EffectofRiceHuskAshonCementMortarandConcrete

SudishtMishra, Faculty Civil Engineer. Deptt NERIST, Itanagar,Prof(Dr.)S.V.Deodhar, Principal,SSVPSBSDCollegeofEngineering,Dhule.Introduction

Workability, strength, and durability are three basics properties ofconcrete. Amount of useful internal work necessary to overcomethe internal friction to produce full compaction is termed asWorkability.Size,shape,surfacetextureandgradingofaggregates,watercement ratio, use of admixtures and mix proportion areimportant factors affecting workability. Strength is to bear thedesiredstresseswithinthepermissiblefactorofsafety inexpectedexposurecondition.The factor influencing thestrengthare:qualityof cement, watercement ratio, grading of aggregates, degree ofcompaction, efficiency of curing, curing temperature, age at thetimeof testing, impact and fatigue.Durability is sustenanceof shape, size and strength resistance toexposure conditions, disintegration and wearing under adverse conditions. Variation in concreteproduction,loadingconditionsinservicelifeandsubsequentattackbytheenvironmentfactorsaremaindeteriorating factor of concrete. Properly compacted and cured concrete used in RCC continues to besubstantially water tight and durable till capillary pores and microcracks in the interior areinterconnectedtoformpathwaysuptosurface.

Durability is mainly influenced by environmental exposure condition, freezing thawing, contact toaggressivechemicals, typeandqualityofconstituentmaterials,watercement ratio,workability,shapeand size of the member, degree of compaction, efficiency of curing, effectiveness of cover concrete,porosity and permeability. During service life of structures, penetration of water and aggressivechemicals, carbonation, chloride ingress, leaching, sulphate attack, alkalisilica reaction and freezingthawingareresultingdeterioration.Loadingandweatheringinterlinkvoidsandmicrocrackspresentintransition zoneandnetworkof samemicro cracksgets connected to crackson concrete surfacewhichprovides primary mechanism of the fluid transport to interior of concrete. Subsequent increase ofpenetrability leads to easy ingress of water, oxygen, carbon dioxide and acidic ions etc into concreteresultingcracking,spalling,lossatmass,strengthandstiffness.

Lowpermeability is key todurability and it is controlled by factors likewatercement ratio, degree ofhydration, curing, entrapped air voids, micro cracks due to loading and cyclic exposure to thermalvariations. Admixture improves workability, compactibility, strength, impermeability, resistance tochemicalattack,corrosionofreinforcementandfreezingthawingetc.andinturntodurability.Forthisstudy durability is interpreted in terms of porosity,moisturemovement, surface strength, ultra soundpulse velocity and elasticitymodulus of concrete. Optimum use of Rice Husk Ash (RHA), obtained byopenfieldburningmethod,isdecidedforimprovingworkability,strengthanddurabilityofconcrete.RiceHuskAsh

RHA, produced after burning of Rice husks (RH) has high reactivity and pozzolanic property. IndianStandard codeof practice for plain and reinforced concrete, IS4562000, recommendsuseofRHA inconcrete but does not specify quantities. Chemical compositions of RHA are affected due to burningprocessandtemperature.Silicacontentintheashincreaseswithhighertheburningtemperature.AsperstudybyHouston,D.F.(1972)RHAproducedbyburningricehuskbetween600and700Ctemperaturesfor 2 hours, contains 9095% SiO , 13% K O and

Portlandcementcontains60to65%CaOand,uponhydration,aconsiderableportionoflimeisreleasedasfreeCa(OH) ,whichisprimarilyresponsibleforthepoorperformanceofPortlandcementconcretesinacidicenvironments.SilicapresentintheRHAcombineswiththecalciumhydroxideandresultsexcellentresistanceof thematerial to acidic environments.RHA replacing10%Portland cement resists chloridepenetration,improvescapillarysuctionandacceleratedchloridediffusivity.

Pozzolanic reaction of RHA consumes Ca(OH) present in a hydrated Portland cement paste, reducessusceptibletoacidattackandimprovesresistancetochloridepenetration.Thisreduces largeporesandporosity resultingvery lowpermeability.ThepozzolanicandcementitiousreactionassociatedwithRHAreducesthefreelimepresentinthecementpaste,decreasesthepermeabilityofthesystem,improvesoverallresistancetoCO attackandenhancesresistancetocorrosionofsteel inconcrete.HighlymicroporousstructureRHAmixedconcreteprovidesescapepaths for the freezingwater insidetheconcrete,relievinginternalstresses,reducingmicrocrackingandimprovingfreezethawresistance.NonDestructiveTests(NDT)

NDT, systems required for assessing strength in service feature, is defined as a test which does notimpairtheintendedperformanceoftheelementormemberunderinvestigation,carriedoutonsite,withabilitytodeterminethestrengthanddurabilityofcriticalconstructionswithoutdamaging.

ForconductingNDTests,Reboundhammer,Protimetermoisturemeasurementsystem,PorositesterandpulseUltrasonicNonDestructiveIndicatingTester(PUNDIT)equipmentareused.

