Date post: | 17-Dec-2015 |
Category: |
Documents |
Upload: | lesley-park |
View: | 215 times |
Download: | 0 times |
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
5
Mixture Proportioning
• Process of determining the quantities of concrete ingredients available i.e. choosing what to use to get what
you want
6
Design and Proportioning
• Who should choose what?StrengthSlumpAir contentw/cmCement contentSCM percentageAggregate gradingAdmixture dosage
7
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 modulusMeans 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 Procedure
Choose the Aggregate System• Combined gradation• Determine void ratio• Account for shape and texture
Proposed Mixture Proportioning Procedure
Choose the Aggregate System• Influences
WorkabilitySegregationPaste 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
WorkabilitySettingHardened 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
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!