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Citation for published version:Colangelo, F, Roviello, G, Ricciotti, L, Ferrandiz-Mas, V, Messina, F, Ferone, C, Tarallo, O, Cioffi, R &Cheeseman, C 2018, 'Mechanical and thermal properties of lightweight geopolymer composites', Cement &Concrete Composites, vol. 86, pp. 266-272. https://doi.org/10.1016/j.cemconcomp.2017.11.016
DOI:10.1016/j.cemconcomp.2017.11.016
Publication date:2018
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1IntroductionExpandedpolystyrene(EPS)isanextremelylightweightthermoplasticthathaslowthermalconductivity,highdurabilityandlow-cost.EPSiswidelyusedinmanythermalinsulationapplicationsandaslightweightpackaging[1].Theendofliferecyclingandreuse
optionsforEPSarelimitedanditisnormallyeitherlandfilledorincinerated.Thiscancauseenvironmentalproblemsincountrieswhereappropriatestandardsarenotenforced[2].SeveralrecyclingprocesseshavebeendevelopedforEPS[3],buttheseoftenrequirethe
useofhazardoussolvents[4].Thisresearchhas investigatedusingwasteEPSasa lightweightaggregate inmetakaolinderivedgeopolymer.Theobjectivewastodevelop lightweight thermally insulatingmaterialswithmechanicalpropertiessuitable foruse innon-
structuralapplications.Atthesametime,arecyclingoptionforEPSthatallowsthismaterialtoremainintheeconomiccycleisprovidedthroughuseinnewsustainablematerials.WasteEPShasreducedenvironmentalimpactcomparedtomanyothertypesofwaste
Mechanicalandthermalpropertiesoflightweightgeopolymercomposites
F.Colangeloa,b
G.Rovielloa,b,∗
L.Ricciottia,b
V.Ferrándiz-Masc,e
F.Messinaa,b
C.Feronea,b
O.Tarallod
R.Cioffia,b
C.R.Cheesemane
aDipartimentodiIngegneria,UniversitàdegliStudidiNapoliParthenope,CentroDirezionale,IsolaC4,80143Napoli,Italy
bINSTM,ConsorzioInteruniversitarioperlaScienzaeTecnologiadeiMateriali,ViaG.Giusti,9,50121Firenze,Italy
cDepartmentofArchitectureandCivilEngineering,UniversityofBath,Bath,BA27AY,UK
dDipartimentodiScienzeChimiche,UniversitàdegliStudidiNapoli“FedericoII”,ComplessoUniversitariodiMonteS.Angelo,viaCintia,80126Napoli,Italy
eDepartmentofCivilandEnvironmentalEngineering,ImperialCollegeLondon,SW72BU,UK
∗Correspondingauthor.DipartimentodiIngegneria,UniversitàdegliStudidiNapoliParthenope,CentroDirezionale,IsolaC4,80143Napoli,Italy.
Abstract
Thisresearchhasinvestigatedthepropertiesofthermally insulatinggeopolymercompositesthatwerepreparedusingwasteexpandedpolystyreneaslightweightaggregate.Thegeopolymermatrixwassynthetizedusingmetakaolinandanalkaline
activatingsolution.Toimproveitsmechanicalproperties,thismatrixwasmodifiedbytheadditionofanepoxyresintoformanorganic-inorganiccomposite.Moreover,inordertoreducedryingshrinkagemarblepowderwasusedasaninertfiller.Thematerials
obtainedwerecharacterizedintermsofphysico-mechanicalproperties,thermalperformanceandmicrostructure.ThegeopolymerexpandedpolystyrenecompositehaveimprovedpropertiescomparedtoPortlandcement-basedmaterials,withhigherstrengths
andlowerthermalconductivity.Theresearchdemonstratesthemanufactureofsustainablelightweightthermallyinsulatinggeopolymercompositesusingwasteexpandedpolystyrene.
Keywords:Expandedpolystyrene;Geopolymer;Composite;Thermalinsulation
derivedmanufacturedlightweightaggregates[5–11].
