1. High Performance Concrete
Ken Day

2. 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.

3. 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).

4. Ultra High Strength Concrete
How High?
Strengths of MPa 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

5. 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

8. Self-Compacting Concrete
Ken Day

9. The Important Properties
Self-compactability
Avoidance of bleeding and segregation
Low shrinkage
Low permeability
Strength as needed

10. The Benefits Less dependent on skill on site
Safer, quieter sites (no vibration)
Better appearance
Better durability
Strength as needed

11. What’s Different?
Segregation resistance from mortar viscosity, not aggregate grading
Workability through admixtures, not water content

12. What’s The Snag? Higher cost – especially if high strength not needed
Plant control has to be better

13. 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

14. 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

15. 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

16. 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!

18. Why Does It Look Better?
Perfect compaction
No bleeding

19. 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

20. I leave you with a look at my website: