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Indian Journal of Science and Technology Vol. 4 No. 6 (June 2011) ISSN: 0974- 6846

Research article Portland Cement V.V.Reddy et al.

Indian Society for Education and Environment (iSee) http://www.indjst.org Indian J.Sci.Techno

643

Effectofmagnesiumchloride(MgCl2)onordinaryPortlandcementconcrete

V.VenkateswaraReddy1,N.V.Ramana2,K.Gnaneswar3andC.Sashidhar2

1JNTUHCollegeofEngineering,Hyderabad,AndhraPradesh-500085,India,2JNTUACollegeofEngineering,Anantapur,AndhraPradesh515002,India,

3IrrigationandCADDepartment,TBPHLCCircle,Anantapur,AndhraPradesh-515004,India.

[email protected];[email protected];[email protected];[email protected] AbstractThispaperreportstheeffectofMagnesiumchloride(MgCl2)onOrdinaryPortlandCement(OPC)concrete.TheOPCconcretewasproducedwithMgCl2dosageof0.2,0.5,1.0,1.5and2.0g/litanddeionisedwaterwasusedinconcretemix (M20 &M50). Inaddition to this, control specimens were preparedwith deionisedwater (withoutMgCl2) forcomparison.Thecompressiveandtensilestrengthswereevaluatedfor28and90days.Theresultsshowthat,astheMgCl2concentrationincreases,thecompressionandtensilestrengthsdecrease.TheX-raydiffractionanalysisforconcretehasbeencarriedoutat1.5g/litconcentration.Keywords:Portlandcement,concreteIntroduction

The chemical impurities of industrial effluents canimposedeleteriouseffectonconcrete.Thiscreatesgreatconcern onmixing ofwater inhydration of cement andthe properties of resultant concrete. The water duringpreparationofconcreteusuallycomesfromtwosources,namely the added water and the moisture in theaggregates. Most specifications on quality of waterconcentrateontheaddedwaterratherthanthemoisturecontained in the aggregates (fine and coarse). Thequality of water is usually ignored with the expectationthataddedpotablewaterwoulddiluteanycontaminant.The presence of dissolved inorganic substances ingroundwaterismostlythroughmineraloriginandwouldbe expected in varied concentrations geographically.Water maycontain salts of sodium, potassium,calciumandmagnesiumetc.

There is a need to investigate effect ofpolluted/chemical water on hardened concrete strengthand durability. Kejin et al. (2005) reported the damageimpact of various deicing chemicals and exposureconditions on concrete materials, results indicated thatthe various deicing chemicals penetrated at differentratesintoagivenpasteandresultingindifferentdegreeof damages to concrete. Gorniniski et al . (2007)presented anassessment of the chemical resistance ofeight different compositions of a polymeric mortars.

Adnanetal.(2009)reportedtheeffectsofenvironmentalfactorsontheadditionanddurabilitycharactersofepoxybondedconcreteprisms.Fikret etal.(1997)investigatedtheresistanceofmortarstomagnesiumsulphateattackandresultsreportedthatthereisasignificantchangesincompressive and flexural properties. VenkateswaraReddy et al . (2006) studied the influence of strongalkalinesubstances(sodiumcarbonateandbi-carbonate)in mixing water on strength and setting properties ofconcrete. Hence, there is need to assess the effect ofmagnesium chloride presence in the water in various

concentrationsonsettingtimesofcementandstrengthsofconcrete.Materials and methodsCement:53gradeordinaryPortlandcementwasusedithisinvestigation.ThecompositionsofmajorcompoundspresentinthecementarepresentedinTable1.Fine Aggregate: Locally available river sand was usedandthepropertiesarepresentedinTable2.

Coarse Aggregate: Machine Crushed granite stone omaxsize20mmconfirmingtoIS383-1970wasusedandthepropertiesarepresentedinTable2.

