IRC: 51-1992

GUIDELINES FOR THE USEOF

SOIL-LIME MIXES IN ROADCONSTRUCTION

(First Revision)

THE INDIAN ROADS CONGRESS1992

mc~51-1992

GUIDELINES FOR THE USEOF

SOIL-LIME MIXES IN ROADCONSTRUCTION

(FirstRevision)

Published byTHE INDIAN ROADS CONGRESSJamnagar House, Shahjahan Road,

New Dethi-ilOOll1992

PriceRs.2*4N40(Piuspacking& postage)

1RC:51-1992

FirstPublished:June,1973Reprinted:February,1980First Revision:June,1992

(RightsofPublicationandTranslationarereserved)

Printedat SagarPrinters& Publishers,NewDelhi(1000copies)

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IRC: 51-1992

1. Introduction2. Scope3. Materials4. DesignConsiderations5. Mix Design6. ConstructionOperations7. Quality Control8. Limilations

TABLE

CONTENTS

Page

123499

1416

Table I.

APPENDICES

Appendix1:

Appendix2:

Soil PulverisationRequirementforLimeStabilisation

Procedurefor theDeterminationof MoistureAbsorption

Methodof SievingforWetSoils to Determinethe Degreeof Pulverisation

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IRC: 51-t992

GUIDELINES FOR THE USE OF SOIL-LIME

MIXES IN ROAD CONSTRUCTION

1. INTRODUCTION

1.1. Addition of lime to soils is known to improve their strengthandreduceplasticitywhichin turncontrolsvolumechange.Becauseof thesead-vantages,this techniquehasbeenusedextensivelyfor improvingqualityofsub-gradeandproducingahigh strengthmaterial for sub-bases.

1.2. Lime reactswith mostof the medium,moderatelyfine, andfinegrainedsoils to decreaseplasticity, increaseworkability, reduceswell,andincreasestrength.In generalterms,the soils thataremostreactiveto limeincludeclayeygravels,siltyclaysandclays.SoilsclassifiedaccordingtotheIndianStandardsystemasCH,CL, MN, ML, CL-ML, SC,SM,GC andGMshouldbeconsideredaspotentiallycapableof beingstabilisedwith lime.

1.3. In thecaseof soil-lime construction,bestresultsareobtainedwhenmixing is homogeneousthroughout.This is best achievedby mechanicalmethodsof construction.Use of mechanisedmethod is, therefore,verydesirable.If foranyunavoidablereason,manualmethodistobeadopted,caremustbe takento ensureproperpulverisationof soil anduniform mixing oflime.

1.4.TheguidelineswereoriginallypublishedasIRC: 51-1973“Recom-mendedDesignCriteriafor theUse of Soil-LimeMixes in RoadConstruc-tion”. The reviseddocumentin the presentform was preparedby theGeotechnicalEngineeringCommittee(personnelgivenbelow),andconsid-ered by the Highways Specificationsand StandardsCommitteein itsmeetingheldon the16thApril, 1990.TheCommitteerequestedaSub-Groupconsistingof Shri R,P.Sikka,Dr. P.J.Rao,Shri T,K. NatarajanandDr. L.R.Kadiyali to modify the draft.

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IRC: 51-1992

TX. Natarajan ... Coavenor

P1Rao .,, Member-Secretary

Members

D.S.N. Ayyar Director,UP. P.W.D. Research Institute(RavindraKumar)

P. Dayal Director,KeralaHighwayResearchInstitute

3M. Malhotra Director, Geological Survey of India, NorthernRegion(P.N.Naçula)

i.B. Mathur Director (ER),Dept of Environment

Dr. SN.Ramaswamy Rep~ofB-in-C, ArmyHeadquarters(5K, Gupta)

Prof.G.V, Rao Rep.of DGBR (S.D.Aphale)

B-K. Roy ThePresident,mcRu Saxena (VP. Kandar) --Ex--officio

N. Sivaguru TheDG (liD)(K.K. Sann) --Ex--officto

Dr. C.SubbaraoTheSecretary,mc

DharaniVir (D.P.Gupta) --Ex--officio

Director, HRS,Madras

Corresponding Members

NV. Merasti Prof. S.D. Ramaswainy

Prof. Shainsher Prakash Dr. N. Rabu Shankar

1.5. The modifieddraftwas subsequentlyconsideredandapprovedbythe HighwaysSpecifications& StandardsCommittee, theExecutiveCom-mitteeandtheCouncilof theIndianRoadsCongressin their meetingsheldon 30thOctober1990,18thNovember1990and 8thDecember1990respec-tively.

