Effect of nanoclay on durability and mechanical properties of flax fabric reinforced geopolymer composites

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Journal of Asian Ceramic Societies

ISSN: (Print) 2187-0764 (Online) Journal homepage: https://www.tandfonline.com/loi/tace20

Effect of nanoclay on durability and mechanical

properties of flax fabric reinforced geopolymer

composites

H. Assaedi, F.U.A. Shaikh & I.M. Low

To cite this article:

H. Assaedi, F.U.A. Shaikh & I.M. Low (2017) Effect of nanoclay on durability

and mechanical properties of flax fabric reinforced geopolymer composites, Journal of Asian

Ceramic Societies, 5:1, 62-70, DOI: 10.1016/j.jascer.2017.01.003

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https://doi.org/10.1016/j.jascer.2017.01.003

© 2017 The Ceramic Society of Japan and

the Korean Ceramic Society

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Journal

of

Asian

Ceramic

Societies

jo u r n al h om ep ag e :w w w . e l s e v i e r . c o m / l o c a t e / j a s c e r

Full

Length

Article

Effect

of

nanoclay

on

durability

and

mechanical

properties

of

flax

fabric

reinforced

geopolymer

composites

H.

Assaedi

,

F.U.A.

Shaikh

,

I.M.

Low

a_{DepartmentofImaging&AppliedPhysics,CurtinUniversity,GPOBoxU1987,Perth,WA6845,Australia} b_{DepartmentofPhysics,UmmAl-QuraUniversity,P.O.Box715,Makkah,SaudiArabia}

c_{DepartmentofCivilEngineering,CurtinUniversity,GPOBoxU1987,Perth,WA6845,Australia}

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received12August2016 Receivedinrevisedform 15November2016 Accepted10January2017 Availableonline13February2017

Keywords: Geopolymer Nanoclay Mechanicalproperties Flaxfibres Durability

a

b

s

t

r

a

c

t

Themainconcernofusingnaturalfibresasreinforcementingeopolymercompositesisthedurability ofthefibres.Geopolymersarealkalineinnaturebecauseofthealkalinesolutionthatisrequiredfor activatingthegeopolymerreaction.Thealkalinityofthematrix,however,isthekeyreasonofthe degra-dationofnaturalfibres.Thepurposeofthisstudyistodeterminetheeffectofnanoclay(NC)loading onthemechanicalpropertiesanddurabilityofflaxfabric(FF)reinforcedgeopolymercomposites.The durabilityofcompositesafter4and32weeksatambienttemperatureispresented.The microstruc-tureofgeopolymermatriceswasinvestigatedusingX-raydiffraction(XRD),Fouriertransforminfrared spectroscopy(FTIR)andscanningelectronmicroscopy(SEM).Theresultsshowedthattheincorporation ofNChasapositiveimpactonthephysicalproperties,mechanicalperformance,anddurabilityofFF reinforcedgeopolymercomposites.ThepresenceofNChasapositiveimpactthroughacceleratingthe geopolymerization,reducingthealkalinityofthesystemandincreasingthegeopolymergel.

©2017TheCeramicSocietyofJapanandtheKoreanCeramicSociety.Productionandhostingby ElsevierB.V.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/ licenses/by-nc-nd/4.0/).

1. Introduction

OrdinaryPortlandCement(OPC)isbelievedtoberesponsibleof generating5%oftheglobalcarbondioxideemission[1].Oneofthe mostattractivealternativesofOPCisgeopolymerbinderduetoits comparablemechanicalpropertiestotheOPC.Thedevelopment ofgeopolymerconcreteis notonly importantbecausetheyare environmentalfriendlymaterials,butalsoduetotheirwiderange ofrawwastematerialstoproduceworthyconstructionmatrices, resultinginlowcostmaterialwithsimilarmechanicalproperties tothatofcementconcrete[2].Geopolymersareproducedby acti-vatingasolidaluminosilicatesourcesuchascoalderivedfly-ash, meta-kaolinandslagwithalkalinesolutions,amorphousnetworks oftetrahedralSiO4andAlO4connectedbysharingoxygenatoms [3].TheformationofgeopolymergelcanbedescribedbyEq.(1) [3].

n(Si2O5,Al2O2)+ 2nSiO2+ 4nH2O+ NaOH→ Na++ n(OH)3 −Si −O− Al− −O− Si −(OH)3 |

(OH)2

(1)

∗Correspondingauthor.Fax:+61892662377.

