Civil Engineering Reference
In-Depth Information
6.5.4 Resilient modulus test
The resilient modulus (Mr) test method detailed in ASTM D4123 was used
in this study. The specimens were tested at 5, 25 and 40°C and the loading
frequency applied at each temperature was 0.5 Hz. Pulse period and recov-
ery time were set at 500 and 1500 ms, respectively. Resilient modulus
depends on the test temperature and the loading frequency (ASTM D4123,
1995). Increase in modulus as plotted in Fig. 6.10 shows that nanoclay-
modifi ed mixture has a greater value than the unmodifi ed mixture at all
test temperatures. An increase in modulus due to the addition of 2-7% of
nanoclay modifi cation varies from 8% to 40% for Cloisite-15A and from
3% to 18% for Nanofi ll-15, depending on the test temperature.
6.5.5 Dynamic creep tests
Creep tests are used to evaluate the permanent deformation of the unmodi-
fi ed and modifi ed mixtures at high temperatures. Accumulated permanent
axial strain has three distinct stages with increasing number of cycles:
primary stage, with a relatively large deformation during a short number of
cycles; secondary stage, where the rate of accumulation of permanent defor-
mation remains constant; and tertiary stage, which is the fi nal stage where
the rate of deformation accelerates until complete failure takes place. This
stage is usually associated with the formation of cracks. The start of the
tertiary stage is usually represented by the fl ow number,
FN
. This number
is used as a rutting resistance indicator of asphalt mixtures (see Fig. 6.11).
In this test only modifi ed mixture with 7% nanoclay was used and the
results are compared to those of the unmodifi ed mixture. The loading pulse
was half sine with duration of 200 ms and a rest period of 800 ms. The
specimens were tested at 40 and 60°C and the results are shown in Figs 6.12
and 6.13.
40
Cloisite 2%
Cloisite 4%
Cloisite 7%
Nanoill 2%
Nanoill 4%
Nanoill 7%
30
20
10
0
5
25
40
5
25
40
Temperature (°C)
Temperature (°C)
6.10
Modulus increment and temperature for nanoclays.
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