4- Harichane et al. 2011a.pdf

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RESEARCH ARTICLE

Inuence of natural pozzolana and lime additives on the

temporal variation of soil compaction and shear strength

Khelifa HARICHANE ()1, Mohamed GHRICI1, Hani MISSOUM2

1 Civil Engineering Department, Chlef University, Chlef 02000, Algeria

2 Civil Engineering Department, Mostaganem University, Mostaganem 27000, Algeria

Higher Education Press and Springer-Verlag Berlin Heidelberg 2011

Abstract Soil stabilization has been practiced for quitesome time by adding mixtures, such as cement, lime andy ash. The additives of lime (L), natural pozzolana (NP)or a combination of both were investigated here on theimpact on the temporal variation of geotechnical char-acteristics of two cohesive soils. Lime and natural

pozzolana were added at the content of 08% and 020%, respectively. The soil specimens were cured for 1, 7,28 and 90 days and then tested for shear strength. Our datashow that a combination of lime with natural pozzolanacauses the increase in the maximum dry density but thedecrease in the optimum moisture content in the gray soil,and vice verse in the red soil. The shear stress of both

cohesive soils stabilized with lime or with the combinationof lime and natural pozzolana was found to increase withtime. The cohesion and the internal friction angle in lime-added samples were demonstrated to increase with time.The combination of lime with natural pozzolana exhibits asignicant effect on the enhancement of the cohesion andthe internal friction angle at later stages. The lime-natural

pozzolana combination appears to produce higher shearparameters than lime or natural pozzolana used alone.

Keywords cohesive soil, lime (L), natural pozzolana(NP), compaction, shear strength

1 Introduction

Civil engineering projects located in areas with weak soilsare one of the most common problems in the world. Theconventional method of soil stabilization is to remove theweak soil and replace with a stronger material. The highcost of this method has driven researchers to look for

alternative methods, and one of these methods is theprocess of soil stabilization.Soil stabilization is a technique introduced many years

ago with the main purpose to render the soils capable ofmeeting the requirements of the specic engineering

projects (Kolias et al., 2005). In addition, when the soilsat a site are poor or when they have undesirable propertymaking them unsuitable for use in a geotechnical projects,they may have to be stabilized. In recent years, a variety ofscientic techniques have been introduced for soilstabilization (Rogers et al., 1997). The techniques of soilstabilization often use the additives as cementing agentsincluding cement, lime or industrial by-products, and

extensive studies have been carried out on the stabilizationof soils using various additives such as lime and cement(Basha et al., 2005).

The potential for using industrial by-products to stabilizeclayey soils is promising (Al Rawas and Goosen, 2006).These by-products and their combination with cement andlime have been used as soil stabilizers such as limestone(Okagbue and Yakubu, 2000), y ash (Prabakar et al.,2004;Al Rawas et al., 2005; Goswami and Singh, 2005;Parsons and Kneebone, 2005;Sezer et al., 2006;Hossain etal., 2007;MuAzu, 2007), rice husk ash (Rahman, 1986;Muntohar and Hantoro, 2000; Basha et al., 2003;

Muntohar, 2005; Senol et al., 2006; Al Hassan andMustapha, 2007; Choobbasti et al., 2010), silica fume(Bagherpour and Choobbasti, 2003; Kalkan, 2009) andcement kiln dust (Miller and Azad, 2000).

However, limited researches have been conducted on theadditive of natural pozzolana (NP) in soil stabilization.Hossain et al. (2007) utilized volcanic ash (VA) fromnatural resources of Papua New Guinea as an additive andinvestigated the resulted compaction, unconned com-

pressive strength and durability, but not the shear strengthbehavior. Natural pozzolana is found abundantly inextensive areas of Beni-Saf quarry in the West of Algeria(Ghrici et al., 2007). The use of natural pozzolana and its

Received February 9, 2011; accepted March 15, 2011

E-mail: [email protected]

Front. Earth Sci. 2011, 5(2): 162169DOI 10.1007/s11707-011-0166-1


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combination with lime as soil additives need to beinvestigated. As the soil is a good source of alumina, theeffects of lime treatment can be enhanced to a great extentif the apparent shortage of silica can be adequatelysupplemented by the addition of natural pozzolana whichis enriched in reactive silica. However, the literature

indicates minimal studies on the stabilization of cohesivesoils in Algeria.This paper presents the results of the effectof the curing time on the shear strength of two Algeriancohesive soils, stabilized with the combination of lime andnatural pozzolana.

