stabilization and utilization of dune sand in road engineering
TRANSCRIPT
Arab J Sci Eng (2014) 39:1517–1529DOI 10.1007/s13369-013-0721-z
RESEARCH ARTICLE - CIVIL ENGINEERING
Stabilization and Utilization of Dune Sand in Road Engineering
Abderrahmane Ghrieb · Ratiba Mitiche-Kettab ·Abderrahim Bali
Received: 4 June 2012 / Accepted: 10 July 2013 / Published online: 5 September 2013© King Fahd University of Petroleum and Minerals 2013
Abstract The aim of the work presented in this paper isthe valorization of dune sand, which is abundant in Djelfa(Algeria). This study consists of valorizing a local materialin road construction. Several stages were considered in thisinvestigation. A method of formulation of the mixtures hasbeen proposed, which is based on the stabilization of thestudied sands using a hydraulic binder and a granular correc-tor. For each mixture, the optimum Proctor, the compressivestrength with and without immersion and the tensile strengthwere determined. After that, an analysis of the results wasmade to examine the influence of the sand origin and the sta-bilization agent proportion on the physical and mechanicalcharacteristics of mixtures. The stabilized sands were classi-fied according to current standards; the optimal formulationswere then selected, on which additional tests were carriedout. The results obtained show that the formulations selectedhave sufficient performances to be used in road foundationlayers.
Keywords Dune sand · Granular corrector ·Hydraulic binder · Stabilization · Mechanical performances ·Valorization · Road material
A. Ghrieb (B)Civil Engineering Department, University of Djelfa,17000 Djelfa, Algeriae-mail: [email protected]
R. Mitiche-Kettab · A. BaliLaboratory of Construction and Environment, Polytechnic NationalSchool of Algiers, 16000 Algiers, Algeriae-mail: [email protected]
A. Balie-mail: [email protected]
1 Introduction
In the region of Djelfa, an abundant presence of noble aggre-gates can be noticed. However, their abusive use can cause along-term problem. It has been therefore thought that it mightbe judicious to use other local materials in substitution suchas dune sands, to preserve the resources of the region andavoid excessive pollution, as well as a negative impact on theenvironment.
Dune sands are considered as poor quality materials (highporosity, low bearing capacity, poorly graded), giving insuf-ficient mechanical performances [10,11]; their stabilizationis therefore essential.
The term “stabilization” means a set of proceduresaimed at improving the characteristics of the soil, particu-larly its mechanical strength, to decrease its sensitivity towater and its swelling and to increase the wear resistance[8,9].
In our study, the stabilization of the studied sands ismade by the addition of a hydraulic binder and a granularcorrector with different percentages. Seventy-two mixtures
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Fig. 1 Vicinity map showinglocations of the studied sands
DJELFA
50 km
Medea
Tissemsilt
M'sila
Biskra
Oua
rgla
Laghouat
Tiaret
GhardaiaLimit of Djelfa
N
E
S
W
5°E4°E3°E2°E
4°E3°E2°E 5°E
33°N
34°N
35°N
33°N
34°N
35°N
Location ofsand SM
Location ofsand FS
Location ofsand SZ
Location ofsand SA
were prepared and tested at the compressive strength, tensilestrength and resistance to immersion.
The objective of the work presented is to evaluate the influ-ence of sand origin and the percentage of stabilizing agent onthe physical and mechanical characteristics of the mixtures.The next step consists in classifying the mixtures accordingto the standards in force and valorizing the stabilized sandsin road construction.
The results obtained show that the studied sands of Djelfacan be valorized in road foundation layers.
2 Identification of Used Materials
2.1 Characterization of Studied Sands
2.1.1 Sampling Site
This work was undertaken on three types of dune sand in theregion of Djelfa (Algeria): of El-masrane (SM) (municipalityof Hassi Bahbah located about 35 km north of the centre ofDjelfa), of Zaafrane (SZ) (municipality of Zaafrane locatedabout 57 km northwest of the centre of Djelfa), and of El-amra
(SA) (municipality of Ain El-Ibil located approximately 40km southwest of the centre of Djelfa). Figure 1 shows thelocations of the studied sands.
