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Figure2-ComparisonofCO2EmissionsforTypical50MPaConcretesWithVaryingFlyAshContentfollowingreferences1720and21By-ProductRecoveryandReuseIn2010Australiancoalredpowerindustryproducedinexcessof14milliontonnesofcoalcombustionproductswhichincludes-yashofwhichalmost1.9milliontonnesor14wasusedinconcreteproductmanufacture24.Flyashhasgreattechnicalmeritandisavaluablematerialwithenormouspotentialforincreaseduseinconcrete.Thereuseof-yashanditsdiversionfromlongtermstoragepondsishighlyeconomicalaswellasprovidingenvironmentalandsocialbenetsinlinewiththeobjectiveofconcretesustainability.ReductioninNaturalResourceUseCementproductionplacesasignicantdemandonournaturalresourcesintermsoftheprocessesinvolvedinmanufactureandinputs.Itrequiresminingofnaturalrawmaterialsincludinglimestoneclayandshaleaswellascoalandgasforenergytodrivetheclinkeringprocess.Theuseof-yashasapartialcementreplacementreducestheamountofcementrequiredinconcretethisreducingthisprocessinhelpingtopreservenaturalresources.DurabilityandServiceLifeTheabilityof-yashtoenhancethedurabilitypropertiesofconcreteiswellestablished7.Morerecentlythelinkbetweenenhanceddurabilityandsustainabilityhasbeenexplored25.Durablestructuresthatarebetterdesignedtowithstandchemicalattackandphysicalstresshaveanincreasedservicelifeandreducedneedformaintenance.Thismaximisesthereturnontheoriginalcapitalaswellasthenaturalresourceuseinthestructuretranslatingintoahigherlevelofsustainabilitymeasuredoverthelifecycleoftheconcretestructure.OPPORTUNITIESFORTHEUSEOFFLYASHINSUSTAINABLECONCRETETheopportunitiesforusing-yashintheproductionofsustainableconcreteareextensiveandwillcontinuetogrowasconcretetechnologyevolvesthusallowingthemeritsof-yashtobecommerciallyrealised.Withanunderstandingofthein-uencesof-yashontheearlyageandmechanicalpropertiesofconcrete7itispossibletoincorporateitinanappropriateproportionrelevanttothedesignandconstructionrequirements.Someapplicationsandopportunitiesfor-yasharegivenbelowIncorporationintoNormalclassconcretesdenedinAS1379wherepossibletolevelswhereminimum7daycompressivestrengthrequirementsareachieved26.Typicalproportionswouldbe15to25for20-32MPaconcreteand25to35forhigherstrengthgrades.IncorporationintoSpecialclassconcretes24ataproportionwhereperformancecriteriacanbeachieved.Thismayvaryfrom15to30forpost-tensionedapplicationswhereearlyagecriteriadominatetovaluesof40andoverforapplicationswhereearlystrengthisnotrequiredandacceptanceagemaybeextendedto56or90days.IntheGreenStarspecicationachievingreductionsinPortlandcementcontentsinconcreterelativetoReferenceCaselevelsintheconcretematerialscredit4.SpecicallyreducingthePortlandcementcontentby30toachieve1pointor40cementreductionfor2points.Upto7.5inclusionasamineraladditioninthemanufactureofcement27.Asthemainingredientinalkali-activatedcementatechnologybasedonusinganalkalinesolutiontoactivatethepolymerisationof-yashandorslagtoproduceanalternativetobindersandconcretesoneexamplebeinggeopolymerbasedmaterial.Muchresearchisbeingundertakeninthisarea28andwhileproductsarenotyetincommonuseitisonetechnologythatprovidessolutionsforthefuture.3