2 Experimental investigation

2.1 Materials used

The rst soil used in this study was obtained from an

embankment project site, and the second soil was obtainedfrom a highway project site both near Chelif town in theWest of Algeria. Previous soil investigations carried out atthe sites indicated the presence of weak clays. These weakclays were encountered at a depth of about 4 to 5 m. Thedisturbed soil was excavated, placed in plastic bags, andtransported to the laboratory for preparation and testing.Laboratory tests were carried out to classify each type ofsoil. The engineering properties of clayey soils are

presented in Table 1.

The NP used in this investigation was collectedfrom Beni-Saf in the West of Algeria. The NP wasground in a laboratory mill to the specic surface area of420 m2/kg. The chemical composition of NP is presentedin Table 2. The lime (L) used was a commercially availablelime typically used for construction purposes. Thechemical and physical properties of the lime are presentedin Table 3.

2.2 Laboratory tests of compaction and shear strength

A series of laboratory tests of compaction and shear

strength were conducted on the two clayey soils selected.Extensive combinations of natural pozzolana with limewere used to stabilize the two soils. The NP content was 0,10% and 20%, and the lime content was 0, 4% and 8%.A total of 18 combinations based on soil 1 and soil 2with single and mixed modes of stabilizers were studied(Table 4).

Proctor standard compaction test according to ASTMD698-00 (2000) was applied to determine the maximumdry density (MDD) and the optimum moisture content(OMC) of the soils. The soil mixtures, with and withoutadditives, wait for 1 h to reach thorough equilibrium priorto compaction. The rst series of compaction tests were

Table 1 Physical characteristics of the soils

Basic characteristics Soil 1 Soil 2

Color Gray Red

Depth/m 4 m 5 m

Natural water content/% 32.87 13.77

Specic gravity 2.71 2.84

Passing 80 m sieve/% 85 97.5

Liquid limit/% 84.8 47.79

Plastic limit/% 32.78 23.23

Plasticity index/% 52.02 24.56

Classication (USCS) CH CL

Optimum water content/% 28.3 15.3

Maximum dry density/(kN$

m3) 13.8 16.9

Unconned compressive strength/kPa 55.6 222.5

Table 2 Chemical composition of natural pozzolana

Chemical composition Natural pozzolana/ %

SiO2 46.4

Al2O3 17.5

Fe2O3 9.69

CaO 9.90

MgO 2.42

CaO free

SO3 0.83

Na2O 3.30

K2O 1.51

TiO2 2.10

P2O3 0.80

Loss of ignition 5.34

Table 3 Physical and chemical properties of lime used hereChemical name L

Physical appearance Dry white powder

CaO > 83.3

MgO < 0.5

Fe2O3 < 2

Al2O3 < 1.5

SiO2 < 2.5

SO3 < 0.5

Na2O 0.40.5

CO2 < 5

CaCO3 < 10

Specic gravity 2

Over 90m/% < 10

Over 630m/% 0

Insoluble material/% < 1

Bulk density/(g$L1) 600900

Khelifa HARICHANE et al. Inuence of pozzolana and lime on the variation of shear strength 163


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aimed at determining the compaction properties of theunstabilized soils, and then carried out to determine the

proctor compaction properties of the clay upon stabiliza-tion with varying amounts of lime and natural pozzolana.The direct shear tests were performed following ASTM

D6528-00 (2000), and were conducted on treated anduntreated samples compacted at maximum dry density andoptimum moisture content. Since the specimens were notsaturated, excessive pore water pressure would not beexpected in them. The direct shear test was unconsolidatedand the load was applied at a rate of 1 mm/min. The normalstress was chosen to be 50, 100 and 200 kPa for all thespecimens. Six specimens from each mixture were

prepared for each curing period. To avoid excessivemoisture loss, the specimens were wrapped up with a

polyanelm after demolding. The specimens were kept inthe laboratory at the temperature of 25C and the relativehumidity of 50% until the test time (1, 7, 28 and 90 days).

