Nondestructive 

Methods of Evaluating 

Quality of Wood in 

Preservative-Treated 

Piles 

Xiping Wang 

Robert J. Ross 

John R. Erickson 

John W. Forsman 

Gary D. McGinnis 

Rodney C. De Groot 

United States

Department of 

Agriculture 

Forest Service 

Forest 

Products 

Laboratory 

Research 

Note 

FPL−RN−0274
Abstract 

Stress-wave-based nondestructive evaluation methods were 

used to evaluate the potential quality and modulus of 

elasticity (MOE) of wood in used preservative-treated 

Douglas-fir and southern pine piles. Stress wave measurements were conducted on each pile section. Stress wave 

propagation speeds in the piles were then obtained to estimate their MOE. This was followed by a sequence of tests 

conducted on octagon-shaped cants, on boards, and on small, 

clear wood specimens obtained from the piles. Statistical 

regression analyses revealed a strong correlation between the 

stress-wave-based MOE (MOEd) of piles and octagons and 

the corresponding flexural properties of boards and small, 

clear wood specimens determined by transverse vibration 

and static bending techniques, respectively. The results 

also indicated that used preservative-treated wood piles 

still contain material that has potential for use in exterior 

structural applications. 

Keywords: nondestructive evaluation, piles, recycling 

March 2000 

Wang, Xiping; Ross, Robert J.; Erickson, John R.; Forsman, John W.; 

McGinnis, Gary D.; De Groot, Rodney C. 2000. Nondestructive methods of 

evaluating quality of wood in preservative-treated piles. Res. Note 

FPL–RN–0274. Madison, WI: U.S. Department of Agriculture, Forest 

Service, Forest Products Laboratory. 9 p. 

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Contents 

Page

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

Materials ................................................................................1 

Experimental Procedure.........................................................2 

Stress Wave Measurements................................................2 

Density Determination .......................................................2 

Transverse Vibration Tests ................................................3 

Static Bending Tests ..........................................................3 

Results and Discussion...........................................................4 

Physical Properties of Used Creosote-Treated Piles..........4 

Board MOE and Stress Wave Properties of Piles and 

Octagon Cants....................................................................4 

Relationships Between Stress Wave Properties and 

Flexural Properties.............................................................5 

Variation of Stress Wave Properties Within a Pile ............6 

Conclusions............................................................................8 

References..............................................................................9 
Nondestructive Methods of 

Evaluating Quality of Wood 

in Preservative-Treated Piles

Xiping Wang, Research Scientist

Robert J. Ross, Supervisory Research General Engineer

Forest Products Laboratory, Madison, Wisconsin 

John R. Erickson, Research Scientist

John W. Forsman, Assistant Research Scientist

Gary D. McGinnis, Professor

School of Forestry and Wood Products 

Michigan Technological University, Houghton, Michigan 

Rodney C. De Groot, Research Plant Pathologist (retired) 

Forest Products Laboratory, Madison, Wisconsin 

Introduction 

Preservative-treated wood products are important construction materials. Preservative-treated wood piles, after removal 

from service, constitute a major disposal problem for managers of waterfront facilities. For example, 7,000 to 8,000 tons 

of mechanically or biologically deteriorated wood piles are 

currently removed from U.S. Naval facilities annually at a 

cost of at least $20 million per year (Pendleton and Hoffard 

1998). While many of these piles are no longer useful because of damage on their outer layers, a considerable amount 

of the interior wood could be reused for other exterior applications. Examples of the options include fence posts, retaining walls, landscaping timbers, unexposed sheathing, and 

other general structural applications. A key component in 

determining the potential use for sound wood in these piles 

is the development of a nondestructive evaluation (NDE) 

method that could be used to assess the potential quality 

of the wood. 

Stress-wave-based nondestructive testing techniques have 

been investigated extensively during the past few decades 

and have shown much promise for predicting the mechanical 

properties of wood. A variety of wood-based materials ranging from small, clear wood specimens to wood-based composites have been investigated. In recent years, research has 

been conducted to determine if longitudinal stress wave 

techniques could be used to determine the quality of logs. 

