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1、Polymerlatex–cementinteractionsacausefretardationXiangmingKong1SebastianEmmerling2JoachimPakusch31.DepartmentofCivilEngineeringTsinghuaUniversityBeijing100084China2.AdvancedMaterialsSystemsResearchBASFSELudwigshafen67056

2、Germany3.GlobalDevelopmentConstructionBASFSELudwigshafen67056GermanyAbstractPolymerdispersionsarewidelyusedincementitiousmaterialsknownaspolymermodifiedmtar(PCM)concretepolymercomposite(CPC).Thecompositeisthuscomposedoft

3、wobinderspolymercement.Intheidealcasebothbinderscomplementeachothertoresultinamaterialwithimprovedperfmance.Typicallyoneaimsatimprovingtheadhesiontosubstratesthepermeabilityofthematerialaswellasitsflexibility.Itisofutmos

4、timptancetoundersthowbothbindersinteractindertoprojectwhatmacroscopicpropertiesthecompositewillexhibit.Ithasbeenknownthatthelatexparticlesadsbonsurfaceofcementgrainsdrivenbyelectrostaticinteraction.Afirststeptowardsunder

5、stingtheinteractionofbothbindersisfollowingtheadsptionofthepolymerlatexesonthesurfaceofcementgrains.Basedontheresultsgatheredwewereabletoestablishaconnectionbetweenthecoverageofcementgrainswithlatexesthehydrationkiicsoft

6、hecement.Twostyreneacrylatedispersionswithdifferentsurfacegewereusedinthisstudyonewithanionicallygedlatexesonewithneutrallatexes.Anovellighttransmissionmethodwasdevelopedindertodeterminetheamountofadsbedlatexesoncementqu

7、antitatively.Themethodwasvalidatedbyseparatingtheserumfromfreshlypreparedpolymer–cementmixturesmeasuringtheirsolidcontent.Theresultsofbothmethodswerefoundtobeingoodagreement.Inadditionweemployedconfocallaserscanningmicro

8、scopy(CLSM)indertoobserveinsituthedistributionofpolymerlatexesinthefreshcementpastes.Theresultsobtainedbythedescribedmethodsindicatethattheneutrallatexeshavealowertendencytoadsbonthecementgrainscomparedtotheanionicallyge

9、dlatexes.Finallyisothermalcalimetrywasemployedtoinvestigatetheinfluenceofthepolymerdispersionsonthecementhydration.Theresultsobtainedbyisothermalcalimetryshowthattheinfluenceonthehydrationkiicsofthecementishigherinthecas

10、eoftheanionicallygedlatexes.Onthebasisofthepresentedresultsitcanbeconcludedthattheanionicpolymerlatexesretardthecementhydrationintwomannersnamely1)the“slowingdown”effectacterizedbyareducedmainhydrationpeakduringtheaccele

11、rationperiodreferredtoasphysicalretardation2)the“postponing”effectrepresentedbyadelayedhydrationpeakwhichisrelatedtothecomplexationofCa2ionsbypolymerchainscontainingcarboxylatefunctionalities.Thisisdefinedaschemicalretar

12、dation.NeutralCrespondingauths:ghua.sebastian.emmerling@Tel:861062783703496216042679Fax496216040855onthecementsurface.Ontheotherhthecoveringlayercanexhibitadiffusionlimitingeffectbyfmingasemipermeablemembraneonthecements

13、urfacethatdeceleratesthediffusionofwaterionsacrosstheinterfacebetweenmineralaqueousphase.Thispublicationaimsatdisclosingtheretardationmechanismofpolymerdispersionsoncementhydrationbyusingtwostyreneacrylatecopolymerdisper

14、sionswithvariedsurfacegepropertiesofthelatexes.2.MaterialsPtlcementCEMI52.5R–MilkepremiumcomplyingDINEN1971wasprovidedbyHeidelbergCementAG.Theblainvalueofthecementis5250cm2g.Table1.Chemicalmineralcompositionofcement(wt%)

15、.ChemicalcompositionMineralcompositionSiO2Al2O3Fe2O3CaOMgOK2ONa2OSO3LOIC3SC2SC3AC4AFCaSO4CaSO4?0.5H2O22.653.651.4267.150.680.710.163.131.2761.810.53.62.33.81.4TwostyrenenbutylacrylatecopolymerdispersionsprovidedbyBASFSEw

16、ereusedinthisstudy.BasicpropertiesofthetwolatexesarelistedinTable1.DispersionL1consistedofnegativelygedlatexesduetothefactthat2%methacrylicacidawatersolublemonomerwasusedinthesynthesis.DispersionL2containedlatexeswithnog

17、esbasedoncarboxylicgroupsascanbeseenfromthelastcolumninTable2DispersionL2wasthusregardedasneutralfthisstudy.Bothdispersionshadamonomodalparticlesizedistributionthelatexeshadasimilarsizeof320338nmrespectivelyasmeasuredbyh

18、ydrodynamicchromatography.Table2.Basicpropertiesofthetwopolymerdispersionsusedinthisstudy.Dispersion#SolidContent(wt%)InitialpHParticleSize(nm)byHDCTg(?C)SO32SO42groupsonpolymerlatex(mmol100glatex)COOHgroupsonpolymerlate

19、x(mmol100glatex)L1(ged)514.632090.64L2(neutral)512.5338180.40.3Itiswellunderstoodfromthetheyofemulsionpolymerization[45]thatwatersolublemonomers(WSM)commonlyemployedinrelativelysmallamountscanimpartspecialpropertiestopol

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