UTILIZATION OF UNCONTROLLED BURNT RICE ... - Teknik Sipil …tekniksipil.umy.ac.id/wp-content/uploads/2011/06/CIV02040207.pdf · Jurusan Teknik Sipil, Fakultas Teknik Sipil dan Perencanaan

DIMENSI TEKNIK SIPIL VOL. 4, NO. 2, September 2002 : 100 - 105

Jurusan Teknik Sipil, Fakultas Teknik Sipil dan Perencanaan - Universitas Kristen Petrahttp://puslit.petra.ac.id/journals/civil/

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UTILIZATION OF UNCONTROLLED BURNT RICE HUSK ASHIN SOIL IMPROVEMENT

Agus Setyo MuntoharResearch Assistant, Department of Civil and Environmental Engineering, University of Malaya,

50603 Kuala Lumpur, Malaysia

ABSTRACT

Expansive soil has been a problem in Indonesia as in other countries. Current research found thatthere is a potential use of silica waste, resulting from burnt rice husk, as a pozzolanic material. Thispaper presents the results of study on the utilisation of ashes produced from uncontrolled rice huskburnt in Yogyakarta (Indonesia).

In this research, a series of laboratory tests has been conducted. The tests were carried outindividually or in a combination in which the Rice Husk Ash (RHA) content were varied from 7.5, 10,and 12.5 percent, and the lime content from 2, 4, 6, and 10 percent (by the dry weight of soil). All thesamples have been remoulded at their optimum moisture content (OMC) and maximum dry density(MDD). The research shows that lime – rice husk ash decreased the swell of expansive soil andimproved its strength and bearing capacity.

Keywords: soil improvement, expansive soil, uncontrolled – burnt, rice husk ash.

INTRODUCTION

Several methods of soil improvement usingpozzolanic materials have been developed andused successfully in practice. It has been appliedin a variety of civil engineering works, like inthe construction of base courses where goodmaterials are not economically available; forreducing the permeability and compressibility ofsoils in hydraulic and foundation works; forstabilisation of slopes, embankments andexcavations. A considerable amount of researchconcerning stabilisation of soil with additivessuch as cement, lime, lime – fly ash and salt,bitumen and polymers is available in theliterature. But soil stabilisation with lime andrice husk ash (RHA) is a relatively new method.

In recent years the use of various wasteproducts in civil engineering construction hasgained considerable attention in view of theshortage and high costs of suitable conventionalaggregates, the increasing costs of wastedisposal and environmental constraints. Ricehusk is major agricultural by–product obtainedfrom the food crop of paddy. Generally, it wasconsidered a worthless by–product of the ricemills. Note: Discussion is expected before November, 1st 2002. Theproper discussion will be published in “Dimensi TeknikSipil” volume 5 number 1 Maret 2003.

Rice husk has a chemical composition, whichtypically corresponds to the following: cellulose(40 – 45 %), lignin (25 – 30 %), ash (15 – 20 %),and moisture (8 – 15 %). The ash is mainlyderived from the opaline, which is present in thecellular structure of husk and about 90 % ofwhich is silica. The silica content in the ricehusk depends on the following: (a) the variety ofthe rice, (b) soil and climate conditions, (c)prevailing temperature, and (d) agriculturalpractices ranging from application of fertilisersand insecticides etc. The normal method ofconversion from rice husk to ash is byincineration.

Chemically, RHA consists of 82 – 87 % silicaexceeding that of fly ash. Materials, containinghigh reactive silica (SiO2) is suitable to be usedas lime-pozzolana mixes and as substitution ofPortland cement [1, 2]. The high percentage ofsiliceous materials in the RHA makes it anexcellent material for stabilisation.

Many industries used rice husk as a relativelycheap fuel. Concomitantly, abundance of the ash(RHA) can be a potential waste product.Indonesia produced paddy annually around 50million tons for last five years. The amount ofrice husk is 12.5 million tons; the ash producedis approximately 4 million tons [3]. This paperpresents result of a study using open–field burntRHA and lime on the selected geotechnicalproperties of expansive soil.

ULTILIZATION OF UNCONTROLLED-BURNT RICE HUSK ASH IN SOIL IMPROVEMENT (Agus Setyo Muntohar)


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MATERIALS

RHA studied in this research was producedlocally. This was obtained from rice husks burntas fuel in a brick industry. The combustionprocess occurred under uncontrolled condition.As a stabilizing material, the RHA was sievedwith ASTM sieve size #200 (0.074 mm). Thelime, in this study, was used in powder-hydrated lime. This mixture is termed as lime-rice husk ash (LRHA). This admixture was usedto modify the expansive soils from Kasihanterrain, in D.I. Yogyakarta Province. Theproperties of the soil are given in the Table 1.