2. SCOPE

The guidelinesrelateto soil-lime mixes intendedfor useas improvedsubgradeor asasub-basein highwaypavements.It ispresumedthattheworkwill be carriedoutin accordancewith appropriateconstruction specificationsandadequatesite supervisionwouldbeexercisedas regardsthe quality ofconstituentmaterials andprocessof construction.

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3. MATERIALS

3.1. Propertiesof lime-soil mixes aredependent onmany variablesviz.soil type, limetype,limepercentage,finenessof lime andlime purity inadditiontotheconditionsoftemperatureandmoisture.Someof the variablesrelated to materialsarediscussedbelow.

3.2.Soil

3.2.1.Samples: Before takingrecourseto lime stabilisation,it isdesir-abletoexamine thesuitabilityofsoilfor thistreatment.Thisis doneby takingsamplesof thesoilatappropriatelocations.Disturbedsamplesarenormallyadequatefor thispurpose.Thenormalpracticefollowed in thefield is to takeatleastthreesamplesin astretchof onekilometrealongthealignmentof themadif thesametypeofsoil is foundthroughout.In casethesoiltypechangesearlier,atleastonesampleistakenfrom eachnewstretchofsoil. Also,whenthe soil typechanges with depthwithin a borrowPitt at leastonesampleshould becollectedfrom eachstrata.

3.2.2.Suitability: Clayey soils includingheavyclays,moorums andothersoilsmetwithin thealluvial plainscanbeeffectively treatedwith lime.Sincethegain in strengthis basedonpozollanicreactionsbetweenlime andclayminerals,it isessentialthatanysoil selectedforstabilisationshouldhaveenoughclay minerals. Foreffectivestabilisation,asoil musthaveafractionpassing425micronmeshnotlessthan15percentandits P1shouldbeatleastlOpercent.Foreffectivestabilisation,it is desirablethatthepercentretainedon 425 micronmeshshouldbewell gradedwith uniformity coefficientnotlessthan5. Besides,clay mineralsshould belongto illitic, montmorilloniticor kaolinitic group. Generally clayeysoils including blackcotton soils,moorumandotheralluvial typesof soils,canbeeconomicallystabilisedwithlime. Organicmatterin thesoil selectedfor limestabilisation shouldnotbemorethan2.0percentandsulphatecontentshouldnot exceed0.2percent.A pH valueof 10 or 11 is desiredfor thepozollanicreactionto takeplacebetweenclay mineralsandlime for the formation of cementitiouscom-pounds.Whereorganicmatterandsolublecarbonate/sulphatecontentsin thesoilarein excessof 2.0and0.2percent respectively,special studieswouldbe necessaryto determinewhetherlime stabilisation would prove to bepracticableandeconomical.

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IRC: 51~1992

3.3. Lime

3.3.1. Type of lime: Lime for lime-soil stabilizationwork shall becalciticdry lime, commerciallyavailable,slakedatsite, orpre-slakedlimedeliveredatsitein suitablepacking.Useof dolomitic limeisnot consideredsuitable.

3.3.2.Purity:Purityof limeaffectsthestrengthoflime soilstabilisation.Theeffectivenessof lime in its reactionwith claymineralsisdependentto agood extenton its chemicalcompositioni.e. the amountof calcium oxidepresentin the lime. The purity of lime is expressedas thepercentageofcalciumoxidepresentin thelime. It isgenerallyrecommendedthatlimeusedforsoil stabilisationshould haveapurity of 50percent.Theadditionof limeshould becorrespondinglyincreasedwheneverthefield testsshowa lesserpurity.

Calcium oxidecontentin lime shouldbedeterminedasspecifiedin IS:1514-1959“IndianStandardMethodof SamplingandTestfor QuickLimeand HydratedLime” or IS: 712-1984“Indian StandardSpecification forBuilding Limes.”

