Performance of magnesium phosphate cement at eleva

PerformanceofmagnesiumphosphatecementatelevatedtemperaturesPerformanceofmagnesiumphosphatecementatelevatedtemperaturesLiYuea,b,ShiTongfeia,b,ChenBingc,?,LiYaqianga,baTheKeyLaboratoryofUrbanSecurityandDisasterEngineering,MOE,BeijingUniversityofTechnology,Beijing100124,PRChinabBeijingKeyLabofEarthquakeEngineeringandStructuralRetro?t,BeijingUniversityofTechnology,Beijing100124,PRChinacDepartmentofCivilEngineering,ShanghaiJiaotongUniversity,Shanghai202140,PRChinahighlightsWestudiedeffectofelevatedtemperatureonMPC.PropertiesofMPCafterexposuretohightemperaturewereevaluated.Thepresenceof?yashandsanddecreaseresidualstrengthofMPC.MicrostructuralexaminationofMPCafterexposuretohightemperatures.articleinfoArticlehistory:Received17February2021Receivedinrevisedform25March2021Accepted1May2021Availableonline16May2021Keywords:MPCHightemperatureResidualstrengthMicrostructureabstractThisresearchstudiedeffectofelevatedtemperatureonpropertiesofmagnesiumphosphatecement(MPC).Properties,includingstrength,colour,massloss,andmicrostructure,ofMPCspecimensbeforeandafterexposuredifferenthightemperatureweremeasuredorobservedinthispaper.Sevensamplemixturescontainedvaryingamountsof?yashandsandareconsideredintheexperimentalprogram.ThemechanicalpropertiesofMPCweremeasuredbyheating40?40?160mmsampleto130,500and1000°Catarateof10°C/min.TheobtainedresultsdemonstratethatstrengthofMPCdecreasedsig-ni?cantlywhenthetemperaturepassed130°C.After130°C,theamplitudeofstrengthdecreasedofMPCbecamelesswiththeincreasingoftemperature.TheresultsofDifferentialthermalanalysis(DTA)andthermo-gravimetricanalysis(TG)indicatethatthecrystalwaterinMKPá6H2Owerelostatthetempera-tureof125°C.ThelossofcrystalwaterinMKPá6H2OwasthemainreasonofstrengthdecreasingandmasslossofMPCafterexposuretohightemperature.Theresultsalsoshowthatthepresenceof?yashandsanddecreaseresidualstrengthofMPC.ó2021ElsevierLtd.Allrightsreserved.1.IntroductionMPCs,formedbythrough-solutionacid-basedreactionbetweendeadburntmagnesiaandphosphatesalts,were?rstdiscoveredanddevelopedasdentalcementinthelate19thcentury[1–4].In1970,magnesiumphosphatecementsweredevelopedasrapidrepairmaterialsincivilengineering[5].Duringdecadesofdevel-opment,MPCshavebeenemployedinmany?elds.Theseincludetheusesof:stabilizedandsolidi?ed,lightmagnesiumphosphatecementfoamedmaterial,dentalorbonerestorations,repairandrehabilitationofstructureand3Dpowderprintingmaterials[6–12].MPCshaveseveraladvantagesagainstconventionalPortlandcementsuchasrapidsettingtime,highearlystrength,goodbondingwithPortlandcement,littledryingshrinkageandgoodresistancetoabrasion[13–16].ThesesuperiorpropertiesendowMPCswiththepotentialtobewidelyusedinstructures.Traditionalmagnesiumphosphatecementwaspreparedfromthechemicalreactionofdeadburnedmagnesiaoxide(MgO)andammoniumdihydrogenphosphate(NH4H2PO4)[9–19].Thechem-istryandstructureofsimilarmaterialswerestudiedbyAbdelrazigetal.[13].Thehexahydratewasidenti?edasthemainreactionproductinthecommercialMPCmortar,whichisthemoststable.However,themainproblemwiththesemortarsisthatduringfor-mationandevenafter,theytendtoreleaseammonia.Hence,thoughtheyarecomparativelyinexpensive,theiruseislimitedtooutdoorapplication.But,oneinterestingfeatureofSugamaandKukacka’sstudy[18]attractsresearchers’attention,isthatthestrengthkeptrisingastheyheatedthiscementupto1300°C.ThestabilityofMPCsathightemperatureisanimportantcharacteristicsbecauseconventionalPortlandcementsarenotstableathightemperaturesand,hence,cannotbeusedforrefrac-toryapplications.Phosphatecementscanbeveryusefulinthisó2021ElsevierLtd.Allrightsreserved.?Correspondingauthor.Tel.:+86139********.E-mailaddress:hntchen@(B.Chen).respectbecausetheycanbecastintorequiredshapesatroomtem-peratureandsinteresathightemperature.Duetothereleaseofpungentammonia,potassiumdihydrogenphosphate(KH2PO4)wasproposedtoreplaceammoniumdihydrogenphosphatetopre-pareMPCs,whichsolvedthedrawbackofthepreparationoftheMPCandprovedthatthemainproductwasMgKPO4á6H2O.Chauetal.[15]investigatedthestructureofthehydrationproductthataddsKH2PO4andindicatedthatthestructureofMgKPO4á6H2Owasthesameasthatofstruvite.However,theliteratureonMKPmin-eralisscare.Sivaprasadetal.andWaghetal.considerthismaterialasananalogueofstruvite,inwhichNH4isreplacedbyK,andhavedetermineditscrystallinestructure.Differentialthermalanalysis(DTA)andthermo-gravimetricanalysis(TG)indicatedthatthe6molwaterinthecrystalarelooselyboundandescapeuponheat-ingat120°C,whichindicatesthatstabilityofMPCsformedbypotassiumphosphateathightemperatureisdifferentfromthoseMPCsformedbyammoniumphosphates.Tillnow,thereisnoresearchconcerninghigh-temperatureperformanceofMPCsformedbypotassiumphosphate.Inthiswork,anexperimentalstudyontheperformanceofMPCsformedbypotassiumphosphateafterexposuretohightem-peraturewascarried.Thecompressiveand?exuralstrengthsofMPCspecimenswith?yashornotafterexposuretohightemper-atures,wereexamined.Thecrystalli