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 With minimum impact (environment / cost)

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!

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

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

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

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

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 volume with sand

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

Absolute Volume Approach Shortcomings Little account for: Supplementary cementitious materials Admixtures Aggregate texture

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

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

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

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

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

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

Proposed Mixture Proportioning Procedure Choose Paste Volume Influences Workability Hardened 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!