3.3.3.Fineness:Foreffectivestabilisationwith lime, uniformmixing isapre-requisiteandthedegreeof mixing dependsonthe finenessof lime. Withfine lime,therewill bequickandeffectivereactionwith claymineralsto formcementitious compounds.Limeforstabilizationshallconformto thefinenessrequirementof ClassC hydratedlime asspecifiedin IS: 1514andIS: 712,which is asunder:

Stevesize (in micron) %Passing

850 100

300 95 (Minimum)

212 99 (Minimum)

4. DESIGNCONSIDERATIONS

4.1. Evaluation of Lime Requirement

4.1.1.Beforeconstructionof lime stabilisédroadis undertaken,survey

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of soil depositsexistingon thealignedroute is done (pant3.2.1.).A smalladdition of lime to clayey soil results in considerableincreasein theworkability of the soil, possibly due to baseexchangeor flocculationphenomenonor acombinationof thetwo. With suchsmalldosagesof lime,noappreciable gain in strengthof themixtureresults.As thedoseof lime isincreased,the strengthof themixture increases.Thissuggeststhatthelimeaddedinitially in smalldosagesis utilisedin satisfyingtheaffinity of thesoilfor lime. Thequantityoflime neededfor satisfying thisaffinity is termedaslime fixation point or lime retentionpoint. Lime neededfor thispurposeisusually1 to 3 percent.

4.1.2.Thestrengthof lime soilmixture is dependentto agreatextentonthequantityof lime addedabove thelimefixation point.Thetangibleeffectof lime soil stabilisationin increasingthestrengthof themixturebeginsto befelt as thelime contentis increasedabovelime fixation point.Thisis duetopozzolanicreactions resultingin theproductionofcementitiouscompounds.It is generallyfoundthatbeyondacertainpercentageof lime, the increaseinstrengthceasesandin fact a lowering in strengthmay resultdue to thepresenceof unreactedfree lime indicatingthatthereexistsanoptimumlimecontentfor maximum strengthgain.Sometentativevaluesofoptimumlimecontentforsoilsof differentmineralogicalcompositionareindicatedbelow:

Kaoliniiic so~1 - 4 per cent

Ifliticsoil - Spercent

Montmorillonitic soil - lOper cent

Theoptimumlimecontentasexplainedabovemaybe determinedby oneof thefollowing methods:

(i) pH Method

Theoptimumlimerequirementof soilis alsodeterminedby findingoutthepH valueof thetreated soilwithagiven percentageof lime.Percentageof lime which gives soil-lime mix apH of 12.4, is takento be the rightpercentageof lime requiredfor stabilisationof the givensoil. To find theoptimumlimerequirementof soil 20gofthesoil samplepassing425 micronmeshis takenin abottle.A givenpercentageof limeis addedby weightandmixed thoroughly. To this is added 100cc of distilled waterand mixedthoroughly.Theslurrysoformediskeptatroomtemperature(25°C)andafter

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anhour,it is shakenagainto ensureauniform mixing of ingredientsanditspH is determinedby a pH meter.The minimumpercentageof lime whichgivesapHof 12.4whenmixedwithsoil in theformof slurry,is the optimumpercentageof lime for stabilisation.

(ii) Moisture Absorption Method

Capillaryabsorptionof water is an intrinsic property of every soil.Besides other factors,thisdependsmainlyon themineralogicalcompositionand particlesize distribution.The addition of lime to soils bringsaboutachange in the particlesize distribution due to chemical reactionsandthemoistureabsorptioncharacteristicsof soilschangewith theaddition of lime.Thechangein moistureabsorptioncontinuesupto acertainlimecontentde-pendingupon thesoil. With further addition of lime,the changein moistureabsorptionisnegligible.Thelime contentat which shesoil attainsasteadymoistureabsorptionis termedas the optimum requirementof lime for aparticular soil. The methodto carry moistureabsorptiontest is given inAppendix-I.

4.1.3.After ascertainingoptimumliflie contentthestrengthof soil-limemix is determinedeitherby CaliforniaBearingRatioor UnconfinedCom-pressiveStrength(seepara4.2.).Samplesof CBR/UCSshouldbepreparedatmaximumdry densityandoptimum moisture contentasper IS: 2720(PartVII) or IS: 2720(PartVIII) asspecified.Thespecimenthus preparedshouldbecuredfor 3days followedby 4dayssoakingin water.At leastthreespeci-mensshould betested.UCS design procedure shouldbepreferredsinceit ismore realisticas comparedto CBR designcriteria.

4.1.4. If the strength valuesof the soil-lime mix obtainedat optimumlime-contentaremuchmorethanthoserequiredfrom designconsideration,strengthtestsmaybeconductedwith reducedlime contenttofix thedesignmix. However,in no caseshouldthelime contentbelessthantheminimumvalueof lime requiredfrom durability (Para4.5.) andleaching(Para4.6.)considerations.