2.1.2 Analysis of the Physical Properties
This is to determine the physical characteristics of the stud-ied sands. It is a necessary step before any attempt to valorizethese materials for constituting a pavement. The selectedparameters are those defined in the technical guideline onembankment and capping layer construction (abbreviated toits French acronym GTR) [13], such as water content, grad-ing, apparent density, specific gravity, sand equivalent andfineness modulus. The different results, except grading, aresummarized in Table 1.
Figure 2 shows the grading curves of the studied sands.It can clearly be seen that 90 % of the elements are lowerthan 0.5 mm. These sands can be classified from a granularviewpoint as fine sands [7].
The grading is very tight; nearly 90 % of the grains have adimension ranging between 0.1 and 0.5 mm. The sand alonecould not have a sufficiently large compactness and thus non-adequate mechanical performances (compressive and tensile
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Table 1 Physical characteristics of the studied sands
Physical characteristics Sands
SM SZ SA
Apparent density (g/cm3) 1.4 1.44 1.42
Specific gravity (g/cm3) 2.58 2.56 2.60
Porosity (%) 46 44 45
Compactness (%) 54 56 55
Visual sand equivalent (%) 74 53 57
Sand equivalent with the piston (%) 71 44 52
Blue value (for 100 g) 0.09 0.07 0.06
Fineness modulus 1.47 0.88 1.28
0
10
20
30
40
50
60
70
80
90
100
0,01 0,1 1 10
Grain size (mm)
% o
f p
assi
ng
Sand SM
Sand SZ
Sand SA
Fig. 2 Grading curves of the studied sands
strength). It should be noted that the considered sands need,therefore, to be granularly corrected.
The grading of sand SM is more spread out than SZ andSA; sand SM could give better mechanical performances thanthe others.
According to the classification of the GTR 2000 [13] ofroad materials, the studied sands belong to the D1 class(belong to the SP class according to the Unified Soil Clas-sification System). According to the suggestion of the GTR,these sands are unaffected by water, without cohesion and arepermeable. With their grading often fine grained and poorlygraded, they are highly erodible and have poor trafficabil-ity. To improve their mechanical properties, treatment with ahydraulic binder (cement) is recommended.
2.1.3 Analysis of the Chemical Properties
Chemical analysis (NF EN 1744-1) was made to determinethe percentage of organic matter, sulphates and chloridescontained in the studied sands. These elements can affectthe results beyond tolerable limits. Table 2 shows the pro-
Table 2 Proportions of essential elements contained in the studiedsands
Chemical composition Sands
SM SZ SA
Silica (%) 97.63 97.43 97.14
2.8 1.2 0.9
Sulphates (%) Traces Traces Traces
Chlorides (%) 0.85 0.82 0.78
Organic matter (%) 1.17 0.93 0.76
portions of the essential elements contained in the studiedsands.
The chemical composition shows that the studied sandsare principally made up of silica. The contents of the essen-tial harmful substances (sulphates and chlorides) lie withintolerable limits recommended by standard NF P 18-011 (thisstandard gives the definition and classification of chemicallyaggressive environments). This allows us to use Portlandcement as a binder or as an agent of stabilization. The choiceof a cement of class CEM I (OPC) or CEM II (Portland com-posite cement) is very suitable.
Because the organic matter content is lower than 3 %and the methylene blue value (test executed to measure theamount of active and harmful clay contained in materials(ASTM C837-09 Standard)) is lower than 0.2, the studiedsands are clean and not organic [13].
2.2 Characterization of the Agents of Stabilization
2.2.1 Fillered Sand (FS)
This sand comes from the Ben Labiad crushing centre(municipality of Zakkar), located approximately 40 kmsouth-east of the centre of Djelfa (Fig. 1).
The addition of this sand improves the grading of the stud-ied sands (porosity about 45 %) by reducing these voids.This increase in the compactness permits developing bettermechanical performances.
Sand FS is of calcareous nature, consisting mainly of cal-cite (95.23 %), and its specific gravity is 2.64 g/cm3. TheFig. 3 presents its grading curve.