PreviousresearchhasinvestigatedEPSinPortlandcementcomposites[12–25].ThesestudiesreportthatasubstantialdecreaseincompressivestrengthisassociatedwithincreasingtheEPScontent,andthisrequirestheadditionofmaterials,suchassilica
fumeandsteelfibrestoimprovemechanicalperformance.ThepropertiesofEPSconcretedependonthemixdesignandtheEPSparticlesizedistribution[26].Increasedshrinkageandcreepdeformationarereportedandresultfromareductionintherestrainteffect
comparedtonaturalaggregates,whichhavemuchhigherstaticmodulusofelasticity[27–30].Additional issuesrelatedtoEPSlightweightaggregateconcreteareEigenstress-drivencrackingandincreasedbulkshrinkage[31].EPS-containingconcretehasreduced
spallingresistanceathightemperatureduetothermaldecompositionofEPS[18].TheembeddedCO2isincreasedwithEPSadditionduetothehighcarboncontentofEPScomparedtonormalinorganiccementbindersandaggregates.
SeveralstrategieshavebeenproposedforreducingtheembeddedCO2inthebuiltenvironment[32,33].Geopolymersareinnovativebindersthathavebeenextensivelyresearchedinrecentyearsconsistingofamorphousaluminosilicatesthataresynthesized
usingalkalineactivationofsolidprecursorssuchasflyash[34–36],calcinedclays[37–40]andblastfurnaceslag[41–43].GeopolymersareapotentialalternativetotraditionalPortlandcementinselectedapplications,becausetheycombinereducedenvironmentalimpact
withexcellentmechanicalproperties.However,theyhaverelativelylowtoughnessandlowflexuralstrengthandinordertoimprovethesepropertiesgeopolymercompositematerialshavebeenformedbytheinsituco-reticulationofageopolymermatrixwithanepoxy
basedorganicresin[44–49].Thesemodifiedgeopolymermaterialsshowenhancedcompressiveandflexuralstrengthcomparedtonormalgeopolymerswithanalogouscompositionsduetothesynergisticeffectsbetweentheinorganicandtheorganicphasesarisingfrom
interfacialforcesatnanometrescale.Thepropertiesarecontrolledbycompositionandprocessingmethodandthesemodifiedgeopolymermaterialshavepotentialtobeusedinstructural[50],photo-catalytic[51],fire-resistantandthermalinsulating[52,53]applications.
Lightweightgeopolymershavebeenpreparedwithdifferentmixproportionsbyfoaming[54]andusingdifferentlightweightaggregates[55–61] (pleasereplace[55-61]with[55-62]).Inthisresearch,lightweightgeopolymerconcrete(LWGC)hasbeeninvestigated
usingrecycledEPSasaggregate.Geopolymermatrixpreparationusedmetakaolin(MK)andanalkalineactivatingsolution(AAS).Epoxyresinswithtailoredcompositionandstoichiometrywereaddedtoobtaingeopolymerorganiccomposites.Wastecalciumcarbonate
powderfromprocessingmarblehasbeenusedasafillerasthis improvesthemechanicalpropertiesofgeopolymersandreducesdryingshrinkage[63].Thiswaste isamajorproblemthateffectstheenvironment[63].TheLWGCsamplespreparedweretestedfor
physico-mechanicalandthermalpropertiesandtheinterfacialzonesbetweenEPSparticlesandthegeopolymermatrixcharacterizsedbymicrostructuralanalysis.
2Materialsandmethods2.1Materials
Thecompositionofmetakaolin(MK,NeuchemS.r.l.)sodiumsilicatesolution(SS,ProchinItaliaS.r.l)andmarblepowder[64,65]areshowninTable1.ReagentgradesodiumhydroxidewassuppliedbySigma-Aldrichandtheepoxyresin(Epojet®)wassuppliedby
MapeiS.p.A.EPSwasobtainedfromawastetreatmentplantinCampania,Italyandconsistedof<5mmparticleswithanapparentdensityof1.6±0.3×10−2g/cm3.TheEPSwasfrompolystyreneseedtraysusedinagricultureandthesewereprocessedbymillingto
produceEPSbeads.Wastemarbleslurrywasdriedat105°Cfor4handmilledtoproducemarblepowder(MP)withparticlesizesrangingbetween10and300μm.
