Use of thermally modified wood in building constructions
Prof.dr. Franc [email protected]
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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