Several studies have shown a good relationship 

(R2 = 0.44–0.89) between longitudinal stress-wave-based 

modulus of elasticity (MOE) in logs and static MOE of 

lumber cut from the log (Aratake and Arima 1994, Aratake 

and others 1992, Arima and others 1990, Iijima and others 

1997, Koizumi and others 1997a,b, Ross and others 1997, 

Sandoz and Lorin 1994). However, no effort has been expended to investigate the use of these techniques to evaluate 

the potential quality of used preservative-treated wood pilings. The objective of this study was to investigate the use 

of longitudinal stress wave NDE methods to assess the 

quality of used preservative-treated wood piles removed 

from service. 

Materials

Nine used creosote-treated wood piles (six Douglas-fir 

(Pseudotsuga menziesii) and three southern pine (Pinus 

spp.), designated DF1 to 6 and SP1 to 3) were removed from 

U.S. Navy shore facilities and used for this study. The first 

batch of piles (five Douglas-fir) were cut on-site into approximately 6-ft (1.8-m) sections and transported to the 

Institute of Wood Research (IWR) at Michigan Technological University (MTU), in Houghton, Michigan. The second 

batch of piles (one Douglas-fir and three southern pine) was 

transported to MTU in the whole length, and the piles were 

then cut into 8.5-ft (2.59-m) sections. Altogether, 57 pile 

sections were obtained from these used piles—44 sections 

from Douglas-fir and 13 sections from southern pine. 

These creosote-treated piles had been used as fenders in piers 

and wharves. The outer portions of these piles were severely 

damaged mechanically or biologically during their years of 

service. Splits, decay, and marine borer damage were the 

major visual defects observed on these piles. More splits and 

marine borer damage were found in the Douglas-fir piles. 

The Douglas-fir piles ranged from 30 to 62 ft (9.14 to 

18.90 m) long and 14 to 15.7 in. (35.6 to 39.9 cm) in diameter (butt), with creosote penetrating into the wood from 0.25 

to 2 in. (0.64 to 5.1 cm) deep. The southern pine piles ranged 
2 

from 40 to 47 ft (12.2 to 14.3 m) long and 14.5 to 15.75 in. 

(36.8 to 40.0 cm) in diameter (butt), with creosote penetrating into the wood from 1.5 in. (3.8 cm) to near the pith, 

depending on the pile. 

Experimental Procedure 

Figure 1 shows the experimental procedures we used. Longitudinal stress wave NDE methods were used to assess the 

piles and the octagon cants cut from them. Transverse vibration and static bending tests were performed on boards and 

small, clear wood specimens obtained from the octagons. 

To obtain an estimate of the maximum yield of solid wood, 

we selected 18 sample sections from the piles that contained 

less creosote and cut them into octagon-shaped cants, thereby 

removing most of the creosote-treated outer shell. This outer 

shell material was saved for another study, which was on 

remediation and potential use of this material in the manufacture of composite board material. Stress wave measurements 

were conducted on each pile section and each octagonshaped cant. Samples of shells and sawdust were provided 

for creosote content analysis. Octagon cants were then sawed 

into 4/4 (1-in., 2.5 cm) boards, followed by a series of stress 

wave, transverse vibration, and static bending tests (destructive) on boards and small, clear wood specimens cut from 

boards to obtain an estimate of MOE of boards to correlate 

with the E-rating values obtained from piles and cants. 

Figure 2a shows a typical sawing scheme we used to obtain 

boards from octagon cants. One-inch boards were sawn from 

octagon cants with the board width increasing from either 

side to the middle. This sawing scheme allowed the maximum yield of solid wood from the piles. The number of 

boards obtained from the octagon cants may change because 

of the different diameters of the pile sections. Figure 2b 

shows the cutting of the small, clear wood specimens from 

the boards. From two middle boards and two side boards, 

1- by 1- by 16-in. (25.4- by 25.4- by 406-mm) small, clear 

specimens were cut. The 12 shaded specimens shown in 

Figure 2b, 2 from each sideboard, 4 from each middle board, 

were used to conduct static bending tests for destructively 

determining the wood strength and stiffness. In addition, to 

investigate the variation of stress wave and static properties 

of wood in the radial direction within the cross section of 

piles, all small, clear wood specimens that we obtained from 

the two middle boards of the pile sections designated DF6B 

and S2B (B designates the second section from the butt end 

of the pile) were nondestructively (stress wave) and destructively (static bending) tested. 

