Concept of High Performance Concrete (HPC)
A concrete mixture which has high workability, high strength, high modulus of physical property, high density, high dimensional stability, low permeability and resistance to chemical attack is generally said to be high performance concrete.
The American Concrete Committee on High Performance Concrete includes the following six
- Ease of placement
- Long term mechanical properties
- Early-age strength
- Life in severe environments
The above-mentioned performance requirements can be grouped under the following three general categories.
- Attributes that benefit the construction process.
- Attributes that lead to enhanced mechanical properties.
- Attributes that enhance durability and long-term performance.
Below table shows classification of high performance concrete related to strength
|High Performance Class||Compressive Strength (Mpa)|
Strategic Highway Research Programme (SHRP) has outlined High Performance Concrete for highway application on the subsequent strength, durability, and w/c ratio criteria.
a) It has to satisfy one among the subsequent strength criteria:
- 4 hour strength- 17.5 Mpa
- 24 hour strength- 35.0 Mpa
- 28 days strength- 70.0 Mpa
b) Durability factor should be greater than 80 % after 300 cycles of thawing and freezing action.
c) Water- cement ratio should be less than or equals to 0.35
Characteristics of High Performance Concrete
- Very low porosity through a tight and refined pore structure of the
- It has Very low permeability of the concrete.
- High resistance to chemical attack.
- Low heat of hydration.
- High early strength and continued strength development.
- High workability and control of slump.
- Low water binder ratio.
- Low bleeding and plastic shrinkage
Components/Ingredients used in High Performance Concrete
The assembly of High Performance Concrete involves the subsequent three important interrelated steps:
- Choice of appropriate ingredients for concrete having the required
rheological properties, strength etc.
- Determination of relative quantities of the ingredients in order to
- Careful internal control of each section of the concrete creating method.
Following Ingredients are used in preparation of high performance concrete :
- Physical and chemical characteristics of cement play a significant role in developing strength and controlling rheology of fresh concrete.
- Fineness affects water requirements for consistency.
- Little amount of tricalcium aluminate (C3A) as possible because the lower amount of C3A, the easier to
control the physical science and lesser the issues of cement-superplasticizer compatibility.
- It should contains fair amount of Calcium Aluminates (C3S).
Fine Aggregate :
- Both river sand and crushed stones can be used.
- Coarser sand may be preferred as finer sand increases the water demand of concrete.
- Terribly fine sand might not be essential in High Performance Concrete.
Coarse Aggregate :
The coarse aggregate is the strongest and least porous component of concrete. The strength of High Performance Concrete is also controlled by the strength of the coarse aggregate. Hence the selection of coarse aggregate would be an important step in High Performance Concrete design mix.
Water should be free from acidic content and generally drinking safe water will be good to use.
Mineral Admixtures :
The major difference between conventional cement concrete and high performance concrete is essentially the
use of mineral admixtures in the latter. Some of the mineral admixtures are
- Fly ash
- Silica fumes
- Ground granulated blast furnace slag (GGBFS)
- Fine filler or pozzolonic supplementary cementitious materials
- Anhydrous gypsum based mineral additives
Chemical Admixtures :
Chemical admixtures improves the workability of the concrete mix by increasing the efficiency of the cement paste, which results in decreased water requirement. Some of the important chemical admixtures are: Plasticizers, Super plasticizers, Retarders, Air entraining agents,
Methods for Achieving High Performance
Two approaches to achieve durability through different techniques are as follows.
1) Reducing the capillary pore system such no fluid movement can occur is the first approach. This is very
difficult to appreciate and every concrete can have some interconnected pores.
2) Creating chemically active binding sites which prevent transport of aggressive ions like chlorides is that the second most effective method.
When to use High Performance Concrete
- Severe exposure conditions.
- Increase durability.
- Prevent deterioration of concrete
Also Read : What is Lightweight Concrete ? Types & Uses
Applications of High Performance Concrete
It is widely used in construction of following mega structures :
- High rise buildings
- Nuclear structures
Advantages of HPC
- Reduction in size of Structural members.
- Speed of construction.
- Workability and Pumpability.
- Economical material in Terms of time and money.
- Higher seismic resistance.
- Improved durability.
- Abrasion resistance.
- High tensile strength.
- Reduced maintenance cost
Limitations of HPC
- An extended quality control, as each and every aspect has to be checked as this type of concrete is widely used in the construction of mega structures.
- Cost is generally high due to used of various admixtures and high quality materials.
- Special constituents.
- Manufactured and placed carefully.
Also Read : What is Prestressed Concrete ?