4.2. Strength Criteria

Fortestingthestrengthof stabilisedsoils,theCBR testis widelyusedin

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the case ofgravelly soilswhereasUCS test is ottenusedwith fine texturedsoils.Both testsaredoneat anageof sevendayscomprisingthreedaysmoistcuring followedby four daysimmersionin water.Guidingstrengthcriteriaare asfollows:

(1) CUTest: MinimumCBRvaluefor thelime-stabitised sub-baseshouldbe 15percentfor low traffickedrural roads,20 percent forcumulativetraffic upto2 million standardaxles (MSA) and 30 percentfor traffic exceeding 2MSA. The CBR test should becarriedout on samplescompactedto thedensity specified and moulded at optimummoisturecontent.

(2) UnconfinedCompressionTest: In terms of the unconfinedstrength, the lime ~tabil-isedsoil usedfor sub-baseshould have a strengthof700 KN/Sq.m.

For purposesof design,the CBRvalue in the field shouldbe assumedas 60 to 70percentofthe oneobtainedin the laboratoryinconsiderationoftheanticipatedefficiencyof mixing, placing,curing and other aspectsofconstruction‘in the field,

4.3. Degreeof Pulverisation

4.3.1.Foreffectivestabilisation,thesoil must bein a well pulverisedstatebefore limeisadded.Yet,it maynotbeeconomicaltopulveriseheavyclayslike blackcotton soilto anappreciabledegree. Withthis in view, therequirementsof pulverisationfor different soilsare setforthin Table-i.

Ttat.g1 . Sort. PSJLVEMISATIONRIrQUWEMENI 5’O~LIME S’rAPILIMllON

Sievedesignation Minimum percent by weightpassingthe sieve

Forblack-cottonearl For othereoile

22.4mm 100 1004.00mm 50 60

4.3.2. Todeterminethe degreeof pulverisation,methodof sievingfor

wetcohesivesoils asgivenin Appendix- 2 shallbeused.

4.4. Evaluationof Field Strength

Whenevera largenumberof strengthtestsare done on lime-stabilisedlayer,~significantvariation in resultsis normally witnessed.Thishappensbecauseof certainfactorslike heterogeneouscharacterof the soil-lime mass,non-uniformityin mixing etc.Besides,asmalldeviationin theprocedureof

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IRC~51-1992

preparationof a sample and the testingtechniques inevitably takesplace.Variationin curing temperatureanddurationofcuringalsoaffectthe strengthresults.In the presenceof theseuncertainties,testresults canbeinterpretedstatisticallyin twopossiblemethods,eitherby takingmeanof thetestvaluesor by computing standarddeviationof values.From thesemeasures,otheruseful quantities like coefficient of variation andconfidencelimit for truemeancanbefound. Resultsare takento be fairly consistentif thecoefficientof variationisupto lOpercent.If the testresultslie oneithersideof thedesignvalue andcoefficientof variation is less thanlOper cent, thetest resultsaretakento bein conformitywith thedesignvalue.In casethemeanhappenstobeeitherlessor morethan10 percent,thenallowanceis madein thedesignthicknesseitherbyeffectingacorrespondingincreaseordecreasein itsvalue.

4.5. Durability

Durable soil-lime mixturescan be obtainedwhen reactivesoils arestabilisedwith lime. Although somestrengthreduction andvolumechangemay occurdue to alternate wetting and drying, the residual strengthofstabilisedmaterial is generallyadequateto meet thefield servicerequire-ments. For the climatic conditions prevailingin India, durability underwettinganddryingwould haveto betakeninto consideration and durabilityunderfreeze-thawconditionsdoesnot generally apply.Theminimumsevendaystrengthof 700kN/Sq.m. recommended forsubbaseisexpectedto meetthe durability requirementsof wetting and dryingunder normal circum-stances. However,in situationswherewaterloggingconditionsprevail,theadoptionof soil-lime stabilisationmay not bea satisfactorysolution fromdurabilityconsiderations.It wouldbedesirabletoconsidersuchalternativesascomposite stabilisationinvolving theuseoflime andcement,whichisnotwithin the scopeof these guidelines.

4.6.Preventionof Leaching

The amount of lime leachedout from the lime-soil mix exposedtocontinualflow of water dependson theperiodof curing andtosomeextent,on the quantity of lime added. Testresultshave shown that if the limestabilised sampleis cured for28 daysbeforeit is exposedto leachiqgproc-ess,thelossof lime duetoleachingis notappreciable.Thelossof lim~’rangesfrom 5 to 10 percentof lime added.On considerationof gainin strength,it

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IRC: 51-1992is believedthat percentageof lime to beaddedshould beabout 4.0per cent

or more. If this is done, the leaching problemis takencareof automatically.

