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High Performance Concrete & High Strength Concrete 
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High Performance Concrete High Strength Concrete 
1.What is High Performance concrete? 1. What is High Strength Concrete?
2. What is the difference between High Strength Concrete and the Normal Concrete?
3. How is High Strength Concrete obtained in practice?
4. What is the main  application area of High Strength Concrete?
5. What are the benefits of High Performance Concrete? 5. Is High Strength Concrete same as High Performance  Concrete?
6. Is High Performance Concrete same as High Strength  Concrete?  
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High Performance Concrete
1. What is High Performance Concrete?
The American Concrete Institute (ACI) defines high-performance concrete as concrete meeting special combinations of performance and uniformity requirements that cannot always be achieved routinely when using conventional constituents and normal mixing, placing and curing practices.

A high-performance concrete is something which demands much higher performance from concrete as compared to performance expected from routine concrete.
2. What are the typical performance parameters of High-Performance Concrete?
The High Performance Concrete is normally designed for parameters (one or more) falling under the Srength criterion or/and under the Durabilty criterion,  as tabulated below:-
Strength Criteria Durability Criteria
Compressive Strength Freeze-Thaw
Modulus of Elasticity Scaling
Shrinkage Abrasion
Creep Chloride Permeability
Specification for High Performance Concrete often requires the concrete to meet several criteria.

3. What is the degree of quality control requirement for High Performance Concrete?
High-performance concretes are also more sensitive to changes in constituent material properties than conventional concretes. This means that a greater degree of quality control is required for the successful production of high-performance concrete.
4. How is High Performance Concrete obtained in practice?
By careful selection of raw materials (including chemical/mineral admixtures) & appropriate mix design to achieve the desired performance objectives.

Most high-performance concretes have a high cementitious content and a water-cementitious material ratio of 0.40 or less.
5. What are the benefits of High Performance Concrete?
High Performance Concrete (HPC) is  designed to provide several benefits in the construction of concrete structures as tabulated below:

Performance Benefits

Cost & Other Benefits

  • ease of placement and consolidation without affecting strength
  • long-term mechanical properties
  • early high strength
  • toughness
  • volume stability
  • longer life in severe environments
  • less material
  • fewer beams
  • reduced maintenance
  • extended life cycle
  • aesthetics
6. Is High Performance Concrete same as High Strength  Concrete?
No.
A high-strength concrete is always a high-performance concrete, but a high-performance concrete is not always a high-strength concrete.
High Strength Concrete 
1. What is High Strength Concrete?
ACI defines a high-strength concrete as concrete that has a specified compressive strength for design of 6,000 psi (41 MPa) or greater.

It should be noted that the definition of high strength concretes is continually developing. In the 1950s 34MPs was considered high strength, and in the 1960s compressive strengths of up to 52MPa were being used commercially.  More recently, compressive strengths approaching 138 MPa have been used in cast-in-place buildings. Two buildings in Seattle, Washington, contain concrete with a compressive strength of 19,000 psi (131 MPa).
2. What is the difference between High  Strength Concrete and the Normal Concrete?
The primary difference between high-strength concrete and normal-strength concrete relates to the compressive strength that refers to the maximum resistance of a concrete sample to applied pressure. Although there is no precise point of separation between high-strength concrete and normal-strength concrete, the American Concrete Institute defines high-strength concrete as concrete with a compressive strength greater than 6000 psi (41 MPa).
3. How is High Strength Concrete obtained in practice?
Manufacture of high-strength concrete involves making optimal use of the basic ingredients that constitute normal-strength concrete. Producers of high-strength concrete know what factors affect compressive strength and know how to manipulate those factors to achieve the required strength. In addition to selecting a high-quality portland cement, producers optimize aggregates, then optimize the combination of materials by varying the proportions of cement, water, aggregates, and admixtures.

When selecting aggregates for high-strength concrete, producers consider the strength of the aggregate, the optimum size of the aggregate, the bond between the cement paste and the aggregate, and the surface characteristics of the aggregate. Any of these properties could limit the ultimate strength of high-strength concrete.

Admixtures: Pozzolans, such as fly ash and silica fume, are the most commonly used mineral admixtures in high-strength concrete. These materials impart additional strength to the concrete by reacting with portland cement hydration products to create additional C-S-H gel, the part of the paste responsible for concrete strength.

It would be difficult to produce high-strength concrete mixtures without using chemical admixtures. A common practice is to use a superplasticizer in combination with a water-reducing retarder. The superplasticizer gives the concrete adequate workability at low water-cement ratios, leading to concrete with greater strength. The water-reducing retarder slows the hydration of the cement and allows workers more time to place the concrete.
4. What is the main  application area of High Strength Concrete?
High-strength concrete is specified where reduced weight is important or where architectural considerations call for small support elements. By carrying loads more efficiently than normal-strength concrete, high-strength concrete also reduces the total amount of material placed and lowers the overall cost of the structure.

High-strength concrete columns can hold more weight and therefore be made slimmer than regular strength concrete columns, which allows for more useable space, especially in the lower floors of buildings.

High Strength Concrete are also used in other engineering strucures like bridges.
5. Is High Strength Concrete same as High Performance  Concrete?
No.
A high-strength concrete is always a high-performance concrete, but a high-performance concrete is not always a high-strength concrete.

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Article contributed by:  Steve, Canberra, Australia 
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