geotechnical properties of rice husk ash ......geotechnical properties of rice husk ash enhanced...

Geotechnical Properties of Rice Husk Ash Enhanced Lime-Stabilized Expansive Clay

MEDIA KOMUNIKASI TEKNIK SIPIL36

GEOTECHNICAL PROPERTIES OF RICE HUSK ASH ENHANCED LIME-STABILIZED EXPANSIVE CLAY

Agus Setyo Muntohar1

ABSTRAK

Penambahan dan pencampuran kapur atau semen dengan tanah mengembang merupakantanah cara yang paling banyak digunakan untuk stabilisasi tanah. Dalam penelitian inidigunakan abu sekam padi guna meningkatkan kualitas stabilisasi tanah mengembang dengankapur. Naskah ini menyajikan pengaruh penambahan abu sekam padi tersebut terhadap sifat-sifat geoteknis tanah yang distabilisasi dengan kapur. Hasil penelitian menunjukkan bahwa abusekam padi mampu meningkatkan sifat-sifat geoteknis dengan sangat baik. Berdasarkan hasilpenelitian ini dibuatkan pula grafik sebagai acuan untuk perencanaan pencampuran komposisikapur dan abu sekam padi dalam stabilisasi tanah mengembang.

Kata kunci : sifat-sifat geoteknis, abu sekam padi, stabilisasi dengan kapur, tanah mengembang,rancangan campuran.

1 Senior Lecturer, Department of Civil Engineering, Muhammadiyah University of Yogyakarta, Yogyakarta.

INTRODUCTION

Expansive soils is world wide occurring andhas been reported in numerous countriesincluding Indonesia, India, Cina, SaudiArabia, Turkey, and United States(Muntohar, 2002; Rao et. al, 2001; Shi et.al, 2002; Abduljauwad and Al-Suleimani,1993; Erguler and Ulusay, 2003; Chen,1983). Expansive soils, particularly thoselocated in arid and semi-arid climate regionsrepresent a problem. Geotechnicalengineering community have longrecognized that expansive soils may result inconsiderable distress and consequently insevere damage to overlying structures,particularly to low-rise structures, roads,and buried lifelines. Numerous reports ofexpansive soil problems and relateddamages have been documented indifferent countries (Chen, 1983).

The detrimental effects of expansive soilscan be mitigated by means of stabilization.Soil stabilization may involve a range oftreatment, which modifies soils to meet

specific engineering requirement andweather resistance. There are a number ofmethods which can be used to minimizeswelling of expansive soils for example bycompaction control, prewetting, preventingwater content, and by chemically modifyingsoil properties (Gromko, 1974). The successof any stabilization method depends upon aconsideration of soil conditions and anunderstanding of the application and limitsof that particular method. Chemicalstabilization of expansive soils by chemicaladditives such as lime, cement, fly ash, andother chemical compound have been widelyapplied for many years with varyingsuccess. The selection of a particularadditive depends on costs, benefits,availability, and practicability of itsapplication.

Finding ways for the utilization of wasteswould be an advantageous as they can befreely available at minimal costs. Thepotential secondary stabilizing agents are,for example, rice husk ash (RHA), pulverizedfuel ash (PFA), and granulated-ground

VOLUME 13, NO. 3, EDISI XXXIII OKTOBER 2005

MEDIA KOMUNIKASI TEKNIK SIPIL 37

blast-furnace slag (GGBS). These materialscan be grouped as secondary stabilizingagents that are not very effective on theirown but can be usefully used in conjunctionwith lime or cement. Sometimes, only smallproportion of cement or lime is needed asan activator and the secondary agents maycomprise the major proportion of thestabilizer. Secondary materials may beavailable locally, in quantities that providean economic binder system, withoutcompromising technical properties. Furthermore, blended secondary stabilizingmaterials with lime or cement can haveadded technical advantages, such asreduces permeability and increasesdurability and strength. This paper presentsthe study of RHA utilization to enhancelime-stabilized expansive soil.

Needs for study

The utilization of RHA in geotechnicalapplication has not been readily acceptabledue to low level of confidence in itseffectiveness among geotechnicalengineers. For this reason, there is a needto fill the gaps currently hindering the fullpotential of RHA to be harness. The studypresented in this paper aimed to providefurther understanding and guidance on theuse of RHA as soil stabilizer in particular forexpansive soils.

