Presentation on theme: "High Performance Concrete Ken Day www.kenday.id.au."— Presentation transcript:
High Performance Concrete Ken Day
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 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 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
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 Ken Day
The Important Properties Self-compactability Avoidance of bleeding and segregation Low shrinkage Low permeability Strength as needed
The Benefits Less dependent on skill on site Safer, quieter sites (no vibration) Better appearance Better durability Strength as needed
What’s Different? Segregation resistance from mortar viscosity, not aggregate grading Workability through admixtures, not water content
What’s The Snag? Higher cost – especially if high strength not needed Plant control has to be better
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? 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? 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? 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? Perfect compaction No bleeding
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