Effect of Compaction Moisture Content on the Resilient Modulus of Unbound Aggregates from Senegal (West Africa)

doi:10.4236/gm.2012.21003

Paper Menu >>

Journal Menu >>

Geomaterials, 2012, 2, 19-23

http://dx.doi.org/10.4236/gm.2012.21003 Published Online January 2012 (http://www.SciRP.org/journal/gm)

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: [email protected]

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)).



1, 1,











(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)







 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].

M. BA ET AL.

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”

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.

M. BA ET AL. 21

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

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.

M. BA ET AL.

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

0,5

1,5

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

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).

REFERENCES

[1] E. J. Yoder and M. W. Witczak, “Principles of Pavement

Design,” 2nd Edition, Wiley, New York, 1975.

doi:10.1002/9780470172919

M. BA ET AL.

[2] T. C. Hopkins, T. L. Beckham and C. Sun, “Resilient

Modulus of Compacted Crushed Stone Aggregate Bases,”

Research Report KTC-05-27/SPR-229-01-1F, Kentucky

Transportation Center, College of Engineering, Univer-

sity of Kentucky, Lexington, 2007, p. 89.

[3] F. Lekarp, U. Isacsson and A. Dawson, “State of the Art.

I: Resilient Response of Unbound Aggregates,” Journal

of Transportation Engineering, Vol. 126, No. 1, 2000.

[4] H. B. Seed, F. G. Mitry, C. L. Monismith and C. K. Chan,

“Prediction of Flexible Pavement Deflections from Labo-

ratory Repeated Load Tests,” NCHRP Rep. No. 35, Na-

tional Cooperative Highway Research Program, 1967.

[5] R. G. Hicks and C. L. Monismith, “Factors Influencing

the Resilient Properties of Granular Materials,” Highway

Research Record, Vol. 345, 1971, pp. 15-31.

[6] M. Fall, A. Sawangsuriya, C. H. Benson, T. B. Edil and P.

J. Bosscher, “On the Investigations of Resilient Modulus

of Residual Tropical Gravel Lateritic Soils from Senegal

(West Africa),” Geotechnical and Geological Engineer-

ing Journal, Vol. 26, No. 1, 2008, pp. 109-111.

[7] M. Ba, M. Fall, F. Samb, D. Sarr and M. Ndiaye, “Resil-

ient Modulus of Unbound Aggregate Base Courses from

Senegal (West Africa),” Open Journal of Civil Engineer-

ing, Vol. 1, No. 1, 2011, pp. 1-6.

doi:10.4236/ojce.2011.11001

[8] ASTM C136-06, “Standard Test Method for Sieve Analy-

sis of Fine and Coarse Aggregates,” Annual Book of

ASTM Standards, ASTM International, West Consho-

hocken, 2006.

[9] ASTM D1557-09, “Standard Test Methods for Labora-

tory Compaction Characteristics of Soil Using Modified

Effort (56,000 ft-lbf/ft3(2700 kN-m/m3)),” Annual Book

of ASTM Standards, ASTM International, West Consho-

hocken, 2009.

[10] ASTM C127-07, “Standard Test Method for Density,

Relative Density (Specific Gravity), and Absorption of

Coarse Aggregate,” Annual Book of ASTM Standards,

ASTM International, West Conshohocken, 2007.

[11] ASTM D6928-10, “Standard Test Method for Resistance

of Coarse Aggregate to Degradation by Abrasion in the

Micro-Deval Apparatus,” Annual Book of ASTM Stan-

dards, ASTM International, West Conshohocken, 2010.

[12] NCHRP, “Laboratory Determination of Resilient Modu-

lus for Flexible Pavement Design,” National Cooperative

Highway Research Program (NCHRP) Project 1-28A,

Transportation Research Board of National Academies,

2004.