Reboundhammertestisconductedtoassestherelativestrengthofconcretebasedonthehardnessatornear itsexposedsurface.ConcreteReboundTestHammer isa traditional instrumentused for thenondestructivetestingofhardenedconcrete.Thisprovidesaquickandsimpletestmethodforobtaininganimmediateindicationofconcretestrengthinvariouspartsofastructure.Knobofthisinstrumentiskeptperpendiculartothesurface(i.e.90degreetothesurface)formeasurementand ispushpressedfromthe bottom towards the surface of the concrete, hammer like sound is produced. The button near thebottomoftheinstrumentispressedtolocktheindicatorandreadingistaken.

The surfacemoisture isgenerallynot seen for cleaningand restoring the structureafterdamage fromstorms, floods or fires. For exposed or unseen structural damage, the undetected moisture damagesstrength, durability and reliability. The Protimeter Moisture Measurement System is a powerful andversatileinstrumentformeasuringanddiagnosingsurfacemoistureinbuildings.Thisinstrumentdirectlydisplaysmoisturecontent(%)alongwiththreeconditionsofmateriallikeDRY,WETandRISKcondition.For using Protimeter operationalmodes are selected and information is presented on a large, back litliquidcrystaldisplay.Theradiofrequencysensorispositionedsothatlargenumberofmoisturereadingsistakenquicklyandeasily.

Porositestercontainsof3glasstubeusedtomeasurethewaterpenetration inconcreteatatmosphericpressure.Tubesarefixedwithvacuumplateandvacuumpumpwithoutanysubsequentcleaning.Rubberseal inserted in the tube provides a defined contact surface of dia 25 mm vertical or horizontal.Compressible seals on suction plate and tube permit secure fixing also to uneven surfaces. Currentsupplyisprovidedfroma12Vrechargeablebattery.Vacuumplateispressedagainstthefaadewithawet sponge,motor isplacedonadhesionof theplate is checked.Test tubes are placedunder the clipandsecuredfirmlywithscrews.Testtubesarefilledwithwateruptothezeromarkandagainrefilledafterthedescentofthewaterlevelby1or2mlandreadingsofquantityofpenetratedwaterarenoteddown for 15 minute test time. As per the manual of equipment, water absorption coefficient A iscalculatedbyusingfollowingformula:

Where,

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2

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Figure1:Porositester

X=Amount(level)ofwaterpenetratedinml.

d=Dia.oftesttubeinmm.

t=Timeofpenetrationinminutes.

Figure 1 shows the Porositester mentioned above Pundit is a highly trustworthyequipment for ultrasonic pulse velocity teshon concrete. Pundit plus is used todeterminepulsevelocity,(UPV)modulusofelasticity,cavitiesandcrackspresentin the concrete. Equipment is ruggedly built for onsite reliability for simple,speedyoperationwith integralRS232 interface, automemory store for readings,largeLCDdisplaywithexternalorbatterypowersupply.Thesetupparametersaredefinedforthepreferredmodeofoperationandrespectivevaluesaredisplayed.Workplan

ObjectiveofthisworkistostudytheeffectsofRiceHuskAshasanadmixtureonworkability,strength,durabilityofcementconcreteandcementmortar.Basedontheabove,optimumdoseofRHAisdeterminedtoenhancethedesiredpropertiesofconcretewithoutcausinganyadverseresultonotherproperties.

RiceHusk from local RiceMillswas burnt completely in open field condition andsievedwith150micronISsieve.RiceHuskAshpercentagewasgradualincreasedfrom7.5%,10.0%,12.5%,15.0%and17.5%.M gradenominalmixconcrete(1:1.5:3)andcementmortarofproportion(1:4).Coarseaggregateof20mmgradednominalsize,riversandzoneIIItypeand53gradesPozzolanaPortlandCement(PPC)wereusedforthiswork.Forslumpvalues15mmto35mmandcompactionfactor0.85to0.90,watercementratioforplainandRHAmixedconcretewas0.50and0.575respectively.Forcastingconcreteandmortarcubes,150mmsteelcubemouldsand70.7mmsteelcubemouldswereused.EachsetContainedSixsamplesofplainconcreteandsixofRHAmixed.After 24 hours of casting, samples were opened and kept under tap water curing for 28 days. Laterdestructiveandnondestructivetestswerecarriedoutonsetofthreeseparatecubesandaveragevaluestakenforthisstudy.TestResultsCompressiveStrength

CompressivestrengthforRHAmixedconcretesamplesincreasedupto12.5%ofRHAanddecreasedforhigher%ofRHA.Higheststrengthwasfound30.3N/mm followedby30.07N/mm forRHAcomposition10.00% and 12.5% respectively. In comparison to normal M mix samples, compressive strengthdecreasedby12.94%and19.17%for15.00%and17.5%ofRHAmixedconcretesamples.BetweenRHAcompositions10%and12.5%,compressivestrength increasedverymarginally (0.80%)whereassamevaluewashighest(3.08%)betweenRHAcompositions7.50%and10.00%.

