Abstract :
high
performance concrete (HPC) is that which is designed to give optimised
performance characteristics for the given set of materials, usage and exposure
conditions, consistent with requirement of cost, service life and durability.
The
American Concrete Institute (ACI) defines HPC ‘‘as concrete which meets special
performance and uniformity requirements that cannot always be achieved
routinely by using only conventional materials and normal mixing, placing, and
curing practices.”
High
performance in a broad manner can be related to any property of concrete. It
can mean excellent workability in the fresh state like self-levelling concrete
or low heat of hydration in case of mass concrete, or very rigid setting and
hardening of concrete in case of sprayed concrete or quick repair of roads and
airfields, or very low imperviousness of storage vessels, or very low leakage
rates of encapsulation containments for contaminating material.
HPC is
composed of the same material as normal concrete, but it has been engineered to
achieve enhanced durability or strength characteristics, or both, to meet the
specified demands of a construction project. The main ingredients of high performance
concrete are cement, fine aggregate, coarse aggregate, water, mineral
admixtures and chemical admixtures.
If the
structure of normal strength concrete (NSC) is compared with high performance
concrete (HPC) one notes several differences: The matrix stiffness of HPC is
larger than NSC and approaches the stiffness of the aggregate, the bond
strength between matrix and aggregate is higher for HPC, matrix tensile
strength is higher, Reduced internal cracking in terms of number of cracks and
size of intrinsic cracks before loading. These aspects show that HPC is
more elastic and more brittle than NSC.
High
Performance Concrete is that concrete which meets special performance and
uniformity requirements that cannot always be achieved by conventional material,
normal mixing, placing and curing practices.
Architects,
engineers and constructors all over the world are finding that using HPC allows
them to build more durable structures at comparable cost. HPC is being used for
building in aggressive environments, marine structures, highway bridges and
pavements, nuclear structures, tunnels, precast units.
This
reports aims to discuss the application of HPC particularly for bridge
structures. The use of HPC was found to have added advantages compared with normal
concrete in areas of strengths, service life, construction time, economy, etc.
High-performance
concrete characteristics are developed for particular applications and
environments; some of the properties that may be required include:
• High
strength
• High
early strength
• High
modulus of elasticity
• High
abrasion resistance
• High
durability and long life in severe environments
• Low
permeability and diffusion
•
Resistance to chemical attack
• High
resistance to frost and deicer scaling damage
• Toughness
and impact resistance
• Volume
stability
• Ease of
placement
•
Compaction without segregation
•
Inhibition of bacterial and mold growth
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