Accelerated Aging of 

Preservative-Treated 

Structural Plywood

C. Adam Senalik

Robert J. Ross

Samuel L. Zelinka

Stan T. Lebow

Zhiyong Cai

United States Department of Agriculture

Forest

Service

Forest Products

Laboratory

Research Paper

FPL–RP–691

July

2017
Abstract

In this study, the changes in physical properties and

preservative retention of high-grade plywood when

subjected to artificial aging processes were examined. The 

plywood was 15/32-in.-thick panels manufactured from

southern yellow pine A and C grades of veneer. The

artificial aging processes consisted of three primary

mechanisms of degradation: thermal degradation,

hydrolysis, and swelling and shrinking stresses. Three aging 

processes of various severity were used. The least severe 

was cycled changes in ambient temperature and humidity.

The second most severe was cycles of submersion and

air-drying. The most severe was cycles of soaking first

under a vacuum then under high pressure to elevate the 

moisture content, followed by oven-drying. Additional 

parameters explored included the effects of continuous load

versus no load during the aging processes, and the effects of

salt water versus fresh water on the high-pressure soaking.

After artificial aging, the plywood was tested in flexure and

tensile shear. The changes in the plywood physical

properties and preservative levels with respect to the

increasing number of artificial aging cycles were recorded

and analyzed. 

Keywords: artificial aging, plywood, flexural strength,

tensile–shear, preservative retention, CCA, moisture 

cycling, temperature cycling 

July 2017 

Senalik, C. Adam; Ross, Robert J.; Zelinka, Samuel L.; Lebow, Stan T.;

Cai, Zhiyong. 2017. Accelerated Aging of Preservative-Treated Structural

Plywood. Research Paper FPL–RP–691. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory. 17 p.

A limited number of free copies of this publication are available to the 

public from the Forest Products Laboratory, One Gifford Pinchot Drive,

Madison, WI 53726-2398. This publication is also available online at

www.fpl.fs.fed.us. Laboratory publications are sent to hundreds of libraries

in the United States and elsewhere.

The Forest Products Laboratory is maintained in cooperation with the

University of Wisconsin.

The use of trade or firm names in this publication is for reader information

and does not imply endorsement by the United States Department of

Agriculture (USDA) of any product or service.

Contents

1. Introduction.................................................................... 1

2. Materials and Methods................................................... 1 

2.1 Materials................................................................... 1 

2.2 Aging Treatments..................................................... 2 

2.3 Test Procedures......................................................... 5 

3. Results and Discussion................................................... 6 

3.1 Flexure Test.............................................................. 6 

3.2 Tensile–Shear Test Results....................................... 8 

3.3 Preservative Treatment Test Results......................... 9 

4. Summary ...................................................................... 10

5. Literature Cited ............................................................ 10

6. Additional References.................................................. 11

7. Appendix A—Moisture–Temperature and

Moisture–Temperature under Load Humidity

Chamber Monitoring........................................................ 14

8. Appendix B—Data Tables........................................... 15

Acknowledgments

The authors express their gratitude to others who 

contributed to this project: Sara Fishwild, Steven Halverson, 

Kolby Hirth, and Philip Walsh of USDA Forest Service, 

Forest Products Laboratory.

English unit Conversion factor SI unit

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

pound (lb), mass 0.45359 kilogram (kg)

pound per square 

inch (lb/in2) 

6.894 kilopascal (kPa)

pound per cubic 

foot (lb/ft3) 

16.018 kilogram per cubic 

meter (kg/m3) 

ounce (oz) 28.4 gram (g)

fluid ounce (fl oz) 0.03 liter (L)

T°F T°C = (T°F – 32)/1.8 T°C

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1. Introduction

It is critical to know how wood products will perform 

during their service life, specifically how aging will affect 

performance characteristics of these products. This type of 

information is important to both manufacturers and users of 

wood products. To collect this information with in-service 

products would be very time consuming and cost 

prohibitive. Therefore, scientists and engineers rely on test 

methods that accelerate the aging process. From accelerated 

aging tests, scientists and engineers can estimate the service 

life of a particular product.

Gillespie (1984) presents a historical perspective on the 

development of accelerated aging concepts to estimate 

service life of wood- and fiber-based materials and states 

that the fundamental purpose of accelerated aging is to 

evaluate a material or portion of a structure for its durability, 

serviceability, or long-term performance. Numerous 

technical reports and publications that summarize results of 

research studies aimed at developing these concepts—from 

addressing concerns about paper-based materials for library 

or archival storage to assessing the long-term performance 

of structural composite materials—are reviewed and serve 

as the foundation for Gillespie (1984). Those reports and 

publications are included in this report, listed in Additional 

References.

Subsequent research papers summarized studies that 

focused on development of test methods for accelerated 

aging (Inoue 1992, Hua and Wang 1988, Saad and others 

2016), relationship with in-field aging of wood-based 

materials (Krahmer and others 1992, Okkonen and River 

1996, River 1994), and evaluation of new products, 

adhesive systems, or preservative treatments with 

established test methods (Furuta and others 2013, Sellers 

1989, Sellers and others 1990, Sellers and Gardner 1989, Oh 

and Lee 2004).

The USDA Forest Service, Forest Products Laboratory 

(FPL), recently completed a laboratory study designed to 

examine the accelerated aging of preservative-treated 

structural plywood. The flexural and tensile–shear

properties of samples of chromated copper arsenate (CCA)

treated plywood were evaluated after exposure to several 

accelerated aging tests. This report summarizes the design 

of the study and results obtained.

2. Materials and Methods

This section describes the materials, material handling, 

aging treatments, and testing procedures used in this study.

Figure 1 is a flow chart of the study.

2.1. Materials

The plywood panels examined in this study were 4- by 8-ft 

plywood panels of 15/32-in. thickness and were constructed 

of southern yellow pine veneer. Veneer visual grades A and 

Accelerated Aging of Preservative-Treated 

Structural Plywood

C. Adam Senalik, Research General Engineer

Robert J. Ross, Supervisory Research General Engineer

Samuel L. Zelinka, Supervisory Research Materials Engineer

Stan T. Lebow, Research Forest Products Technologist

Zhiyong Cai, Supervisory Research Materials Engineer

USDA Forest Service, Forest Products Laboratory, Madison, Wisconsin

Figure 1—Project flow chart.
Research Paper FPL–RP–691

2

C were used. The panels were treated with a CCA Type C 

wood preservative to a target retention level of 1 lb/ft3 of 

panel. The resulting panels were rated for exterior exposure.

