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Performance Engineered Concrete Mixtures

Performance Engineered Concrete Mixtures. Peter Taylor National Concrete Pavement Technology Center. With thanks to Jim grove, FHWA, and Dr Ezgi Yurdakul , Verifi. The Goal. Help the industry get: Performance they need With the materials available

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Performance Engineered Concrete Mixtures

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  1. Performance Engineered Concrete Mixtures Peter Taylor National Concrete Pavement Technology Center With thanks to Jim grove, FHWA, and DrEzgiYurdakul, Verifi

  2. The Goal • Help the industry get: • Performance they need • With the materials available • With minimum impact (environment / cost)

  3. 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!

  4. 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

  5. Mixture Design • Process of determining required and specifiable characteristics of a concrete mixture: • i.e. Choosing what you want

  6. Mixture Proportioning • Process of determining the quantities of concrete ingredients available • i.e. choosing what to use to get what you want

  7. Design and Proportioning • Who should choose what? • Strength • Slump • Air content • w/cm • Cement content • SCM percentage • Aggregate grading • Admixture dosage

  8. 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

  9. 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

  10. 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

  11. Absolute Volume Approach • Higher fineness modulus • Means coarser sand • Therefore more mass needed to fit between rock particles • Leads to less coarse aggregate

  12. Absolute Volume Approach • Shortcomings • Little account for: • Supplementary cementitiousmaterials • Admixtures • Aggregate texture

  13. What Do We Really Want • Contractor • Cost • Workability • Strength • Owner • Reliability • Value

  14. Proposed Mixture Proportioning Procedure Choose the Aggregate System • Combined gradation • Determine void ratio • Account for shape and texture

  15. Proposed Mixture Proportioning Procedure Choose the Aggregate System • Influences • Workability • Segregation • Paste requirement

  16. Proposed Mixture Proportioning Procedure Choose a Paste System • Cementitious blend • W/Cm • Air content • Chemical admixtures

  17. Proposed Mixture Proportioning Procedure Choose a Paste System • Influences • Workability • Setting • Hardened properties

  18. Proposed Mixture Proportioning Procedure Choose Paste Volume • All voids must be filled with paste • Additional paste to coat the particles for workability

  19. Proposed Mixture Proportioning Procedure Choose Paste Volume • Influences • Workability • Hardened properties up to a point

  20. Proposed Mixture Proportioning Procedure Aggregate system • Add something = take something else out • Interactions Paste quality Paste quantity

  21. Proposed Mixture Proportioning Procedure Are we there yet? • Aggregate system – some • Paste quality – mostly • Paste volume – some • Interactions – some • Working on it…

  22. Lets discuss!

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