Table 1. Properties of Tested Soil

Properties ResultsNature moisture content, wN (%)Specific Gravity, GsLiquid Limits, LL (%)Plasticity Index, PI (%)Maximum Dry Density, γd (kN/m3)Optimum Moisture Content (%)Coarse particle (%)Fine particle (%)CBR (%)Compressibility Index (Cc) *ActivitySwelling potential (%) *

71.38 2.6373.5941.2513.2034.00 9.2490.76 3.03 0.28 3.0615.13

* Compacted at MDD & OMC (remoulded)

The soil is classified into CH, clay with highplasticity. Any soil with PI > 35 % and swellingpotential > 10 % can be categorized as very highexpansive soil [4]. The chemical properties of theadditives are presented in the Table 2 [5].

Table 2. Composition of Additives

Constituents Clay (%) RHA (%) Lime (%)SiO2 51.39 89.08 0.00Al2O3 17.21 1.75 0.13Fe2O3 9.33 0.78 0.08CaO 3.66 1.29 59.03MgO 1.17 0.64 0.25Na2O 1.72 0.85 0.05K2O 0.39 1.38 0.03MnO 0.25 0.14 0.04TiO2 0.98 0.00 0.00P2O5 0.17 0.61 0.00H2O 4.23 1.33 0.04Loss on ignition 9.48 2.05 40.33

EXPERIMENTAL WORK

To assess the effect of RHA on the expansiveclays properties, the RHA was blended withlime as the lime-pozzolana mix. A series oflaboratory tests were conducted namely the

physical and index properties, compaction, CBR,consolidation, and UU-triaxial test. The testswere carried out individually or in acombination in which the RHA content wasvaried from 7.5, 10, and 12.5 percent, and thelime content from 2, 4, 6, and 10 percent (by thedry weight of soil). All the samples have beenremoulded at their optimum moisture content(OMC) and maximum dry density (MDD). Thesamples were cured for 3 days and kept inplastic bags to prevent the loss of moisture andto allow modification process to proceed.

RESULTS AND DISCUSSION

The tests result such as liquid limits, plasticlimits, particles composition, CBR, compressi-bility index, MDD, OMC, and maximum axialstress, are presented in the Table 3.

Table 3. Geotechnical Properties of TreatedSamples

MDD = maximum dry density;OMC = optimum moisture content

Consistency Limits

The effect of varying concentration of RHA, limeand LRHA on the expansive soil is shown inFigure 1.

In all admixtures content, the liquid limitsdecreased, whereas, plastic limits increased.Figure 2 shows effect of additives on theplasticity index. It is observed that addition ofRHA show less reduction than lime. However,RHA–lime mixture achieved considerable reduc-tion of plasticity index, approximately 90%, from41.25% down to 4.74%.

Gromko [6] reviewed that plasticity index and,especially, shrinkage index are early indicatorsof potential expansion because most soilexpansion occurs at water contents betweenthese indices.



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0

10

20

30

40

50

60

70

80S R1

R2

R3 L1 L2 L3 L4

LR1

LR2

LR3

Samples code

Wat

er c

onte

nt (%

)

LL PL PI

Figure 1. Consistency Limits of Samples

0

5

10

15

20

25

30

35

40

45

50

0 2 4 6 8 10 12 14 16 18 20

Admixture content in soil (%)

Pla

stic

ity

Inde

x (%

)

Soil + Lime

Soil + RHA

Soil +LRHA

Figure 2. Variation of Plasticity Index With AdmixtureContent in Soil

Physical Properties

Reduction of fine particles may be inferred fromflocculation of soil particle to be coarsermaterials. The effect of additives on thediminution of fine particles is illustrated inFigure 3.

At ordinary temperatures and in the presence ofwater, RHA also can react with Ca(OH)2,forming Ca1.5SiO3.5·xH2O. The reaction betweenthe SiO2 in RHA and Ca(OH)2 can yields bondedgel (C-S-H) [7]. It caused agglomeration of fineparticles to become bigger particles, except withRHA where only slighter alteration wasachieved as indicated in Figure 3.