Upon arrival at FPL, seven plywood panels were taken from 

the supplied shipment of panels and assigned letter 

identifiers A through G. From each 4- by 8-ft panel, 56 

specimens measuring 3 in. wide by 20 in. long were cut. A 

total of 392 specimens were obtained from panels A through 

G. Approximately 6 months into the study, the scope was 

expanded and additional specimens were needed; therefore, 

three additional plywood panels were selected, labeled H 

through J, and cut into 176 specimens with dimensions of 

3 by 20 in.

To minimize property variation among the groups, the 

specimens were presorted based on dynamic modulus of 

elasticity (MOE) using the stress wave timing technique 

(Ross 2015). The dimensions and mass of each specimen 

were measured and the density calculated. A Metriguard 

239A Stress Wave Timer was used to measure the transit 

time of stress waves along the length of the specimens.

From the transit time, the stress wave velocity for each 

specimen was calculated. The stress wave velocity and 

density were used to calculate dynamic MOE as shown in 

Equation (1):

2 E = ρc [1]

where E is dynamic MOE, ρ is wood density, and c is stress 

wave velocity.

The specimens were ordered according to dynamic MOE

and then distributed into each of the five groups, which 

resulted in each group having a similar range and 

distribution of dynamic MOE values. After each group was 

subjected to its respective aging process, the specimens 

were brought into a conditioning room set at constant 70 °F 

and 65% relative humidity (RH). The specimens remained 

in the conditioning room for 2 weeks to approach an 

equilibrium moisture content of approximately 12%. After 

conditioning, the specimens were tested to obtain material 

properties.

2.2. Aging Treatments

Artificial aging treatments for plywood primarily use three 

sources of degradation: thermal degradation, hydrolysis, and 

swelling and shrinking stresses (Gillespie and River 1976).

Exposure to elevated temperatures accelerates temperature 

effects that would be experienced in service. Hydrolysis is a 

chemical breakdown of a compound while interacting with 

water and can degrade glues used to construct plywood.

Swelling and shrinking stresses can cause internal damage 

to the plywood, which weakens the structure and degrades 

the plywood material characteristics. Combinations of these 

factors have been used in artificial aging procedures for 

more than 50 years to simulate exposure during in-service 

use (Gillespie 1965). Several factors contribute to in-service 

exposure including location, weather, temperature, and 

function. Plywood in service for a year in Phoenix, Arizona,

will probably look different than a similar piece in service 

for a year in Gulfport, Mississippi. When possible, material 

properties of artificially aged plywood should be compared 

with plywood taken from 

in-service use to determine the severity and duration of 

artificial aging processes needed to achieve properties 

similar to those of the in-service pieces.

In this study, five specimen groups were constructed from 

the specimens cut from plywood panels A through G. The 

five groups included a control group and four other groups 

to undergo different aging treatments. The aging treatments 

were moisture–temperature cycling (MT), moisture–

temperature cycling with load (MT+L), vacuum soak–ovendry (VSD), and vacuum soak with salt water and oven-dry 

(VSD+S). Three specimen groups were constructed from 

the specimens cut from plywood panels H through J. The 

three groups included a submersion control group and two 

other groups to undergo aging treatments submersion 

unloaded (SU) and submersion loaded (SU+L). The 

submersion control group and the original control group 

were statistically compared, and no statistical difference was 

found between the groups at 95% confidence interval; 

therefore, the original control group and the submersion 

control group were combined into a single combined control 

group, which, hereafter, is referred to simply as the control 

group. The total number of specimens per group and the 

number of spare specimens are shown in Table 1.

2.2.1. Moisture–Temperature Cycling and Moisture–

Temperature Cycling under Load

The first accelerated aging exposure consisted of moisture–

temperature cycling both unloaded and under load. This 

type of exposure degrades the plywood via both thermal 

degradation and contributes to shrinking and swelling 

stresses. During the MT aging process, plywood specimens 

were placed in a temperature- and humidity-controlled 

chamber. The room environment alternated between a 

15-day period of high humidity and high temperature (HH) 

and a 15-day period of low humidity and low temperature 

(LL). The prescribed conditions during the HH cycle were 

80% ± 5% RH and a temperature of 90 ± 6 °F. The 

conditions during the LL cycle were 50% ± 5% RH at a 

temperature of 70 ± 6 °F. One HH and one LL period 

constituted a single cycle. Figure 2a shows the plywood 

specimens in the temperature- and humidity-controlled 

chamber.

In addition to the MT aging process, a sample group 

(MT+L) was subjected to temperature and moisture cycling 

while placed under constant load. The MT and MT+L aging 

processes occurred in the same chamber; therefore, the 

environmental conditions and cycle durations were identical 

for both groups. A 40-lb weight was placed on each 

specimen in a manner analogous to the subsequent flexure 

test (Fig. 3). Figure 2b shows the MT+L samples in the 

environmental chamber.
Accelerated Aging of Preservative-Treated Structural Plywood

3

Fluctuation in chamber temperature and RH measured 

during the aging process is shown in Figure 4. Additional 

temperature and RH data are provided in Appendix A. The 

temperature remained within the prescribed range during 

96% of the aging process; it fell below the range 3% of the 

time and was above the range <1% of the time. The RH 

remained within the prescribed range during 63% of the 

process; it fell below 20% of the time and was above the 

range 16% of the time. The effect of the RH being out of 

prescribed range would be a lessening of the severity of the 

aging process. Specimens were subjected to 3, 6, 9, or 12 

cycles. At the end of the prescribed number of cycles, 

specimens were removed from the humidity chamber and 

placed in a conditioning room at 70 °F and 65% RH for a 

period of 2 weeks prior to material property testing.

2.2.2. Submersion Unloaded and Loaded

The second accelerated aging exposure consisted of 

submersing plywood samples in a water tank both unloaded 

and loaded. This method is used to investigate how the 

combination of hydrolysis and shrinking and swelling 

stresses degrade the mechanical performance of plywood.

During the submersion aging process, plywood specimens 

are subjected to periods of complete submersion in water 

purified through reverse osmosis filtering followed by a 

period of air-drying.

Large tanks were set up to hold the specimens during the 

aging process (Fig. 5a). The room holding the tanks was a 

temperature- and humidity-controlled chamber with 

temperature set to 73 °F and 50% RH. The tanks contained 

unloaded and loaded specimens as shown in Figure 5b. For 

the loaded specimens, a 40-lb weight was placed on each 

specimen in a manner analogous to the subsequent flexure 

test shown in Figure 3. The water level was sufficiently high 

to completely submerge the plywood specimens but was 

below the rectangular bar stock comprising the majority of 

the load. The specimens were submerged until the following 

three criteria were met: (1) a minimum of 3 days had 

passed, (2) the change in specimen weight was less than 4% 

for two consecutive measurements taken 24 hours apart, and 

(3) a moisture content (MC) of 65% was achieved.

Unloaded specimens were used only to monitor the criteria 

because it was necessary to keep the loaded specimens 

under stress continuously for the duration of the cycles.