3 Results and discussion

3.1 Compaction characteristics

The compaction test was to determine the effect ofstabilizers on MDD and OMC. The MDD and OMC ofsoils mixed with lime, natural pozzolana or their

combinations are reported in Figs. 1 and 2.The results show that the OMC increases but the MDD

decreases with the increase of lime addition. Similarbehavior was observed before in lime stabilized clayeysoils (Ola, 1977;Rahman, 1986;George et al., 1992;Bell,1996; Gay and Schad, 2000; Hossain et al., 2007;Manasseh and Olufemi, 2008). The following reasonscould explain this behavior; 1) the lime added causes theaggregation of the particles to occupy larger spaces andhence alters the effective grading of the soils, 2) thespecic gravity of lime is generally lower than that of thesoils tested, and 3) the pozzolanic reaction between theclay present in the soils and the lime is responsible for the

increase in OMC.Figures 1 and 2 show the effect of the NP content on

both OMC and MDD. The OMC decreases and the MDDincreases as the NP content increases from 0 to 20%. Theincrease in MDD is an indicator of the improvement of soil

properties. Hossain et al. (2007) observed an increase inOMC and a decrease in MDD when the content of volcanicash added increases from 0 to 20%. This is different fromour study in NP.

The decrease in OMC observed in our study couldapparently have resulted from the lower afnity of NP forwater. In addition, the increase in MDD is probablyattributed to the relatively higher specic gravity of the NP.The addition of a combination of lime with natural

pozzolana to the gray soil decreases the OMC andincreases the MDD. But for the red soil, the combinationof lime with natural pozzolana increases the OMC andreduces the MDD, particularly at 20%NP content. Severalresearchers (Ola, 1977;Rahman, 1986;Basha et al., 2005)found that the change in MDD occurs due to thedifferences in both the particles size and specic gravity

between the soil and stabilizers.Recently, a power function model shown below (Eq. (1))

was developed to represent the optimum density-moisturerelationship (Di Matteo et al., 2009), on the basis of 30 soilsamples collected in central Italy and 41 soils described inthe literature, all of which are tested in modied proctor.

Table 4 Stabilizer combination scheme for stabilized soils

Designation Sample mixture/%

Soil NP L

P0L0 100 0 0

P0L4 96 0 4

P0L8 92 0 8

P10L0 90 10 0

P20L0 80 20 0

P10L4 86 10 4

P20L4 76 20 4

P10L8 82 10 8

P20L8 72 20 8

Fig. 1 Compaction characteristics of the gray soil under the

different combinations of additives

Fig. 2 Compaction characteristics of the red soil under the

different combinations of additives

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MDD 35635 OMC0:2564: (1)

The confrontation of our experimental results tothose acquired by the model (Eq. (1)) was presented inFig. 3. According to Fig. 3, we could note a goodagreement between our results and those predicted by the

model developed by Di Matteo et al. (2009). It appears thatour soil stabilized samples follow the same behavior asthose investigated by Di Matteo et al. (2009). Also, itshould be noted that the slight overestimate of themodel compared to our experimental results is explained

by the modied proctor compaction used by Di Matteoet al. (2009).

3.2 Shear strength

3.2.1 Temporal variation of the shear stress

The effect of L, NP and their combinations on the temporalvariation of the maximum shear stress of the gray and red

soils was shown in Figs. 4 and 5, respectively.The shear stress of both cohesive soils tested increases

Fig. 3 Maximum dry density (MDD) versus optimum moisture

content (OMC) for soils tested

Fig. 4 Shear stress produced under normal stress of gray soil in different curing time. (a) 1 day; (b) 7 days; (c) 28 days; (d) 90 days



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with the curing time. The addition of lime has a signicanteffect on the shear stress, particularly beyond 28 days, andin the samples containing 8% lime for both gray and redsoils tested.The addition of natural pozzolana alone has anegligible effect on the temporal variation of the shearstress in gray soil, but leads to a marginal increase in theshear stress at later stages (90 days) in the red soil,

In the samples stabilized with the combination of limeand natural pozzolana, a considerable increase in the shearstress was observed beyond 7 days and particularly atlater stages. In both soils, the combination of 20% NPand 8% L exhibits a high increase in the shear stress

beyond 28 days. This trend was particularly noticeable inthe red soil.