E-mailaddress:j.low@curtin.edu.au(I.M.Low).

Hitherto, nanomaterials have received increased attention in geopolymer and cement research; especially in producing nanocompositesthatpossesssuperiormechanicalproperties[4–6]. Severalkindsofnanomaterialshavebeenincorporatedefficiently ingeopolymerpastes.Forinstance,ithasbeenfoundthat nano-silicaandnano-aluminaparticleshave theability toreducethe porosity and water absorption of geopolymer matrices [6]. In anotherstudy [7], nano-aluminaand nano-silica particles have been incorporated in geopolymermatrices giving them higher mechanical performance. Thenanoparticles arenot only acting as fillers, but alsoenhancingthe geopolymeric reaction.A fur-ther study on the effect of adding carbon nanotubes (CNT) to flyash-basedgeopolymerhasshownanincreaseinthe mechani-calandelectricalpropertiesofgeopolymernano-compositeswhen comparedtothecontrolpaste[8].WeiandMeyerreportedthe

propertiesofcement/nanoclaycomposites,wherethe nanoparti-clesreducetheporosityofcementmatrices,aswellasimprove thestrength ofcementmatrix throughpozzolanic reactions[9].

http://dx.doi.org/10.1016/j.jascer.2017.01.003

2187-0764/©2017TheCeramicSocietyofJapanandtheKoreanCeramicSociety.ProductionandhostingbyElsevierB.V.ThisisanopenaccessarticleundertheCCBY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Farzadnia et al. [10] reported that incorporation of 3wt% hal-loysitenanoclayintocementmortarsincreasedthecompressive strengthbyupto24%comparedtothecontrolsample.Ina pre-viousstudy,weinvestigatedtheeffectofnanoclay(Cloisite30B) onthemechanicalandthermalpropertiesofgeopolymer compos-ites[11].Nanoclayparticleswerefoundtohelpdevelopingdenser geopolymermatrices,therebyproducinggeopolymerwith supe-riormechanicalperformance.

Despitethepotentialimprovementofpropertiesof geopoly-mers,thegeopolymermatrixstillsuffersfrombrittlefailurereadily underappliedforceandgenerallyexhibitslowmechanicalstrength

[12,13].One way to resolve this limitation is through utilizing natural fibresto fabricatefibre-reinforcedgeopolymer compos-ites.Theadvantagesofusingnaturalfibresincompositesinclude thelowdensity,flexibilityandthehighspecificmodulus[14,15]. Cottonfibresandfabricshavebeenusedtoimprovethefracture toughnessand mechanicalperformanceofgeopolymer compos-ites [16,17]. Also, flax and woolfibres have presented positive effects whenincorporated in geopolymermatrices; they signif-icantlyimprovedthemechanicalproperties ofthenatural fibre reinforcedgeopolymercomposites[1,18].Inourpreviouswork, geopolymercompositeswerereinforcedwithwovenflaxfabricand testedformechanicalpropertiessuchasflexuralstrength,flexural modulus,compressivestrength,hardness,andfracturetoughness. Theresultsshowedthatallmechanicalpropertieswereimproved byincreasingtheflaxfibrecontents,andshowedsuperior mechan-icalpropertiesoverthepuregeopolymermatrix[19].Inafurther study,geopolymermatriceswerereinforcedwithacombinationof nanoclay(NC)andflaxfabrics(FF)anditwasfoundthattheaddition ofNCtogeopolymersimprovedtheadhesionbetweenthenatural fibresandthematricesduetothehighamountofgeopolymergel formed,resultinginhighermechanicalresults[20].

However,thereareconcernsinutilizingnaturalfibresin alkali-based matrices. The main concern is regarding the long-term durabilityofnaturalfibrereinforcedcomposites.Naturalfibrescan bedegradedanddamagedinhigh-alkalineenvironment;thereby adverselyaffectingthemechanicalpropertiesanddurabilityofthe composites[21–23].Naturalfibredegradationsinalkaline environ-mentswasstudiedbyGram[24]andhedescribedthedegradation mechanismasthedecompositionofhemicelluloseandlinenwhich leadstothesplittingofnaturalfibresintomicro-fibrils[24].This effecthasbeenobservedusingSEMinthecase ofjutefibresin cementmatrix, where thenatural fibressplit-up and fibrillised resultinginreductioninthetensilestrengthofjutefibresby76%

[25].Toreducethedegradationimpact,nanoparticlescanplayan importantrole.Theeffectofnanoclayparticlesonthedurability offlaxfibresreinforcedcementcompositesat28daysandafter 50wet/drycycleshasbeeninvestigatedbyAlyetal.[21].Samples loadedwith2.5wt%nanoclayparticlesshowedlowerdeterioration intheflexuralstrength whencompared toitscounterpart con-trolsamples.Thiswasattributedtotheeffectofnanoparticlesin reducingthedegradationofflaxfibres.

