K Veerappan, GM & Head of Procurement, L&T Construction Apart from saving the environment from pollution, use of fly ash in cement and concrete blend actively helps in strengthening the structure. It is no longer just a cement substitute, nor is its use just a way to dispose of waste material. Fly ash is rapidly becoming a choice of leading construction companies. ICR interacts with K Veerappan to know what the leaders in the industry think about using fly ash. Excerpts from the interaction.
Do you use fly ash in your cement/concrete blends? We use fly ash as a replacement for cement. It varies from 15 per cent to 35 per cent of cementitious content in concrete depending on its grade.
How do you grade the quality of fly ash? We take regular samples to analyse the quality of fly ash. The samples are tested for their physical as well as chemical properties as per the IS 3812, Part 1 requirements. On receiving the sample at site we do 45 microns wet sieve analysis for product acceptance. Depending on the fineness the fly ash is graded accordingly. Finer the fly ash, better is the quality.
How is the availability of good quality fly ash in the country? Chemically all the fly ashes available are active and conform to IS 3812, Part 1 requirement. Fly ash available from Field 1 of ESP is coarser and sometimes fails in the 45 microns test. Fly ashes processed and supplied by Ashtech India, Dirk, JSW, Hitech are generally used for blending in concrete as they are of good quality.
Please list a few examples of your noteworthy projects where fly ash was used? We have been using fly ash in almost all our projects as a cement replacement material.
Some of the noteworthy projects where fly ash was used in significant quantities include: Mumbai International Airport, Delhi International Airport, Hyderabad International Airport, Bangalore International Airport, Tata Consultancy Service (TCS), Chennai, and Cognizant Technology Services, in Chennai.
What is the scope for further rise in fly ash consumption? For many projects, structural consultants restrict the use of fly ash. Even if permitted, the replacement level is restricted to 10 to 20 per cent. Using fly ash increases the durability of concrete. In the present scenario, with upcoming tall towers and high performance concrete, use of fly ash is inevitable to produce durable structures.
Fly ash is used not only in concrete, but can also be used in various other construction activities. It can be substituted in finishing activities to an extent of 25 per cent in brickwork, plastering and other masonry works. This will also take care of efflorescence effect (white patches on finished surface.
Considering the benefits, if uniform blending is ensured, fly ash usage can be permitted in all civil engineering activities. Bricks made out of fly ash or fly ash based products should be given more preference. Use of fly ash will help us nurture environment by reducing cement consumption and cut down carbon dioxide emission.