Water: De-ionisedwaterspikedwithMagnesiumchloride(MgCl2)atdifferentconcentrationsi.e.0.2,0.5,1.0,1.5&2.0g/lit.Experimental program: The influence of MgCl2 onconcrete was studied. For this, MgCl2 at differenconcentrations (0.2,0.5, 1.0, 1.5 & 2.0g/lit) was spikedwithdeionisedwater.Testsampleswerecomparedwiththe control samples. This comparison is may not bepossible in case of control samples made with locallyavailable potable water since it varies in chemicacompositionfromplacetoplace.WiththeabovereasonMgCl2atthedosageof0.2,0.5,1.0,1.5& 2.0g/litwasmixed with deionised water. This water was used fopreparationofsamplesforsettingtimes(initial&final)of

Table1.Compositionsofmajorcompoundsincement

Nameofthecompound %

TricalciumSilicate(3CaOSiO2) 11.70

DicalciumSilicate(2CaOAl2O3) 23.30

TricalciumAluminate(3CaOAl2O3) 9.31TetracalciumAluminoFerrite(4CaOAl2O3Fe2O3) 51.40

Table2.Propertiesofaggregate

Property Coarseaggregate FineaggregateSpecificgravity 2.62 2.53Bulkdensity 15.65kN/m 15.54kN/mFinenessmodulus 6.65 2.84


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Fig.2.VariationofcompressivestrengthofOPCconcretecorrespondingtovariousconcentrationsof

MgCl2indeionisedwater

Fig.1.VariationofsettingtimesofcementcorrespondingtovariousconcentrationsofMgCl2indeionisedwater

cement and M20 & M50 grade concrete. The IS mixdesign was adopted for M20 and M50 grade concretemix.Vicatapparatuswasusedforfindingtheinitialand

finalsettingtimesofthecement.Atotalof168standardspecimens were cast and tested for predictingcompression (84cubes) andsplit tension (84cylindersstrengths.Results and discussion

TheeffectofMagnesiumchloride(MgCl2)onsetting

timesofcement,compressiveandsplittensilestrengthsofordinaryPortlandcementconcreteispresentedbelow.Effectonsettingtimesofcement

The initial and final setting times of cement, fodifferentMgCl2concentrationsarecomparedwithcontrosamples. If the difference is less than 30 minutes, thechangeisconsideredtobenegligibleandifthedifferenceismorethan30minutes,thechangeisconsideredtobesignificant.

TheeffectofMgCl2oninitialandfinalsettingtimesisshowninFig.1.Boththeinitialandfinalsettingtimesgotretarded with an increase in magnesium chlorideconcentration in deionised water. The retardation was

significantwhenthemagnesiumchloridecontentis1.5g/and0.5g/lrespectively.Withregardtoinitialsettingtimesignificant change occurred at relatively higheconcentration, i.e., at 1.5 g/l onwards. Howeversignificantchangeinthefinalsettingtimehasoccurredarelatively lower concentration, i.e. at 0.5 g/l. At themaximumconcentration(1.5g/l)theinitialandfinalsettingtimesare37and59minutesmorethanthoseofcontrolmix.EffectonstrengthofOPCconcrete

Average compressive strength of three cubes andsplit tensile strength of three cylinders prepared withdifferentconcentrationsofMgCl2iscomparedwiththatofthreesimilarspecimenspreparedwithdeionisedwater.If

the difference in the strength is less than 10%, it isconsideredtobeinsignificantandifitisgreaterthan10%it is considered tobe significant. This 10% is taken asreferenceforthediscussion.

TheeffectofMgCl2concentrationonthecompressivestrength and tensile strength of concrete of ordinaryPortlandcement concrete ispresented inFig. 2 and 3Decreaseincompressivestrengthandtensilestrengthofordinary Portlandcement concrete specimenspreparedwith MgCl2 solution is observed as the magnesiumchloride concentration increases, the maximumconcentrationbeing2g/l.ThereissignificantdecreaseinthecompressivestrengthofconcretecubesofM20(90t

day)andM50(28th

day&90th

day)atconcentrationof1.5g/l, whereas this significant decrease in compressivestrength observed for M20 (28th day) samples aconcentrationof2.0g/l.WhenMgCl2concentrationis2.0g/l, thedecrease incompressive strength is17.15% foM20(28thday)gradeconcreteand18.02%forM50(28t

day) grade concrete respectively, when compared withthatofcubespreparedwiththedeionisedwater(controsample).Similarly,significantdecreaseintensilestrengthisobservedwhentheconcentrationofMgCl2is1.5g/lfoM20(90thday)andM50(28thday&90thday)samples;