5. MIX DESIGN

5.1.Theproportion of lime for stabilisation shouldbe determined in thelaboratoryin accordancewith the following procedure:

(1) Thesoil shouldbe testedfor N. fractionpassing425micron sieve, sulphatecontentand

organiccontentin orderto evaluateits suitability for stabilitation(vide pare 3.2.2.).

(2) Moisturedensity relationship forthesoil should be establishedaspertS: 2720 (PastVII) - 1980 or IS: 272.0(Part VIII) - 1983.

(3) Lime to be used for stabitisation shoutd be tested for available calcium oxidecontentin accordancewith IS: 1514-1959or 15: 712-1984.

(4) Evaluation of time requirement is carried out as perpars4.1.

(5) After pulverisingthesoil tothedegreestatedinpsra3.5.specimensforCBRIUCS testsarepreparedwith optimumpercentageoflime, compactedatmaximum dry densityandoptimummoisturecontentcorrespondingto IS: 2720 (PartV1l)orIS: 2720(PartVIII).The specimensthusprepared shouldbe curedinitially for 3 days and then soakedinwater for 4 daysbefore testingthemfor CI3R/UCSasperIS: 2720(Part XVI)- 1979/IS:2720(PartX)-1973.At least 3 specimensshould betestedfor eachlime concentration.

(6) On thebasisoftheseresults, themix design shouldbeselectedusing criteria setforthin psra 4.1. and 4.2.

6. CONSTRUCTION OPERATIONS

6.1.PulverisationandMixing

6.1.1.Full benefitof lime stabilisationcan behadonly if thelime addedto thesoil is thoroughlymixed. Fromthisconsiderationmechanicalmethod

should bepreferred. Manual methodof mixing maybeacceptedononly smallor less important works. The method of mixing, whether mechanical or

4 manual, should in any caseensure that lime is thoroughly and uniformlymixed with thesoil. Thecompactedthicknessof soil-limelayer or lift shallbe in Ik,: rangeof 75-200mmdependingon efficiencyof mixing and layingequipment.

6.1.2.Mechanicalmethods:Stabilised soil courseshall preferablybe

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constructedby mechanicalmethodof construction.Mechanical methodsofmixing lime-soil may be broadlygroupedinto two categories e.g.mix-in-place methodandstationary plant method.Becauseof better controls,thestationaryplant methodshouldgenerallygivebetterresults.

(i) Mix-in-placemethod

Themix-in-placemethod permits rapidconstructionwithasmalllabourforceandatrelativelylow cost.Theequipmentrequiredis simple andalargedaily output can be maintained.Its disadvantagesare the difficulty ofobtaininguniformity of mix anddifficultyof ens~Itingauniform thicknessoftheprocessedsoil. In themix-in-placemethod,thefollowing operationsareinvolved:

(a) Pulverisationof soil(b) Spreading lime(c) Mixing(d) Addition of water(e) Final grading(1) Compaction, and(g) Curing

Pulverisationcomprisesof two stages,first scarifying the soil to therequired depth of treatmentand secondpulverisingthe scarifiedsoil until itis broken down to asize suitablefor mixing with lime. Suitableplant forcuttingup the soil to the required depthcomprisesaplough or robust tillerwith a positivedepth control.While scarifying the areathe plough shouldmove thesoil towardsthe centreof theroad;this leavesavertical faceof thesoil attheshouldersandpreventsprocessingbeingcarriedoutsidethe limitsoftheroad.Rotarytillers areusedfor pulverisation,but discharrowscan alsobeadvantageously employedfor some soils.When thepulverisationiscom-pleted,the loosematerial is shapedwith a graderto giveevendistributionalong thelength and width of theroad.Lime canbe spreadeither mechani-cally or by hand. The mixing of soilwith lime is usuallydonewith thesameplant as is used for pulverising thesoil. Rotavatorscan also be usedadvantageouslyfor performingthe twin jobs of pulverisation andmixing.Wateris addedto thesoil-lime mix by meansofwaterdistributors.Thewaterdistributor is followedby themixing machineand theprocessingiscpnlinuedtill optimum moisturecontentis obtained.Whenmixing is complete,it isnecessaryto shapethesurfaceagainwith abladegrader beforecompaction.