Accordingtothebestofknowledgeofauthors,nostudyhasbeen reportedonthedurabilityofnaturalfibresingeopolymer matri-ces.Thepresence ofnanoclay particles isanticipated toreduce thedegradationofnaturalfibresbyconsumingcertainamounts ofalkalinesolution,whichreducesthealkalinityofthemedium. Nanoclayisalsoexpectedtoproducehigheramountof geopoly-mergel,increasesinmatrixdensity,fibre-matrixadhesion,andthe concomitantimprovementinmechanicalproperties.Inthispaper, inordertoimprovethedurabilityandreducethedegradationof flaxfabric(FF)ingeopolymercomposites,geopolymermatrices weremodifiedbytheadditionofnanoclay(NC)particles.Thisstudy presentedtheeffectofdifferentloadingsofnanoparticlesonthe durabilityandmechanicalpropertiesofFF-reinforcedgeopolymer nanocomposites.Themediumtolongtermdurabilityofallsamples

Table1

Formulationofsamples.Eachsamplesisamixof:1.0kgEraringflyash,214.5g sodiumhydroxide(8M)and535.5gsodiumsilicate.

Sample NC(g) FF(layers) GP 0 0 GPNC-1 10 0 GPNC-2 20 0 GPNC-3 30 0 GP/FF 0 10 GPNC-1/FF 10 10 GPNC-2/FF 20 10 GPNC-3/FF 30 10

hasbeendiscussedintermsofflexuralstrengthobtainedat4and 32weeks.ThemicrostructurewasinvestigatedusingX-ray diffrac-tion,Fouriertransforminfraredspectroscopy(FTIR)andscanning electronmicroscopy(SEM).

2. Experimentalprocedure 2.1. Materials

Low-calcium flyash (ASTM class F) with specific gravity 2.1 obtainedfromtheEraringpowerstationinNSWwasusedto pre-parethegeopolymericnano-composites.Thealkalineactivatorfor geopolymerisationwasacombinationofsodiumhydroxide solu-tionandsodiumsilicategradeDsolution.Sodiumhydroxideflakes with98%puritywereusedtopreparethesolution.Thechemical compositionofsodiumsilicateusedwas14.7%Na2O,29.4%SiO2

and55.9%waterbymass.

Flaxfabric(FF)andnanoclay(Cloisite30B)wereusedforthe reinforcementofgeopolymercomposites.Thefabric,suppliedby PureLinenAustralia,ismadeupofyarnswithadensityof1.5g/cm2_.

Thenanoclay(NC)withspecificgravityof1.98hasbeenprovided bySouthernClayProducts,USA.

Topreparethegeopolymerpastes,analkalinesolutiontofly ashratioof0.75wasusedandtheratioofsodiumsilicatesolution tosodiumhydroxidesolutionwasfixedat2.5.Theconcentration ofsodiumhydroxidesolutionwas8M,whichwaspreparedand combinedwiththesodiumsilicatesolutiononedaybeforemixing.

2.2. Preparationofgeopolymernanocomposites

Thenano-clayparticles(NC)wereaddedtotheflyashatthe loadingsof1.0,2.0and3.0%byweight.Theflyashand nanoparti-cleswerefirstdrymixedfor5mininacoveredmixeratlowspeed andthenmixedforanother10minathighspeeduntil homogene-itywasachieved.Thealkalinesolutionwasthenaddedslowlyto theflyash/nanoparticlesmixtureinaHobartmixeratalowspeed untilthemixturebecamehomogeneous,followedbyfurther mix-ingforanother10minonhighspeed.Theresultantmixturewas thenpouredintowoodenmoulds.Thewoodenmouldswerethen placedonavibrationtablefor2minbeforetheywerecoveredwith aplasticfilmandcuredat80◦Cfor24hinanovenbeforedemolding.