Chemical analysis shows that this sand contains almostno harmful elements (0.23 % of chlorides and 0.01 % ofsulphates).
2.2.2 Cement
The cement used is of class CEM II/A 42.5 (Portland compos-ite cement); it has been manufactured by the cement companyof Algeria. Its specific gravity is 3.06 g/cm3 and its specific
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0
10
20
30
40
50
60
70
80
90
100
0,001 0,01 0,1 1 10
Grain size (mm)
% o
f p
assi
ng
Fig. 3 Grading curve of sand FS
Table 3 Mineralogical composition of clinker (%)
C3S C2S C3A C4AF
81.18 2 .79 6.85 9.18
surface is equal to 3,918 cm2/g. The mineralogical compo-sition of clinker is presented in Table 3.
3 Composition of Mixtures
The stabilization of the studied dune sands was made by:
– Mechanical stabilization: reduction of voids by the com-paction operation.
– Physical stabilization: correction of the grading of studiedsands by addition of a granular corrector (sand FS).
– Chemical stabilization: obtaining mechanical strength byaddition of a hydraulic binder (cement).
The cement percentage ranges from 0 to 10 % with a stepof 2 %, and that of the fillered sand from 0 to 30 % witha step of 10 % (the percentages based on the weight of drymixture). Seventy two (72) mixtures are to be studied in thisinvestigation.
The mixtures are denoted by SX-PS-PC-PFS, where Xrepresents the sand source, PS the percentage of sand, PCthe percentage of cement, and PFS the percentage of filleredsand, respectively. Details of the proportions of mixtures aregiven in Table 4.
For each mixture, the optimal normal Proctor (ONP), thecompressive strength with and without immersion (resistanceto immersion) and the tensile strength were determined.
4 Evolution of the Physical and MechanicalCharacteristics
4.1 Evolution of the Proctor Characteristics
The mixtures are compacted by using normal Proctor energyaccording to ASTM D1557-09 Standard [1]. The test wascarried out just after mixing operation and therefore couldnot take into account the effect of the hydration of cement.
4.1.1 Optimal Water Content
The curves of Fig. 4a represent the evolutions of the optimalwater content according to the quantity of cement added. Wenotice that, for a fixed sand FS proportion, the increase inpercentage of cement leads to a continuous reduction in theoptimal water content. The same situation can be noted forthe variation in water content according to the percentage ofsand FS (Fig. 4b).
The optimal water content varied from 14, 15.9 and 17.1%, respectively, for sands SM, SZ and SA without any addi-tion and decreased with the cement and sand FS content toa minimum value of about 9.3, 9.8 and 10.5 %, respectively,for 10 % cement and 30 % sand FS addition.
It should be also noticed that for a constant sand SF andcement proportion, the optimal water content for each sandis different, which explains that the origin of sand affectsvery significantly the optimal water content of mixtures(Fig. 4a, b).
4.1.2 Maximum Dry Density
Figure 5a proves that for a constant sand FS proportion, theincrease in the quantity of cement added to the mixture influ-ences positively and in a very significant way the maximumdry density. This indicates that the addition of cement par-ticipates in the improvement of the maximum dry density ofmixture. The same remark can be made concerning the influ-ence of sand FS proportioning on the maximum dry density(Fig. 5b).
The increase in dry density (due to the use of cement) isalso ascribed to the higher specific gravity of cement as com-pared to that of the three sands. In addition, the added cementin the presence of water tends to lubricate the sand particles,thereby resulting in denser packing during the compactionprocess. Moreover, the cement particles tend to occupy thevoids between the studied sand particles, hence, resulting ina denser sand matrix [16] (the cement participates in improv-ing the compactness of mixtures).
The increase in the maximum dry density with sand FSaddition is attributed to the increase in the compactness ofmixtures (the value of specific gravity of the studied sandsand of sand FS are close).