Stress Wave Measurements 

Figure 3 shows the experimental setup for stress wave measurements. The specimens (pile sections and octagon-shaped 

cants obtained from selected pile sections) were laid on the 

ground and tested in the longitudinal direction. Longitudinal 

stress waves were generated on one end using a hand-held 

hammer with the accelerometer (Model 3021, Columbia 

Research Labs, Inc., Woodlyn, Pennsylvania) attached to the 

opposite end. Following a mechanical impact, a stress wave 

propagates back and forth along the length of the specimen. 

The stress wave signals were detected by the accelerometer, 

and the waveform was monitored and recorded by a personal 

computer. Figure 4 shows a typical stress waveform obtained 

by monitoring the propagation of longitudinal stress waves 

 in a pile section. The stress waveform consists of a series of 

equally spaced pulses whose magnitude decreases exponentially with time. The stress wave speed (SWS) can be determined by coupling measurements of the time ∆t between 

pulses and the length L of the specimen by 

 SWS = 2L/∆t (1) 

Based on stress wave measurements, the dynamic MOE 

(MOEd) of piles and cants may be calculated using a onedimensional wave equation: 

 MOEd = (SWS)2 ρ (2) 

where ρ is the density of the specimen. 

Density Determination 

After stress wave measurement, each pile section and octagon cant was weighed with a scale. For the pile sections, 

diameters of both large and small ends were measured and 

the bulk volume of the pile section was calculated using the 

following equation: 

 Vpile = (π/12) L (D1

2

 + D2

2

 + D1D2) (3) 

Figure 1—Experimental procedures. 
3 

where D1 is the diameter of the large end, D2 the diameter of 

the small ends, and L the length of pile section. For octagon 

cants, the circumference of the cant was measured at two 

ends and the bulk volume was calculated as 

L l V

2

octgon 2 6

3 



 



 = (4) 

where l is the average circumference of an octagon cant and 

L is the length of the cant. Then the density was determined 

using the bulk weight and bulk volume. 

A disk was cut from the middle section for each pile to investigate its density distribution and determine the moisture 

content of the piles. The disks were wrapped with a plastic 

bag tightly and brought back to the laboratory. Nine small 

samples (1 by 1 by 1 in (25.4 by 25.4 by 25.4 mm)) were 

immediately cut from each disk, four from the outer part, 

four from the middle part, and one from the center of the 

disk. 

Transverse Vibration Tests 

Transverse vibration technique was used to obtain an estimate of the MOE of boards cut from the octagon cants. 

As a potential lumber grading method, the transverse vibration testing technique measures natural frequencies of the 

vibration in a very short time, which in turn provides the 

MOE of the test material since the natural frequencies of a 

member are governed by its MOE and other easily measured 

parameters of test specimens (Ross and Pellerin 1994). Previous results revealed a very strong relationship between 

transverse-vibration-determined MOE (MOEv) and static 

MOE (MOEs) with a correlation coefficient r = 0.99 (Ross 

and others 1991). In this study, a Metriguard Model 340 

E-computer (Pullman, Washington) was used to conduct 

transverse vibration tests on all boards obtained from the 

octagon cants. The board under test was supported at one end 

by a knife-edge support and at the opposite end by the loadcell transducer with a load bottom. The dimensions of the 

boards were physically measured, and the weight and natural 

frequency of the boards were automatically determined using 

the load-cell transducer interfaced to the Metriguard 

E-computer. The MOEv of boards was then determined by 

the following equation: 

2 46 g

MOE

2

r v . I

WL f = (5) 

where fr is natural frequency (Hz), 

 W, weight of board (lb (kg)), 

 L, span of board between supports (in. (m)), 

 I, moment of inertia (in4 (m4

)), and 

 g, gravitational constant (386 in/s2

 (9.8 m/s2)). 