LIME AND LIME-RHA STABILIZATION

Lime stabilization is extensively applied forexpansive clay soils. This stabilizationdevelops from base exchange andcementation processes between clayparticles and lime. Lime stabilization isparticularly important in road constructionfor modifying subgrade soils, subbase, andbase materials (Little, 2000). Thestabilization process occurs for over a longperiod of time. In the shorter-term, limemodifies and immediately improvesworkability, placeability, compactability ofsoils, and effectively shrinks theconstruction costs (ICI, 1986). The initial

modification reaction occurs as a result ofcation exchange of calcium ions (Ca2+). Theresult of cation exchange is increasingflocculation of clay particles and changes inthe plasticity properties of clay (Boardman,et al, 2001). The cementation processdevelops from the reaction between calciumpresent in lime and silica and alumina in thesoil, forming calcium-silicate hydrate (CSH)and calcium-aluminate (CAH) or calcium-aluminate-silicate. The cementitiouscompounds produced are characterized bytheir high strength and low-volume change.

Various conclusions have been deduced byprevious researchers concerning uses ofblended rice husk ash with lime or cement.Lazaro and Moh (1970) concluded that theaddition of RHA in combination with lime toboth Thai and Philippine soils does notproduce any significant increasing ofstrength as compared to the use of limealone. Whereas, Ali et al. (1992) pointed outthat both of lime-stabilized and cement-stabilized residual soils from Malaysiaenhance the strength and durability byadding RHA. Balasubramaniam et al. (1999)and Muntohar and Hantoro (2000) showedthat addition of RHA to lime-stabilized soilsexhibits ductile behavior associated withhigh strain and low strength.

TEST PROGRAM

Materials used

The expansive soil used in this study isprepared using kaolin and bentonitemixtures. This expansive clay is engineeredto suit desired properties besides that it ismuch easier for controlling the variability ofsoil compositions and properties. A study ofsoil mixtures have shown that the mixturecomposed of 10% bentonite and 90% kaolinwas found to be a potentially expansive soil(Muntohar and Hashim, 2002). This soil isdesignated as KB, the properties of whichare presented in Table 1. The grain sizedistributions of the soils used in the studyare presented in Figure 1.



0

10

20

30

40

50

60

70

80

90

100

0.0001 0.001 0.01 0.1 1 10

Particle size, D (mm)

Perc

ent F

iner

than

D (%

)

KB2 Soil Kaolin Bentonite RHA

Clay Silt Sand Gravel

Figure 1. Grain Size Distribution Curves of Soil Used and RHA

The hydrated lime was used in thisresearch. To reduce the carbonation effect,the lime was stored in an airtight container.Rice husk ash was obtained by burning therice husks in an incinerator. The husks werecollected from rice mills disposal in KualaSelangor, Malaysia. X-ray diffraction test,Figure 2, shows that the RHA possessedamorphous silica, while the lime wascomprised of predominantly calciumhydroxide, Ca(OH)2.

Sample Preparation For Swelling AndCompressive Strength Tests

A conventional oedometer apparatus wasused for the determination of the swellingand compressibility of soil mixtures.Required quantities of soil mixtures, atoptimum moisture content, were transferredto consolidation ring of 50 mm internaldiameter and 20 mm height. All the soilmixtures were compacted statically to theirMDD and OMC. Unconfined compressivestrength was used to observe the strength.The samples, 50 mm diameter and 100 mmheights, were compacted at their maximumdry density by static compaction method.The calculated amount of soil was placed

into cylindrical mould and then compressedusing the hydraulic jack.

Testing Program

The focus of this study is to investigate theeffect of adding RHA on the geotechnicalproperties of lime-stabilized expansive soils.Toward this aim, the aspects studied coversconsistency limits, swelling, compressivestrength and durability of stabilized soil.

RESULTS AND DISCUSSION

Effect of Stabilization on ConsistencyLimits

Chemically, RHA is lacking in cementitiousmaterials, but it contains pozzolanicmaterials. The uses for soil stabilizationalone would not yield a worthy improvement(Hossain, 1986). The effect of RHA additionon the consistency limit of lime-stabilizedsoil is presented in Figure 3. In general, theplasticity index reduces associated withaddition of RHA as shown in Figure 3c. Thereduction of plasticity index is an indicatorof improvement which can be related to theincrease in soil strength and the decrease inswelling and compressibility.



