Experimental Hygrothermal Study in Wood and Wood-based Materials

Transcription

1 Experimental Hygrothermal Study in Wood and Wood-based Materials S = r = Y Axis (units) X Axis (units) N. Shukla, D. Elliott, D. Kumar, C. Misiopecki, J. Kosny September 9 th, 2013

2 Table of Content Introduction & Background Moisture Content (MC) Measurement Methods Experimental Setup Testing Procedure Results and Discussion Conclusions

3 Background and Scope 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

4 Drying Mechanisms in Wood MC = weight of water in wood weight of oven dry wood 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. Above FSP, moisture movement is through capillary forces Material permeability, density etc affect drying rate

5 MC Measurement Methods Direct Methods Indirect Methods Thermogravimetric Analytical Electrical Optical Radiometric Thermal Oven dry Infrared drying Microwave drying K.-Fisher Titration Distillation Calcium Carbide Resistance Capacitive

6 Equipments Suitable balance, accuracy 1% Drying chamber temperature range (103 ± 2) C Cutting tools for sample preparation e.g. bandsaw, circular-saw, knife Procedure Oven-Dry Method Oven-drying in environmental chamber at (103 ± 2) C until constant weight is achieved 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 ) Easy, inexpensive, and accurate method Destructive and time consuming method MC mw m = m0 0

7 R = ρ * l A R = f(mc) Equipments Procedure Electrical Resistance Method Material Resistivity ρ (Ω-m) at 20 C Silver 1.6 x 10 8 Water Wood (oven dried) Glass In the range 0 MC FSP, resistance varies between 100 Ω and 100 TΩ Above FSP, decrease in resistance is smaller Sensors: metallic screws, nails, needles Resistance measuring device e.g. multi-meter, potential divider Find calibration curve for resistance as a function of MC

8 Experimental Setup Dry weight Introduce moisture Air dry Measure periodically Weight Handheld reading Resistance

9 Instrumentation Pins Nails Screws Typical depth of 5/16 (same as handheld meter) Voltage divider circuit DAQ and breadboard with 1MΩ reference resistance

10 Wood Specimens Poplar, red oak, pine, 4 layer plywood, OSB, and 5-layer plywood from Brunswick house

11 Calibration Procedure Weigh dry sample Weigh wet sample Measure resistance, weight, handheld

12 Calibration Results MC Log(Resistance)

13 Wood Drying Characteristics Mois sture Content (%) Poplar Red Oak Pine Ply OSB Brunswick plywood Capillary regime Time (hours) Diffusion regime Water diffusivity in wood 2 α = L /τ

14 Wood Drying Characteristics Wood species Length (cm) Width (cm) Thickness (cm) Density (kg/m 3 ) Time Const (h) Diffusivity (cm 2 /s) Poplar E-05 Red Oak E-05 Pine E-05 Plywood E-05 OSB E-05 Ply Brunswick E-05 Drying rate: poplar pine OSB > oak > ply Material permeability, density etc affect drying rate

15 Hand-held Meter Calibration Red Oak Reading Ideal Linear (Reading) y = x R² = Moisture Con ntent (Weight) Moisture Content (Handheld)

16 Hand-held Meter Calibration 5-Layer Ply 40 Reading Ideal Moisture Con ntent (Weight) Linear (Reading) y = x R² = Moisture Content (Handheld)

17 Hand-held Meter Calibration All Samples 40 Poplar Red Oak Pine R² = R² = R² = Moisture Co ontent (Weight) Layer Plywood OSB 5-Layer Plywood Ideal +20% Boundary -20% Boundary +/-40% Boundary +/-40% Boundary Linear (Poplar) R² = R² = R² = Linear (Red Oak) Moisture Content (Handheld) Linear (Pine) Linear (4-Layer Plywood) Linear (OSB) Linear (5-Layer Plywood)

18 Resistance Calibration Poplar Shifted Power Fit: y=a*(x-b)^c Coefficient Data: a = E+001, b = E+001, c = E S = r = Y Log(R) Axis (unit ts) % Moisture X Axis (units) Content

19 Resistance Calibration Poplar Linear Fit: y=a+bx Coefficient Data: a = E+001, b = E S = r = Y Log(R) Axis (uni its) % Moisture X Axis (units) Content

20 Resistance Calibration OSB Shifted Power Fit: y=a*(x-b)^c Coefficient Data: a = E+000, b = E+000, c = E S = r = Y Axis Log(R (uni nits) ) % Moisture X Axis (units) Content

21 Resistance Calibration OSB Linear Fit: y=a+bx Coefficient Data: a = E+000, b = E S = r = Y Axis Log(R) (uni its) % Moisture X Axis (units) Content

22 Calibration Relation for All Specimens Wood Power Fit, Specimen y=a*(x-b)^c a b c CC Poplar Red Oak Pine OSB Linear Fit, y=a+bx a b CC Wood Specimen Power Fit, y=a*(x-b)^c a b c CC 4-L Ply Linear Fit, y=a+bx a b CC L Ply L Ply (using sensors) nail E

23 Conclusions & Summary 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 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