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