Geomaterials, 2012, 2, 19-23
http://dx.doi.org/10.4236/gm.2012.21003 Published Online January 2012 (http://www.SciRP.org/journal/gm)
19
Effect of Compaction Moisture Content on the Resilient
Modulus of Unbound Aggregates from Senegal
(West Africa)
Makhaly Ba, Meissa Fall, Oustasse Abdoulaye Sall, Fatou Samb
Laboratoire de Mécanique et Modélisation (L2M), UFR Sciences de l’Ingénieur, University of Thies, Thies, Senegal
Email: makhaly.ba@univ-thies.sn
Received October 22, 2011; revised November 29, 2011; accepted December 22, 2011
ABSTRACT
This paper presents the results of research conducted to investigate the effect of compaction moisture content on Resil-
ient Modulus (Mr) of unbound aggregates. Three different aggregates (GRB, Basalt and Bandia limestone) was collect-
ed from different sites within Senegal and then subjected to repeated load triaxial tests. Test results showed that the ef-
fect of compaction water content is more significant in the dry side than in the wet side. The compaction water content
has less effect on the GRB and the Basalt than on the Bandia limestone. GRB and Basalt are cohesionless materials and
allow water to drain even during the compaction procedure. Change in water content increases as the compaction water
content increases because of the drainage of the excess water during the compaction and loading procedures. For GRB
and Basalt, at Wopt + 1.5%, most of the excess water is drained during the compaction of the sample and continue to be
drained during the Resilient Modulus test. For the Bandia limestone, this drainage is less significant due to cohesion,
absorption and hydratation.
Keywords: Resilient Modulus; Summary Resilient Modulus; Quartzite; Basalt; Bandia Limestone
1. Introduction
Proper characterization of the mechanical response of un-
bound aggregate materials is a key element in the design
and rehabilitation of pavement structures [1]. The Resil-
ient Modulus (Mr) is used as the mechanical property to
describe stress-stain relationship of unbound material un-
der cyclic loading and given physical conditions. Resil-
ient modulus (Mr) represents the elastic modulus that ac-
count for the non linear behavior of unbound base and sub-
base courses.
Under given confining pressure, the Resilient Modulus
is defined as the slope of the deviator stress-axial strain cur-
ve (Figure 1) [2], or the ratio between the deviator stress
(
d) and the recoverable axial strain (ε1,r) (Equation (1)).

13
1, 1,
d
r
rr
M


(1)
where Mr is the Resilient Modulus, σ1 is the major prin-
cipal stress, σ3 is the minor principal stress and σd is the
deviatoric stress (σ1 σ3).
Many constitutive equations have been developed to
model the resilient behavior of unbound base and sub-
base courses [3]. A bulk stress of θ = 208 kPa is used in
this study to calculate a Summary Resilient Modulus acc-
ording to the Seed et al. model [4] (Equation (2)):
2
1
k
r
a
Mk
P