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in the mix-in-placeconstructionby usingstabiliser,theplantshall becapableofpulverisingthesoil tothespecifieddegreeto thefull thicknessofthelayerbeingprocessed,thereby,achievingthe desireddegreeof mixingand uniformity of thestabilisedmaterial.Theplantshallbeeitherof singlepassormultiplepasstype.With singlepassequipment,theforwardspeedofthemachine will be soselectedthat therequireddegreeof mixing, pulveri-sationanddepthof processingis obtained.

in themultiple passprocessing,thesoil ontheprepared subgradeshall bepulverisedto the requireddepth with successivepassesof the plant andmoisturecontentadjustedtobewithin theprescribedlimits.Lime shallthenbe spreaduniformly and mixing continued with successivepassesuntil therequired depth anduniformity of processinghasbeenobtained.

(ii) Stationaryplant method

Stationaryplantsareessentiallyof twotypes,continuousandbatchmix.

In thecaseofcontinuousmix typeplantanelevatingloadersuppliessoilto ahopperwith ameasuringgate.A beltconveyordischargesit to apugmill,wherewateror fluid stabilizer may beaddedthrough spraynozzlesaridmixedinto the soil. Sometimelime is addedon the conveyorbelt. The mixedmaterial is thendischargedinto lorries.

On smalljobs,concretebatLhmixerscanbe usedfor mixing soil, limeandwater. However,bestresultsare achievedby double-paddlemixers, pugmills or roller pan typemachines,in which soil lumps areeasilybrokenup.

Usually mixtures producedby stationaryplant cost more thanthoseformedby themix-in-placemethod,but certainadvantagesaccruefrom theuseof this method. Advantagesclaimedfor stationaryplantmethodincludegreater uniformity ofthe mix, greatereaseof controloftheproportionsof themixture,greatereasein supplying waterto the mix andfewerdelaysduetobadweather.

The sequenceof operationsinvolved in the plant mix method is asfollows:

(a) Site preparation(b) Collectionandpulverisation

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(c) Mixing(d) Transporting andspreading(e) Compaction,and(0 Curing

After preparingtheformation,the subgradeis thoroughlycompacted byrolling befOresoil-limelayerissuperimposed.Thesoil whichhasbeentestedandfoundsuitable,isexcavatedfrom theroadsiteor from borrowareasasthecasemaybe,by means ofsuitable implements.All clodsandlumpsin thesoilarebrokenupandwhen pulverisationis completed,it is stokpilednearthemixing plant.Mixing of soil,limeandwaterisdonein themixer.Themixedmaterialis thentransportedto thesite, tipped,spread andcompactedin thenormalmanner.

6.1.3.Manualmixing: Themanual methodis more labour intensive,but becauseof its limitations in pulverisingandmixing, it should be usedfor small jobs only. The successof manual method dependson strictquality controlatsite duringpulverisation,mixing and compaction.Wheremanualmixing is permitted,the soil is excavatedfrom the borrow areasafter it is cleanedof all vegetation and placedon preparedsubgrade.Thesoil shall thenbe pulverisedwith crowbars,pick axesetc. A sprinkling ofwateris givenif theclodsaredry andthesoil isaheavyclay.Thecalculatedquantityof lime storedin bagsis placedon thetrackwith equalspacings.Ifthesoil iswetwith excessivemoisture,it isallowedto dry sothatitsmoistureis reducedto the optimumvalue. If the soil is on the drier side, requiredquantityof waterisaddedtobring it to the optimum moisturecontent. Limeis spreadin requisite quantity on the excavatedsoil. To account forconstructionlosses,unevendistributionof lime etc. add onepercent extralimein themix to get thedesigned fieldpercentage.With thehelpof ashovel,the soil is turnedupsidedown.Thisprocessis startedfrom one end andiscontinueduptotheotherend cross-sectionally.This makesoneturnandthesameis repeatedalong the wholestretchof theroad.Experiencehasshownthat4-5 turnsareenoughtoobtainathoroughmixing of the material.Alter-natively,thesoilis excavatedandisstackedalong thetrackof theroadpave-ment.Big clodsarebroken downto thedesiredsize.Calculated amountoflime is sprinkled andwater is addedto bring it to the optimum moisturecontent.Mixing is donewith shovelin thesameway asstatedearlier.Lime-soil mix is spreadon the trackand shapedwith a bladegrader beforeit iscompacted.

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6.2. Addition of Lime

Limemaybeaddedtothepreparedmaterialeitherin slurryformorin drystate.Notraffic otherthanmixingequipmentwill beallowedtopassoverthespreadmaterialuntil thecompletionof mixing.Mixing shallcontinuetill thematerialis freefrom anypocketwherelimeisdeficient.Themoisturecontentshall beequalto theoptimummoisturecontentandshallnotexceedOMC bymore than2.0percent.Thelimecontentof samplestakenfromthecompletedmixture shallnotvary aboveor belowthedesignatedlime content,by morethan 1 percent by weight.