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Table 4 Mixtures’ proportionsMixtures % of dune sand % of cement % of sand FS
SM series SZ series SA series
SM 100-00-00 SZ 100-00-00 SA 100-00-00 100 0 0
SM 98-02-00 SZ 98-02-00 SA 98-02-00 98 2
SM 96-04-00 SZ 96-04-00 SA 96-04-00 96 4
SM 94-06-00 SZ 94-06-00 SA 94-06-00 94 6
SM 92-08-00 SZ 92-08-00 SA 92-08-00 92 8
SM 90-10-00 SZ 90-10-00 SA 90-10-00 90 10
SM 90-00-10 SZ 90-00-10 SA 90-00-10 90 0 10
SM 88-02-10 SZ 88-02-10 SA 88-02-10 88 2
SM 86-04-10 SZ 86-04-10 SA 86-04-10 86 4
SM 84-06-10 SZ 84-06-10 SA 84-06-10 84 6
SM 82-08-10 SZ 82-08-10 SA 82-08-10 82 8
SM 80-10-10 SZ 80-10-10 SA 80-10-10 80 10
SM 80-00-20 SZ 80-00-20 SA 80-00-20 80 0 20
SM 78-02-20 SZ 78-02-20 SA 78-02-20 78 2
SM 76-04-20 SZ 76-04-20 SA 76-04-20 76 4
SM 74-06-20 SZ 74-06-20 SA 74-06-20 74 6
SM 72-08-20 SZ 72-08-20 SA 72-08-20 72 8
SM 70-10-20 SZ 70-10-20 SA 70-10-20 70 10
SM 70-00-30 SZ 70-00-30 SA 70-00-30 70 0 30
SM 68-02-30 SZ 68-02-30 SA 68-02-30 68 2
SM 66-04-30 SZ 66-04-30 SA 66-04-30 66 4
SM 64-06-30 SZ 64-06-30 SA 64-06-30 64 6
SM 62-08-30 SZ 62-08-30 SA 62-08-30 62 8
SM 60-10-30 SZ 60-10-30 SA 60-10-30 60 10
The maximum dry density varied from 1.67, 1.67 and 1.63g/cm3, respectively, for sands SM, SZ and SA, without anyaddition, and increased with the cement and sand FS contentto a maximum value of about 1.95, 1.94 and 1.90 g/cm3,respectively, for 10 % cement and 30 % sand FS addition.
The influence of the sand origin on the maximum drydensity is very clear. It has been found that the density ofthe mixtures based of SM sand is higher than that of themixtures based of SZ; the mixtures based on SA give thelowest densities. This can be explained by the distinct gradingof each sand.
4.2 Evolution of Compressive Strength
The compression test is carried out according to EN 13286-41 standard [2], on specimens made up at the optimal normalProctor. The moulds used allow obtaining a cylindrical speci-men of 80 mm in diameter and 80 mm in height. The prepara-tion of specimens was made by static compression accordingto EN 13286-53 standard [6]. This operation allows obtain-ing ends of the specimens perfectly perpendicular with thecylinder axis (not taking into account the effect of the endson the compressive strength). The specimens were preserved
in tight bags at a temperature of 20 ± 2◦C, until the time oftest (28 days).
The results of Fig. 6a show that for a constant percentageof sand FS, the compressive strength increases very signif-icantly with the increase in the quantity of cement. Beyond10 % of sand FS, the effect of the sand origin on com-pressive strength becomes significant. The curves of Fig. 6breflect that beyond 2 % of cement, the compressive strengthincreases proportionally with the increase in the percentageof sand FS, which explains the effectiveness of the granu-lar corrector used to improve the compactness of the mix-tures and consequently their mechanical performance. Forcement proportioning higher than 4 %, the influence of thesand source on compressive strength becomes very signifi-cant (Fig. 6b).
For a cement content equal to 10 %, the granulometriccorrection with 30 % of sand FS can give a gain in compres-sive strength equal to 128 % for sand SM, 73 % for sandSZ and 63 % for sand SA. These values vividly demonstratethe effectiveness of sand FS in improving the compressivestrength of the stabilized sands.
The mixtures containing sand SM, exhibit the highestcompressive strengths. This is mainly due to its grading,which is relatively better than that of sands SZ and SA.
