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1、PortlandcementPortlandcement(oftenreferredtoasOPC,fromOrdinaryPortlandCement)isthemostcommontypeofcementingeneralusearoundtheworldbecauseitisabasicingredientofconcrete,mortar,stuccoandmostnon-specialtygrout.ItisafinepowderproducedbygrindingPortlandcementclinker(morethan
2、90%),alimitedamountofcalciumsulfate(whichcontrolsthesettime)andupto5%minorconstituentsasallowedbyvariousstandardssuchastheEuropeanStandardEN197.1ASTMC150definesportlandcementas"hydrauliccement(cementthatnotonlyhardensbyreactingwithwaterbutalsoformsawater-resistantproduc
3、t)producedbypulverizingclinkersconsistingessentiallyofhydrauliccalciumsilicates,usuallycontainingoneormoreoftheformsofcalciumsulfateasanintergroundaddition."Clinkersarenodules(diameters：0.2-1.0 inch[5–25 mm])ofasinteredmaterialthatisproducedwhenarawmixtureofpredetermine
4、dcompositionisheatedtohightemperature.Thelowcostandwidespreadavailabilityofthelimestone,shales,andothernaturallyoccurringmaterialsmakeportlandcementoneofthelowest-costmaterialswidelyusedoverthelastcenturythroughouttheworld.Concretebecomesoneofthemostversatileconstructio
5、nmaterialsavailableintheworld.Portlandcementclinkerismadebyheating,inakiln,ahomogeneousmixtureofrawmaterialstoasinteringtemperature,whichisabout1450°Cformoderncements.Thealuminiumoxideandironoxidearepresentasafluxandcontributelittletothestrength.Forspecialcements,suchas
6、LowHeat(LH)andSulfateResistant(SR)types,itisnecessarytolimittheamountoftricalciumaluminate(3CaO.Al2O3)formed.Themajorrawmaterialfortheclinker-makingisusuallylimestone(CaCO3)mixedwithasecondmaterialcontainingclayassourceofalumino-silicate.Normally,animpurelimestonewhichc
7、ontainsclayorSiO2isused.TheCaCO3contentoftheselimestonescanbeaslowas80%.Secondrawmaterials(materialsintherawmixotherthanlimestone)dependonthepurityofthelimestone.Someofthesecondrawmaterialsusedare:clay,shale,sand,ironore,bauxite,flyashandslag.Whenacementkilnisfiredbycoa
8、l,theashofthecoalactsasasecondaryrawmaterialHistoryPortlandcementwasdevelopedfromnaturalcementsmadeinBritainin