Table1Chemicalcomposition(weight%)ofthemetakaolin(MK),marblepowder(MP)andsodiumsilicatesolution(SS).
alt-text:Table1
Metakaolin Marblepowder Sodiumsilicate
SiO2 52.90 1.12 27.40
Al2O3 41.90 0.37 –
CaO 0.17 52.26 –
Fe2O3 1.60 0.11 –
MgO 0.19 0.87 –
K2O 0.77 0.10 –
Na2O – 0.14 8.15
Water – – 64.45
LoI – 40.74 –
*LoI=LossonIgnition.
ThecompositionsoftheLWGCmixesaregiveninTable2.Thealkalineactivatingsolutionwaspreparedbydissolvingsolidsodiumhydroxideintothesodiumsilicatesolution.Thesolutionwasthenallowedtoequilibrateandcoolfor24h.Thecompositionofthe
solutioncanbeexpressedasNa2O·1.4SiO2·10.5H2O.GeopolymerpasteswereobtainedbymixingMKfor10minwiththeactivatingsolution,atasolidtoliquidratioof1:1.4byweight,usingaHobartmixer.EPSbeadsandMPwerethenaddedandthesystemmixedfor
afurther5min.ThisprocedurewasusedfortheLWGCsamplesthatdidnotcontainepoxyresin.TheseweretheGMK-65,GMK-MP-65,GMK-72.5andGMK-MP-72.5mixes.GMK-XXsamplescontainedEPS,whereXXreferstotheamountofEPSv/v%.GMK-MP-YY
samplesaresamplecontainingEPSandMP,whereYYreferstothesumofEPSandMPv/v%.
Table2Composition(weight%)ofthematerialspreparedinthisresearch.
alt-text:Table2
Sample MK SS NaOH Resin MPfillera EPSbeadsa
Wt. Vol.
GMK-65 41.6 50.0 8.4 – – 1.9 65.0
GMK-MP-65 41.6 50.0 8.4 – 7.5 1.7 63.3
GMK-72.5 41.6 50.0 8.4 – – 2.8 72.5
GMK-MP-72.5 41.6 50.0 8.4 – 7.5 2.8 70.8
GMK-E10-65 37.4 45.0 7.6 10 – 1.9 65.0
GMK-E10-MP-65 37.4 45.0 7.6 10 7.5 1.7 63.3
GMK-E10–72.5 37.4 45.0 7.6 10 – 2.8 72.5
GMK-E10-MP-72.5 37.4 45.0 7.6 10 7.5 2.8 70.8
a Calculatedwithrespecttogeopolymerpasteand/orgeopolymercomposite(withresin)paste.
Epoxyresingeopolymercomposites(GMK-E10-XXandGMK-E10-MP-YY)wereproducedbyadding10w/w%byweightofEpojet®resintothefreshly-preparedgeopolymersuspensionandmixingfor5min.Epojet®resinwascuredatroomtemperaturefor
10minbeforeaddingtothegeopolymermixwhenitwasworkableandbeforecross-linkingandhardeninghadoccurred.
Aftermixingthepasteswerecastintoprismatic(40×40×160mm)andcubic(100×100×100mm)mouldsandcuredsealedat40°Cfor24h.Thespecimenswerekeptsealedatroomtemperaturefor6daysandthenstoredinairatroomtemperaturefora
further21days.