After all three conditions were satisfied, the tanks were 

drained and the specimens were allowed to air-dry until the 

previously mentioned conditions one and two were met or 

the original specimen weights prior to the start of the 

submersion aging process were achieved. A period of 

Table 1—Number of specimens in each group

Specimen group

Number 

of 

groups

Specimens 

per group Spares Total

Specimens tested per group

Flexure

CCAa

retention

Tensile

–shear

Control 1 62 0 62 62 10 20

Moisture–temperature cycling 4 15 10 70 15 3 10

Moisture–temperature cycling + load 4 15 5 65 15 3 10

Vacuum soak–oven-dry 5 10 5 55 10 3 10

Vacuum soak–oven-dry + salt 5 10 5 55 10 3 10

Submersion unloaded 4 15 0 60 15 3 10

Submersion loaded 4 15 0 60 15 3 10

a

CCA, chromated copper arsenate.

Figure 2—Plywood specimens in a humidity- and 

temperature-controlled chamber: (a) unloaded specimens; 

(b) specimens loaded with 40-lb weights.

Figure 3—Moisture–temperature cycling under load (MT+L) 

plywood specimens under constant load.
Research Paper FPL–RP–691

4

submersion followed by a period of air-drying constituted a 

single cycle. Specimens were subjected to 3, 6, 9, or 12 

cycles. At the end of the prescribed number of cycles, 

specimens were removed from the humidity chamber and 

placed in a conditioning room set at constant 70 °F and 65% 

RH for approximately 2 weeks prior to material property 

testing.

The average MC of the sampled specimens at the end of the 

wet portions of the cycles was 68%, with a range between 

59% and 75%. The MCs at the end of the wet portion of 

three of the twelve cycles were below 65% and measured 

59%, 62%, and 64%. Criteria 1 and 2 were satisfied during 

wet portions of all cycles. The average MC of the sampled 

specimens at the end of the dry portions of the cycles was 

20%, with a range between 18% and 23%. Criteria 1 and 2 

were satisfied during dry portions of all cycles.

2.2.3. Vacuum Soak–Oven-Dry with and without Salt

The third accelerated aging exposure is a widely used 

procedure for accelerated aging of plywood that involves 

exposing plywood specimens to a series of alternating 

vacuum soaking in water purified through reverse osmosis 

filtering and oven-drying cycles. This method is used to 

investigate how the mechanical performance of the plywood 

specimens changes when exposed to all three forms of 

degradation: thermal, hydrolysis, and shrinking and swelling 

stresses. A second set of tests were performed that were 

identical to the first with the exception that salt was added to 

the purified water. It was hypothesized that the salt would 

provide an additional avenue for degradation by mechanical 

destruction of the wood cells through formation of salt 

crystals during the drying process, chemical breakdown of 

the wood in the presence of salt solution, or both. The 

VSD+S aging process was expected to be the most severe of 

all the aging processes; the VSD process was expected to be 

less severe than the VSD+S but more severe than the other 

aging processes. In this study, specimens were subjected to 

cycles of vacuum impregnation with warm (100 °F) water, 

which better replicates expected in-service conditions, 

followed by oven-drying at 180 °F. Separate procedures 

were conducted using purified (reverse osmosis) water and a 

salt solution composed of purified water and 35,000 ppm 

salt (NaCl). The salt used was Morton (Chicago, IL) 

Culinox 999 Food Grade Salt, which contains no iodide or 

other additives. The specimens were sorted and assigned 

into groups of 10, as previously described, for exposure to 

either 5, 10, 20, 30, or 40 cycles of soaking and drying. The 

specimens were initially conditioned at 68 °F and 65% RH, 

weighed, and measured for length, width, and thickness.

The objective of the vacuum soaking was to increase the 

MC of the plywood above the fiber saturation point of 30%.

Preliminary trials demonstrated that this could be readily 

achieved with a 30-min initial vacuum followed by 

immersion and a 30-min equilibration at atmospheric 

pressure. In each of two preliminary trials, three specimens 

were vacuum-soaked and allowed to surface-dry and cool 

for 1 h. Moisture meter pins were driven to the midpoint of 

the plywood thickness on three locations on both wide faces 

(six total measurements per specimen). The moisture meter 

used was a Protimeter Timbermaster, Model BLD5604 

currently manufactured by Amphenol Advanced Sensors 

(Wallingford, CT). The electrodes were Hammer Electrode, 

Model BLD5055, with insulated pins. Although resistancebased volumetric moisture meters become less accurate 

above the fiber saturation point, the values observed indicate 

volumetric MCs well in excess of 30%. Previous research 

indicates that the presence of CCA wood preservative has 

relatively little effect on resistance-based moisture meter

measurements (Richards 1990).

Prior to vacuum impregnation, the specimens were bundled 

into groups of 10 and spaced to allow fluid flow between the 

specimens. The bundles were secured to a stainless steel 

rack that was placed into the stainless steel vacuum 

cylinder. Plastic mesh was placed between the specimens to 

ensure water access to all surfaces. An initial 30-min 

vacuum at –11.7 lb/in2 (gauge) was applied to the specimens 

followed by introduction of preheated water (100 °F) while 

still under vacuum. After the specimens were fully 

immersed, the vacuum cylinder was vented to atmospheric 

pressure and the specimens remained submerged for an 

additional 30 min. The temperature of the water was 

Figure 4—Temperature and percentage relative humidity 

(%RH) during moisture–temperature (MT) and moisture–

temperature under load (MT+L) aging processes.

Figure 5—Tanks containing submersion plywood 

specimens: (a) all tanks in the temperature- and humiditycontrolled chamber; (b) layout of submersion unloaded 

(SU) and submersion loaded (SU+L) specimens in the 

tank.
Accelerated Aging of Preservative-Treated Structural Plywood

5

maintained during the immersion period by steam coils 

within the vacuum cylinder. Following the immersion 

period, the specimens were removed from the cylinder and 

allowed to air-dry 4 h to allow time for excess water to 

leave the specimens. They were then dried for 18 to 24 h in 

a forced air-drying oven maintained at 180 °F. Following 

drying, the specimens were returned to the vacuum cylinder 

for vacuum impregnation. After five vacuum impregnation–

oven-drying cycles, one set of 10 specimens was removed 

from the group and returned to the conditioning room to 

await mechanical properties testing. Subsequent sets of 

10 specimens were removed after 10, 20, 30, and 40 cycles.

Water was reused during several vacuum impregnation 

cycles. The same water was used for cycles 1 through 5.

After five vacuum impregnation cycles, the water was 

changed for fresh purified water because most of the water 

soluble wood extractives and poorly fixed preservative 

components would have been freed within the first five

cycles. The same water was used for cycles 6 through 40.

