Sudhir Hoshing, CEO-Roads, Reliance Infrastructure Though the regulatory systems are yet to evolve and embrace the new construction material, fly ash has already proved its worth in several large-scale construction projects all over the world. Fly ash has been used in tall building structures like the Petronas Towers in Malaysia. Eurotunnel, the second largest rail tunnel had fly ash mixed in the concrete. In India it has been used in Bhakhra Dam, Rihand Dam, Rajasthan Atomic Power Plant, private builders like Hiranandani Developers, DLF have been using fly ash in residential buildings. ICR interacts with Sudhir Hoshing, CEO-Roads, Reliance Infrastructure, to gauge how the trend is catching up in India.

What are the benefits of blending fly ash in cement?
Fly ash, being a by-product of coal combustion, offers environmental advantages by diverting the material from the waste stream, reducing the energy investment in processing virgin materials, conserving virgin materials, and by allaying pollution.

It also improves the performance and quality of concrete as it:

• Affects the plastic properties of concrete by improving workability, reducing water demand, reducing segregation and bleeding, and by lowering heat of hydration.
• Fly ash increases strength, reduces permeability, reduces corrosion of reinforcing steel, increases sulphate resistance, and reduces alkali-aggregate reaction.
• Fly ash reaches its maximum strength more slowly than concrete made with only Portland cement.
• Reduces requirement of cement for same strength of concrete thus making the mix economical.
• No special technique is needed to use fly ash blended concrete. It is to be used as per standard established method.

Does blending vary, based on the type of fly ash or application?
Based on the type of coal used, two different types of fly ashes are produced. Anthracite and bituminous coal produces fly ash classified as Class F. Class C fly ash is produced by burning lignite or sub-bituminous coal. For sulfate environments, only Class F fly ash will be permitted and under no circumstances will Class C fly ash be used.

Class F fly ash will typically require an air entraining agent to be added. Class C fly ash will not.

How is the availability of good quality fly ash in the country?
In India fly ash is being used to produce fly ash based PPC. Because in India the power plants basically use lignite and sub-bituminous coal, the Class F fly ash is relatively easy to obtain.

Do you use fly ash in your cement/concrete blends? To what extent?
Currently, we are not using fly ash in cement/concrete blends due to regulatory issues. However, fly ash is permitted for use in embankments, earthwork, etc. Generally, 15 to 28 per cent fly ash is used in such applications.

No special technique is needed to use fly ash blended concrete.