2.2MethodsTheapparentdensityofsampleswasdeterminedastheratioofthemasstoagivenvolumebyhydrostaticweighingusinganOHAUS-PA213balance.ThecompressiveandflexuralstrengthswereevaluatedaccordingtoEN196-1.Thetestswereperformed
after28dayscuringandthevaluesreportedaretheaverageofsixstrengthtests.FlexuralstrengthtestsonprismaticsamplesusedaControlsMCC8multipurposetestingmachinewithacapacityof100kN.Compressivestrengthmeasurementsoncubicsamplesuseda
ControlsMCC8hydraulicconsolewith2000kNcapacity.Thermalconductivity testswereperformedon100×100×100mmcubesamplesusingaHotDiskM1analyser(Thermal InstrumentsLtd).This isanon-destructive testbasedonthetransientplanesource
techniqueaccordingtoISO22007–2:2015.Microstructuralanalysisbyscanningelectronmicroscopy(SEM)usedaPhenomProXMicroscopeonfreshlypreparedfracturesurfaces.Opticalimageswereobtainedfrompolishedsurfaces.
3Experimentalresultsanddiscussion3.1Morphologicalcharacterization
Fig.1isaSEMimageofanEPSparticleshowingthetypicalcellularstructure[66].
Duetothegrindingprocess,thesecellsarenotevenlydistributedandvaryindimensions.
Fig.2showsopticalmicrographsofpolishedsurfacesofGMK-72.5andGMK-E10–72.5samples.
TheEPSbeadsareembeddedinthegeopolymermatrixanddistributeduniformlywithnoevidentaggregationphenomena.Moreover,thespecimensshowacompactstructurewithnocracking,asconfirmedbySEMimagesofthesesamplesthatwasusedin
ordertoinvestigateindetailthemicrostructureofthesamplesandthebondingcharacteristicsbetweenthegeopolymermatrixandEPSparticlesandMPaggregate(Fig.3).Thisdemonstratesthatatmicroscopiclevel,thematrixiscompactandhomogeneous.TheSEM
imagesinFig.3(AandA′,sampleGMK-72.5)indicatethatthereisverygoodadhesionbetweenEPSparticlesandthematrix.EPSparticlesarecompletelyembeddedinthegeopolymeranditisdifficulttoclearlyidentifytheinterface.Thiscompatibilitywasobtained
withouttheuseofanyadditives.
Fig.1SEMimageofanEPSparticle.Scalebaris100μm.
alt-text:Fig.1
Fig.2OpticalmicrographofpolishedsurfacesofA)GMK-72.5andB)GMK-E10–72.5.
alt-text:Fig.2
TheadhesionbetweenEPSparticlesandthematrixisalsogoodforsamplespreparedusingthecompositematrixcontainingepoxyresin(Fig.3B,B′,sampleGMK-E10–72.5).Themajordifferenceisinthematrixmicrostructure,whichshowsthepresenceof
microspheresofresinofvarioussizesasdiscussedinourpreviouswork[47].
TheadditionofMP(Fig.3C,C′,sampleGMK-E10-MP-72.5)asfillerdoesnotcompromisethebondingbetweenphasesinthegeopolymermatrixthusnotaffectingsignificantlythemicrostructure.Theparticlesarewelldispersedandthestrongadhesionimproves
themechanicalproperties.
3.2Physico-mechanicalcharacterization
Fig.3SEMimagesofaninterfaceareabetweenanEPSparticleembeddedinthegeopolymermatrix:A,A′)neatgeopolymermatrix(sampleGMK-72.5);B,B′)compositegeopolymermatrix(sampleGMK-E10–72.5);C,C′)compositegeopolymermatrixcontainingalsomarblepowder(sampleGMK-E10-MP-72.5).Inallcases
averygoodadhesionbetweenEPSparticlesandthematrixisapparent.
alt-text:Fig.3
Fig.4ashowstheapparentdensityofsamples.Asexpected,densitydecreasesasthecontentofEPSaggregateincreases.Sampleswith65%volumeofaggregateshaddensitiesrangingfrom646±51kg/m3(GMK-65)to827±91kg/m3(GMK-E10-MP-65).