2.3. Test Procedures

2.3.1. Flexure Tests

Two-point flexure tests were conducted in accordance with 

ASTM D3043, Method B (ASTM 2011b). A diagram of the 

test setup is shown in Figure 6a. In Figure 6b, a photograph 

of the actual test setup is shown. The span between supports 

was 18 in. on center. The rocking support surfaces allowed 

the plywood specimen to remain in flat contact across the 

support surface throughout the test. The two load points 

were spaced 9 in. from each other and 4.5 in. from each 

support. The two load points were connected through a 

pivot point to the moving cross head, and a load cell on the 

cross head measured the load during testing. The measured 

load was recorded electronically. To monitor deflection, a 

steel 1/2-in. washer was affixed to the bottom surface of the 

plywood specimen using hot melt glue. The washer was 

placed at the specimen midpoint with respect to both the 

longitudinal and lateral axes. A string was connected 

between a linear variable differential transformer (LVDT) 

and a rare earth magnet. The LVDT was affixed to the load 

frame beneath the plywood specimen. The rare earth magnet 

was placed in contact with the washer on the plywood 

specimen. This configuration allowed the center deflection 

of the plywood specimen to be measured by the LVDT 

directly and eliminate any concerns regarding compliance in 

the load frame and test setup during loading. The deflection 

was recorded electronically.

2.3.2. Tensile–Shear Tests

After the plywood specimens were tested in flexure, a 

portion of the specimen was used to conduct a tensile–shear 

test. Tensile–shear tests were conducted in accordance with 

ASTM D906-98 (ASTM 2011a). The purpose of this test 

was to estimate the relative performance of the adhesive 

bond in plywood. Five pairs of tensile–shear tests were 

performed on each artificially aged group. The control 

group had 10 pairs of tensile–shear tests, as shown in 

Table 1. All specimens were conditioned (73 °F and 63% 

RH) prior to testing. The testing apparatus and custom grips 

are shown in Figure 7.

A 3.25-in. portion of the failed flexure specimen was 

selected to construct the tensile–shear specimens. The 

portion selected was between the inner and outer locations 

of loading during the flexure test as shown in Figure 8a,b.

The removed portion was then cut into smaller segments 

measuring 3.25 by 1 in. as shown in Figure 8c. The 

specimens were prepared per ASTM D906 part 6, with the 

notches cut so as to test both lathe check directions (check 

pulled open and check pulled closed), as shown in 

Figure 8d,e. The peak load in pounds and the percentage

wood breakage were determined from the tensile–shear 

tests. The peak load was recorded during the tensile–shear 

test, and the percentage wood breakage was visually 

estimated after the test was completed.

2.3.3. Preservative Retention

The CCA retentions were determined by inductively 

coupled plasma atomic emission spectroscopy (ICP), as 

explained in American Wood Protection Association 

(AWPA) methods A7 (digestion) (AWPA 2014a) and A21 

(ICP analysis) (AWPA 2014b).

Figure 6—Plywood specimen flexure test setup: (a) diagram of setup; (b) actual test setup.
Research Paper FPL–RP–691

6

To prepare the samples for ICP, wood samples weighing 

approximately 0.018 oz were digested by placing them into 

0.17 fl. oz of nitric acid (70% concentration). The solution 

was heated with microwave radiation to 302 °F for 20 min 

under pressure and then brought up to 1.7 fl. oz volume with 

water. The 0.018-oz samples were removed from the outer 

ply of the plywood. In some cases, a 0.018-oz splinter was 

digested. However, in most cases, the wood was ground to 

20 mesh (0.0331-in. openings) in a Wiley mill prior to 

digestion to homogenize any spatial distributions of the 

elements within the wood. Duplicate samples from the same 

ply were run for each condition as a quality control check.

The digested solution was then run through the ICP. The 

signal intensities for each element were compared with

calibration curves created with five known concentrations to 

determine the sample concentration, which resulted in the 

elemental concentrations for chromium, copper, and arsenic 

(in ounces of element per ounces of wood).

To calculate the CCA retention, the elemental compositions 

were converted to the equivalent amount of metal oxide.

These could then be used to calculate the CCA retention 

based on the concentration of each element by the ratio of 

the elemental oxides for CCA-C specified in AWPA P5 

(AWPA 2014c) and the oven-dry specific gravity of the 

wood (taken as 0.5). This resulted in three CCA retentions 

(one based on each element), which were averaged to give 

the reported CCA concentration.

3. Results and Discussion

3.1. Flexure Test

Flexure testing methods are discussed in Section 2.3.1 and 

were used to determine specimen MOR and static MOE 

properties. The load and displacement data were exported 

into a spreadsheet program in which they were used to 

calculate the stress and strain during testing. The MOR was 

the maximum stress achieved during the testing. The MOE 

was the slope of the stress–strain curve between 20% and 

40% of the MOR. The average, standard deviation (SD), 

and coefficient of variance (COV) were calculated for each 

group. Tables of these values are shown in Appendix B.

Tables B1 through B3 show values for MOR and MOE,

which were derived from the raw data collected during the 

flexure testing.

The MOR values for the MT, MT+L, SU, and SU+L groups 

are shown in Figure 9. The symbols indicate the average 

values for the aged groups. The vertical bars extending from 

the symbols indicate the range of values for the aged group.

Although a noticeable drop occurs between the control and 

the 3-cycle group, there is not a noticeable continuing 

downward trend for the 6-, 9-, and 12-cycle groups. The 

average values for the MT and MT+L groups tended to be 

higher than those of the SU and SU+L groups.

The MT and MT+L cycles had a deleterious effect on the 

MOR of the plywood specimens, but a definitive trend did 

not appear. The largest magnitude drop in average MOR for 

Figure 7—Tensile–shear testing equipment: (a) test of 

setup; (b) custom shear grips. Figure 8—Tensile–shear test specimens: (a) failed flexure 

specimen showing locations of loading during test;

(b) removed portion between loading locations;

(c) removed portion cut into sized coupons; (d) tensile–

shear specimen notched so lathe checks are pulled 

closed; (e) tensile–shear specimen notched so lathe 

checks are pulled open.

Figure 9—Modulus of rupture values of moisture–

temperature (MT), moisture–temperature under load 

(MT+L), submersion unloaded (SU), and submersion 

loaded (SU+L) groups. The symbols indicate the average 

value for the group. The vertical bars indicate the range 

for the group.
Accelerated Aging of Preservative-Treated Structural Plywood

7

the MT groups, a 16% decrease from control, occurred in 

the 3-cycle group. The largest magnitude drop in average 

MOR for the MT+L groups, a 23% decrease from control, 

occurred in the 6-cycle group. All MT and MT+L average 

MOR values decreased with respect to the control value.

