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Experimental Hygrothermal Study in Wood and
Wood-based Materials
S = 0.10728630r = 0.98340844
Y A
xis
(uni
ts)
4.21
4.72
5.22
5.72
6.22
6.73
© Fraunhofer USA
N. Shukla, D. Elliott, D. Kumar, C. Misiopecki, J. Kosny
September 9th, 2013
X Axis (units)
7.0 17.0 27.0 37.0 47.0 57.0 67.0 77.0 87.03.71
Introduction & Background
Moisture Content (MC) Measurement Methods
Experimental Setup
Testing Procedure
Results and Discussion
Table of Content
© Fraunhofer USA
Results and Discussion
Conclusions
Advance our understanding of moisture detection
Develop test methodology for inexpensive, accurate
measurement of moisture in building envelope
Focus on wood and wood-based products
6 Samples: Poplar, Red Oak, White Pine, OSB, 4- & 5-
Layer Plywood
Background and Scope
© Fraunhofer USA
Layer Plywood
Fiber saturation point (FSP) is the MC when
wood cell wall is completely saturated with
bound water, but no water is present inside
the cell cavity.
Drying Mechanisms in Wood
wooddryovenofweight
woodinwaterofweightMC
−=
© Fraunhofer USA
the cell cavity.
Above FSP, moisture movement is through
capillary forces
Material permeability, density etc affect
drying rate
http://timber.ce.wsu.edu/Supplements/Moisture/moisture%20page2.htm
Direct
Methods
Indirect
Methods
Thermo-
gravimetric
Analytical Electrical Optical
Radiometric Thermal
MC Measurement Methods
© Fraunhofer USA
Radiometric Thermal
Oven dry
Infrared
drying
Microwave
drying
K.-Fisher
Titration
Distillation
Calcium
Carbide
Resistance
Capacitive
−=0
0
m
mmMC w
Equipments
Suitable balance, accuracy 1%
Drying chamber temperature range (103 ± 2) °C
Cutting tools for sample preparation e.g. band-
saw, circular-saw, knife…
Procedure
Oven-drying in environmental chamber at
(103 ± 2) °C until constant weight is achieved
Oven-Dry Method
© Fraunhofer USA
Constant weight condition is reached when
loss in weight is in an interval of 6 h is less
than 1%.
Salient Features
Reference method in wood industry (DIN EN-
13183-1)
Easy, inexpensive, and accurate method
Destructive and time consuming method
A
lR
*ρ=
Material Resistivity
ρ (Ω-m) at 20 °C
Silver 1.6 x 10–8
Water 20 − 2000
Wood (oven dried) 1014 − 1016
Glass 1011 − 1015
R = f(MC)
Electrical Resistance Method
© Fraunhofer USA
Procedure
Find calibration curve for resistance as a function of MC
Equipments
Sensors: metallic screws, nails, needles…
Resistance measuring device e.g. multi-meter, potential divider…
http://www.fs.fed.us/ccrc/topics/urban-forests/docs/physical%20properties%20and%20moisture%20relations%20of%20wood.pdfhttp://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivity#Resistivity_of_various_materials
R = f(MC)
In the range 0 ≤ MC ≤ FSP, resistance varies between 100 Ω and 100 TΩ
Above FSP, decrease in resistance is smaller
Dry weight
Introduce moisture
Air dry
Measure periodically
Experimental Setup
© Fraunhofer USA
Weight
Handheld reading
Resistance
Pins
Nails
Screws
Typical depth of 5/16
” (same
Instrumentation
© Fraunhofer USA
Typical depth of /16
(same
as handheld meter)
Voltage divider circuit
DAQ and breadboard with
1MΩ reference resistance
Wood Specimens
© Fraunhofer USA
Poplar, red oak, pine, 4 layer plywood, OSB, and 5-layer
plywood from Brunswick house
Weigh dry
sample
Weigh wet
Calibration Procedure
© Fraunhofer USA
Weigh wet
sampleMeasure
resistance,
weight,
handheld
Calibration Results
© Fraunhofer USA
Log(Resistance)
MC
30
40
50
60
70
80
90
100M
ois
ture
Co
nte
nt
(%)Poplar
Red Oak
Pine
Ply
OSB
Brunswick plywoodCapillary
regime
Wood Drying Characteristics
© Fraunhofer USA
0
10
20
30
0 100 200 300 400
Mo
istu
re C
on
ten
t (%
)
Time (hours)
τα /2L=Water diffusivity in wood
Diffusion
regime
Wood species
Length
(cm)
Width
(cm)
Thickness
(cm)
Density
(kg/m3)
Time Const
(h)
Diffusivity
(cm2/s)
Poplar 15.3 15.2 1.975 392 16.5 6.56E-05
Red Oak 15.45 14.65 1.9275 711 17.5 5.89E-05
Pine 15 14.9 1.91 340 15.9 6.38E-05
Plywood 15.25 14.85 1.2775 588 17.4 2.61E-05