Static Bending Tests 

Static bending tests were performed on a limited number 

of small, clear wood specimens (1 by 1 by 16 in. (25.4 by 

25.4 by 406 mm)) obtained from selected octagon cants 

using a SATEC Universal Testing Machine. These tests 

were conducted according to ASTM D143 standards 

(ASTM 1988). The specimen was supported at two ends on a 

round block resting on a relatively stiff steel L support, 

loaded across a 14-in. (356-mm) span. A load was applied at 

Figure 2—(a) Boards sawn from octagon cant and 

(b) small, clear wood specimens cut from two side 

boards and two middle boards. 

Figure 3—Experimental setup for stress wave 

measurement. 

Figure 4—Time history of a typical stress waveform 

observed in a treated pile section (SP1C). 
4 

the center of the specimen using a bearing block of steel. 

A deflectometer was used to measure the deflection of the 

specimen. A computer data acquisition system was used to 

monitor the process of the bending test and record the test 

data. An average value from all 12 specimens for each pile 

was assumed to be the average value for static bending of the 

solid wood in the piles. 

Results and Discussion 

Physical Properties of Used 

Creosote-Treated Piles 

Table 1 summarizes the various physical characteristics of 

creosote-treated piles used in this study. The average moisture content of the piles ranged from 12.7% to 59.3% for the 

Douglas-fir piles and 22.7% to 88.6% for the southern pine 

piles. The moisture contents of Douglas-fir piles DF1, DF2, 

and DF3 as well as southern pine pile SP3 were below fiber 

saturation point (about 30%). Whereas for Douglas-fir piles 

DF4, DF5, and DF6 and southern pine piles SP1 and SP2, 

the average moisture contents exceeded or were close to the 

fiber saturation point. The significant difference in moisture 

content from pile to pile may imply different service conditions or service history. According to the information provided by the U.S. Navy, Douglas-fir DF4, DF5, and DF6 and 

southern pine SP1 and SP2 were older piles, and Douglas-fir 

DF1, DF2, and DF3 and southern pine SP3 were relatively 

newer piles. This can be reflected by their moisture content 

differences. The older piles have higher moisture contents 

than the newer piles, and they also exhibit more moisture 

content changes in a radial direction than the newer piles. 

Further investigation indicated that the outer layer of a pile 

has lower moisture content than the middle layer or center 

part of the pile. This may be caused by natural drying effects 

after removal from the waterfront facilities. 

Density of material is an important component in the determination of stress-wave-based dynamic MOE (MOEd). In 

this study, densities of used piles were determined in two 

different ways. Bulk density values for the Douglas-fir piles 

ranged from 32.01 to 53.10 lb/ft3

 (0.51–0.85 g/cm3), and 

those for the southern pine piles ranged from 49.15 to 

53.63 lb/ft3

 (0.79–0.83 g/cm3). Density values obtained 

from small samples ranged from 29.18 to 52.02 lb/ft3 

(0.47–0.83 g/cm3) for the Douglas-fir piles and 49.69 to 

58.78 lb/ft3

 (0.80–0.94 g/cm3) for the southern pine piles. 

This indicated that bulk density values are basically in 

agreement with the average density values of small samples 

cut from the piles.

Board MOE and Stress Wave 

Properties of Piles and Octagon Cants 

Stress wave speeds (SWS) measured in piles and octagon 

cants are summarized in Table 2. After the piles were cut into 

octagon cants by removing creosote-treated outer layers, the 

wood density decreased 6.2% to 26.1% for Douglas-fir piles 

and 18.6% for southern pine pile SP1. The SWS measured in 

octagons increased 2% to 19.1% for Douglas-fir and about 

12% for southern pine compared with that measured in pile 

sections This supports the hypothesis that creosote penetrated 

into wood has a significant attenuation effect on stress wave 

propagation. It was also found that defects, such as splits (if 

crossing the wave propagation line), decay, and marine borer 

damage have strong negative effects on stress wave propagation in piles. 

