Performance Engineered Concrete Mixtures
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Transcript of Performance Engineered Concrete Mixtures
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Performance Engineered Concrete Mixtures
Peter TaylorNational Concrete Pavement Technology Center
With thanks to Jim grove, FHWA, and Dr Ezgi Yurdakul, Verifi
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The Goal
• Help the industry get:Performance they needWith the materials availableWith minimum impact (environment /
cost)
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When did you last “design” a mixture?
• Readymix operatorSome regularly, others never
• ConsultantMay review before “approving”
• OwnerMmm
• ContractorOnly for bidding
• ResearchersOf course!
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View Points
• To the readymix operator - Push the envelope
• To the consultant - Crunch those numbers• To the contractor - Make it flow, then
magically set• To the materials
suppliers - Use more of our stuff
• To the owner - Make it last forever
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Mixture Design• Process of determining required and
specifiable characteristics of a concrete mixture: i.e. Choosing what you want
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Mixture Proportioning• Process of determining the quantities of
concrete ingredients available i.e. choosing what to use to get what
you want
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Design and Proportioning• Who should choose what?
StrengthSlumpAir contentw/cmCement contentSCM percentageAggregate gradingAdmixture dosage
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Current Proportioning Technologies• Developed
Before water reducersBefore supplementary cementitious
materials• Primarily focused on structural concrete
100 mm (4”) slump30 MPa (~4000 psi)
• ACI 211 last revised in 1991
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Common Misconceptions• More cement means stronger concrete• Supplementary cementitious materials are
dilutants• Stronger concrete is more brittle & that is bad• Strength and
workability are correlated
• Strength and durability are correlated
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Absolute Volume Approach• Paste volume based on coarse aggregate
size• Coarse aggregate volume based on
subtracting the fineness modulus (FM) of sand from a fudge factor
• Fill the remaining volumewith sand
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Absolute Volume Approach• Higher fineness modulus
Means coarser sandTherefore more mass needed to fit
between rock particlesLeads to less coarse aggregate
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Absolute Volume Approach
• ShortcomingsLittle account for:
Supplementary cementitious materials
AdmixturesAggregate texture
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What Do We Really Want
• ContractorCostWorkabilityStrength
• OwnerReliabilityValue
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Proposed Mixture Proportioning ProcedureChoose the Aggregate System• Combined gradation• Determine void ratio• Account for shape and texture
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Proposed Mixture Proportioning ProcedureChoose the Aggregate System• Influences
WorkabilitySegregationPaste requirement
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Proposed Mixture Proportioning ProcedureChoose a Paste System • Cementitious blend• W/Cm• Air content• Chemical admixtures
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Proposed Mixture Proportioning ProcedureChoose a Paste System• Influences
WorkabilitySettingHardened properties
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Proposed Mixture Proportioning ProcedureChoose Paste Volume• All voids must be filled with paste• Additional paste to coat the particles
for workability
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Proposed Mixture Proportioning ProcedureChoose Paste Volume• Influences
WorkabilityHardened properties up to a point
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Proposed Mixture Proportioning Procedure
• Add something = take something else out• Interactions
Aggregate system
Paste quality Paste
quantity
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Proposed Mixture Proportioning Procedure
Are we there yet?• Aggregate system – some• Paste quality – mostly• Paste volume – some• Interactions – some
• Working on it…
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Lets discuss!