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High Performance Concrete. Ken Day www.kenday.id.au. High Performance Concrete. Concrete may be regarded as high performance for several different reasons: high strength, high workability high durability – and perhaps also improved visual appearance. .

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high performance concrete

High Performance Concrete

Ken Day

www.kenday.id.au

high performance concrete2
High Performance Concrete

Concrete may be regarded as high performance for several different reasons:

  • high strength,
  • high workability
  • high durability

– and perhaps also improved visual appearance.

high performance concrete3
High Performance Concrete

High strength concrete (HSC) might be regarded as concrete with a strength in excess of 60MPa and such concrete can be produced as relatively normal concrete with a higher cement content and a normal water-reducing admixture.

However ultra high performance concrete (UHPC) will more usually contain cement replacement materials and a high-range water-reducer (HRWR) or superplasticiser(SP) (different names for the same thing).

ultra high strength concrete
Ultra High Strength Concrete
  • How High?
  • Strengths of 150-200MPa were reported in several papers at a recent symposium
  • How is it done?
  • Using only fine sand as an aggregate, a high content of cement and silica fume, a high dosage of HRWR admixture plus steel fibres
ultra high strength concrete5
Ultra High Strength Concrete
  • In what kind of structures?
  • Thin shell roofing (2cm thick) and “bulb” double and single tees were reported
  • Both insitu and precast applications
  • Flexural and tensile strengths also high, allowing omission of secondary reinft.
  • Concrete in tees was generally self- compacting
self compacting concrete

Self-Compacting Concrete

Ken Day

www.kenday.id.au

the important properties
The Important Properties
  • Self-compactability
  • Avoidance of bleeding and segregation
  • Low shrinkage
  • Low permeability
  • Strength as needed
the benefits
The Benefits
  • Less dependent on skill on site
  • Safer, quieter sites (no vibration)
  • Better appearance
  • Better durability
  • Strength as needed
what s different
What’s Different?
  • Segregation resistance from mortar viscosity, not aggregate grading
  • Workability through admixtures, not water content
what s the snag
What’s The Snag?
  • Higher cost – especially if high strength not needed
  • Plant control has to be better
will it happen
Will it happen?
  • My guess is that 50% of concrete will be self-compacting within 10 years
  • In USA a very large proportion of precast concrete is already SCC
what is the secret
What is the secret?

Paste Viscosity! Attained by one of three means:

  • High cement content
  • High content of Fly Ash, Silica Fume etc
  • Use of Viscosity Modifying Admixture

Plus low water content using HRWR

how to check suitability
How to Check Suitability?

There are many new tests: V-funnel, L-box, U-box, Fill-box, Orimet, GTM Screen + Slump Flow and J-ring

While several of these may be used in mix development, only the latter will find site use

what is slump flow test
What is Slump Flow Test?

Measuring spread rather than height plus:

  • Speed of flow outwards
  • Ability to pass through J-ring
  • Observation of edge during flow

Interesting to note that it works better with the cone upside down!

why does it look better
Why Does It Look Better?
  • Perfect compaction
  • No bleeding
conclusion
Conclusion
  • We are going to expect concrete that is a little more expensive per cubic metre to buy
  • BUT
  • It will require less skill and effort to place
  • It will look better with no appearance defects
  • It will be more durable
  • It will require more skill at the batching plant