Use of thermally modified wood in building constructions

Prof.dr. Franc Pohlevenfranc.pohleven@bf.uni-lj.si

University of LjubljanaBiotechnical Faculty,Department of Wood Science and Technology,Rona dolina, Cesta VIII/34SI1000 Ljubljana, Slovenia

INTRODUCTIONDifferent wood modification process:ThermalChemicalEnzimatic

INTRODUCTIONDIFFERENT HEATING MEDIA: nitrogen, steam, oil VACUUM A SLOVENIAN METHODExposure to high temperatures cause severe degradation of cellulose and losses in mechanical properties

INTRODUCTIONTemperatures from 160 C to 260 CAbsence of oxygenProcess of wood modificationChemical changes in wood cell wallsChanges of wood (=modified wood)

MATERIALS AND METHODS - modificationSOFTWOOD or HARDWOOD

Phases of process (24 h)

drying at 103 Cvacuuming up to 0,05 barheating to 150 Cheating to T of modif. (3 h)cooling down

PROPERTIES OF THERMALLY MODIFIED WOODImprovement of durability and dimensional stabilityRemoving of resinsImprovement of resonant (acoustic) propertiesMass lossChange of physical properties:ColourReduction of strength and stiffnessBending strength 10 % 50 %

Results - change of colour

SBH

Elm wood

MASS LOSSESSpruce:3 % (190 C) 24 % (230 C) Larch:5 % (190 C) 31 % (230 C)

MATERIALS AND METHODS decay testsDECAY TESTSmini-block test (Bravery)

cross-section: 10 mm 5 mmlength: 30 mmGloeophyllum trabeum Coniophora puteana exposure: 8 weeks

DECAY samples treated at 200 CRESULTS decay tests

Mass loss (%)GtCpSpruceuntreated35,25,45612treated1,51,18,94,4Larchuntreated34,27,729,02,9treated1,170,180,900,21

MATERIALS AND METHODS dimensional stabilityDIMENSIONAL STABILITYASE soaking/ovendrying test (3 cycles)

shrinkage () in r, t dim.

20 mm 20 mm 20 mm

50 mm 20 mm 20 mmunoriented ABSORPTION OF WATER VAPOUR AT 83 % AIR HUMIDITY AND T = 25 C

Exposure at 83 % RH and 25 C

RESULTS: absorption of water vapour spruce wood

RESULTS: absorption of water vapour beech wood

RESULTS: absorption of water vapour oak wood

DIMENSIONAL STABILITY (spruce)

DIMENSIONAL STABILITY (beech)

DIMENSIONAL STABILITY (oak)

APPROXIMATION OF REDUCTION OF DIMENSIONS OF MODIFIED WOOD SPECIMENS (spruce)

APPROXIMATION OF REDUCTION OF DIMENSIONS OF MODIFIED WOOD SPECIMENS (beech)

APPROXIMATION OF REDUCTION OF DIMENSIONS OF MODIFIED WOOD SPECIMENS (oak)

MATERIALS AND METHODS MOE AND MORMOE, MOR static three-point bending testZwick Z-100

300 mm 20 mm x 20 mm, absolute dry

10 mm/min

MATERIALS AND METHODS - MOEMOE non-destructivelynatural vibration analysis in clamped-free conditions

300 mm 20 mm 10 mm, absolute dry

MATERIALS AND METHODS - MOEMOE non-destructivelyinductive proximity sensor FFTndynamic signal analyzer

MOR AND MOE of absolute dry samplesRESULTS MOE and MOR

Grafikon1

9430733095504442111582480568.5568.5556.5556.5774774962962261.5261.5774774

8804872193417504109275331622.5622.5431.5431.5871.5871.5688.5688.5332.5332.5871.5871.5

107921041197337712100845487372.5372.5862862418.5418.5324.5324.5715.5715.5418.5418.5

13342130431308010636MOE (larch-vibration)MOE (larch-vibration)231231607.5607.5267.5267.5555.5555.5

Untreated

Treated, 190 C

Untreated

Treated, 210 C

Untreated

Treated, 230 C

MPa

List1

9430568.51,137100 x MOR (spruce-bending)

7,3309621,924

9,5505571,113

4,442262523

11,1589751,949

2,4807741,548

8,8046231,245MOE (spruce-bending)

8,7216891,377

9,341432863

7,504333665

10,9279301,859

5,3318721,743

10,792373745MOE (spruce-vibration)

10,411325649

9,7338621,724

7,7127161,431

10,0847111,422

5,487419837

13,342231462MOE (larch-vibration)

13,043268535

13,0806081,215

10,6365561,111

List1

000000568.5568.5556.5556.5774774962962261.5261.5774774

000000622.5622.5431.5431.5871.5871.5688.5688.5332.5332.5871.5871.5

000000372.5372.5862862418.5418.5324.5324.5715.5715.5418.5418.5

0000231231607.5607.5267.5267.5555.5555.5

Untreated

Treated, 190 C

Untreated

Treated, 210 C

Untreated

Treated, 230 C

MPa

List2

List3

Laboratory chamber for thermal wood modification

Industrial chamber for thermal wood modification

Silvaprodukt d.o.o., Ljubljana, Sovenia

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

CONCLUSIONSThe best characteristics of the products made of modified wood were achieved with wood, modified at temperatures between 180C and 210 CIn spite of the treatment, the mechanical properties of modified wood are still appropriate for wood to be used in constructionsWood modification process can ensure appropriate resistance for diverse ways of utilisation of wooden products, especially in in wet conditions

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