3.2.2 Temporal variation of shear parameters

The effect of L, NP and their combinations on the temporalvariation of the shear parameters, cohesion and internalfriction angle of the gray and red soils was shown in

Figs. 6 and 7, respectively. In slope stability analysis,the maximum shear strength is generally of primaryimportance. For this reason only the shear parametersusing the maximum shear stresses were calculated here.

The temporal variation of the cohesion of the gray andred soils was shown in Figs. 6(a) and 7(a). The addition oflime has a signicant effect on the temporal variation of thecohesion. A considerable increase in cohesion was noticedat later stages and in the samples containing 8% lime.Similar behavior was found by Gay and Schad (2000).This behavior is probably due to the self-hardening effectrelated to the lime. Ola (1978) considered the increase incohesion with the lime content, to be due to the bonding of

particles to form larger aggregates so that the soil behavesas a coarse-grained, strongly bonded particulate material.Others (Lees et al., 1982; Bell, 1989) explained this

behavior by the cementation and pozzolanic reactionswhich occur over time.

The addition of natural pozzolana alone has a marginaleffect on the cohesion with increased curing time. This

Fig. 5 Shear stress produced under normal stress of red soil in different curing time. (a) 1 day; (b) 7 days; (c) 28 days; (d) 90 days

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effect may be slightly pronounced in the gray soil at 90days. In comparison, however, a considerable increase incohesion was found at later stages in the samples stabilizedwith the combination of lime with natural pozzolana.

In both soils, the combination of 20% NP with 8% Lexhibits a high increase in the cohesion beyond 28 days.This trend is particularly noticeable in the gray soil.

It can be seen from Figs. 6(b) and 7(b) that in bothstabilized soils, the internal friction angle increases withtime as the lime content increases. However, in the graysoil there is a considerable increase in the internal frictionangle beyond 28 days. Similar trend was found by Sezer etal. (2006). The latter used very high lime y ash, and theyconcluded that this behavior is probably due to the fact thatthe internal friction angle of the y ash is more than that ofthe soil.

On the other hand, the addition of natural pozzolana

alone has a marginal effect on the internal friction anglewith the curing time. In contrast, in the samples stabilizedwith the combination of lime and natural pozzolana, thereis a signicant increase in the internal friction angle at later

stages. However, in the gray soil, the combination of20% NP with 8% L has a negligible effect on the internalfriction angle independent of the curing period.

The improvement in the cohesion and internal frictionangle values may be due to the pozzolanic activity and self-cementitious characteristics of the mixed lime-natural

pozzolana. This behavior is more pronounced beyond 28days.

4 Conclusions

This paper presented the effect of curing time on the shear

Fig. 6 Temporal variation of shear strength characteristics in the gray soil. (a) Cohesion; (b) friction angle

Fig. 7 Temporal variation of shear strength characteristics in the red soil. (a) Cohesion; (b) friction angle



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strength of cohesive soils stabilized with lime, naturalpozzolana or a combination of both. On the basis of the testresults from 18 stabilized soil mixtures, the followingconclusions can be drawn.

The maximum dry density of lime-stabilized soilsdecreases with the increase in the lime content, in contrast

with the natural pozzolana-stabilized soils. A combinationof lime with natural pozzolana causes the maximum drydensity increased in the gray soil but decreased in the redsoil. The optimum moisture content of lime-stabilized soilsincreases with the increase in the lime content, in contrastwith pozzolana-stabilized soils. A combination of limewith natural pozzolana causes the optimum moisturecontent decreased in the gray soil but increased in thered soil.

The shear stress of both cohesive soils stabilized withlime or with the combination of lime and natural pozzolanawas found to increase with cure time. A considerable

increase was particularly observed at later stages.There is a considerable increase in the cohesion and theinternal friction angle in the samples containing lime withthe increase of curing period. The addition of natural

pozzolana results in a marginal effect on the cohesion andthe internal friction angle with the increase in the curing

period. The combination of lime with natural pozzolanaexhibits a signicant effect on the enhancement of thecohesion and the internal friction angle at later stages. In

both soils and particularly in the gray soil, the combinationof 20%NP and 8%L exhibits a high increase in thecohesion beyond 28 days but has a negligible effect on theinternal friction angle independent of the curing period.

The results indicate the combination of lime with naturalpozzolana produces higher shear parameters than lime ornatural pozzolana used alone.

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