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0% of FS
0 2 4 6 8 10
% of cement
9
10
11
12
13
14
15
16
17
18
Opt
imal
wat
er c
onte
nt (
%)
Opt
imal
wat
er c
onte
nt (
%)
10% of FS
0 2 4 6 8 10
% of cement
20% of FS
0 2 4 6 8 10
% of cement
30 % of FS
0 2 4 6 8 10
% of cement
Sand SMSand SZSand SA
0% Cement
0 10 20 30
% of FS
9
10
11
12
13
14
15
16
17
18
2% Cement
0 10 20 30
% of FS
4% Cement
0 10 20 30
% of FS
6% Cement
0 10 20 30
% of FS
8% Cement
0 10 20 30
% of FS
10% Cement
0 10 20 30
% of FS
Sand SMSand SZSand SA
(a)
(b)
Fig. 4 a Evolution of the optimal water content according to the percentage of cement. b Evolution of the optimal water content according to thepercentage of sand FS
In accordance with the classification of NF EN 14227-1 standard (classification according to the compressivestrength at 28 days) [5], the stabilization of the studied sandswith cement and sand FS can give strengths of C5/6 class(compressive strength between 6 MPa and 10 MPa) in thecase of sand SM and SZ, and of C3/4 class (compressivestrength between 4 and 6 MPa) in the case of sand SA (theslenderness of specimens is taken into consideration).
4.3 Evolution of the Tensile Strength
The tensile test was performed according to EN 13286-42standard [3], on cylindrical specimens of slenderness equalto 1 with a diameter of 80 mm, made up at optimal normalProctor. The preparation of specimens was made by static
compression according to EN 13286-53 standard. The spec-imens have been preserved in tight bags at a temperature of20 ± 2◦C, until the time of test (90 days).
The curves of Fig. 7a illustrate the evolution of split-ting tensile strength according to cement proportion. Thetensile strength increases with the proportion of the addedcement. The curves of Fig. 7b show that, beyond 2 % ofcement, the tensile strength increases with the quantity ofsand FS added, which explains the effectiveness of the gran-ular corrector used to improve this characteristic. Beyond4 % of cement, the influence of the sand origin on tensilestrength becomes significant. The same observation men-tioned in the case of the compressive strength can be noticed;the mixtures containing sand SM always give the bestperformances.
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0% of FS
0 2 4 6 8 10
% of cement
1,60
1,65
1,70
1,75
1,80
1,85
1,90
1,95
2,00
Max
imum
dry
den
sity
(g/c
m3)
Max
imum
dry
den
sity
(g/c
m3)
10% of FS
0 2 4 6 8 10
% of cement
20% of FS
0 2 4 6 8 10
% of cement
30% of FS
0 2 4 6 8 10
% of cement
Sand SMSand SZSand SA
0% Cement
0 10 20 30
% of FS
1,60
1,65
1,70
1,75
1,80
1,85
1,90
1,95
2,002% Cement
0 10 20 30
% of FS
4% of Cement
0 10 20 30
% of FS
6% Cement
0 10 20 30
% of FS
8% Cement
0 10 20 30
% of FS
10% Cement
0 10 20 30
% of FS
Sand SMSand SZSand SA
(a)
(b)
Fig. 5 a Evolution of the maximum dry density according to the percentage of cement. b Evolution of the maximum dry density according to thepercentage of sand FS
For a cement content equal to 10 %, the granulometriccorrection with 30 % of sand FS can give a gain in tensilestrength equal to 108 % for sand SM, 57 % for sand SZand 67 % for sand SA. These values vividly demonstrate theeffectiveness of sand FS in improving the tensile strength ofthe stabilized sands.
Sands stabilized with hydraulic binders can be used inbase course for traffic lower than 6,000 vehicles a day, whentheir splitting tensile strength at 90 days is higher than 0.50MPa [7]. The stabilization of sand SM with 8 % of cementand 30 % of sand FS is sufficient to obtain the performancesrecommended for the base course. For sand SZ, these perfor-mances are obtained for a proportion of cement equal to 10% and a minimal percentage of sand FS equal to 10 %. Thesame remark can be made for sand SA but with a minimal
proportioning of sand FS equal to 20 %. Table 5 gives themixtures selected in this stage.
The mixtures selected will be classified according to theirmodulus of elasticity and their tensile strength in accordancewith the standard NF EN 14227-1.