0

20

40

60

80

100

0 2 4 6 8 10 12 14 16 18 20


Fine

par

ticle

s (%

)

Soil + Lime Soil + RHA Soil + LRHA

Figure 3. Effect of Admixture on The Fine ParticleContent

Compaction, Consolidation, and CBRCharacteristics

Figure 4 shows the compaction behaviour ofseveral of the soil mixes. It has been observedthat the OMC of expansive soil slightly lessenedon the addition of lime to it, whereas, theaddition of RHA increased the OMC. However,the admixtures diminished the MDD to a low11.50 kN/m3 as attained from the LR1 and LR3samples. The MDD of additives – soil mixturesis reduced by the presence of additives owing toits relatively low specific gravity. The increasein OMC may be caused by the absorption ofwater by the additives to precede chemicalreaction.

5

6

7

8

9

10

11

12

13

14

15 20 25 30 35 40 45 50

Water content (%)

Dry

den

sity

(kN

/m3 )

S (soil) R1R3 L1L3 LR2

Figure 4. Standard Proctor’s Test of Various Admixtures

Compression index (Cc) was obtained from thee–log p curves of the consolidation test (Fig. 5).



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Effect of the additives on the compressibility ofremoulded soil is shown in Figure 6. It revealsthat lime is more effective, relatively, than RHAto reduce compressibility of soil. In general, theaddition of the additives dropped thecompressibility index from 0.28 (un-stabilizedsoil) to 0.001 (LR3). When the RHA contentexceeds of the amount required for reaction,they will be filled between the void of soilbecause of their fines particles are finer thansoil. A more compact state of soil is probablyattained, concomitantly the compressibility ofsoil diminish.

0.80

0.85

0.90

0.95

1.00

1.05

10 100 1000

Log p (kPa)

Voi

d ra

tio,

e

S

R1

R2

R3L1

L3

LR1

Figure 5. Consolidation Behaviour

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0 2 4 6 8 10 12 14 16 18 20 22


Com

pres

sibi

lity

Inde

x


Figure 6. Compressibility Index (Cc) of Treated Soil

The CBR is also a value that corresponds tostrength of soil. Figure 7 exhibits increasing ofCBR values with increase in amount of

additives. The CBR value of treated soil withlime is greater than soil treated with RHA.

RHA cannot be used solely in the soilstabilisation because of its lack of cementitiousproperties. However, addition of RHA with 6percent lime attained highest CBR.

0

4

8

12

16

20

0 2 4 6 8 10 12 14 16 18 20


CB

R v

alue

s (%

)

Soil + Lime

Soil + RHA Soil + LRHA

Figure 7. CBR Behaviour of Treated Expansive Clay

The gain of strength of lime–stabilised soil isregarded primarily as a result of pozzolanicreaction between amorphous silica and/oralumina in the soil and lime to form varioustypes of cementing agents. By introducing RHAto the soil, additional amounts of amorphoussilica are available for reaction with limeresulting in further increases in strength.

Swelling Potential

The result of swelling potential of the naturalexpansive soil and treated soil is presented inFigure 8. Increasing the amount of admixturewhether lime or RHA reduce the expansion.RHA can reduce the heave by 64% soil from itsnatural state (15.13%). In this case, lime wasmore effective reducing swelling than RHA.Mixing both of these materials give betterresult. For example with a combination of 6 %lime and 12.5 % RHA, the swelling potential is2.60 %.

Seed et al [8] gave relationship between swellingpotential, percentage of clay type, and plasticityindex. Further, the value of swelling potentialdepends on the same factors that influence thesoil volume change such as: mineral type andamount, density, load conditions, soil structure,and water content [6].



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0

2

4

6

8

10

12

14

16

0 2 4 6 8 10 12 14 16 18 20


Swel

ling

pote

ntia

l (%

)

Soil + Lime

Soil + RHA

Soil + LRHA

Figure 8. Swelling Potential of Treated Expansive Soil

Shear Strength Behaviour

The shear strength parameter such as cohesionand internal friction angle of soil was obtainedfrom UU triaxial test. The effect of admixture onthe internal friction angle and cohesion is shownin Figure 9 and Figure 10 respectively. Theaddition of additives tends to increase theinternal friction angle of soil, but there is only aslight difference in the cohesion.

0

5

10

15

20

25

0 2 4 6 8 10 12 14 16 18 20

Admixture content (%)

Inte

rnal

fric

tion

angl

e (d

egre

e)


Figure 9. Internal Friction Angle With Admixture Variation

The addition of 10 percent lime (L4) showsbrittle behaviour as shown in Figure 11. AddingRHA makes it more ductile, though the level ofstrength attained is not high. This is inagreement with Balasubramaniam et al [9].

