Increasing construction challenges in combination with new innovations in materials and construction techniques have revolutionized the use of concrete as a major construction material.

It is not a commodity but a range of products each specially designed to satisfy, in the most effective way, the performance requirements for the intended applications. The general attributes of the concrete can be broadly classified into:

• Those that benefit the construction process
• Those that enhance mechanical properties
• Those that enhance durability.

• It shall have one of following strength characteristics:

1. 4 – hour strength greater than or equal to 17.5 Mpa

2. 24 – hour strength greater than or equal to 35 Mpa

3. 28 – day strength greater than or equal to 35 Mpa

• It shall have durability factor > 80% after 300 cycles of freezing and thawing
• It shall have a water-cementitious materials ratio < 0.35.

One of the main governing factors of HPC is permeability of concrete to both liquids and gases. The main characteristics of HPC compared to normal concrete are uniform and homogeneous microstructure. For normal concrete, the special microstructure of the transition zone is apparently related to the formation of water filled spaces around the aggregates. The permeability characteristics of the HPC are improved by the addition of silica fumes. It has been observed that HPC with silica fume is not as crystallized and porous as normal concrete. It is well documented that this improved microstructure is closely related to the reduced permeability and improved performance of HPC.

Since HPC is characterized by low porosity and a more uniform microstructure compared to that of normal concrete, it indicates a high resistance to the penetration to CI ions into concrete. It has also been observed that the electrical resistivity of HPC is above the level where the corrosion of the embedded steel takes place. If steel should become deactivated, the rate of corrosion will also be controlled by the oxygen availability.

• In leaching corrosion all or a part of the cement phase from the hardened concrete is removed from the concrete. Normally this is caused by the action of water of low carbonate hardness of carbonic acid content.
• Corrosion by exchange reaction between the readily soluble compounds of the hardened cement phase and the aggressive solutions;
• Swelling corrosion is the process in which the formation of new and stable compounds in the hardened cement paste takes place.
• Silica fumes used in HPC is very effective in reducing the calcium hydroxide and hence increases resistance to sulphate attack.

Fire resistance of HPC is generally lower than that of normal concrete. HPC is known to be more vulnerable to elevated temperatures than normal concrete.

By virtue of its very high strength HPC is known to have a good deal of abrasion resistance. Mechanical abrasion is dominant in case of pavement and bridge decks exposed to high traffic. Generally the abrasion of the concrete is higher when it is dry and lower when it is wet. HPC is known to have lower moisture content due to its dense packing and higher impermeability. Hence HPC is being used abroad in large scale in bridge decks, run ways, industrial floors etc.