Table 3 shows dynamic MOE (MOEd) of piles and octagons 

determined by stress wave methods and the MOE of boards 

determined by the transverse vibration method. It can be seen 

that the stress-wave-based MOEd of piles and octagons 

tended to be higher than the average MOE of boards sawn 

Table 1—Physical characteristics of creosote-treated Douglas-fir and southern pine piles 

 Length Bulk Depth of creosote 

 of pile Number of Moisture content (%) density penetration (in.)a 

Pile no. (ft)a sections Average Minimum Maximum (lb/ft3)

a Minimum Maximum 

Douglas-fir 

DF1 57.4 10 14.8 11.0 17.8 35.21 0.25 2.00 

DF2 62.2 11 12.7 9.9 15.2 37.39 0.25 2.00 

DF3 40.5 7 13.2 10.7 15.2 32.01 0.25 2.00 

DF4 38.1 7 34.1 25.6 56.9 37.02 0.25 1.00 

DF5 29.1 6 42.1 28.1 62.5 53.10 1.00 7.00 

DF6 36.0 4 59.3 45.5 85.1 51.30 1.50 4.00 

Southern pine 

SP1 46.0 5 28.2 17.9 43.8 49.15 2.00 6.50 

SP2 47.0 5 88.6 39.5 153.9 53.63 2.50 6.00 

SP3 39.5 4 22.7 18.5 26.8 53.51 b b 

a 1 ft = 0.3 m; 1 lb/ft3

 = 16.01 kg/m3; 1 in. = 25.4 mm. 

b

Fully penetrated. 
5 

from piles but were close to the MOE of the bark-side boards 

cut near the outer surface of the piles. (The maximum value 

of board MOE in Table 3 is the MOE of the bark-side 

board.) The same phenomenon was observed in further 

investigations on the variation of SWS and MOE in the 

middle boards cut from piles. This may imply that the stress 

waves tend to lead in the outer portion of wood (towards the 

bark) while they travel through piles or octagons. 

The results of these experiments indicated that used preservative-treated wood piles still contain wood of good quality. 

The MOE of boards obtained from used piles ranged from 

0.89 × 106

 to 2.42 × 106 lb/in2 (6.14 to 16.68 GPa) for Douglas-fir and 1.17 × 106

 to 1.94 × 106 lb/in2 (8.07 to 13.37 GPa) 

for southern pine. Static bending tests conducted on small, 

clear wood samples cut from boards support these results. 

Therefore, it should be possible to remove some of the damaged outer shell wood and reuse the center core for other 

exterior applications. 

Relationships Between Stress Wave 

Properties and Flexural Properties 

Results obtained from various regression analyses are summarized in Table 4. Correlation coefficients obtained from 

these analyses indicate that good relationships existed between stress wave properties of piles and octagons and the 

corresponding flexural properties of boards and small, clear 

wood specimens. 

Figure 5 shows stress-wave-based MOEd of piles compared 

with stress-wave-based MOEd of octagons that were cut from 

piles. It can be seen that a strong correlation existed between 

the MOEd of piles and that of octagons. This revealed that 

the stress wave properties of used piles could reflect the 

properties of solid wood within the piles, although creosote 

and surface defects in used piles have effects on stress wave 

propagation and stress wave measurements as mentioned 

before. Figures 6 and 7 show the relationships between 

stress-wave-based MOEd of piles and octagons and the average MOE of boards determined by the transverse vibration 

method. Good correlation (r = 0.85 to 0.91) was found between stress wave MOEd and board MOE. It was also observed that MOEd of piles has better correlation with the 

MOE of a bark-side board than with the average MOE of 

boards.

Table 2—Stress wave speeds in piles 

and octagon cants 

 Stress wave speed (ft/s)a,b 

Pile no. Pile Octagon cant

Douglas-fir 

DF1 16,657 17,051 

DF2 16,939 17,257 

DF3 14,977 15,322 

DF4 15,479 15,965 

DF5 12,162 14,485 

DF6 13,612 14,265 

Southern pine 

SP1 12,671 14,249 

SP2 10,682 11,923 

SP3 10,971 — 

a

Average value of all sections obtained 

 from each pile. 

b

1 ft/s = 0.31 m/s. 

