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Performance Engineered Concrete Mixtures
Peter Taylor National 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 need With the materials available With minimum impact (environment / cost)
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When did you last “design” a mixture?
Readymix operator Some regularly, others never Consultant May review before “approving” Owner Mmm Contractor Only for bidding Researchers Of 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? Strength Slump Air content w/cm Cement content SCM percentage Aggregate grading Admixture dosage
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Current Proportioning Technologies
Developed Before water reducers Before supplementary cementitious materials Primarily focused on structural concrete 100 mm (4”) slump 30 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 volume with sand
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Absolute Volume Approach
Higher fineness modulus Means coarser sand Therefore more mass needed to fit between rock particles Leads to less coarse aggregate
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Absolute Volume Approach
Shortcomings Little account for: Supplementary cementitious materials Admixtures Aggregate texture
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What Do We Really Want Contractor Cost Workability Strength Owner Reliability Value
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Proposed Mixture Proportioning Procedure
Choose the Aggregate System Combined gradation Determine void ratio Account for shape and texture
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Proposed Mixture Proportioning Procedure
Choose the Aggregate System Influences Workability Segregation Paste requirement
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Proposed Mixture Proportioning Procedure
Choose a Paste System Cementitious blend W/Cm Air content Chemical admixtures
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Proposed Mixture Proportioning Procedure
Choose a Paste System Influences Workability Setting Hardened properties
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Proposed Mixture Proportioning Procedure
Choose Paste Volume All voids must be filled with paste Additional paste to coat the particles for workability
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Proposed Mixture Proportioning Procedure
Choose Paste Volume Influences Workability Hardened 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!
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