pacted, then placed in the coldroom (34C), and
slices was determined to develop a top-to-bottom
moisture profile of each specimen.
saturated by raising the water table at the rate of
25 mm/hour. The water table was maintained at
CBR tests are an index of the shearing resis-
the top of the samples overnight. The next morn-
tance of a soil or the soil strength. The test meas-
ing, the water table was lowered to 10 mm above
ures the strength of a soil for specific moisture
the sample bottoms and the samples were
and density conditions. The shearing resistance is
allowed to drain. All four samples had a constant
obtained by forcing a steel piston into a com-
water supply during testing. The specimens were
pacted soil sample at the rate of 1.27 mm/minute.
then placed on the bottom warming/cooling
The force required to reach 2.54 mm and 5.08 mm
plate. Thermocouples were installed in the sam-
of penetration is measured. The measured force is
ples at the top, bottom and depths of 25, 50, 75,
converted into a ratio and compared against stan-
100, and 125 mm. The top cooling plates were
dard test values to obtain the CBR. The CBR is not
placed on the samples along with a 5.5-kg sur-
an exact measure of the shearing modulus
charge weight that simulates the weight of a 150-
because of a slight influence of the confining
mm-thick asphalt concrete pavement surface.
effect of the mold. CBR generally falls between 0
The box was then filled with loose granular insu-
and 100% with a higher value, indicating a
lation.
stronger soil. CBR testing was conducted before
The samples were conditioned at 3C top and
and after frost-susceptibity tests were run to
bottom for the first 24 hours. Following this con-
determine the loss of strength in the Tilcon mater-
ditioning period, the samples were subjected to
ial. The results are given in Table 1.
four freezethaw cycles, rather than the ASTM
The samples in the unsaturated case were pre-
standard of two cycles. Each freezethaw cycle
pared and tested in the same manner as the satu-
consists of an initial 8-hour freeze of 3C top and
rated samples with three exceptions: the samples
3C bottom. This is followed by a 16-hour freeze
were not saturated when placed in the coldroom,
at 12C top and 0C bottom to freeze the entire
a constant water supply was not connected to the
sample from top to bottom. A 16-hour thaw
samples during testing, and due to time con-
period follows at 12C top and 3C bottom. At
straints, the unsaturated samples were only sub-
completion of the thaw, the samples are again sta-
jected to two freezethaw cycles. An illustration
bilized at 3C top and bottom for 8 hours before
of the testing apparatus is shown in Figure 2.
the next freeze begins.
Testing data were collected every 5 minutes by
Following the final thaw period, the samples
a Northgate 486DX2 computer. LabVIEW for
were removed from the coldroom. California
Windows, Version 4, was used to control two
Bearing Ratio (CBR) tests (ASTM test method
Neslab RTE-110 circulating baths. The baths con-
D1883) were conducted on the samples but
trolled the temperature of the top and bottom
limited to a penetration of 7.6 mm. The samples
plates on the samples, which regulated the tem-
were then sliced horizontally into six approxi-
perature gradient and the rate of freeze in the
mately equal slices. The moisture content of these
samples. The temperature data from each ther-
Table 1. Summary of Raymark test data.
Pretest
Post-test
Pretest
Pretest
Post-test
Heave
Frost
moisture
moisture
density
CBR
CBR
rate
design
(g/cm3)
Sample
(%)
(%)
(%)
(%)
(mm/day) Classification classification*
1
7.66
10.33
2.26
45
4
20.2
Very high
F2
2
7.56
10.20
2.24
40
3
15.4
High
F2
3
7.11
10.04
2.45
43
3
15.0
High
F2
4
7.72
9.96
2.24
35
4
14.9
High
F2
5
8.35
7.91
2.25
44
10
6
Low
F2
6
8.25
8.03
2.26
45
9
4
Medium
F2
7
8.36
8.00
2.23
34
8
4
Medium
F2
8
8.77
8.12
2.24
39
9
4
Medium
F2
Note: Samples 14 are tested under saturated conditions; samples 58 are tested under in-situ
conditions.
*An F2 classification indicates a frost-susceptible material with 6 to 15% of the material finer than
0.02 mm by weight (U.S. Army and the Air Force 1985).
3
Previous Page