2.3. PreparationofFF-compositeandnanocomposites

Similar mixtures were prepared to produce the FF-nanocomposites.Four samplesof geopolymerpastesreinforced withtenlayersofFF(see Table1)werepreparedbyspreading a thin layerof the pastein a well-greasedwooden mould and carefullyplacingthefirstlayersofFFonit.Thefabricwasfully saturatedwiththepastebyaroller,andtheprocessrepeatedfor tenlayers;eachspecimencontainedadifferentweightpercentage of nanoclay particles. The samples werethen leftunder heavy weight(20kg)for1htoreduceentrappedairinsidethesamples.

Allsampleswerecoveredwithplasticfilmandcuredat80◦Cfor 24hinanovenbeforedemoulding.Theywerethendriedunder ambientconditionsfor28days.

Allsamples werethencategorized intwo series.In thefirst series,sampleswerecuredunderambientconditionstobetested after4weeks,andthesamplesofsecondserieswerestoredinthe sameconditionfor32weeks.Theformulationofsamplesisgiven inTable1.

2.4. Characterization

Thesampleswerecrushedand groundtofinepowder.They werethenmeasuredonaD8AdvanceDiffractometer(Bruker-AXS, Germany)usingcopperradiationand aLynxEyeposition sensi-tivedetector.Thediffractometerwerescannedfrom7.5◦ to60◦ usinga scanning rateof 0.5◦/min. XRD patternswereobtained byusingCuk˛lines(k=1.5406Å).Crystallinephaseswere

iden-tifiedusingsoftwareEVAversion11.Thechemicalcompositions ofNCwereanalyzedusingX-rayfluorescence(XRF).XRFwas out-sourcedtoacommerciallaboratory(BureauVeritas,Perth).AnFTIR scanwasperformedonaPerkinElmerSpectrum100FTIR spec-trometerintherangeof4000–500cm−1_{atroomtemperature.The}

spectrumwasanaverageof32 scansata resolutionof2cm−1, correctedforbackground.Themicrostructuresofgeopolymer com-positeswereexaminedusingZeissNeonfocusedionbeamscanning electronmicroscope(FIB-SEM).Thespecimensweremountedon aluminiumstubsusingcarbontapeandthencoatedwitha thin layerofplatinumtopreventchargingbeforeobservation.

2.5. Physicalandmechanicalproperties

Measurementsofbulkdensityandporositywereconductedto definethequalityofgeopolymernanocomposite.Densityof sam-ples () withvolume (V) anddrymass (md)wascalculatedusing

Eq.(2):

=md

V (2)

The value of apparent porosity (Pa) was determined using

Archimedes’principleinaccordancewiththeASTMStandard (C-20) [26]. Pure geopolymer and nano-composite samples were immersedincleanwater,andtheapparentporosity(Pa)was

cal-culatedusingEq.(3):

Pa= ma − md ma − mw×

100 (3)

wheremaismassofthesaturatedsamplesinair,andmwismass

ofthesaturatedsamplesinwater.

ALLOYDMaterialTestingMachine(50kNcapacity)witha dis-placementrateof0.5mm/minwasusedtoperformthemechanical tests.Rectangularbarsof60×18×15mm3_{werecutfromthefully}

curedsamplesforthree-pointbendtestwithaspanof40mmto evaluatetheflexuralstrengthandmodulus.Fivesamplesofeach groupwere usedto evaluatetheflexural strength and flexural modulusofgeopolymercomposites.Thevalueswererecordedand analyzedwiththemachinesoftware(NEXYGENPlus)andaverage valueswerecalculated.Theflexuralstrength(F)wasdetermined

usingtheequation[27]:

F=

3 2

PmS

WD2 (4)

wherePmisthemaximumload,Sisthespanofthesample,Disthe

specimenwidth,andWisthespecimenthickness.

Table2

Densityandporosityforpuregeopolymerandgeopolymernano-composites.

