Studyonanhydriteplasterfromwastephosphogypsumforus

StudyonanhydriteplasterfromwastephosphogypsumforuseinpolymerisedflooringcompositionManjitSingh*,MridulGargEnvironmentalS&TDivision,CentralBuildingResearchInstitute,Roorkee–247667,IndiaReceived25March2003;receivedinrevisedform27April2003;accepted29April2004AvailableonlineAbstractThepaperdealswithaninvestigationabouttheproductionofhighstrengthplasterfromthewastephosphogypsumanditsuseinmakingflooringtiles.Toachievethisobjective,phosphogypsumwascalcinedat900–1000
Ctoanhydritewhichwasmixedwithsuitablechemicalactivators(alkali/alkalineearthhydroxides,sulphates,carbonates)andfinelyground(400m2/kgBlaine’s)toachievehighcompressivestrength(36–37MPa).Theanhydriteplasterwasblendedwith2–3%ofpredeterminedquantityofamonomermethylmethacrylate(MMA)withacompatiblecatalyst,metalicoxidepigments,flyashorredmud,choppedglassfibres(E-type,12mmlong)andquartzsandtoformflooringtilesbyvibrationmouldingtechniquefollowedbyhighhumiditycuring,drying,grindingandpolishing.Theadditionofchemicalactivatorsincreasetherateofdissolutionofanhydriteforrapidtrans-formationintohardstronggypsummatrixwhiletheMMAgetspolymerisedduringhydrationofanhydriteintopolymethylmethacrylatewhichfillsupvoidsandporesofhydratinganhydriteandthusimprovesdensity,strengthanddurabilityofthean-hydriteplasteragainstwater.Thedurabilityofanhydriteplasterbyalternatewettinganddryingandheatingandcoolingcyclesisreportedalongwithhydrationmechanism.Theuseofphosphogypsumanhydriteformakinghighstrengthplasterandflooringtilesisrecommended.2004PublishedbyElsevierLtd.Keywords:Anhydriteplaster;Chemicalactivators;Polymer;Flooringtiles1.IntroductionGypsumisoneoftheimportantbuildingmaterialssincetimeimmemorial.Gypsumandlimewerefamiliarfortheiruseinantiquity.GypsumwasverypopularamongthePersiansas‘garch’,‘gypsos’inGreekand‘gypsum’inLatin.InGermany,gypsumplasterwasusedasmortarinwallsandbuildingsduringtheBo-roqueandRococodynasty[1].Gypsumisavailablebothfromthenaturalandtheby-productofvariouschemicalprocesses.Innature,gypsumexistwithsomedepositsofanhydritealso.Amongtheby-productgyp-sumproduction,phosphogypsum,fluorogypsumandFGDgypsumarethewasteproductsofphosphoricacid,hydrofluoricacidandthedesulfurizationoffluecombustiongasesofcoal,foundary,oilrefineriesorpowerstationsrespectively.Gypsumproductsareknownfortheirfireresistance,thermalinsulationandacousticproperties.Gypsumhasadequatestrengthbutisnotmoistureresistant.ResearcheshavebeencarriedoutbyZapoletal.[2]tomakegypsumplasterwater-resistantbyaddinggran-ulatedslagblastfurnacetotheplaster.Thereductioninwaterabsorption(upto40%)bytheuseofparaffinwaxingypsumplasterhasbeenreported[3].Attemptshavebeenmadeinthelastfewdecadestomakegyp-sumplasterandgypsumproductswater-resistantbytheadditionofflyash,cement,lime,polymers,etc.[4–8].However,concertedeffortsareneededtomakegypsumproductswater-resistanthavingsufficientstrengthanddurability.Therearetwomajorobjectivesofthestudyreportedinthepaper(1)todevelophighstrengthanhydriteplasterfromphosphogypsumusingsuitablechemical*Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](M.Singh).0950-0618/$-seefrontmatter2004PublishedbyElsevierLtd.doi:10.1016/j.conbuildmat.2004.04.038ConstructionandBuildingMaterials19(2005)25–29ConstructionandBuildingMATERIALS(2)toproduceflooringtilesfromtheactivatedanhydriteplasteradmixedwithmonomer,glassfibre,pigments,etc.StudieshavebeenmadeattheCentralBuildingRe-searchInstitute,Roorkeetoproducehighstrengthgypsumplasterbycalciningthewastephosphogypsumtoformb-anhydriteandthentoblenditwithsuitablechemicalactivatorsfollowedbyfinegrinding.Thean-hydriteplasterthusproducedwasmixedwithoptimumquantitiesofpredeterminedmonomermethylmethac-rylateproperlycatalysed,differentmetallicoxidepig-ments,flyashandredmud,cutglassfibres(E-type)andthequartzsandtocastflooringtilesbyvibrationmouldingprocessfollowedbymoistcuringatambienttemperature,grindingandpolishing.Thepropertiesoftilessuchasdensity,waterabsorption,abrasionresis-tance,compressivestrengthandmodulusofruptureweredeterminedasperIndianStandards.Thehydrationandthedurabilitycharacteristicsofthepolymerisedanhydriteascheckedbyalternatewettinganddryingandheatingandcoolingcyclesisreportedinthispaper.Theapplicationsofthepolymerisedanhydriteplasterotherthanproducingflooringtileshasbeendiscussed.2.Experimental2.1.RawmaterialsPhosphogypsum,flyashandtheredmudsamplescollectedfromvarioussourcesinIndiawereanalysedfortheirchemicalcomposition(Table1).Thesematerialswereusedalongwithmethylmethacrylatemonomerandpigments(ironoxide,chromiumoxide,prussianblue,TiO2)asperrelevantIndianStandards,laboratorygradechemicalactivatorsandtheglassfibre(E-type,12mmlong)astherawmaterialformouldingtheflooringtiles.2.2.ProductionofanhydritefromphosphogypsumAnhydritewasproducedbyheatingphosphogypsumatanoptimumtemperatureof1000
Cinthefurnaceforaperiodof4–5h,cooledandgroundtopass75lmISsieve(450–500m2/kgBlaine).At1000
C,theimpurityofCaHPO4
2H2Opresentinthegypsumlatticeisconvertedintob-Ca2P2O7(calciumpyrophosphate)whichiswat