4.4 Evolution of the Resistance to Immersion
The resistance to immersion (Rimm) is a ratio betweenthe compressive strength with immersion and that withoutimmersion:
Rimm = Rci
Rc28
Rci: compressive strength with immersion in water
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0% of FS
0 2 4 6 8 10
% of cement
-1
0
1
2
3
4
5
6
7
8
9
10
Com
pres
sive
str
engt
h at
28
days
(M
Pa)
10% of FS
0 2 4 6 8 10
% of cement
20% of FS
0 2 4 6 8 10
% of cement
30% of FS
0 2 4 6 8 10
% of cement
Sand SMSand SZSand SA
0% ciment
0 10 20 30
% of FS
-1
0
1
2
3
4
5
6
7
8
9
10
Com
pres
sive
str
engt
h (M
Pa)
2% cement
0 10 20 30
% of FS
4% cement
0 10 20 30
% of FS
6% cement
0 10 20 30
% of FS
8% cement
0 10 20 30
% of FS
10% cement
0 10 20 30
% of FS
Sand SMSand SZSand SA
(a)
(b)
Fig. 6 a Evolution of the compressive strength according to the percentage of cement. b Evolution of the compressive strength according to thepercentage of sand FS
Rc 28: compressive strength without immersion at 28 days
For determining the resistance to immersion, the compres-sive strength obtained at 28 days in tight bags is compared tothat obtained by preserving the specimens at 21 days in tightbags and then at 7 days of immersion in water at 20 ± 2◦C [7].
The curves of Fig. 8a show that the resistance to immersionincreases slightly with the proportion of the added cement.It should be noted that it is slightly influenced by the originof sand. Figure 8b shows that the effect of the percentage ofsand FS on the resistance to immersion is not significant; thisexplains why the addition of sand SF to the mixtures doesnot participate in the improvement of the durability in water.
The resistance to immersion is satisfactory for the basecourse for a minimum value fixed at 0, 6 [7]. We note thatthis value is guaranteed for mixtures with cement proportionhigher or equal to 2 %.
5 Classification of Mixtures and Choice of OptimalFormulations
At this stage, a couple, tensile strength and modulus of elas-ticity (Rt , E), should be determined for the mixtures whichhave a tensile strength higher than 0.5 MPa at 90 days. Thiscouple is used to define the strength class of the stabilizedsands according to the classification of NF EN 14227-1 stan-dard [5].
The modulus of elasticity Et was measured on cylindricalspecimens of 50 mm diameter and 100 mm height. The ten-sile strength was determined by splitting tensile strength oncylindrical specimens of slenderness equal to 1, with a diam-eter of 80 mm, according to the NF EN 13286-42 standard.The modulus of elasticity was valued by a compression testaccording to the NF EN 13286-43 standard [4].
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0% FS
0 2 4 6 8 10
% of cement
-0,1
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
1,1
Ten
sile
str
engt
h at
90
days
(M
Pa)
10% FS
0 2 4 6 8 10
% of cement
20% FS
0 2 4 6 8 10
% of cement
30% FS
0 2 4 6 8 10
% of cement
Sand SMSand SZSand SA
0% Cement
0 10 20 30
% of FS
-0,1
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
1,1
Ten
sile
str
engt
h (M
Pa)
2% Cement
0 10 20 30
% of FS
4% Cement
0 10 20 30
% of FS
6% Cement
0 10 20 30
% of FS
8% Cement
0 10 20 30
% of FS
10% Cement
0 10 20 30
% of FS
Sand SMSand SZSand SA
(a)
(b)
Fig. 7 a Evolution of the splitting tensile strength according to the percentage of cement. b Evolution of the splitting tensile strength according tothe percentage of sand FS
Table 5 Mixtures selected
Series
SM SZ SA
Mixtures selected SM 62-08-30
SZ 80-10-10
SM 80-10-10 SA 70-10-20
SZ 70-10-20
SM 70-10-20 SA 60-10-30
SZ 60-10-30
SM 60-10-30
The modulus of elasticity and the tensile strength weredetermined after 28 days of conservation. The results were
then estimated at 360 days using the estimated coefficientsgiven by the NF EN 14227-1 standard (the studied sandsare not organic and the used cement is standardized). Theparameters Rt360and E360 are, respectively, estimated by thecoefficients 0.6 and 0.65. These values are then inserted inthe diagram of classification, to evaluate the strength classof the stabilized sands. Standard NF EN 14227-1 cites sixstrength classes of T0–T5; the description of these classes isgiven in Table 6. It also recommended that the stabilizedsands of T2, T3 and T4 classes are usually used in roadfoundation.