Similarly, the SU and SU+L cycles had a deleterious effect 

on the MOR of the plywood specimens, but a definitive 

trend did not appear. There was a drop in average MOR 

values between the control and the 3-cycle group; thereafter, 

the average MOR values did not consistently increase or 

decrease from the 3-cycle group value. The largest 

magnitude drop in average MOR for the SU groups, a 23% 

decrease from control, occurred in the 6-cycle group. The 

largest magnitude drop in average MOR for the SU+L 

groups, a 16% decrease from control, occurred in the 

6-cycle group. None of the average MOR values from any 

of the SU or SU+L groups were higher than the control 

value.

The average static MOE values for MT, MT+L, SU, and 

SU+L groups are shown in Figure 10. The symbols and 

lines have the same meaning as those in Figure 9.

The average static MOE values for the MT group ranged 

from 8% below the control group to 2% above control. For 

the MT+L group, the range was 8% below to 2% below 

control. The range of average static MOE values for the SU 

and SU+L groups were larger than the MT and MT+L 

groups. The SU group had values ranging from 16% below 

to 3% above control. The SU+L group had a range of 13% 

below to 7% below control. No definitive trend with respect 

to number of cycles appeared in the MT, MT+L, SU, or 

SU+L groups with respect to average static MOE.

The MOR values for VSD and VSD+S groups are shown in 

Figure 11. The symbols and lines have the same meaning as 

those in Figure 9. The VSD and VSD+S cycles had a 

deleterious effect on the MOR of the plywood specimens 

with increasing cycles. None of the average MOR values 

from any of the VSD or VSD+S groups were higher than 

the control value. There was a noticeable downward trend 

for the VSD+S group that continued for cycles 5, 10, and 

20. At cycle 20, 30, and 40, the averages tended to have 

more consistent values and the downward trend was no 

longer present. The largest magnitude drop in average MOR 

for the VSD+S group, a 44% decrease from control, 

occurred in the 20-cycle group. An overall downward trend 

of MOR values was also noticeable in the VSD specimens 

for increasing cycles; however, the trend was not as 

consistent as the low-cycle VSD+S groups. The largest 

magnitude drop in average MOR for the VSD group, a 23% 

decrease from control, occurred in the 40-cycle group.

The MOE values for VSD and VSD+S groups are shown in 

Figure 12. The symbols and lines have the same meaning as 

those in Figure 9. The VSD and VSD+S cycles tended to 

have a deleterious effect on the MOE of the plywood 

specimens with increasing cycles. All of the average static 

MOE values decreased with respect to the control value.

The trends of the MOE values mirrored those of the MOR 

values. There was a noticeable downward trend for the 

VSD+S group that continued for cycles 5, 10, and 20. The 

largest magnitude drop in average MOE for the VSD+S 

group, a 25% decrease from control, occurred in the 

20-cycle group. At cycle 20, 30, and 40, the averages tended

to have more consistent values and the downward trend was

no longer present. An overall downward trend of MOE 

values was also noticeable in the VSD specimens for 

increasing cycles; however, the trend was not as consistent 

as that for the low-cycle VSD+S groups. The largest 

magnitude drop in average MOE for the VSD group, a 19% 

decrease from the control, occurred in the 40-cycle group.

Figure 10—Modulus of elasticity values of moisture–

temperature (MT), moisture–temperature under load 

(MT+L), submersion unloaded (SU), and submersion 

loaded (SU+L) groups. The symbols indicate the average 

value for the group. The vertical bars indicate the range 

for the group.

Figure 11—Modulus of rupture values of vacuum soak–

oven-dry (VSD) and vacuum soak–oven-dry plus salt 

(VSD+S) groups. The symbols indicate the average value 

for the group. The vertical bars indicate the range for the 

group.
Research Paper FPL–RP–691

8

3.2. Tensile–Shear Test Results

As shown in Figure 13, no trends were readily apparent for 

peak load values with respect to increasing number of cycles 

for the MT, MT+L, SU, and SU+L groups. The MT peak 

values ranged from 2% to 10% below the control value. The 

SU peak values ranged from 3% to 12% below the control 

value. The 3-cycle MT+L group was 8% lower than the 

control value, but all other MT+L values were greater than 

the control with the 12 cycle having the highest value at 

14% above the control value. The 6-cycle SU+L group was 

6% greater than the control value, but all other SU+L peak 

values were less than the control with the 3 cycle having the 

lowest value at 16% below the control value.

As shown in Figure 14, the average percentage wood 

breakage for the MT and MT+L group equaled or exceeded 

the control group for the 3- and 6-cycle groups of MT and 

MT+L. The peak values for the 9- and 12-cycle groups fell 

below the control. The MT+L 9- and 12-cycle groups were 

2 percentage points below the control value. The MT 9- and 

12-cycle groups were 15 and 10 percentage points below the 

control value, respectively. For both the MT and MT+L 

groups, there was an initial increase between the control 

group and the 3-cycle group, followed by a slight downward 

trend with respect to increasing number of cycles.

The average percentage wood breakage for the SU and 

SU+L group fell below the control value (Fig. 14). The 

highest average percentage wood breakage of the SU and 

SU+L groups was the 9-cycle SU, which was 26 percentage 

points lower than the control. All other average percentage

wood breakage values for SU and SU+L were less than 

30 percentage points below the control with the SU 6-cycle 

group being the lowest at 50 percentage points below the 

control.

As shown in Figure 15, the average peak loads of the VSD 

and VSD+S groups were lower than the average peak load 

of the control group for all cycle groups. For both VSD and 

VSD+S, a general downward trend with respect to number 

of cycles was apparent. With the exception of the 10-cycle 

groups, the average peak loads for the VSD+S groups were 

lower than those of the VSD groups. Within the VSD set, 

the 10-cycle group had the lowest average peak load value 

at 64% of control. The lowest value within the VSD+S set 

was the 30-cycle group, which was 53% of the control

value.

As shown in Figure 16, there was no noticeable trend in 

percentage wood breakage with respect to number of cycles 

Figure 12—Modulus of elasticity values of vacuum soak–

oven-dry (VSD) and vacuum soak–oven-dry plus salt 

(VSD+S) groups. The symbols indicate the average value 

for the group. The vertical bars indicate the range for the 

group.

Figure 13—Peak load recorded during tensile–shear 

testing of moisture–temperature (MT), moisture–

temperature under load (MT+L), submersion unloaded 

(SU), and submersion loaded (SU+L) groups. The vertical 

bars indicate the range for the group.