Table 3—Stress-wave-based MOEd of piles and octagon-shaped cants and MOE of 

boards sawn from piles 

Stress wave MOE (×106

 lb/in2)

a Vibration MOE of boards (×106

 lb/in2)

a 

Pile no. Pile Octagon cant Average Minimum Maximum 

Douglas-fir 

DF1 2.12 1.98 1.40 0.96 2.05 

DF2 2.32 2.26 1.89 1.51 2.42 

DF3 1.55 1.44 1.16 0.89 1.32 

DF4 1.88 1.80 1.55 1.23 1.93 

DF5 1.69 1.59 1.36 1.23 1.53 

DF6 2.05 1.88 1.55 1.34 1.92 

Southern pine 

SP1 1.85 1.71 1.52 1.34 1.94 

SP2 1.17 1.63 1.33 1.17 1.55 

SP3 1.39 — — — — 

a

1 lb/in2 = 6.895 kPa. 
6 

Regression analyses also revealed good relationships between MOEd of piles and octagons and the static MOE andMOR of small, clear wood specimens. The correlation coefficients are listed in Table 4. It therefore can be concluded 

that stress-wave-based MOEd is a good predictor for assessing the quality of wood in used piles. 

Variation of Stress Wave 

Properties Within a Pile 

The close relationships between stress wave properties of 

piles and octagons and the corresponding flexural properties 

of boards and small, clear wood obtained from piles are well 

recognized from the above results. To gain a better understanding of the stress wave behavior in piles and assist in the 

interpretation of stress wave results, it was necessary to 

characterize the variability of stress wave speed as well as 

stress-wave-based MOEd within a pile. 

The variation of stress wave speed along the length of a 

whole pile is shown in Figure 8. Stress wave speeds in both 

Douglas-fir and southern pine piles generally decreased from 

the larger end to the small end. However, with Douglas-fir 

piles, the butt section (larger end) exhibited lower values of 

SWS than the next several sections, whereas the top section 

(small end) had somewhat higher values than the section just 

before it. This can possibly be attributed to the different 

service conditions that these two sections experienced. 

As mentioned earlier, these preservative-treated piles were 

used as fenders in piers and wharves with the small end 

embedded in the ground under water. The wood in the small 

end might have experienced environmental conditions that 

preserved its strength. Conversely, the large end of the piles 

was out of the water, exposed to air and subjected to severe 

biological and physical factors. As a consequence, wood in 

the large end of used piles was more likely to suffer serious 

degradation. For southern pine piles, a 4-ft (1.22-m) butt 

section was cut off and not included in stress wave measurements because that portion was already seriously rotted. 

One Douglas-fir pile section (DF6B) and one southern pine 

pile section (SP2B) were selected to investigate the variation 

of stress wave properties in radial direction within the cross 

section of piles. Boards and small, clear samples were coded 

from one side to another side through the pith. Two middle 

boards contained both mature wood and juvenile wood, 

whereas two bark-side boards were totally mature woods. 

Small, clear specimens were cut from two middle boards and 

ranged from mature wood to juvenile wood. Stress wave 

measurements were conducted on all boards and small, clear 

wood using the end-attached method. 

Figure 9 shows the variation of stress wave speed in an octagon along the radial direction across the board increment. 

Board position 1 and 8 indicate bark side and 4 and 5 indicate middle boards. It is clear that stress waves travel faster 

in the bark-side boards than in the middle boards. The stress 

wave speed in Douglas-fir boards varied from 13,127 ft/s 

(4,001 m/s) at the middle board to 15,289 ft/s (4,660 m/s) 

at the bark-side board, and in southern pine boards, it varied 

from 11,332 ft/s (3,454 m/s) at the middle board to 

12,628 ft/s (3,849 m/s) at the bark-side board. 

