22-12-2012, 06:43 PM
High Performance Concrete
High Performance.ppt (Size: 2.49 MB / Downloads: 329)
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 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
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
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
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