Civil Engineering Reference
In-Depth Information
At 40°C (Fig. 6.12), it can be seen that, for applied load levels of 100 kPa
and 200 kPa, none of the modifi ed and unmodifi ed mixtures reached the
tertiary stage before 6500 load repetitions. For applied load levels of
400 kPa, the unmodifi ed mixture reached the tertiary stage at about 3200
pulses, whereas the modifi ed mixture did not reach the tertiary stage before
6500 pulses. At 400 kPa, excessive deformation was shown in the unmodi-
fi ed mixture and specimens failed before the 6500 maximum pulse limit.
The modifi ed mixture did not show shear deformation failure till 6500
pulses and at all applied load levels, the primary deformations of unmodi-
fi ed mixture are bigger compared to those of the modifi ed mixture samples.
At 60°C (Fig. 6.13), it can be seen that, after the 6500 pulses, none of the
nanoclay modifi ed mixtures reach the tertiary stage for applied load levels
of 100 kPa and 200 kPa. All types of mixtures reached the tertiary stage if
applied load was 300 kPa and the unmodifi ed mixtures reached the tertiary
stage after about 3000 pulses, whereas the Nanofi ll-15 modifi ed mixtures
reached the tertiary stage after about 4100 pulses, and Cloisite-15A modi-
fi ed mixtures reached the tertiary stage after about 5500 pulses. Unmodifi ed
mixture specimens had larger deformations in the primary stage and failed
by excessive deformation at about 3800 pulse counts, whereas the Cloisite-
15A and Nanofi ll-15-A modifi ed mixture specimens did not fail completely
at 5300 and 6500 pulse, counts respectively, at the 300 kPa loading.
6.5.6 Fatigue resistance test
Indirect tensile testing with diametric compressive loading was used to
evaluate the fatigue resistance of unmodifi ed and modifi ed mixtures. A
constant repetitive load was applied and the vertical defl ection was mea-
sured in relation to pulse counts. The fatigue life is defi ned as the number
of load repetitions at specimen fracture. As in the creep tests, only modifi ed
mixture with 7% nanoclay was used in this test to compare test results with
those of the unmodifi ed mixture. Fatigue resistance tests were performed
at 5°C and 25°C. The results in Figs 6.14 and 6.15 show a linear fi t between
N
f
and
at 5 and 25°C. The
R
2
values are very close to 1 for all mixture
types. The slope of the fatigue line at 5°C is larger than the slope of the
fatigue line at 25°C for the modifi ed mixture and the unmodifi ed mixture.
Based on the result, shown in Fig. 6.16, at low temperatures (5°C) and
almost for all loading conditions, the unmodifi ed mixture performed better
under fatigue compared to nanoclay modifi ed mixtures. The average fatigue
life ratio between fatigue lives of the modifi ed and unmodifi ed mixtures is
about 93% for Nanofi ll-15 and about 80% for Cloisite-15A. At a low loading
stress, the fatigue life ratio for the modifi ed mixture is about 100% and at
a high loading stress, the fatigue life ratio decreased to 85% (Fig. 6.16). At
high temperatures (25°C), for all loading conditions, the modifi ed mixture
σ
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