Figure 10 shows the variations of stress-wave-based MOEd

and board MOEv along the radial direction across the board 

increment. The variability of stress wave speed and that of 

stress-wave-based MOEd is very similar along the radial 

direction. It can be seen that MOEd decreased from bark-side 

to pith. Also, MOEd follows the same trend with board 

MOEv. The average MOEd is about 10% to 12% higher than 

board MOEv for Douglas-fir and southern pine piles. This 

indicates that the variations of stress wave properties reflect 

the inherent changes of wood mechanical properties in terms 

of board positions within the cross section of a pile. 

Table 4—Results of linear regression analyses for the correlations between MOEd of piles and octagon 

cants and properties of boards and small, clear wood obtained from pilesa

 Properties of boards Linear regression model 

 and small, clear wood MOEd Y = a + b X

 Y X a b r Syx 

Average board MOEv MOEd of piles 0.3443 0.5889 0.85 0.123 

Average board MOEv MOEd of octagons 0.1408 0.7403 0.91 0.101 

Bark-side board MOEv MOEd of piles 0.0677 0.8752 0.90 0.144 

Bark-side board MOEv MOEd of octagons −0.1447 1.0514 0.91 0.137 

MOEs of small,clear wood MOEd of piles 0.7114 0.3355 0.76 0.103 

MOEs of small,clear wood MOEd of octagons 0.5064 0.4669 0.85 0.084 

MOR of small, clear wood MOEd of piles 510.24 4,133.9 0.69 1,538.9 

MOR of small, clear wood MOEd of octagons −757.00 5,059.0 0.68 1,566.0 

a

The small, clear wood specimens were tested in static bending according to ASTM D143 standards; MOEd, 

 stress-wave-based dynamic modulus of elasticity; MOEv, modulus of elasticity determined by transverse vibration 

 method; MOEs, static modulus of elasticity; r, correlation coefficient; Syx, standard error of estimate. 
7 

Figure 5—MOEd of piles plotted with MOEd of octagons 

(1 lb/in2

 = 6.895 kPa). 

Figure 6—Average MOEv of boards plotted with MOEd 

of piles (1 lb/in2 = 6.895 kPa). 

Figure 7—Average MOEv of boards plotted with MOEd 

of octagon cants (1 lb/in2 = 6.895 kPa). 

Figure 8—Variation of stress wave speed along the 

length of a pile (1 ft/s = 0.31 m/s). 

Figure 9—Variation of stress wave speed in an octagon 

along the radial direction across the board increment 

(1 ft/s = 0.31 m/s). 

Figure 10—Variation of MOE in an octagon along the 

radial direction across the board increment 

(1 lb/in2

 = 6.895 kPa). 

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

r = 0.91 

MOEd of octagon cants (x106

 lb/in2)

Average MOEv of boards (x106 lb/in2

) 1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

MOEd of octagons (x106 lb/in2

) 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

r = 0.92 

MOEd of piles (x106 lb/in2)

6000

8000

10000

12000

14000

16000

18000

20000

Stress w ave s peed (ft/s)

1 2 3 4 5 6 7 8 9

Position of pile sections

Douglas-fir 

Southern pine

1 - butt end

9 and 5 - top end

 

6000

8000

10000

12000

14000

16000

18000

20000

Stress wave speed (ft/s)

1 2 3 4 5 6 7 8

Board position

Southern pine (S2B) 1 and 7 – Bark-side

Douglas-fir (DF6B) 1 and 8 – Bark-side

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

MOE (x106 lb/in2

)

1 2 3 4 5 6 7 8

Board position

MOEd (Douglas-fir) MOEv (Douglas-fir)

MOEd (southern pine) MOEv (southern pine)

1 and 8 – Bark-side (Douglas-fir) 

1 and 7 – Bark-side (southern pine) 

 

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

Average MOEv of boards (x106 lb/in2

)

1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6

MOEd of piles (x106 lb/in2)

r = 0.85
8 

Figure 11—Variation of stress wave speed (SWS) in the 

middle board along the radial direction (1 ft/s = 0.31 m/s). 

