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.
|