Sampleswitha72.5%volumecontentofaggregateshaddensitiesrangingfrom516±43kg/m3(GMK-72.5)to549±52kg/m3(GMK-E10-MP-72.5).Forneatgeopolymersamples(GMK-65andGMK-72.5),increasingthevolumetriccontentofEPSbylessthan10%turns
outinadecreasedofthedensityby∼20%.MorepronounceddecreasesindensitywereobservedforthesamplescontainingepoxyresinandMP.Inparticular,correspondinglytothesameincreaseofEPScontent,thesampleswithepoxyresininthegeopolymermatrix
(GMK-E10-65andGMK-E10–72.5)showedadecreaseofdensity∼24%,whileinthecaseoftheadditionofMP(GMK-MP-65andGMK-MP-72.5),thedecreaseofdensityis∼27%.Finally,inthecaseoftheadditionofbothorganicresinandMP(GMK-E10-MP-65and
GMK-EP10-MP-72.5)thedecreaseofdensityis∼33%.Moreover,fromthedatareportedinFig.1, it isapparentthattheorganicresinandMPadditionshaveamorelimitedinfluenceonthedensityofsamplescontaining72.5%EPSinrespecttothoseatlowerEPS
content(forexample,theadditionoftheorganicresinandMPturnsoutinanincreaseofdensityof∼28%inthecaseofthesampleswith65%volofEPSbeadsandofonly6%inthesampleswith72,5%volofEPS).
ThegeopolymersampleshadcomparabledensitiestoEPS-containingPortlandcementmatrices [14]andcommercialEPS-containingconcretemixturesforwhichvaluesaround1000kg/m3arereported [67].ThemechanicalperformanceofEPS-containing
geopolymerconcretecorrelateswithdensity.Thevolumetriccontentofaggregateinfluencesbothcompressiveandflexuralstrengths(Fig.4bandc).Thecompressivestrengths(Fig.4b)ofLWGCsamplescontaining65%volumeofEPSbeadsrangedfrom3.4±0.5to
6.0±1MPa,whileforhigherEPSvolumes(72.5%)compressivestrengthsrangedfrom1.8±0.3to2.4±0.2MPa.Itisapparentthattheadditionofbothmarblepowderandepoxyresinsignificantlyimprovedthemechanicalpropertiesofsamples.Thebestcompressive
strengthvalueswereobtainedforspecimensGMK-E10-MP-65andGMK-E10-MP-72.5,andthevaluesobtainedwerecomparabletocommercialalternatives[67]andgreaterthantheliteraturedataonEPS-containingPortlandcementcomposites.
Asimilartrendtocompressivestrengthwasobservedforflexuralstrength(Fig.4c).ForEPScontentsof65%theflexuralstrengthvariedfrom0.32±0.08MPaforgeopolymersamplesto0.6±0.1MPaforcompositematrixsampleswithMP.WithgreaterEPS
contents(72.5%)theflexuralstrengthrangedfrom0.22±0.07to0.33±0.09MPaandonlyaminorimprovementinmechanicalpropertieswasassociatedwiththeadditionofMPandepoxyresin.ItcouldbearguedthatinthesesampleswithhigherEPScontent,thevery
poormechanicalpropertiesandhighcompressibilitybehaviourofpolystyreneparticlesneutralizethebeneficialeffectonthemechanicalpropertiesoftheadditionofepoxyresinandMP(thatinsteadisevidentinthesetofsampleswithlowerEPScontent)bycausingthe
formationofmicro-cracksattheinterfacebetweenthegeopolymermatrixandtheEPSparticles.
