High Performance Concrete (HPC) refers to concrete with a specified compression
strength of 6,000 psi (40 MPa) and greater. In fact, Prairie has had great
success with HPC mix designs at upwards of 21,000 psi.
HPC can be specified for a number of applications:
The most common use of high-strength concrete is for construction of high-rise
buildings. At 969 ft, Chicago's 311 South Wacker Drive uses concrete with
compressive strengths up to 12,000 psi (41 MPa) and is the tallest concrete
building in the United States.
To put concrete into service earlier, such as opening pavement to traffic in
three days.
To reduce the column size and increase usable space in high-rise buildings.
To build the superstructures of long span bridges and the durability of bridge
decks.
To satisfy specific needs such as durability, modulus of elasticity, and
flexural strength for special applications. These include parking garages,
dams, grandstand roofs, etc.
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.
Manufacture of high-strength concrete involves making optimal use of the basic
ingredients that constitute normal-strength concrete. Prairie knows which
factors affect compressive strength and knows how to manipulate those factors
to achieve the required strength. In addition to selecting a high-quality
portland cement, we 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, Prairie considers 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 create additional strength 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.
Information provided by the Portland
Cement Association
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