Figure 14—Percentage wood breakage during tensile–

shear testing of moisture–temperature (MT), moisture–

temperature under load (MT+L), submersion unloaded 

(SU), and submersion loaded (SU+L) groups.
Accelerated Aging of Preservative-Treated Structural Plywood

9

for the VSD and VSD+S group. The average percentage

wood breakage was below the control for all VSD and 

VSD+S groups. For all cycles, the values of the VSD+S 

groups were lower than those of the VSD groups. Large 

variations in percentage wood breakage per group existed 

from one cycle group to the next. The 10-cycle VSD group 

was 4 percentage points below the control, but the 20-cycle 

VSD group was 30 percentage points below the control. The 

10-cycle VSD+S group was 5 percentage points below the 

control, but the 20-cycle VSD+S group was 44 percentage 

points below the control.

3.3. Preservative Treatment Test Results

The CCA retentions by cycle are shown in Figure 17 for the 

MT, MT+L, SU, and SU+L groups and in Figure 18 for the 

VSD and VSD+S groups. Tables of the values can be found 

in Appendix B. The values presented assumed a specific 

gravity of 0.5 for the plywood. The CCA retention estimates 

are proportional to the specific gravity. After oven-drying, 

the average specific gravity for the test specimens was 

found to be 0.545 with a standard deviation of 0.035, which

indicates that the CCA retention values presented in this 

report are likely to be conservatively low. Ten control 

replicates were tested, and the average CCA retention was 

1.01 lb/ft3

. The highest standardized CCA retention level is 

0.80 lb/ft3 for use in AWPA use category 4C (piles) (Lebow 

2010). The fact that the control material is treated in excess 

of what is required for use category 4C suggests that it is 

unlikely that this wood will experience biodeterioration.

The 95% confidence interval of the control samples was 

found to be 0.89 to 1.13 lb/ft3 (calculated from standard 

Figure 15—Peak load recorded during tensile–shear 

testing of vacuum soak–oven-dry (VSD) and vacuum 

soak–oven-dry plus salt (VSD+S) groups. The vertical 

bars indicate the range for the group.

Figure 16—Percentage wood breakage during tensile 

shear testing for vacuum soak–oven-dry (VSD) and 

vacuum soak–oven-dry plus salt (VSD+S) groups.

Figure 17—Chromated copper arsenate (CCA)

concentration moisture–temperature (MT), moisture–

temperature under load (MT+L), submersion unloaded 

(SU), and submersion loaded (SU+L) groups. The vertical 

bars indicate the range for the group.

Figure 18—Chromated copper arsenate (CCA) 

concentration vacuum soak–oven-dry (VSD) and vacuum 

soak–oven-dry plus salt (VSD+S) groups. The vertical 

bars indicate the range for the group.
Research Paper FPL–RP–691

10

deviation 0.19 lb/ft3 on 10 replicates). In general, CCA 

retentions depend on the capillary uptake of the treating 

solution during the treatment process and are known to vary 

widely throughout a piece of wood and from piece to piece.

For CCA retentions of the MT, MT+L, SU, and SU+L 

groups, there were no trends in the data and the averages for 

all conditions except the 6- and 9-month SU+L and the 

9-month SU fell within the 95% confidence interval of the 

control. Similarly for the VSD group, there were no 

apparent trends in the data and in most conditions (except 

the 30-cycle group), the average retentions fell within the 

95% confidence interval of the control. However, for the 

VSD+S specimens, all groups subjected to 20 cycles or 

more fell outside of the 95% confidence interval of the 

control. One potential explanation is that some leaching 

occurred during the VSD+S process, with concentrations as 

low as 0.60 lb/ft3 (standard deviation 0.04 lb/ft3

) after 

30 cycles. Interestingly, the 40-cycle group had a higher 

concentration of CCA (0.79 lb/ft3

).

It appears that for most of the groups, CCA retention 

remained within the statistical variations of the CCA 

retentions in the control group. For the VSD+S, there 

appeared to be some leaching, with average values falling 

outside of the 95% confidence interval of the control after

20 cycles. However, even the lowest measured retention of 

0.60 lb/ft3 is still an extremely high loading of CCA and is 

in excess of the amount required for use category 4 for 

everything except piles.

4. Summary

A comprehensive study was undertaken to investigate the 

effects that several accelerated aging methods have on the 

mechanical properties of preservative-treated structural 

plywood. Plywood specimens where subjected to cycles of 

varying MC, temperature, load, and water quality. The 

following testing regimes were used to artificially age the 

specimens: MT, MT+L, VSD, VSD+S, SU, and SU+L.

After aging, the specimens were tested in flexure to 

determine their MOE and MOR. Tensile–shear specimens 

obtained from the failed flexure specimens were then tested 

to failure.

As expected, the VSD+S aging process resulted in the 

largest changes in both flexural properties and tensile–shear 

strength. The VSD and VSD+S processes provided the most

severe conditions of the three sources of degradation. The 

temperatures to which the specimens were exposed during 

the VSD and VSD+S were higher than those for the other 

artificial aging processes, increasing the likelihood and 

severity of thermal degradation. The maximum MC of the 

specimens of the VSD and VSD+S were higher than those 

of the other artificial aging processes (16.3% and below for 

MT and MT+L, 59% to 76% for SU and SU+L, and 86% to 

111% for VSD and VSD+S), increasing the likelihood of 

hydrolysis degradation. The VSD and VSD+S had the 

largest MC change between wet and dry portions (Δ5% for 

MT and MT+L, Δ47% for SU and SU+L, and Δ>76% for 

VSD and VSD+S). During the wet portion of the aging 

cycles, the MC crossed the fiber saturation point for the SU, 

SU+L, VSD, and VSD+S processes; however, during the 

dry portion of the cycles, the SU and SU+L did not drop 

below 17% and the VSD and VSD+S had MC below 10%.

As a result, the shrinking and swelling stresses to which the 

plywood specimens undergoing the VSD and VSD+S

processes would have been subjected were equal to or 

greater than those of the SU and SU+L. Shrinking and 

swelling stresses result in bond line and substrate 

deterioration weakening the plywood. The salt solution used 

in the VSD+S could provide an additional avenue for 

degradation by mechanical destruction of the wood cells 

through formation of salt crystals during the drying process, 

chemical breakdown of the wood in the presence of the salt 

solution, or both. Lastly, the VSD and VSD+S had a greater 

number of cycles than did the MT, MT+L, SU, and SU+L 

processes; however, a comparison was made between a like 

numbers of cycles for each aging process. The flexural 

strength and tensile–shear strength of the VSD+S 10-cycle 

group was compared with the MT, MT+L, SU, and SU+L 

12-cycle groups. In each case, the average value for the 

VSD+S was less than the average value for any of the other 

artificially aged groups. The VSD+S process caused the 

most severe degradation of all the artificial aging processes.

Future work will include attempting to model the degrading 

effect of the artificial aging on the plywood. In addition, the 

artificial aging will be tied to real world weathering in an 

attempt to determine how much real world weathering time 

is equivalent to each cycle of the different artificial aging 

processes. Lastly, microscopic analysis of the VSD+S group 

will expand our understanding of the degradation 

mechanisms associated with that particular artificial aging 

process.

