performance engineered concrete mixtures

Performance Engineered Concrete Mixtures

Peter TaylorNational Concrete Pavement Technology Center

With thanks to Jim grove, FHWA, and Dr Ezgi Yurdakul, Verifi

The Goal

• Help the industry get:Performance they needWith the materials availableWith minimum impact (environment /

cost)

When did you last “design” a mixture?

• Readymix operatorSome regularly, others never

• ConsultantMay review before “approving”

• OwnerMmm

• ContractorOnly for bidding

• ResearchersOf course!

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

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

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

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

Absolute Volume Approach• Higher fineness modulus

Means coarser sandTherefore more mass needed to fit

between rock particlesLeads to less coarse aggregate

Absolute Volume Approach

• ShortcomingsLittle account for:

Supplementary cementitious materials

AdmixturesAggregate texture

What Do We Really Want

• ContractorCostWorkabilityStrength

• OwnerReliabilityValue

Proposed Mixture Proportioning ProcedureChoose the Aggregate System• Combined gradation• Determine void ratio• Account for shape and texture

Proposed Mixture Proportioning ProcedureChoose the Aggregate System• Influences

WorkabilitySegregationPaste requirement

Proposed Mixture Proportioning ProcedureChoose a Paste System • Cementitious blend• W/Cm• Air content• Chemical admixtures

Proposed Mixture Proportioning ProcedureChoose a Paste System• Influences

WorkabilitySettingHardened properties

Proposed Mixture Proportioning ProcedureChoose Paste Volume• All voids must be filled with paste• Additional paste to coat the particles

for workability

Proposed Mixture Proportioning ProcedureChoose Paste Volume• Influences

WorkabilityHardened properties up to a point

Proposed Mixture Proportioning Procedure

• Add something = take something else out• Interactions

Aggregate system

Paste quality Paste

quantity

Proposed Mixture Proportioning Procedure

Are we there yet?• Aggregate system – some• Paste quality – mostly• Paste volume – some• Interactions – some

• Working on it…

Lets discuss!