3.3ThermalpropertiesFig.5showsthermalconductivitydatafortheLWGCsamplespreparedinthisstudy.Asfordensitydata(Fig.4a),twodifferentgroupsofspecimenscanbeidentified.Samplescontaining65v/v%ofaggregateshadgreaterthermalconductivitythanthesamples
Fig.4Apparentdensity(a),compressivestrength(b)andflexuralstrength(c)ofLWGCsamplesprepared.Ina)andb),thedatafortwocommercialproducts(LatermixCemMini©andLatermixCemClassic©,http://www.laterlite.es/wp-content/uploads/2014/03/General-Catalogue.pdf)arealsoreportedforcomparison.
alt-text:Fig.4
containing72.5v/v%ofEPS.Forexample,sampleGMK-65hadathermalconductivityof0.158±0.001W/m·KwhilesampleGMK-72.5hadathermalconductivityof0.121±0.001W/m·K,a23.4%reduction.Itisapparentthat,asexpected,thepresenceofEPSparticles
causesasignificantreductioninthermalconductivity.ThecorrelationbetweenthermalconductivityanddensityforLWGCsamplesisshowninFig.6.Thesampleswiththehighestthermalconductivity(0.207±0.001W/m·K)wassampleGMK-E10-MP-65whichhadthe
highestbulkdensity(827±91kg/m3),whilethesamplewiththelowestthermalconductivity(0.121±0.001W/m·K),sampleGMK-72.5,hadthelowestdensity.TheinfluenceofMPandepoxyresinonthermalconductivityisnotclearastheseareminorcomponentsinthe
samplestested.
TheadditionofMPandepoxyresintogeopolymersproducedLWGCwithsignificantlyimprovedmechanicalpropertiescomparedtolightweightmortarsmadewithPortlandcementwithsimilarthermalconductivity.Forexample,sampleGMK-72.5retainedgood
mechanicalpropertiesandhadverylowthermalconductivity(0.121±0.001W/m·K).This is15%lower thanPortlandcementbasedcommercialproductswithsimilardensity [67].Thereduction inthermalconductivity increasesto92%whencomparedtoanalogous
materialswiththesamedensitythathadpoormechanicalpropertiescomparedtothesamplespreparedinthisstudy[19].
4ConclusionsLightweightthermallyinsulatingmaterialsbasedongeopolymerconcretecontainingexpandedpolystyrene(EPS)asinsulatingaggregatewerepreparedandcharacterized.ThemicrostructuralcharacterizationshowedahomogeneousstructurewithEPSbeads
uniformlydispersedandembeddedinthegeopolymermatrix.CompressiveandflexuralstrengthsdecreasedwithincreasingEPScontent.Theadditionofanorganicresintothegeopolymersignificantlyincreasedbothcompressiveandflexuralstrengths.Asimilareffect
wasobservedwiththeadditionofmarblepowder.Allsamplesstudiedwerecharacterizedbyverylowthermalconductivity.Thiswasmuchlowerthananalogouslightweightmaterialswithsimilardensitiesreportedintheliterature.Theresearchhasdemonstratedthe
Fig.5ThermalconductivityofLWGCsamples.Datafortwocommercialproducts(LatermixCemMini©andLatermixCemClassic©),arealsoreportedforcomparison[67].
alt-text:Fig.5
Fig.6CorrelationbetweenthermalconductivityanddensityofLWGCsamples:fullcircles(●)arerelatedtoLWGCsamples;emptycircles(○)arerelatedtotwocommercialproducts(LatermixCemMini©andLatermixCemClassic©,[67]).
alt-text:Fig.6
productionofgeopolymermatrixEPScompositesthatarelightweightthermallyinsulatingmaterialswithexcellentmechanicalproperties.
Uncitedreference[62].
AcknowledgementsTheauthorsthankNeuvendisS.p.A.forthemetakaolinsupplyandProchinItaliaS.r.l.forthesilicatesolutionsupply.Mr.GiovanniMorierieMrs.LucianaCiminoarewarmlyacknowledgedforassistanceinlaboratoryactivities.Universitàdi
Napoli“Parthenope”isacknowledgedforfinancialsupportwithagrantwithinthecall“SupportforIndividualResearchforthe2015-17Period-Annuity2016”issuedbyRectorDecreeno.954(28/11/2016).
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Answer:
Query:CouldyoupleaseprovidethegrantnumberforUniversitàdiNapoli“Parthenope”,ifany?
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Answer:checked
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retainedinthissection.Thankyou.
Answer:pleasereplace[55-61]with[55-62]
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