Mayur Shah, Managing Director, Marathon Group

Availability of good quality fly ash is not an issue. And the methods for testing it are well established as well. Construction leaders have now realised the merits of blending fly ash, and some, like the Marathon Group, are using fly ash in all their projects. The challenge however, is to blend it perfectly, says Mayur Shah, in an interaction with ICR. Excerpts from the interview.

How often, and how much of fly ash do you blend in cement?
We have used fly ash blended concrete in all our projects. We have been replacing cement with 28 per cent of fly ash in our blends. We produce high performance concrete using fly ash, GGBS, etc. Apart from blended concrete, we are using fly ash bricks too for construction. These bricks have better density and strength as compared to the conventional ones.

What encourages you to use fly ash in such significant quantities?
We at Marathon believe that our buildings should last for 75 years without any deterioration despite adverse weathering conditions. We also aim to reduce the cost of building repairs. In order to gain maximum benefits, we use high quality materials for in the construction process. Fly ash is one such material used by us.

How does fly ash contribute to concrete strength?
Fly ash is rich in silica. After primary cement hydration reaction, free lime available in concrete reacts with silica of fly ash and forms calcium silicate hydrate gel, which further adds to the strength of concrete as well as reduces porosity. This is called secondary reaction and it continues for at least a year. It increases durability of the structure over time. As (part of) cement content in the mix is substituted by fly ash, the heat of hydration gets reduced, which in turn eliminates the cracks in concrete.

Can you name some of your noteworthy projects where fly ash was used in significant quantity?
We have successfully completed many projects in which fly ash has been used:

• Residential tower Marathon Era – 36 storeys in South Mumbai
• Commercial Tower Marathon Futurex – 25 storeys in South Mumbai
• Residential Tower Monte Vista – 33 storeys in Mulund, Mumbai
• Residential Complex Marathon Nagari at Badlapur – winner of Best Low Cost Housing Apartments, at the CREDAI Real Estate Awards in 2012.

How do you ensure quality of your fly ash-cement blend?
Manual blending of fly ash is prone to errors. It is not possible to get desired quality of concrete consistently unless there is strict supervision on the site. So we use computerised batching plants at our sites to ensure proper blending of fly ash with concrete. There is no need for human intervention in the production of concrete. This eliminates any possible blending errors and helps us make good quality concrete consistently.

How do you assess the quality of fly ash?
Fly ash is broadly classified as Grade I or Grade II. As per IS 3812-2003, when silicon dioxide (SiO2), aluminium oxide (Al2O3) and Iron (Fe2O3) quantiles are more than 70 per cent it is classified as Grade I. We have been using the Grade I fly ash, which has at the most 5 per cent loss on ignition. Also, retention on 45 micron must be less than 34 per cent (by wet sieving method) as per IS: 3812 (Pt-I)-2013. We have also been using fly ash having 20 per cent retention on 45 micron sieve. We conduct sieve analysis test on site to ensure that the material retention on 45 micron sieve is in desired range.

What about the availability of good quality fly ash in the country?
Fly ash is generated as a by-product while burning coal at power plants. We are sourcing it from Dahanu and Nashik power plants. This raw fly ash is graded on the basis of its silica, alumina and iron content. We are not facing any issues in sourcing good quality fly ash.