Compressive strengthof normalmortar cubeswas10.39N/mm and same increased to 16.43N/mmand 17.44 N/mm for RHA composition 7.5% and 10.00% respectively. For higher proportion of RHA,12.50%,15.00%and17.50%,compressivestrengthdecreasedto12.74N/mm ,10.73N/mm and7.71N/mm respectively. Maximum increase in strength was 67.85% followed by 58.13% for 10.00% and7.50%RHAcompositionrespectively.

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2 2

20

2 2

2

2 2

2

ReboundHammerTest

SurfacestrengthofM gradeconcrete cubewas20.05N/mm .For RHAmixed samples, same valuesincreasedtoamaximumof28.00N/mm andminimum23.00N/mm (Table1)for10%and17.5%ricehusk respectively. For RHA mixed mortar samples, surface strength increased marginally from 16.67N/mm to17.33N/mm (3.96%)which further showed a decreased value of 16.67N/mm formortarcubes with 17.5%RHA. For concrete samples, strength increased upto 10%RHA and later it starteddecreasingbutforthemortarsamplessametrendcontinuedupto15%RHA.Interpretedfromthegraphthat the strength is increased rapidly from 7.5% to 15% and it starts decreasing with increase inpercentageofadmixture.ThereferencemortarcubeishavingstrengthofN/mm .

SurfaceMoistureTestResults

Surfacemoistureforconcretecubeswas17.31%whichincreasedto17.97%for7.5%RHAcontent.Forhigher% of RHA, it showed a decreased trend with minimum value 17.2% for 17.5% RHA. For RHAmixedmortarcubes,maximumvaluewas17.32%with10%RHAwhichfurtherdecreasedto15.89%for17.5%RHA.

Figure2(a):VariationofNDTPropertiesofMortarCubes

PulseVelocityTest

20 2

2 2

2 2 2

2

Pulsevelocitywasobserved3258m/sec. innormal concrete cubeswhich increased tomaximum3736m/sec.in15.00%RHAmixedcubes.Increaseinpulsevelocitywas6.78%,10.25%,12.68%,14.67%and13.51%forcorrespondingRHA7.5%,10%,12.5%,15%,and17.5%respectively.

Elasticmodulusincreasedfrom3.83GN/m toamaximum5.97GN/m (55.87%)for12.5%RHAmixedsamples.

Figure2(b):VariationinCompressiveStrength,ReboundHammerStrengthandSurfaceMoisture

Porosity

FornominalmixM gradeconcretecubes,waterabsorptioncoefficientwasfound1.19Kg/m /min.InRHAmixedconcretesamples,waterabsorptioncoefficientsexhibiteddecreasingtrendtoaminimumof1.34(29.84%)for12.5%ofRHAbutthesameincreasedwithhigherpercentageofRHA.FormaximumproportionofRHA(17.5%)itwasfound1.63Kg/m /min,15.18%higherthantheminimumvalue.

2 2

20 2

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Figure2(c):VariationinCompressiveStrength,ReboundHammerStrengthandSurfaceMoisture

Conclusion

InnominalmixM gradeconcreteand1:4cementmortarRHAwasaddedasanadmixturefrom7.50%to17.50%with anuniformvariation of 2.5%.Duringdestructive test, compressive strengthofmortarcubes and rebound hammer strength of concrete samples found increasedwithmaximum variation of67.85% and 39.65% for 10% RHA. Maximum variations of elastic modulus were 55.87% followed by27.94% for 12.50% and 10%RHAmixed samples. Compressive strength of concrete samples showedmaximumincrease3.08%betweenRHA7.50%to10.00%whichdecreasedfurtherforhigherpercentageofRHA.

Reduction in water absorption, from results obtained from 6 tests concrete and 3 tests on mortarsamples,itisobservedthatupto10%RHAwithconcreteandmortarenhancesallproperties(Figures2ato c) and it is observed that12.5%ofRiceHuskAshbymassof cementas theoptimumdoses tobeaddedinconcreteproductionofM particularlywhenthehuskisburntunderfieldconditiontoutilizetheeasily available and low cost resources for betterment of concrete structurewith respect to economy,durabilityandstrength.Sobestapplicablepercentageofricehuskashasperfieldcondition10.00%foroptimalstrengthanddurability.References

BronzeoakLtd,RiceHuskAshMarketStudy,ETSUU/00/00061/REPDTI/PubURN03/668,2003.

SatishChandra,Wastematerialsused in concretemanufacturing,WilliamAndrew Inc.Norwich,NY13815,2002.

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Hwang, C. L., andWu, D. S., Properties of Cement Paste Containing Rice Husk Ash, ACI SP114,1989.

Anderson,L.L.andTillmanD.A.,Fuelsfromwaste.AcademicPressInc.,NewYork,U.S.A,1978.

E.B.OyetolaandM.Abdullahi,TheUseofRiceHuskAsh inLowCostSandcreteBlockProduction,Department of Civil Engineering, Federal University of Technology, P.M.B. 65,Minna,Nigeria, June2006.

NBMCWOctober2010

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