OSB 15.45 14.85 2.085 512 18.4 6.57E-05
Wood Drying Characteristics
© Fraunhofer USA
Drying rate: poplar ≈ pine ≈ OSB > oak > ply
Material permeability, density etc affect drying rate
Ply Brunswick 15 14.8 1.25 505 18.7 2.32E-05
y = 0.9853x
R² = 0.8979
20
30
40M
ois
ture
Co
nte
nt
(We
igh
t)
Reading
Ideal
Linear (Reading)
Hand-held Meter Calibration – Red Oak
© Fraunhofer USA
0
10
0 10 20 30 40
Mo
istu
re C
on
ten
t (W
eig
ht)
Moisture Content (Handheld)
y = 0.7061x
R² = 0.7117
20
30
40M
ois
ture
Co
nte
nt
(We
igh
t)
Reading
Ideal
Linear (Reading)
Hand-held Meter Calibration –5-Layer Ply
© Fraunhofer USA
0
10
20
0 10 20 30 40
Mo
istu
re C
on
ten
t (W
eig
ht)
Moisture Content (Handheld)
R² = 0.9236
R² = 0.8979
R² = 0.885
R² = 0.8575
R² = 0.8349
R² = 0.7614
20
30
40
Mo
istu
re C
on
ten
t (W
eig
ht)
Poplar
Red Oak
Pine
4-Layer Plywood
OSB
5-Layer Plywood
Ideal
+20% Boundary
Hand-held Meter Calibration – All Samples
© Fraunhofer USA
0
10
0 10 20 30 40
Mo
istu
re C
on
ten
t (W
eig
ht)
Moisture Content (Handheld)
+20% Boundary
-20% Boundary
+/-40% Boundary
+/-40% Boundary
Linear (Poplar)
Linear (Red Oak)
Linear (Pine)
Linear (4-Layer Plywood)
Linear (OSB)
Linear (5-Layer Plywood)
Shifted Power Fit: y=a*(x-b)^c
Coefficient Data: a = 4.578859E+001, b = -1.086970E+001, c = -5.317763E-001
S = 0.28245972r = 0.98535971
Y A
xis
(uni
ts)
7.95
8.87
9.78
Resistance Calibration – Poplar
© Fraunhofer USA
X Axis (units)
Y A
xis
(uni
ts)
2.5 14.2 25.8 37.5 49.2 60.8 72.54.30
5.22
6.13
7.04
7.95
% Moisture Content
Lo
g(R
)
Linear Fit: y=a+bx
Coefficient Data: a = 1.02451297226E+001, b = -1.31521540670E-001
S = 0.18482587r = 0.98360959
Y A
xis
(uni
ts)
8.45
9.03
9.61
Resistance Calibration – Poplar
© Fraunhofer USA
X Axis (units)
Y A
xis
(uni
ts)
6.1 10.6 15.0 19.4 23.9 28.3 32.86.14
6.72
7.30
7.88
8.45
% Moisture Content
Lo
g(R
)
Shifted Power Fit: y=a*(x-b)^c
Coefficient Data: a = 7.813615E+000, b = 5.307216E+000, c = -1.437527E-001
S = 0.10728630r = 0.98340844
Y A
xis
(uni
ts)
5.72
6.22
6.73
Lo
g(R
)
Resistance Calibration – OSB
© Fraunhofer USA
X Axis (units)
Y A
xis
(uni
ts)
7.0 17.0 27.0 37.0 47.0 57.0 67.0 77.0 87.03.71
4.21
4.72
5.22
5.72
% Moisture Content
Lo
g(R
)
Linear Fit: y=a+bx
Coefficient Data: a = 6.37917764240E+000, b = -4.68542672033E-002
S = 0.21316184r = 0.88875732
Y A
xis
(uni
ts)
6.00
6.50
7.00
Resistance Calibration – OSB
© Fraunhofer USA
X Axis (units)
Y A
xis
(uni
ts)
8.0 13.0 18.0 23.0 28.0 33.0 38.04.00
4.50
5.00
5.50
6.00
% Moisture Content
Lo
g(R
)
Calibration Relation for All Specimens
Wood Specimen
Power Fit, y=a*(x-b)^c
Linear Fit, y=a+bx
abcCC
abCC
Poplar 45.78859-10.86970-0.5317763
0.985
10.2451297226
0.1315215406700.984
Red Oak 11.443125.322800-0.2591502
9.60329583551-
Wood Specimen
Power Fit, y=a*(x-b)^c
Linear Fit, y=a+bx
abcCC
abCC
4-L Ply 18.5912156119-
0.39473358326
0.943
9.57335961590-
0.2044556698540.901
5-L Ply 8.080417 7.8479182
© Fraunhofer USA
-0.25915020.988
-0.197775784
9550.941
Pine 20.22023-2.500867-0.3467718
0.994
10.0842707969-
0.1490935103810.953
OSB 7.8136155.307216-0.1437527
0.983
6.37917764240-
0.0468542672030.89
5-L Ply 8.0804178.466054
-0.172450576
10.993
7.84791820854-
0.1106659010780.939
5-L Ply(using nailsensors)
7.3485128.820771-0.1392499
0.988
7.33219315574E
-0.0908540591330.930
Developed a practical, continuous and inexpensive methodology to
measure moisture content in wood and wood-based species
Fabricated testing setup for oven-dry and resistance procedures
Screw sensors for reliable, consistent and long-term data collection
Determined water diffusivity in wood samples
Calibrated hand-held meter with oven-dry method
Determined corrections for hand-held meter
Conclusions & Summary
© Fraunhofer USA
Found good sensitivity for resistance with MC
Determined relationship between MC as a function of resistance for six
different species of wood
Develop methodology for brick and cementitious products
Further lab measurements
Hygrothermal simulations
Ongoing Work
Recommended