The results of Fig. 9 show that all the formulations stud-ied have adequate mechanical performances for use in roadfoundation layer (class of material higher or equal to theclass T2). The value of modulus of elasticity increases with
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0% of FS
2 4 6 8 10
% of cement
0,60
0,65
0,70
0,75
0,80
0,85
0,90
0,95
1,00
Res
ista
nce
to im
mer
sion
10% of FS
2 4 6 8 10
% of cement
20% of FS
2 4 6 8 10
% of cement
30% of FS
2 4 6 8 10
% of cement
Sand SM Sand SZ Sand SA
2% cement
0 10 20 30
% of FS
0,60
0,65
0,70
0,75
0,80
0,85
0,90
0,95
1,00
Res
ista
nce
to im
mer
sion
4% cement
0 10 20 30
% of FS
6% cement
0 10 20 30
% of FS
8% cement
0 10 20 30
% of FS
10% cement
0 10 20 30
% of FS
Sable SM Sable SZ Sable SA
(a)
(b)
Fig. 8 a Evolution of the resistance to immersion according to the percentage of cement. b Evolution of the resistance to immersion according tothe percentage of sand FS
Table 6 Classification of sandsstabilized with hydraulic binders[5]
E (MPa) Rt (MPa) Minimumthicknessof layer (cm)Lower limit of category 2,000 5,000 10,000 20,000 40,000
T5 0.97 1.50 1.93 2.35 2.60 15
T4 0.67 1.00 1.26 1.49 1.70 20
T3 0.52 0.73 0.90 1.05 1.20 25
T2 0.34 0.47 0.57 0.67 0.75 35
T1 0.19 0.26 0.32 0.38 0.43 50
T0 <0.19 <0.26 <0.32 <0.38 <0.43 −
the increase of the quantity of sand FS, which explains theeffectiveness of the granular corrector used to improve thismechanical characteristic. It should also be noticed that fora constant sand SF and cement proportion, the formulationscontaining sand SM give the best mechanical performances.
The stabilization of sand SM with 10 % cement and30 % sand FS (SM 60-10-30) makes it possible to obtainmechanical performances positioned at the top of the T3class (Fig. 9a). For sands SZ and SA, this position can onlybe achieved if the cement content is higher than 10 %. The
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0,1
1
10
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SM 60-10-30
SM 80-10-10
SM 70-10-20
SM 62-08-30
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SZ 80-10-10
SZ 70-10-20
SZ 60-10-30
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SA 70-10-20
SA 60-10-30
(a)
(c)
(b)
Fig. 9 a Classification of mixtures containing sand SM. b Classifi-cation of mixtures containing sand SZ. c Classification of mixturescontaining sand SA
addition of 8 % cement and 30 % sand FS to sand SM (SM62-08-30) allows obtaining mechanical performances posi-tioned at the top of the T2 class (Fig. 9a). For sands SZ andSA, this position can only be achieved if the cement con-tent is equal to 10 % (Fig. 9b, c). This is mainly due tothe grading of sand SM, which is relatively better than thatof sands SZ and SA (grading of sand SM is more spreadout).
The valorization of the elaborated sand-cement representsa real technical—economical interest if the considered sta-bilizations are situated at least in T3. It is possible to use astabilization positioning in T2, but the thickness of courseand therefore the cost of its implementation are then higher[12,15].