30

50

70

90

110

130

0 2 4 6 8 10 12 14 16 18 20

Admixture content (%)

Coh

esio

n (k

Pa)


Figure 10. Variation of Soil Cohesion With Admixture

0

100

200

300

400

500

600

700

0 5 10 15 20 25

Axial strain (%)

Axi

al s

tres

s (k

Pa)

S R2R3 L3L4 LR1LR2 LR3

Figure 11. Axial Stress and Strain Under 98.10 kPa CellPressure.

Reducing the fine particles implies that LRHAaltered the soil texture. Consequently, theswelling potential and compressibility werereduced while the soil bearing capacity wasgreater than before.

Application

In tropical countries; such as Indonesia,Thailand, Malaysia, etc.; where rice husks areabundant and considered as waste materials,utilisation of RHA in the construction of roads,airfields, and other geotechnical works isintensely attractive. This would generally lead



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to low construction costs, help alleviate disposalcosts and environmental impact and conservehigh – grade construction materials for higherpriority uses.

The results obtained during this investigationas discussed in the previous sections showedencouraging signs for the used of RHA in soilimprovement schemes. The results showed thatalthough the RHA used in the study wasobtained from an uncontrolled burning, it couldstill be effective in improving the properties ofthe expansive soil.

Hence, it implies that the necessary technologyrequired for controlled burning can be omittedreducing the cost of utilizing RHA for soilimprovement.

CONCLUSION

The study has been successfully conducted toassess the geotechnical properties of expansivesoils improved with RHA wastes and lime. RHAand lime altered the texture of clay soil byreducing the fine particles.

Lime and RHA reduce the liquid limits whilethe plastics limits increased. As a result, theplasticity indices reduced. Swelling potential ofexpansive soil diminished with the addition ofadmixtures. The compressibility of soil reduceswith blend of lime and RHA.

In terms of compaction, the OMC moves to wetside, and MDD enhanced marginally. Itindicates that the additives, especially RHA;imbibe much water to attain the MDD.

Furthermore, the CBR values enhanced. Tenpercent lime content produced brittle failureunder compression. Whereas, soil treated withcombination of RHA and lime revealed a ductilebehaviour, but the strength increasedmarginally.

ACKNOWLEDGMENTS

The author would like to thank Mr. GendutHantoro, for his opinion and suggestion. Theassistance of technician and assistants inperforming some laboratory testing are alsoacknowledged.

REFERENCES

1. Payá, J., Monzó, J., Borrachero, M.V.,Mellado, A., Ordoñez L.M., Determination ofamorphous silica in rice husk ash by rapidanalytical method, Journal of Cement andConcrete Research, Vol. 31, 2001, pp. 212–231.

2. Jauberthie, R., Rendell, F., Tamba, S., Cisse,I., Origin of the pozzolanic effect of rice husks,Journal of Construction and BuildingMaterial. Vol. 14, 2000, pp. 419 – 423.

3. Muntohar A.S., Swelling characteristics ofexpansive clay stabilized with LRHA,Proceeding National Seminar on theEngineering Science. Yogyakarta: 2001, pp.62 – 68.

4. Chen, F.H., Foundation on Expansive Soil,Elsevier Scientific Publishing Company, NewYork, USA, 1985.

5. Muntohar, A.S., Hantoro, G., Influence of therice husk ash and lime on the engineeringproperties of Clayey Subgrade, ElectronicJournal of Geotechnical Engineering.Oklahoma State University, Vol. 5, 2000, pp.#0193.

6. Gromko, G.J., Review of expansive soils,Journal of Geotecnical Engineering Division,ASCE, Vol. 100, No. 6., 1974, pp. 667–687.

7. Qijun Yu., Sawayama, K., Sugita, S., Shoya,M., Isojima, Y., The reaction between ricehusk ash and Ca(OH)2 solution and thenature of its product, Journal of Cement andConcrete Research. Vol. 29 (1), 1999, pp. 37–43.

8. Seed, H.B., Woodward, R.J., Lundgren, R.,Prediction of swelling potential for compactedclays, Journal of the Soil Mechanics andFoundation Division, ASCE, SM3, June,1962, pp. 53–87.

9. Balasubramaniam, A.S., Lin, D.G., Acharya,S.S.S., Kamruzzaman, A.H.M., Behaviour ofsoft Bangkok clay treated with additives,Proceeding of 11th Asian Regional Conferenceon Soil Mechanic and GeotechnicalEngineering. Seoul. Vol. 1: 11–14, 1999.

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UTILIZATION OF UNCONTROLLED BURNT RICE ... - Teknik Sipil …tekniksipil.umy.ac.id/wp-content/uploads/2011/06/CIV02040207.pdf · Jurusan Teknik Sipil, Fakultas Teknik Sipil dan Perencanaan