10 15 20 25 30 35 40 45 50 55 60

Diffraction Angle (2 )

CC

CH

CH

CH

CH: Calcium HydroxideC : Clacite

RHA

CH

CHCH

Lime

Figure 2. X-Ray Diffraction Test of Lime And Rice Husk Ash

RHA (%)

0 6 12 18 24

Liqu

id L

imits

(%)

70

75

80

85

90

95

0%

3%

6%

9%

(a)

RHA (%)

0 6 12 18 24

Plas

tic L

imits

(%)

4045505560657075

0%

3%

6%

9% (b)

RHA (%)

0 6 12 18 24

Plas

ticity

Inde

x (%

)

1520253035404550

0%

6%

9%

3%

(c)

Figure 3. Effect of RHA addition on consistency limit of lime-stabilized expansive soil (Note:numbers in percents are referring to percentage of lime content.

It was observed that there is differentbehavior in reduction of plasticity index withdifferent stabilizers. The plasticity index ofRHA-treated soil reduced significantly theplasticity index as the liquid limitsdiminished and increased in plastic limits.The liquid limit and plastic limit of lime-stabilized soil increase in conjunction withaddition of RHA as shown in Figure 3a andFigure 3b respectively. The plastic limitincreased steeply concomitantly reducingthe plasticity index. The effect of RHA-

stabilized can be attributed non-plasticproperties of RHA rather than cementitiousreaction between soil and RHA. Soil–lime–RHA mixtures were identified to resultcementitious reaction forming cementingagent that coat and bind clay particles tobecome coarser. The coarser particles wouldlead to random/flocculated particlesarrangement and alter the plasticity asshown in Figure 4.

For treated-clay soil containingmontmorillonite clay minerals, a contribution



to the water content arises from the waterentrapped in large void spaces of theflocculated soil fabrics (Prakash et al.,1989). Thereby, it explains the increased inthe liquid limits as discussed earlier.Stiffening (self-hardening) of lime-RHA

treated soil requires greater amount ofmoisture to enhance workability i.e. toenable rolling to a 3 mm thread. Hence, theplastic limits increased in conjunction withthe addition of lime and RHA.

0

1 0

2 0

3 0

4 0

5 0

6 0

0 2 0 4 0 6 0 8 0 1 0 0

L i q u i d L i m i t s , L L ( % )

Pla

sti

cit

y I

nd

ex

, P

I (

%)

K B 2 S o i l S o i l + R H A S o i l + R H A + 3 % L i m e S o i l + R H A + 6 % L i m e S o i l + R H A + 9 % L i m e S o i l + L i m e

A - L i n e

U - L i n e

M H o f H i g hC o m p r e s s i b i l i t y o r O HM L / O L

C L / O L

C H o rO H

C L - M L

Figure 4. Plasticity chart of stabilized expansive soil

Effect of Stabilization on SwellingCharacteristics

The effect of lime and RHA addition toexpansive soils is shown in Figure 5. Theswell was measured for 10 days ofinundation after 1-day moist cured under aseating pressure, and then the swellingpressure is determined by increasing theload such that the initial height of thespecimen was recovered. The figure depictsdecreasing of swelling and swelling pressurecorresponds to addition of lime.

When lime was added to a clay soil, it hasan immediate effect on the properties of thesoil. Cation exchange begins to take placebetween the ions associated with thesurfaces of the clay particles and thecalcium ions of the lime. Clay particles aresurrounded by a diffuse hydrous doublelayer, which was modified by the ionexchange of calcium. This alters the densityof the electrical charge around the clayparticles, which lead to them being attractedcloser to each other to form flocs. It is aprocess which is responsible for loss of

plasticity in clay. It reduces the tendency ofclay to swell. In addition to cationexchange, reaction occurs between thesilica and some alumina of the lattices of theclay minerals, especially at the edges of clayparticles. The reaction products contributeto flocculation by bonding adjacent soilparticles together and as curing occurs, theystrengthen the soils.