Sample Density(g/cm3_{) Porosity(%)}

GP 1.84±0.02 22.2±0.4

GPNC-1 1.92±0.02 21.3±0.3

GPNC-2 2.05±0.02 20.6±0.3

GPNC-3 1.98±0.03 21.0±0.2

Valuesofflexuralmodulus(E_f)werecomputedusingtheinitial slopeoftheloaddisplacementcurve(P/X)usingtheequation

[27]: EF= S 3 4WD3

3. Resultsanddiscussion

3.1. Densityandporosity

Theresults ofporosity and water absorption of geopolymer paste and geopolymer nano-composites are shown in Table 2. Geopolymernanocompositesrevealeddensermatricesandlower porositieswhencomparedtothecontrolsample.TheadditionofNC hasincreasedthedensityandreducedtheporosityofgeopolymer nano-compositeswhencomparedtocontrolgeopolymerpaste.The optimumadditionwasfoundas2.0wt%of NC,whichincreased densityby11.4%andreducedtheporosityby7.2%whencompared tothecontrolpaste.Thisimpliesthatthenanoparticlesplayeda pore-fillingroletoreducetheporosityofgeopolymercomposites. However,addingexcessiveamountsofNCincreasedtheporosity anddecreasedthedensityofallsamplesduetoagglomerationof NCparticles[11].Thisfindingiscomparablewiththestudywhere theporosityofcementpasteisdecreasedduetoadditionof1.0%wt. ofNCtocementpaste;however,theporosityisincreasedbecause oftheagglomerationeffectwhenmorenanoparticleswereadded

[28].

3.2. X-rayfluorescence(XRF)andX-raydiffraction(XRD)

ThechemicalcompositionandlossonignitionofflyashandNC areshowninTable3.FlyashandNCcontain,inadditiontosilica andalumina,Fe2O3,CaO,K2O,Na2O,MgOandTiO2.

TheXRDspectraofpuregeopolymerandgeopolymer nanocom-positesat4and32weeksareshowninFig.1(a–b),respectively. Thecrystallinephaseswereindexedusingpowderdiffractionfiles (PDFs)fromtheinorganiccrystalstructuredatabase(ICSD).The diffractionpatternsofthesamplesdemonstratesomecrystalline phasesthatwereindexeddistinctly:quartz[SiO2](PDF

00-046-1045)andmullite[Al2.32Si0.68O4.84](PDF04-016-1588).Quartzand

mullitecrystallinephasescanbeseeninallsamples.Accordingto Rickardetal.quartzandmullitearethemaincrystallinecontentof theEraringflyash,andhencetheyarestableandunreactiveinthe alkalineenvironment.At32weeks,anewcrystallinephase,trona [Na3H(Co3)2.2H2O](PDF00-029-1447),appearsonthesurfaceof

geopolymeragedsamples.Tronabelongstosodamineralsgroup, whichcouldbeformedbythereactionofsodiumhydroxidewith waterandcarbondioxideaccordingtothechemicalreaction[29]: 3NaOH+2CO2+2H2O→Na3H(CO3)2·2H2O (6)

Theamorphousbroadphasegeneratedbetween2=17◦ and 30◦forallsamplesrevealsthereactivityofgeopolymers.Itisknown thattheamorphicitydegreeremarkablyinfluencesthemechanical propertiesofgeopolymers.Whentheamorphouscontentishigher, thestrengthofgeopolymersissimilarlyhigher[30].Inprevious study,ithasbeenshownthattheadditionofnanoclayparticlesto geopolymerpastesincreasedtheamorphouscontentof

geopoly-Table3

Chemicalcompositionsofflyashandnanoclay(wt%).

SiO2 Al2O3 CaO Fe2O3 K2O MgO Na2O P2O5 SO3 TiO2 MnO BaO LOI

Flyash 63.13 24.88 2.58 3.07 2.01 0.61 0.71 0.17 0.18 0.96 0.05 0.07 1.45

NC 47.05 16.24 0.29 3.42 0.03 1.75 0.19 0.01 0.11 0.08 0.00 0.00 30.61

Fig.2.FTIRspectraofgeopolymerandgeopolymernanocompositesat:(a)4weeks;(b)32weeks.

mernanocomposites, resulting indensermatrices and superior mechanicalperformance[11].