(2)
13
2

is the bulk stress; k1 and k2 are the mate-
rial properties and Pa is the atmospheric pressure (100
kPa).
Figure 1. Definition of resilient modulus [2].
C
opyright © 2012 SciRes. GM
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.
Copyright © 2012 SciRes. GM
M. BA ET AL. 21
80
90
100
200
300
400
500
600
20304050607080 90100200
Wopt +1.5
Wopt
Wopt - 2
Resilient Modulus, Mr (MPa)
Confining Pressure, 3 (kPa)
Figure 3. Mr vs confining pressure for GRB tested at three
different water contents.
100
1000
20304050607080 90100200
Wopt + 1.5
Wopt
Wopt - 2
Resilient Modulus, Mr (MPa)
Confining Pressure, 3 (kPa)
Figure 4. Mr vs confining pressure for Basalt tested at three
different water contents.
Figures 6-8 show the variation of the Summary Resil-
ient Moduli (SRM) with water content before compac-
tion and after compaction and Resilient Modulus test for
the three materials tested. Each material has been tested
for three compaction water content (Wopt – 2%, Wopt and
Wopt + 1.5%). The SRM of GRB increases about 20%
when the compaction water content decreases from Wopt
to Wopt – 2% and decreases only about 11% when water
content increases from Wopt to Wopt + 1.5%. For the Ba-
salt, the SRM of GRB increases about 29% when water
content decreases from Wopt to Wopt – 2% and decreases
about 10% when water content increases from Wopt to
90
100
200
300
400
500
600
700
20304050607080 90100200
Wopt + 1.5
Wop t
Wopt - 2
Resilient Modulus, Mr (MPa)
Confining Pressure, 3 (kPa)
Figure 5. Mr vs confining pressure for Bandia limestone
tested at three different water contents.
140
150
160
170
180
190
200
234567
Before compaction
After compaction and Mr test
Internal Summary Resilient Modulus (MPa)
Water content, W (%)
Figure 6. Internal SRM vs Water content before compac-
tion and after compaction and Mr test (GRB).
Wopt + 1.5%. The SRM of Bandia limestone in creases
about 81% when the water content decreases from Wopt
to Wopt – 2% and decreases about 25% when the water
content increases from Wopt to Wopt + 1.5%. These results
show that the effect of water content is more significant
in the dry side than in the wet side. The compaction wa-
ter content has less effect on the GRB and the Basalt than
on the limestone. GRB and Basalt are co-hesionless ma-
terials and allow water to drain even during the compac-
tion procedure as shown by the change in water content
of these materials before compaction and after compac-
tion and Resilient Modulus test.
Copyright © 2012 SciRes. GM
M. BA ET AL.
22
Figure 9 shows the change in water content before
compaction and after compaction and Resilient Modulus
test. This change is much more important in the GRB and
the Basalt than in the Bandia limestone. Change in water
content before compaction and after compaction and Mr
test increases as the compaction water content increases
due to drainage of the excess water during the compac-
tion procedure. For GRB and Basalt, at Wopt + 1.5%, most
of the excess water is drained during the compaction of
the sample and continue to be drained during the Resil-
ient Modulus test. For the Bandia limestone, this drain-
age is less significant due to cohesion, absorption and
hydratation.
200
220
240
260
280
300
123456
Before compaction
After compaction and Mr test
Internal Summary Resilient Modulus (MPa)
Water content, W (%)
Figure 7. Internal SRM vs Water content before compac-
tion and after compaction and Mr test (Basalt).
150
200
250
300
350
400
56789
0
0,5
1
1,5
2
2,5
0246810
GRB
Basalt
Bandia limestone
Change in water content, W (%)
Compaction moisture content, W (%)
Figure 9. Change in Water content before and after Mr test
vs compaction moisture content.
4. Conclusion
10
Before compaction
After compaction and Mr test
Internal Summary Resilient Modulus (MPa)
Water content, W (%)
Figure 8. Internal SRM vs water content before compaction
and after compaction and Mr test (Bandia limestone).
Repeated triaxial load test was conducted on three dif-
ferent aggregates collected from different sites within Se-
negal (West Africa) in order to determine the effect of com-
paction moisture content on Resilient Moduli of unbound
aggregates. Specimens were subjected to Resilient Mo-
dulus test in accordance with the NCHRP project 1-28A
[12]. Test results show that the effect of water content is
more significant in the dry side of the compaction curve
than in the wet side. The compaction water content has
less effect on the GRB and the Basalt than on the lime-
stone. GRB and Basalt are cohesionless materials and al-
low water to drain even during the compaction procedure
as shown by the change in water content of these materi-
als before compaction and after compaction and Resilient
Modulus test. Change in water content increases as the
compaction water content increases because of the drain-
age of the excess water during the compaction procedure.
5. Acknowledgements
The authors would like to acknowledge the Geo-Engi-
neering research group of the University of Wisconsin-
Madison for their guidance and valuable input in this
research project; and the “Entreprise Mapathé NDIOU-
CK” for supporting the high price shipping of aggregates
from Senegal to Madison (USA).
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M. BA ET AL.
Copyright © 2012 SciRes. GM
23
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