The variations of stress wave speeds in the middle boards 

along the radial direction are shown in Figure 11. Compared 

with the variation of SWS in octagons, much larger variation 

of SWS was observed in Douglas-fir boards, where SWS in 

the middle board varied from 10,988 ft/s (3,349 m/s) at pith 

to 16,017 ft/s (4,882 m/s) at bark-side. This implies that 

larger variations in mechanical properties of wood may exist 

along the radial direction. For the southern pine section, 

SWS in the middle boards varied from 10,646 ft/s 

(3,245 m/s) at pith to 12,283 ft/s (3,744 m/s) at bark-side, 

which is close to the variation observed in the octagon. It can 

be seen that stress wave propagation in the southern pine 

piles and boards was greatly influenced by creosote 

penetration. 

Figure 12 shows the variations of stress-wave-based MOEd

and static MOE of small, clear wood in the radial direction of 

the middle board. Both MOEd and static MOE of small, clear 

wood exhibit significant variations in the radial direction. 

MOEd and static MOE both continuously decrease from bark 

side to pith. For both Douglas-fir and southern pine piles, 

MOEd of the small, clear wood shows the same trend with 

static MOE. 

When these results are compared with the stress wave 

properties of piles and octagons, it is apparent that the SWS 

measured in the piles and octagons tends to be higher than 

the average SWS measured in the boards and small, clear 

wood but they are close to the SWS in the bark-side board 

and bark-side small, clear wood. The same result can be 

found for stress-wave-based MOEd of piles and octagons. 

This agrees with the results previously observed. It therefore 

can be concluded that stress waves tend to lead in the outer 

portion of wood (towards the bark) while they travel through 

piles or octagons. 

Figure 12—Variation of MOE in the middle board along 

the radial direction (1 lb/in2 = 6.895 kPa). 

Conclusions 

Longitudinal stress wave NDE methods were applied to used 

preservative-treated wood piles to assess the potential quality 

of the wood in them. Based on the results in this study, the 

following conclusions can be drawn: 

1. Longitudinal stress wave methods can be used to evaluate the potential quality of wood in used preservativetreated piles removed from service. Although creosote 

and surface defects in used piles have effects on stress 

wave propagation in piles, good correlation was found 

between stress-wave-based MOEd of piles and corresponding flexural properties of boards and small, clear 

wood specimens obtained from the piles. 

2. Stress wave properties of wood in used piles vary in 

both the longitudinal and radial directions of the pile. 

Stress wave speed and stress-wave-based MOEd basically declined from large end to small end along the 

length of a pile and increased from pith to bark side 

along the radial direction in the cross section of a pile. 

The results further indicated that stress waves tend to 

lead in the outer portion of wood (bark-side) while they 

travel through the piles or octagons. 

3. Results indicated that used preservative-treated wood 

piles still retain wood of good quality. The MOE of 

boards obtained from piles ranged from 0.89 × 106

 to 

2.42 × 106

 lb/in2 (6.14 to 16.68 GPa) for Douglas-fir and 

1.17 × 106

 to 1.94 × 106 lb/in2 (8.07 to 13.37 GPa) for 

southern pine. Static bending tests conducted on small, 

clear wood samples cut from boards support these results. It was therefore concluded that the resulting timber 

and lumber of used piles could be used for other 

applications. 

6000

8000

10000

12000

14000

16000

18000

20000

Stress wave speed (ft/s)

1 2 3 4 5 6 7 8

Position in the middle board

Douglas-fir (DF6B) 1 and 8 – Bark-side

Southern pine (S2B) 2 and 7 – Bark-side

0.6 

0.8

1.0 

1.2

1.4

1.6 

1.8 

2.0 

2.2

2.4

MOE (x106 lb/in2

)

1

 2 3 4 5 6 7 Position in the middle board 

MOEd (Douglas-fir) Static MOE (Douglas-fir)

MOEd (southern pine) Static MOE (southern pine) 

8

1 and 8 – Bark-side 

(Douglas-fir) 

2 and 7 – Bark-side 

(southern pine) 
9 

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