and methods modification
MATERIALS AND METHODS - modification

SOFTWOOD or HARDWOOD


Properties of thermally modified wood
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 %


Results change of colour

Results - change of colour


B

S

H



Spruce: 3 % (190 °C) –24 % (230 °C)Larch: 5 % (190 °C) –31 % (230 °C)


MATERIALS AND METHODS – decaytests

  • DECAY TESTS

mini-block test (Bravery)


RESULTS – decaytests

  • DECAY – samples treated at 200 °C


MATERIALS AND METHODS – dimensionalstability

  • DIMENSIONAL STABILITY

ASE – soaking/ovendrying test (3 cycles)


ABSORPTION OF WATER VAPOUR AT 83 % AIR HUMIDITYAND T = 25 °C

50 mm × 20 mm × 20 mm

unoriented


Exposure at 83 % RH and 25 °C


RESULTS: absorption of watervapour – sprucewood


RESULTS: absorption of watervapour – beechwood


RESULTS: absorption of watervapour – oakwood





APPROXIMATIONOF REDUCTION OF DIMENSIONS OF MODIFIED WOOD SPECIMENS (spruce)


APPROXIMATIONOF REDUCTION OF DIMENSIONS OF MODIFIED WOOD SPECIMENS (beech)


APPROXIMATIONOF REDUCTION OF DIMENSIONS OF MODIFIED WOOD SPECIMENS (oak)


MATERIALS AND METHODS – MOE AND MOR

  • MOE, MOR

static three-point bending test

Zwick Z-100


MATERIALS AND METHODS - MOE

  • MOE non-destructively

natural vibration analysis in clamped-free conditions


MATERIALS AND METHODS - MOE

  • MOE non-destructively

inductive proximity sensor

dynamic signal analyzer

FFT

νn


RESULTS – MOE and MOR

  • MOR AND MOE of absolute dry samples



Industrial chamber for thermal wood modification



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


Conclusions
CONCLUSIONS modified according to “our procedure”

  • 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


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