In the range of 6 – 9% lime-treated soil,cementation is the governing factor, causingclods to form, which in turn acts like coarsesand particles. These clods tend to reducethe permeability of the whole samples,thereby restricting the tendency of the clayto increase in volume (Bell, 1996; Azam etal., 1998). Additions of RHA into 3% lime-treated expansive soils reduce considerablythe swelling as presented in Figure 5b. Thisis due to the addition of non-plasticmaterials and the chemical constituents inthe RHA/lime mixtures. These constituents,and upon the reaction with the amorphoussilica and clay in the presence of water,would add some cementitious propertieswhich stabilize against swelling.



Lime content (%)

0 3 6 9 12

Swel

l (%

)

0

10

20

30

40

Swel

ling

Pres

ssur

e (k

Pa)

0

100

200

300

400SwellPressure

(a)

RHA (%)

0 3 6 9 12 15 18

Swel

l (%

)

0

5

10

15

20

Swel

l Pre

ssur

e (k

Pa)

0

75

150

225

300SwellSwellPressurePressure

(b)

3% Lime

3% Lime

6% Lime

6% Lime

Figure 5. Effect of Lime and RHA on the Swelling and Swelling Pressure of Stabilized Soil

On the other hand, the addition of RHA willfill in the intervoid of soil particles. Thiscauses reduction of permeability andcompressibility. Concomitantly, the swellingand swelling pressure decrease appreciably.The compressibility, in this research, isperformed after the soil has been allowed tocease its swell and then is loaded gradually.Typical swelling and compressibility curvesof stabilized expansive soils with lime andRHA are illustrated in Figure 6.

The figure showed that the swollen soils(unstabilized) experienced steep reductionin volumetric strain compared to stabilized

expansive soil when loading took place. Theswollen soil absorbed much water causingthe soil to become highly compressiblewhen subjected to load. It was observedthat the inflection pressure was about at 50kPa. Expansive soils stabilized withlime/RHA produced a denser soil structureas a result of cementitious reaction. Figure 6illustrates that addition of lime/RHAminimize the compressibility of stabilizedexpansive soils. The whole results verifythat addition of RHA into lime-treated soilsreduces significantly the swelling, swellingpressure and compressibility.

K B 2 S o i l

3 % L im e

- 1 0

- 5

0

5

1 0

1 5

2 0

2 5

3 0

1 1 0 1 0 0 1 0 0 0

L o g P r e s s u r e , P s ( k P a )

Ax

ial

Str

ain

,H

/ H (

%)

L 1R 4 L 1R 1L 1R 2 L 2 R 1

Figure 6. Typical of Swelling – Compressibility of Stabilized Expansive Soils (Note: L1R4: 3%Lime + 3% RHA, L1R1: 3% Lime + 6% RHA, L1R2: 3% Lime + 12% RHA, L2R1: 6% Lime +

6% RHA)



Effect of Stabilization on UnconfinedCompressive Strength

The effect of RHA addition on compressivestrength of lime treated-soil after 1 day and28 days of curing is presented in Figure 7aand Figure 7b respectively. The optimumlime content for the improvement ofcompressive strength was 6% of dry weight.

It was observed that adding RHA to 3%lime does not significantly increase thestrength. It can be simply explained thatbelow the optimum lime content, thereaction of lime with kaolin/bentonite maystill be attributed to ion exchange or minor

pozzolanic activity as investigated previouslyby Boardman et al. (2001). Concomitantly,the strength developed at a relatively slowerrate. The addition of RHA will fill in the voidof soil and react with lime to form cementedmaterials. The presence of excess RHA willthen be regarded as redundant particles.Samples with higher lime content, basically,have greater pozzolanic activities. Thepresence of pozzolanic materials such asRHA with higher lime percentage will form agreater quantity cementitious material. Thischange can largely result in flocculation offines particles to form bigger particlesthrough agglomeration.

RHA (%)

0 3 6 9 12 15 18

Com

pres

sive

Stre

ngth

(kPa

)

0

200

400

600

8006% Lime

3% Lime

9% Lime

0% Lime

(a)

RHA (%)

0 3 6 9 12 15 18

Com

pres

sive

Stre

ngth

(kPa

)

0

500

1000

1500

2000

2500

0% Lime

3% Lime

6% Lime

9% Lime(b)

Figure 7. Effect of RHA Addition on the Unconfined Compressive Strength of Lime-Treated Soil.