3.3. FTIRobservation

FTIRspectraofpuregeopolymerandgeopolymer nanocompos-iteat4and32weeksareshowninFig.2(a–b).TheFTIRspectraof

Fig.3. Flexuralstrengthandmodulusofgeopolymerandnanocompositesat4and32weeks.

allsamplesshowsastrongpeakat∼1000cm−1whichisattributed toSi O SiandAl O Siasymmetricstretchingvibrations,which istheidentificationpeakofthegeopolymerisation[31,32].Abroad peakintheregionaround3400cm−1_{indicatesthattheOHgroupis}

presentattachedtodifferentcentres(Al,Si)andfreewater[33,34]. Theabsorbancepeakat1640cm−1 _{isalsoattributedtothe(OH)}

bendingvibration[35].At32weekschangeshaveoccurred,two peaksat1420and1480cm−1 appearindicatingthepresenceof sodiumcarbonate;thiswasformedduetotheatmospheric car-bonationonthematricessurfaceswhichconfirmstheXRDresults

[29].Duringtheageingperiodthereactionhascarriedonatalow rateconsumingmoreOHgroupsandformingstrongermaterial. Thewatercontentdecreasedtosomeequilibriumlevelduringthis periodresultinginlowerbroadpeakat3400cm−1.

3.4. Flexuralstrengthofgeopolymernanocomposites

Theeffectofageingontheflexuralstrength andmodulusof geopolymermatricesandnanocompositesisshowninFig.3. Over-all,theincorporationofnanoclayintothegeopolymercomposite ledtonoteworthyimprovementinthemechanicalstrengthatall ages.At4weeks,theflexuralstrengthofgeopolymer nanocom-positecontaining1.0,2.0and3.0wt.%NCwasincreasedby13.3, 24.4and15.5%respectively,whiletheflexuralmodulusimproved by16,25and20%,respectivelycomparedtothecontrolsample. ThisenhancementnoticeablyshowsthevalueofNCin support-inggeopolymerreactionandfillingthemicroporesinthematrix

[11–28].Thusthemicrostructureofgeopolymernanocompositeis denserthanthepurematrix,especiallyinthecaseofincorporating 2.0wt.%NC,whichisevidentfromitshigherflexuralstrengthand modulus.However,at32weeks,theflexuralstrengthof nanocom-positesincreasedslightlycomparedtotheirvaluesat4weeks.For instance,theflexuralstrengthofGPNC-2nanocompositeimproved from5.6to6.1MPabyabout9%increase.Thisslightimprovement

in themechanicalperformance couldbeattributedtotheslow reactionoffreesilicaandaluminainthepresenceofNa+_ions

dur-ingtheageingperiod[36,37].Insimilarstudy,Hakamyetal.[23]

reportedthatflexuralstrengthofcementpastescontaining1.0% calcinednanoclayparticlesimprovedfrom7.2to8.2byabout7% after236dayscomparedtoitsstrengthat56days.SEMimages ofthemicrostructureat32weeksofgeopolymerpasteand the geopolymernanocompositecontaining2.0wt.%NCareshownin

Fig.4(a–b).Forgeopolymermatrix,Fig.4adisplaysmorepores showingaweakmicrostructure.Ontheotherhand,Fig.4bshows theSEMmicrographofGPNC-2nanocompositematrix,whichis dif-ferentfromthatofpurematrix,themicrostructureisdenserand morecompactwithfewerporesandmoregeopolymergel.

3.5. Flexuralstrengthofflaxfabricreinforcedgeopolymer nanocomposites

The effect of ageing on the flexural strength and modu-lus of FF-reinforced geopolymer nanocomposites at 4 and 32 weeks is shown in Fig. 5. The incorporation of nanoclay into matricesledtoenhancementintheflexuralstrengthofall rein-forced nanocomposites. For example, at 4 weeks, the flexural strengthandmodulusofGPNC-2/FFincreasedby32.4%and5.2%, respectively when compared to GP/FF composite. However, all composite showed reduction in the mechanical strength after 32 weeks. Fig. 6(a–b) shows the effect of ageing on the load-midspandeflectionbehaviourofGP/FFcompositesandGPNC-3/FF nanocomposites.The“ductile”behaviourcanbeobservedinboth compositeswithandwithoutNC,withhigherloadcapacity(about 29%increases)inthecompositecontainingNC.Itwasobservedthat ductilebehaviourisadverselyaffectedandbendingstressesare reducedduetodegradationprocess.Thisdecreasewasattributed totheligninandhemicellulosedeteriorationofflaxfibreinmatrix byNa+_{ionsattackandbrittlenessofthenaturalfibresduetothe}

Fig.4. SEMmicrographsat32weeksof:(a)geopolymerpaste,(b)nanocompositescontaining2.0wt%NC.

