Table 13. Summary of all RPC test data.
Std. dev. as
Std. dev. as
Size
Grain
Temperature
Moisture
Strength
% of avg.
Modulus
% of avg.
(C)
Tests
Specimens
(in.)
orientation
(%)
(psi)
strength
(psi)
modulus
6 8 12
Compression
DL
x
21
dry
1394
4.3
19,102
36.5
4.5 5.5 6.5
DT
y
21
dry
1767
6.6
30,028
8.0
3 3.5 4.5
DTT
z
21
dry
1774
2.3
25,372
5.3
6 8 12
CDL
x
30
dry
2718
14.8
64,828
12.9
4.5 5.5 6.5
CDT
y
30
dry
3233
8.3
71,035
9.5
3 3.5 4.5
CDTT
z
30
dry
3747
2.2
63,997
3.7
6 8 12
WL
x
21
2.203
1553
12.2
22,471
8.9
4.5 5.5 6.5
WT
y
21
2.240
1858
8.0
31,716
5.4
3 3.5 4.5
WTT
z
21
2.690
2049
1.7
25,622
6.5
6 8 12
WCL
x
30
0.641
2438
4.4
78,204
12.5
4.5 5.5 6.5
WCT
y
30
1.862
3346
7.4
69,338
7.9
3 3.5 4.5
WCTT
z
30
3.115
3646
2.5
60,051
9.0
1 3.25 *
Tension
W
x
21
dry
413
19.3
22,823
27.9
1 3.25
A
y
21
dry
501
20.3
27,820
14.9
1.5 1.5 16
Flexure
DD
x
21
dry
872
18.3
26,574
21.8
1.5 1.5 16
DCD
x
30
dry
1425
12.5
53,390
8.5
1.5 1.5 16
WD
x
21
15.6
783
50.8
17,839
42.5
1.5 1.5 16
WCD
x
30
3.1
1323
23.3
54,141
16.3
* Gage length
SI conversion factors: 1 in. = 25.4 mm, 1 psi = 6.89 kPa, (21C = 70F, 30C = 22F)
variation occurs in the between longitudinal and
caused a small increase (5 to 15%) in the compres-
transverse directions. In the transverse y direction
sive properties, as can be seen by comparing them
the room-temperature compressive strength is
with the test results of the DL, DT, and DTT groups
higher by about 27%, and the modulus by about
of specimens (see Table 13). However, the pres-
57%. In the z direction, the compressive strength
ence of moisture seems to have an opposite effect
is also higher by 27%, and the modulus by about
on the flexural properties, possibly because the
33%. Of course, the modulus value showed a high
failures in these cases were initiated by tension,
variation in results, the standard deviation being
rather than compression. Comparing the results
36.5% of the average. It is arguable, however, that
of the WD specimens, which were kept in water
this variation in directional properties is due to
for a prolonged time (383 hr), with those of the
the variation of the test specimen sizes, the y and
DD (dry) specimens, it is clear that with the 15.6%
z specimens being much smaller than the x speci-
moisture, the strength decreased about 10%, and
mens. This question could not be resolved with-
the modulus about 33%. High moisture ingression
out further investigation and tests. However, in
has a softening effect on the material. A strength
tension tests, when same-sized specimens were
and modulus decrease in flexure is also observed
tested, selecting one batch (W) from the x direc-
in the Douglas fir study. For the same sized speci-
mens (38.1 38.1 406.4 mm, 1.5 1.5 16 in.),
tion specimens and the other (A) from the y direc-
tion, the differences in both strength and modu-
Douglas fir appeared to absorb moisture at about
lus between them were again significant. The
the same rate as the RPC (see Table 11). Its room-
strength and modulus in the y direction specimens
temperature flexural strength decreased about
were much higher than those in the x direction,
18%, and modulus 30%, with a moisture ingres-
which establishes that the RPC material is essen-
sion of about 22%.
tially anisotropic.
Low temperature had the most significant
It is also interesting to note that the variability
effect on both compression and flexural behavior.
of results increases with the reduction of the size
A comparison of compression strain at failure
of specimens. In general, the variability is much
(peak stress), given in Table 7b for room tempera-
ture and Table 7c for low temperature (30C,
lower in large sized compression specimens than
22F), shows that the strain at failure decreased
in small tension and flexural specimens.
About 2 to 3% of the moisture present in the
significantly at low temperature. The decrease
compressive test specimens WL, WT, and WTT
ranged from the lowest, 17% for the DTT speci
39
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