M. BA ET AL.
20
Resilient Modulus of unbound granular materials is
affected by several parameters, some of which are stress
level and moisture content [5]. Apart from stress level,
the compaction moisture content appears to be the most
important factor affecting Resilient Modulus of unbound
base courses. Generally, the Resilient Modulus decreases
as water content increases. But the rate of decreasing de-
pends on the aggregate type and the grain size distribu-
tion.
Several researches were conducted to investigate the
Resilient Modulus of unbound aggregate base courses
from Senegal [6,7]. The effect of density and the input
parameters for Mechanistic-Empirical flexible pavement
design were determined on four different aggregates: Red
quartzite and Black quartzite from Bakel, Basalt from
Diack and Limestone from Bandia. Result show that the
Bandia limestone is stiffer than the basalt but the basalt is
stiffer than the Red and the Black quartzites. The Bandia
limestone is more sensitive to water content than the
quartzites. This paper presents the effect of water content
before compaction and after compaction and Resilient
Modulus test to understand the changes in water content
during the Resilient Modulus test procedure.
2. Material Properties and Testing
Procedure
2.1. Materials
Three different aggregate base or subbase courses were
subjected to Resilient Modulus tests: Red quartzite from
Bakel (GRB), Basalt from Diack (BAS), and Limestone
from Bandia (BAN). Particle size distributions of the
materials tested were conducted according to ASTM
C136-06 [8]. Modified compaction test was conducted
according to ASTM D1557-09 [9]. Specific gravity and
Micro-Deval losses were determined according to C127-
07 [10] and ASTM D6928-10 [11], respectively. Figure
2 and Table 1 present particle size distributions and
physical properties taken from Ba et al. [7]. Repeated
load triaxial test was used to determine the Resilient
Modulus of these aggregates. The three different materi-
als were compacted at 98% of the maximum dry unit wei-
ght for the GRB and the basalt, and 95% of the maxi-
mum dry unit weight for the Bandia limestone [7].
2.2. Resilient Modulus Test Procedure
Specimens with 6 inches diameter and 12 inches height
were subjected to the Resilient Modulus test procedure.
A MTS closed-loop servo-electro-hydraulic testing sys-
tem was used to apply the cyclic loading in a haversine
waveform, with 0.1 second of loading duration and 0.9
second of rest period. Displacements were measured inter-
nally using “Linear Variable Displacement Transducer”
0
20
40
60
80
100
0,010,1110100
GRB
Basalt
Bandia Limestone
Percent finer (%)
Particle size (mm)
Figure 2. Grain size distribution of GRB, BAS and BAN [7].
Table 1. Some physical and mechanical material properties
[7, modified].
Materials ρdmax (kg/m3)Wopt (%) Gs MDE (%)
GRB 2140 5.5 2.65 3.07
BAS 2420 4.2 2.95 5.66
BAN 2065 7.6 2.56 40.0
(“LVDT”) mounted around the specimen inside the cell.
The specimens have been tested using the NCHRP Pro-
tocol 1-28A [12]. Each specimen was conditioned with
103.5 kPa confining pressure, and 1000 cycles of 207
kPa deviator stress. The cycles are repeated 100 times for
30 loading sequences with different combinations of con-
fining pressures and deviator stresses. The last five cy-
cles of each sequence are used to calculate the Resilient
Modulus.
3. Resilient Modulus Results and Analyses
Figures 3-5 present the effect of compaction water con-
tent on the Resilient Moduli of GRB, Basalt and Bandia
limestone, respectively. Each sample has been com-
pacted at three different moisture content (Wopt, Wopt – 2
and Wopt + 1.5). The spread in the data at a constant con-
fining pressure represents the Mr at various deviator
stresses. The curve fit is based on power dependence on
confinement. These figures show that the Resilient Mo-
dulus of GRB increases about 10% and 24% when water
content decreases respectively from Wopt to Wopt – 2 and
from Wopt + 1.5 to Wopt – 2. For the Basalt, Resilient
Modulus increases about 32% and 40% when water con-
tent decreases respectively from Wopt to Wopt – 2 and
from Wopt + 1.5 to Wopt – 2. Resilient Modulus of Bandia
limestone increases about 59% and 87% when water
content decreases respectively from Wopt to Wopt – 2 and
from Wopt + 1.5 to Wopt – 2. Then the Bandia limestone is
much more sensitive to water content than the GRB and
the Basalt.
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