High Performance Concrete

1. High Performance Concrete Ken Day www.kenday.id.au

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 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

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 www.kenday.id.au

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:

21. www.kenday.id.au