Fig.3.VariationoftensilestrengthofOPCconcretecorrespondingtovariousconcentrationsof

MgCl2indeionisedwater


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Fig.4.X-RaydiffractionpatternofpowderedconcretesamplepreparedwithMgCl2(1.5g/l)indeionisedwater

Fig.5.X-Raydiffractionpatternofpowderedconcretesamplepreparedwithdeionisedwater

whereas this significant decrease in tensile strength isobservedforM20(28thday)samplesatconcentrationof2.0 g/l. When MgCl2 concentration is 2.0 g/l, thedecreaseintensilestrengthis17.13%forM20(28thday)grade concrete and 17.91% for M50 (28th day) gradeconcrete respectively, when compared with that of

cylinderspreparedwiththedeionisedwater(controltestsample).

Powder X-ray diffraction analysisPowder X-ray diffraction pattern for the concrete

preparedwithMgCl2(1.5g/l)andforcontrolspecimenisdepictedinFig.4andFig.5.ThecomparisonofMgCl2pattern with that of the control specimen indicates the

formation of brucite [Mg(OH)2] and CaCl2 compounds.Thesearecharacterizedbythesetsofd-spacings2.8182,1.8102and1.3767forMg(OH)2and4.1361,3.2505 and 1.825 for CaCl2 respectively in thispattern,thesepeaksnotbeingpresentinthepatternforthecontrolmix(Fig.5).Theprobablereasonsforabovebehaviour of concrete with MgCl2 in mixing water arediscussed below through corresponding chemicalreaction.

ThepossiblechemicalreactionuponthehydrationofcementwithmixingwatercontainingMgCl2is

MgCl2+Ca(OH)2CaCl2+Mg(OH)2MgCl2solutionreactswithslakedlimetoformCaCl2andMg(OH)2.TheformationofsolubleCaCl2leadstoinitiastrength loss. As Mg(OH)2 is insoluble in water, itsformation does not increase the porosity and thepermeability of the system. Thus the formation omagnesiumhydroxide(brucite)leadstolossofstrength.Conclusions

Initial setting time getsretarded with increase inmagnesium chlorideconcentration and it issignificant from 1.5 g/concentration onwards. Finasettingtimegetsretardedwithincrease in magnesiumchloride concentration and is

significant from 0.5 g/concentration onwardsCompressive and tensilestrengths of OPC concretereduces as magnesiumchloride concentrationincreases.References1. Adnan C, Turgay C and

Ahmet EB (2009) Effectsof environmental factorson the adhesion anddurabilitycharacteristicsofepoxy bonded concreteprisms. Construction &Building Materials. 23.2758.

2. FikretT,FevziyeA,SemaK and Nabi Yuzer (1997Effects of magnesium

sulfate concentration on the sulfate resistance omortars with and without silica fume. Cement &ConcreteRes.27(2),205-214.

3. Gorninsi JP, Dal Molin DC and Kazmierczak CS(2007),Strengthdegradationofpolymerconcreteinacidic environments. Cement & Concrete

Composites.29(2),637-645.4. KejinW,DanielENandWilfridAN(2005)Damagingeffects of deicing chemicals on concrete materialsCement&ConcreteComposites.28(2),173-188.

5. Venkateswara Reddy V, Sudarshan Rao H andJayaveera KN (2006) Influence of strong alkalinesubstances (sodium carbonate and sodiumbicarbonate)inmixingwateronstrengthandsettingpropertiesofconcrete. IndianJ.Engg.&MaterialSci13(2),123-128.

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