M o i s t C u r i n g ( d a y s )

1 7 2 8 5 6 9 0

Co

mp

ress

ive

Str

en

gth

(k

Pa

)

0 . 0

0 . 5

1 . 0

1 . 5

2 . 0

2 . 5

L 1L 1 R 4L 1 R 1L 1 R 2L 2L 2 R 4L 2 R 1L 2 R 2

Figure 8. Development of Compressive Strength Due to Curing



The long-term strength of stabilized soilsmay increase due to pozzolanic reactions.The results showed that the increase incuring has a substantial effect on theunconfined compressive strength. Figure 8shows the effect of curing on compressivestrength of lime stabilized soil mixtures. Thisfigure, again, exhibits that a higher limepercentage produces higher strength. For allsamples, generally, at least 60% of thestrength was achieved after 1 – 2 weeks ofcuring, while further increases in strengthafter 2 weeks is observed to be marginal ornegligible.

Effect of Stabilization on Resistance toImmersion

A stabilized soil should be durable in whichit has ability to retain its integrity and

strength under service environmentalconditions. The conformity to thisrequirement is more critical when thestrength of the stabilized soils is low. Thedetermination of the durability properties ofthe soils mixtures is a problem since it isdifficult to simulate the detrimental action inlaboratory comparable to that produced byweathering in the field. A simple methodwas examined by evaluating thecompressive strength of the cylindricalspecimens (50 mm diameter x 100 mmheight) after 7 days of immersion in water.The specimens were moist-cured for 7 daysand then capillary-soaked for 7 days. Theratio of compressive strength of soakedspecimens and moist-cured specimens wasthen termed as resistance to immersion (Ri)as presented in Table 1.

Table 1. Unconfined compressive strength of soaked and unsoaked specimens

Additives Compressive strength(kPa)

Lime RHA Unsoakeda Soakedb

Resistance toImmersion

(Ri)0 0 264.00 Fail -

3% 0% 492.50 7.88 0.0163% 356.95 8.21 0.0236% 313.75 10.04 0.03212% 334.30 18.37 0.055

6% 0% 812.54 252.70 0.3113% 930.27 344.20 0.3706% 1185.21 568.90 0.48012% 1378.27 951.00 0.690

9% 0% 657.40 316.21 0.4813% 885.88 485.46 0.5486% 1207.27 863.20 0.71512% 1442.18 1321.04 0.916

Note: a 14 days moist cured bThe specimens subject to 7 days moist cured and 7 days capillary soakedunder water.

Figure 9 presents the resistance toimmersion of stabilized soil-mixtures withdifferent method of treatment. In general,the stabilized soil experienced reduction in

the unconfined compressive strengthsubjected to the immersion test indicated byvalues of Ri lower than 1. Specimens solelystabilized by lime showed considerable loss



in strength. Adding RHA to soil sampleswould help to increase the resistance toimmersion. Fig. 9 also depicts that stabilizedclay with 3 % failed to retain their structuralintegrity, which the strength lost isexceeding 90% subjected to immersion.

Adding RHA to 3% lime-stabilized soil didnot significantly increased the durability.Increases in lime and rice husk ash contentserved to increase the percentage ofcementitious materials which led to lowerpermeability and higher strength.

R H A c o n t e n t ( % )

0 3 6 9 1 2 1 5

Re

sis

tan

ce

to

Im

me

rs

ion

0 . 0

0 . 2

0 . 4

0 . 6

0 . 8

1 . 0

3 % L i m e

6 % L i m e

9 % L i m e

Figure 9. Effect of Addition of Lime/RHA to Resistance to Immersion

X-Ray Diffraction (X-RD)

X-ray diffraction is the most widely usedmethod to identify fine-grained soilminerals. It was observed in Figure 10 thatswelling clay mineral, montmorillonite,strongly appeared at 15.32 Å in the testedsoil. The presence of the kaolinite mineralwas strongly found at 7.16 Å and 3.57 Å.Quartz and illite appeared strong at 3.35 Åand 3.19 Å respectively. Themontmorillonite peak disappeared at 15.32Å of basalt spacing (CuKlime and RHA were blended with expansive

soil. This could be possibly attributed to thechemical reaction between clay mineral andlime-RHA mixtures that altered the mineralor reduced their intensities. The kaoliniteand quartz minerals remained pronounce,but the intensities were reduced by theaddition of lime and RHA. The cementitiousmaterials were detected as calcium silicategel (CSH) at 3.04 Å and 2.79 Å (CuKradiation) in both soils tested. While,hydrated calcium aluminate silicates(C3ASnHn-2) strongly appeared at 3.28 Å.



