Transcript Presentation Materials

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
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?
Strength
Slump
Air content
w/cm
Cement content
SCM percentage
Aggregate grading
Admixture dosage
7
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
Aggregate
system
Paste
quality
Paste
quantity
• Add something = take something else out
• Interactions
Proposed Mixture Proportioning
Procedure
Are we there yet?
• Aggregate system – some
• Paste quality – mostly
• Paste volume – some
• Interactions – some
• Working on it…
Lets discuss!