For sand SM, a proportion of cement of 10 % and sand FSof 20 % make it possible to obtain a class T3 sufficient for roadfoundation layers. The formulation with a proportion of sandFS of 30 % makes it possible to reach better performances,but from an economic viewpoint it is less interesting (Fig. 9a).Then SM 70-10-20 can be chosen as the optimal formulationfor the SM series. For sands SZ and SA, a proportion ofcement equal to 10 % and sand FS equal to 30 % make itpossible to obtain a class T3 (Fig. 9b) and (Fig. 9c). Thus,SZ 60-10-30 and SA 60-10-30 can be chosen as the optimalformulations for the SZ and SA series.
6 Physical and Mechanical Performancesof the Optimal Formulations
The mechanical performances developed by the optimal mix-tures are satisfactory for considering their valorization inroad foundation layers. Table 7 summarizes the physical andmechanical performances of the three optimal formulationschosen.
7 Conclusion
This study was conducted to assess the possibility of utiliz-ing Portland cement and fillered sand to stabilize three typesof dune sands of the region of Djelfa (Algeria) and of val-orizing them in road engineering. Based on the results of theexperimental program conducted in this investigation, thefollowing main conclusions could be drawn:
– The studied dune sands of the region of Djelfa belong tothe D1 class according to the classification of the technicalguideline on embankment and capping layer construction(GTR). They are poorly graded and contain a high pro-portion of fine elements (high porosity); their stabilizationrequires the addition of a granular corrector.
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Table 7 Physical andmechanical performances of theoptimal formulations
Mechanical performances Optimal formulations
SM 70-10-20 SZ 60-10-30 SA 60-10-30
Optimal water content (%) 9.6 9.8 10.5
Maximum dry density (g/cm3) 1.91 1.94 1.90
Age authorizing the circulation ofmachinery (when the compressivestrength is higher than 1MPa) [14]
Second day Second day Second day
Resistance to immersion (Rci /Rc60) [14] >0.80 >0.80 >0.80
– Rc60: Compressive strength at 60 daysof normal maturation
– Rci : Compressive strength after 28days of normal curing
followed by 32 days of immersion inwater at 20 ± 2 ◦C
CBR value immediate (%) (ASTM D1883Standard)
20–30 20–30 20–30
CBR value with immersion (%) (ASTMD1883 Standard)
250–260 240–250 220–230
Performances in long term : tensilestrength at 90 days (MPa)
0.67–0.72 0.66–0.68 0.64–0.65
Medium Modulus of elasticity at 28 days(MPa)
6918 6687 6118
Compressive strength at 28 days (MPa) 7.05–7.39 5.93–6.04 5.63–5.80
– The maximum dry density increased with cement addi-tion, owing to the higher absolute density of the cement.However, the optimal water content decreases.
– The increase in the maximum dry density with sand FSaddition is attributed to the increase in the compactnessof the mixtures.
– The addition of sand FS takes part in a very positive way tocorrect the grading of the studied sands (porosity about 45%), by improvement of the compactness of the mixturesand consequently the mechanical performance, particu-larly the compressive and the tensile strength.
– The effect of the origin of sand on the physical andmechanical characteristics is very significant. This isattributable to the relative distinction of grading for eachsand.
– The value of resistance to immersion is high for any per-centage of cement (higher than 0.75 for 2 % of cement).It is slightly influenced by the proportion of the cementadded and the sand origin. The effect of the percentageof sand FS on this characteristic is not significant. Thisexplains why the addition of sand SF to the mixtures doesnot help in the improvement of the durability in water.
– The use of sand FS improves the mechanical perfor-mances tested (tensile and compressive strength and mod-ulus of elasticity) and does not reduce the resistance toimmersion (the effect of this sand is not negative). There-fore, the use of this sand is very important.
– The stabilization of sand SM with 8 % of cement and 30 %of sand FS is sufficient to obtain the performances recom-
mended for the base course (splitting tensile strength at90 days is higher than 0.50 MPa). For sand SZ, these per-formances are obtained for a proportion of cement equalto 10 % and a minimal percentage of sand FS equal to 10%. The same observation can be noticed for sand SA butwith a minimal percentage of sand FS equal to 20 %.
– The optimal formulations are chosen in class T3, accord-ing to the classification of the EN 14227-1 standard. Theydevelop satisfactory mechanical performances to con-sider their valorization in road foundation layers.
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