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Tyne, J.R. 1978. The effect of humidity changes on the 

deflections of ply-web beams. School of Environ., Occas. 

Pap. No. 3. Polytechnic of Central London.

USDA Forest Service. 1978. Structural flakeboard from 

forest residues. Gen. Tech. Rep. WO-5. Washington, DC: 

U.S. Department of Agriculture, Forest Service.

Vajda, P. 1980. The historical development of waferboard 

plant equipment. In: Proc. Canadian waferboard 

symposium. Quebec, Canada: Forintek Canada Corp.: 147-

161.

Weissberg, S.G.; Jessup, D.A.; Weber, C.G. 1939. Stability 

of sheathing papers as determined by accelerated aging.

Building Mater. and Struct. Rep. BMS 35. Washington, DC: 

U.S. Department of Commerce, National Bureau of 

Standards, Washington, DC.

West Coast Adhesive Manufacturers Association Technical 

Committee. 1966. A proposed new test for accelerated aging 

of phenolic resin-bonded particleboard. Forest Products

Journal. 16(6): 19-23.

West Coast Adhesive Manufacturers Association Technical 

Committee. 1970. Accelerated aging of phenolic-resin 

bonded particleboard. Forest Products Journal. 20(10): 26-

27.

W.J. Barrow Research Laboratory. 1964.

Permanence/durability after Book II test data of naturally 

aged papers. Richmond, VA: Virginia Historical Society 

Building.
Research Paper FPL–RP–691

14

7. Appendix A—Moisture–Temperature and Moisture–Temperature under 

Load Humidity Chamber Monitoring

Table A1—Temperature and percentage relative humidity of moisture–temperature cycling and 

moisture–temperature cycling under load humidity chamber

Cycle

Percentage relative humidity Temperature (°F) Datesa

Datea of 

weight 

measurement

Ending 

approx. 

moisture 

Avg. content (%)

Time fraction in desired 

range

Avg.

Time fraction in desired 

range

Below Within Above Below Within Above Start End

Wet 1 76.57 0.02 0.78 0.20 88.89 0.00 0.93 0.07 11/10/15 11/25/15 11/24/15 16.24

Dry 1 50.55 0.02 0.98 0.00 70.31 0.02 0.98 0.00 11/26/15 12/9/15 12/9/15 12.63

Wet 2 79.68 0.00 0.96 0.03 89.78 0.00 1.00 0.00 12/10/15 12/24/15 12/23/15 16.23

Dry 2 50.21 0.01 0.99 0.00 69.95 0.00 1.00 0.00 12/25/15 1/8/15 1/8/15 12.82

Wet 3 79.69 0.01 0.96 0.04 89.72 0.00 1.00 0.00 1/9/15 1/23/15 1/22/15 16.21

Dry 3 53.00 0.23 0.77 0.00 70.38 0.01 0.99 0.01 1/24/15 2/7/15 — —

Wet 4 73.03 0.00 0.45 0.54 91.23 0.17 0.83 0.00 2/8/15 2/22/15 2/19/15 13.27

Dry 4 52.73 0.16 0.84 0.00 70.22 0.03 0.97 0.00 2/23/15 3/9/15 3/9/15 13.01

Wet 5 79.91 0.03 0.90 0.07 89.76 0.00 1.00 0.00 3/10/15 3/24/15 3/24/15 15.92

Dry 5 53.76 0.42 0.58 0.00 69.98 0.00 1.00 0.00 3/25/15 4/8/15 4/7/15 13.08

Wet 6 78.17 0.11 0.59 0.30 89.79 0.00 1.00 0.00 4/9/15 4/23/15 4/23/15 15.45

Dry 6 56.23 0.63 0.37 0.00 69.99 0.00 1.00 0.00 4/24/15 5/8/15 5/8/15 13.59

Wet 7 77.30 0.08 0.46 0.46 89.78 0.00 1.00 0.00 5/9/15 5/23/15 5/21/15 15.50

Dry 7 59.15 0.84 0.16 0.00 70.02 0.00 1.00 0.00 5/24/15 6/7/15 6/4/15 13.79

Wet 8 79.85 0.02 0.95 0.03 89.81 0.00 0.99 0.00 6/8/15 6/22/15 6/22/15 15.82

Dry 8 54.97 0.61 0.37 0.02 69.99 0.00 1.00 0.00 6/23/15 7/7/15 7/7/15 13.30

Wet 9 71.57 0.02 0.36 0.62 89.35 0.00 0.99 0.01 7/8/15 7/22/15 7/22/15 15.14

Dry 9 55.56 0.71 0.29 0.00 69.99 0.00 1.00 0.00 7/23/15 8/6/15 8/6/15 13.40

Wet 10 80.00 0.03 0.91 0.06 89.76 0.00 1.00 0.00 8/7/15 8/21/15 8/21/15 15.74

Dry 10 49.96 0.17 0.56 0.26 70.15 0.00 1.00 0.00 8/22/15 9/5/15 9/3/15 11.91

Wet 11 71.14 0.04 0.60 0.36 89.75 0.00 1.00 0.00 9/6/15 9/20/15 9/17/15 15.46

Dry 11 46.74 0.04 0.69 0.27 70.00 0.00 1.00 0.00 9/21/15 10/5/15 10/5/15 11.53

Wet 12 75.35 0.09 0.35 0.56 89.81 0.00 1.00 0.00 10/6/15 10/20/15 10/20/15 14.86

Dry 12 46.62 0.56 0.34 0.09 70.45 0.58 0.42 0.00 10/21/15 11/9/15 11/9/15 11.78

a

Month/day/year.
Accelerated Aging of Preservative-Treated Structural Plywood

15

8. Appendix B—Data Tables

Table B1—Modulus of rupture (MOR) and modulus of elasticity (MOE) of moisture–temperature cycling 

(MT) and moisture–temperature cycling under load (MT+L) groups by cycle (SD, standard deviation; COV, 

coefficient of variation)

Property Value Control

MT cycles MT+L cycles

3 6 9 12 3 6 9 12

MOR

(lb/in2)

Average 5468 4569 4680 5346 5222 5279 4231 4354 5329

SD 1314 1284 1249 1433 1456 1634 1221 1580 1239

COV 0.24 0.28 0.27 0.27 0.28 0.31 0.29 0.36 0.23

MOE

dynamic

(×106

lb/in2)

Average 1.33 1.35 1.35 1.36 1.36 1.35 1.36 1.36 1.34

SD 0.28 0.34 0.35 0.36 0.36 0.34 0.35 0.36 0.35

COV 0.21 0.25 0.26 0.27 0.26 0.25 0.26 0.27 0.26

MOE

static

(×106

lb/in2)