5 10 15 20 25 30 35 40

D iffr ac tion A ng le (2 )

E

K

C

Q

K B : 1 0 % B en t o n it e + 9 0 % K ao lin M ix t ure s

6% Lime + 3% RH A

6% Lime + 6% RH A

6% Lime + 12% RH A

6% Lime

K

K

K

K

K

Q

Q

Q

CSH c

CSH g

CSH g

CSH c

CSH c

CSH c

Note: I: Illite, K: Kaolinite, M: Montmorillonite, Q: Quartz, E: Ettringite, CSHg: calcium silicates hydrate (gel)CSHc: calcium silicates hydrate (crystallized), CAS: calcium aluminate silicates hydrate

Figure 10. X-Ray Diffraction Pattern (Cuk

(d )

R H A (% )0 6 1 2 1 8 2 4

Lim

e (%

)

0

3

6

9

1 2

0 .50 .4

0 .7

0 .6

0 .6

0 .80 .9

Figure 11. Mixtures Design Chart Based onthe Reduction of Plasticity Index (Note:

numbers on the chart are referring to theplasticity index ratio of stabilized to

unstabilized soil)

Mixtures design of lime-RHA stabilizedexpansive soil

Lime – RHA stabilization has providedstructural improvement due to testedexpansive soils. This research proposed adesign chart as an approximate mixtures

design between lime and RHA, as presentedin Fig. 11 and 12. Fig. 11 presents a mixturedesign based on the reduction in plasticityindex. This parameter is well known close tothe many geotechnical properties such asswelling and strength of soils (Wroth andWood, 1978). The numbers shown on thechart refer to the ratio between theplasticity index of stabilized soil andunstabilized soil, where unstabilized soil hasratio equal to 1. The chart presented in Fig.12 is established based on the increasing incompressive strength. Herein, the numberdisplayed on the chart is the ratio betweencompressive strength of stabilized andunstabilized soil, which the unstabilized soilsubjected to ratio equal to 1. Using thesechart will assist for design a lime-RHAmixture to obtain a desired properties, forexample if it need to reduce the plasticityindex to become 0.5, 6% lime and 14%RHA can be mixed or mixed the othermixtures between 10% lime and 6% RHA.



R H A ( % )0 6 1 2 1 8

Lim

e (%)

0

3

6

9

1 2

23

4

56

1

Figure 12. Mixtures Design Chart Based onthe Increasing of Unconfined CompressiveStrength (Note: numbers on the chart arereferring to the compressive strength ratio

of stabilized to unstabilized soil)

CONCLUSIONS

Based on the experimental findings of thisresearch the following conclusions can beoutlined:1. In general, addition of RHA solely

decreases the plasticity of expansivesoil, as a result of reducing liquid limitand increasing plastic limit. Addition ofRHA significantly reduce the plasticityindex, whereas as much as 80% ofreduction is achieved by addition of RHAin greater lime content. It is noticedthat 6% lime addition is enough toimprove the consistency limits ofexpansive soils.

2. The swelling and swelling pressure ofexpansive soils decrease in concomitantwith the addition of lime and RHA. Theswelling of expansive soil is almost zerowhen it is added with 6% lime and 6%RHA.

3. Addition of RHA to lime – stabilizedexpansive soil increases enormously thevalue of unconfined compressivestrength. In general, the stabilised soilloses the unconfined compressivestrength subjected to the immersion.Lime-stabilised soils alone lose in

strength greatly. Adding of RHA is ableto increase the resistance to immersion.

4. Presences of cementitious materialssuch as calcium silicate hydrates (CSH)gel and calcium aluminate silicatehydrates (CAS) are detected in thelime-RHA treated expansive soil.Indicating the pozzolanic reaction hastaken place in the stabilized soil.

ACKNOWLEDGEMENT

The author is gratefully thanks to thesupport provided from the Ministry ofScience, Technology and Environment,Malaysia through the financial aid forIntensify Research in Priority Area (IRPA)RM#7 2002. Sincere thanks also goes to Dr.Roslan Hashim, Professor at Department ofCivil Engineering, University of Malaya, forhis assistance during the research carriedout.

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