mineralizationoffibrecellwallingeopolymerpastes[38–40].In general,allnatural fibressuffer variousdegree ofdeterioration whenexposedtoalkalineenvironment[41].Thisdegradationin alkalimatricesultimatelyledtoweakenthefibre–matrixbonding, andconsequentlyreducedthemechanicalperformanceof geopoly-mercomposites.TheflexuralstrengthofGP/FFcompositedropped to23.0%oftheinitialstrengthat4weeks,whereas theflexural strengthofGPNC-1/FF,GPNC-2/FFandGPNC-3/FFnanocomposites reducedbyabout14.4%,13.7%and13.5%compared toitsvalue at4weeks.Basedonthisoutcome,itcanbeconcludedthatthe reductioninthemechanicalperformancefornanocompositeswas lessthanthereductionofcontrolsamplecompositeafter32weeks ageingperiod.Thismaybeattributedtothefact thatnanoclay particlesconsumeamountsof thealkalinesolutionthus reduc-ingthealkalinityofthemedium,andproducinghigheramountof geopolymergel,whichhenceenhancesthedensityofthe matri-cesand thefibre–matrix adhesion [20]. In a similar study,the effectofcalcinednanoclayonthedurabilityofhempfabric rein-forcedcementnanocompositesandthedegradationofhempfibres arereported[23],thenanoparticleswerefoundtoimprovethe durabilityandreducesthedegradationofhempfibres.Inanother investigation,Alyetal.[21]reportedthattheadditionofnanoclay andwasteglasstocementmortarcouldimprovethedurabilityand mitigatethedegradationofflaxfibresimplementedinthe com-positesbyreducingthealkalinityofthematrix.Filhoetal.[40]

investigatedthe durabilityof sisalfibrereinforced mortarwith theadditionofmetakaolinat28daysandafter25wet/drycycles.

Theyobservedthattheflexuralstrengthofmetakaolin compos-itesdecreasedby23%whencomparedtoitscontrolcompositesat 28days.Theyreportedthat50%metakaolinreplacement signifi-cantlypreventedthesisalfibresfromthedegradationincement matrix.Inthecurrentinvestigation,theNCeffectivelyprevented theflaxfabricdegradationbyreducingthealkalinityofthematrix throughgeopolymerreaction.Thus,thedegradationofflaxfibres innanocompositewasmostlyreducedandtheFF-nanocomposite matrix interfacial bonding was typically improved. Fig. 7(a–b) showsthechangesinthefibressurfaceinGP/FFandGPNC-2/FF at4 weeks. Thefibres lookmore regularand free of anysigns ofdegradationinbothcases.After32weeks,however,thefibres extractedfromcontrolspecimen(Fig.7c)revealsignsof degra-dationandthefibrilsareclearlysplittingup,whichinfluencethe flexuralstrengthofthecomposite,whereasthefibresextracted fromGPNC-2/FFafterageingperiod(Fig.7d)donotpresentsigns ofsignificantdamage.

4. Conclusions

Geopolymercompositesandnanocompositesreinforcedwith flax fabric (FF) and nanoclay (NC) have been fabricated and characterized. The effect of NC on the durability of FF rein-forced geopolymer nanocomposites and the degradation of FF is reported.Theoptimum content of NCwas2.0wt.%. After32 weeks, theflexural strength of GP/FF composites decreased by 23.01%whereas flexuralstrengthof GPNC-2/FFnanocomposites

Fig.5. Flexuralstrengthandmodulusofflaxfabricreinforcedgeopolymercompositesandnanocompositesat4and32weeks.

decreasedbyonly13.7%.SEMmicrographsindicatedthatflaxfibres inGP/FFcompositessuffermoredegradationthanthatin GPNC-2/FFnanocomposites.Basedontheseobservations,theadditionof NChasgreatpotentialinimprovingthedurability offlaxfabric reinforcedgeopolymernanocompositesduringageing.

Acknowledgement

TheauthorswouldliketothankMs.E.Millerfromthe Depart-mentofAppliedPhysicsatCurtinUniversityfortheassistancewith SEM.

Fig.7. SEMimagesoftheflaxfibresextractedfrom(a)GP/FFat4weeks,(b)GPNC-2/FFat4weeks(c)GP/FFat32weeks,and(d)GPNC-2/FFat32weeks.

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