6.3. Time BetweenMixing andCompaction

6.3.1. Time interval between the mixing of lime and soil, andcompactionof mix, hasa definite effect on the gain achievedin strength.Long delaybetweenthetimingsofthesetwooperationsresultsin lessdensityand hencereducedstrengthof the soil-lime mix for thesamecompactiveeffort. If thesamedensityandstrengthareto beachieved,extracompactiveeffort is requiredwhich involvesextracost andthus escalatesthe expen-ditureof theproject.Both laboratoryandfield observationshaveshownthattimegapbetweenmixing andcompactionshouldnot exceedthreeto fourhours.

6.4. Rolling

Immediatelyafterspreading,gradingandlevelling of the mixedmate-rial, compactionshallbecarriedout with 8-10tonnesmoothwheelroller orvibratoryroller. Rolling shallstartfrom theedgesandprogresstowardsthecentre.Duringrolling, thesurfaceshall befrequentlycheckedforgradeandcamber.Irregularitiesduring rolling shall be correctedby looseningthematerialandremovingoraddingfreshmaterial.Compactionshallcontinuetill atleast100percentofthemaximumdrydensitydeterminedin accordancewith IS: 2720(PartVII) or IS: 2720(PartVIII), asdecidedby thedesigner,is achievedin thefield.

6.5. Curing

Durationof the curingperiodandthetemperatureatwhichcuringtakesplace,haveasignificantinfluenceonthestrengthachieved.Longerperiodof

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curing is conduciveto attaininghigher strengthssincechemicalreactionscontinueto takeplacefor alongtime. Normalperiodof curing varies from7 to28daysatnormaltemperature underwetconditions.Curingprogressesfasterin warmconditions.As acompromisebetweentheobjectiveofachiev-ing high strengthandmaintaininga statisfactoryscheduleof progress,it issuggestedthat aminimum 7dayscuring shouldbegivento thelime-soil mixunder moist conditions.

Two common methods employed for curing areasphalticmembranecuring and moist curing. In membranecuring~,a prime coat of cut-backbitumenis appliedatarateofabout0.45to 1.1 Litre/Sq.mwithin onedayofrolling. Theprimecoatismeanttoassistcuringof stabilisedsoil by inhibit-ing the evaporationof moisture.Noequipmentor traffic shouldbepermittedon lime stabilisedsurfaceduringfirst 3daysafter.applying the primecoat.Ifthecompactedstabilisedlayerisnotruttedordistortedby theequipment,theimmediate placementof overlay is permitted.This overlaymaintainsthemoisture content of the compactedlayer and is an adequatemedium forcuring.

The othermethodof curing is moistcuring.In thismethod,thesurfaceis keptdampby light sprinkling of waterat frequent intervalsto preventdryingwith light rollers beingusedtokeepthesurfaceknittedtogether.Lightvehiclesmaybe permittedonthefinish..*i sw facebut heavy trafficshouldnotbe allowed for 10 to 15 days.

7. QUALITY CONTROL

7.1. Depth of theTreatment and Uniformity of Mixing

Sincelime elevatesthe pH value of the soil, phenolphthalein alcoholindicatorsolutioncanbesprayedon thesoiltodeterminethepresenceof lime.If lime is present,areddishpink colourdevelopsandindicatesthe depthofmixing.

Non uniformity of colourreaction,whenthe treatedmaterial is testedwith the standardphenolphthaleinalcohol indicator, will be consideredevidencefor inadequate mixing.Onetest per500Sq.m should be carriedoutfor determinationof depthanduniformity of mixing.

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7.2.Purity of Lime

One test should be carriedout for each consignmentcorresponding toIS: 1514-1959or IS: 712-1964,subjecttoaminimum of onetestperStonnesof lime. The test shall be donejust before lime is usedin the stabilisationwork.

7.3. Lime Content Immediately After Mixing

Onetestper 250Sq.m should be carriedout correspondingto IS: 4332

(Part VII1)-1969.

7.4. Degreeof Pulverization

Degreeof pulverization shall be checkedregularly and the sameshall

conformto the specificationgiven in Table 1.

7.5.Moisture Content Prior to Compaction

MoisturecontentshouldbedeterminedasperIS: 2720(PartII)-1973 at

arateof one testper 250Sq. m.7.6. Dry Density of CompactedLayer

Density shouldbecheckedaccordingto IS: 2720 (PartXXVIII)-1974.Onetest per500 Sq.m shouldbe carriedout.