Average 1.50 1.49 1.39 1.38 1.53 1.42 1.47 1.39 1.44

SD 0.29 0.20 0.21 0.28 0.31 0.25 0.26 0.25 0.33

COV 0.19 0.14 0.15 0.20 0.20 0.18 0.17 0.18 0.23

Table B2—Modulus of rupture (MOR) and modulus of elasticity (MOE) of submerged unloaded (SU) 

and submerged loaded (SU+L) groups by cycle (SD, standard deviation; COV, coefficient of variation)

Property Value Control

SU cycles SU+L cycles

3 6 9 12 3 6 9 12

MOR

(lb/in2)

Average 5468 4772 4231 4751 4453 4638 4584 4683 4777

SD 1314 927 875 929 741 1065 855 1363 741

COV 0.24 0.19 0.21 0.20 0.17 0.23 0.19 0.29 0.16

MOE

dynamic

(×106

lb/in2)

Average 1.33 1.32 1.32 1.33 1.32 1.32 1.33 1.32 1.32

SD 0.28 0.23 0.23 0.21 0.20 0.23 0.23 0.21 0.20

COV 0.21 0.17 0.17 0.16 0.15 0.17 0.17 0.16 0.15

MOE

static

(×106

lb/in2)

Average 1.50 1.55 1.27 1.53 1.30 1.31 1.37 1.30 1.40

SD 0.29 0.27 0.38 0.18 0.22 0.40 0.30 0.35 0.30

COV 0.19 0.17 0.30 0.12 0.17 0.31 0.22 0.27 0.22
Research Paper FPL–RP–691

16

Table B3—Modulus of rupture (MOR) and modulus of elasticity (MOE) of vacuum soak–oven-dry (VSD) and 

vacuum soak–oven-dry plus salt (VSD+S) groups by cycle (SD, standard deviation; COV, coefficient 

of variation)

Property Value Control

VSD cycles VSD+S cycles

5 10 20 30 40 5 10 20 30 40

MOR

(lb/in2)

Average 5468 5047 5429 4702 4724 4235 4930 4139 3065 3306 3469

SD 1314 639 1088 1745 1287 666 920 782 1040 1118 1015

COV 0.24 0.13 0.20 0.37 0.27 0.16 0.19 0.19 0.34 0.34 0.29

MOE

dynamic

(×106

lb/in2)

Average 1.33 1.37 1.36 1.37 1.38 1.38 1.35 1.35 1.3494 1.35 1.37

SD 0.28 0.35 0.35 0.36 0.39 0.41 0.35 0.35 0.3527 0.36 0.40

COV 0.21 0.26 0.26 0.26 0.28 0.30 0.26 0.26 0.2614 0.26 0.29

MOE

static

(×106

lb/in2)

Average 1.50 1.46 1.38 1.36 1.33 1.23 1.31 1.21 1.131 1.16 1.20

SD 0.29 0.22 0.27 0.32 0.26 0.24 0.24 0.18 0.287 0.36 0.17

COV 0.19 0.15 0.19 0.24 0.19 0.19 0.18 0.15 0.2537 0.31 0.14

Table B4—Tension–shear peak load and percentage wood breakage of moisture–temperature cycling (MT)

and moisture–temperature cycling under load (MT+L) groups by cycle (SD, standard deviation; 

COV, coefficient of variation)

Property Value Control

MT cycles MT+L cycles

3 6 9 12 3 6 9 12

Peak load

(lb)

Average 152 140 138 144 144 140 157 155 174

SD 35.3 26.1 31.9 20.6 36.6 24.3 25.7 38.9 53.3

COV 0.232 0.187 0.232 0.143 0.254 0.174 0.164 0.252 0.307

Percentage

wood 

breakage

Average 66 68 66 51 56 74 66 64 64

SD 30 34 34 17 30 25 32 26 24

COV 0.45 0.49 0.51 0.33 0.54 0.33 0.49 0.41 0.37

Table B5—Tension–shear peak load and percentage wood breakage of vacuum soak–oven-dry (VSD) 

and vacuum soak–oven-dry plus salt (VSD+S) groups by cycle (SD, standard deviation; COV, coefficient 

of variation)

Property Value Control

VSD cycles VSD+S cycles

5 10 20 30 40 5 10 20 30 40

Peak load

(lb)

Average 152 135 97.7 125 105 111 126 109.5 93 81 100

SD 35.3 18.5 25.7 27.7 19.5 21.6 15.8 18.7 21.6 24.9 23.2

COV 0.232 0.138 0.263 0.222 0.184 0.195 0.125 0.171 0.234 0.307 0.233

Percentage

wood 

breakage

Average 66 54 62 38 47 52 42 61 22 42 26

SD 30 24 36 27 26 32 27 32 21 33 21

COV 0.45 0.44 0.58 0.71 0.56 0.63 0.63 0.52 0.99 0.79 0.80
Accelerated Aging of Preservative-Treated Structural Plywood

17

Table B6—Tension–shear peak load and percentage wood breakage of submerged unloaded (SU) 

and submerged loaded (SU+L) groups by cycle (SD, standard deviation; COV, coefficient of variation)

Property Value Control

SU cycles SU+L cycles

3 6 9 12 3 6 9 12

Peak load

(lb)

Average 152 143 144 134 148 128 161 146 140

SD 35.3 33.4 34.3 28.3 31.1 32.4 51.1 25.2 27.0

COV 0.232 0.23 0.24 0.21 0.21 0.25 0.32 0.17 0.19

Percentage

wood 

breakage

Average 66 34 16 40 29 31 25 34 30

SD 30 19 16 31 23 35 29 28 27

COV 0.45 0.56 1.00 0.78 0.80 1.13 1.17 0.85 0.91

Table B7—Chromated copper arsenate (CCA) retention by cycle for 

moisture–temperature cycling (MT), moisture–temperature cycling under load 

(MT+L), submerged unloaded (SU), and submerged loaded (SU+L) groups

Specimen group

CCA retention

(lb/ft3)

0 cycles 3 cycles 6 cycles 9 cycles 12 cycles

MT 1.01 1.06 1.03 0.99 0.98

MT+L 1.01 1.03 0.94 0.98 1.07

SU 1.01 1.10 1.14 0.86 0.96

SU+L 1.01 0.98 0.84 0.84 0.93

Table B8—Average chromated copper arsenate (CCA) retention by cycle for the vacuum 

soak–oven-dry (VSD) and vacuum soak–oven-dry plus salt (VSD+S) groups

Specimen group

CCA retention

(lb/ft3)

0 cycles 5 cycles 10 cycles 20 cycles 30 cycles 40 cycles

VSD 1.01 0.99 0.88 1.05 0.80 0.94

VSD+S 1.01 0.87 0.89 0.84 0.65 0.79