7.7. LayerThicknessandLongitudinal Profile

Layerthickness shouldbe measuredregularlyby thickness blocksorcoresto conformto specifiedthickness.

Actual finishedlevelsofdifferentcoursesshallnotvaryfrom thedesignlevelsbeyondthe tolerances mentionedbelow:

Sub-grade ±25 mmSub-base ±20mm

7.8, Surface Regularity

The surface regularity of stabilised subgrade and sub-base in

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IRC: 51-1992

longitudinal andtransversedirectionsshallbe within thetolerancesindicatedbelow:

Layer LongitudinalProfile with3 m straight edge

Ctouprofile

Max. Max. Numberofpermissible Permissibleundulations undulationsin

any 300m. lengthexceeding

Max.pemüssiblevanationfromspecifiedprofileundercambertemplate

18mm 12mm mm

SubgradeSub-base

24 30 —

15 — 301512

7.9. CBRIUCSTestson Mixed Materials

Onetestper3000Sq.m should becarriedOutcorrespondingto IS: 2720

(Part-XVI)-l979 for CBR andIS: 2720(PartX)-1973 for UCS.

7.10.Deleterious Constituentsof Soil

Soil shouldbetestedregularlyfordeleteriousconstituentcorrespondingto IS: 2720 (PartXXII)-1972.

7.11.Curing

A recordshouldbemaintainedfor the curing period to ensure proper

curing for 7daysor anyotherperiodas specified.8. LIMITATIONS

Apart from organicsoilsandsomeraresoilswhichreactunfavourablywith limebecauseof chemicalcontamination,theonly otherphysicalfactorslimiting theuseof soils for stabilisationare:

(i) That it mustbepossibleto breakthesoil to a fine tilth in ordersomix in a stabiliser,

(ii) That thesoil shouldhaveanadequatelystabkgrading,

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IRC: 51-1992

(iii) That necessaryclay minerals aretherein the soil for thestabilisation reaction toproceed.A usefulworking limit is thatsoil should contain at least15 per centoffinespassing 425micron sieve andhave a plasticity indexof at least lOper cent.

(iv) Lime-soil stabilisationshouldnotbedonewhen theairtemperaturein the shadeisless

than 1(?C.

(v) Lime stabilizationshould not be carried out during rains.

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IRC: 514992

PROCEDURE FOR THE DETERMINATION OFMOISTURE ABSORPTiON

Appendix-I

Apparatus

I. Trough2. PorousPlate (thickness 2 cm and73 cmdiameter)3. Filter paper (Whatman 42)4. Distilled water5,6,7,8.9,

SpatulaPhysical balance, sensitivity 0.01 gmWeight boxOven for dryingPeth dish

Theporous plate is cleaned by boiling in water for about 15 minutes, The plate is taken outand placed in the trough. l)issilled water is poured in the trough so that its level reaches about 1 cmbelow the top ofthe porous plate. A dry filter paper cut to the same diameter as that of the plate iscarefully placed on the top of the porous plate.

15-20 gm of soil or soil4inte mix is carefully stacked loosely to a height of about 1 cm.(Fig. I)and is allowed to absorbmoisture from the trough for 1 hour. Theporousplate is taken outand the excess moisture is allowed to drain off for 5 minutes,. Moisture content of the sample isdetermined according to Indian Standards No. IS: 2720 (Pars-Il)-1973. This moisture consent istenned as moisture absorption.

Average of 3 such determinations should he taken.

FIg. I. Ass.mblage for moisture absorption

S

Index

I Trough2 Porous Plate3 Filter Paper4 Soil Sample5 Distilled Water

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IRC: 51-1992

Appendix-2

METHOD OF SIEVING FOR WET SOILS TO DETERMINE

THE DEGREE OF PULVERISATION1. A sampleof pulverisedsoil approximately1 kg by weightshouldbe takenand weighed

(WI).

2. It shouldbespreadon thesieveandshakengently,carebeingtakento breakthelumpsofsoil aslittleaspossible.Weightof soil retainedon thesieveshouldberecorded(W2).Lumpsoffiner soilsin theretainedmaterialshouldbebrokenuntil all the individualparticlesfinerthantheaperturesizeofthe sieveareseparated.

3~ The soil should beagainplacedon thesieveand shakenuntil sieving is completed.Theretainedmaterialshouldbeweighed(W3).

4. Weightof soil by percentpassingthesievecanthenbecalculatedfromtheexpression:

(W1-W2) 100

(W1-W3)

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